The effect of diazotrophs and chemical fertilizers on yield attributing characters and economics of okra cultivation was evaluated. Application of highest dose of NPK @100% in combination with vermicompost (5 t ha-1) ...The effect of diazotrophs and chemical fertilizers on yield attributing characters and economics of okra cultivation was evaluated. Application of highest dose of NPK @100% in combination with vermicompost (5 t ha-1) and biofertilizers with FYM increased the fruit yield of okra (cultivar Mahyco-10) considerably with yield varying between 80.00 q ha-1 to 227.13 q ha-1 and 80.49 q ha-1 to 229.62 q ha-1 during 2010 and 2011 respectively. In okra cv. Utkal Gaurav the fruit yield varied from 47.68 q ha-1 to 129.84 q ha-1 in 2010 and 47.27 q ha-1 to 131.35 q ha-1 in 2011. As regards the net return, highest net profit of Rs 87,630 and Rs. 89,370 ha-1 from the okra was realized over an investment of Rs. 71,360 ha-1 during both the years with a benefit cost ratio of 2.23 and 2.25 when 100% NPK integrated with vermicompost @5t ha-1 and biofertilizers with FYM applied in okra cv.Mahyco-10. The highest net return of Rs. 14,350 in 2010 and Rs. 15,260 in 2011 with an investment of Rs. 63,550 each year was found in cultivar Utkal Gaurav under highest level of nutrient application.展开更多
Dinitrogen(N_(2))fixed by a group of prokaryotes(diazotrophs)is the dominant process adding bioavailable nitrogen into the ocean.Although it has been intensively studied how N_(2) fixation is controlled by resources(b...Dinitrogen(N_(2))fixed by a group of prokaryotes(diazotrophs)is the dominant process adding bioavailable nitrogen into the ocean.Although it has been intensively studied how N_(2) fixation is controlled by resources(bottom-up factors),it is unclear whether the grazing(top-down control)effectively impacts growth and distribution of different diazotroph groups.In this study,we evaluate this question by conducting log-log regression of diazotroph biomass onto corresponding N_(2) fixation rates in the global ocean.The slope of the regression for Trichodesmium is~0.8,indicating that a small portion of the increase in N_(2) fixation does not accumulate as its biomass.This leads to a conclusion that Trichodesmium is under a substantial top-down control,although bottom-up control still dominates.We also analyze the residuals of the regression in the North Atlantic,concluding that free trichomes of Trichodesmium are subject to stronger top-down control than its colonies.The weak correlation between the biomass and N_(2) fixation of unicellular cyanobacterial diazotrophs indicates that the degree of top-down control on this type of diazotrophs varies greatly.The analyses obtain unrealistic results for diatom-diazotroph assemblages due to complicated nitrogen sources of these symbioses.Our study reveals the variability of top-down control among different diazotroph groups across time and space,suggesting its importance in improving our understandings of ecology of diazotrophs and predictions of N_(2) fixation in biogeochemical models.Measurements of size-specific N_(2) fixation rates and growth rates of different diazotroph groups can be useful to more reliably analyze the top-down control on these key organisms in the global ocean.展开更多
Enhancement of nitrogen fixation in the rhizo-sphere of cereals has attracted a wide interestin biological and agricultural research,insteadof chemicals,for supplying higher plants withcombined nitrogen.Bacteria in as...Enhancement of nitrogen fixation in the rhizo-sphere of cereals has attracted a wide interestin biological and agricultural research,insteadof chemicals,for supplying higher plants withcombined nitrogen.Bacteria in association withrice plant.s were sensitive to the surroundingfactors in the soil,such as NH~+ or O,whichrepressed associative nitrogen fixation between展开更多
Mountain systems are unique for studying the responses of species distribution and diversity to environmental changes along elevational gradients.It is well known that free-living diazotrophic microorganisms are impor...Mountain systems are unique for studying the responses of species distribution and diversity to environmental changes along elevational gradients.It is well known that free-living diazotrophic microorganisms are important to nitrogen cycling in mountain systems.However,the elevational patterns of free-living diazotrophs and the underlying ecological processes in controlling their turnover along broader gradients are less well documented.Here,we investigated the pattern of diazotrophic diversity along the elevational gradient(1800 m-4100 m)in Mount Gongga of China.The results showed that the α-diversity of diazotrophs did not change with the elevation from 1800 m to 2800 m,but decreased at elevations above 3000 m.Such diversity pattern was driven mainly by soil total carbon,nitrogen,and plant richness.Various diazotrophic taxa showed differential abundance-elevation relationships.Ecological processes determining diazotrophic community assemblage shift along the elevations.Deterministic processes were relatively stronger at both low and high elevations,whereas stochastic processes were stronger at the middle elevation.This study also suggested a strong relationship among aboveground plants and diazotrophs,highlighting their potential interactions,even for free-living diazotrophs.展开更多
