Variations of root turnover rate of Kobresia humilis populations along a soil moisture gradient in an alpine meadow

Root turnover rate can measure the renewal capacity of plant roots and is sensitive to changes in soil moisture. Five sample plots were set up along the natural soil moisture gradient in an alpine meadow, the Dongda Mountains, southeastern Tibet. The soil moisture plots Ⅰ and Ⅱ are wet habitats (soil moisture > 25%), whereas the plots Ⅲ～Ⅴ are arid habitats (soil moisture < 25%), and were sampled in 2017 and 2021 to analyze the dynamics of root turnover rate of Kobresia humilis populations during habitat aridification. The results showed that 1) the population coverage decreased significantly with the decrease of soil moisture (P < 0.05) and the density of bud bank varied significantly among soil moisture levels (P < 0.05), but the correlation with soil moisture was not significant; in the wet habitat, the seasonal dynamic changes of root biomass were consistent in both years, while they were irregular in the arid habitat. 2) Net root growth and turnover rate were significantly and positively correlated with soil moisture in both years (P < 0.01), with significant interannual differences in root turnover rate in the arid habitat (P < 0.05). 3) The root system consisted mainly of fine roots (diameter ≤ 1 mm), which accounted for > 80% of the total roots in soil, and the proportion was significantly positively correlated with soil moisture (P < 0.05). The turnover rate of fine roots was significantly greater than that of coarse roots (diameter > 1 mm) in each site (P < 0.05). 4) Root turnover was significantly and positively correlated with population coverage (P < 0.05), and inter-annual differences in root turnover were significantly and positively correlated with inter-annual differences in coverage and underground density of bud bank (P < 0.05). During habitat aridification, the root renewal capacity of K. humilis was reduced, and the seasonal dynamics of root biomass and inter-annual variation in turnover rate increased. These fluctuations were not conducive to the growth and renewal of the population, and drought stress increased the risk of a decrease in community stability.