CO2 fluxes following simulated monsoon rain events

Rene AguileraMentor: Shirley Kurc, University of Arizona

August 16th, 2007Sevilleta 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 chamberLicor-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.

Licor-7500 sensor head

Flags outline measured area

Fan

Tripod to mount sensor head

Apply chamber

Water increases as plants transpire

Remove Chamber

Example of How Water Bends

Water increases as plants transpire

Water flux is the slope of this line!

Example of How Water Bends

12000

12200

12400

12600

12800

13000

13200

13400

13600

13800

14000

0 20 40 60 80 100 120 140 160 180 200

sec

CO

2 u

mo

l/m3

Example of How Carbon Dioxide Bends

Rainfall applied:0 mm control5 mm small10 mm large

Control has smallest response!

Large has largest response!

7 hours following 1st stimulated rainstorm on July 12

Rainfall applied:0 mm control5 mm small10 mm large

7 hours following 1st stimulated rainstorm on July 12

(+) Respiration

( - ) Uptake

Uptake in all 3 cases

Lagged ‘respiration’ after small storm?

Continued uptake after large storm?

Net Ecosystem Exchange of CO2

NE

E (

um

ol/

m2

/s)

Water Fluxes

-6

-4

-2

0

2

4

6

0 1 2 3 4 5 6 7 8 9

Days

ET

(m

mo

l/m2/

s)

Control

Small

Large

Natural Rain Event

One week after July 12

Net Ecosystem Exchange of CO2

-6

-4

-2

0

2

4

6

0 1 2 3 4 5 6 7 8 9

Days

NE

E (

um

ol/m

2s)

Control

Small

Large

One week after July 12

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