Environmental similarity is more important than distance in the community structuring processes of ammonia-oxidizing archaea in agricultural soils

Abstract

Archaeal ammonia oxidizers (AOA) are important in converting ammonia into nitrates in soils. While many aspects of their community structure have been studied, the relative importance of stochastic versus deterministic processes has been poorly understood. We compared AOA communities across the North China Plain, targeting the amoA gene. A phylogenetic null modelling approach was used to calculate beta-nearest taxon index (beta-NTI) to quantify the influence of stochastic and deterministic processes. We found that spatial distance between samples predicted the perceived processes involved in community structuring, with stochastic processes dominating at more local scales. At greater distances, stochasticity became weaker. However, differences in soil pH – which were also the strongest determinant of AOA community – were a much stronger predictor of the community structuring, leaving distance effects redundant as an explanation of community structuring processes. AOA communities differing by less than 1 pH unit differ mainly stochastically in terms of OTU composition. At larger pH differences, deterministic processes based on heterogeneous selection between clades become increasingly dominant. It appears that AOA community composition is largely determined by environment. The exception is amongst very similar pH environments, whether spatially near or far, in which stochastic effects dominate in causing differences in community composition.