Nitrogen nutrition and water stress effects on leaf photosynthetic gas exchange and water use efficiency in winter wheat

The responses of gas exchange and water use efficiency to nitrogen nutritio n for winter wheat were investigated under well-watered and drought conditi ons. The photosynthetic gas exchange parameters of winter wheat are remarka bly improved by water and nitrogen nutrition and the regulative capability of nitrogen nutrition is influenced by water status. The effects of nitroge n nutrition on photosynthetic characteristics and on the limited factors to photosynthesis are not identical under different water status. Intrinsic w ater use efficiency (WUEt) of the plants at the high-N nutrition was decrea sed by a larger value than that of the plants in the low-N treatment due to a larger decrease in photosynthetic rate than in transpiration rate. Carbo n isotope composition of plant material (delta(p)) is increased by the incr ease of drought intensity. The delta(p) at a given level of C-i/C-a is redu ced by nitrogen deficiency. Leaf carbon isotope discrimination (Delta) is i ncreased by the increase of nitrogen nutrition and decreased by the increas e of drought intensity. Transpirational water use efficiency (WUEt) is nega tively correlated with Delta in both nitrogen supply treatments and increas ed with the nitrogen supply. (C) 2000 Elsevier Science B.V. All rights rese rved.