Role of permafrost thaw on organic carbon and nitrogen mineralization through affecting dissolved organic matter composition and microbial community in headwater rivers

Dissolved inorganic carbon and ammonium are essential nutrients that support aquatic primary productivity. However, the patterns and potential mechanisms of organic carbon and nitrogen mineralization under permafrost thaw caused by global warming remain unclear. We usedFourier transform ion cyclotron resonance mass spectrometry, stable isotopic measurements (water, carbon, and nitrogen), as well as microbial high-throughput sequencing to explore the response of organic sourced dissolved inorganic carbon (DICoc) and ammonification rates to permafrost thaw in headwater rivers. The results revealed that permafrost thaw significantly altered dissolved organic carbon concentration, dissolved organic matter (DOM) optical and molecular composition, and was responsible for changes in microbial diversity and community composition. Furthermore, partial least squares path models further revealed that DICoc and ammonification rates were indirectly regulated by permafrost thaw through DOM composition and microbial community. This study highlights that permafrost thaw caused by global warming has a profound impact on organic carbon and nitrogen mineralization in headwater rivers, with increased inorganic carbon and ammonium release potentially threatening the stability of river ecosystems in high-latitude regions.