Season and vegetation condition influence soil microbiota in endangered grey box grassy woodlands

Soil microbiota are key to ecosystem functions, including nutrient cycling and plant symbiotic interactions.While ecosystem degradation and seasons are well-known drivers of soil microbiota, they are seldom studied together, particularly in grassy ecosystems.Studying them in tandem is important for understanding how short-term seasonal dynamics interact with longer-term vegetation changes to shape soil microbial communities.Here, we examined how season and vegetation condition jointly shape soil bacterial and fungal communities in grey box grassy woodlands, a nationally Endangered ecosystem in Australia.We used 16S and ITS rRNA amplicon sequencing to characterise soil microbial community composition across the four seasons and a gradient of vegetation condition at 20 grey box grassy woodland sites in southern Australia.Both bacterial and fungal communities varied by season, with bacteria showing stronger seasonal turnover than fungi.Interestingly, vegetation condition consistently influenced bacterial community composition across seasons, whereas fungal communities were only influenced in spring.This may reflect bacterial sensitivity to vegetation shifts in the quantity and quality of organic residues derived from exotic annual plants, which can alter soil nutrient availability.Seasonal changes in soil moisture and nitrate were key correlates of microbial turnover, highlighting tight linkages between abiotic fluctuations and microbial dynamics.These findings indicate that poorer vegetation condition (characterised by higher proportions of exotic groundcover and midstory plants) is consistently associated with shifts in bacterial community composition across seasons, linkages that may contribute to the persistence of degraded ecosystem states.