Effects of deficit irrigation strategies on cluster microclimate for improving
fruit composition of Moscatel field-grown grapevines
Accepted in Scientia Horticulturae
Partial rootzone drying irrigation affects cluster microclimate improving fruit
composition of ‘Moscatel’ field-grown grapevines
TIAGO P. SANTOSA, CARLOS M. LOPESA; M. LUCÍLIA RODRIGUESA, CLAUDIA R. DE
SOUZAB, JORGE M. RICARDO-DA-SILVAA, JOÃO P. MAROCOC, JOÃO S. PEREIRAA and M.
Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Tapada da Ajuda, 1349-017
Laboratório de Ecofisiologia Molecular, Instituto de Tecnologia Química e Biológica, Apartado
127, 2780-901 Oeiras, Portugal.
Instituto Superior de Psicologia Aplicada, Rua Jardim do Tabaco, 34, 1149 - 041 Lisboa,
The grapevine plays a very important role in the economic, social and cultural sectors of
many regions; however vineyards are often grown in regions under stressful conditions and
thus they are vulnerable to climate change. The objective of this research was to investigate
the effect of partial root-zone drying (PRD) irrigation on vine water relations, vegetative
growth, plant microclimate, berry composition and yield components, compared to
conventional deficit irrigation (DI – 50% ETc), full irrigation (FI – 100% of ETc) and non
irrigated vines (NI). The study was undertaken in mature „Moscatel‟ grapevines (Vitis vinifera
L.) grown in Pegões, South of Portugal. Compared to the other irrigated treatments, PRD
vines showed a better microclimate at the cluster zone with higher incident photosynthetic
photon flux density (PPFD). Within the more open canopies of NI and PRD treatments, berry
temperatures were higher than those of denser ones (DI and FI). Compared to the
conventional irrigation technique the better microclimate observed in PRD vines was a
consequence of a reduction in vine growth, where lower values of leaf layer number, leaf
area, canopy wideness, water shoots and shoot weight were observed. In PRD vines we
observed a tendency to a development of a deeper root system, while DI and FI showed a
more homogeneous root distribution throughout the different soil layers. PRD showed an
improvement in berry quality with higher values of flavour precursors, and total phenols
concentration without any significant yield reduction compared to DI and FI.
Keywords: berry temperature, canopy microclimate, fruit quality, partial rootzone drying,
roots, Vitis vinifera L..
Abbreviations used: DI, deficit irrigation; ETc, crop evapotranspiration; FI, full irrigation;
G-G, glycosyl glucose; IFT, total phenol index; LLN, leaf layer number; NI, non irrigated;
PRD, partial rootzone drying; PPFD, photosynthetic photon flux density; Tb, berry
The Grapevines, namely for wine production is one of the most important crops within the
Portuguese agriculture. Global environmental change with a predicted increase in aridity
(Rizza et al. 2004), mainly in South Europe, will force modifications within the network of
national and European regulations for grapevine/wine (Schultz, 2000; Chaves et al., 2004).
These regulations aim at the optimization of wine quality for a given combination of
geographical, soil, climate, cultivation and winemaking parameters. Due to climate change,
there is a risk for a change in the quality of vine/wine, and consequently for its economic
value. Although the impact of climate change is not likely to be uniform across all varieties
and regions (Jones et al., 2005), a profound change in the distribution of suitable varieties
within Europe may occur (Schultz, 2000).
Water resources in South of Portugal are limited leading to the re-evaluation of the current
strategies of water use. Water is a renewable resource although it is distributed unevenly both
geographically and time wise. Irrigation is a powerful management tool for improving vine
performance provided it is properly managed. Irrigation management during the growing
season is critical for control of vine vigour, berry size and berry quality. Excessive water
induces a stimulus in vegetative growth that leads to denser canopies, and lower fruit
exposure and, consequently, lower fruit quality and higher disease problems (Crippen and
Morrison, 1986a,b; Dokoozlian and Kliewer, 1996; Keller and Hrazdina, 1998). Lateral shoot
growth is particularly promoted, what will imposed competition for photosynthates and
shading, creating conditions for an increase in berry and leaf diseases, and delaying berry
maturation (Smart, 1994). On the contrary when water deficits occur, the vine responds by
closing stomata to limit water loss. The different processes in the vine plant respond
differently to water stress. Vegetative growth and early berry growth are very sensitive to
water deficit while leaf photosynthetic function and post veraison berry growth are less
sensitive processes (Shackel et al. 1987; Lu and Neumann 1998). When drought increases
stomata closes for longer periods of time, limiting photosynthesis and the production of sugar
leading to poor fruit quality and reduced yield. An early stress will not allow an adequate
shoot elongation and leaf development (Mathews et al. 1987). On the other hand a severe
water deficit after veraison can result in a high basal leaf senescence providing too much light
at cluster zone (Kliewer et al. 1983; Smart and Robinson 1991), with negative effects on
berry quality. So, an optimal irrigation management will impose a plant water status that
allows a good leaf physiological activity and at the same time reduces excessive shoot
growth. Therefore a more open and balanced canopy will be achieved improving berry quality
namely total phenols concentration (Smart et al, 1988; Keller & Hrazdina 1998, Spayd et al.
Deficit irrigation strategies are relatively new tools for managing grapevine growth,
improving fruit quality and water use efficiency, while maintaining yields. One of these
strategies is the regulated deficit irrigation (RDI) which has been explored to control
vegetative growth and improve fruit yield and quality (Goodwin and Jerie, 1992; McCarthy,
1997) by removing or reducing the irrigation input for specific periods during the growing
cycle. According to Dry et al. (2001) RDI is used to manipulate winegrape quality by
applying a short duration of water deficits immediately after berry set in order to control berry
size and vegetative growth. A short period of water stress may also be imposed after veraison
in order to enhance anthocyanin accumulation. Matthews et al., (1987) also observed that
reduced irrigation prior to veraison caused a greater reduction in berry size than less irrigation
after veraison did. This reduction in berry size is important because the flavour compounds
which determine wine quality are mainly located in the berry skin and an increase in skin to
flesh ratio might improve fruit quality (Dry et al., 2001).
In drying soil, shoot growth can be limited as a result of hydraulic insufficiency, and of
chemical signalling, involving transfer of chemical information from roots to the shoots via
the xylem (Davies et al., 1994). Based on this fact a new irrigation technique called Partial
root-zone drying (PRD) has been studied by many authors (Dry and Loveys, 1998; Souza et
al. 2003; Santos el al., 2005; Wakrim et al., 2005). It is an irrigation technique designed to
keep part of the root-zone in drying soil and the rest of the root-zone well watered (Dry and
Loveys, 1999; Stoll, 2000). The root-zones alternate every few weeks between dry and
irrigated. It has been hypothesized that the water stress induced on one side of the root system
will lead to the sending of signals to the shoots via the xylem (Dodd et al., 1996) stimulating
the whole plant to utilize water more efficiently (Dry and Loveys, 1998). These signals (like
ABA) lead to a partial stomatal closure and a reduction in shoot growth (Dry et al., 1996). So,
PRD has the effect of controlling excessive vegetative growth in grapevines, leading to a
reduction in canopy density and a better plant balance with decreased costs of maintenance
(Dry et al., 2001; Santos et al., 2003). In addition, some studies had shown in PRD plants an
increment increase in rooting depth (Dry et al, 2000) and root biomass (Mingo et al., 2004)
compared to well-watered plants. At the end of other experiment unchanged shoot:root ratio
was found in stressed vines receiving 100% of total plant transpiration in one pot with water
withheld from the other, compared with control (Poni et al., 1992). This plant response may
represent an increased ability to access soil resources, namely water and nutrients.
Furthermore, several works on PRD showed that this irrigation method appears to provide
benefits in fruit quality (Loveys et al. 2000, Santos et al., 2005).
Research studies found that grape glycosides act as flavour precursors having a high
importance in wine aroma determination especially because most of varietals aromatic
compounds in grape, musts and wines are present in bound-glycosylated forms (Sefton et al.,
1993, 1994). The analysis of glycosylated secondary metabolites in grapes could give an
objective measure of grape quality and be a useful parameter to allow the assessment of the
effect of viticultural and winemaking practices (Williams et al., 1995). Although there are
hundreds of glycosides present in grapes, with very different chemical structures, the
determination of glycosyl-glucose (G-G) concentration gives the total concentration of
glycosylated secondary metabolites (Francis et al., 1998), which are mainly related to
aromatic compounds in the case of white grape varieties (Williams et al., 1995).
The aim of the present study was to provide a better understanding of the effect of
different irrigation strategies, namely those where the same amount of water was applied, in
the control of grapevine plant vigour, cluster microclimate and consequently berry quality and
plant water-use efficiency.
2. Materials and methods
2.1. Field conditions and plant material
The field trial was carried out in 2002 at a commercial vineyard located at Pegões,
Southern Portugal (70 Km south of Lisbon). The climate is of the Mediterranean type, with
hot and dry summers and mild winters, having an average annual rainfall of 550 mm, with
400 mm falling during the autumn and winter months. The soil is derived from podzols,
mostly sandy and with a clay rich (low permeability) horizon at ca 1 m depth. The five-year-
old vines of the white variety „Moscatel de Setúbal‟ syn. „Muscat of Alexandria‟ (Vitis
vinifera L.), grafted on 1103 Paulsen rootstock, has a North-South row orientation. The vines
were spaced 2.5 m between rows and 1.0 m along rows and trained on a vertical shoot
positioning with two pairs of movable wires and spur pruned on bilateral Royat Cordon
system at a height of 60 cm. The top of the canopy was approximately 1.40 m from the soil
which gives a canopy height of 80 cm. All vines were uniformly pruned to 12 nodes per vine.
