Compared with plant diversity and soil fungal diversity, soil bacterial diversity drives ecosystem multifunctionality during the vegetation restoration process

Restoring vegetation enhances ecosystem multifunctionality (EMF). Species diversity, which includes plant, bacterial, and fungal diversity, plays a fundamental role in maintaining EMF. However, continuous monitoring of the effects of plant and microbial diversity on ecosystem functions across various vegetation restoration strategies remains insufficient. Over 5 years (2017–2021), we investigated the impact of different vegetation restoration methods—Medicago sativa (alfalfa) replanting (AF), Bromus inermis (smooth brome) replanting (SB), and natural restoration (CK)—on both aboveground EMF (AEMF, based on plant productivity) and belowground EMF (BEMF, based on nutrient cycling indicators) in degraded lands of North China. The results indicated that AF primarily enhances EMF by elevating AEMF, while SB predominantly improves EMF by enhancing BEMF. Regression analysis revealed that the EMF and BEMF of AF and SB treatments followed an initial increase, followed by a subsequent decline, with the progression of restoration time. Notably, bacterial diversity—rather than plant or fungal diversity—was positively correlated with EMF during the restoration process. The findings also highlight the dynamic relationship between bacterial community network stability and soil multifunctionality during vegetation restoration. The structural equation model indicates that pH has a direct negative impact on EMF and also indirectly regulates EMF by influencing microbial diversity. These findings enhance our understanding of how biodiversity relates to ecosystem functioning during vegetation restoration, to help develop more accurate and effective restoration strategies.