Response of soil properties and fungi community to rainfall reduction in a subtropical natural Castanopsis carlesii forest.

Water is one of the important factors in forest soil environment, the changes of which affect the composition of soil fungal communities and soil ecosystem functions. Taking the natural forest of Castanopsis pilosula in Sanming, Fujian Province as the research object, we set up treatments with 30% or 60% rainfall exclusion, and natural control. We collected surface soil samples (0-10 cm) after 6-yr rainfall exclusion to analyze soil properties and fungal community structure and diversity by 18S rRNA gene high-throughput sequencing technology. The results showed that soil water content and ammonium nitrogen content was significantly decreased by 16.4% and 29.5% respectively under the 60% rainfall exclusion treatment, while the total organic carbon, soluble organic carbon, microbial biomass carbon, soluble organic nitrogen, nitrate nitrogen content, and pH of the soil did not change. Soil soluble organic nitrogen content under the 30% rainfall exclusion significantly decreased by 13.8%, while other soil physical and chemical indicators changed little. The relative abundance of Basidiomycota and Ascomycota accounted for over 40% of the fungal community under all treatments, which were the dominant fungal group. The ACE index of soil fungal communities significantly decreased under the 60% rainfall exclusion treatment, while other diversity indices showed no significant differences among the three treatments, indicating that the structure of soil fungal communities was relatively stable. Results of Mantel test showed that the phyla Ascomycota and unclassified fungi (norank_k_Fungi, unclassified_k_Fungi) were significantly positively correlated with soil water content, which might be a key factor driving the changes in soil fungal communities. Our results provide scientific basis for a deeper understanding of the maintenance of forest soil ecosystem functions under climate change.