Standard cultural practices in the region were applied to all treatments. Shoots were trimmed
at about 30 cm above the higher movable wire, two times between bloom and veraison.
2.2. Irrigation and experimental design
Water was applied with drip irrigation method with two drippers per vine and with drip
lines independently controlled and placed 30 cm from the vine trunk, out to both sides of the
row. Watering was applied according to the crop evapotranspiration (ETc), estimated from the
potential evapotranspiration (ETo), which was calculated from the Class A pan evaporation
and using the crop coefficients (Kc) proposed by Prichard (1992). Each irrigated treatment
was equipped with timing-valve assembly to control water delivery. The treatments were: full
irrigated (FI, 100% of the ETc, half of water supplied to each side of the root system with 4
Lh-1 drippers); deficit irrigated (DI, 50% of the ETc, half of water supplied to each side of the
row with 2 Lh-1 drippers); partial root drying (PRD, 50% of ETc periodically supplied to only
one side of the root system with 4 Lh-1 drippers) and non irrigated (NI) treatment which was
allowed to dry. The first change of the irrigation side was done after 1 month and then
alternating sides every 15 days); non irrigated (NI; rain fed). Watering was done twice a
week, from fruit set (middle June) until three weeks before harvest which occurred on
September 24. The total water amount supplied to FI plants was 196.8 mm (493 L per vine).
The PRD and the DI vines received half of that quantity.
The experimental design was a Latin square with four treatments and four replications per
treatment. Each replicate (plot) had three rows with 15 to 20 vines each and all the
measurements were made on the central row.
2.3. Plant and soil water relations
Pre-dawn leaf water potential (pd) was measured weekly from the beginning of berry
development until harvest. Measurements were carried out on one adult leaf of six replicate
plants from each treatment using a Scholander pressure chamber (Model 1000; PMS
instrument Co., Corvallis, OR, USA). Leaves were enclosed in a plastic bag, immediately
severed at the petiole and sealed into the humidified chamber for determination of the
Soil water content was monitored twice a week (before and after each irrigation) during
the growing season using a Diviner 2000TM capacitance probe (Sentek Environmental
Technologies, Stepney, Australia). Water content in the soil profile was determined using
access tubes located 0.1 m from the row in four plants per treatment. Measurements were
done each 0.1 m from soil surface to 0.9 m depth.
2.4. Root distribution
Roots were sampled after harvest using cylinders of soil (0.77 x 10 -3 m3), taken at four
depths (m), 0.05–0.25, 0.25–0.45, 0.45-0.65, 0.65-0.85 and close to the drippers at two
positions relative to the plant, on the right and left side in the row. For each treatment twelve
plants were used. Each sample was stored in polyethylene bags and frozen until laboratory
analysis. The roots were recovered by soil washing and root mass density (gm-3) by depth
calculated after the determination of root dry mass.
2.5. Canopy density and cluster microclimate
Canopy density was assessed by point quadrate analysis (Smart and Robinson, 1991), by
inserting a needle at regular intervals into the fruit zone. Eighty horizontal insertions per
treatment (twenty per plot) were made using a pre-marked sampling guide.
Leaf area per shoot (8 shoots per treatment) was assessed periodically in count shoots
from bud break onwards in a non-destructive way, using the methodologies proposed by
Lopes and Pinto (2000). The area of single leaves was estimated using an empiric model
based on the relationship between the length of the two main lateral leaf veins and leaf area
measured with a leaf area meter (LI-3000; LI-COR Lincoln, Nebraska, USA). Leaf area per
plant was calculated multiplying the leaf area per shoot by the shoot number.
Light at the cluster zone was measured on sunny days at midday using a Sunflek
Ceptometer (model SF-40, Delta T Devices Ltd, Cambridge, UK) inserted horizontally at the
cluster zone along the row. The values of incident photosynthetic photon flux density (PPFD)
were expressed in percentage of a reference PPFD, measured over the canopy top. Berry
temperature (Tb) was determined on clear sunny days using two representative exterior
clusters per treatment of each canopy facing (east and west). Measurements were made
continuously using fine-wired (36 American Wire Gauge [AWG]) two-junction
thermocouples (type T [copper-constant]) which were manually inserted into the berries and
connected to a data logger (Delta-T Devices Ltd, Cambridge, UK).
2.6. Yield, fruit quality and pruning weight
Berry ripening was followed from veraison until harvest. Sampling was done by
collecting cluster fractions (3-4 berries per cluster) using a 200 berries sample per plot,
collected in all vines and representative of all cluster positions within the canopy and of all
positions within the cluster (Carbonneau, 1991). Sub-samples per plot were used for fresh
berry analysis for weight and volume, pH, soluble solids (º Brix) using refractometry and
titratable acidity by titration with NaOH as recommended by OIV (OIV, 1990). Another berry
sub-sample per plot was frozen at –30ºC for later glycosyl-glucose and total phenolic
compounds analysis. Total phenols were determined by spectrophotometry, by measuring
Ultraviolet absorption at 280 nm (IFT) (OIV, 1990). Quantification of glycosides
(glycosilated-volatile compounds or bound form of aromatic compounds) in grapes was
obtained, measuring the glycosyl-glucose (G-G), according to Williams et al. (1995) and
Iland et al. (1996). At harvest (September 24), yield components and fruit quality were
assessed, following manual harvesting and weighting the production on-site. Cluster number
and yield per vine were recorded for all vines on each plot. Irrigation water use efficiency
(WUE) was estimated as the ratio of yield over the amount of applied water. At winter
pruning, shoot number and pruning weight were also recorded and shoot weight was
2.7. Data analysis
Statistical data analysis was performed by analysis of variance (ANOVA). Tukey HSD
tests were carried out to test the significance of differences between treatment means, using
the STATISTICA software (ver. 5.0, Statsoft, Inc. Tulsa, OK, USA).
3.1. Climate and soil-plant water relations
The growing season of 2002 was drier than the 30-year average, with the exception of
March, with a total rainfall of 390 mm between January and September. Nevertheless, the air
temperature followed the average pattern.
As shown in Fig. 1, the soil water content in the profile 0-0.9 m gradually decreased for
NI plots from June to August. In the three irrigated treatments the soil water content was
almost constant during June and July although a slight decline was observed in August
resulting from the reduction in the irrigation amount. During the growing season, mean soil
water content was in average three folds in FI and two folds in DI and PRD when compared
to NI. In PRD the right side of the root-zone, the first one to be irrigated, had soil water
content values almost 150 % higher from those of the left side. The reverse occurred when the
irrigation side was switched.
Soil moisture (mm)
20 NI 20
DI Rigth side
PRD Left side
17-06 01-07 15-07 29-07 12-08 26-08 17-06 01-07 15-07 29-07 12-08 26-08
Figure 1. The change of soil water content (0-0.9m) during the 2002 growing season in Moscatel
grapevines. Each arrow indicates the day when the change of rootzone-irrigated side took place in
PRD treatment. Each point represents the average of 4 measurements with standard error.
Pre-dawn leaf water potential (pd) of FI vines remained constant and close to –0.2 MPa
throughout the growing season, while in NI ones pd decreased from June onwards, reaching
mean values of –0.6 MPa at the end of August (Fig. 2). In PRD and DI plants, predawn water
potential decreased slightly from the beginning of the irrigation, with PRD showing a more
favourable water status in some dates than DI.
ns Irrigation starting NI
0,0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 -0,8
Pre-dawn leaf water potential (M Pa)
Figure 2. Seasonal change of pre-dawn leaf water potential in Moscatel grapevines during the
2002-growing season. Each symbol represents the average of 6 measurements with standard error.
3.2. Vegetative growth and root biomass
At veraison total leaf area per vine was significantly higher (P< 0.05) in FI than in NI and
PRD treatments while DI plants showed values not significantly different from those of the
other treatments (Table 1). These differences were mainly due to differences in the lateral
shoot leaf area since main leaf area was similar in FI, DI and PRD and lowest in NI.
NI and PRD plants presented the narrowest canopies and FI the widest ones (Table 1)
while DI showed an intermediate canopy wideness. Accordingly NI plants showed the lowest
leaf layer number (LLN) while PRD showed a significantly lower LLN relative to FI and DI
While no significant differences were observed among treatments in the shoot number per
vine, significant differences were registered in the number of water shoots (developed on the
old woody stem), with NI showing the lowest value and PRD showing a significantly lower
value than those of the other irrigated treatments. NI vines presented the lowest pruning
weight per vine, which was significantly different from the FI and DI ones. PRD pruning
weight was significantly lower than FI value, although not significantly different from DI
(Table 1). Weight per shoot measured at winter pruning presented significantly lower values
in PRD and NI relatively to FI, although no significant differences were observed between DI
and the other three treatments.
Table 1. Growth parameters measured at veraison or at pruning time (*) in Moscatel grapevines
under four water treatments (NI, PRD, DI, NI) during the 2002 growing season. Columns of data
within a row , followed with different letters, are significantly different at P<0.05.
NI PRD DI FI HSD P
Shoot number per vine* 15.6 16.7 17.5 16.6 1.31 ns
Water shoots per vine* 1.5 c 2.0 b 3.0 a 3.0 a 0.59 ≤ 0.001
Pruning weight (kgvine )* 0.45 c 0.48 bc 0.52 ab 0.54 a 0.59 ≤ 0.001
Shoot weight (g)* 29.2 b 28.8 b 31.1 ab 33.4 a 4.23 ≤ 0.001
Leaf layer number (nº) 1.9 d 2.4 c 3.5 b 4.0 a 0.43 ≤ 0.001
Canopy wideness (cm) 45.4 c 45.0 c 57.1 b 64.8 a 3.04 ≤ 0.001
Main leaf area (m vine ) 2.8 b 3.2 ab 4.0 ab 4.5 a 1.55 ≤ 0.05
Lateral leaf area (m vine ) 1.9 b 1.7 b 2.1 ab 3.6 a 2.36 ≤ 0.05
Total leaf area (m vine ) 4.7 b 4.9 b 6.0 ab 8.1 a 3.10 ≤ 0.01
a 0.05-0.25 m
Root mass density ( gm-3 )
300 0.45-0.65 m
NI PRD DI FI
Figure 3. Root dry weight in Moscatel grapevines under four water treatments (NI, PRD,
DI, NI) in the 2002 growing season. Values shown represent the mean of 80 measurements
with standard error. Different letters show statistically significant differences between
different soil layers in each treatment at P0.05.
