Rhizophagus irregularis inoculation reshapes root exudates, metabolomes and rhizosphere microbiomes to enhance perennial ryegrass adaptation under heat and cold stress

Perennial ryegrass ( Lolium perenne L.) holds promise for bioenergy and biochemical production, yet thermal extremes constrain its performance. Arbuscular mycorrhizal fungi (AMF) offer a sustainable avenue for stress mitigation, but the mechanisms by which arbuscular mycorrhizal (AM) symbiosis links organ-level metabolism, root exudation, and rhizosphere assembly under heat and cold stress remain poorly understood. Perennial ryegrass inoculated with Rhizophagus irregularis was subjected to heat stress and cold stress and profiled by GC–MS metabolomics, 16S/ITS sequencing, and soil physicochemical/enzymatic assays. Across both stresses, AMF stabilized growth, photosynthesis, and antioxidant status and increased soil available P, NH₄⁺–N, and C/N- cycling enzyme activities. Under heat stress, AMF triggered a root-centered program: amino acids (e.g., proline, asparagine) increased, selected organic acids (e.g., quinic and galacturonic acids) were reallocated, and root sterols/long-chain lipids rose; concurrently, exudates released fewer sugars but more nitrogenous metabolites. Under cold stress, AMF promoted a shoot-centered sugar regime (sucrose, glucose, fructose, trehalose) with concomitant accumulation of organic acids and membrane-related lipids that stabilize cellular structures; exudates shifted toward soluble sugars and nitrogenous compounds. In the rhizosphere, Bacillus and Massilia increased together with fungal Talaromyces , Trichoderma , and Penicillium under heat condition, whereas Bacillus and Pseudomonas increased and Fusarium declined under cold condition. Structural equation modeling (SEM) supported an AMF-triggered cascade from improved soil properties through exudates and community structure to organ metabolomes, with tolerance mediated mainly by root metabolism under heat condition and by shoot metabolism under cold condition. These results clarify how AMF coordinate plant metabolism and the rhizosphere microbiome to enhance heat and cold tolerance, and provide a basis for low-input, environmentally friendly turf and forage management. • AM inoculation reprograms perennial ryegrass metabolites under temperature stress. • AMF-driven shifts in root exudates enabled recruitment of beneficial microbes. • Root metabolism drove heat tolerance and shoot metabolism drove cold tolerance. • AMF triggered stepwise soil-microbe-metabolite cascades enhancing adaptation.