Biological and terrestrial influences on dissolved organic matter in Antarctic surface waters: Insights from mass spectrometry and metagenomic analysis.

Global warming increases the surface waters and biodiversity in polar regions. However, the intrinsic biological sources of dissolved organic matter (DOM) in Antarctic surface waters remain poorly understood. This work evaluated the sources and driving mechanisms of DOM in Antarctic lakes systematically, based on fluorescence excitation-emission matrices, ultrahigh-resolution mass spectra, biological detection, and metagenomic analyses. The most abundant DOM in the water was peptides (37.02%), which differed from those in soil (lignins: 26.33%) and penguin guano (lipids: 50.71%). The relative abundance of CHON and CHOP compounds in water was significantly correlated with the distance from the penguin colony (p < 0.05). Both the fluorescence and mass spectrum fingerprints of water and soil/faeces showed low similarities using end-member source tracking methods. This could be attributed to the facilitation of guano-derived nutrients to phytoplankton proliferation, whereas the concentrations of NH4+-N, NO3--N, total phosphorus, and total organic carbon were significantly higher in the penguin-intensive area than in the other areas. Algae had significant positive effects on carbohydrates and amino sugars and positive effects on lignins, compared to zooplankton and bacteria. Zooplankton had significantly more positive effects on peptides than phytoplankton. Secondary bacterial metabolic activity can be positively linked with CHO compounds. Carbohydrates and amino sugars co-occurred with carbohydrate-active enzyme genes and nitrogen cycling genes in one module of the co-occurrence network, whereas the other module was characterised by the co-occurrence patterns of condensed aromatic structures with carbohydrate-active enzyme genes and nitrogen cycling genes. These results emphasise the roles of secondary metabolites from algae and bacteria in species-specific sources of DOM, shedding light on the driving mechanisms of the biogeochemical cycling of DOM in the Antarctic water environment.