Abstract:

The study was conducted in the field in the Tarim River basin,with a typical desert riparian forest plant,Populus euphratica as the study object and set five different groundwater depth gradients (0~2 m,2~4 m,4~6 m,6~8 m and 8~10 m). Physiological indicators (MDA,PAL,leaf water content,chlorophyll) and leaf reflectance spectra were analyzed by measuring Populus euphratica under different groundwater burial depth gradients. The results showed that the changes of leaf water content and MDA content tended to decrease at first and increase afterwards with increasing depth of groundwater burial,while the changes of chlorophyll density and PAL activity tended to increase at first and decrease afterwards. Both MDA content and PAL activity magnitude were more sensitive to changes in groundwater burial depth,while the possible salt stress at low burial depths had a greater effect on plants than drought stress,and had a greater effect on chlorophyll density and MDA content at burial depths of 0~2 m. However,the differences in leaf water content at the five burial depths were small. In the 350~900nm band,poplar had the characteristics of "one peak and two valleys". In the "blue valley",the order of poplar reflectance at different burial depths was: 4~6m>0~2m>6~8m>8~10m>2~4m. At the "Green Peak",the order of poplar reflectance at different depths was: 4~6m>6~8m>0~2m>8~10m>2~4m,which was consistent with the difference at the "Red Valley". By correlation analysis of physiological indexes and spectra,the original spectra and leaf water content all reached a highly significant negative correlation after the wavelength of 429 nm,and reached the maximum value of negative correlation at the wavelength of 645 nm (r of -0.60530),with a small overall change. However,the correlation coefficient between the chlorophyll density and the spectrum had a maximum at 710nm on the red side (r of -0.63655). The "trilateral" parameters of the poplar spectra varied greatly at different depths of burial,and the water content of the leaves reached a highly significant level with the red valley amplitude,with the strongest correlation (r of -0.577).The variation characteristics of these indicators and spectral curves are intended to provide some basis for the research and identification of drought resistance of Populus euphratica,and the construction of ecological environment and vegetation restoration in arid areas.

Key words: Populus euphratica, groundwater, different burial depths, characteristics of change, physiological parameters, reflection spectrum