Plant–Microbiome Interactions for Environmental Resilience: Rhizosphere Ecology, Climate Adaptation and Ecosystem Sustainability

Drought, extreme heat, soil salinity and flooding are the abiotic stresses most likely to intensify under climate change, and each already constrains crop yield across large agricultural regions. Plant-associated microorganisms, including rhizosphere and endophytic bacteria, arbuscular mycorrhizal fungi and other fungal endophytes, can modify how plants experience and recover from these stresses. Interest in harnessing such microorganisms has expanded rapidly, yet the literature remains fragmented by stressor, by microbial group and by experimental scale, and many published claims rest on single-strain, single-host experiments under controlled conditions. This critical narrative review evaluates evidence published from 2000 onwards, together with foundational earlier work, identified through structured searches of multidisciplinary and life-science indexes, citation tracking and examination of recent reviews and meta-analyses. The synthesis is organised around four questions: which mechanisms are supported for each stressor, how consistently they operate across hosts and environments, what costs and conflicts accompany microbial benefits, and which translational routes are credible. The evidence is strongest for ethylene modulation through bacterial              1-aminocyclopropane-1-carboxylate deaminase, for mycorrhizal effects on plant water relations and sodium exclusion, and for drought-driven restructuring of root microbiomes that enriches monoderm bacteria such as Streptomyces. Evidence for heat tolerance is mechanistically striking but taxonomically narrow, and evidence for flooding tolerance is the least developed, with anaerobic shifts frequently depleting putatively beneficial taxa. Benefits are strongly context dependent: they vary with host genotype, soil history, stress intensity and combinations of stresses, and mycorrhizal carbon costs, growth–defence interactions and opposing hormonal requirements across stressors can reverse apparent advantages. Greenhouse findings predict field outcomes poorly, and in vitro screening for growth-promoting traits has limited predictive value. Synthetic communities, host-mediated selection, breeding for microbiome recruitment and the use of microbial legacies represent promising but largely unvalidated routes. Progress now depends on multi-site field trials with standardised tolerance metrics, mechanistic validation with microbial and plant mutants, explicit accounting of costs, and studies of combined and sequential stresses. Microbiome-mediated tolerance is best regarded as a conditional, manageable component of crop resilience rather than a generic substitute for breeding or agronomic adaptation.