地下水矿化度对黄河三角洲柽柳光合及耗水特征的影响

为了解黄河三角洲地下水浅埋区柽柳（Tamarix chinensis Lour.）对地下水矿化度的适应特征,运用叶片气体交换和树干液流技术,测定了地下水埋深为0.9 m时淡水、微咸水（3 g·L^-1）、咸水（8 g·L^-1）和盐水（20 g·L^-1）四种矿化度下柽柳的光合作用和水分利用等参数。结果表明：随地下水矿化度升高：（1）土壤水、盐含量和土壤溶液绝对浓度均逐渐升高。（2）叶片最大净光合速率和光饱和点在咸水下最高;表观量子效率、气孔导度、蒸腾速率、胞间CO₂浓度、树干液流速率等在微咸水下最高;以上指标均在盐水矿化度下最低。水分利用效率和气孔限制值在微咸水下最低,盐水下最高。在地下水埋深0.9 m时,咸水矿化度下柽柳光合效率高,光照生态幅宽,水分利用效率高,适于柽柳幼苗的生长。

Effects of groundwater salinities on photosynthesis and water consumption characteristics of Tamarix chinensis in the Yellow River Delta

Tamarix chinensis Lour. is a constructive species of the saline-alkali wetland in the Yellow River Delta, and shallow groundwater is the main water source for the growth of T. chinensis in this area. To explore the response mechanism of T. chinensis to groundwater salinity in shallow groundwater area in the Yellow River Delta, parameters of photosynthesis and water consumption were determined under 4 groundwater salinity gradients of fresh (0 g·L^-1), brackish (3 g·L^-1), saline (8 g·L^-1) and salt (20 g·L^-1) water at simulated groundwater level of 0.9 m via leaf gas-exchange and stem sap flow (SF) techniques. The results showed that: (1) With increasing groundwater salinity, soil water content, soil salt content and absolute concentration of soil solution increased gradually; (2) Parameters of the max net photosynthetic rate (P_nmax), apparent quantum yield (AQY), light saturation point (LSP), stomatal conductivity (G_s), transpiration rate (T_r), intercellular CO₂ concentration (C_i) and stem SF rate increased first and then decreased with the increase of groundwater salinities, reaching the maximum values respectively under brackish groundwater (G_s, AQY, T_r, C_i, and SF rate) and saline groundwater (P_nmax and LSP) treatments, while all values of the above parameters reached the minimum values under salt groundwater treatment; (3) With the increase of groundwater salinity, the water use efficiency (WUE) and stomatal limitation value (L_s) of T. chinensis decreased before increasing, achieving the lowest level under brackish groundwater and the highest under salt groundwater. Under the condition of groundwater depth of 0.9 m, the salinity of groundwater significantly affects the characteristics of soil water and salt contents. The increase of soil water and salt contents, especially the absolute concentration of soil solution, further affects the photosynthetic efficiency and water use strategy of T. chinensis. Moderate groundwater salinity (brackish and saline groundwater) could improve photosynthetic capacity and reduce WUE of T. chinensis, while excessive high groundwater salinity (salt groundwater) would inhibit photosynthesis severely and improve WUE. T. chinensis has high photosynthetic capacity, wide light ecological amplitude and high WUE under saline groundwater conditions at the groundwater level of 0.9 m. This research can be used for the further study of the relationship between plant photosynthetic processes and soil water and salt contents, and can provide theoretical reference for the restoration and reconstruction of soil and water conservation shelterbelts in the Yellow River Delta.