Research Details Microbial Carbon Cycling Shifts Under Warming and Carcass Decomposition

Animal decomposition is a process that releases nutrients into terrestrial and aquatic ecosystems. Annually, animal carcasses contribute carbon-rich fluids that modify water chemistry and microbial activity. Aquatic systems are particularly relevant due to their role in global primary production and carbon cycling, processes regulated by microorganisms through specialized carbon cycling genes. While temperature affects microbial metabolism, the combined impact of temperature and sudden carbon inputs, such as those from carcass decomposition, has been less understood at the functional gene level.\n\nA study published on December 5, 2025, in Biocontaminant by Huan Li's team at Lanzhou University, investigated how climate warming and abrupt carbon inputs interact to influence microbial carbon cycling, with implications for greenhouse gas emissions and aquatic ecosystem health.\n\nThe researchers conducted a controlled microcosm experiment involving carcass decomposition in water across five temperature gradients, ranging from 23 to 35 °C. Metagenomic sequencing was utilized to characterize microbial communities and their functional genes involved in aquatic carbon cycling. Multivariate statistics, network analysis, and pathway reconstruction were integrated to identify key drivers and mechanisms.\n\nThe analysis revealed that microorganisms possessing carbon-cycling genes included bacteria, eukaryotes, viruses, and archaea, with bacteria constituting the dominant group (mean 99.81%). Proteobacteria, Actinobacteria, and Bacteroidetes were identified as the most abundant bacterial phyla. Both temperature and carcass decomposition influenced microbial community structure. Warming alone enriched Acidobacteria, Actinobacteria, Chloroflexi, Spirochaetes, and Firmicutes. During carcass decay, Verrucomicrobia, Proteobacteria, and genera such as Novosphingobium, Acidovorax, and Nocardioides were favored.\n\nFunctionally, carcass treatments resulted in a unimodal alpha-diversity pattern of carbon-cycling KEGG orthologs (KOs), peaking near 30 °C, and significantly altered beta diversity. Carbon-degradation pathways, including reductive TCA-related routes, gluconeogenesis, and the ethylmalonyl pathway, were enriched. Glycosyltransferases dominated carbohydrate-active enzyme (CAZy) profiles, with specific genes (e.g., GT2, GT4, CBM50, GH23, GT51) and numerous differential CAZy genes becoming more prevalent under carcass conditions. Rising temperatures reduced carbon-cycling gene diversity in uncontaminated water; however, this effect was buffered in carcass-contaminated systems by high nutrient availability.\n\nApproximately 50% of all carbon-cycling genes and over 33% of CAZy genes demonstrated temperature sensitivity. Substrate specificity varied: warming promoted the degradation of complex carbohydrates in control conditions, but only simple carbohydrate ester degradation increased with temperature during carcass decay, suggesting a preferential use of readily available carbon. Total carbon levels increased by nearly 87% following carcass decomposition, establishing it as a significant factor linking physicochemical conditions to functional gene structure. Network and pathway analyses indicated a carcass-driven shift towards carbon degradation and fermentation, marked by increased acetate and ethanol production and reduced methane oxidation and certain aspects of carbon fixation. This indicates that carbon degradation predominates aquatic carbon cycling during carcass decomposition under warming conditions.\n\nThese findings contribute to the prediction of carbon fluxes in the context of climate change. As global temperatures increase, aquatic environments subjected to sudden carbon inputs—such as from mass fish deaths, livestock carcass disposal, or wildlife mortality—may experience accelerated carbon turnover and elevated emissions of carbon dioxide and other greenhouse gases. Identifying the microbial genes responsive to warming can refine carbon cycling models and inform ecosystem management strategies, particularly for freshwater bodies vulnerable to eutrophication and pollution.