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This document is a summary of a scientific article discussing the role of plant-soil microbe feedbacks in driving seedling establishment during secondary forest succession. It emphasizes the importance of understanding the mechanisms governing forest successional pathways for effective forest restoration and conservation strategies. The article highlights the role of soil microbes, including pathogens and mycorrhizal fungi, in plant-soil feedback and vegetation succession. It presents a table summarizing potential evidence for the successional stage hypothesis during secondary forest succession, providing key findings from different studies in various ecosystem types. The authors propose a "successional stage hypothesis" and conducted a greenhouse experiment to test it, finding that soil microbial legacies from different successional stages had varying effects on seedling growth. They suggest that understanding these feedback effects can inform forest restoration strategies, but note that more research is needed to explore the temporal variation in plant-soil microbe interactions during succession. [Extracted from the article]

Purpose: Soil nematodes are among the most important fauna in soils and participate actively in soil ecological processes. However, whether and how soil nematodes are involved in the effects of tree species type on soil fertility remain unclear, especially during subalpine forest secondary succession. Methods: A monoculture pot experiment of two broadleaf (Betula platyphylla and Betula albosinensis) and two coniferous (Picea asperata and Abies faxoniana) trees, using sterilized soils inoculated with unsterilized soils beneath dominant plants from different successional stages, was conducted in a greenhouse. After a period of plant growth, soil nematode communities and soil fertility in each pot were investigated. Results: Significant differences were noted in nematode community composition under the broadleaf and coniferous trees. Coniferous trees accumulated more abundant microbivores and omnivore-predators than broadleaf trees. Moreover, the contrasting effects of tree species type on soil nematode communities were associated with successional stages, with the greatest differences noted in the early successional stages. In addition, soil nematodes might play a significant mediating role in the effects of broadleaf and coniferous trees on soil fertility. However, the indirect regulatory effects induced by soil nematodes weakened with the successional stages. Conclusion: Overall, our study suggested that tree species type might affect soil fertility by regulating soil nematode communities across successional stages. Compared with broadleaf trees, more abundant microbivores under coniferous trees might contribute to the improvement of soil nitrogen mineralization but not to the increase in soil carbon storage, which might be limited by new carbon input into soils. [ABSTRACT FROM AUTHOR]

Background and aims: Community dynamics, functions and driving factors of rhizosphere and bulk soil bacteria during secondary forest succession remain poorly understood in subalpine regions. Methods: Three typical successional stages (grassland, shrubland and secondary forest) were selected to analyse bacterial communities, functions and interactions in the rhizosphere and bulk soils using high-throughput sequencing technology. Results: The results showed no significant difference in the bacterial α-diversity in the rhizosphere soil, whereas the bacterial α-diversity in the bulk soil of the grassland was significantly lower than that of the shrubland and secondary forest. Bacterial β-diversity in the rhizosphere soil differed significantly among the three succession stages, while the bacterial β-diversity in the bulk soil in the shrubland and secondary forest was significantly different from that in the grassland. However, the potential bacterial functions of the carbon, nitrogen and sulfate cycles revealed a consistent response in the rhizosphere and bulk soils to secondary forest succession. The soil total phosphorus, ammonium nitrogen, ratio of carbon to phosphorus and pH were the main factors affecting bacterial communities and potential functional groups. Bacterial network complexity was highest in the secondary forest rhizosphere soil and the shrubland bulk soil. Different keystone bacteria were detected in the rhizosphere and bulk soils among the three successional stages; they play major role in maintaining ecosystem function and community structure. Conclusion: Our results demonstrate that the bacterial communities and interactions in the rhizosphere and bulk soils respond differently to secondary forest succession, while the bacterial functional groups revealed a consistent response. [ABSTRACT FROM AUTHOR]

