The biogeography of fungal communities in paddy soils is mainly driven by geographic distance

The aim of this study is to answer how the biogeographic patterns of fungi are affected by spatial and environmental factors in paddy soils characterized by unique field management. Given the generally low C/N ratios of paddy soils, we also want to test a hypothesis that the dominant fungi in paddy soils are Ascomycota, which reportedly prefer habitats with low soil C/N ratios. Using quantitative PCR and barcoded pyrosequencing, we investigated the abundance, diversity, and community composition of fungal communities in 30 surface paddy soil samples collected from 10 rice cultivation regions of China. Pearson's correlation, analysis of variance, partial least squares regression, principal coordinates analysis, and variation partition were performed for analyses of gene copy numbers, alpha-diversity, beta-diversity, and relative abundances of fungal taxa and their relationships with environmental factors. The abundance of fungal 18S rRNA gene varied from 10(6.4) to 10(8.6) copies g(-1) soil, and was positively correlated with soil sand, organic matter, and total nitrogen content, and negatively correlated with soil chloride concentration. Ascomycota comprised 88% of total fungal sequences and increased in relative abundance with increasing soil pH and decreasing mean annual temperature (MAT) and precipitation (MAP). The predominance of Ascomycota in fungal communities is probably due to the low soil C/N ratios (9-15) in the paddy soils studied. The alpha-diversity increased with MAT, MAP, and soil nitrate-N and total nitrogen content but decreased with soil pH, clay content, chloride concentration, and C/N ratio. Variation partition revealed that fungal beta-diversity was mainly driven by geographic distance. In paddy soils which are characterized by intensive rice cropping practices, fungal abundance is mainly influenced by soil properties, fungal alpha-diversity is constrained by both climatic factors and soil properties, while fungal community compositions are mainly structured by geographic distance.