Physiological trade-offs of stomatal closure under high evaporative gradients in field grown soybean

Abstract

Limited rainfall is the main constraint to agriculture, making agricultural research to understand plant behaviour that leads to avoidance of soil water deficit a matter of priority. One focus has screened for crop varieties that decrease stomatal conductance under high vapour pressure deficit (VPD), a proxy for the leaf evaporative gradient. However, the link between stomatal closure and physiological consequences in field environments is not yet clear. A field experiment on soybeans demonstrated that considerable variation in leaf temperature relative to air temperature occurred, leading to evaporative gradients differing substantially from VPD. Thus, transpiration is decreased by stomatal closure at high VPD, but to compensate, transpiration is somewhat increased due to higher leaf temperatures. Soil water deficit led to lower stomatal conductance, particularly under low evaporative conditions, not just under hot conditions. Non-stomatal photosynthetic limitations were observed due to combined occurrence of stomatal closure and high temperature under high VPD. Although leaves reached temperatures higher than the threshold for a decrease in maximum photochemical efficiency, and displayed non-stomatal photosynthetic limitations, no photoinhibition or damage was observed by night-time. The results demonstrate that more understanding of physiological strategies for achieving altered water use is needed to avoid trade-offs and heat stress.

Low stomatal sensitivity to vapor pressure deficit in irrigated common, lima and tepary beans

“…A limited transpiration rate at high vapor pressure deficit (VPD) for well-watered 40 conditions has been used as a mechanism to breed water conservative crops (Sinclair et VPD would correspond to limited transpiration, and has been applied, for example, to soybean 48 (Gilbert et al, 2011;Medina and Gilbert, 2016) and peanut (Shekoofa et al, 2015). However, little 49 work has determined whether this behavior is found in common bean (Phaseolus vulgaris L.) or 50 other domesticated Phaseolus species.…”

Near‐surface turbulence as a missing link in modeling evapotranspiration‐soil moisture relationships

“…Experimental results and model predictions in Figure reveal the coupled (and nonlinear) effects of soil moisture and atmospheric conditions on transpiration rates. At certain soil moisture contents (<0.28 in this case – Figure ), higher atmospheric evaporative demand would give lower transpiration fluxes: a seemingly counterintuitive atmospheric flux response accounting for emerging land‐surface feedback in a changing climate [ Reynolds‐Henne et al ., ; Teskey et al ., ; Medina and Gilbert , ; Sulman et al ., ; Schauberger et al ., ]. This implies a varying soil‐plant resistance under different atmospheric and soil moisture conditions [ Denmead and Shaw , ; Newman , ; Mallick et al ., ] which is successfully accounted for by the proposed parametric transpiration model (equation and Figure ).…”

“…The proposed transpiration scheme (equations and ) couples stomatal conductance, leaf energy balance, and transport of water through the soil‐plant‐atmosphere continuum, improving our mechanistic understanding of stomatal response to soil water and atmospheric controls. This is of particular importance for developing predictive capabilities quantifying land‐atmosphere coupling under future climate change scenarios [ Reynolds‐Henne et al ., ; Chaves et al ., ; Combe et al , ; Medina and Gilbert , ].…”

Forcing variables in simulation of transpiration of water stressed plants determined by principal component analysis

“…Well-watered bean plants of the FI treatment linearly increased transpiration rate, whereas plants under water stress (DI treatment) showed an increasing trend in transpiration rate for some days after irrigation had been suspended but it decreased with time as the soil dried out. This suggests that transpiration was limited by water shortage in the soil and in this case the atmospheric demand for water vapour did not affect the transpiration rate, as discussed by Tuzet et al (2003) and Medina and Gilbert (2016). By the end of the period, an irrigation gift of ~ 15 mm was applied to guarantee plant survival and the trend of transpiration rate was to increase.…”