Habitat fragmentation shifts soil microbial composition but not alpha diversity

Island Biogeography Theory has been used widely as a framework to study animals and plants in fragmented ecosystems, but there is a clear gap in empirically testing how it applies to soil microbial communities. This is an important knowledge gap to fill as soil microbes contribute substantially to ecosystem function and no clear framework exists to predict their responses to habitat fragmentation. As a test of IBT-inspired species-area expectations in this system, we characterised soil microbial communities in 28 fragments of grey box ( Eucalyptus microcarpa ) grassy woodlands across a gradient of habitat fragment size, shape, and connectivity in southern Australia. We found that habitat fragment spatial characteristics (e.g., perimeter, perimeter:area, shape complexity, distance to nearest neighbour fragment) were associated with soil microbial community composition but had no influence on alpha diversity. As such, we did not detect species-area or isolation-alpha diversity relationships in this peri-urban woodland system. Therefore, further theoretical and empirical research is required to progress our understanding of how soil microbial communities respond to habitat fragmentation. • No clear framework exists to predict microbial response to habitat fragmentation. • 16S and ITS rRNA amplicon sequencing were used to characterise soil microbiota. • Habitat fragmentation influenced soil microbial community composition. • Our findings highlight the importance of edge effects in shaping soil microbiota.