Response of cbbL Carbon-Fixing Microorganisms to Flooding Depth During the Growing Season in Qinghai Lake Lakeshore Wetlands

Abstract

Lake-level rise driven by changing precipitation is increasing inundation in littoral wetlands, but responses of cbbL-harboring carbon-fixing microorganisms remain uncertain. A controlled soil-column experiment included four hydrological regimes: unflooded soil (CK), water level aligned with the soil surface (S0), and standing-water depths of 10 cm (S10) and 20 cm (S20). Amplicon sequencing of cbbL showed that the Shannon index was significantly higher in S20 than in CK (p = 0.0394), whereas Simpson, Chao1, and ACE did not differ significantly among treatments. Overall amplicon composition also lacked a significant treatment effect (PERMANOVA: R2 = 0.344, p = 0.112). Pseudomonadota represented 96.9–97.7% of taxonomically assigned sequences and remained dominant across treatments, although several genera varied in relative sequence proportion. Exploratory LEfSe screening identified Rhodoblastus-, Hydrogenophaga-, and Azospirillum-related lineages as candidate indicators of CK, S10, and S20, respectively. Multivariate soil profiles did not differ significantly among treatments (PERMANOVA: R2 = 0.374, p = 0.220). After collinearity filtering, EC had the highest normalized mean absolute out-of-fold SHAP contribution among EC, pH, and TC (43.8–59.1%). However, outer leave-one-out cross-validation produced negative predictive R2 values (−0.43 to −0.11), indicating limited model generalizability. Overall, S20 was associated with higher Shannon diversity than CK, while Pseudomonadota remained dominant and several genera varied in relative sequence proportion. EC should therefore be regarded as an exploratory candidate correlate of cbbL alpha diversity rather than a validated environmental driver, and this association requires further evaluation under natural hydrological conditions.