Bacterial and fungal diversity, community composition, functional groups, and co-occurrence network succession in dryland and paddy soils along a 3000-year chronosequence

There is a limited understanding of soil microbial community successional trajectories during dryland and paddy soil long-term management after wetland reclamation. We examined the effects of long-term reclamation on the microbial diversity, community composition, functional groups, and co-occurrence network in dryland and paddy soils using a 3000-year soil chronosequence established in the floodplain of the middle and lower Yangtze River, employing the "space-for-time" method and 16S rRNA and ITS amplicon sequencing. Over time, reclaimed land experienced varying losses in microbial richness and diversity, with paddy soils exhibiting higher alpha diversity than drylands due to greater resources and ecological niches. Proteobacteria dominated drylands, Chloroflexi prevailed in paddy soils, and fungal communities in both land-use types were primarily Ascomycota and Basidiomycota. Functional predictions showed higher chemoheterotrophy and aerobic_chemoheterotrophy in dryland soils and more animal_parasites_or_symbionts and dung_saprotrophs in paddy soils. During the 2000-3000 year reclamation, the abundance of pathogens increased, posing risks to agricultural production. Cooccurrence network analysis indicated that, compared to paddy soils, dryland soils may form a more complex and stable microbial cooperative network. Soil organic carbon and pH influenced microbial communities in drylands, while bulk density and cation exchange capacity were crucial in paddy soils. Partial least squares path modeling indicated that reclamation duration impacts microbial network complexity and diversity, with soil properties regulating paddy soil microbial networks. These findings broaden our understanding of microbial community succession in dryland and paddy soils after long-term wetland reclamation, supporting soil health and sustainable agriculture.