Soil structure and pH shape prokaryotic communities in lowland soils across Denmark

Abstract

Agricultural activity in drained lowlands accelerates peat decomposition and greenhouse gas emissions. Rewetting is increasingly adopted across Europe to mitigate these emissions, but its effects on soil microbial communities remain poorly understood. We examined prokaryotic communities and network structure in Danish lowland soils designated for potential rewetting to improve our understanding of these communities and their drivers. We included less-studied soil properties linked to hydrology and structure (soil water content at field capacity, van Genuchten pore-size distribution index (n), and soil water repellency (SWR)) in addition to common properties such as pH and organic carbon (OC). We analysed 113 soil samples across land-use types (grass, fallow, crop, other) spanning mineral to organic soils with gradients in pH (2.0–7.6), OC (0.025–0.499 kg kg^-1), SWR (33.9-71.3 mN m^-1), and soil structure (n: 1.1-1.3). Prokaryotic alpha diversity (Shannon-Wiener index: 2.9–5.7) was best predicted by pH, followed by porosity and n. Together, pH, porosity, n, and OC accounted for 24.5% of the variance in community composition. Hierarchical clustering identified three prokaryotic clusters strongly aligned with pH. Network analysis revealed marginal differences when comparing samples from fallow and grass, while complexity increased progressively across clusters. Interestingly, high-pH soils showed the highest alpha diversity but the least complex networks, while low-pH soils showed the opposite. In conclusion, soil pH emerged as the dominant driver of prokaryotic communities in Danish lowlands, but hydrological and structural properties also played important roles. Network complexity provided complementary insights into ecosystem organisation beyond diversity alone.