Effects of grazing exclusion on root trait characteristics of dominant plants in the desert steppe

Examining the changes in plant root system characteristics is of great significance to further understanding vegetation changes during grazing exclusion. In this study, four dominant plants, Stipa breviliora, Agropyron mongolicum, Lespedeza potaninii and Glycyrrhiza uralensis, were studied under different grazing exclusion times (0, 3, 7, and 15 years) in Ningxia desert grassland. The effects of grazing exclusion on plant root characteristics and the association of aboveground plants and soil characteristics with root traits were analyzed. The results showed that: 1) Root traits of different plants varied under grazing exclusion. The root surface area, average root diameter, and total root volume of S. breviflora decreased significantly with the extension of the grazing exclusion period (P < 0.05), and its specific root length and specific root area were the highest after 7 years of grazing exclusion. The total root length and root surface area of A. mongolicum were the highest after 3 years of grazing exclusion. The effect of grazing exclusion on the root traits of L. potaninii and G. uralensis was not significant. 2) The underground biomass of L. potaninii at 0－40 cm was the highest after 3 years of grazing exclusion, and that of A. mongolicum and G. uralensis was the highest in grassland with grazing exclusion for 7 years. The root biomass of S. breviliora and A. mongolicum in the 30－40 cm soil layer and G. uralensis in the 10－20 cm soil layer was the highest after 7 years of grazing exclusion. 3) Correlation analysis demonstrated that soil organic matter, available nitrogen, and soil bulk density significantly affected plant roots in the desert steppe. Root traits had a significant positive correlation with vegetation coverage and aboveground biomass (P < 0.05). In conclusion, grazing exclusion improved plant root traits in desert steppe to a certain extent. However, the effects observed in different plants varied. As it was difficult for a single grazing exclusion measure to achieve notable effects in the short term, grazing exclusion was combined with other measures to speed up the vegetation restoration process.