Lake carbon loss driven by changed microbial carbon utilization through increased anthropogenic land-use intensity

Abstract The conversion of intrinsic lands to anthropogenic uses has increased nutrient inputs for lake microbes, profoundly influencing biogeochemical processes, particularly carbon cycling. Microbial carbon utilization is crucial in lake carbon sequestration, but its general changes under anthropogenic disturbances remain controversial. We combined carbon utilization assays with Biolog EcoPlates and 16S rRNA gene amplicon sequencing to examine microbial carbon utilization and carbon loss in lakes along a 3369 km gradient of land-use intensities spanning the Yangtze River and its front basin across China. Our results demonstrated that >30% land-use conversions from intrinsic to anthropogenic lands (farmland and built areas) resulted in >50% carbon loss in lakes. The large carbon loss was primarily driven by elevated nutrient concentrations, which stimulated microbial carbon utilization. Microbes in water were more responsive to environmental changes than those in sediment. We further identified distinct preferences of microbial carbon utilization driven by compositional shifts in core species. Specifically, nutrient-sensitive species ( Roseomonas and Methylocystis ) were replaced by nutrient-preferential species ( Desertimonas and Clostridium sensu stricto ), which collectively enhanced the utilization of substrates such as itaconic acid, phenylethyl-amine and glycerol, thereby accelerating carbon loss. This study quantifies the relationship between microbial carbon utilization and carbon loss, emphasizing the importance of regulating land-use changes and nutrient inputs to mitigate their impacts on lakes.