Intrinsic water use efficiency (WUEi) is a critical parameter that encapsulates the equilibrium between carbon assimilation and the concomitant water expenditure. Enhancing the WUEi of crops is not only instrumental in bolstering their resilience to drought but also enables higher carbon fixation efficiency under conditions of scarce water resources. Improving the WUEi of crop varieties has become a major goal because water has become a critical limiting factor in crop productivity within the context of global change. The WUEi, traditionally calculated by WUEi=(Ca−Ci)/1.6(Ca, atmospheric CO2 concentration; Ci, intercellular CO2 concentration), may vary from that derived from WUEi=A/gsw(A, net photosynthetic rate; gsw, stomatal conductance to water vapor). In the study, the LI-6400 portable photosynthesis system was used for monitoring the leaf gas exchange of two C3 (soybean and wheat) and two C4 (maize and grain amaranth) species under changing irradiance (I) and CO2 concentration conditions. One paired-sample t test was used to compare the significant differences between WUEi values calculated by different equations and the observed values. The results showed that WUEi=(Ca−Ci)/1.6 significantly overestimated the calculated WUEi values than their corresponding observations by at least 17.78 %, 23.20 %, 9.07 %, and 14.26 % in light-response of WUEi (WUEi–I) and by at least 23.28 %, 22.02 %, 13.44 %, and 12.59 % in CO2-response of WUEi (WUEi–Ci) curves for soybean, wheat, maize, and grain amaranth, respectively. However, the relationship between net photosynthetic rate (A) and stomatal conductance to CO2 (gsc) can be improved by incorporating an empirical slope (g1) and residual stomatal conductance (g0), which can be characterized asA=(gsc–g0)(Ca–Ci)/g1. Consequently, WUEi can be calculated by WUEi=11.6g1(1−1.6g0gsw)(Ca−Ci). It is highlighted that this modified equation can not only more accurately characterize the WUEi in responses to varying I and CO2 concentration conditions but also yields a remarkably high coefficient of determination (R2 > 0.989) for the four species. These findings will provide plant physiologists and agronomists with a precise calculation tool to better understand and optimize crop water use efficiency in the face of environmental challenges.

中文翻译：

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残余气孔导度对 2 种 C3 和 2 种 C4 物种内禀水分利用效率的影响


固有水分利用效率 （WUEi） 是一个关键参数，它封装了碳同化和随之而来的水支出之间的平衡。提高作物的 WUEi 不仅有助于增强其抗旱能力，而且在水资源稀缺的情况下可以提高固碳效率。提高作物品种的 WUEi 已成为一个主要目标，因为在全球变化的背景下，水已成为作物生产力的关键限制因素。WUEi，传统上由 WUEi=（Ca−Ci）/1.6（Ca，大气 CO2 浓度;Ci，细胞间 CO2 浓度），可能与 WUEi=A/gsw（A，净光合速率;gsw，气孔对水蒸气的导度）得出的浓度不同。在该研究中，LI-6400 便携式光合作用系统用于监测两种 C3 （大豆和小麦） 和两种 C4 （玉米和谷物苋菜） 物种在辐照度 （I） 和 CO2 浓度变化条件下的叶片气体交换。采用 1 对样本 t 检验比较不同方程计算的 WUEi 值与实测值之间的显著差异。结果表明，WUEi=（Ca−Ci）/1.6 显著高估了计算的 WUEi 值，比其相应的观测值高估了至少 17.78 %、23.20 %、9.07 % 和 14.26 %，大豆、小麦、玉米和谷物苋菜的 WUEi （WUEi-Ci） 的 CO2 响应曲线分别高估了至少 23.28 %、22.02 %、13.44 % 和 12.59 %。然而，净光合速率 （A） 和气孔导度对 CO2 （gsc） 之间的关系可以通过结合经验斜率 （g1） 和残余气孔导度 （g0） 来改善，其特征可以是 A=（gsc–g0）（Ca–Ci）/g1。 因此，WUEi 可以通过 WUEi=11.6g1（1-1.6g0gsw）（Ca-Ci） 计算。结果表明，这个修改后的方程不仅可以更准确地表征响应不同 I 和 CO2 浓度条件的 WUEi，而且可以产生非常高的四种物质的决定系数 （R2 > 0.989）。这些发现将为植物生理学家和农学家提供精确的计算工具，以更好地了解和优化作物在面对环境挑战时的水分利用效率。