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Rene Aguilera

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					CO2 fluxes following simulated
     monsoon rain events

              Rene Aguilera
  Mentor: Shirley Kurc, University of Arizona

               August 16th, 2007
      Sevilleta LTER - REU Symposium




                                     Photo Credit: Doug Moore
     How do ecosystems respond to changes in
     precipitation patterns?

Photo Credit: Greg Greene
Monsoon Rainfall Manipulation Experiment (MRME):
Water addition alters size and frequency of rainstorms
during the summer monsoon (July – Sept) at the black
grama grassland.

Treatment 1: Ambient rainfall only               Control

Treatment 2: One 5 mm storm each week            Small

Treatment 3: One 20 mm storm each month          Large

     Same amount of water addition, different timing!
Hypothesis 1:
In the first day or two following all rainfall events, CO2 will
be released, followed by a period of lagged CO2 uptake
(Potts et al. 2006, Huxman et al. 2004)

Hypothesis 2:
Over the course of the monsoon season, there will be less
CO2 response following the treatment of more frequent
small storms than infrequent large storms. (Spoonseller
2007).
How do I measure CO2 flux?
    Whole plant chamber
    Licor-7500

 ~ 380 ppm




             Either soil is releasing carbon (respiration) or plants are taking
             up carbon (sequestration), so that concentration in chamber
             will become higher or lower than ambient.
          Flags outline measured area



Licor-7500 sensor head




                   Fan

                      Tripod to mount
                      sensor head
       Example of How Water Bends


Apply chamber



                                    Remove
                                    Chamber


                Water
                increases as
                plants transpire
        Example of How Water Bends



Water flux is the
slope of this line!




                      Water
                      increases as
                      plants transpire
                          Example of How Carbon Dioxide Bends
              14000



              13800



              13600



              13400



              13200
CO2 umol/m3




              13000



              12800



              12600



              12400



              12200



              12000
                      0    20   40   60   80   100   120   140   160   180   200
                                               sec
7 hours following 1st stimulated rainstorm on July 12
                                            Large has largest
                                            response!


               Rainfall applied:
               0 mm control
               5 mm small
               10 mm large




                                   Control has
                                   smallest response!
7 hours following 1st stimulated rainstorm on July 12
                                     Net Ecosystem Exchange of CO2

                                  Rainfall applied:
                                  0 mm control
                                  5 mm small                Lagged
                                  10 mm large               ‘respiration’ after
                                                            small storm?


                  (+) Respiration
NEE (umol/m2/s)




                  ( - ) Uptake




                                 Uptake in all 3 cases           Continued uptake
                                                                 after large storm?
                                  One week after July 12
                                              Water Fluxes


                 6



                                                                 Natural Rain Event
                 4




                 2
ET (mmol/m2/s)




                                                                                          Control
                 0                                                                        Small
                      0   1   2      3    4            5     6        7     8         9   Large



                 -2




                 -4




                 -6
                                                Days
                                  One week after July 12
                                         Net Ecosystem Exchange of CO2


                 6




                 4




                 2
NEE (umol/m2s)




                                                                                         Control
                 0                                                                       Small
                      0   1   2      3          4          5             6   7   8   9   Large



                 -2




                 -4




                 -6
                                                    Days
More measurements to
come, including a diurnal
measurement in September.
     Results thus far:
•Large less frequent storms
trigger grasses to sequester
more C, which alters
carbon storage.
•H2O availability drives
carbon storage
              Acknowledgments

•   Jennifer Johnson
•   Shirley Kurc
•   Scott Collins
•   Chris Chen
•   Ben Gutzler
•   Tori, Ash, Jarrod, Enrico, Kate, Alexandra & Judd
•   Kathy McQueen
•   Mom & Dad



                                       Photo Credit: Doug Moore

				
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posted:11/23/2012
language:English
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