Nitrogen fixation is one of the most important sources of new nitrogen in the ocean and thus profoundly affects the nitrogen and carbon biogeochemical processes.The distribution,controlling factors,and flux of N2 fixa...Nitrogen fixation is one of the most important sources of new nitrogen in the ocean and thus profoundly affects the nitrogen and carbon biogeochemical processes.The distribution,controlling factors,and flux of N2 fixation in the global ocean remain uncertain,partly because of the lack of methodological uniformity.The^(15)N_(2)tracer assay(the original bubble method→the^(15)N_(2)-enriched seawater method→the modified bubble method)is the mainstream method for field measurements of N2 fixation rates(NFRs),among which the original bubble method is the most frequently used.However,accumulating evidence has suggested an underestimation of NFRs when using this method.To improve the availability of previous data,we compared NFRs measured by three^(15)N_(2)tracer assays in the South China Sea.Our results indicate that the relationship between NFRs measured by the original bubble method and the^(15)N_(2)-enriched seawater method varies obviously with area and season,which may be influenced by incubation time,diazotrophic composition,and environmental factors.In comparison,the relationship between NFRs measured by the original bubble method and the modified bubble method is more stable,indicating that the N2 fixation rates based on the original bubble methods may be underestimated by approximately 50%.Based on this result,we revised the flux of N2 fixation in the South China Sea to 40 mmol/(m2·a).Our results improve the availability and comparability of literature NFR data in the South China Sea.The comparison of the^(15)N_(2)tracer assay for NFRs measurements on a larger scale is urgently necessary over the global ocean for a more robust understanding of the role of N2 fixation in the marine nitrogen cycle.展开更多
Antibiotic resistance genes(ARGs)are a well-known environmental concern.Yet,limited knowledge exists on the fate and transport of ARGs in deep freshwater reservoirs experiencing seasonal hydrological changes,especiall...Antibiotic resistance genes(ARGs)are a well-known environmental concern.Yet,limited knowledge exists on the fate and transport of ARGs in deep freshwater reservoirs experiencing seasonal hydrological changes,especially in the context of particle-attached(PA)and free-living(FL)lifestyles.Here,the ARG profiles were examined using high-throughput quantitative PCR in PA and FL lifestyles during four seasons representing two hydrological phenomena(vertical mixing and thermal stratification)in the Shuikou Reservoir(SR),Southern China.The results indicated that seasonal hydrological dynamics were critical for influencing the ARGs in PA and FL and the transition of ARGs between the two lifestyles.ARG profiles both in PA and FL were likely to be shaped by horizontal gene transfer.However,they exhibited distinct responses to the physicochemical(e.g.,nutrients and dissolved oxygen)changes under seasonal hydrological dynamics.The particle-association niche(PAN)index revealed 94 non-conservative ARGs(i.e.,no preferences for PA and FL)and 23 and 16 conservative ARGs preferring PA and FL lifestyles,respectively.A sharp decline in conservative ARGs under stratified hydrologic suggested seasonal influence on the ARGs transition between PA and FL lifestyles.Remarkably,the conservative ARGs(in PA or FL lifestyle)were more closely related to bacterial OTUs in their preferred lifestyle than their counterparts,indicating lifestyle-dependent ARG enrichment.Altogether,these findings enhanced our understanding of the ARG lifestyles and the role of seasonal hydrological changes in governing the ARG transition between the lifestyles in a typical deep freshwater ecosystem.展开更多
基金The National Natural Science Foundation of China under contract Nos 42076042 and 41721005the Fund of Ministry of Science and Technology of China under contract No.2017FY201403the Fund of China Ocean Mineral Resources R&D Association under contract No.DY135-13-E2-03.
文摘Nitrogen fixation is one of the most important sources of new nitrogen in the ocean and thus profoundly affects the nitrogen and carbon biogeochemical processes.The distribution,controlling factors,and flux of N2 fixation in the global ocean remain uncertain,partly because of the lack of methodological uniformity.The^(15)N_(2)tracer assay(the original bubble method→the^(15)N_(2)-enriched seawater method→the modified bubble method)is the mainstream method for field measurements of N2 fixation rates(NFRs),among which the original bubble method is the most frequently used.However,accumulating evidence has suggested an underestimation of NFRs when using this method.To improve the availability of previous data,we compared NFRs measured by three^(15)N_(2)tracer assays in the South China Sea.Our results indicate that the relationship between NFRs measured by the original bubble method and the^(15)N_(2)-enriched seawater method varies obviously with area and season,which may be influenced by incubation time,diazotrophic composition,and environmental factors.In comparison,the relationship between NFRs measured by the original bubble method and the modified bubble method is more stable,indicating that the N2 fixation rates based on the original bubble methods may be underestimated by approximately 50%.Based on this result,we revised the flux of N2 fixation in the South China Sea to 40 mmol/(m2·a).Our results improve the availability and comparability of literature NFR data in the South China Sea.The comparison of the^(15)N_(2)tracer assay for NFRs measurements on a larger scale is urgently necessary over the global ocean for a more robust understanding of the role of N2 fixation in the marine nitrogen cycle.
基金supported by the National Natural Science Foundation of China(U1805244 and 31870475)the 9th China-Croatia Science and Technology cooperation committee program(9e21)+1 种基金the Youth Innovation Project of Xiamen(3502Z20206093)BA was supported by the CAS-TWAS president PhD fellowship programme.
文摘Antibiotic resistance genes(ARGs)are a well-known environmental concern.Yet,limited knowledge exists on the fate and transport of ARGs in deep freshwater reservoirs experiencing seasonal hydrological changes,especially in the context of particle-attached(PA)and free-living(FL)lifestyles.Here,the ARG profiles were examined using high-throughput quantitative PCR in PA and FL lifestyles during four seasons representing two hydrological phenomena(vertical mixing and thermal stratification)in the Shuikou Reservoir(SR),Southern China.The results indicated that seasonal hydrological dynamics were critical for influencing the ARGs in PA and FL and the transition of ARGs between the two lifestyles.ARG profiles both in PA and FL were likely to be shaped by horizontal gene transfer.However,they exhibited distinct responses to the physicochemical(e.g.,nutrients and dissolved oxygen)changes under seasonal hydrological dynamics.The particle-association niche(PAN)index revealed 94 non-conservative ARGs(i.e.,no preferences for PA and FL)and 23 and 16 conservative ARGs preferring PA and FL lifestyles,respectively.A sharp decline in conservative ARGs under stratified hydrologic suggested seasonal influence on the ARGs transition between PA and FL lifestyles.Remarkably,the conservative ARGs(in PA or FL lifestyle)were more closely related to bacterial OTUs in their preferred lifestyle than their counterparts,indicating lifestyle-dependent ARG enrichment.Altogether,these findings enhanced our understanding of the ARG lifestyles and the role of seasonal hydrological changes in governing the ARG transition between the lifestyles in a typical deep freshwater ecosystem.
