Contrasts in niche breadth and its drivers between soil microbes and plants in alpine grasslands

Niche breadth reflects the extent to which taxa or communities can tolerate environmental variations, indicating their potential to respond to environmental changes. However, it remains unclear whether micro- and macro-organisms share similar patterns of niche breadth along the same environmental gradients, and which environmental filters regulates niche breadth across different trophic levels. In this study, 180 soil samples were collected from the northeastern and central Qinghai-Tibet Plateau. By integrating microbiome sequencing with plant community surveys, we quantified niche breadth for bacteria, fungi, and plants within a multidimensional environmental space defined by principal component analysis of environmental variables. We then compared niche breadth among the three groups and identified their primary environmental drivers. The results showed that fungal communities exhibited the broadest niche breadth overall, whereas plant communities displayed the greatest variability in mean niche breadth amongst sites. Elevation was a shared determinant of niche breadth in all groups, although with contrasting response patterns. Bacterial and fungal communities exhibited broader niche breadths at higher elevations, whereas plant communities reached their maximum niche breadths at mid-elevations, suggesting contrasting adaptive strategies. A combination of abiotic (geography and environment) and biotic (community diversity and composition) factors better explained the variation in niche breadth. In particular, compared with the niche breadth of fungal communities, that of bacterial and plant communities was more strongly regulated by biotic factors such as community composition. We further confirmed that abiotic factors influenced the niche breadth of the three biological groups, both directly and indirectly, by shaping their biotic attributes. From the perspective of niche breadth, this study revealed distinct environmental adaptation patterns and the underlying mechanisms of different biological groups in alpine grassland ecosystems. Better understanding of niche breadth patterns amongst different kingdoms of life may provide improved prediction of turnover and resilience of soil ecosystems under environmental change.