In DI and FI no significant differences were found in the dry weight of roots between the
different soil layers. On the contrary, in PRD plants a tendency was observed to the
development of a deeper root system. Also, in NI plants the highest root dry weight occurred
in the layer 0.45-0.65 m. Comparing the different soil layers between treatments we observed
significant differences in the layer 0.05-0.25 m where NI presented a lower root dry weight
compared to FI while PRD and DI showed intermediate values. In the layer 0.65-0.85 m PRD
showed a significant higher root dry weight compared to NI.
3.3. Canopy microclimate
FI vines had the highest LLN and, consequently, they displayed the lowest incident PPFD
values during ripening at the cluster zone Fig. 4. On the contrary, NI plants presented the
highest cluster exposure. Within the irrigated treatments the reduction in vegetative growth
observed in PRD resulted in a more open canopy as indicated by the significantly higher
values of PPFD (10.2±0.9 %) received by the clusters when compared to DI (4.2±0.5 %) and
FI (2.7 ±0.3 %).
10.2 + 0.9 b DI
DI 10,8 + 0,8 16%
c 13% c
4.2 + 0.5 6,1 + 0,5
a 2.7 + 0.3 d
FI a 4,1 + 0,3 FI
14.9 + 1.0
9% 17,1 + 1,2 11%
Figure 4. Incident photosynthetic photon flux density at the cluster zone expressed as a % of a
reference measured on top of the canopy in Moscatel grapevines under four water treatments during
the 2002 growing season. Values shown represent the mean of 80 measurements with standard error.
Different letters show statistically significant differences at P0.05.
The diurnal courses of berry temperature analysed at veraison for similar days of August
(clear sky and high air temperature) on exterior clusters are shown in Fig.5. In all treatments
berry temperature (Tb) progressively increased from dawn, reaching maximum values about
11:00 h in the east canopy side and at 16:00 h in the west side. Berry temperatures were
always higher in NI and PRD than in FI and DI vines, which presented denser canopies. The
largest differences between air and berry temperature were reached at the east side around
11:00 h, the berries on NI presenting a temperature 5.5 ºC higher than the air (Ta) as
compared to 4 ºC in FI, while in PRD and DI Tb exceeded Ta by 5.8 ºC and 3.4 ºC,
respectively. During the night no differences between Tb and Ta were apparent except for DI
and FI berries in the east canopy side which presented lower temperatures than the air.
East side NI A NI B
Berry temperature (ºC)
30 Air temperature 30 Air temperature
16:00 18:30 21:00 23:30 2:00 4:30 7:00 9:30 12:00 14:30 16:00 18:30 21:00 23:30 2:00 4:30 7:00 9:30 12:00 14:30
East side West side
PRD C PRD D
Berry temperature (ºC)
30 Air temperature 30 Air temperature
18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 3:00 6:00 9:00 12:00 15:00
Figure 5. Daily change of berry temperature at the cluster zone for exterior Moscatel grape clusters
on the east and west sides of the canopy, during the 2002 growing season. A: FI and NI in east side; B:
FI and NI in west side; C: PRD and DI in east side; D: PRD and DI in the west side.
3.4. Yield components and fruit composition
Cluster number per vine was independent of the soil water availability, although a
significant increase in cluster weight was obtained as a result of irrigation with no differences
between the irrigated treatments (Table 2).
Table 2. Yield components and berry composition at harvest in Moscatel grapevines under four
water treatments (NI, PRD, DI, NI) during the 2002 growing season. Columns of data within a row,
followed with different letters, are significantly different at P<0.05.
NI PRD DI FI HSD P
Cluster number/vine 27.4 28.7 28.8 28.7 3.39 ns
Cluster weight (g) 377.5 b 407.0 a 398.0 a 395.3 a 1.48 ≤ 0.001
Yield/vine (kg) 9.18 b 11.45 a 11.53 a 11.45 a 1.48 ≤ 0.001
WUE (gberryL-1) na 46.6 a 46.8 a 23.3 b 4.75 ≤ 0.001
Brix 15.8 17.0 15.9 15.6 3.28 ns
Phenols (IFT) 8.7 ab 8.7 a 8.0 bc 7.7 c 1.31 ≤ 0.05
Titratable acidity (gL-1) 3.4 b 3.4 b 3.5 ab 3.8 a 0.56 ≤ 0.05
pH 3.81 3.84 3.84 3.78 0.26 ns
0,10 a a
NI PRD DI FI
Figure 6. Glycosyl-glucose in berries of Moscatel grapevines under four water treatments (NI,
PRD, DI, FI) during the 2002 growing season. Values shown represent the mean of 4 measurements
with standard error. Different letters show statistically significant differences at P0.05.
When compared to NI, irrigation treatments had no significant effect on berry total soluble
solids (ºBrix) and pH (Table 2). Despite the absence of statistical significance PRD treatment
displayed the highest total soluble solids value, when compared to NI, DI and FI. The
titratable acidity was significantly higher in FI compared to NI and PRD while DI showed
intermediate values. Among the irrigated treatments PRD presented the highest total phenols
content which was similar to NI. Glycosyl-glucose (GG) was significantly higher in NI and
PRD compared to FI and DI (Figure 6). There was a significant increment in the total
concentration of glycosylated secondary metabolites, like aromatic compounds, in PRD
compared to the other irrigated treatments.
Irrigation water use efficiency (WUE, yield per unit of water applied) in PRD and DI
treatments was the double of that observed in FI, which received the double amount of water.
The evolution of plant water status during the ripening period was in concert with changes
of soil water content (Fig. 1). A mild water stress was experienced by DI and PRD plants
which significantly decreased their plant water status comparatively to FI (Fig. 2), while NI
plants gradually decreased their predawn water potential to about -0.65 MPa, therefore
exhibiting a more intense water deficit. Although the unwatered side of the root zone in PRD
plants had a low water content (Fig. 1), available water on the wet side was sufficient to
supply water to the aerial part, enabling a similar or even better plant water condition in PRD
than in DI plants which, received the same amount of water. These results were consistent
with those obtained in previous experiments in 2000 and 2001 with „Castelão‟ and „Moscatel‟
grapevines (Santos et al., 2003, 2005).
Water scarcity inhibits plant growth (Chaves et al., 2004) and in fact in the vines
subjected to NI treatment a consistent reduction in vegetative growth was observed.
Nevertheless, PRD had significant lower values of leaf layer number, percentage of water
shoots and canopy wideness when compared to the other irrigated treatments, and lower
values of shoot weight, pruning weight and total leaf area when compared with FI. This
indicates a better control of vegetative growth, as also reported by Dry et al. (2001), Bravdo
(2004) and Santos et al. (2005). The growth rate decline in PRD as compared to DI is
apparently a response to signals received from the roots in the drying soil (Davies and Zhang,
1991, Passioura, 1994), since both treatments received the same amount of water and PRD
plants had similar or higher predawn leaf water potentials. Dehydration of fine roots may
promote the production of chemical signals which will restrict not only leaf conductance, but
also plant growth (Loveys and Davies, 2004). Similar results to ours, pointing to a root-to-
shoot signalling mechanism under PRD triggering vegetative growth, were obtained in
passion fruit by Turner et al. (1996). ABA seems to play a central role in the long distance
drought signalling process (Davies and Zhang, 1991; Loveys et al., 2000). In fact, many
studies using split-root system found that when part of the root system experiences water
deficit xylem ABA content increases. However, we did not observe any significant
differences in ABA concentration transported in the xylem of PRD and DI plants (Rodrigues
et al., unpublished). Nevertheless, some other chemical signals, such as cytokinins (Stoll, et
al., 2000, Davies et al., 2001) or alterations in ions content in the xylem sap (Wilkinson and
Davies, 2002) may be involved in that regulation. A possible explanation for the lateral leaf
area suppression and the lower canopy wideness in PRD compared to DI could be the
reduction of cytokinins concentration since these hormones are known to be involved in the
stimulation of growth of lateral shoots (Dry et al., 2001).
It is well known that drought may cause more inhibition of shoot growth than of root
growth and in some cases the absolute root biomass in drying soil may increase when
compared to the well watered soils (Sharp and Davies, 1989). The lower sensitivity of root
growth to water stress appears to occur as a consequence of the rapid root osmotic adjustment
in response to the decrease in soil water content, which allows the maintenance of water
uptake and also due to the enhanced root cell wall loosening ability (Hsiao and Xu, 2000;
Sharp et al, 2004). We observed in the soil profile an alteration in the root distribution in the
plants with their root systems totally exposed (NI) or partially (PRD) to soil water depletion,
expressed by the increased increment of the root biomass in the deeper soil layers.
