PARENT SESSION
Oral Session #44: Global Change and Climate Change.
Presiding: C. Wessman
Tuesday, August 6. 1:00 PM to 4:45 PM. Grand Ballroom West, Radisson.

Plants reverse warming effect on ecosystem water balance in a California grassland.

Zavaleta, Erika^*,1, Thomas, Brian², Chiariello, Nona², Asner, Gregory³, Shaw, Rebecca³, Field, Chris³, ¹ University of California-Berkeley, Berkeley, CA² Stanford University, Stanford, CA³ Carnegie Institution of Washington, Stanford, CA

ABSTRACT- Models predict that global warming may increase aridity in water-limited ecosystems by accelerating evapotranspiration. We show that interactions between warming and the dominant biota in a grassland ecosystem produced the reverse effect. In a two-year field experiment, simulated warming increased spring soil moisture by 5-10% under both ambient and elevated CO₂. Warming also accelerated the decline of canopy greenness (NDVI) each spring by 11-17% by inducing earlier plant senescence. Lower transpirational water losses resulting from this earlier senescence provide a mechanism for the unexpected rise in soil moisture. Our findings illustrate the potential for organism-environment interactions to strongly modify global change effects on ecosystem function.

KEY WORDS: climate change, soil moisture, NDVI, phenology