Shrub encroachment in alpine meadows facilitates soil carbon and nitrogen storage by redistributing soil water

Increased encroachment of shrubs into alpine meadows in the context of warming and humidifying climates has altered meadow plant composition and soil properties. Given the critical role of alpine meadows in soil carbon and nitrogen storage and soil conservation, changes in meadow soil moisture that may increase the potential for soil carbon and nitrogen loss are of particular concern. However, the effects of plant and soil moisture changes on soil carbon and nitrogen storage during shrub encroachment in alpine meadows are rarely reported. To address this issue, we assessed multiple plant and soil moisture variables closely associated with soil carbon and nitrogen storage along a gradient of shrub encroachment on the northeastern Tibetan Plateau (no shrubs and light, moderate, and heavy). Shrub encroachment did not lead to a decrease in soil carbon and nitrogen storage, but instead led to an increase in soil organic carbon, total nitrogen, and microbial biomass carbon and nitrogen, compared to the area without shrub encroachment, organic carbon (SOCS) and total nitrogen storage (STNS) increased by 32.20 % and 24.69 %, respectively, in the heavily-encroached area. Shrub encroachment directly enhances SOCS and STNS by increasing plant biomass above and below ground to promote organic matter inputs. Increased soil infiltration and water-holding capacity promote water enrichment in shrub patches, and improved water conditions further stimulate plant growth and create positive feedback of carbon and nitrogen inputs, while high infiltration promotes the deposition of organic matter from the ground surface to the soil and reduces runoff losses. This study emphasizes the important role of vegetation and soil moisture dynamics in the increase of SOCS and STNS under shrub encroachment.