The interaction of rising CO₂and temperatures with water use efficiency

TLDR

The paper reviews recent data on how elevated CO₂ affects water use efficiency (WUE) and instantaneous transpiration efficiency (ITE), discusses the view that elevated CO₂ may reduce regional transpiration, and examines experimental data and model outputs on the interaction of increased temperature with elevated CO₂ on WUE, ITE, and yield. The mechanisms involve changes in stomatal conductance, assimilation, and respiration.

Abstract

Abstract. Recent data concerning the impact of elevated atmospheric CO 2 upon water use efficiency (WUE) and the related measure, instantaneous transpiration efficiency (ITE), are reviewed. It is concluded from both short and long‐term studies that, at the scale of the individual leaf or plant, an increase in WUE or ITE is generally observed in response to increased atmospheric CO 2 levels. However, the magnitude of this increase may decline with time. The opinion that elevated CO 2 may substantially decrease transpiration at the regional scale is discussed. The mechanisms by which elevated CO 2 may cause a change in these measures are discussed in terms of stomatal conductance, assimilation and respiration responses to elevated CO 2 . Finally, recent experimental data and model outputs concerning the impact of the interaction of increased temperature with elevated CO 2 on WUE, ITE and yield are reviewed. It is concluded that substantially more data is required before reliable predictions about the regional scale response of WUE and catchment hydrology can be made.