The microbial network analysis revealed crucial interactions among the fungal community in permafrost affected soils. Fungal community of cryosols in Herschel island

Permafrost affected soils (PAS) store a significant amount of organic carbon (C). Identifying biological constraints of soil organic matter (SOM) transformation, e.g., interaction of major soil microbial taxa, is crucial for understanding C vulnerability in PAS. Fungi are important players in the decomposition of SOM and often interact in various mutualistic relationships during this process. We investigated four different soil horizon types (including specific horizons of cryoturbated SOM (cryoOM)) across different types of PAS in the Western Canadian Arctic, determined the composition of fungal communities by sequencing the fungal internal transcribed spacer region, assigned fungal lifestyles, and by determining the co-occurrence fungal network properties identified the topological role of keystone fungal taxa. The compositional analysis revealed a significantly higher relative proportion of the litter saprotroph Lachnum and the root-associated saprotroph Phialocephala in topsoil and ectomycorrhizal close-contact exploring Russula in cryoOM. The proportion of ectomycorrhizal and wood saprotrophs were significantly higher in cryoOM compared to the topsoil, but no significant difference in fungal lifestyles was found between cryoOM and the surrounding subsoil. Co-occurrence network analysis revealed the lowest modularity and average path length, and the highest clustering coefficient in cryoOM which suggested lower network resistance to environmental perturbation. The Zi-Pi plot analysis suggested that some keystone taxa changed their role from generalist to specialist, Cladophialophora from the topsoil, saprotrophic Mortierella from cryoOM, and Penicillium from subsoil were classified as generalists for respective horizons but specialist for the other. These results suggested that fungal communities from cryoOM were more susceptible to environmental change and some taxa may shift their role, which may lead to changes in carbon storage in PAS.

受永久冻土影响的土壤（Permafrost Affected Soils, PAS）储存着大量有机碳（C）。明确土壤有机质（Soil Organic Matter, SOM）转化的生物学限制因素——例如主要土壤微生物类群间的相互作用——对于理解永久冻土受影响土壤的碳脆弱性至关重要。真菌是土壤有机质分解过程中的关键参与者，且在此过程中常以多种互利共生关系相互作用。本研究在加拿大西部北极地区的不同类型永久冻土受影响土壤中，调研了四类不同的土壤发生层（包括冻土扰动形成的土壤有机质（cryoturbated SOM, cryoOM）的特定发生层）；通过对真菌内转录间隔区（internal transcribed spacer, ITS）进行测序以解析真菌群落组成，对真菌营养型进行归类，并通过分析真菌共现网络的拓扑属性，明确了关键真菌类群的拓扑生态位。群落组成分析结果显示，表层土壤中枯落物腐生真菌（litter saprotroph）Lachnum与根际腐生真菌（root-associated saprotroph）Phialocephala的相对丰度显著更高，而冻土扰动有机质层则以外生菌根（ectomycorrhizal）-紧密接触型探索类Russula占比更高；相较于表层土壤，冻土扰动有机质层中外生菌根真菌与木质腐生真菌（wood saprotroph）的占比显著更高，但冻土扰动有机质层与其周围的下层土壤之间，真菌营养型并无显著差异。共现网络分析结果表明，冻土扰动有机质层的网络模块性（modularity）与平均路径长度（average path length）最低，聚类系数（clustering coefficient）最高，这意味着该层的真菌群落网络对环境扰动（environmental perturbation）的抵抗能力较弱。Zi-Pi图分析显示，部分关键类群的生态位角色会从泛化类群（generalist）转变为特化类群（specialist）：表层土壤的Cladophialophora、冻土扰动有机质层的腐生真菌Mortierella，以及下层土壤的Penicillium，在各自所在的发生层中被归类为泛化类群，但在其他发生层中则为特化类群。上述结果表明，冻土扰动有机质层的真菌群落对环境变化更为敏感，且部分类群可能发生生态位角色的转变，这或会对永久冻土受影响土壤的碳储存能力产生影响。