Leaf Functional Traits of Caragana microphylla Linked to Soil Microbial Communities Along a Restoration Chronosequence in Alpine Sandy Land

Vegetation restoration is accompanied by changes in plant functional traits, soil properties, and microbial communities, yet how these components covary along long-term restoration chronosequences remains poorly understood. We investigated Caragana microphylla plantations with 5, 10, 15, 23, and 36 restoration years in alpine sandy ecosystem to examine variations in leaf functional traits, soil properties, and soil microbial communities, as well as their associations during vegetation restoration. Leaf functional traits exhibited pronounced stage-dependent variation rather than simple linear patterns across the restoration chronosequence. During the early-to-middle restoration stages, C. microphylla exhibited relatively higher LTD and LDMC but lower SLA and LNC, with the most pronounced conservative trait combination observed at 15 Y of restoration. With later restoration stages, increased SLA and LNC at later stages suggested a tendency toward more acquisitive resource-use characteristics. The soil microbial community composition also changed with restoration years, with Actinobacteriota, Proteobacteria, Chloroflexi, and Acidobacteriota dominating the bacterial community, whereas Ascomycota and Basidiomycota dominating the fungal community. Fungal α-diversity generally increased with restoration years, whereas bacterial Shannon and Simpson indices exhibited unimodal patterns. Correlation analyses revealed strong associations among leaf functional traits, soil properties, and soil microbial communities. Partial least squares path modeling (PLS-PM) suggested that variations in soil properties and microbial communities were associated with changes in leaf functional traits, with soil properties showing the strongest association. Microbial communities exhibited weaker direct associations with leaf traits but may be indirectly linked to leaf trait variation through their relationships with soil conditions. These findings indicate that changes in leaf resource-use characteristics of C. microphylla during restoration years are closely associated with variation in soil conditions and microbial communities, highlighting the coordinated variation among plant, soil, and microbial components during the restoration of alpine sandy ecosystems restoration.