Cotton is well adapted to dry areas, but progressive water deficits can lead to declines in net photosynthesis (A), ultimately reducing yield. However, the exact mechanism responsible for this decline in net photosynthesis (stomatal or non‐stomatal) is not fully understood under field conditions, partially due to limitations in the ability to collect critical data. To our knowledge, no other study has compared the drought responses of Pima and upland cotton using both CO2 response and chlorophyll fluorescence under field conditions. To this end, a field study was conducted to quantify the impact of progressive mild drought, as measured by midday stomatal conductance to water vapour (gs), on cotton leaf metabolism in Pima and upland cotton. Survey gas exchange and rapid photosynthetic CO2 response (RACiR) were conducted during flowering on the same leaf. The study observed decline in A as gs declined for both species. Correlation analysis indicated typical relationships with A and parameters associated with stomatal limitations such as decreased CO2 inside the leaf and at the site of carboxylation; however, it was found that while Pima exhibited a strong relationship between maximum electron transport rate (Jmax) and electron transport rate (ETR), upland cotton did not. Furthermore, when ETR is broken down into proportions contributing to net photosynthesis and photorespiration (ETRA, ETRP, respectively), we found that a greater proportion of ETR is being shuttled to the photorespiratory pathway in upland, relative to Pima as gs decreases. Our results fill critical knowledge gaps that can be useful for modellers and breeders when preparing for future climate change scenarios.

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两种棉属叶片光合参数的干旱响应模型

棉花非常适应干旱地区，但逐渐缺水会导致净光合作用 (A) 下降，最终降低产量。然而，在野外条件下，导致净光合作用（气孔或非气孔）下降的确切机制尚未完全了解，部分原因是收集关键数据的能力有限。据我们所知，没有其他研究比较过皮马棉和陆地棉使用二氧化碳的干旱反应2现场条件下的响应和叶绿素荧光。为此，进行了一项实地研究，以量化渐进性轻度干旱的影响，通过中午气孔导度对水蒸气的测量来衡量（Gs），对皮马棉和陆地棉棉叶代谢的影响。调查气体交换和快速光合作用CO2响应（RACiR）是在同一片叶子的开花期间进行的。该研究观察到 A 的下降Gs两个物种的数量均有所下降。相关分析表明与 A 和与气孔限制相关的参数（例如 CO 减少）的典型关系2叶内和羧化位点；然而，人们发现，虽然 Pima 与最大电子传输速率（J最大限度）和电子传递率（ETR），而陆地棉则没有。此外，当 ETR 分解为净光合作用和光呼吸贡献的比例时（ETRA, ETR磷，分别），我们发现相对于 Pima，在高地，更大比例的 ETR 被穿梭到光呼吸途径：Gs减少。我们的结果填补了关键的知识空白，对于建模者和育种者在为未来的气候变化情景做准备时非常有用。