Department of Plant Physiology, College of Life Science, Northwest A&F University, Yangling, Shaanxi 712100, China.
J Environ Sci (China). 2013 Mar 1;25(3):585-95. doi: 10.1016/s1001-0742(12)60081-3.
The efficient use of water and nitrogen (N) to promote growth and increase yield of fruit trees and crops is well studied. However, little is known about their effects on woody plants growing in arid and semiarid areas with limited water and N availability. To examine the effects of water and N supply on early growth and water use efficiency (WUE) of trees on dry soils, one-year-old seedlings of Robinia pseudoacacia were exposed to three soil water contents (non-limiting, medium drought, and severe drought) as well as to low and high N levels, for four months. Photosynthetic parameters, leaf instantaneous WUE (WUEi) and whole tree WUE (WUEb) were determined. Results showed that, independent of N levels, increasing soil water content enhanced the tree transpiration rate (Tr), stomatal conductance (Gs), intercellular CO2 concentration (Ci), maximum net assimilation rate (Amax), apparent quantum yield (AQY), the range of photosynthetically active radiation (PAR) due to both reduced light compensation point and enhanced light saturation point, and dark respiration rate (Rd), resulting in a higher net photosynthetic rate (Pn) and a significantly increased whole tree biomass. Consequently, WUEi and WUEb were reduced at low N, whereas WUEi was enhanced at high N levels. Irrespective of soil water availability, N supply enhanced Pn in association with an increase of Gs and Ci and a decrease of the stomatal limitation value (Ls), while Tr remained unchanged. Biomass and WUEi increased under non-limiting water conditions and medium drought, as well as WUEb under all water conditions; but under severe drought, WUEi and biomass were not affected by N application. In conclusion, increasing soil water availability improves photosynthetic capacity and biomass accumulation under low and high N levels, but its effects on WUE vary with soil N levels. N supply increased Pn and WUE, but under severe drought, N supply did not enhance WUEi and biomass.
高效利用水和氮（N）以促进果树和作物的生长和增加产量已经得到了充分的研究。然而，对于在水资源和 N 供应有限的干旱和半干旱地区生长的木本植物，其对水和 N 的影响却知之甚少。为了研究水分和 N 供应对干旱土壤中树木早期生长和水分利用效率（WUE）的影响，对一年生刺槐幼苗进行了为期四个月的处理，处理因素包括三种土壤含水量（非限制、中度干旱和重度干旱）以及低 N 和高 N 水平。测定了光合参数、叶片瞬时 WUE（WUEi）和整树 WUE（WUEb）。结果表明，无论 N 水平如何，增加土壤含水量都会提高树木蒸腾速率（Tr）、气孔导度（Gs）、胞间 CO2 浓度（Ci）、最大净同化率（Amax）、表观量子产量（AQY）、光合作用有效辐射（PAR）范围（由于光补偿点降低和光饱和点升高）以及暗呼吸速率（Rd），从而导致净光合速率（Pn）增加，整树生物量显著增加。因此，低 N 下 WUEi 和 WUEb 降低，而高 N 下 WUEi 增加。无论土壤水分供应情况如何，N 供应都会增强 Pn，同时增加 Gs 和 Ci，降低气孔限制值（Ls），而 Tr 保持不变。在非限制水分条件和中度干旱下，生物量和 WUEi 增加，在所有水分条件下，WUEb 增加；但在重度干旱下，N 应用对 WUEi 和生物量没有影响。总之，增加土壤水分供应可提高低 N 和高 N 水平下的光合能力和生物量积累，但对 WUE 的影响随土壤 N 水平而异。N 供应增加了 Pn 和 WUE，但在重度干旱下，N 供应并未提高 WUEi 和生物量。
