[Investigation of Soil Fungal Communities and Functionalities within Karst Paddy Fields]

Fungi are important drivers of soil biogeochemical cycles. However, the characteristics of fungal community structures and functional groups within karst area (KA) soils remain understudied. Top soil samples were collected from paddy fields within a KA and non-karst area (NKA) containing red soil, in the Maocun karst experimental site of Guilin. The fungal community structure was analyzed via high-throughput sequencing, and FUNGuild was used to predict the function of fungi. The average relative abundance of Mucormycota in KA was 4.87%, which was significantly lower than that in NKA (29.92%); The average relative abundance of Mortierellomycetes in KA was 3.36%, which was significantly lower than that in NKA (29.15%). However, in KA, the average relative abundances of Glomeromycetes, Chytridiomycetes, and Exobasidiomycetes were 0.91%, 0.98%, and 0.23%, respectively, significantly higher than those in NKA (0.47%, 0.28%, and 0.04%). In KA, the average relative abundances of Ramophialophora and Emericellopsis were 2.39% and 1.25%, respectively, significantly higher than those in NKA (0.05% and 0.09%). However, the average relative abundance of Mortierella was 3.04% in KA, which was lower than that in NKA (28.34%). KA contained 32 dominant OTUs, including OTU141, 99, and 192. There was more connectivity between OTU69 (Emericellopsis terricola) and OTU138 (Westerdykella globosa) with the cation exchange capacity (CEC), exchangeable Ca²⁺, and total phosphorus (TP) in the correlation network. In KA, the average abundances of symbiotroph and pathotroph-saprotroph fungi were 1.29% and 1.50%, respectively, significantly higher than those in NKA (0.08% and 0.09%). The average abundance of the saprotroph-symbiotroph fungi in KA was 10.81%, which was significantly lower than that in NKA (63.69%). In KA, dung saprotroph-wood saprotroph fungi were dominant, with an abundance of 9.73%, whereas in NKA, endophyte-litter saprotroph-soil saprotroph-undefined saprotroph fungi were dominant, with an abundance of 45.93%. The above results suggest that the soil factors of KA, such as CEC, exchangeable Ca²⁺, and TP, alter the structures and functions of fungi.