ABSTRACT
Fungi play an important role in the accumulation and transformation of soil organic matter (SOM) and nutrient cycling. To investigate the relationship between the fungal community and soil organic carbon functional groups under gradient SOM contents in arable mollisols, arable mollisols with 2%-9% SOM content were collected in Northeast China. Solid-state 13C-NMR technology was used to explore the differences in the functional group structure of SOM, and ITS high-throughput sequencing was used to investigate the fungal community structure. The potential interactions between different taxonomic groups of soil fungal community and their associations with organic carbon molecular structures were compared by constructing molecular ecological networks under low SOM (2%-5%) and high SOM (7%-9%) conditions. The 13C-NMR results indicated an increase in the relative abundance of Alkyl C (25.8% to 35.9%). The decrease in Alkyl C/O-Alkyl C indicated a smaller degree of decomposition in high SOM soils. Sordariomycetes and Mortierellomycotina dominated the fungal community and their relative abundance increased with the SOM gradient (P<0.05) from 14.33% to 28.17% and from 7.32% to 23.14%, respectively. The network analysis showed simpler ecological topological properties of the fungal community in low SOM soils, with lower numbers of nodes, edges, and average clustering coefficients than those in high SOM soils. A closer relationship between fungi and organic carbon functional groups, especially LOC, was observed in low SOM soils. The random forest model showed that LOC had the largest amount for fungal interactions in low SOM soils (10%), followed by recalcitrant organic carbon (ROC). In comparison, LOC contributed less to the variations in fungal interactions in high SOM soils (7.4%). With globally increasing soil carbon loss, the limition of the carbon resources, especially the reduction of LOC, may reduce the stability and ecological functions of soil fungal communities.
