Grazing exclusion is an effective management strategy for restoring degraded grasslands worldwide, but the effects of different exclusion durations on vegetation structure and soil properties remain unclear. Therefore, we evaluated vegetation characteristics and soil properties in an alpine meadow-steppe under grazing exclusion of different lengths (with grazing and with 3-year, 6-year, 9-year and 11-year grazing exclusions) on the Qinghai-Tibetan Plateau (QTP). We also explored the relationships among above-ground biomass, biodiversity and soil properties to ascertain the mechanism underlying the impact of grazing exclusion on these factors. The results showed that the above- and below-ground biomass, total number of plant species, community density, Shannon–Wiener diversity index, evenness index, richness index, soil and vegetation carbon (C) and nitrogen (N) storage and ecosystem C and N storage exhibited a hump-shaped pattern in response to the length of grazing exclusion with a 6-year threshold. In addition, structural equation modelling showed that the bulk density, soil moisture content, micro sand content and clay and silt contents were the most important determining factors leading to an increase in above-ground biomass in the alpine meadow-steppe after grazing exclusion, whereas the soil total N, available N, available phosphate and soil organic C content were the most important determining factors leading to a decrease in biodiversity. Considering the stability of the plant community and the C and N pools, long-term grazing exclusion (>9 years) is unnecessary, and the optimum exclosure duration of the moderately degraded Elymus nutans - Kobresia humilis type alpine meadow-steppe is six years on the north-eastern QTP.

Soil respiration (Rs) plays a critical role in the global carbon (C) balance, especially in the context of globally increasing nitrogen (N) deposition. However, how N-addition influences C cycle remains unclear. Here, we applied seven levels of N application (0 (N0), 54 (N1), 90 (N2), 126 (N3), 144 (N4), 180 (N5) and 216 kg N ha⁻¹ yr⁻¹ (N6)) to quantify their impacts on Rs and its components (autotrophic respiration (Ra) and heterotrophic respiration (Rh)) and C and N storage in vegetation and soil in alpine meadow on the northeast margin of the Qinghai-Tibetan Plateau. We used a structural equation model (SEM) to explore the relative contributions of C and N storage, soil temperature and soil moisture and their direct and indirect pathways in regulating soil respiration. Our results revealed that the Rs, Ra and Rh, C and N storage in plant, root and soil (0–10 cm and 10–20 cm) all showed initial increases and then tended to decrease at the threshold level of 180 kg N ha⁻¹ yr⁻¹. The SEM results indicated that soil temperature had a greater impact on Rs than did volumetric soil moisture. Moreover, SEM also showed that C storage (in root, 0–10 and 10–20 cm soil layers) was the most important factor driving Rs. Furthermore, multiple linear regression model showed that the combined root C storage, 0–10 cm and 10–20 cm soil layer C storage explained 97.4–97.6% variations in Rs; explained 94.5–96% variations in Ra; and explained 96.3–98.1% in Rh. Therefore, the growing season soil respiration and its components can be well predicted by the organic C storage in root and topsoil in alpine meadow of the north-eastern Qinghai-Tibetan Plateau. Our study reveals the importance of topsoil and root C storage in driving growing season Rs in alpine meadow on the northeast margin of Qinghai-Tibetan Plateau.

A field grazing experiment was conducted in Jingtai County, Gansu Province, China, from 2003 to 2010. The grazing intensity treatments included light grazing (LG, 0.45 sheep unit/ha), moderate grazing (MG, 0.75 sheep unit/ha), heavy grazing (HG, 1.50 sheep unit/ha), and no grazing (NG). Soil physical, chemical, and biological properties were measured. The results showed that, with increasing grazing intensities, the concentrations of total nitrogen, available nitrogen, organic matter, available phosphorus, available potassium, urease, catalase, and alkaline phosphatase in the soil decreased significantly with LG being mostly the greatest (P < 0.05). Soil bulk density for HG and NG was greater than that for LG and MG (P < 0.05). The concentrations of copper, manganese, and zinc were lower than their critical levels for plant growth, whereas iron was greater than its critical level. Correlation and principal component analyses revealed that soil trace elements were the secondary principal component compared with the primary elements, i.e., soil moisture, bulk density, etc.

