CO 2 fluxes following simulated monsoon rain events Rene Aguilera Mentor: Shirley Kurc, University of Arizona August 16 th, 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 onlyControl Treatment 2: One 5 mm storm each weekSmall Treatment 3: One 20 mm storm each monthLarge Same amount of water addition, different timing!

Hypothesis 1: In the first day or two following all rainfall events, CO 2 will be released, followed by a period of lagged CO 2 uptake (Potts et al. 2006, Huxman et al. 2004) Hypothesis 2: Over the course of the monsoon season, there will be less CO 2 response following the treatment of more frequent small storms than infrequent large storms. (Spoonseller 2007).

How do I measure CO 2 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.

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

Example of How Carbon Dioxide Bends

Rainfall applied: 0 mm control 5 mm small 10 mm large Control has smallest response! Large has largest response! 7 hours following 1 st stimulated rainstorm on July 12

Rainfall applied: 0 mm control 5 mm small 10 mm large 7 hours following 1 st 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 NEE (umol/m2/s)

Natural Rain Event 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