Litter-, soil- and C:N-stoichiometry-associated shifts in fungal communities along a subtropical forest succession

Suites of fungal adaptation to nutrient acquisition and allocation of vegetations are observed along forest succession gradients. However, the mechanisms behind seral shifts in plant-associated fungi need to be uncovered. To bridge this knowledge gap, the current study investigated the litter and soil chemical variables as well as the fungal community using high-throughput Illumina MiSeq sequencing along a 30a-100a succession gradient of a subtropical forest ecosystem in Xishuangbanna, southwestern China. Litter nitrogen (N) content changed consistently with fungal alpha-diversity and the relative abundances of functional guilds, such as saprotrophs and arbuscular mycorrhizal (AM) fungi. However, this trend was opposite to that observed for ectomycorrhizal (EcM) fungi and litter carbon (C) content. The total and water-soluble C and N contents as well as the C/N ratios in soil decreased with stand age, while the relative abundances of Rozellomycota, Chytridiomycota and lichens as well as the microbial C and N use efficiencies exhibited increasing trends across succession stages. Multivariate analysis and multiple linear regression showed that the seral shifts in fungal diversity and composition were closely related to the C:N stoichiometry of soil and litter. Specifically, the litter C content either negatively explained the alpha-diversity and saprotroph abundance or positively explained the abundance of EcM fungi. In contrast, the litter N content presented opposite trends. Further, the variances in the abundances of Rozellomycota and AM fungi were negatively explained by water-soluble C content but positively explained by water-soluble N content in the soil. These findings confirm that the replenishment and reduction of available nutrients are determined by plant-fungus interactions via the C:N stoichiometry of litter and soil along the forest chronosequence.