Lakeshore land use modulates microbial carbon metabolism: The role of hydrochemistry and DOM composition

Caohai Lake, southwestern China. Lakeshore land use can modify dissolved organic matter (DOM), hydrochemistry, and microbially mediated carbon metabolism in lakes, yet these linkages remain insufficiently resolved. We investigated four functional zones in Caohai Lake: the urban lakeshore zone (CW), the urban-adjacent lake zone (CN), the wooded-meadow lakeshore zone (MW), and the wooded-meadow-adjacent lake zone (MN). Microbial communities, carbon-metabolism genes, DOM properties, and environmental variables were compared to determine how contrasting anthropogenic and natural lakeshore settings regulate lake carbon metabolism. Lakeshore land use strongly shaped microbial community structure and carbon-metabolism genes in Caohai Lake. The CW zone was affected by domestic sewage, exhibiting reduced abundance of bacteria and genes, and a simple network structure. In contrast, the CN, MN, and MW areas, which were far from the towns, had reduced environmental pressure, increased microbial community and gene abundance, and a more stable and complex network structure. DOM composition was the main factor influencing the differences in microorganisms and carbon metabolism genes. Specifically, humic-like fractions and high concentrations of DOC promoted the diversity of microbial communities and gene abundance. Water chemical ions such as Ca 2 + , Mg 2+ , and HCO 3 - regulate carbonate precipitation and inorganic carbon supply. The study revealed the effects and drivers of lakeshore land use change on lake microbiology and carbon metabolism. • Lakeshore land use reshaped hydrochemistry, organic matter, and microbes. • Urban waters had simpler networks and lower carbon metabolism gene abundance. • Wooded meadow zones supported more stable networks and microbial resilience. • Humic components and dissolved organic carbon drove carbon metabolism genes. • Lake transition zones favored refractory carbon degradation and carbon fixation.