LB 2-15 - Revegetation promotes soil microbial network stability in a novel riparian ecosystem

Soils harbor highly diverse microbial communities with complicated associations among co-existing microorganisms, which can be represented as microbial networks with species as nodes and their relationship as links. Such complex microbial interactions are of crucial importance for ecological processes and ecosystem functions. Nevertheless, whether and how their co-occurrence networks respond to the restoration of degraded ecosystems remains poorly understood. Here, we examined the effects of revegetation on the structure and function of the soil microbiome, including soil microbial network complexity and stability, in a novel riparian ecosystem with winter submergence opposite to the natural hydrological regime. Plant richness, soil properties (moisture, pH, total organic carbon, total nitrogen, total carbon, NH4+-N, and NO3--N content), microbial characteristics (diversity, composition, functional fungi groups, niche width, network complexity, and stability), and greenhouse gas fluxes (CO2, CH4, and N2O) were measured at two restoration sites, active revegetation site and natural regeneration site, under three different flooding intensities from 2016 to 2018, including extreme flooding intensity with 30 meters submergence up to 286 days per year, severe flooding intensity with 20 meters submergence up to 237 days per year, and moderate flooding intensity with 10 meters submergence up to 169 days per year. We found that extreme flooding intensity reduced microbial α-diversity and network stability (robustness), but increased network complexity including network connectivity, connectance, and average clustering coefficient over a three-year period, and those effects were mitigated by active revegetation in comparison with natural regeneration. According to the structural equation modeling, revegetation increased microbial network stability directly by decreasing network complexity, while extreme flooding indirectly regulated network stability by changing the soil total carbon content. Nevertheless, those dynamics of microbial network were coupling with soil microbial functions such as greenhouse gas fluxes and nutrient cycling. In conclusion, active revegetation not only decreases the sensitivity of microbial communities to flooding, but also improves microbial network stability and hence, the linked soil microbial functions would also be less vulnerable to the intensive flooding environment. This study provides evidence to support the critical role of revegetation in preserving soil microbial network stability and functions under changing hydrological regime.