Soil water retention in alpine meadows under different degradation stages on the northeastern Qinghai-Tibet Plateau

Alpine meadow degradation has become serious in recent decades due to the combined effects of overgrazing, human activities and rodents, but very few studies focus on the possible impact of alpine meadow degradation on soil water retention on the Qinghai-Tibet Plateau. In this study, four degradation stages (non-degradation, ND; light degradation, LD; moderate degradation, MD; heavy degradation, HD) were selected. Results showed that (1) the aboveground biomass decreased with increasing degradation, while the belowground biomass first increased and then decreased with a maximum value in MD. (2) As the degree of degradation increased from ND to MD, the 0–10 cm soil bulk density (BD) and soil compaction (SC) decreased with the minimum values in MD (0.61 g cm−3 for BD and 1619.51 kPa for SC), while soil organic matter (SOM) increased with maximum value in MD (247.36 g kg−1), the 0–10 cm SOM in MD was the 1.5 times of that in ND. However, the 0–10 cm particle size distribution did not change significantly with increasing degradation, while the 20–40 cm clay content in HD was significantly higher than those of the other three degradation stages, (3) The MD stage displayed a strong water holding capacity in 0–10 cm soil layer due to its higher soil organic matter induced by the thick mattic epipedon. Meanwhile, the water holding capacity in the HD stage was higher than that of the other three degradation stages in the 20–40 cm soil layer owing to its higher capillary porosity. Furthermore, the soil water retention was greatly affected by the mattic epipdon through its effects on soil properties such as reducing BD and increasing SOM. Our results suggested that the mattic epipdon may play a crucial role in water retention in alpine ecosystems.