夏玉米三叶期持续干旱下不同叶位叶片含水量变化及其与光合作用的关系

植物干物质的累积依赖于群体光合速率,而群体光合速率又与单叶的光合能力密切有关。叶片光合作用与其含水量密切相关,目前关于不同叶位叶片含水量对持续干旱的响应及其与光合作用的关系还未见报道。以华北夏玉米郑单958为材料,设置6个不同灌水处理,模拟不同灌溉量下持续干旱对夏玉米不同叶位叶片生理特性的影响,分析夏玉米顶部开始的第一、三、五叶位叶片的水分变化及其与净光合速率的关系。结果表明:夏玉米不同叶位的叶片最大含水量不同,且随干旱进程的推进叶片含水量的变化速率也不同,第一叶的叶片含水量下降速率高于第三、第五叶,第一叶的最大含水量高于第三、五叶,且可进行光合产物积累的叶片含水量下限随叶位的增加而增大。同时,第一叶的叶片含水量与土壤水分呈显著相关,且与净光合速率的相关性也非常强。第一叶可进行光合产物积累的叶片水分下限(净光合速率为零时的叶片含水量)最小,表明其耐旱性最强,对干旱具有指导意义。研究结果可为提高冠层光合作用模拟的准确性及夏玉米干旱发生发展的监测预警提供参考。

Leaf water content at different positions and its relationship with photosynthesis when consecutive drought treatments are applied to summer maize from the 3-leaf stage

The accumulation of dry matter in plants depends on the canopy photosynthetic rate, which is closely related to single leaf photosynthetic capability. Leaf photosynthesis is also highly correlated with its water content. Compared to soil water content, leaf water content can directly reflect crop growth and development and might be the best index for showing the degree of water profit and loss. Leaf water content and photosynthesis at different positions have been investigated in a number of studies. However, there have been fewer reports on the change in leaf water content (LWC) at different positions and its relationship with photosynthesis under consecutive drought stress. In this study, six different watering treatments were designed to simulate the response of leaf characteristics at the different leaf positions of summer maize "Zhengdan 958" that had been subjected to persistent drought. The simulated experiment was conducted in Baoding City, Hebei Province, northern China. After analyzing the change in leaf water content (LWC) at different positions and its relationship with net photosynthesis, the results indicated that the change in leaf position in summer maize can influence the falling rate for leaf water during consecutive drought periods and the estimated maximum leaf water content. The falling rate for leaf water and the estimated maximum leaf water content in Leaf 1 were more than in Leaf 3 and Leaf 5. When leaf photosynthesis (P_n) fell to zero (the lowest leaf water content that can maintain net photosynthesis), the leaf water contents of Leaf 1, Leaf 3, and Leaf 5 increased as the leaf position increased. This indicated that the photosynthesis response to leaf water content was different at each position. The leaf water content of Leaf 1 had strong relationships with soil water content and photosynthesis. The minimum leaf water content that could maintain net photosynthesis in Leaf 1 was lower than all the other leaf positions, which meant Leaf l had better drought tolerance. This suggests that the use of Leaf 1 in drought monitoring could be developed further in the future. These results will contribute to the accurate simulation of canopy photosynthesis and to the development and monitoring of drought in summer maize.