Hongyu Qian

Ecological restoration of alpine sandy lands plays an important role in promoting vegetation recovery and enhancing ecosystem functions. However, the response characteristics of plant functional groups and nitrogen (N) and phosphorus (P) dynamics under different restoration treatments remain unclear. Taking three typical ecological restoration treatments in the alpine semi-humid sandy land on the eastern edge of the Qinghai–Tibet Plateau—fencing + sand barrier establishment + mixed grass seeding (MG), fencing + sand barrier establishment + shrub planting alone (SA), and fencing + sand barrier establishment + shrub–grass combination (SG)—as the study objects, and unrestored natural sandy land as the control (CK), this study investigated the characteristics of plant biomass and diversity, as well as the content and stoichiometric characteristics of N and P in the plant–litter system under different restoration treatments, and analyzed the response relationships between plant diversity and changes in N and P in the plant–litter system. The results showed that all three restoration treatments increased plant community biomass and diversity indices. Among them, the SG treatment had the highest aboveground biomass and diversity, whereas the MG treatment had the largest belowground biomass. All three restoration treatments increased the N and P contents of herbaceous plants and litter, with the greatest increases observed under the SG treatment. The results for plant functional groups showed that legumes had the highest N content, while forbs had the highest P content. The N:P ratios of aboveground plant parts ranged from 5.85 to 8.82 and were lower in the SA and SG treatments, suggesting that plants under the restoration treatments may be N-limited. In conclusion, the SG treatment is the most effective restoration approach for promoting vegetation recovery and nutrient content in alpine sandy lands. These results provide a scientific basis for selecting ecological restoration treatments for alpine sandy lands and for improving restoration effectiveness and efficiency.

Although vegetation restoration is widely applied to reverse desertification in alpine sandy lands, its duration-dependent coordination of soil phosphorus (P) pools and biological P cycling remains unclear. We examined alpine sandy lands restored with Salix cupularis for 5, 10, 15, and 20 years on the eastern Qinghai-Tibet Plateau, using non-restored natural sandy land (CK) as the control. Systematic measurements included soil total P (TP), available P (AP), the P activation coefficient (PAC), labile, moderately labile, and non-labile P fractions, microbial biomass P (MBP), five phosphatase activities, and the relative abundances of phoC, phoD, and pqqC. Relative to CK, restoration significantly increased every measured indicator except non-labile P. After 20 years of restoration, surface-soil AP and PAC exceeded the control by 174.9% and 133.7%, respectively. Non-labile P content remained statistically unchanged, although its proportional contribution declined as TP and the more available P pools increased. Exploratory partial least-squares structural equation modeling summarized positive associations from P-cycling genes to enzymes (path coefficient = 0.980), from enzymes to active P fractions (0.893), and from active P fractions to P-availability indicators (0.800; all p < 0.01). Whereas, the direct enzyme–P availability association was not significant. This study shows that restoration duration is associated with P accumulation and coordinated microbial–enzymatic cycling that redistributes soil P toward more available pools without detectable depletion of non-labile P.

The rhizosphere serves as a critical interface for plant–soil–microorganism interactions. Rhizosphere soil refers to the soil directly adhering to root surfaces, while non-rhizosphere soil denotes the surrounding soil not in direct contact with roots. This study investigated the characteristics of soil microbial community structure, diversity, and enzyme activity dynamics in both rhizosphere and non-rhizosphere soils of Salix cupularis (shrub) across different restoration periods (4, 8, 16, and 24 years) in alpine sandy lands on the eastern Qinghai–Tibet Plateau, with unrestored sandy land as control (CK), while analyzing relationships between soil properties and microbial characteristics. Results demonstrated that with increasing restoration duration, activities of sucrase, urease, alkaline phosphatase, and catalase in Salix cupularis rhizosphere showed increasing trends across periods, with rhizosphere enzyme activities consistently exceeding non-rhizosphere levels. Bacterial Chao1 and Shannon indices followed similar patterns to enzyme activities, revealing statistically significant differences between rhizosphere and non-rhizosphere soils after 8 and 24 years of restoration, respectively. Dominant bacterial phyla ranked by relative abundance were Actinobacteria > Proteobacteria > Acidobacteria > Chloroflexi > Gemmatimonadetes. The relative abundance of Actinobacteria exhibited highly significant positive correlations with carbon, nitrogen, phosphorus, and enzyme activity indicators, indicating that Salix cupularis restoration promoted improvements in soil physicochemical properties and nutrient accumulation, thereby enhancing bacterial community diversity and increasing Actinobacteria abundance. These findings provide fundamental data for restoration ecology and microbial ecology in alpine ecosystems, offering a scientific basis for optimizing ecological restoration processes and improving recovery efficiency in alpine sandy ecosystems.