Conversely, FI and DI plants showed a homogeneous root mass density in the different layers
of the soil profile. This contrasts with other studies where irrigation promoted shallow rooting
systems (Proffitt et al., 1985, Carmi et al., 1992). However, our results in NI plants are in
accordance to those obtained in other species, such as faba bean, where drought lead to an
increased increment on rooting depth and root density (Husain et al. (1990) or maize where
root dry biomass and length were increased under drying soil when compared to well-watered
conditions (Schmidhalter et al., 1998). On the other hand, some studies using PRD in potted
plants evidenced that development in both root length and dried mass was significantly
enhanced in maize (Kang et al., 2002) and tomato (Mingo et al., 2004). Also Dry et al. (2000)
observed in grapevines a significantly larger root area for ≥ 15 cm depth in „dry‟ than in „wet‟
Berry temperatures changed mostly in response to incident solar radiation being lower in
the denser canopies of FI and DI than in the more open ones of NI and PRD. Higher berry
temperatures were observed on the sun-exposed clusters of the west side of the canopy due to
the normally higher ambient temperatures that occurred after noon (Spayd et al., 2002).
Exposure to sunlight influenced berry composition through temperature and incident
radiation (Smart and Robinson, 1991; Dokoozlian and Kliewer, 1996; Bergqvist et al., 2001;
Dokoozlian and Bergqvist, 2001). In our experiment the higher temperature and PPFD values
observed in NI and PRD compared to FI and DI were positively correlated with the higher
values of G-G and total phenols concentration, as also found by Spayd et al. (2002).
Accordingly, Dry et al. (1996) and Loveys et al. (1998) had shown that the reduction in
canopy density due to PRD enabled a better fruit quality expressed by higher concentrations
of anthocyanins, phenols and glycosil-glucose. Concerning the values of glycosylated
aromatic precursors (G-G) that we obtained, they were consistent with those found in the
literature for white grape varieties (Francis et al., 1998), although slightly lower, presumably
as a result of the higher grape yields reached in this vintage (2002). The higher values of
aromatic precursors obtained in PRD and NI berries, when compared to FI and DI ones may
represent a quality improvement.
The higher concentrations of total phenols observed in NI and PRD can be explained by
the better light microclimate at the cluster zone (17 and 10 % of reference PAR respectively)
and also by the higher percentage of exposed clusters, as a result of the more open canopy.
Additionally the higher concentration of total phenols in NI compared to FI may be explained
by the lower berry weight observed in the NI treatment. It is generally assumed that smaller
berries have a higher surface:volume ratio leading to a higher concentration of secondary
metabolites in berry juice (Hardie et al. 1997). As we did not find significant differences in
berry weight between DI and PRD grapevines the main reason for the differences in total
phenols seems to be the indirect effect of the cluster microclimate (Williams and Matthews,
1990; Van Leeuwen and Seguin, 1994; Lopes et al., 2001, Santos et al., 2003, 2005) as a
result of the lower canopy density obtained with PRD.
Cluster number per vine was independent of the water treatment, so the lower yields
obtained in NI compared to the irrigated treatments were due to the lower cluster weight. The
significant loss in weight of NI berries can be explained by the lower values of soil water
content during all the growing season and the higher temperatures on berry cell elongation
period, leading to a reduction in cell division in pericarp tissue (McCarthy, 1999) and to a
shrinkage of berries during advanced stages of ripening (Crippen and Morrison, 1986a).
The effects of water availability on soluble sugar content are dependent on the cultivar.
For example, Schultz (1996) reported a decrease in soluble sugar content for Grenache but not
in Syrah for the same intensity of water stress. Irrigation did not significantly affect berry
sugar accumulation confirming our previous studies (Santos et al., 2003, 2005). The low berry
sugar content observed in all treatments can be explained by the very high yields obtained in
our experiment, which is a characteristic of this variety. The higher titratable acidity observed
in fully irrigated plants was consistent with results obtained in the 2000 and 2001 growing
seasons (Santos et al. 2003, 2005). Indeed the increase of must titratable acidity is a common
response to irrigation (Williams and Matthews 1990) and may be beneficial for the wines of
some varieties that have low acidity. In PRD and NI the lower titratable acidity was attributed
to increased malic acid degradation due to the higher temperatures of exposed fruit (Kliewer,
1971). So a controlled water deficit may be an important tool to the musts deacidification in
some varieties as defended by Matthews and Anderson (1988).
We can conclude that 50% of ETc (PRD and DI) is sufficient to guarantee all the
„Moscatel‟ yield potential since with half of the water applied in FI no significant yield
reduction was observed leading to the double water use efficiency (amount of fruit produced
per unit of water applied). Our results underline the interest of the PRD as a strategic
irrigation management to reduce both water consumption and canopy density improving fruit
quality as far as phenols and G-G, without affecting yield.
We thank to DRARO, namely to the Centro Experimental de Pegões for the experimental
vineyard facilities and G. Rodrigues from I.S.A. for the technical assistance in measuring fruit
composition parameters. This research was funded by the UE project IRRISPLIT (ICA - 1999
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Deficit irrigation in grapevine improves water-use efficiency while
controlling vigour and production quality
Accepted in Annals of Applied Biology
Running title: Deficit irrigation in grapevines
Deficit irrigation in grapevine improves water-use efficiency while controlling vigour
and production quality
M M CHAVES1,2 *, T P SANTOS1,2, C R SOUZA2,4, M F ORTUÑO1,2, M L
RODRIGUES1, C M LOPES1, J P MAROCO2,3, J S PEREIRA1
Instituto Superior de Agronomia, Universidade Técnica de Lisboa. Tapada da Ajuda,
1349-017 Lisboa, Portugal.
Laboratório de Ecofisiologia Molecular, Instituto de Tecnologia Química e Biológica,
Avenida da República, Apartado 127, 2780-901 Oeiras, Portugal.
Instituto Superior de Psicologia Aplicada. Rua Jardim do Tabaco, 34. 1149-047 Lisboa,
Laboratório de Sementes e Fisiologia Vegetal. EMBRAPA SEMI-ÁRIDO. Brasil.
Grapevine irrigation is becoming an important practice to guarantee wine quality or even
plant survival in regions affected by seasonal drought. Nevertheless, irrigation has to be
controlled in order to optimize source to sink balance and avoid excessive vigour. The results
we present here in two grapevine varieties (Moscatel and Castelão) during three years,
indicate that we can decrease the amount of water applied by 50% (as in DI, deficit irrigation
and in PRD, partial root drying) in relation to full ETc (FI vines) with no negative effects on
production and even get some gains of quality (in the case of PRD). We report that in NI and
in several cases in PRD vines exhibit higher concentrations of berry skin anthocyanins and
total phenols than those presented by DI and FI vines. We showed that these effects on quality
were mediated by a reduction in vigour, leading to an increase on light interception in the
cluster zone. Because plant water status during most of the dates along the season was not
significantly different between PRD and DI, and when different, PRD even exhibited a higher
leaf water potential than DI vines, we conclude that growth inhibition in PRD was not a result
of a hydraulic control. The gain in crop water use in DI and PRD was accompanied by an
increase of the 13C values in the berries in DI and PRD as compared to FI, suggesting that we
can use this methodology to assess the integrated WUE over the growing season.
Keywords: Deficit irrigation, grapevines, water-use efficiency, vigour, production
A large proportion of vineyards are located in regions with seasonal drought (e.g., climate
of the Mediterranean type) where soil and atmospheric water deficits, together with high
temperatures, exert large constraints in yield and quality. In recent years, the number of dry
days per year has increased in southern Europe (Luterbacher et al., 2006) and this trend is
likely to increase in the future, according to global change scenarios (Petit et al., 1999;
Miranda et al., 2006). This will have an impact in viticulture (Schultz, 2000), with
viticulturists in these regions having to rely more and more on irrigation to stabilize yield and
improve wine quality. However, there is still some controversy concerning the positive and
negative effects of grapevine irrigation practice in traditional viticulture because if water is
applied in excess it can reduce colour and sugar content and produce acidity imbalances in the
wine (Bradvo et al., 1985; Matthews et al., 1990; Esteban et al., 2001). On the contrary, a
small water supplement can increase grape yield, maintaining or even improving quality
(Reynolds & Naylor, 1994; Ferreyra et al., 2003; Santos et al., 2003). The question of when
and how much water should be applied in a given environment and variety is still standing.
A key to improve winegrape quality in irrigated vineyards is to achieve an appropriate
balance between vegetative and reproductive development, as an excess of shoot vigour may
have undesirable consequences for fruit composition (McCarthy, 1997). A mild water stress,
maintained through partial irrigation, may reduce vine vigour and competition for
carbohydrates by growing tips, as well as promoting a shift in the partition of
photoassimilates towards reproductive tissues and secondary metabolites. These changes in
plant metabolism by mild water stress may increase the quality of the fruit and wine produced
(Matthews & Anderson, 1988, 1989).
With enhanced pressure on water resources, the increasing demand for vineyard irrigation
will only be met if there is an improvement in the efficiency of water use (Davies et al 2002;
Chaves & Oliveira, 2004; Flexas et al., 2004; Cifre et al., 2005; Souza et al., 2005a). New
approaches for irrigation management will have to reduce both water consumption and the
detrimental environmental effects of current agricultural practices. This goal may be achieved
in several ways, deficit drip-irrigation being a widely used practice with the aim of saving
water and simultaneously improve wine quality. Currently, the two most important irrigation
tools, based on physiological knowledge of grapevine and other crops response to water
stress, are Regulated Deficit Irrigation (RDI) and Partial Rootzone Drying (PRD).
In RDI water input is removed or reduced for specific periods during the crop cycle,
improving control of vegetative vigour, in order to optimize fruit size, fruitfulness and fruit
quality (Chalmers et al., 1986; Alegre et al, 1999; Dry et al., 2001). RDI has been used
successfully with a number of crops, reducing water use in crops such as olive trees (Alegre et
al., 1999; Goldhamer, 1999; Wahbi et al., 2005), peaches (Mitchell & Chalmers, 1982; Li et
al., 1989; Boland et al., 1993), pears (Mitchell et al., 1989; Caspari et al., 1994; Marsal et al.,
2002) and grapevines (Battilani, 2000; Goodwin & Macrae, 1990). However, this technique
needs control of water application, which is difficult to achieve in practice.
