Response of Tamarix spp and Phragmites communis to Ecological Water Conveyance in the Lower Reaches of the Tarim River, Xinjiang

Based on the analysis of the monitoring data from 2000 to 2002, the response of Phragmites communis and Tamarix spp to the ecological water conveyance is discussed. The ecological water conveyance has obvious effect on the groundwater table, which gradually rises during the process of conveyance. In the four ecological water conveyances, the depth of groundwater has risen from 9.87 m before conveyance to 7.74 m, 3.79 m, 3.61 m and 2.66 m, respectively. The influence range of conveyance on groundwater table is about (1 000) m. Moreover, the depth of groundwater rises greatly nearby the watercourse, and rises less far from the watercourse; uplifted amplitude of groundwater depth in the upriver section is the maximum, accounting for 84%, and that in the lower section is the minimum, accounting for 12%. The composing and type of vegetation closely relate to the depth of groundwater. The vegetation grows well near the watercourse, but get worse far way from the watercourse. Different plants have different ecological response to the change of groundwater, because their growth requirement to the groundwater depth is different. Plant physiological response exists obvious difference and presents a gradient change at various plots. It is found that the sensitive-areas of response for Phragmites communis and Tamarix spp are 150～200 m and 200～250 m, respectively. Analyzing the change of plant s physiological index, it is found that SOD and POD are safeguard enzyme of plant cellular membrane, and the activity of them exist temporal complementarity. The change of SOD and POD contents of Tamarix spp and Phragmites communis has the same regularity. Tamarix spp and Phragmites communis have suffered from drought-stress to different degrees. The degree of drought stress is aggravated with increase in groundwater depth. The change of Phragmites communis Proline and POD content is less when groundwater depth is at 2.5 m, meeting Phragmites communis growth. When the groundwater depth is more than 3.5 m, Phragmites communis's Proline and POD content rapidly accumulate from 0.327 mg·g~(-1)·dw~(-1) and 88.18 active unit·g~(-1)·FW~(-1) to 0.569 mg·g~(-1)·dw~(-1) and 89.37 active unit·g~(-1)·FW~(-1), respectively, showing that Phragmites communis has already suffered from water stress. When the groundwater depth is more than 4 m, Proline content of Tamarix spp obviously increases from 26 μg·g~(-1)·FW~(-1) to 64 μg·g~(-1)·FW~(-1). The stress groundwater depth for Phragmites communis and Tamarix spp is 3.5 m and 4.0 m, respectively, according to the analysis and field investigation.