High salt stress increases archaeal abundance and network connectivity in saline agricultural soils

Archaea are present in most ecosystems and are known to play a pivotal role in many ecological and biogeochemical processes. However, archaeal biogeographic patterns and driving processes in saline agricultural ecosystems remain poorly understood. To address this, we conducted a regional-scale survey of archaeal communities in saline agricultural soils throughout northwest China. While archaeal abundance was positively correlated with soil organic matter and total nitrogen levels, archaeal diversity was positively associated with salinity and ammonium-nitrogen (NH₄⁺-N) levels. Dominant phyla belonged to Thaumarchaeota (45.52%) and Euryarchaeota (37.32%), however, the environmental factors affected these two phyla in opposing ways. Archaeal spatial distribution patterns and environmental preferences were also assessed and significant distance-decay relationships for dissimilarity in archaeal community structures were identified. Soil physicochemical properties, particularly salinity and organic matter, were strong determinants of archaeal community variation. Sixty percent of the variation could be explained by edaphic factors (34.5%) and spatial parameters (25.7%). Archaeal co-occurrence patterns were explored and more intra- than inter-kingdom associations were observed. The network topological features revealed that archaeal networks under the highest soil salinity level (>20 g kg⁻¹) were more complex and had greater associations than those under a medium salinity level (5–20 g kg⁻¹). Phylogenetic null modeling of community assembly suggested that archaea may transition from stochasticity in medium salinity soils to determinism in higher salinity soils. Overall, these findings offer new insight into the distribution patterns and drivers of archaeal community assembly in saline soils.