Land-Use Change Simplifies Multidimensional Edaphic Space and Weakens Deterministic Assembly in Tropical Soil Bacteria

Abstract Land-use change is a major driver of shifts in soil biodiversity, but it remains unclear whether its effects arise primarily from altered environmental conditions or from changes in multidimensional organisation of environmental gradients that shape ecological filtering. Here, we show that conversion of tropical lowlands reshapes not only the magnitude and organisation of soil heterogeneity, but also the multidimensional structure of edaphic space, with consequences for microbial diversity and community assembly. Using spatially explicit sampling, soil physicochemical profiling, and near full-length 16S rRNA sequencing across co-occurring primary forest, logged forest, and oil palm plantation in Borneo, we found that forest sites maintain multidimensional gradients of acidity, stoichiometry and cation balance that coincide with strong deterministic community assembly. Plantation soils exhibited greater within-site heterogeneity but reduced multidimensional organisation, with environmental variation concentrated along fewer dominant ecological axes and deterministic filtering weakened relative to forest sites. Soil pH governed broad-scale community turnover, nutrient stoichiometry (particularly the N:P ratio) contributed to phylogenetic community differentiation, whereas Ca:Mg ratio was positively associated with local phylogenetic diversity. Together, these results identify the dimensional structure of edaphic space as a critical mechanism linking anthropogenic disturbance to microbial community assembly.