In vineyards under Mediterranean conditions it has been a common practice to manage the
water deficit during the final phases of grape development (Williams & Matthews, 1990).
However, in Australia, for example, the most common practice is to apply less water early in
the season (McCarthy et al., 2000). Both of these practices have shown to benefit wine, in one
case reducing the grape size by limiting available water and in the other one by limiting the
potential for grape growth. Flavour compounds, which determine wine quality, are located
principally in the berry skin, therefore a smaller size in the grape berries improves fruit
quality due to the increase in skin to flesh ratio (McCarthy, 1997). Yet, crops such as apple
trees are negatively influenced by the latter (Leib et al., 2006).
PRD is a new irrigation technique which requires that approximately half of the root
system is maintained in a drying state while the remainder of the root system is irrigated.
Theoretically, roots of the watered side maintain a favourable plant water status, while
dehydrating roots will synthesize chemical signals, which are transported to the leaves in the
transpiration stream, leading to the reduction of stomatal conductance and/or growth and
bringing about an increase in water use efficiency (WUE) (Loveys, 1984; Davies & Zhang,
1991; Dodd et al., 1996; Dry et al., 1996; Loveys et al., 2000; Davies et al., 2000; Stoll et al.,
2000; Liu et al., 2001; Souza et al., 2003, Antolín et al., 2006). There is also the indication
that PRD irrigation may have impact on root growth leading to an increased root development
in the deeper layers as shown by Dry et al. (2000) and Santos et al. (unpublished) in
grapevine or in the overall root system, as shown in tomato by Mingo et al. (2003). It has also
been reported that, as a result of drying roots in PRD, non-hydraulic signalling could occur,
leading to increases in ABA production and in xylem pH (Stoll et al., 2000; Davies & Zhang,
1991; Dry et al., 1996; Dry & Loveys, 1999) as well as a reduction of cytokinins (Stoll et al.,
2000; Davies et al., 2005)
The frequency of switching irrigation between rows in PRD will have to be determined
according to the soil type and other factors such as rainfall, temperature and evaporative
demand, but in most of the published data in grapevines, the PRD cycles were around 10-15
days (Davies et al., 2000; Stoll et al., 2000; Santos et al., 2003). The agronomic and
physiological effects of the PRD technique have been tested on several horticultural crops and
fruit trees, in studies done either in pot or field conditions. These include apple (Gowing et al.,
1990), citrus (Hutton, 2000), almond (Heilmeier et al., 1990), pear (Kang et al., 2002, 2003),
olive (Wahbi et al., 2005), tomato (Davies et al., 2000; Mingo et al., 2003), soybean (Bahrun,
2003) and recently common bean (Wakrim et al., 2005). The results are variable as a
consequence of species differences and the characteristics of each experiment: soils, climate
and agronomic practices. The debate in the literature over the effects and underlying causes of
PRD functioning is still very intense. For example, according to Bravdo (2005), an absolute
control of root drying is not possible under field conditions and also hydraulic redistribution
from deeper to shallower roots may prevent that the clear results obtained in potted plants, are
achieved under field conditions. Other authors, e.g., Gu et al. (2004), argue that the amount of
water used rather than the application system explain the effects of PRD.
We studied the effects of different irrigation regimes in physiology and production of two
grapevine varieties (Moscatel and Castelão), during three years, under the framework of the
EU project IRRISPLIT. The treatments applied were full irrigation for minimum water deficit
(FI, 100% of the ETc), deficit irrigated (DI, 50% of the ETc, half of water supplied to each
side of the row), partial root drying (PRD, 50% of ETc periodically supplied in alternation, to
only one side of the root system whereas the other one was allowed to dry) and rainfed, non-
irrigated grapevines (NI). In the present paper we review the most important results obtained,
illustrating them with data obtained in the two cultivars, during the three years of
2. Material and methods
2.1. Experimental conditions
Our research was conducted during three seasons (2000-2002) in a commercial vineyard
at the Centro Experimental de Pegões, southern Portugal (70 Km East of Lisbon). The climate
is of the mediterranean type, with hot and dry summers and mild and rainy winters. Long-
term (1976 - 2005) mean annual rainfall is 550 mm yr-1, with 400 mm falling during winter
months (INMG, 1991). The mean annual air temperature is 16ºC. Figure 1 shows the monthly
rainfall and the mean air temperature at the experimental site during the three years of the
experiment and the average values of 30 years (1976 - 2005).
Air temperature (ºC)
Jan Feb Mar Apr May Jun Jul Aug Sep
R (mm) (1976/2005) R (mm) (2000) R (mm) (2001) R (mm) (2002)
Ta (ºC) (1976/2005) Ta(ºC) (2000) Ta (ºC) (2001) Ta (ºC) (2002)
Figure 1. Total rainfall (bars) and monthly mean air temperature (lines) at the experimental site
during 2000, 2001 and 2002 season and average values of 30 years (1976-2005).
The soil is derived from podzols, with a sandy surface layer (0.6-1.0 m) and clay at 1m
depth. Two cultivars of Vitis vinifera L were studied, cv. Moscatel (syn. Muscat of
Alexandria), a white variety (used for wine and table grapes) and cv. Castelão, a red wine
variety, both grafted on 1103 Paulsen rootstock in 1997 and 1996 respectively. We have
chosen the two varieties because, in addition of producing different wine types (white versus
red), they are the most important varieties in the wine region (98%), and they are contrasting
in precocity (Castelão starting vegetation earlier than Moscatel) and in resistance to drought
(Moscatel tends to resist better than Castelão). The vines were spur pruned on a bilateral
Royat Cordon system (~16 buds per vine) using a vertical shoot positioning with a pair of
movable wires. Shoots were trimmed at about 30 cm above the higher fixed wire, two to three
times between bloom and veraison. The vineyard has a planting density of 4000 vines per
hectare the vines being spaced 2.5 m between and 1.0 m along rows.
Irrigation water was applied with drip emitters (4 L h-1 for FI and PRD and 2 L h-1 for DI),
two per vine, positioned 30 cm from the vine trunk (out to both sides of the rows), and
distributed in both sides of the root system. The water was supplied according to the crop
evapotranspiration (ETc=ET0*Kc) calculated from the evaporation of a Class A pan (ETo),
corrected with the crop coefficient (Kc), We used the most suitable Kc for our conditions,
according to Prichard (1992) and Allen et al.(1999). This Kc was 0.6 in June and 0.7 in July
and August. The irrigation treatments were: rain fed, non-irrigated (NI); partial rootzone
drying (PRD, 50% of the ETc was supplied to only one side of the root system, alternating
sides each 15 days approximately); deficit irrigation (DI, 50% of the ETc was supplied to both
sides of the vine, 25% in each side); full irrigation (FI, 100 % of the ETc was supplied to both
the sides of the root system, 50% in each side). Water was supplied twice per week since the
beginning of berry development (June) until harvest (September). Cumulative rainfall during
the experimental period (mid-June until the end of August) was 19.4 mm in 2000, 6.3 mm in
2001 and 0.5 mm in 2002 growing season (the driest year). The total amount of water
supplied to FI, PRD and DI vines are shown in Table 5. During the growing season, mean soil
moisture was on average 125 % higher in FI and 65 % in DI and PRD when compared to NI
(see Santos et al., 2005 for more details). In PRD the right side of the root-zone, the first one
to be irrigated, had soil moisture values around twice (95 mm) those of the left side (40 mm).
The reverse occurred when the irrigation side was switched.
2.2. Vegetative growth
Leaf area per shoot (8 shoots per treatment) was assessed periodically in count shoots
from bud break onwards in a non-destructive way, using the methodologies proposed by
Lopes & Pinto (2000). Primary leaf area was estimated using a mathematical model with four
variables: shoot length, leaf number and area of the largest and the smallest leaf. Lateral leaf
area estimation was done by another model that uses the same variables with the exception of
lateral shoot length. The area of single leaves was estimated using an empiric model based on
the relationship between the length of the two main lateral leaf veins and leaf area on 1645
leaves of all sizes, using a leaf area meter (LI-3000; LI-COR Lincoln, Nebraska, USA). Leaf
area per plant was calculated multiplying the average leaf area per shoot by the mean shoot
At winter pruning, shoot number and pruning weight were recorded and shoot weight and
crop load (yield/pruning weight) were calculated.
Light at the cluster zone was measured on sunny days at midday using a Sunflek
Ceptometer (model SF-40, Delta T Devices Ltd, Cambridge, UK) inserted horizontally at
cluster zone along the row. The values of incident photosynthetic photon flux density (PPFD)
were expressed in percentage of a reference PPFD, measured over the canopy top.
2.3. Water relations and gas exchange
Pre-dawn (pd) leaf water potential was measured weekly with a Scholander-type
pressure chamber (Model 1000; PMS Instrument Co., Corvallis, OR, USA), from the
beginning of berry development until harvest. The measurements were done in six fully
expanded leaves per treatment in five dates from June to August, just prior to the irrigation.
Net CO2 assimilation rate (A) and stomatal conductance (gs) were measured on sun-
exposed fully mature leaves (from primary shoots) using a portable Li-6400 IRGA (Licor,
Lincoln, Nebraska, USA). All measurements were replicated 4-8 times. A and gs values were
used to calculate the instantaneous intrinsic water use efficiency (A/gs). The relative stomatal
limitation (RSL) was estimated from (A/Ci) response curve, as described in Souza et al.,
(2005a). The maximum ratio of Rubisco carboxylation (Vcmax) and maximun electron
transport capacity at saturating light (Jmax) were obtained by fitting the model of Farquhar
(1980) with modifications by Sharkey (1985) to A/ci response curves as described by Maroco
et al (2002).
