Meadow degradation increases spatial turnover rates of the fungal community through both niche selection and dispersal limitation

The alpine meadow ecosystem, as the main ecosystem of the Qinghai-Tibet Plateau, has been heavily degraded over the past several decades due to overgrazing and climate change. Although soil microorganisms play key roles in the stability and succession of grassland ecosystems, their response to grassland degradation has not been investigated at spatial scale. Here, we systematically analyzed the spatial turnover rates of soil prokaryotic and fungal communities in degraded and undegraded meadows through distance-decay relationship (DDR) and species area relationship (SAR), as well as the community assembly mechanisms behind them. Although the composition and structure of both fungal and prokaryotic communities showed significant changes between undegraded and degraded meadows, steeper spatial turnover rates were only observed in fungi (Degraded Alpine Meadow β = 0.0142, Undegraded Alpine Meadow β = 0.0077, P < 0.05). Mantel tests indicated that edaphic variables and vegetation factors showed significant correlations to the β diversity of fungal community only in degraded meadow, suggesting soil and vegetation heterogeneity both contributed to the variation of fungal community in that system. Correspondingly, a novel phylogenetic null model analysis demonstrated that environmental selection was enhanced in the fungal community assembly process during meadow degradation. Interestingly, dispersal limitation was also enhanced for the fungal community in the degraded meadow, and its relative contribution to other assembly process (i.e. selection and drift) showed a significant linear increase with spatial distance, suggesting that dispersal limitation played a greater role as distance increased. Our findings indicated the spatial scaling of the fungal community is altered during meadow degradation by both niche selection and dispersal limitation. This study provides a new perspective for the assessment of soil microbial responses to vegetation changes in alpine areas.