Seasonal variation of diversity and co-occurrence patterns of arbuscular mycorrhizal fungal communities in mixed broadleaf-conifer forests

Arbuscular mycorrhizal (AM) fungi are an important determinant of plant performance. The temporal distribution patterns of AM fungal communities, important groups in forest soil, are affected by various environmental factors. However, the effect of seasonal variation on AM fungal communities in forest soil is still not fully understood. To improve knowledge regarding the seasonal dynamics of AM fungal communities in forest soil, the Juglans mandshurica rhizosphere soil in a 30-year-old natural J. mandshurica and Larix gmelinii mixed forest in northeastern China was sampled and studied during different seasons. AM fungal community composition and structure in the rhizosphere soil were determined by using the Illumina MiSeq sequencing platform. The results showed that forest type significantly affected soil pH and the microbial biomass carbon (C-mic), microbial biomass nitrogen (N-mic), C, N, P, NH4+-N and NO3--N contents. Similarly, soil moisture significantly decreased with seasonal progression in all forest types. Glomus and Diversispora were the dominant genera. The Shannon, Sobs and Chao1 indices of the mixed forest were higher in July than in May and September. The NO3--N and watersoluble phenol (WSPh) contents were the most important factors driving the shift in the soil AM fungal community across the seasonal gradient. Network analysis revealed that AM fungal network structure was significantly different between seasons, and the number of links between species significantly increased with time. We observed a clear tendency for mixed forest management to significantly affect AM fungal community structure and composition but not diversity. Furthermore, the co-occurrence network and keystone taxa among AM fungi can change in response to environmental filtering due to mixed management in different seasons.