102: Trophic Dynamics

The carbon (C) and water cycles are intimately linked in terrestrial ecosystems. Thus, an understanding o f the processes regulating transfers o f water in terrestrial ecosystems requires an understanding o f the carbon cycle, and in particular, the factors constraining carbon movement in the soii-piant-atmo sphere continuum and through trophic levels in ecosystems. The linkages between the C and the water cycles are mediated primarily through biological processes, and are bidirectional in nature. For example, precipitation (and hence ecosystem water avaiiabiiity) strongly regulates plant growth and biogeochemicai cycling in soils. Subsequently, plant growth and soil biogeochemistry strongly influence evaporation and atmospheric water vapor (and hence precipitation). Plant growth and soil processes are also cyciicaiiy linked. Thus, plant and soil interactions can have important implications fo r water cycling. However, while major climatic variables (including precipitation) may drive biological patterns and processes at large scales, other ecological interactions also regulate both plant and soil processes. An appreciation o f these ecological factors is important to understanding the relationship between C and water, and to predicting how global environmental change is likely to affect the interactions between the C and water cycles