The interactions between rhizobacteria and arbuscular mycorrhizal fungi enhance global soil carbon sequestration in drylands: A global meta-analysis

BACKGROUND: Drought is a major constraint in arid and semi-arid regions, leading to a reduction in soil organic carbon (SOC) by suppressing microbial activities and limiting organic matter inputs. The decrease in soil health frequently threatens agricultural productivity and ecosystem sustainability. Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) can offer a sustainable strategy to enhance SOC in drylands. AIM OF REVIEW: While the sole effects of AMF or PGPR are often studied, their interactive effects on global SOC sequestration under drought conditions remain systematically unexplored. This review aims to address this critical knowledge gap by conducting, for the first time, a comprehensive meta-analysis of global studies from 1998 to 2025. The objective is to quantitatively evaluate the interaction effect of AMF and PGPR co-inoculation on SOC dynamics and its underlying mechanisms in adaptation to drought environments. KEY SCIENTIFIC CONCEPTS OF REVIEW: Based on 989 observations, the meta-analysis reveals that both single and co-inoculation of AMF and PGPR significantly improve SOC levels. This increase is driven by enhancing key SOC fractions, including microbial biomass carbon, easily oxidizable carbon, dissolved, light fraction, and particulate organic carbon accumulation. The AMF-PGPR co-inoculation strategy is particularly effective across diverse conditions, significantly enhancing SOC in coarse (46%) and medium-textured (54%) soils across acidic (48%) and alkaline (48%) pH in various cropping systems by improving root and shoot traits. Different genera of AMF (Glomus, Rhizophagus) and PGPR (Bacillus, Pseudomonas) synergetically enhance SOC through glomalin production (48-51%), hyphal architecture (122%), phytochrome production (52%), and microbial enzymatic activities. AMF and PGPR co-inoculation enhances SOC accumulation by improving enzymatic activities (39-90%) and plant traits (44-251%). This meta-analysis concludes that AMF-PGPR co-incoulation is a sustainable strategy for increasing global soil carbon sequestration, thereby improving soil health and crop productivity in dryland ecosystems.