The indiscriminate use of chemical fertilizers has led to adverse environmental impacts and poor crop quality and accelerates the depletion of mineral reserves used for fertilizer production. Microbes are vital in soil nutrient cycling, and some effectively enhance soil nutrient supply and reduce chemical fertilizer usage. Biocontrol bacterium Lysobacter enzymogenes LE16 can produce various hydrolases against plant pathogens to mineralize soil organics via enzyme production. Therefore, the enzyme production, soil organic P and N mineralization, and crop agronomic performances induced by L. enzymogenes LE16 were investigated by pure culture, soil incubation, and greenhouse pot experiments. L. enzymogenes LE16 can hydrolyze lecithin and protein and convert them to inorganic P and NH₄⁺-N. Similarly, available P and N increased as this bacterium was inoculated and grown in the tested soil. In the greenhouse pot experiment, phosphomonoesterase and protease produced by L. enzymogenes LE16 inoculant effectively mineralized soil organic P and N and enhanced soil available nutrients, thereby improving the nutrient uptake, fertilizer utilization rate, and agronomic efficiency of lettuce and pepper seedlings. Bacterial inoculation increased the lettuce yield by 6.43–11.30% and pepper fruit yield by 43.82–70.32%, even with less chemical fertilizer application. Therefore, L. enzymogenes LE16 can hydrolyze lecithin and protein in pure cultures, and mineralize organic P and N in soils, thus improving crop yield and quality and reducing chemical fertilizer application via the production of phosphomonoesterase and protease. L. enzymogenes LE16 shows potential for sustainable agriculture beyond plant protection.

The mechanisms underpinning the soil microbial community assembly are important, particularly in the fragile karst forest ecosystem. Despite such significance, relevant topics remain limited. We investigated a typical karst area, the Maolan National Nature Reserve in China. For this purpose, 30 forest dynamics plots were established on three restoration gradients in degraded karst forests, namely shrub, pioneer tree, and climax communities. Using vegetation surveys, we explored the diversity patterns, driving factors, and community assembly of the soil microbial communities during the restoration of degraded karst forest ecosystems. In addition, the soil physicochemical properties and macrogenomic sequencing data were examined. One-way analysis of variance and principal coordinates analysis showed no significant changes in soil microbial α-diversity during restoration, and the opposite pattern was observed for β-diversity. Variation partitioning analysis revealed that the combined effect of both soil microbial β-diversity and soil was significant (28% and 32% for bacteria and fungi, respectively). Pearson correlation analyses showed that plant species diversity and soil multifunctionality correlated significantly with soil microbial β-diversity. In contrast, the direct effect of plants was smaller (2% and 3% for bacteria and fungi, respectively). According to the dispersal–niche continuum index, stochastic processes were responsible for the assembly of the bacterial and fungal soil microbial communities. During restoration, the dominant influence of stochastic effects on the assembly of bacterial communities intensified. In contrast, the reverse tendency was observed in soil fungi. The investigation of the diversity pattern of soil microbial communities and their assembly can provide theoretical references for the restoration of degraded ecosystems.

The biodiversity–ecosystem function (BEF) relationship is the basis for studying the restoration of degraded ecosystems, and the simultaneous assessment of multi-trophic-level biodiversity and ecosystem multifunctionality relationship is more conducive to unravelling the restoration mechanism of degraded ecosystems, especially for degraded forest ecosystems with harsh habitats and infertile soils such as karst. In this study, we evaluated the biodiversity and soil multifunctionality (SMF) of degraded karst forests (scrub, SB; secondary growth forests, SG; old-growth forests, OG) in the Maolan National Nature Reserve, China, using 30 sample plots. Biodiversity and soil multifunctionality (SMF) at three trophic levels (plant–soil fauna–soil microorganisms), were assessed through vegetation surveys and soil sampling. One-way ANOVA showed that SMF increased with natural restoration, but multi-trophic level biodiversity showed different trends. Pearson’s correlation analysis showed a positive correlation between plant species diversity and SMF (p < 0.001), whereas soil fauna and soil microorganisms were negatively correlated with SMF. Structural equation modeling revealed a cascading effect of the multi-trophic level on the stimulation of the SMF during restoration. Only soil microorganisms exhibited a direct driving effect on SMF (p < 0.001), whereas plants indirectly influenced soil microorganisms through soil fauna, which subsequently affected the SMF. Although we observed the negative effects of increased plant diversity on soil fauna and soil microbial diversity in terms of quantitative relationships, the increase in soil fauna species and the evenness of soil microbial function still contributed to SMF restoration. This study revealed the cascading effects of multi-trophic diversity in promoting SMF restoration and emphasized that soil microbes are key to unraveling restoration mechanisms and processes, whereas soil fauna is an important intermediate link.

Microorganisms play a pivotal role in transforming and making phosphorus (P) available in soil through various mechanisms. However, their specific contributions to alleviating P limitation and enhancing P utilization efficiency in plants within the context of a P-deficient karst ecosystem remains unclear. In this study, eco-stoichiometric methods were employed to evaluate the P utilization efficiency of plants grown in the surveyed karst forest located in Guizhou Province, China. Metagenomic sequencing was utilized to further explore the functional genes and microorganisms involved in soil P cycling. The N:P ratio for 18 out of the 20 surveyed plants exceeded 16, indicating widespread P limitation in karst plants. Among them, plants with high P utilization efficiencies (Nandina domestica Thunb.; Mahonia bodinieri Gagnep.; Pyracantha fortuneana (Maxim.) Li) exhibited higher relative abundances of genes involved in soil P cycling compared to plants with low P utilization efficiencies (Tirpitzia sinensis (Hemsl.) Hallier f.; Albizia kalkora (Roxb.) Prain; Morella rubra Lour.), indicating greater potentials within their rhizosphere microbiomes for soil P transformation. The relative abundance of these functional genes had a significant and positive effect on plant P utilization efficiencies. Structural equation modeling further indicated that microbial P cycling gene abundance directly drove the increase in plant P utilization efficiencies. Specifically, genes involved in soil organic P mineralization (G6PD, suhB, phoD, ppx) and the P uptake and transform system (pstS, pstA, pstB, pstC) contributed to the enhancement of plant P utilization efficiencies. Soil microbial communities involved in P cycling were predominately attributed to Proteobacteria (45.16%–60.02%), Actinobacteria (9.45%–25.23%), and Acidobacteria (5.90%–9.85%), although their contributions varied among different plants. The rhizosphere functional microbial community can thus alleviate P limitation in karst plants, thereby enhancing plant P utilization efficiencies. This study investigated the strong synergism between karst plants and rhizosphere microorganisms and their associated underlying mechanisms from genetic and microbial perspectives.