Plant community and soil water characteristics under different grazing intensities of alpine meadow on southern slope of Qilian Mountains

To investigate the effects of different grazing intensities on plant community succession and water conservation function in alpine meadows on the southern slope of the Qilian Mountains, a typical meadow was used to investigate plant community characteristics and the water-holding capacity of the soil under light (LG, 4.5 sheep·hm⁻²), medium (MG, 7.5 sheep·hm⁻²), heavy (HG, 15 sheep·hm⁻²), and severe (SG, 30 sheep·hm⁻²) grazing conditions by methods of field monitoring and laboratory experiments. The results showed that: 1) with an increase in grazing intensity, the plant community structure first stabilized and then significantly changed. From LG to HG, the importance values of herbs, Cyperaceae (sedge family), and miscellaneous grasses remained stable at 52.3%, 4.2%, and 43.5%, respectively. Under SG, the importance values of herbs significantly decreased by 92.6% compared with those of HG (P < 0.05), and sedges and miscellaneous grasses significantly increased, respectively, by 202.6% and 100.2% compared with that of HG ( P < 0.05) . 2) From LG to HG, there were no significant changes in the mean height, cover, or characterization index of the plant community. Under SG, the mean vegetation height, cover, Shannon-Wiener index, and Patrick index significantly decreased by 94.8%, 25.0%, 41.8%, and 68.5%, respectively, compared with those under HG. 3) From LG to HG, the aboveground biomass and the ratio of aboveground biomass to belowground biomass gradually increased, whereas the belowground biomass and total biomass did not change significantly. For SG, the aboveground biomass, belowground biomass and total biomass were significantly reduced by 71.9%, 55.96%, and 58.7%, respectively, compared with those under HG. 4) The effects of grazing intensity on soil bulk density, water-holding capacity, and hydraulic conductivity of alpine meadows on the slope were mainly concentrated at depths of 0－10 cm. With an increase in grazing intensity, the indices for this depth range first stabilized and then significantly changed. From LG to HG, there were no significant changes in the soil bulk density, saturated hydraulic conductivity, or saturated water-holding capacity. For SG, soil bulk density at the 0－10 cm depth significantly increased by 12.6% compared to that of HG, and saturated hydraulic conductivity and saturated water-holding capacity at the 0－10 cm depth were decreased by 50.0% and 5.9%, respectively. Maintaining the proper thickness of mattic epipedons (dense organic layer comprising living and dead roots) is the key factor in maintaining the water conservation function of inclined alpine meadows, and more attention will be required for their protection during the utilization of alpine meadows in these regions.