The interactive effects of water, temperature, and community composition on California grassland CO2 fluxes.
St.Clair, Sam*,1, Fisher, Marc2, Torn, Margaret2, Ackerly, David1, 1 University of California, Berkeley, Berkeley, CA2 Lawrence Berkeley National Laboratory, Berkeley, CA
ABSTRACT- Terrestrial ecosystem function is controlled by integrated biotic responses to key environmental controllers several of which are changing at unprecedented rates. We have initiated a project that examines how a California annual grassland ecosystem and its component parts (with a focus on plant-microbe interactions) respond to the interactive effects of altered water availability (low, ambient, high), temperature (ambient, +5°C)and variation in the starting composition of the plant and soil/microbial communities. A broad array of plant, microbe, soil and ecosystem processes are being tracked. We present here leaf photosynthesis and whole ecosystem CO2 flux results. Relative to the ambient water treatment, leaf photosynthesis and stomatal conductance of grasses in both mixed and monoculture communities were strongly decreased in response to low water availability. About half of the grasses also showed moderate decreases in leaf gas exchange under elevated water. Erodium the dominant forb showed strong decreases in stomatal conductance with decreasing water availability but maintained constant and high carbon fixation rates across water treatments. Increases in whole ecosystem carbon fixation, in mixed grass-forb communities, in response to increased water availability were strongest under elevated temperature (ambient +5°C). Whole ecosystem respiration was reduced or unaffected by water availability except for the elevated temperature treatment where respiration was significantly increased. Monoculture grass communities (Avena) had decreased whole ecosystem CO2 fluxes in response to elevated water in less fertile soils. CO2 flux differences were not observed in response to water treatments on more fertile soils. These result highlight the importance of interactions among key environmental variables on leaf and ecosystem gas exchange in California grassland systems.
Key words: climate change, grasslands
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