Soil microbial traits shift on contrasting timescales following restoration of former grazing lands

Native vegetation restoration is a key strategy for restoring degraded lands globally. While this process can reshape belowground microbial communities, the extent to which such changes restore soil ecosystem functions, and whether different microbial traits recover synchronously or on distinct timescales remains less clear. Understanding the sequence of functional recovery is essential for evaluating restoration success, as distinct microbial traits drive different ecosystem services, from carbon storage to plant growth promotion, and serve as meaningful indicators of long-term ecological recovery. To address this, we applied deep metagenomic sequencing to characterise soil microbial responses following native vegetation restoration (spanning 1-31 years prior to sampling) on grazing agricultural lands. We found that microbial functional changes occurred in distinct phases: an early, rapid restructuring of core soil health processes, detectable as early as three years, including enrichment of nutrient retention and carbon fixation pathways, followed by a more gradual development of plant growth-promoting traits as the plant community matures. Genome-resolved analyses of nearly 500 metagenome-assembled genomes revealed a fundamental shift in dominant microbial life history strategies. Specifically, communities transitioned from a resource-scavenging and stress tolerance profile in grazing soils to strategies that prioritise biosynthesis and growth yields in restored soils. These lifestyle shifts have important implications for enhancing the microbial biomass and carbon sink potential of soils. Together, these findings show that microbial functional shifts following restoration are temporally structured - informing expectations for when key restoration targets may be achieved, and providing a practical framework for monitoring ecosystem recovery.