Divergent shift of normal alpine meadow towards shrub and degraded meadows reduces soil water retention and storage capacity

Abstract

Soil saturated hydraulic conductivity (Ks) is a critical ecohydrological parameter for assessing the capacity of soil layers in grassland ecosystems to respond to precipitation efficiency, recharge groundwater and supply freshwater to rivers, which is significantly impacted by shifts in vegetation composition. Nevertheless, few studies focused on the effects of the shifts in vegetation composition on Ks of alpine grassland ecosystems. This study examined the effects of normal alpine meadow transition into shrub and severely degraded meadow stages on Ks and further qualified the driving processes. The results showed that the divergent shift of normal alpine meadows altered the soil and meadow properties. Soil water retention and storage capacity of the topsoil was reduced due to the divergent shift of the normal meadow transition into shrub meadow or severely degraded meadow. Ks and field moisture capacity (FMC) reduced by 73.1% and 64.9% in the 0–10 cm soil layer during the transition from normal to degraded meadow, while their variation in the 0–10 cm soil layer were not significant but water consumption increased during the shift from normal to shrub meadow. At the state of normal alpine meadow shift toward severely degraded meadow, the dominant factors affecting Ks were meadow cover (MC), root mass density (RMD), clay content and total porosity, with total effect coefficients of 0.48, 0.42, 0.39 and 0.69, respectively. Meanwhile, when normal alpine meadow shift toward shrub meadow, dominant factors affecting Ks were MC, non-capillary porosity, clay and sand contents, with total effect coefficients of 0.47, −0.86, −0.54 and −0.50, respectively. This study helps understanding the impacts of the shifts in vegetation composition on the ecohydrological processes in alpine meadow ecosystems in response to climate change and overgrazing.