Keystone fungal taxa play a more vital role in regulating rhizosphere soil ecosystem multifunctionality than keystone bacterial taxa in early succession

Soil ecosystem multifunctionality (EMF) is crucial in regulating nutrient cycling, enhancing biodiversity, and maintaining ecosystem stability. However, how keystone taxa affect soil EMF in early succession remains unclear. Here, we investigated changes in soil properties, microbial characteristics, and soil EMF in seedlings’ rhizosphere across different canopy densities, including forest gap (FG), forest edge (FE), medium canopy density (0.4-0.6, MCD), and high canopy density (0.7-0.9, HCD), and further clarified the primary factors regulating soil EMF. Our results revealed that canopy density significantly affected soil properties, microbial characteristics, and soil EMF (p < 0.05). Specifically, rhizosphere soil nutrient concentrations (i.e., soil available potassium (SAK), ammonium nitrogen (NH4+–N), soil organic carbon (SOC), and total nitrogen (TN)) and soil EMF in FE were significantly higher than those in other treatments. Soil microbial communities were limited by phosphorus in all canopy densities. Co-occurrence network analysis showed that average degrees and linkage densities of bacterial and fungal networks peaked in FG and HCD, respectively. Spearman's analysis demonstrated that keystone bacterial and fungal taxa diversities were significantly affected by soil nutrients and enzymatic activity characteristics. Random forest revealed that soil EMF was simultaneously influenced by soil properties, enzymatic activity, microbial biomass, and keystone taxa diversity. Both variance partitioning analysis and structural equation modeling illustrated that keystone fungal taxa played more crucial roles than keystone bacterial taxa in regulating soil EMF. Overall, the findings indicated that the forest edge was conducive to maintaining soil EMF and highlighted the importance of keystone fungal taxa in regulating soil EMF.

土壤生态系统多功能性（Soil ecosystem multifunctionality, EMF）在调控养分循环、维持生物多样性及维系生态系统稳定性方面发挥着关键作用。然而，在早期演替阶段，关键类群（keystone taxa）如何影响土壤EMF，目前仍未明确。
本研究针对不同冠层密度下幼苗根际的土壤性质、微生物特征及土壤EMF变化展开调查，涵盖林隙（forest gap, FG）、林缘（forest edge, FE）、中等冠层密度（medium canopy density, 0.4~0.6, MCD）与高冠层密度（high canopy density, 0.7~0.9, HCD）四类样地，并进一步明确了调控土壤EMF的核心驱动因子。
研究结果显示，冠层密度对土壤性质、微生物群落特征及土壤EMF均存在显著影响（p < 0.05）。具体而言，林缘样地的根际土壤养分含量（即速效钾（soil available potassium, SAK）、铵态氮（ammonium nitrogen, NH4+–N）、土壤有机碳（soil organic carbon, SOC）与全氮（total nitrogen, TN））及土壤EMF均显著高于其余处理组。所有冠层密度下的土壤微生物群落均受到磷素限制。
共现网络分析（co-occurrence network analysis）结果表明，细菌与真菌网络的平均度及连接密度分别在林隙与高冠层密度样地达到峰值。
斯皮尔曼相关性分析（Spearman's analysis）显示，细菌与真菌关键类群的多样性显著受土壤养分及酶活性特征调控。
随机森林（Random forest）分析结果揭示，土壤EMF同时受到土壤性质、酶活性、微生物生物量及关键类群多样性的共同影响。
方差分解分析（variance partitioning analysis）与结构方程模型（structural equation modeling）均证实，真菌关键类群在调控土壤EMF方面的作用显著强于细菌关键类群。
综上，本研究结果表明林缘生境有助于维持土壤EMF，并凸显了真菌关键类群在调控土壤EMF过程中的重要性。