Does mineralization and pH control the distribution of ammonia-oxidizing archaea in temperate forest soils?

Abstract

Ammonia-oxidizing archaea (AOA) are a primary contributor to nitrification – a key process in nutrient cycling that influences the concentration of nitrate in forest ecosystems. This study addressed (1) how AOA community composition changes across upland forest stands in Manistee National Forest and (2) how environmental factors such as pH and net N mineralization may be associated with AOA distribution. From collected soil samples, amoA (a functional gene involved in ammonia oxidation) was amplified and sequenced to detect AOA. Sequences were classified based on the known taxonomy of AOA, and the relative abundances of AOA taxa were compared between stands and along changes in pH and mineralization. Results of PERMANOVA and Mantel tests show that both pH and net N mineralization are significantly associated with AOA distribution (p < 0.05). Moreover, pH is a stronger predictor of AOA distribution than mineralization, contributing to up to 23% of variations in community composition, while mineralization contributes 8%. Phylogenetic analyses revealed that two AOA lineages are represented in the stands: Nitrososphaeales and Ca. Nitrosotaleales. Titan analyses revealed that within these lineages, specific taxa can be negatively correlated or positively correlated with pH and mineralization. Furthermore, the relative abundance of these lineages and their clades are markedly different across stands. These results show that AOA communities can be very distinct within similar ecosystem types. Furthermore, AOA taxa do not share a single directional response to pH or net mineralization, emphasizing the diversity of AOA and their interactions with the environment. In this study, we were able to contribute to an understanding of how a gradient of environmental factors is associated with the distribution of nitrifying microorganisms, and we recommend to incorporating AOB abundances into future research on the composition and relative contributions of ammonia-oxidizing organisms to nitrification.