Fast-growing pioneer tree species play a crucial role in triggering late successional development in forests. Experimental evidence of the soil legacy effects of pre-existing plants on pioneer tree performance is lacking. We explored the legacy effects of soils conditioned by early successional herbs (Poa poophagorum Bor and Potentilla fragarioides L.) and mid-successional shrubs (Rhododendron fortunei Lindl. and Enkianthus quinqueflorus Lour.) on late-successional ectomycorrhizal (ECM) pioneer tree (Betula platyphylla Sukaczev) seedling growth. The soils were analyzed for soil nutrient status and fungal and bacterial compositions using ITS and 16S rRNA gene sequencing. B. platyphylla seedlings produced higher biomass in soils conditioned by shrubs. Soil organic carbon (SOC) and bacterial and fungal legacies most impacted pioneer tree seedling growth. Additionally, the partial least squares path model revealed that soil nutrients, especially SOC, indirectly affected seedling biomass by their direct effects on the bacterial and fungal communities. The changes in bacterial community composition had a stronger effect on seedling biomass than those of fungi because bacteria with shorter turnover times are generally considered to be more efficient than fungi in enhancing nutrient availability. Our study integrates soil microbial and nutrient legacies to explain the potential mechanisms of pioneer tree regeneration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nematode community structure varies among forest successional stages. • Forest succession leads to higher nematode abundance and maturity index. • Increasing fungivores and decreasing herbivores occur with forest succession. • Forest succession exhibits layer-specific effects on nematode community structure. Nematodes are among the most important faunal groups in soil food webs and serve as important bioindicators in evaluating subsurface ecological processes and ecosystem functioning. Although previous studies have reported the effects of vegetation types on soil nematode communities, the community patterns of soil nematodes at different soil depths during secondary forest succession remain unclear. Through a field survey, we investigated how soil nematode community characteristics changed at two soil depths (0–10 cm and 10–20 cm) across subalpine forest successional stages consisting of grasslands, shrublands and forests in Southwest China. We measured soil properties and microbial biomass to analyze significant environmental factors influencing variations in soil nematode communities. With forest succession, we observed increases in the total nematode abundance and maturity index and a decreased plant parasitic index, indicating more stable food webs and lower root herbivory hazards in forests than in grasslands and shrublands. Fungivore diversity was significantly increased and herbivore diversity was significantly decreased during forest succession, despite no significant difference existing in the total nematode diversity among the three successional stages. The abundances of the dominant nematode genera Helicotylenchus and Tylencholaimus were significantly correlated with forest succession. In addition, the variations in soil nematode communities differed between the two soil depths, presumably due to various soil variables. NO-3-N and pH were the dominant determinants of the variations in soil nematode communities at 0–10 cm soil depth, while SOC was the dominant determinant at 10–20 cm soil depth. Overall, our results suggested that forest succession exhibited layer-specific effects on soil nematode communities via different soil variables, and that specific nematode genera could serve as useful bioindicators during forest succession. [ABSTRACT FROM AUTHOR]

• Herb root exudates promote P. asperata , but inhibit B. albosinensis and B. platyphylla. • Root exudates increase soil bacterial richness and diversity. • Soil bacteria have a greater role on seedling growth than soil properties and fungi. • Root exudates affect seedling growth of subalpine trees by regulating soil bacteria. Root exudates play an important role in belowground ecological processes, by which plants can regulate the soil ecosystem. However, studies on the effects of root exudates on aboveground plant emergence and growth and thus vegetation regeneration are still lacking, particularly in subalpine forests. In this study, we collected the root exudates of dominant plants at different successional stages (early-stage herbs, mid-stage shrubs and late-stage broadleaf and coniferous trees) in a subalpine region of southwestern China, and used them to condition the soil collected in the field. Using the conditioned soil, a pot experiment on the seed germination and seedling growth of subalpine dominant trees (Betula albosinensis , Betula platyphylla and Picea asperata) was conducted in an artificial climate chamber. The seed germination rate and seedling biomass of the subalpine trees, as well as the soil properties and microbial community structure in the potting soils, were measured. Our results showed that root exudates of different successional stages had significant and distinct effects on the seed germination and seedling growth of the subalpine trees, and these effects differed among the tree species. Specifically, the seed germination rate and seedling biomass of P. asperata were promoted, while those of B. albosinensis and B. platyphylla were inhibited under the addition treatments of the herb root exudates. Furthermore, our study suggested that the soil bacterial community contributed more than soil properties and the fungal community to the variations in the seedling biomass of subalpine trees, and the effects of root exudates on seedling biomass were significantly mediated by the soil bacterial community. Overall, these results implied that root exudates of different successional stages could affect the seedling growth of subalpine trees by regulating soil microbial communities, highlighting the critical role of root exudates during forest succession and providing important insights into the potential rhizosphere mechanisms of forest succession. [ABSTRACT FROM AUTHOR]