Nitrogenase is a metalloprotein complex that catalyses the reaction of biological nitrogen fixation. At least three genetically distinct nitrogenase systems have been confirmed in diazotrophs, namely Nil, Vnf, and Anf...Nitrogenase is a metalloprotein complex that catalyses the reaction of biological nitrogen fixation. At least three genetically distinct nitrogenase systems have been confirmed in diazotrophs, namely Nil, Vnf, and Anf, in which the active-site central metals are Mo, V, and Fe, respectively. The present review summarizes progress on the genetic, structural, and functional investigations into the three nitrogenases and discusses the possibility of the existence of other novel nitrogenases.展开更多
Biological nitrogen fixation is a very valuable alternative to nitrogen fertilizer. This process will be discussed in the “Biological Nitrogen Fixation” book. A wide array of free-living and associative nitrogen fix...Biological nitrogen fixation is a very valuable alternative to nitrogen fertilizer. This process will be discussed in the “Biological Nitrogen Fixation” book. A wide array of free-living and associative nitrogen fixing organisms (diazotrophs) will be covered. The most extensively studied and applied example of biological nitrogen fixation is the symbiotic interaction between nitrogen fixing “rhizobia” and legume plants. While legumes are important as major food and feed crops, cereals such as wheat, maize and rice are the primary food crops, but do not have this symbiotic nitrogen fixing interaction with rhizobia. It has thus been a “holy grail” to transfer the ability to fix nitrogen to the cereals and this topic will be also addressed in these books.展开更多
Three soils with different Electrolytic Conductivity (EC) from the former Lake Texcoco (soil with low EC 1.2 dS·m<sup>-1</sup>, medium with EC 83.1 - 107.8 dS·m<sup>-1</sup>, and high...Three soils with different Electrolytic Conductivity (EC) from the former Lake Texcoco (soil with low EC 1.2 dS·m<sup>-1</sup>, medium with EC 83.1 - 107.8 dS·m<sup>-1</sup>, and high with EC 137.3 - 152.5 dS•m<sup>-1</sup>) were used to isolate nitrogen-fixing bacterial strains through enrichment cultures in nitrogen-free media. The medium and high EC in the soil affected negatively the nitrogen-fixing activity, which was generally ten times lower compared to the activity in the soil with low EC. Twenty-one bacterial strains were isolated, identified and characterized for their nitrogen fixation capacity. The diazotrophic genetic potential of all isolates was confirmed by amplification and sequencing of partial nifH and nifD genes and diazotrophic activity quantified by the acetylene reduction assay. Azospirillum brasilense, and several species of Paenibacillus (P. fujiensis, P. durus, P. borealis, P. graminis, P. massiliensis and P. wynnii) were identified. Isolates belonging to the Paenibacillus genus were found in the three soils. Paenibacillus fujiensis and P. durus showed a high nitrogenase activity. The phylograms based on nifH and nifD gene sequences were consistent with 16S rRNA gene phylogeny.展开更多
In the present study, we report N2 fixation rate(15N isotope tracer assay) and the diazotroph community structure(using the molecular method) in the western tropical North Pacific Ocean(WTNP)(13°–20°N, 120&...In the present study, we report N2 fixation rate(15N isotope tracer assay) and the diazotroph community structure(using the molecular method) in the western tropical North Pacific Ocean(WTNP)(13°–20°N, 120°–160°E). Our independent evidence on the basis of both in situ N2 fixation activity and diazotroph community structure showed the dominance of unicellular N2 fixation over majority of the WTNP surface waters during the sampling periods.Moreover, a shift in the diazotrophic composition from unicellular cyanobacteria group B-dominated to Trichodesmium spp.-dominated toward the western boundary current(Kuroshio) was also observed in 2013. We hypothesize that nutrient availability may have played a major role in regulating the biogeography of N2 fixation.In surface waters, volumetric N2 fixation rate(calculated by nitrogen) ranged between 0.6 and 2.6 nmol/(L·d) and averaged(1.2±0.5) nmol/(L·d), with <10 μm size fraction contributed predominantly(88%±6%) to the total rate between 135°E and 160°E. Depth-integrated N2 fixation rate over the upper 200 m ranged between 150 μmol/(m^2·d)and 480 μmol/(m^2·d)average(225±105) μmol/(m^2·d). N2 fixation can account for 6.2%±3.7% of the depthintegrated primary production, suggesting that N2 fixation is a significant N source sustaining new and export production in the WTNP. The role of N2 fixation in biogeochemical cycling in this climate change-vulnerable region calls for further investigations.展开更多
