Drought-associated changes in root metabolites and microbial functional potential in the rhizosphere and rhizosheath of Hibiscus syriacus

Drought alters root metabolism and root-associated microbial communities. However, microbial responses in the rhizosphere (RH) and rhizosheath (RS), and their associations with root metabolism, remain poorly resolved. We combined soil metagenomics with untargeted root metabolomics to examine these responses in Hibiscus syriacus , focusing on amino acid and carbohydrate metabolism. Drought was associated with changes in microbial composition and functional gene abundance in RH and RS. Actinomycetota increased in relative abundance, whereas Pseudomonadota decreased. Nocardioides and Cladophialophora increased significantly in RH, while Nitrospira decreased significantly in RS. In RH, genes associated with branched-chain amino acid biosynthesis (ilvA and ilvE) and aromatic compound degradation (paaF, paaB and mhpA) increased in abundance. These changes suggest altered genetic potential for amino acid biosynthesis and aromatic substrate utilization. In RS, pdhB, sdhC/frdC and galE increased, whereas putA decreased. Root metabolomics detected 750 features that met the differential-abundance criteria. These included increases in L-alanine and L-tyrosine and decreases in fumaric acid and 2-oxoglutaric acid. Correlation analyses identified associations between microbial taxa, microbial genes and root metabolites. Together, these results describe drought-associated changes in microbial functional potential across two operationally defined soil fractions alongside changes in the root metabolome.