2.4. Carbon isotope composition
Samples to determine carbon isotope composition of mature leaves were collected in
primary shoots from six plants per treatment, at harvest. Berry samples consisted of 30 berries
per replicate (six replicates per treatment) taken randomly from exposed clusters. We
measured whole berries in the three years of study, and in 2001 and 2002 the pulp berry also.
The dried leaves and berry samples were ground into a fine homogeneous powder and 1 mg
sub-samples were analysed for 13C using an Europa Scientific ANCA-SL Stable Isotope
Analysis System (Europa Scientific Ltd. Crewe UK). Carbon isotopic composition was
expressed as 13C = ((Rs – Rb)/Rb) x1000, where Rs is the ratio 13C/12C of the sample and Rb
is the 13C/12C of the PDB (Pee Dee Belemnite) standard.
2.5. Yield and fruit quality
Berry composition was studied at harvest. Sampling was done by collecting cluster
fractions using a 200 berries sample per plot, collected in all vines (3-4 berries per cluster)
and representative of all positions within the clusters (Carbonneau, 1991). Sub-samples per
plot were used for fresh berry analysis of weight and volume, pH, soluble solids (º Brix) by
refractometry and titratable acidity by titration with NaOH as recommended by OIV (OIV,
1990). Another sub-sample of berries per plot was frozen at –30ºC for anthocyanin and total
phenolic compounds analysis. Total phenols were determined by spectrophotometry, by
measuring ultraviolet absorption at 280 nm (IFT) (OIV, 1990). Anthocyanins were measured
by the sodium bisulphite discoloration method (Ribéreau-Gayon and Stonestreet, 1965). At
harvest, yield components were assessed, following manual harvesting and weighing the
production on-site. Cluster number and yield per vine were recorded for all vines on each
2.6. Statistical analyses
Factorial analyses of variance (ANOVA), with year, sampling time and/or treatments as
main factors, were used to test the main effects and factor interactions on the physiological,
biochemical and growth parameters evaluated. Where ANOVA led to the detection of
significant factor effects, Tukey HSD tests were applied, a posteriori, to identify which factor
levels (treatments, years, sampling times) were significantly different. Statistically significant
differences were assumed for p<0.05 and statistical data analysis were performed with
Statistica (v5, Statsoft, Tulsa, OK).
3.1. Leaf water status, vegetative growth and canopy microclimate
In both varieties we observed that FI vines maintained a high pd throughout the growing
season (see the values for 2002 in Fig. 2).The minimum pd was measured in middle August
in 2002 (the driest year), attaining -0.22 MPa for Moscatel and -0.26 MPa Castelão (Table 1)
On the contrary, NI vines showed a progressive decline in pd from July onwards and the two
deficit irrigation treatments (PRD and DI) had pd values intermediate between FI and NI
(see also Fig. 2). In Castelão, pd of PRD vines was significantly higher than in DI. The pd
of Castelão NI vines at middle August reached lower values (ca -0.78 MPa) than those of NI
in Moscatel (-0.64 MPa).
Pre-dawn leaf water potential (MPa)
17-06 01-07 15-07 29-07 12-08 26-08 17-06 01-07 15-07 29-07 12-08 26-08
Figure 2. Seasonal evolution of pre-dawn leaf water potential for all water treatments (- NI, -
PRD, - DI, - FI), in Moscatel (A) and Castelão (B) during 2002 growing season. Each point
represents the average of 8 measurements with standard error. Bars not visible indicate standard error
(SE) smaller than symbol.
Water availability affected vine growth: the average weight per shoot measured during the
winter pruning and the total pruning weight per vine were significantly lower in NI (and in
PRD in the variety Castelão) than in FI and DI in the three years of studies (Table 2). Similar
differences were observed in the number of water shoots (epicormic shoots grown from the
old woody stem), with NI and in some cases PRD showing values significantly lower than FI
and DI (Table 2).
Table 1. Predawn leaf water potential and stomatal conductance measured at 10 a.m. in the
middle of August in Castelão and Moscatel grapevines for the 4 water treatments (NI, PRD, DI, NI)
and the three years 2000, 2001 and 2002.
2000 2001 2002
pd sx gs sx pd sx gs sx pd sx gs sx
NI -0.58 0.00 0.10 0.00 -0.39 0.06 0.13 0.00 -0.64 0.02 0.13 0.02
PRD -0.23 0.02 0.23 0.01 -0.29 0.01 0.15 0.02 -0.42 0.00 0.19 0.05
DI -0.34 0.00 0.27 0.07 -0.19 0.02 0.20 0.02 -0.44 0.01 0.22 0.03
FI -0.15 0.01 0.29 0.01 -0.11 0.00 0.25 0.02 -0.22 0.01 0.23 0.04
2000 2001 2002
pd sx gs sx pd sx gs sx pd sx gs sx
NI -0.68 0.00 0.24 0.02 -0.51 0.04 0.09 0.01 -0.78 0.02 0.11 0.03
PRD -0.37 0.01 0.31 0.01 -0.30 0.05 0.17 0.01 -0.43 0.00 0.21 0.03
DI -0.40 0.03 0.27 0.01 -0.28 0.02 0.25 0.02 -0.46 0.01 0.22 0.03
FI -0.28 0.00 0.37 0.02 -0.15 0.01 0.30 0.02 -0.26 0.01 0.26 0.02
Table 2. Vigour parameters measured at pruning time or at veraison (the case of leaf parameters)
in Castelão and Moscatel grapevines for the 4 water treatments (NI, PRD, DI, NI) in 2000, 2001 and
2002. Different letters show statistically significant differences among treatments at P 0.05.
2000 2001 2002
NI PRD DI FI NI PRD DI FI NI PRD DI FI
SHOOT (at pruning)
Shoot number per vine 11 a 11 a 9a 9a 13 a 12.0 a 13 a 12.0 a 16 a 17 a 18 a 17 a
Pruning weight (kg/vine) 0.52 b 0.56 ab 0.57 ab 0.64 a 0.46 b 0.51 ab 0.52 ab 0.58 a 0.45 c 0.48 bc 0.52 ab 0.54 a
Shoot weight (g) 49.0 b 53.4 b 64.3 a 69.0 a 36.4 b 41.2 b 42.6 b 50.8 a 29.2 b 28.8 b 31.1 ab 33.4 a
Water shoots per vine na na na na 8.0 b 9.4 b 12.7 a 12.9 a 1.5 c 2.0 b 3.0 a 3.0 a
LEAF (at veraison)
Leaf layer number (veraison) 2.6 c 3.2 b 3.8 a 3.8 a 2.4 b 2.7 b 3.6 a 3.8 a 2.1 c 2.2 c 3.2 b 3.6 a
Main leaf area (m2/vine) 2.0 a 1.9 a 2.1 a 1.9 a na na na na 2.5 b 3.1 ab 3.4 ab 4.0 a
Lateral leaf area (m2/vine) 1.6 b 2.4 b 2.8 ab 4.4 a na na na na 1.9 b 1.7 b 1.8 b 3.7 a
Total leaf area (m2/vine) 3.6 c 4.3 bc 4.9 ab 6.3 a na na na na 4.3 b 4.9 b 5.2 ab 7.6 a
2000 2001 2002
NI PRD DI FI NI PRD DI FI NI PRD DI FI
SHOOT (at pruning)
Shoot number per vine 14 b 16 ab 16 ab 17 a 16 a 18 ab 20 b 19 b 19 a 19 a 21 a 20 a
Pruning weight (kg/vine) 1.1 c 1.4 bc 1.6 ab 1.8 a 1.1 b 1.2 b 1.5 a 1.5 a 0.9 b 1.1 b 1.5 a 1.5 a
Shoot weight (g) 70.1 c 89.8 b 102.5 ab 105.8 a 64.9 b 67.8 b 76.8 a 77.8 a 47.9 b 56.1 b 76.2 a 74.9 a
Water shoots per vine na na na na 11.2 a 14.0 a 21.5 b 20.8 b 2.7 b 2.9 b 5.5 a 4.7 a
LEAF (at veraison)
Leaf layer number (veraison) 2.3 b 2.6 b 3.4 a 3.4 a 2.4 b 2.6 b 3.4 a 3.6 a 1.6 d 2.3 c 3.3 b 3.7 a
Main leaf area (m2/vine) 0.8 c 1.3 b 1.3 b 2.5 a na na na na 4.4 a 4.6 a 5.5 a 6.2 a
Lateral leaf area (m2/vine) 2.5 b 3.2 ab 3.4 a 3.6 a na na na na 0.8 b 1.0 ab 1.5 a 1.5 a
Total leaf area (m2/vine) 3.4 b 4.5 b 4.7 ab 6.0 a na na na na 5.2 c 5.6 bc 7.0 ab 7.7 a
20 a a
a b b b
b c c
c c d
18-Jul 6-Aug 20-Aug 24-Jul 7-Aug 21-Aug 5-Sep
Figure 3. Incident photosynthetic photon flux density (PPFD) at the cluster zone expressed as a %
of a reference (PPFD at the top of the canopy) in Castelão and Moscatel grapevines under four water
treatments (- NI, - PRD, - DI, - FI) during the 2002 growing season. Values shown represent
the mean of 80 measurements with SE.
Total leaf area per vine at véraison presented, in both varieties, significantly higher values
(P< 0.05) in FI than in NI and PRD vines; DI plants had intermediate values (Table 2). The
differences of total leaf area observed between treatments were mainly due to differences in
the lateral shoot leaf area as primary shoot leaf area was similar in the different watering
The reduction in vegetative growth observed in NI and in many instances in PRD,
resulted in a more open canopy as indicated by the significant increase in the PPFD received
by the clusters in these treatments when compared to DI and FI (Fig. 3).
