Abstract: Improving plantation quality is a key strategy for mitigating climate change. However, the mechanisms by which microbial diversity and interactions jointly affect ecosystem quality remain poorly understood. Here, we evaluated how arbuscular mycorrhizal fungi (AMF) and protistan consumer diversity and interactions were related to soil (SQI) and vegetation (VQI) quality across 108 Pinus tabuliformis and Ulmus pumila plantation plots during spring and autumn. We found that AMF richness and network robustness exhibited significant seasonal and host-dependent variation (P < 0.05), whereas consumer richness showed no significant differences (P > 0.05). U. pumila plantations maintained higher soil and vegetation quality across both seasons. Multiple regression models showed that mean annual temperature was the dominant predictor of SQI and VQI in P. tabuliformis plantations, whereas soil properties and network robustness emerged as primary predictors of SQI and VQI in U. pumila plantations. SEMs identified reciprocal associations between network robustness and ecosystem quality in U. pumila plantations, whereas no significant direct associations were detected in P. tabuliformis plantations, where soil properties were positively associated with SQI. Our findings reveal that the relative importance of belowground biotic interactions in relation to plantation quality is host-dependent. U. pumila exhibited reciprocal associations between network robustness and ecosystem quality, whereas variation in P. tabuliformis plantation quality was more strongly associated with abiotic factors. These findings underscore the importance of microbial interaction network configuration, with network stability serving as a potential indicator for optimizing tree species configurations and enhancing plantation quality.

Key words: network robustness, arbuscular mycorrhizal fungi, protist consumers, climate factors, soil quality, vegetation quality