4.2 Reduced interactivity lead to T.matsutake extinction
Interactions among community members are an important contributor to community stability and species diversity (Mougi & Kondoh, 2012, Haleet al. , 2020). The interactions could be cooperation and competition in metabolism, immune, stress tolerance, and appeared as positive or negative interactions (Mougi & Kondoh, 2012).
As interactivity within the soil microbial community decreased during degradation, T.matsutakelost cooperative interactions (Fig.3C) that may have been capable of enhancing the rates of certain ecological processes (Corbett & Watkin, 2018, Cui et al. , 2019), stimulating energy conservation by individual members (Malik et al. , 2018), and even allowing the coexistence of certain species (Cai et al. , 2020). The loss of cooperation increases the cost of survival for that species. We found that T.matsutake was marginalized from a central module to a peripheral one within the networks (Fig.2B). As a module is a collection of members (nodes) that are potentially highly functionally related (Deng & Zhou, 2015), this indicated that T.matsutake could not rely on the original functional groups for metabolic cooperation, and resulted in extinction. (Gill et al. , 2000, Xu et al. , 2015). Thus, our result support the hypothesis that loss of cooperation due to reduced interactivity of the microbial community was responsible for the extinction of T.matsutake (Gill et al. , 2000, Xuet al. , 2015). This was further confirmed by regression analysis that showed the extent of T.matsutake extinction was most linearly correlated to network interaction indicators than to soil properties, community composition or biodiversity (Fig.4).
However, our study found that all of the 13 OTUs that competed withT.matsutake had also decreased in their relative abundance during degradation, which indicated that groups with functions similar toT.matsutake were also facing the threat of extinction due to environmental stress. Competition also contributes to community stability as it is involved in resource partitioning and functional redundancy among community members (Pianka, 1981, Pinsky, 2019). The community could retain functional stability by trade-offs between the functions of several phylogenetic groups under stress (Pianka, 1981, Pinsky, 2019). Thus, it became an open question as to whether the community possessed any other groups that could functionally replaceT.matsutake and its competitors. As the ectomycorrhizal species of the keystone plant (Gill et al. , 2000), T.matsutake and its competitors were helpful for maintaining the dominance of the host plant by assisting in nutrient uptake and defense against stress and disease (Liang et al. , 2020). Over the long term, the extinction of T.matsutake and its competitors are a potential threat to keystone vegetation and even other animals that inhabit the local environment (Gill et al. , 2000, Weisskopf et al. , 2021).
In summary, the microbial community, during the degradation ofT.matsutake , was demostrated variation in composition and diversity, and a switch from an interactive state where metabolite and signal functions predominated to stress tolerance state. The decreased interactivity marginalizedT.matsutake from a large center module to a peripheral module and reduced its interactions, leading to its extinction. The extinction caused by the degradation of microbial community directly impacts the ecosystem and is a potential long term threat to aboveground biodiversity through rhizosphere activity and the food-web. This study highlights that the key characteristic of microbial community degradation and the mechanism for microbial species extinction during degradation is the reduced interactivity. For future studies focusing on conservation and on microbial community, an understanding of the relationships among stress, microbial community properties, and the extent of the microbial community degradation, will allow for improved comprehensive conservation measures that target both below- and above-ground communities.