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Aim: Species–area relationships (SAR) are widely utilized for estimating the species richness and its spatial turnover across various scales. Despite the prevalent characterization of SAR using the power law in many microbial community studies, its efficacy remains unvalidated. This study aims to characterize the microbial SAR and its mechanisms in alpine grassland soils on the Qinghai‐Tibet Plateau (QTP). Location: Qinghai‐Tibet Plateau, China. Time Period: August 2014. Major Taxa Studied: Soil bacteria. Methods: Soil samples were collected from five alpine grassland sites on the QTP. Employing a nested sampling strategy at each site, soil samples were collected in plot sizes ranging from 0.5 × 0.5 m2 to 2048 × 2048 m2. Soil bacterial communities were analysed by sequencing 16S ribosomal RNA gene amplicons using an Illumina MiSeq. Results: The bacterial SAR exhibited a logarithmic power law (R2: 0.952–0.999), outperforming the power law (R2: 0.701–0.852). Consequently, the most widely adopted power law led to an overestimation of species richness by up to 15.07% in areas >256 × 256 m2, and the regional maximum theoretical richness based on Chao1 by up to 9.88%. Mechanistically, the passive sampling hypothesis was refuted through the rarefied species richness analysis, and the disproportionate effect hypothesis was rejected based on analyses of the effective numbers of species number conversions for the probability of interspecific encounters (SPIE). Notably, Pearson and multiple linear regression analyses indicated that the spatial turnover of bacterial richness was determined by the environmental heterogeneity (R2: 0.855–0.999), rather or better than environmental variables themselves, supporting the 'environment heterogeneity hypothesis'. Main Conclusions: Soil bacterial SAR in alpine grasslands exhibited a logarithmic power relationship. Spatial turnover was primarily governed by the environmental heterogeneity. In contrast, the traditional power law leads to an overestimation of soil bacterial diversity at the regional scale. [ABSTRACT FROM AUTHOR]

Background and aims: Dissolved organic nitrogen (DON) has been increasingly recognized as a crucial component of the terrestrial nitrogen (N) cycle that regulates the ecosystem feedback to climate change. Yet, little information is available about the factors that control soil DON in the alpine ecosystems of the Tibetan Plateau, a region that is extremely sensitive to climate change. Methods: Here, we examined the relationship between DON and climate, plant, and soil attributes along a precipitation gradient in five alpine ecosystems (alpine wetland, alpine meadow, alpine shrub, alpine steppe, and alpine desert) across 20 sites that were up to 4000 km apart on the Tibetan Plateau. Results: Results showed that soil DON concentration varied significantly across these alpine ecosystems, and had a positive relationship with mean annual precipitation. Belowground biomass, soil moisture, micro biomass carbon (MBC), and soil total phosphorus (TP) explained 84% of the variation in DON concentrations. The percentage of DON in soil total dissolved N (TDN) varied with vegetation type, with the lowest percentage observed in the alpine meadow (52%) and the highest in the alpine desert (77%), indicating the slow turnover of DON into inorganic N in systems with low litter input and microbial activity. Conclusions: Precipitation and plant biomass input determine the concentration and turnover of soil DON on the Tibetan Plateau. A warmer and wetter climate that has been predicted for the Tibetan grasslands may lead to a larger and more active DON pool. [ABSTRACT FROM AUTHOR]

• Soil microbial community profiles were significantly altered in the degraded patches. • Soil microbial abundance remained unaffected by the degraded path formation. • Degraded path formation increased soil nitrifier and plant pathogen proportions. • Degraded path formation altered the soil microbial co-occurrence pattern. • Degraded path formation impeded the recovery of degraded alpine meadows. Approximately half of global grasslands are degraded. Although soil microbes play a key role in ecosystem functioning, their response to grassland degradation has not been fully investigated. In particular, degraded patch formation is the main feature of alpine meadow degradation, but little is known about its effect on soil microbes. In this study, soils were collected from three patch-degraded Tibetan alpine meadows to examine the effects of degraded patch formation on soil microbial communities. The alpine meadows at the three sites were in the third to fifth stages of degradation, respectively. Soil microbial abundance and community structure were determined through real-time PCR and MiSeq sequencing, respectively. The results showed that the degraded patch formation significantly decreased microbial respiration rates, changed the interaction patterns among microbial taxa, and increased fungal diversity, but did not significantly affect microbial abundance. Additionally, both prokaryotic and fungal community composition was significantly altered by the degraded patch formation. The functional predictions based on FAPROTAX and FUNGuild suggested that degraded patch formation significantly increased the proportion of nitrifiers, plant pathogenic fungi, and saprotrophic fungi, especially when mattic epipedons were eroded. The increased relative abundance of nitrifiers and pathogenic fungi can aggravate the risk of nitrogen leaching and plant diseases, respectively. Therefore, degraded patch formation can impede the recovery of degraded alpine meadows by changing soil microbial community composition. [ABSTRACT FROM AUTHOR]