3.2. Photosynthetic performance and water use efficiency
Diurnal time courses of gas exchange and intrinsic water use efficiency in a typical day in
August of 2002 are shown in Fig. 4. A and gs decreased throughout the day, with differences
between treatments being more marked in the late afternoon and in the variety Castelão as
compared with Moscatel. NI vines showed the lowest A and gs. Although most differences
between PRD and DI were not statistically significant, the values of gs in PRD were closer to
NI than to DI vines. Midday gs values recorded in mid-August for the two varieties and the
three years are shown in Table 1. Because they represent the lowest attained stomatal
conductances, we conclude that only in NI treatments gs reached values close to or lower than
0,1 mol m-2 s-1.
A/gs (2002 values) did not show significant differences among treatments in Moscatel,
except in the afternoon (16.00 h), where FI exhibit lower A/gs than the other treatments (see
Fig. 4). In Castelão, the highest values in A/gs throughout the day were observed in NI.
15 A B 15
mol m-2 s-1)
(mol CO2 mol H2O )
(mol CO2 mol H2O )
(mol photons m-2s-1)
(mol photons m-2s-1)
10 14 16 10 14 16
Figure 4. Diurnal course of photosynthesis (A), stomatal conductance (gs), intrinsic water use
efficiency (A/gs) and photosynthetic photon flux density (PPFD) in cultivars Moscatel (A) and
Castelão (B) measured, respectively in 5 and 8 of August 2002 for all water treatments (- NI, -
PRD, - DI, - FI). Values are the means SE.
Stomatal limitation of gas exchange (relative stomatal limitation, RSL) of Moscatel NI
vines was significantly higher than of FI and DI vines in two out of the three studied years
(2000 and 2002, see Table 3). PRD was not significantly different either from NI or from FI
and DI. In Castelão (only measured in 2002) RSL of NI vines was significantly higher than of
FI, DI and PRD vines (see also Table 3).
The estimated maximal velocity of carboxylation (Vcmax) was not significantly different
between treatments in the variety Moscatel, in any of the years of study (Table 3). The same
result was obtained for Castelão, in measurements made in 2002.
However, in the variety Moscatel, the rate of electron transport (Jmax) was lower in NI than
in FI in the three years, with PRD being closer to NI and DI closer to FI in 2000. In Castelão
no differences between treatments were observed (see also Table 3).
Table 3. Estimated model parameters (Vcmax and Jmax) and relative stomatal limitations (RSL) for
the irrigation treatments in Moscatel during years 2000, 2001 and 2002, and in Castelão during 2002.
Values are mean SE. Different letter suffixes show statistically significant differences (P<0,05).
Vcmax Jmax RSL
Treatment -2 -1 -2 -1
(mol m s ) (mol m s ) (%)
Moscatel – 2000
NI 44.92 4.82 a 125.18 5.03 a 38 0.03 a
PRD 46.09 3.67 a 136.62 6.03 a 29 0.02 ab
DI 53.63 6.69 a 171.09 13.34 b 23 0.03 b
FI 54.91 3.38 a 180.35 15.65 b 24 0.01 b
Moscatel – 2001
NI 44.89 2.14 a 154.414.67 a 37.33 7.56 a
PRD 54.14 1.70 a 186.143.63 ab 31.33 ±1.47 a
DI 49.23 4.11 a 177.22 11.58 ab 24.65 2.86 a
FI 53.42 5.70 a 206.437.77 b 25.750.87 a
Moscatel – 2002
NI 44.96 5.10 a 127.50 5.51 a 37.14 4.37 a
PRD 42.88 3.87 a 219.16 15.78 b 27.68 7.69 ab
DI 44.35 2.93 a 203.13 7.84 ab 18.88 2.03 b
FI 53.99 3.67 a 235.11 6.18 c 19.77 1.79 b
Castelão – 2002
NI 53.81 1.73 a 217.97 10.73 a 38.96 2.94 a
PRD 50.24 6.02 a 196.49 9.82 a 25.75 3.03 b
DI 48.82 4.92 a 193.90 6.03 a 25.47 2.45 b
FI 61.65 2.45 a 220.33 18.87 a 26.69 2.56 b
3.3. Carbon isotopic composition (13C)
The effects of the treatments on the 13C values of bulk leaf tissue (primary and lateral
leaves), whole berry and pulp berry are shown in Table 4 for the two varieties, and, in the
case of Moscatel, for the three years.
Table 4. Carbon isotope composition (13C) in leaves, whole berries and pulp of grape subjected to
different water treatments. Different letter suffixes show statistically significant differences (P<0,05)
2000 2001 2002 2002
Treat leaf berry leaf berry pulp leaf berry pulp leaf berry pulp
NI -25.75 a -24.33 a -26.83 a -25.02 a -24.61 a -26.23 a -24.68 a -24.43 a -26.83 a -24.04 a -23.23 a
PRD -26.63 b -25.43 b -27.08 a -25.37 b -25.14 b -26.77 a -25.18 b -25.22 b -27.53 b -25.72 b -24.89 b
DI -26.67 b -25.88 bc -26.82 a -25.41 bc -25.30 bc -26.72 a -25.45 bc -25.31 bc -28.08 bc -25.43 bc -25.22 b
FI -27.26 b -26.34 c -26.91 a -25.71 c -25.54 c -27.03 a -25.86 c -25.79 c -28.34 c -26.61 c -26.04 c
-22 Leaves Leaves NI -22
2 2 PRD
R =0.28 R =0.26
-24 DI -24
-22 Pulp Pulp -22
R =0.60 R =0.70
-30 C -30
40 60 80 100 120 40 60 80 100 120
(mol CO2 mol H2O-1)
Figure 5. Relationship of 13C in leaves and berry pulp with intrinsic water use efficiency (A/gs) in
Moscatel (A,C) and Castelão (B,D). Each point represents one replicate of the water treatments. The
measurements of A/gs were made in August 2002.
The tissues of NI plants were less depleted in 13
C (higher 13C, lowest discrimination
C) than the other treatments, and FI vines showed the lowest 13C (higher
discrimination against C). Deficit irrigation treatments (PRD and DI) showed intermediate
values. In general, significant differences between NI and FI were observed in berries and
pulp where a substantial enrichment of 13C is apparent as compared with the other tissues. The
highest values of 13C were shown in berry pulp as compared to leaves. A good relationship
was established between pulp 13C and intrinsic water use efficiency (Fig. 5). This is not the
case between A/gs and 13C in leaves.
3.4. Yield and fruit composition
As for the yield components, the number of clusters per vine was independent of soil
water availability. However, cluster weight was significantly lower in NI than in FI, (except
in Moscatel in 2001) resulting in a significant yield decrease in the former. The three irrigated
treatments showed no significant differences among them in 2001 and 2002 (Table 5).
Table 5. Yield components, berry composition and irrigation amount at harvest in Moscatel and
Castelão grapevines for 4 water treatments (NI, PRD, DI, NI) in 2000, 2001 and 2002. Different letters
show statistically significant differences among treatments at P 0.05
2000 2001 2002
NI PRD DI FI NI PRD DI FI NI PRD DI FI
Mean cluster number per vine 15.6 a 15.0 a 15.8 a 15.3 a 18.2 a 18.5 a 20.0 a 19.6 a 27.4 a 28.7 a 28.8 a 28.7 a
Mean cluster weight (g) 475.9 b 515.9 b 502.0 b 592.8 a 472.2 a 506.0 a 473.4 a 502.5 a 377.5 b 407.0 a 398.0 a 395.3 a
Yield (ton/ha) 28.9 b 30.9 b 31.6 ab 36.0 a 33.2 b 36.4 ab 36.8 ab 38.8 a 36.7 b 45.8 a 46.1 a 45.8 a
Total soluble solids (ºBrix) 21.0 a 21.8 a 20.6 a 20.6 a 17.7 a 18.6 a 17.9 a 18.4 a 15.8 a 17.0 a 15.9 a 15.6 a
Anthocyanins (mg.l-1must) na na na na na na na na na na na na
Total phenols index (TFI) 15.6 a 15.8 a 13.0 b 12.8 b 17.6 a 16.8 a 17.2 a 16.8 a 8.7 ab 8.7 a 8.0 bc 7.7 c
Titratable acidity (g. l-1) 3.5 b 3.6 b 3.8 ab 3.9 a 4.0 a 4.0 a 4.0 a 4.2 a 3.4 b 3.4 b 3.5 ab 3.8 a
pH 4.07 a 4.07 a 3.99 b 3.97 b 3.95 a 3.95 a 3.91 a 3.90 a 3.81 a 3.84 a 3.84 a 3.78 a
IRRIGATION AMOUNT (l per vine) 0 183.0 183.0 366.1 0 210.7 210.7 421.4 0 246.5 246.5 493.0
2000 2001 2002
NI PRD DI FI NI PRD DI FI NI PRD DI FI
Mean cluster number per vine 15.5 a 15.6 a 17.2 a 16.2 a 19.9 a 18.8 a 19.9 a 21.5 a 21.7 a 23.9 a 23.1 a 24.9 a
Mean cluster weight (g) 114.9 b 141.1 a 122.3 ab 151.5 a 203.9 b 245.8 a 236.2 a 236.2 a 188.0 b 260.8 a 275.9 a 254.2 a
Yield (ton/ha) 7.2 a 8.8 a 8.4 a 10.0 a 16.2 b 18.5 ab 18.8 ab 20.3 a 16.1 b 24.6 a 25.3 a 25.4 a
Total soluble solids (ºBrix) 23.4 a 24.1 a 23.5 a 23.1 a 22.4 a 22.3 a 23.0 a 22.2 a 19.0 a 19.7 a 18.7 a 18.9 a
Anthocyanins (mg.l-1must) 646.4 a 490.2 b 453.7 bc 351.2 c 703.6 a 445.2 b 438.4 b 364.0 b 799.1 a 820.6 a 682.2 b 646.4 b
Total phenols index (TFI) 21.8 a 17.0 b 15.9 bc 12.2 c 14.2 a 13.6 ab 10.4 c 11.4 bc 20.6 b 23.2 a 19.2 b 18.9 b
Titratable acidity (g. l-1) 3.48 c 3.90 b 4.08 b 4.48 a 3.3 a 4.3 b 4.1 b 3.9 ab 3.9 b 3.9 b 4.3 ab 4.8 a
pH 4.22 a 4.22 a 4.16 a 4.07 a 4.2 a 4.1 a 4.2 a 4.1 a 3.92 a 3.88 a 3.81 a 3.82 a
IRRIGATION AMOUNT (l per vine) 0 183.0 183.0 366.1 0 210.7 210.7 421.4 0 246.5 246.5 493.0
Berry composition at harvest changed with treatments. In Castelão, skin anthocyanins
accumulation was higher in NI and PRD (only significantly different in 2002) grapevines as
compared to DI and FI. NI and PRD presented the highest total phenols when compared with
the other treatments, and FI and DI the lowest (except in 2001 in Moscatel when no
differences between treatments were observed) (see Table 5). Irrigation had no significant
effect on berry total soluble solids (ºBrix) and pH. However must titratable acidity increased
significantly in FI as related to NI, in both varieties and in two years (2000 and 2002). PRD
and DI also presented higher must titratable acidity than NI in the variety Castelão in 2000
and 2001 (see Table 5).
