资源环境科技发展态势分析平台

Evapotranspiration and photosynthetic carbon uptake are both constrained by water availability, with presumed water-limited and water-independent but energy-limited regimes. We investigate water availability's relationships with evaporative fluxes and photosynthetic measures at continental scale using surface and satellite-based observations. The observation-driven approach is independent of prior model-based estimates. We find water-limited and water-independent regimes for both energy and carbon cycle processes in spatial and temporal aggregate, differences in water-limitation relationships across ecohydrological regions, and more consistent signs of water limitation in photosynthetic than evaporative processes. Ecosystem water use efficiency's response to water availability changes in sign with aridity state across time and space generally but shows negative correlations in temporal anomalies.

Plain Language Summary Evaporation and plant CO2 uptake both require water to be available at the land surface. From satellite and weather station data, we find simple relationships between these processes and the amount of available water. Even though evaporation and CO2 uptake are linked through water loss from plant leaves, we find that the relationships between each of these and the amount of available soil water are different; it seems that plant CO2 uptake is similarly sensitive to the amount of available water, in wet and dry environments, while evaporation is much more sensitive in dry environments. The amount of water used in the landscape for similar amounts of photosynthesis changes with soil wetness in the Western United States but remains relatively constant in the eastern United States.