Rhizophagus clarus and phosphorus co-regulate oat rhizosphere metabolome–microbiome under drought: a candidate hub metabolite perspective

Abstract

The interaction between arbuscular mycorrhizal fungi (AMF) and phosphorus (P) availability could enhance plant drought tolerance. Yet whether this interaction modulates nutrient uptake and grain yield in oat by reshaping rhizosphere metabolite and microbial networks remains unresolved. A pot experiment was conducted across three relative water contents (75%, 55%, and 35% relative water content, designated WW, MDS, and SDS), two AMF treatments, and three P levels (0, 40, and 80 mg kg − ¹ soil, designated P0, P1, and P2). Untargeted metabolomics and metagenomics were applied to characterize rhizosphere metabolite profiles and bacterial community structure, and to assess their relationships with nitrogen (N) and P status in the plant–soil system, grain yield and β-glucan. Drought significantly reduced grain yield, whereas moderate drought increased β-glucan accumulation; the beneficial effects of AMF on both traits were strongly modulated by soil P level. Under drought, AMF inoculation and P addition synergistically promoted N and P accumulation across oat organs; relative to P0AMF, P2AMF significantly elevated total N and P concentrations in roots, stems, leaves, panicles, and grains. Water availability was the dominant driver of rhizosphere metabolome and bacterial community variation. Under drought, AMF–P interaction further enriched rhizosphere metabolites, including amino acids and derivatives, organic acids, and benzene and substituted derivatives, while shifting the signature bacterial taxa toward Pseudomonadota (P1AMF) and Myxococcota and Gemmatimonadota (P2AMF). Network analysis identified isopentenyl pyrophosphate (IPP) as a highly connected hub metabolite, exhibiting the strongest associations with N and P nutrition, grain yield, β-glucan, and bacterial community composition. Exogenous IPP application significantly increased oat plant height, stem dry weight, and average root diameter under drought and markedly elevated the relative abundances of several rhizosphere bacterial taxa. Collectively, these findings indicate that AMF inoculation combined with P addition is associated with restructuring of the rhizosphere metabolite–microbe network under drought, and that IPP represents a candidate metabolite that warrants further investigation in these plant–microbe–soil interactions. This study provides a correlative framework linking this dual strategy to shifts in rhizosphere microbial communities and crop yield and functional quality under water-limited conditions, although mechanistic validation will require future experimental work.