Effects of ecological restoration measures on vegetation and soil properties in semi-humid sandy land on the southeast Qinghai-Tibetan Plateau, China

Land desertification directly impacts the services and functions of grassland ecosystems globally, especially in alpine regions. Ecological restoration measures (e.g., erecting fences, establishing plant barriers, and planting native shrubs and grasses) are essential for combating desertification and restoring functions of degraded alpine grassland on the Qinghai-Tibetan Plateau (QTP). However, the combined effects of ecological restoration measures on the plant-soil system have yet to be systematically evaluated and compared in the alpine-cold semi-humid area. In this study, we compared vegetation and soil properties upon the application of three typical restoration measures [i.e., fencing enclosure (FE), establishing Salix cupularis sandy barrier (SCSB), and establishing Salix cupularis sandy barrier plus planting grasses (SCSBPPG)], along with severely degraded sandy land as a control (CK). Soil physicochemical (i.e., particle-size distribution, water content (SWC), bulk density (SBD), soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), and total potassium (TK)), and microbiological properties [i.e., microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP), urease, dehydrogenase, catalase, acid phosphatase, polyphenol oxidase, and β-glucosidase activities] were measured in soil layers at depths of 0–10, 10–20, and 20–30 cm. The results showed that the vegetation coverage, aboveground biomass, Margalef richness index, and Shannon–Weiner diversity index significantly increased by 13.54, 13, 3.09, and 1.80 times with FE, and by 11.24, 10.50, 1.05, and 0.83 times with SCSBPPG, respectively (P < 0.05), in comparison to CK. At the same time, SCSB had no significant influence on these four indexes. In addition, the most pronounced improvements of soil clay content, SOM, TN, and TP occurred in the 10–20 cm soil layer, with enhancements by 419%, 243.62%, 93.94%, and 68.97% in FE, and by 73%, 118.46%, 45.45%, and 41.38% in SCSBPPG, respectively. Moreover, MBC and the activities of urease, dehydrogenase, acid phosphatase, and polyphenol oxidase were higher with the artificial recovery interventions than those in CK, with the most significant increases found in 10–20 cm at 22.04%, 44.80%, 46.84%, 44.58%, and 87.50% for FE, and 17.85%, 34.30%, 47.43%, 31.78%, and 41.85% for SCSBPPG, respectively. Finally, SCSB significantly decreased the SOM, TN, TP, MBC, MBN, MBP, and the activities of urease, dehydrogenase, polyphenol oxidase, and β-glucosidase. Our study showed that FE is an efficient management measure for restoring semi-fixed dunes. Combining this with planting grasses and shrubs, rather than establishing plant barriers, is recommended to restore moving dunes in alpine-cold semi-humid sandy regions. This research can provide a reference for optimizing the ecological restoration measures and designing sustainable environmental strategies for conserving grassland at risk of desertification in QTP, China.