Coupled rhizosphere microbial community assembly and plant trait adaptation of Caragana korshinskii across a dune microtopographic gradient

Global desertification poses a severe ecological challenge, and understanding how plants and microorganisms in arid regions respond to heterogeneous habitats is essential for ecological restoration in these regions. In this study, the typical pioneer shrub Caragana korshinskii in the Kubuqi Desert was selected as the target species. Three key dune microtopographic positions, namely the windward slope, leeward slope, and interdune lowland, were investigated by integrating rhizosphere soil physicochemical analyses, high-throughput sequencing, and measurements of plant functional traits. The results showed that (1) microtopography was associated with distinct changes in rhizosphere soil physicochemical conditions, characterized by higher pH and ammonium nitrogen on the windward slope and higher organic matter and available phosphorus in the interdune lowland, which corresponded to shifts in the distribution patterns of rhizosphere microbial communities. (2) Bacterial α-diversity peaked in the interdune lowland, and bacterial community structure differed markedly among microtopographic positions, with oligotrophic taxa, such as Acidobacteriota, predominating on the windward slope and copiotrophic Pseudomonadota enriched in the interdune lowland. In contrast, fungal community structure was more conservative and responded to environmental heterogeneity mainly through local enrichment of specific taxa, such as Basidiomycota and Mortierellomycota. (3) At the functional level, microorganisms on the windward slope tended to adopt a high-biomass storage strategy to buffer resource fluctuations, whereas those on the leeward slope shifted toward higher metabolic efficiency, and those in the interdune lowland exhibited a low-biomass conservative strategy. Partial least squares path modeling and co-occurrence network analyses further indicated that microbial biomass, especially microbial biomass phosphorus, was a core positive factor associated with root traits, whereas specific fungal taxa, such as Mortierellomycota, were negatively associated with root nutrient traits. (4) In terms of plant responses, C. korshinskii showed three root functional phenotypes, including a robust storage-oriented phenotype on the windward slope, a fine acquisitive phenotype on the leeward slope, and a carbon-rich, nitrogen-poor phenotype in the interdune lowland, which were coordinated with leaf trait variation. Overall, this study established a conceptual framework for coordinated environment-microbe-plant adaptation across dune microtopographic gradients, highlighting that the adaptation of C. korshinskii to heterogeneous habitats is closely associated with the rhizosphere microenvironment, microbial attributes, and coordinated belowground-aboveground functional traits. These findings provide new insights into the mechanisms that maintain desert ecosystem stability and offer a theoretical basis for ecological restoration in sandy regions.