Effects of Nitrogen Nutrition on Water Status and Photosynthesis in Wheat Under Soil Drought
XUE Qing-Wu, CHEN Pei-Yuan(Northwestern Institute of Soil and Water Conservation, Academia Sinica and the Ministry of Water Resource, Yangling Shaanxi 712100)
The objective of this study was to evaluate the effects of nitrogen nutrition on water status and photosynthesis in wheat under soil drought. Plants were grown at three kinds of nitrogen levels (HN, 0.57g urea/pot; MN, 0.28g urea/pot; LN, without urea). The water potential (ψ_w) and relative water content in leaves (LRWC) did not decrease markedly under mild soil drought, and the photosynthetic rate (P_n) in high N leaves was much higher than that in low N leaves. When plants were subjected to moderate or severe soil drought, the ψ_w and LRWC decreased markedly, the reduction in high N leaves being greater than that in low N leaves, so was the reduction of P_n. P_n in high N leaves decreased more quickly with decreasing ψ_w because of more severe stomatal limitation of photosynthesis, but the photosynthetic capacity of mcsophyll in high N leaves was higher. Although soil drought could cause osmotic adjustment of high N leaves to increase more than that of low N leaves, the ability to maintain stomatal conductance and P_n by osmotic adjustment was limited in extent.