Bermudagrass (Cynodon dactylon), a salt-tolerant species surviving in environments with pH up to 9.3, and it exhibits variable germination responses under salt and alkaline stress. This study evaluates the impact of neutral and alkali salts with varying pH levels on bermudagrass seed germination. Six bermudagrass germplasm accessions were analyzed using neutral (NaCl: Na₂SO₄ = 1:1, pH 6.12–7.14) and alkali (NaHCO₃:Na₂CO₃ = 1:1, pH 9.62–9.90) salt treatments. Salt concentrations ranged from 0 to 250 mmol/L, with increments of 25 mmol/L. The assessed parameters included seed germination rate, germination potential, germination index, radicle length, plumule length, seedling weight, and radicle and plumule length ratio. The salt tolerance threshold of each germplasm was calculated using a linear regression fitting model. Critical indicators of salt tolerance were selected through stepwise regression, and the salt-alkali tolerance ranking was determined using a combined membership function and discriminant analysis. The results indicated that the total score decreased with increasing salt concentration under neutral salt stress. Alkali salt stress was more damaging to bermudagrass seedlings than neutral salt stress, inhibiting germination at 50 mmol/L. Neutral salt tolerance thresholds ranged from 31.7 to 207.7 mmol/L, while alkaline salt tolerance thresholds ranged from 16.9 to 53.3 mmol/L. The six germplasm accessions exhibited different responses to salt and alkali stress. Key indicators for neutral salt tolerance included plumule length, radicle and plumule length ratio, and seedling weight. For alkali salt tolerance, key indicators were germination potential, radicle length, and seedling weight, which can be used to screen for resistant germplasms. Our study demonstrates that alkaline salts inhibit seed germination and seedling growth more than neutral salts, and pH affects root growth and the radicle-to-plumule length ratio in seedlings. This research has significant ecological implications, providing insights into the adaptation strategies of bermudagrass in salt-affected and alkaline environments, which could aid in the restoration and management of degraded ecosystems.

Grazing exclusion is a widely implemented restoration strategy for degraded grasslands, but its effects on soil organic carbon (SOC) remain highly variable, and the ecological pathways associated with these changes—particularly the roles of soil microorganisms—are still insufficiently understood. To investigate context-dependent SOC responses, we conducted a 12-year grazing exclusion study across three contrasting grassland sites representing an environmental gradient (temperate desert, temperate steppe, and mountain meadow) on the northern slope of the Tianshan Mountains. By integrating multidimensional vegetation–soil–microbe observations with microbial network analysis and community assembly approaches, we examined how plant, soil, and microbial characteristics were associated with SOC variation under grazing exclusion. Our results showed that grazing exclusion was associated with significant increases in surface SOC content across all three investigated sites (16–81%), but these increases corresponded to distinct site-specific ecological association patterns. At the temperate desert site, SOC variation was mainly associated with soil conditions and microbial characteristics, where soil moisture and nutrient availability, together with fungal network complexity, showed significant associations with SOC content. At the temperate steppe site, vegetation recovery represented an important ecological component associated with SOC variation, while bacterial community assembly patterns were also related to SOC differences. At the mountain meadow site, plant, soil, and microbial characteristics showed multiple associations with SOC variation. Across all sites, grazing exclusion was consistently associated with changes in microbial network structure and community assembly processes, and these microbial ecological characteristics showed significant statistical relationships with SOC content. Our findings indicate that SOC responses to grazing exclusion are context-dependent and involve different ecological association pathways across contrasting grassland ecosystems, highlighting the importance of considering local environmental conditions when evaluating grassland restoration outcomes and carbon management strategies.

Introduction: Long-term grazing exclusion is widely used to restore degraded grasslands, yet whether its effects on soil microbial metabolism–particularly nutrient limitation and carbon use efficiency (CUE)–vary among grassland types remains poorly understood. Methods: We investigated three typical grassland types in Xinjiang, China: temperate desert (TD), temperate steppe (TS), and mountain meadow (MM), under 12 years of grazing exclusion and free grazing. We measured soil extracellular enzyme activities, assessed microbial nutrient limitation via vector analysis, and calculated microbial CUE. Results: Grazing exclusion produced contrasting effects among grassland types. In TD, all three enzyme activities significantly increased ( P < 0.01); in TS, C- and N-acquiring enzymes decreased ( P < 0.05); and in MM, only C-acquiring enzyme increased ( P < 0.001), accompanied by a significant reduction in CUE ( P < 0.01). Grazing exclusion generally intensified microbial C limitation (increased vector length) while alleviating N limitation (vector angles shifted toward 45°), though all vector angles remained below 45°, indicating persistent N limitation. Partial least squares structural equation modeling revealed distinct regulatory pathway: an indirect “soil → dissolved nutrients → microbial biomass” pathway in TD; a direct “soil → microbial biomass” pathway in TS; and a longer cascade pathway in MM that enhanced C limitation but reduced CUE. Discussion: Our findings demonstrate that grazing exclusion effects on microbial metabolism are strongly grassland-type dependent. Grazing exclusion promoted favorable microbial functional responses in TD and TS, but intensified C limitation and reduced CUE in MM. Vector length and angle serve as sensitive indicators of microbial nutrient limitation during restoration. These findings highlight the need for ecosystem-specific restoration strategies in arid and semi-arid regions.

Grazing exclusion is an effective and economical tool for restoring degraded grasslands. Yet, less attention is paid to the changes of rare and abundant bacterial taxa and their connections with soil organic carbon changes after grazing exclusion (GE). Using high-throughput sequencing and multiple statistical methods, we assessed shifts in rare and abundant bacterial taxa and contributions to soil organic carbon in five typical sagebrush (Xinyuan, Bole, Qitai, Hutubi, Manasi) desert experimental plots in Xinjiang, northwest China. The results demonstrated that rare bacterial α-diversity decreased significantly in Xinyuan, Bole, and Qitai plots, while Hutubi and Manasi plots significantly increased during GE (p < 0.05). GE increased the edges/nodes ratio from 29.60% to 44.90% and changed network complexity by shifting the nodes and topological properties, cohesion, and robustness in the bacterial network. The changes in rare bacterial diversity are tightly correlated with changes in soil organic carbon. The results not only underline the pivotal role of rare bacterial taxa in response to GE and soil organic carbon changes but also provide novel insights into the mechanisms of soil organic carbon changes after GE.