Fern species and seasonal variation alter arbuscular mycorrhizal fungal colonization and co-occurrence patterns in the Heishiding Natural Reserve, South China

The establishment of arbuscular mycorrhizal fungi (AMF) symbiosis is generally considered an important pathway that assists ferns in their adaption to a variable environment in the forest ecosystem. However, how both fern species and seasonal variation affect the symbiotic characteristics and AMF community structure remains largely unknown. In this study, the AMF colonization status of 19 fern species in the Heishiding Nature Reserve located in south China was assessed. The effects of seasons on AMF colonization and community structure were also determined. The results showed that both seasons and species significantly affected AMF colonization rate (1.88-56.03 %) and spore density (94-546/25 g dry soil). In addition, according to principal component analysis, in spring, AMF colonization and spore density differed considerably from other seasons. The total AMF sequences detected in spring were significantly higher than in winter (p < 0.05). Glomus was the dominant genus, accounting for >75 % of all sequences. The AMF Chao1 and Faith PD indexes of Blechnum orientale Linn as well as the Shannon and Simpson indexes of Selaginella doederleinii Hieron were significantly higher in spring than in winter (p < 0.05). According to partial least squares path modeling, season had a significant influence on AMF colonization by varying the AMF alpha diversity rather than their community composition. Notably, network analysis showed that seasonal variation induced differences in AMF network structure, keystone taxa, and the number of links between species. This study highlights the symbiotic relationship between ferns and AMF in different seasons. The results provide novel insights on terrestrial ecosystem management and fern conservation from the perspective of plant-AM symbiosis.