Two key features influencing community assembly processes at regional scale: Initial state and degree of change in environmental conditions

Abstract

Belowground microbial communities strongly influence ecosystem function such that predicting function may rely on understanding ecological processes that assemble communities. Uncertainty remains, however, in what governs the relative contributions of different ecological processes. To help fill this knowledge gap, we test the general hypothesis that both initial state and degree of change in environmental conditions govern the relative contributions of different ecological assembly processes. To do so, we leveraged regional‐scale nutrient and organic matter addition experiments and used soil organic matter (SOM) as a proxy of integrated soil environmental conditions. Consistent with our hypothesis, we found that both the initial amount of SOM and the degree of change in SOM—in response to nutrient addition—influenced the relative contributions of different ecological assembly processes. These influences were most clearly observed at the regional scale, suggesting potential scale dependence. More specifically, nutrient additions homogenized bacterial community composition due to enhanced influences of homogenizing dispersal when SOM content was initially high. In contrast, nutrient additions led to divergence in community composition due to variable selection when initial SOM was low and/or when SOM increased significantly in response to nutrient additions. Our findings indicate important connections among initial conditions, degree of change in environmental variables and microbial community assembly processes that may influence ecosystem processes. These conceptual inferences highlight a need to strengthen connections between ecological theory and biogeochemical modelling.

Dynamic microbial assembly processes correspond to soil fertility in sustainable paddy agroecosystems

“…For example, bacterial community assembly processes and composition shift in response to increases in SOC due to organic manure application in many agroecosystems (Feng et al, 2015, 2017). The importance of SOC on microbial assembly processes and agricultural sustainability had been observed in previous investigations of upland and paddy soils (Dini‐Andreote et al, 2015; Feng, Chen, et al, 2018), and our work suggests that this relationship could be a general feature of all agroecosystems.…”

“…Recent work of Tripathi et al (2018) and Sengupta et al (2019) has supported this assumption: stochasticity was dominant under mild environmental conditions, whereas determinism contributed a greater proportion of assembly processes under extreme conditions. Flooding can also promote soil fertility in rice paddies and lead to higher resource bioavailability that releases micro‐organisms from environmental stresses (Chen, Zhang, & Effland, 2011; Feng, Chen, et al, 2018; Feng et al, 2017). Collectively, these ecosystem features are likely to enhance stochastic processes relative to determinism.…”

Soil pH and temperature regulate assembly processes of abundant and rare bacterial communities in agricultural ecosystems

“…Environmental filtering is a key determinant of community assembly (Kraft et al ., ) and has been shown to cause phylogenetic clustering in bacterial communities (Horner‐Devine and Bohannan, ). Many studies have shown that soil pH, OMs and salinity can influence bacterial community assembly processes in various environments (Dini‐Andreote et al ., ; Feng et al ., ; Tripathi et al ., ; Zhang et al ., ). Here, we showed that soil pH and MAT mediated the balance between stochastic and deterministic assembly for abundant and rare sub‐communities, respectively, in agro‐ecosystems.…”

“…To advance mechanistic understanding of community assembly processes, the factors that mediate the balance between stochastic and deterministic processes must be elucidated (Feng et al ., ). A study showed that soil pH influences the balance between stochastic and deterministic processes in shaping soil bacterial community assembly during the paedogenic processes (Tripathi et al ., ).…”

“…In addition, it has been observed that increases in soil organic matter (OM) lead to a transition from homogeneous selection to weak selection and stochasticity, and then to variable selection during primary ecosystem succession (Dini‐Andreote et al ., ). The initial amount of and the changes in soil OM due to nutrient addition influence the relative contributions of different assembly processes (Feng et al ., ). However, it is still unclear what underlying environmental factors lead to the dominance of particular assembly processes for abundant and rare bacterial taxa in agro‐ecosystems.…”