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Does water hyacinth _Eichhornia crassipes_ compensate to

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					 Does water hyacinth (Eichhornia crassipes) 
compensate to defoliation? Implications for 
compensate to defoliation? Implications for
           effective biocontrol




        Pushpa G. Soti and John C. Volin
            Florida Atlantic University
            University of Connecticut
                           Water Hyacinth
Worldwide Distribution: Tropical 
Worldwide Distribution: Tropical
and subtropical regions worldwide, 
native to Amazon basin
US Distribution: Gulf coast states, 
Florida, Georgia, South Carolina, 
Sacramento River Delta (California)

Ecological: reduces DO, outcompetes 
native species, loss of water (high 
transpiration), etc.

Economic Importance: Most 
important nuisance aquatic plant 
worldwide, and in US ($5M/yr in 
Florida), impacts fishing, recreation, 
            p           g
provides mosquito breeding habitat, 
etc. 
Control of Water Hyacinth
                          Biological Control

 Seven species introduced around the World
•Seven species introduced around the World

•Most effective are the Neochetina weevils

•Not as effective as expected in Florida

     interference with other management
    -interference with other management                   
            practices
    -high growth rate of plant
     plant regulation (bottom up control)
    -plant regulation (bottom‐up control)
    -plant compensation or                        http://www.saj.usace.army.mil/Divisions/Operations/Branches/InvSpecies/Imag
                                                  es/ControlMethods/biocontrol_NeochetinaEichhorniae_collage.jpg
        overcompensation
Grazing Optimization Hypothesis
Grazing Optimization Hypothesis
                 Objective and Hypotheses
We investigated whether the high amount of nutrient availability, 
as found in the canals of southern Florida, is facilitating water 
hyacinth plants to either compensate or overcompensate in growth 
h i th l t t ith                    t                      t i     th
to a low level of chronic simulated herbivory.

       (1) under high nutrient conditions water hyacinth would 
       ( )       h h                            h      h     l
       overcompensate for low levels (i.e., 10%) of continuous simulated 
       herbivory;
       (2) under low nutrient conditions compensation for low 
       defoliation would be muted but sufficient to result in no 
       difference in growth between the defoliated and control plants; 
       and
       (3) that high defoliation (80%) would be too great for 
            p                      g                                y
       compensation to occur regardless of nutrient level and thereby 
       result in the lowest overall growth rates.
Hypotheses
Treatments
High and Low Nutrients
(50.5 mg l‐1 N, 2.56 mg l‐1  P;
(50.5 mg l N, 2.56 mg l
   5.5 mg l‐1  N, 0.20 mg l‐1  P)

3 Defoliation Levels (0, 10 and 80%)
3 Defoliation Levels (0, 10 and 80%)

12 mesocosms (100 L) (n=6)
                    Growth Measurements
                                                   (   )
                              Relative Growth Rate (RGR)
                               RGR = [ln(final mass) – ln(initial mass)]/time

                              Allocational:
                                  LMR=leaf mass/plant mass
                                  SMR=stem mass/plant mass
                                  StMR=stolon mass/plant mass
                                  StMR stolon mass/plant mass
                                  RMR=root mass/plant mass
                                  FMR=flower mass/plant mass


Morphological:
   SLA=leaf area /leaf mass

Physiological:
   Photosynthesis
           y
Harvesting
Photos
     synthesis (         1
                mol m2 s‐1)                                           cm
                                                   Specific Leaf Area (c 2 g‐1)
                                                            100
                                                                   150
                                                                          200
                                                                                  250




                                               0
                                                     50




                               High nutrient
                               Low nutrient
                                                     y = 2E‐06x + 0.0472
                                                         R² = 0.9245
      0.09

      0.08

      0.07

      0.06
RGR




      0.05

      0.04

      0.03

      0.02

      0.01

        0
             0     2000   4000   6000     8000   10000   12000   14000

                                 SLA*PS
                                               l 1 1
                 Mass‐based Photosynthesis (nmol g‐1 s‐1)
                 M    b d Ph t      th i (
                      Summary
• No overcompensation occurred in the 10% 
  defoliated plants in high nutrients (first hypothesis 
  d f li d l        i hi h      i     (
  not supported)
       d f li d l                     d f ll i l
• 10% defoliated plants compensated fully in low 
  nutrient concentration (second hypothesis 
  supported) 
  supported)
• Lowest growth rate occurred in the 80% 
  defoliated plants but still maintained fairly high 
  defoliated plants but still maintained fairly high
  growth rate (third hypothesis supported)

                              Soti and Volin 2010 (Biological Control)
                        Summary 
                        Summary

  Water hyacinth can switch its biomass allocation 
• Water hyacinth can switch its biomass allocation
  strategy depending on the stress

   – Allocates more to roots in low nutrient conditions

   – Allocates more to seed production in low nutrient 
     conditions (seeds can remain dormant 15‐20 years)

   – Allocates more to asexual reproduction in high nutrients
         Considerations for Restoration
         Considerations for Restoration
• Water hyacinth appears to fully compensate for 
  low levels of continuous defoliation in high and 
  l   l l f        ti      d f li ti i hi h d
  low nutrient levels

   - Lowering nutrients or removing significant 
                                   y
   amounts of leaf biomass is likely insufficient for 
   water hyacinth control – although both need to 
   be used as management tools
   - Evaluation of biocontrol efficacy is arguably 
   the most important phase of biocontrol
Questions?
Q    i ?

				
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posted:8/25/2011
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