Phosphorus (P) is essential for plant growth, but its soil availability depends on the characteristics of P fractions. However, few studies have examined soil P fractions under ecological restoration in alpine and semi-humid regions. This study investigated three restoration methods on the eastern Tibetan Plateau: planting mixed grasses (MG), planting Salix cupularis alone (SA), and planting Salix cupularis in combination with grasses (SG), restored for 14 years, with untreated sandy land (CK) as control. Through field sampling and laboratory analysis, soil P fractions and physicochemical properties were analyzed. The findings demonstrate that the three ecological restoration modes could increase total P and total organic P content and reduce inorganic P content. Ecological restoration can improve the content of soil labile P (resin-Pi, NaHCO3-Pi, and NaHCO3-Po) by activating NaOH-Pi and HCl-P, thus improving the availability of soil P and increasing the potential P (residual-P) source. Soil P fractions content positively correlated with SWC, SOC, and TN (p < 0.05) but negatively with BD and pH (p < 0.05). The experimental outcomes of this study will help to understand the P availability and its potential sources during ecological restoration while providing a scientific foundation for selecting optimal restoration strategies in alpine sandy land.

Soil aggregate stability and carbon–nitrogen content are critical indicators for assessing the vegetation restoration effects. Salix cupularis plays a vital role in rehabilitating desertified alpine meadows on the eastern Qinghai–Tibet Plateau. However, research remains limited about how afforestation influences the soil aggregate stability and associated carbon and nitrogen dynamics. In this study, sandy land (0 years) served as the control, and the spatial time replacement method was used to examine changes in the soil water-stable aggregate composition, stability, organic carbon (OC) and total nitrogen (TN) contents, and density at a 0–60 cm depth after 5 and 10 years of afforestation restoration (Salix cupularis). Ecological restoration significantly enhanced the proportion of macroaggregates (>0.25 mm) in the topsoil (0–20 cm), and improved aggregate stability. After 10 years of restoration, macroaggregates increased by 45.04% and 51.32%, respectively. The average weight diameter and geometric mean diameter of the aggregates increased by 51.32% and 59.53%, respectively. Following restoration, there was a gradual increase in the OC and TN contents in the soil, with the highest increase observed in the 0–10 cm layer (266.67% and 391.67%). The OC and TN of the aggregates also displayed a similar trend. Correlation analysis results indicated a significant positive relationship between the soil OC and TN contents and density, OC content in aggregates of various diameters, and the stability of these aggregates. The Pearson’s correlation coefficient for OC in aggregates > 1 mm was the highest. Compared with 5 years, 10 years of recovery were more conducive to the formation of macroaggregates, enhancement in aggregate stability, and the accumulation of OC and TN. Therefore, vegetation restoration on the Zoige Plateau can significantly enhance the soil water-stable aggregate composition and stability and can also increase the soil and OC and TN contents and density, thereby enhancing the soil ecological quality. This study provides fundamental data and theoretical support for rehabilitating desertified grasslands on the eastern Qinghai–Tibet Plateau.

Wetlands provide important ecosystem services, such as water conservation, biodiversity protection, and carbon sequestration. The Zoige alpine wetland is the largest high-altitude swamp in the world and plays a critical role in regional ecological balance and climate change. However, little is known about the fate of its soil organic carbon (SOC) storage. In this study, we estimated the degradation status of the wetland over the past 35 years and used machine learning to investigate the dynamics and driving factors of SOC at different soil depths of the Zoige wetland in 1985, 2000, and 2020. We also simulated the future SOC balance under different scenarios. The results showed that the area of Zoige wetland has degraded by 378.71 km² in the past 35 years. Increased precipitation and solar radiation offset the adverse effects of global warming, making the soil act as a carbon sink in the past 35 years. The total SOC storage of the wetland soils in 1985, 2000, and 2020 was estimated to be 2.03 Pg, 2.05 Pg, and 2.21 Pg, respectively, with 46.95% of SOC distributed in the subsoil layers. Climate change was the most important driving factor controlling the SOC storage of the Zoige wetland, explaining 51.33% of the SOC changes in the soil. Temperature change was always the most important factor controlling wetland SOC, and precipitation had a greater impact on the topsoil. Under the temperature control targets of 1.5 °C and 2 °C, the SOC pool of the Zoige wetland will decrease by 60.21 Tg C and 69.19 Tg C, respectively. Under scenarios of a 10% and 20% increase in precipitation, the wetland soil will accumulate an additional 46.53 Tg C and 118.89 Tg C, respectively. The study results provide important references for the sustainable management of the Zoige wetland under the background of global climate change.