A mixed nitrate (NO_(3)^(–)) and ammonium (NH_(4)^(+)) supply can promote root growth in maize (Zea mays),however,the changes in root morphology and the related physiological mechanism under different N forms are sti...A mixed nitrate (NO_(3)^(–)) and ammonium (NH_(4)^(+)) supply can promote root growth in maize (Zea mays),however,the changes in root morphology and the related physiological mechanism under different N forms are still unclear.Here,maize seedlings were grown hydroponically with three N supplied in three different forms (NO_(3)^(–)only,75/25 NO_(3)^(–)/NH_(4)^(+)and NH_(4)^(+)only).Compared with sole NO_(3)^(–)or NH_(4)^(+),the mixed N supply increased the total root length of maize but did not affect the number of axial roots.The main reason was the increased total lateral root length,while the average lateral root (LR) length in each axle was only slightly increased.In addition,the average LR density of 2nd whorl crown root under mixed N was also increased.Compared with sole nitrate,mixed N could improve the N metabolism of roots (such as the N influx rate,nitrate reductase (NR) and glutamine synthase (GS)enzyme activities and total amino content of the roots).Experiments with exogenously added NR and GS inhibitors suggested that the increase in the average LR length under mixed N was related to the process of N assimilation,and whether the NR mediated NO synthesis participates in this process needs further exploration.Meanwhile,an investigation of the changes in root-shoot ratio and carbon (C) concentration showed that C transportation from shoots to roots may not be the key factor in mediating lateral root elongation,and the changes in the sugar concentration in roots further proved this conclusion.Furthermore,the synthesis and transportation of auxin in axial roots may play a key role in lateral root elongation,in which the expression of ZmPIN1B and ZmPIN9 may be involved in this pathway.This study preliminarily clarified the changes in root morphology and explored the possible physiological mechanism under a mixed N supply in maize,which may provide some theoretical basis for the cultivation of crop varieties with high N efficiency.展开更多
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
Natural nitrogen isotope composition(δ^(15)N) is an indicator of nitrogen sources and is useful in the investigation of nitrogen cycling in organisms and ecosystems. δ^(15)N is also used to study assimilation of ino...Natural nitrogen isotope composition(δ^(15)N) is an indicator of nitrogen sources and is useful in the investigation of nitrogen cycling in organisms and ecosystems. δ^(15)N is also used to study assimilation of inorganic nitrogen. However, the foliar δ^(15)N of intact plants, which is a consequence of nitrate assimilation occurring in the roots and shoots, is not suited for studying nitrate assimilation in cases where nitrate is the sole nitrogen source. In this study, Orychophragmus violaceus(Ov) and Brassica napus(Bn) plantlets, in which nitrate assimilation occurred in the leaves, were used to study the relationship between foliar δ^(15)N and nitrate assimilation.The plantlets were grown in vitro in culture media with different nitrate concentrations, and no root formation occurred for the plantlets during the multiplication stage.Nitrogen isotope fractionation occurred in both the Ov and the Bn plantlets under all treatments. Furthermore, the foliar nitrogen content of both the Ov and Bn plantlets increased with increasing nitrate concentration. Foliar nitrogen isotope fractionation was negatively correlated with foliar nitrogen content for both the Ov and Bn plantlets. Our results suggest that the foliar nitrogen isotope fractionation value could be employed to evaluate nitrate assimilation ability and leaf nitrate reductase activity.Moreover, high external nitrate concentrations couldcontribute to improved foliar nitrogen content and enhanced nitrate assimilation ability.展开更多
基金supported by the National Natural Science Foundation of China(31421092)the Central Publicinterest Scientific Institution Basal Research Fund,China(1610232023023)。
文摘A mixed nitrate (NO_(3)^(–)) and ammonium (NH_(4)^(+)) supply can promote root growth in maize (Zea mays),however,the changes in root morphology and the related physiological mechanism under different N forms are still unclear.Here,maize seedlings were grown hydroponically with three N supplied in three different forms (NO_(3)^(–)only,75/25 NO_(3)^(–)/NH_(4)^(+)and NH_(4)^(+)only).Compared with sole NO_(3)^(–)or NH_(4)^(+),the mixed N supply increased the total root length of maize but did not affect the number of axial roots.The main reason was the increased total lateral root length,while the average lateral root (LR) length in each axle was only slightly increased.In addition,the average LR density of 2nd whorl crown root under mixed N was also increased.Compared with sole nitrate,mixed N could improve the N metabolism of roots (such as the N influx rate,nitrate reductase (NR) and glutamine synthase (GS)enzyme activities and total amino content of the roots).Experiments with exogenously added NR and GS inhibitors suggested that the increase in the average LR length under mixed N was related to the process of N assimilation,and whether the NR mediated NO synthesis participates in this process needs further exploration.Meanwhile,an investigation of the changes in root-shoot ratio and carbon (C) concentration showed that C transportation from shoots to roots may not be the key factor in mediating lateral root elongation,and the changes in the sugar concentration in roots further proved this conclusion.Furthermore,the synthesis and transportation of auxin in axial roots may play a key role in lateral root elongation,in which the expression of ZmPIN1B and ZmPIN9 may be involved in this pathway.This study preliminarily clarified the changes in root morphology and explored the possible physiological mechanism under a mixed N supply in maize,which may provide some theoretical basis for the cultivation of crop varieties with high N efficiency.
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 Key Research and development Program of China (2016YFC0502602)the National Natural Science Foundation of China (U1612441)the project of high-level innovative talents of Guizhou Province [2015(4035)]
文摘Natural nitrogen isotope composition(δ^(15)N) is an indicator of nitrogen sources and is useful in the investigation of nitrogen cycling in organisms and ecosystems. δ^(15)N is also used to study assimilation of inorganic nitrogen. However, the foliar δ^(15)N of intact plants, which is a consequence of nitrate assimilation occurring in the roots and shoots, is not suited for studying nitrate assimilation in cases where nitrate is the sole nitrogen source. In this study, Orychophragmus violaceus(Ov) and Brassica napus(Bn) plantlets, in which nitrate assimilation occurred in the leaves, were used to study the relationship between foliar δ^(15)N and nitrate assimilation.The plantlets were grown in vitro in culture media with different nitrate concentrations, and no root formation occurred for the plantlets during the multiplication stage.Nitrogen isotope fractionation occurred in both the Ov and the Bn plantlets under all treatments. Furthermore, the foliar nitrogen content of both the Ov and Bn plantlets increased with increasing nitrate concentration. Foliar nitrogen isotope fractionation was negatively correlated with foliar nitrogen content for both the Ov and Bn plantlets. Our results suggest that the foliar nitrogen isotope fractionation value could be employed to evaluate nitrate assimilation ability and leaf nitrate reductase activity.Moreover, high external nitrate concentrations couldcontribute to improved foliar nitrogen content and enhanced nitrate assimilation ability.
