Chunnan Fan

Soil bacteria, fungi and nematodes are three of the most abundant groups in the belowground micro-food web, yet how they change together during forest recovery after disturbance remains poorly understood. We examined a temperate forest secondary successional sequence in northeastern China, measuring soil nutrients and the diversity, taxonomic composition and functional composition of the three groups, and used structural equation modelling to test how their linking network changes among successional stages. Nutrients did not accumulate uniformly. Available potassium increased stage by stage, carbon and nitrogen fluctuated without a clear trend, and phosphorus peaked at the poplar stage. The diversity of each group tracked a characteristic nutrient most closely, potassium for fungi, nitrogen for nematodes, and carbon broadly for both microbial groups. Taxonomic and functional responses were decoupled. Bacterial and fungal communities diverged strongly among stages, while nematode taxonomic composition stayed largely unchanged, yet nematode feeding composition shifted markedly and fungivorous nematodes reached their highest share at the intermediate broadleaf stage. The pathway network linking nutrients, microorganisms and nematodes kept the same structure in all four stages, so succession changed the strength of these associations rather than the pathways themselves. For soil nematodes, recovery therefore reshapes what the community consumes rather than which taxa it contains, and feeding traits rather than taxonomic counts better capture how the nematode community tracks forest recovery.

Introduction: The ecological restoration of degraded grassland has been widely studied in terms of plants, soil, and microbes. The microbial network and its relationship with plants are essential indicators of the grassland restoration process. Across restoration statuses, how the microbial network affects plant-microbe interactions and reflects grassland restoration remains unclear. Methods: We examined changes in soil microbial networks, plant biomass, and soil properties across early, moderate, and late restoration, as well as stable community status, over a 5-year restoration period. We calculated the grassland restoration index (GRI) to evaluate the restoration process and constructed microbial co-occurrence networks to assess changes in microbial communities over 5 years. Results: Our results showed the dominant species shifting from Kochia sieversiana to Chloris virgata in early restoration status, and the bacterial network complexity fluctuated over the 5 years, indicating a restoration in early restoration status. In moderate and late restoration statuses, the complexity of bacterial networks gradually increased, suggesting the increased recovery potential in the grassland. However, the GRI showed that the moderate and late restoration statuses did not progress to the next successional status over the 5 years. Moreover, the random forest regression model revealed that high soil pH may limit the restoration process by regulating soil microbial networks. Conclusion: Our study illuminates the signaling roles of soil microbial networks in the restoration process and suggests that moderate and late restoration statuses may take longer to recover to a stable community status. We emphasized that soil pH may be a key constraint in the different restoration statuses, warranting further experimental testing of pH regulation as a restoration intervention.

Biodiversity loss has accelerated over decades and probably exerted adverse impacts on ecosystems. As a key forest ecosystem function, tree productivity and its relationship with the change in species diversity are a hotspot in ecology research. However, the changing patterns of the relationships between these two variables across ecosystems with different environmental conditions and the underlying mechanisms are not well understood but key to make environmental context-specific strategies for forest ecosystem conservation and management. Here, we examined changes in relationship (R_DI-AGB) between the tree species diversity index (DI) and aboveground biomass (AGB) across temperate forest ecosystems with different environmental contexts on a small spatial (plot) scale as well as clarified the driving mechanisms using ground-based data from 3 natural reserves in northeastern China, surveying 22,139 trees across 77 species and 185 plots. We found substantial changes in R_DI-AGB across natural reserves with different environmental conditions on a small spatial scale. These changes were probably modulated by site-specific factors. A positive R_DI-AGB was attributed to positive impacts of local climate conditions (i.e., mean annual temperature and potential evapotranspiration) and stand age on both DI and AGB, which was observed in the Changbai Mountains Natural Reserve. In contrast, a negative R_DI-AGB was likely due to opposite directions in the effects of the site-dependent factors (elevation, mean annual precipitation, vapor pressure deficit, and seasonality of temperature) on DI and AGB, appearing in the Honghuaerji Natural Reserve. In addition, complex impacts of site factors on DI and AGB leading to no obvious R_DI-AGB was observed in the Shengshan Natural Reserve. Our results highlight the importance of site-dependent factors in modulating species diversity–productivity relationships and the need to use site-specific strategies in management and conservation for forest-dominated natural reserves and other forest ecosystems with heterogeneous environmental conditions.