The effect of atmospheric water vapor (AV) on plants has mostly been neglected in climate impact studies. The objectives of this study were to determine the effect of AV on photosynthesis (Pn), dry matter production (DM), transpiration (Tr), leaf conductance (gl) and water use efficiency (WUE), in climate controlled chambers. The relative humidity (RH) was held near 30, 60, and 85%. DM and WUE increased with RH. δDM/δRH ~ 0.3 from 30% to 60% and ~2.2 from 60% to 85%, δWUE/δRH ~0.2 for all RH's. The improved WUE at a rate of 0.2 units for each percent of increased RH resulted from a synergy between larger gl and lower Tr at high RH. This conclusions carries a bleak message to dry regions.
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Ben‐Asher et al. (2013) studied this question.
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