Multiple factors drive the abundance and diversity of the diazotrophic community in typical farmland soils of China

Abstract

Biological nitrogen fixation plays an important role in nitrogen cycling by transferring atmospheric N2 to plant-available N in the soil. However, the diazotrophic activity and distribution in different types of soils remain to be further explored. In this study, 152 upland soils were sampled to examine the diazotrophic abundance, nitrogenase activity, diversity and community composition by quantitative polymerase chain reaction, acetylene reduction assay and the MiSeq sequencing of nifH genes, respectively. The results showed that diazotrophic abundance and nitrogenase activity varied among the three soil types. The diazotrophic community was mainly dominated by Bradyrhizobium, Azospirillum, Myxobacter, Desulfovibrio and Methylobacterium. The symbiotic diazotroph Bradyrhizobium was widely distributed among soils, while the distribution of free-living diazotrophs showed large variation and was greatly affected by multiple factors. Crop type and soil properties directly affected the diazotrophic ɑ-diversity, while soil properties, climatic factors and spatial distance together influenced the diazotrophic community. Network structures were completely different among all three types of soils, with most complex interactions observed in the Red soil. These findings suggest that diazotrophs have various activities and distributions in the three soil types, which played different roles in nitrogen input in agricultural soil in China, being driven by multiple environmental factors.

Multiple role of diazotrophs in coupling nitrogen and iron biogeochemical processes through vertical soil profiles of different paddy soil types

“…Furthermore, our data showed that geographic distance exerted greater impacts on microbial community structure than environmental dissimilarity did ( Figure S6, Table S5). By contrasting to the overwhelming contribution of soil depth over paddy soil groups to microbial community studied here, the great impact of soil types on microbiomes was reported previously at larger scales [3,6,18,24] . Han et al reported that soil types possessed signi cant divergence in diazotrophic community in the topsoil of farmland, which was signi cantly affected by spatial distance, climate and soil properties [3] .…”

“…By contrasting to the overwhelming contribution of soil depth over paddy soil groups to microbial community studied here, the great impact of soil types on microbiomes was reported previously at larger scales [3,6,18,24] . Han et al reported that soil types possessed signi cant divergence in diazotrophic community in the topsoil of farmland, which was signi cantly affected by spatial distance, climate and soil properties [3] . Bai et al (2017) showed that soil type exerted more signi cant impacts on bacterial and fungal diversity than soil pro le did with distant geographic distances (e.g.…”

“…Along the pedogenesis, soil gradually differentiate into different phenotypes, depended on soil-forming factors, including climate, parent material, organisms, relief and time [2] . The characteristics and functionality of varied phenotypes are highly variable [3][4][5][6] . Soil types impose strong selection pressures for microbiome with traits re ecting different resource needs and tolerances to environmental conditions [6,7] .…”

“…Divergent assembly pattern of microbial taxonomic and functional compositions have been observed between the topsoil and deeper layers, which directly coupled with soil biogeochemical processes [9,14,15] . Previous studies showed that soil horizons exerted overwhelming in uence on bacterial and fungal community structures than sampling locations [13,16,17] , depending on geographical distance, climate and edaphic properties [3,6] . Bai et al (2017) reported the strong effects of soil parent material characteristics over soil horizons [18] .…”

“…As the key driver for global nitrogen (N) dynamics, diazotrophs also participate other major biogeochemical cycles directly or indirectly, such as for carbon sequestration, iron (Fe) and sulfur (S) cycling [19,[21][22][23] . The abundance, composition and N 2 -xing capacity of diazotrophs varied greatly across soil types, while only studied in the plough layer (0-15 cm), which processes are determined by soil properties, climate and geographical distance [3,24] . Previous studies presented that diazotrophic population was more abundant in surface soils due to larger organic matter contents and available N limitation [25,26] .…”