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Aim: Methane oxidation driven by soil aerobic methanotrophs exhibits the largest methane sink capacity in forest ecosystems and plays important roles in the alleviation of global warming. Many studies have revealed the distribution of methanotrophs in forest ecosystems at field scales; however, the biogeographical patterns of methanotrophic communities and related ecological processes and the drivers shaping methanotrophic communities at a large scale remain poorly understood. Location: China's forests. Time period: 2012–2013. Major taxa studied: Methanotrophic communities. Methods: We evaluated the geographical distributions of soil methanotrophic communities across 26 forests along a 4,000‐km north–south transect in China using a MiSeq high‐throughput sequencing technique. The assembly processes and drivers of the methanotrophic communities were evaluated using the phylogenetic null model approach and structural equation modelling, respectively. Results: The results showed that the upland soil cluster α (USCα) and ammonia‐ oxidizing bacteria‐related (AOB‐rel) methanotrophs were the most abundant taxa in forest soils and exhibited contrasting distributions of relative abundance across different climate zones, suggesting that they occupy different environmental niches. The α‐diversity pattern of the soil methanotrophic community followed a hump‐shaped pattern along a large latitudinal gradient. Statistical analyses suggest that aridity and vegetation productivity [here represented with the normalized difference vegetation index (NDVI)] are major drivers of the α‐diversity of the methanotrophic community, whereas soil pH is the key environmental factor shaping the β‐diversity of the methanotrophic community at a large scale. Additionally, the community assembly of the methanotrophs primarily resulted from deterministic processes, among which heterogeneous selection had a greater contribution in shaping the methanotrophic community than homogeneous selection. Main conclusions: Our study provides new insights into the biogeographical distributions, assembly processes and ecological predictors of the methanotrophic community in forest soil at a large scale. These results can be used to improve simulation models for the better prediction of ecosystem functions under predicted global changes. [ABSTRACT FROM AUTHOR]

Aim: Many studies have found that diazotrophic distribution is mainly determined by soil properties from field to regional scales. However, we lack strong evidence for the relative importance of different drivers controlling broad‐scale biogeography of forest diazotrophs, especially for soil multi‐nutrients. Location: China's forests. Time period: 2012−2013. Major taxa studied: Diazotrophic communities. Methods: We investigated the distribution of soil diazotrophic communities from 146 sites along a 3,900‐km south–north transect by sequencing N‐fixing nifH gene amplicons. The relative contributions of environmental variables were assessed using a combination of stepwise multiple regression, variation partitioning analysis, multiple regression on distance matrices and partial least squares path modelling. Results: Overall, aridity index and temperature were the predominant parameters governing diazotrophic community diversity and structure, mainly through their indirect effects on soil pH, nutrient contents and plant productivity. Although soil multi‐nutrients (Ca, Mg, Fe, Mn, Na, Cu and Zn) were included in the statistical analysis, they still exhibited lower impacts on diazotrophic communities than climate. Intriguingly, the microelement Mo could not explain the diazotrophic community patterns, despite its significance in nitrogenase enzymes. This unexpected phenomenon was attributed to the relatively high Mo supply in our work. Moreover, the distinct responses of diazotroph taxa to climatic factors and large heterogeneity of diazotrophic diversity among forests in different climatic zones further support the dominant role of climatic variation. These results indicate the presence of differentiated climatic niches for diazotrophs, such as warm‐adapted Bradyrhizobium and cool‐adapted Azospirillum. Main conclusions: Our findings suggest for the first time that unlike prior studies, the key roles of soil nutrient limitation (even for Mo) and pH‐dependent mechanisms in small‐scale diazotrophic communities can be surpassed by large‐scale climatic gradients. Future changes in drought severity and temperature might greatly shape diazotrophic distribution and its potential function in forest N2 fixation. [ABSTRACT FROM AUTHOR]