Our results show the potential to utilize deficit irrigation, particularly PRD, to control the
redistribution of photoassimilates, through a reduction in vigour, with a positive effect on
light interception in the cluster zone and in the berry composition. We showed also that the
pattern of physiological responses to water deficits was identical in both varieties but most of
the effects of deficit irrigation are more pronounced in the variety Castelão than in Moscatel.
This can be explained by the low sensitivity to water stress in Moscatel plants (Regina &
Carbonneau, 1996). By irrigating PRD and DI grapevines with 50% of ETc, we imposed a
mild water deficits that led to leaf predawn water potentials at the end of the season that were
intermediate (-0.2 to -0.4 MPa in both treatments and the two varieties) between FI (-0.1 to -
0.3 MPa) and NI vines (-0.6 to -0.8 MPa) (see Table 1). In July 2002, we observed that PRD
vines exhibited slightly higher pd than in DI (Fig. 2), which might be explained by the
tendency for some stomatal closure (lower gs) during the afternoon in PRD, as shown in Fig.
4. Another evidence for the mild water deficits induced in PRD and DI vines was that the
estimated relative stomatal limitation (RSL) of photosynthesis in PRD and DI was not
significantly higher than in FI (see Table 3).
Crop water use efficiency (amount of fruit produced per unit of water applied) in PRD and
DI was twice that in FI, as a result of these plants (PRD and DI) having utilized half of the
irrigation water for a similar yield in FI (see Table 5). However, the intrinsic water use
efficiency estimated throughout the day or as an integral along the season (Souza et al. 2005b)
was not significantly different in the three irrigated treatments (PRD, DI and FI). These
results might be explained by the fact that flowering buds are preset and ½ water supply was
enough to maintain a “normal” sink supply and because the effects of water deficits on
stomata and photosynthesis were proportional, as it seems to be the case in both varieties (see
Interestingly, 13C values in the berries of DI and PRD vines were intermediate between
FI and NI (see Table 4 and Fig. 5), suggesting a higher integrated water use efficiency over
the season in DI and PRD than in FI. This might be the result of stomata of DI and PRD
remaining closed for more hours in the day than in FI along the growing season. The
correlation between 13C and WUE has been well documented in several crops (Farquhar &
Richards, 1984), including grapevines (Gaudillère et al., 2002; Souza et al., 2005b). The
results that we obtained point out to the interest of using integrated measures of physiological
performance in order to evaluate long-term responses of plants to the environment and to
The higher 13C values found in berries as compared to leaves may have two explanations,
(1) the fact that berry filling results from current photosynthates, which were produced during
the summer, reflecting the effects of mild water stress on stomatal closure as compared to the
spring when leaves were formed; (2) the δ13C of leaves may be more depleted than that of
berries because there are more post-photosynthetic fractionation processes (namely
respiration) in berries, which might result in differences in the carbon isotope composition of
the two organs (Badeck et al., 2005).
When comparing the two deficit irrigation treatments, one of the striking observations
made in the three years of the study was the reduction in vigour observed in PRD as
compared to FI, which did not occur in DI vines (see Table 2). As stated above, this effect
was more marked in variety Castelão than in Moscatel. Because plant water status during
most of the dates along the season was not significantly different between the two treatments,
and when different, PRD even exhibited a higher leaf water potential than DI vines, we
conclude that these effects are not a result of an hydraulic control, but rather support the
hypothesis of a long distance signalling originated in dehydrating roots. Indeed, in recent
years strong evidence has accumulated suggesting that stomatal closure and growth slow-
down observed in the early stages of soil water deficits (Hsiao, 1973; Kramer, 1983) may be
mediated by chemical signals produced in drying roots, namely ABA or cytokinins and
transported to the shoot in the transpiration stream (Wilkinson & Davies, 2002). Even though
some studies reported an increase in xylem ABA concentration in PRD plants (Stoll et al.,
2000), which we did not find in the present study (Rodrigues et al, unpublished), we think
that other chemical signals, such as cytokinins, ethylene, alterations in ion contents of the
xylem sap or changes in apoplastic pH in the leaves might be involved in that regulation
(Wilkinson & Davies, 2002; Sobeih et al., 2004).
We cannot discard the interpretation that by applying the water only in one side of the
plant may affect plant water status as a result of alterations in the dimension and architecture
of the root system. In fact, we observed some changes in the pattern of root distribution, PRD
vines showing a tendency for producing more roots in the deeper layers than the other
treatments (Santos et al., accepted). Effects of PRD in the root system were also reported by
Dry et al. (2000) in grapevines and by Mingo et al. (2003) showing an overall increase in root
biomass in potted tomato plants growing under PRD.
Taken together our results showed that the effects of PRD are dependent on the variety
studied and the climatic conditions during the growing season (see also Souza et al., 2003,
2005a,b; Santos et al., 2003, 2005). This is consistent with the knowledge that environmental
factors (such as PPFD, temperature or VPD) that influence shoot physiological processes will
interact with factors that affect the rhizosphere, determining the final nature and intensity of
chemical signalling (Wilkinson, 2004). As a consequence, plant WUE will reflect the multiple
environmental stimuli perceived and the ability of the particular genotype to sense the onset
of changes in moisture availability and therefore fine-tune its water status in response to the
environment. This complexity of responses to the environment together with the difficulty in
maintaining an effective partial root drying under field conditions as a result of root hydraulic
redistribution (Smart et al., 2005), as it was pointed out by Bravdo (2005), makes the impact
of PRD not so clear as under controlled conditions. Soil type may also play a role in the
intensity of the response to PRD. Sandy-type soils, as the one in our experiment, may produce
effects closer to controlled conditions because lateral diffusion of irrigation water is lower
than under clay-type soils (data not shown from an ongoing experiment).
Finally, our results also indicate that, for the region where our study took place
(moderately subjected to water deficits), the differences in yield between irrigated (FI, PRD
and DI) and rainfed vines (NI) only occurred in the driest year (2002). As for fruit quality, NI
and PRD tended to exhibit higher concentrations of berry skin anthocyanins and total phenols
than those presented by DI and FI vines. This suggests that the main impact of the type of
irrigation was produced via the effect of vigour on the light interception and the overall
microclimate in the cluster zone (Williams & Matthews, 1990).
Irrigation did not significantly affect berry sugar accumulation and pH. These results are
in contrast with those obtained by other authors who observed either an increase (Lopes et al.,
2001; Schultz, 1996) or a decrease (Jordão et al, 1998; Pire & Ojeda, 1999) in berry sugars
induced by high soil water availability. So in our experiment berries acted as a preferential
sink for carbohydrates under the moderate water deficits (as occurred in DI and PRD) and
even under full irrigation conditions as observed in FI vines.
It was demonstrated that large fluxes of water are not essential to optimal plant
performance for agriculture purposes and that moderate water deficits, induced under deficit
irrigation practices, might be used successfully in grapevine production to control sink-source
relationships, maintaining or ameliorating fruit quality, while improving water use efficiency
in relation to full irrigated crops. Our data point out to subtle physiological differences
between PRD receiving 50% of ETc (given in alternation to each side of the root system) and
DI (the deficit irrigation receiving equal amount of water as PRD, but distributed by the two
sides of the root system). These differences include slight reductions of stomatal aperture in
PRD as compared to DI, recorded at some dates, but a clear depression of vegetative growth
in PRD. Growth inhibition occurs in spite of similar or even better plant water status in PRD
plants, suggesting a non-hydraulic regulation mechanism. On the other hand, no significant
differences in photosynthetic rates, chlorophyll fluorescence parameters and water use
efficiency were observed between DI and PRD. Growth inhibition in PRD as compared to DI
led to an increase in cluster exposure to solar radiation, with some potential to improve fruit
quality. In fact, we report that NI and in several instances in PRD, vines exhibit higher
concentrations of berry skin anthocyanins and total phenols than those presented by DI and FI
vines. We have also observed that plant responses to deficit irrigation are dependent on the
variety and the environmental conditions during the growing season.
Financial support is acknowledged to the EU Projects IRRISPLIT ICA3-CT-1999-00008
and WATERWEB FP6-2002-INCO-WBC–509163 and the FCT Project
POCI/AGR/59079/2004. M.F. Ortuño was a recipient of a Postdoctoral research fellowship
from M.E.C. of Spain.
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