Temperature and water are critical drivers of alpine plant communities. However, uncertainties persist regarding their combined effects, particular in alpine watersheds experiencing rapid changes in temperature and hydrological process over the past decades. In this study, we investigated how hydrological conditions mediate alpine plant communities’ response to temperature changes at the watershed scale. Our study showed that in water-deficient grasslands, an unimodal response of species richness (p < 0.05) and a linear decrease in coverage (p < 0.001), but non-significant changes in productivity (p > 0.05) were revealed with increasing temperature. These asynchronized changes in coverage and productivity are ascribed to plant adaptation to water stress. Plant communities shifted from low and dense cushions to taller and sparser vegetations, while dominant species changed from small and shallow-rooted species (Kobresia pygmaea) to large and deep-rooted (Potentilla bifurca) ones. In contrast, riverine wetlands showed no significant changes (p > 0.05) in community structure or productivity, likely due to their high hydrological connectivity that promoted propagule dispersal and soil environment homogenisation. Moreover, temperature and its mediated soil properties strongly influenced plant community structure in grasslands and transitional zones (R2 = 0.69 and 0.73 in Structural Equation Modeling, respectively) but not in wetlands (R2 = 0.25 in Structural Equation Modeling). This also indicates the prevailing of homogenization of habitat and species pool via strong hydrological dispersal in wetland community assembly. Overall, this study highlights that complex temperature-water interactions shape alpine plant communities at the watershed scale, which is unlikely to be understood from site-scale warming experiments focusing on a single vegetation. Future studies in these mountainous areas should consider the spatial heterogeneity induced by their complex vegetation types and hydrological conditions, while understanding the effects of intensifying stochastic processes on alpine ecosystems experiencing drastic hydrological changes.

The spatial pattern and community assembly of soil microbial taxa have notable meanings for biodiversity shaping and maintaining mechanisms. Rare fungal taxa may exhibit distinct patterns and assembly mechanisms compared to abundant taxa, but such information is limited, especially at large scales. Here, we investigated distance-decay patterns and underlying assembly mechanisms for abundant and rare fungal taxa in 129 soil samples collected across 4,000 km in Chinese Northern grasslands, based on high-throughput sequencing data. A total of 208 abundant OTUs (relative abundance > 0.1%, 2.73% of entire OTUs) and 5,779 rare OTUs (relative abundance < 0.01%, 75.85% of entire OTUs) were identified. Both abundant and rare fungal taxa showed significant distance-decay relationships (P < 0.001), but the turnover rate for rare taxa (0.0024 per 100 km) was nearly half that of abundant taxa (0.0054 per 100 km) based on the binary Bray-Curtis distance. The lower turnover of rare fungal taxa was likely due to their community assembly mechanism dominated by stochastic processes, which were less influenced by environmental gradients. In contrast, abundant taxa assembly was dominated by deterministic factors like soil variables and plant traits, which varied significantly along the geographic distance. Consistently, rare fungal taxa were also less sensitive to environmental changes, with a lower turnover rate by environmental distance (0.0027 vs. 0.0099) than abundant taxa. In summary, our findings revealed that rare fungal taxa, shaped mainly by stochastic processes, had lower spatial turnover compared to abundant taxa, dominated by deterministic processes, enhancing our understanding of rare microbial biogeography.

Arid and semi-arid vegetation is characterized by plant patches of different sizes, and plant cover is determined by patch size (PS) and number of patches (NP). However, it is still unclear how PS and NP contribute to the restoration of degraded grasslands through grazing exclusion (GE). Transect lines were sampled in six alpine steppe communities in Tibet in 2017 and 2018. Both PS and NP were assessed and compared between inside and outside grazing exclosures. Our results showed that grazing exclosures increased the mean size but decreased the total number of plant patches. This pattern of change was common to other species and could not be attributed to a shift in community composition. The results suggest that the recovery of the degraded alpine steppe is being driven by PS at the expense of NP. By promoting the expansion of the larger patches while excluding the smaller ones, GE led to an aggregating pattern with a higher proportion of bare ground, potentially reducing primary productivity.