Wind-induced leaf transpiration

While the significance of leaf transpiration (f_e) on carbon and water cycling is rarely disputed, conflicting evidence has been reported on how increasing mean wind speed (U) impacts f_e from leaves. Here, conditions promoting enhancement or suppression of f_e with increasing U for a wide range of environmental conditions are explored numerically using leaf-level gas exchange theories that combine a stomatal conductance model based on optimal water use strategies (maximizing the 'net' carbon gain at a given f_e), energy balance considerations, and biochemical demand for CO₂. The analysis showed monotonic increases in f_e with increasing U at low light levels. However, a decline in modeled f_e with increasing U were predicted at high light levels but only in certain instances. The dominant mechanism explaining this decline in modeled f_e with increasing U is a shift from evaporative cooling to surface heating at high light levels. New and published sap flow measurements for potted Pachira macrocarpa and Messerschmidia argentea plants conducted in a wind tunnel across a wide range of U (2-8 m s^-1) and two different soil moisture conditions were also employed to assess how f_e varies with increasing U. The radiative forcing imposed in the wind tunnel was only restricted to the lower end of expected field conditions. At this low light regime, the findings from the wind tunnel experiments were consistent with the predicted trends.