The N/C ratios of dissolved organic matter and their response to lake warming and nutri-ent enrichment
Dissolved organic matter(DOM)is an important source of energy and nutrients for aquatic ecosystems.Its elemental stoichiometry,such as N/C ratios,can reflect the nutrient sources of lake sediments.Its study can help reveal the mechanisms of the impacts of global warming and eutrophication on the water bodies.In this study,we focused on the N/C ratios of DOM obtained by high resolution mass spectrometry,and examined the global distribution of N/C ratios of several habitats such as lakes,rivers,oceans and peatlands by Meta-analysis.The results showed that the mean values of N/C of habitats such as river waters(0.050±0.062),sediments(0.050±0.014)and wastewaters(0.083±0.084)had significantly higher mean values than those of peatlands(0.026±0.037).The N/C ratios of waters were significantly affected by temperature,pH,ammonia nitrogen and dissolved organic carbon,whereas N/C ratios of terrestrial ecosystems such as peatlands were mainly affected by pH,total dissolved organic nitrogen and dissolved organic carbon.Furthermore,to explore the patterns of all molecules and their two fractions in response to tempera-ture and nutrient enrichment,a microcosm experiment with simulated temperature changes and nutrient enrichment was conducted to quantitatively analyze the influence mechanism based on the elevational gradient of Laojun Mountain in Yunnan Province,and classified all molecules into two categories of active and inactive molecules according to the sediment DOM molecular transformation number.The N/C ratio of DOM was averagely 0.112±0.020 for all molecules.The active molecules(0.119±0.017)were signifi-cantly higher than inactive molecules(0.109±0.034).The N/C ratios of all molecules were mainly influenced by nutrients(e.g.,nitrite and nitrate)with an explanation of 63.43％.The N/C ratios of active molecules were mainly influenced by nutrients and en-ergy supply(e.g.,dissolved organic carbon,total organic carbon and chlorophyll-a),whereas the N/C ratios of inactive molecules were mainly influenced by nutrients.Structural equation modelling(SEM)analyses further showed that nutrient enrichment had a greater effect on the N/C ratios of total molecules than temperature changes,mainly through the indirect effects of energy supply and nutrients.For active molecules,nutrients affected the N/C ratios through the indirect effect of energy supply.For inactive mol-ecules,nutrients mostly showed direct effect.Overall,our study explored for the first time the distribution pattern of N/C ratios in various habitats around the globe,revealed the response patterns and mechanisms of sediment dissolved organic matter N/C ratios to global warming and nutrient enrichment,and provided scientific evidence for a better understanding and prediction of the stabili-ty of dissolved organic carbon under a changing world.
万方数据
维普
