Variable hydrological effects of herbs and shrubs in the arid northeastern Qinghai-Tibet Plateau, China

Abstract

This study aims to assess the hydrological effects of four herbs and four shrubs planted in a selfestablished test area in Xining Basin of northeastern Qinghai-Tibet Plateau, China. The Rainfall-Intercepting Capability (RIC) of the herbs and shrubs was evaluated in rainfall interception experiment at the end of the third, fourth and fifth month of the growth period in 2007. The leaf transpiration rate and the effects of roots on promoting soil moisture evaporation in these plants were also assessed in transpiration experiment and root-soil composite system evaporation experiment in the five month’s growth period. It is found that the RIC of the four studied herbs follows the order of E. repens, E. dahuricus, A. trachycaulum and L. secalinus; the RIC of the four shrubs follows the order of A. canescens, Z. xanthoxylon, C. korshinskii and N. tangutorum. The RIC of all the herbs is related linearly to their mean height and canopy area (R2 ≥ 0.9160). The RIC of all the shrubs bears a logarithmic relationship with their mean height (R2 ≥ 0.9164), but a linear one with their canopy area (R2 ≥ 0.9356). Moreover, different species show different transpiration rates. Of the four herbs, E. repens has the highest transpiration rate of 1.07 mg/(m2·s), and of the four shrubs, A. canescens has the highest transpiration rate (0.74 mg/(m2·s)). The roots of all the herbs and shrubs can promote soil moisture evaporation. Of the four herbs, the evaporation rate of E. repens root-soil composite system is the highest (2.14%), and of the four shrubs, the root-soil composite system of A. canescens has the highest evaporation rate (1.41%). The evaporation rate of the root-soil composite system of E. dahuricus and Z. xanthoxylon bears a second-power linear relationship with evaporation time (R2 ≥ 0.9924). The moisture content of all the eight root-soil composite systems decreases exponentially with evaporation time (R2 ≥ 0.8434). The evaporation rate and moisture content of all the plants’ root-soil composite systems increases logarithmically (R2 ≥ 0.9606) and linearly (R2 ≥ 0.9777) with root volume density. The findings of this study indicate that among the four herbs and four shrubs, E. repens and A. canescens possess the most effective hydrological effects in reducing the soil erosion and shallow landslide in this region.