PARENT SESSION
Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Seasonal carbon flux dynamics in Sonoran Desert microbial crusts following precipiation pulses.

Cable, Jessica^*,1, Huxman, Travis¹, ¹ University of Arizona, Tucson, AZ

ABSTRACT- Differential responses of ecosystem components to precipitation pulses may influence seasonal carbon dynamics in arid and semi-arid ecosystems. Microbial crust communities are important components of desert ecosystems through their roles in nitrogen cycling and soil stabilization. Their carbon fixation dynamics relative to ecosystem carbon fluxes following precipitation pulses are not well understood. These dynamics are important to understand because crusts may respond to different sized rain events than vascular plants. To begin to identify crust carbon dynamics following seasonal pulses of water, a one-inch pulse of water was applied to Sonoran desert crusts in the summer and winter. Diurnal patterns of photosynthesis and respiration were measured. Summer photosynthetic responses only compensated carbon loss from respiration, so net carbon gain was negligible. However, winter photosynthetic responses resulted in a net gain of carbon due to lower respiration rates. This is because there is a single temperature response of respiration whereas photosynthesis varies seasonally. The seasonal pattern has implications for whole ecosystem carbon exchange. Following summer precipitation events, microbial crusts do not show net productivity in the soil community but in the winter, there is a greater potential for them to contribute to net ecosystem productivity.

Key words: carbon flux, precipitation pulse, microbial crusts, ecosystem productivity