春小麦对骤旱的响应特征及其阈值分析

与缓慢发展的干旱过程不同，骤旱具有发生速度快，短期内可致害的特点。目前，关于作物骤旱致害的临界阈值及其调控机制尚不清楚。以春小麦为供试作物，通过桶栽试验，模拟研究骤旱过程中小麦受旱致害的过程特征及其控制因素。结果发现，发生骤旱时土壤含水量下降呈先快后慢的变化趋势，叶片水分和叶水势则呈先慢后快的指数变化趋势。叶片光合生理指标对土壤水分的下降存在明显的阈值响应，且不同生理指标的阈值并不完全相同，其中净光合速率与表征叶片光合能力的指标（最大羧化速率）对土壤有效含水量的响应阈值为0.4，气孔导度和蒸腾速率对土壤有效含水量的响应阈值分别为0.5和0.4。而小麦光合生理指标对叶片水分和叶水势的阈值响应并不明显。同时依据各生理指标相关和通径分析结果得出，骤旱发生时引起小麦叶片净光合速率快速降低的主导因子为非气孔因素，而并不是以往作物受旱研究中的气孔因素。本研究结果有望丰富干旱影响认知，并可为科学应对干旱提供依据。

The response characteristics and thresholds of spring wheat to flash drought

Drought is usually thought as being a slowly-developing climate phenomenon. However, flash drought evolves rapidly and reduces time available for impact mitigation. At present, the response characteristics and threshold of flash drought induced disaster for crop is still unclear. In this study, the dry-down experiments were carried out at buckets in different climatic zones. The responses of several leaf photosynthetic parameters to water supply condition were analyzed during flash drought development. The results showed that in the process of flash drought, the soil water content decreased rapidly at first and then slowly. The leaf water content and leaf water potential decreased slowly at first and then rapidly as exponential trends. There were obvious threshold responses of photosynthetic physiological parameters of leaves to the decrease of soil water content, and the thresholds of different physiological parameters were different. The net photosynthetic rate and the maximum carboxylation rate had the identical threshold to available soil water at 0.4. However, the stomatal conductance and transpiration rate had different thresholds to available soil water at 0.5 and 0.4, respectively. The photosynthetic physiological parameters of spring wheat did not respond to the thresholds for leaf water content and leaf water potential significantly. It indicated that the disaster mechanism of flash drought strongly caused by insufficient soil water supply. Furthermore, based on correlation analysis and path analysis, we found that the controlling factors of rapid decrease of net photosynthetic rate of spring wheat leaves were non-stomatal factors, which contrasted with the traditional researcher reflecting the stomatal factor mainly limiting photosynthetic process. This study enriches the cognition of drought impact and provides the scientific basis for drought mitigation.