Abstract:

In order to reveal the response of photosynthesis and water consumption characteristics in Tamarix chinensis leaves to the depth of groundwater table, and define the depth of groundwater table to maintain T. chinensis higher photosynthetic efficiency and suitable growth. By taking three-year-old T. chinensis seedlings as experimental materials, a total of 7 submersible depths of groundwater table (0 m, 0.3 m, 0.6 m, 0.9 m, 1.2 m, 1.5 m and 1.8 m) was designed, and the light response processes of gas exchange parameters and the daily dynamics of sap flow in T. chinensis leaves to different depths of groundwater table were analyzed. The results showed that different depths of groundwater table could significantly change the soil moisture condition, and affect the photosynthetic process and water consumption in T. chinensis leaves. The net photosynthetic rate (P_n), photosynthetic response parameters, water use efficiency (WUE) and sap flow rate in T. chinensis leaves had obvious response to the depth of groundwater table. (1) With the depth of groundwater table rising, the P_n, WUE, transpiration rate, and sap flow rate increased first and then decreased, which showed the maximum value at the depth of groundwater table of 1.2 m with relative soil water content of 40.51%. The stomatal conductance, stomatal limit value increased first and then decreased, while the intercellular CO₂ concentration was the opposite; From 1.2 m to 1.8 m depth of groundwater table or from 1.2 m to 0 m depth of groundwater table, the photosynthetic decrease was mainly due to the stomatal limitation. (2) With the depth of groundwater table rising, the maximum net photosynthetic rate, light saturation point, and apparent quantum efficiency in T. chinensis leaves increased first and then decreased, reaching the maximum value (21.15 μmol·m^-2·s^-1, 1513.4 μmol·m^-2·s^-1, and 0.06 μmol·mol^-1, respectively) at the 1.2 m depth of groundwater table, while the light compensation point was the opposite. (3) The 1.2 m depth of groundwater table was the turning point of photosynthesis from stomatal limitation to non-stomatal restriction. The stomatal regulation made T. chinensis maintain high photosynthetic characteristics under drought stress. The conclusion was that the T. chinensis showed photosynthetic water adaptability to drought-tolerant water and moisture, and the 1.2 m depth of groundwater table under freshwater conditions was suitable for the growth of T. chinensis.

Key words: photosynthesis, water use efficiency, groundwater level, Tamarix chinensis, Yellow River Delta