From microbiome collapse to recovery: a roadmap for microbiome-informed grassland restoration under global change.

Grassland ecosystems depend on soil- and plant-associated microbiomes that regulate nutrient cycling, soil structure formation, plant health, and stress tolerance. This review synthesizes recent progress on how grassland microbiomes are assembled across rhizosphere, endosphere, and bulk soil niches, and how degradation drivers (e.g., overgrazing, drought, salinization, and nutrient enrichment) disrupt microbial diversity, network stability, and functional guilds, often shifting communities toward reduced mutualist capacity and greater disease risk. We then evaluate restoration strategies that aim to re-establish beneficial microbial functions through practices such as organic amendments, inoculation with mycorrhizae or plant growth-promoting microbes, and management approaches that promote habitat recovery and microbial recolonization. Despite rapid advances in sequencing and observational studies, major gaps remain: (i) limited causal evidence linking microbiome changes to process rates (e.g., nitrification, phosphorus mobilization) across field gradients; (ii) underrepresentation of soil viral ecology and its consequences for microbial regulation and ecosystem function; (iii) inconsistent persistence and context-dependence of introduced inoculants; and (iv) a lack of standardized, outcome-oriented indicators for "restoration-ready" microbiomes. Future research should integrate multi-omics with process-based measurements and long-term field experiments, develop locally adapted microbial consortia with monitoring of non-target effects, and strengthen risk assessment and governance frameworks to enable safe, scalable microbiome-informed grassland restoration under global change.