Introduction
Richness-stability relationships (RSRs) are a basic question of increasing concern in modern ecology (McCann 2000; Dixon et al.2021). RSRs describe the most simplified links between species pool and complex system persistence, and could offer a substantial, convenient, and valuable guide to several ecological fields including artificial community composition (Dixon et al. 2021), biological conservation formulation (Griffiths & Philippot 2013), and ecosystem stability assessment (García-Palacios et al. 2018). Unfortunately, according to previous community studies, RSRs can vary widely (Sankaran & McNaughton 1999; Naeem et al. 2000; Arthur & Dech 2016; Baert et al. 2016; O’Brien et al. 2017; Pennekamp et al. 2018), but the potential cause of these differences has yet to be resolved.
Interactions between community members, both positive (e.g., mutualism and cooperation) and negative interactions (e.g., competition and predation), were predicted as a potential influencer of RSRs (May & MacDonald 1978; Damore & Gore 2012). Positive interactions theoretically benefit to extend the niche width of species and offer them the ability to live under conditions that were originally unfavorable, thus increasing their tolerance to stress (Damore & Gore 2012). Negative interactions were also been predicted as beneficial for community stability in several models (Pinsky 2019). However, there is still no empirical evidence to support whether interactions influence RSRs.
The microbial community is a species rich and functionally important component of ecosystems (Griffiths & Philippot 2013). However, the relatively few studies, primarily in aquatic ecosystems, that have investigated microbial community RSRs, have come to contradictory conclusions. For instance, aquatic micro-cultivations utilizing different combinations of 6 ciliate species (total of 690 incubations) reported a negative relationship between richness and resistance (Pennekamp et al. 2018), while a positive relationship between richness and resistance of microbial community was reported from two lakes in Canada (Hillebrand et al. 2018). Yet, the soil microbial community plays an irreplaceable role in decomposition, nutrient cycling, and above-ground community regulation for terrestrial ecosystems (Franciska & Ashley 2013). The variation in community composition caused by environmental stress would threaten the functions relevant to the soil microbial community (Franciska & Ashley 2013). The lack of soil microbial community RSRs research significantly hampers a deeper understanding of terrestrial ecosystem stability and the response to climatic and anthropogenic stresses (Franciska & Ashley 2013).
In order to investigate RSRs of the soil microbial community in terrestrial ecosystems and explore the effect of interactions on RSRs, we selected 5 successional stage ecosystems (bare soil, grass, shrub, deciduous forest, and coniferous forest) from a typical glacial retreat area to compare the microbial community stability components (resistance and resilience) under simulated climatic stress. There were two main reasons for choosing this successional gradient. Firstly, the ecosystems were located in a glacial retreat area of approximately 3km×0.5km with less than 100m difference in elevation, sharing the same regional precipitation and temperature, therefore the types and extents of climatic stress exerted on them could be treated as the same (Li & Xiong 1995). Secondly, the richness and network structure of the microbial community varies among successional stages, offering a natural gradient to analyze how interaction types influence RSRs (Jiang et al. 2018). In this study, we found that balanced positive and negative interactions of the community offered a positive richness-resistance relationship, while unbalanced interactions offered a negative relationship.