Vegetation patchiness is common in degraded grasslands. Vegetation patchiness enhances the spatial variability of grassland soil organic carbon and total nitrogen. Stripped vegetation patches have a great impact on ecosystem carbon (C) and nitrogen (N) storage. Using field surveys, we examined the effects of patches on the ecosystem carbon and nitrogen storage of four typical alpine grass species patches (viz: Leymus secalinus, Koeleria pers, Stipa aliena, and Leontopodium nanum). The results indicated that ecosystem C, N, and respiration were significantly higher in intact vegetation patches than in stripped vegetation patches. Also, stripped vegetation patches recorded higher quantities of soil gravel content than the intact patches. In Leymus secalinus and Koeleria pers species patches, soil approximately contributed about 62% and vegetation about 38% to ecosystem carbon and nitrogen storage, whereas in Stipa aliena and Leontopodium nanum species patches, close to 80% of ecosystem carbon and nitrogen were found in the soil while close to 20% were stored in the vegetation. Soil total phosphorus (TP), total potassium (TK), available phosphorus (AP), soil microbial biomass carbon (MBC), and soil microbial biomass nitrogen (MBN) were higher in intact vegetation patches than in the stripped vegetation patches. Ecosystem carbon and nitrogen were observed to have a significant correlation with soil gravel content and vegetation productivity. Stripped vegetation patches resulted in decreased plant biomass input and an increased rate of soil erosion. We conclude that grassland patchiness resulted in the decline of ecosystem carbon and nitrogen storage due to a reduction in vegetation input and an increase in soil erosion. Grasslands are likely to have a higher possibility of serving as a C sink if the input of organic matter exceeds its output via sustainable management practices.

Globally, grasslands are affected by climate change and unsustainable management practices which usually leads to transitions from stable, degraded and then to desertification. Spatial vegetation patch configurations are regarded as key indicators of such transitions. Understanding the relationships between this grass-land vegetation and its environment is key to vegetation restoration projects. Spatial vegetation patch patterns were chosen across different soil and topographic conditions. Patch numbers, perimeter, and cover of each patch were measured along transects of each patch type. Using field surveys and multivariate statistical analysis, we investigated the differences in vegetation biomass and distribution and soil properties of four typical alpine plant species patches along with a range of environmental and topographic conditions. It was found that topographic conditions and soil properties, particularly soil moisture explained most of the variation in spatial patch vegetation characteristics and thus control vegetation restoration in the alpine grassland. The Kobresia humilis, Blysmus sinocompressus and Iris lactea patches under the drylands recorded small patch sizes, large patch numbers, low connectivity, and large total perimeter per unit area. Generally, species within the high moisture sites recorded small patch numbers, a large fraction of vegetation cover and a small total perimeter per m². Patches in limited soil moisture areas recorded patch configurations indicating they are unstable and undergoing degradation and therefore need urgent restoration attention to forestall their further degradation and its resultant effect of desertification. These results would provide quantitative easy-to-use indicators for vegetation degradation and help in vegetation restoration projects.

Vegetation phenology is an important indicator of global climate change, and the response of grassland phenology to climate change is particularly sensitive in ecologically fragile areas. To enhance the ecological security of the Tibetan Plateau, it is crucial to determine the relationship between fluctuations in the start of the growing season (SOS) and the response to environmental factors. We investigated the trends of the intra-annual (ten-day) and interannual spatiotemporal dynamics of the SOS on the Northeast Qinghai-Tibet Plateau (NQTP) from 2000–2020 with MOD09GA data. We identified the response relationships with environmental factors (climate, terrain) using the maximum value composite method and the Savitzky–Golay filtering and dynamic threshold method. The SOS was concentrated from the 110th to 150th days; the average annual SOS was on the 128th day, with a spatial pattern of “early in the east and late in the west”. The overall trend of the SOS was advanced (45.48%); the regions with the advanced trend were mainly distributed in the eastern part of the NQTP. The regions with a delayed SOS were mainly concentrated in the higher-altitude regions in the southwest (38.31%). The temperature, precipitation and SOS exhibited a reverse fluctuation trend around the midpoint of 2010. Precipitation affected the SOS earlier than temperature. When temperature became a limitation of the SOS, precipitation had a more significant regulatory effect on the SOS. The SOS and aspect, slope and altitude were distributed in axisymmetric, pyramidal and inverted pyramidal shapes, respectively. The SOS on shaded slopes was earlier and more intensive than that on sunny slopes. With increasing slope, the area of the SOS decreased, and it occurred later. The SOS area was largest at 4500–5000 m and decreased at lower and higher altitude intervals. The SOS occurred later as altitude increased.