Endophytic bacteria may influence agricultural production in several ways, including promoting plant growth. Two experiments were conducted in order to evaluate the combination of endophytic bacteria from the Brazilia...Endophytic bacteria may influence agricultural production in several ways, including promoting plant growth. Two experiments were conducted in order to evaluate the combination of endophytic bacteria from the Brazilian Northeast region aims at the commercial introduction of the inoculation of these bacteria in micropropagated sugarcane plants using a temporary immersion bioreactor. One experiment was done in tubes with sterile commercial substrate, and the other was done in pots with soil;both were installed in a greenhouse. A mixed inoculation was performed in six inoculated endophytic diazotrophic bacteria in micropropagated sugarcane plants, variety RB92579. In the experiment with soil, the mixed inoculation significantly increased the shoot dry matter of plants without the addition of nitrogen fertilizer. However, the accumulation of total-N in the tissues showed no significant differences between treatments with and without nitrogen fertilization. The evaluation of micropropagated seedlings showed no increases in the parameters tested. The results showed that the response of inoculation in temporary immersion bioreactor micropropagation is possible, and that the application of homologous strains may have contributed to a better response by the interaction of endophytic bacteria with sugarcane RB92579. Further studies should be conducted to improve the methodology, which indicates a great potential to optimize this process on a commercial scale.展开更多
Maize(Zea mays)requires substantial amounts of nitrogen,posing a challenge for its cultivation.Recent work discovered that some ancient Mexican maize landraces harbored diazotrophic bacteria in mucilage secreted by th...Maize(Zea mays)requires substantial amounts of nitrogen,posing a challenge for its cultivation.Recent work discovered that some ancient Mexican maize landraces harbored diazotrophic bacteria in mucilage secreted by their aerial roots.To see if this trait is retained in modern maize,we conducted a field study of aerial root mucilage(ARM)in 258 inbred lines.We observed that ARM secretion is common in modern maize,but the amount significantly varies,and only a few lines have retained the nitrogen‐fixing traits found in ancient landraces.The mucilage of the high‐ARM inbred line HN5‐724 had high nitrogen‐fixing enzyme activity and abundant diazotrophic bacteria.Our genome‐wide association study identified 17 candidate genes associated with ARM across three environments.Knockouts of one candidate gene,the subtilase family gene ZmSBT3,confirmed that it negatively regulates ARM secretion.Notably,the ZmSBT3 knockout lines had increased biomass and total nitrogen accumulation under nitrogen‐free culture conditions.High ARM was associated with three ZmSBT3 haplotypes that were gradually lost during maize domestication,being retained in only a few modern inbred lines such as HN5‐724.In summary,our results identify ZmSBT3 as a potential tool for enhancing ARM,and thus nitrogen fixation,in maize.展开更多
The diazotrophic community in biological soil crusts(biocrusts)is the key supplier of nitrogen in dryland.To date,there is still limited information on how biocrust development influences the succession of diazotrophi...The diazotrophic community in biological soil crusts(biocrusts)is the key supplier of nitrogen in dryland.To date,there is still limited information on how biocrust development influences the succession of diazotrophic community,and what are the most important factors mediating diazotrophic communities during biocrust succession.Using the high throughput nifH amplicon sequencing,the diazotrophs in soils at different developmental stages of biocrust were comparatively studied.The results evidenced the decreases of TOC/TN ratio and pH value with biocrust development.Nostoc and Scytonema were the most dominant diazotrophic genera at all biocrust stages,while Azospirillum and Bradyrhizobium were abundant only in bare soil.Diazotrophic co-occurrence networks tended to be less complex and less connected with biocrust succession.The soil TOC/TN ratio was the most dominant factor mediating diazotrophic diversity,community composition and assembly processes,while diazotrophic-diversity and NO3–-N/NH4+-N ratio were positively correlated with the nitrogenase activity during biocrust succession.This study provided novel understandings of nitrogen fixation and succession patterns of diazotrophic community,by showing the effects of biocrust succession on diazotrophic diversity,community composition,community assembly and co-occurrence networks,and recognizing TOC/TN ratio as the most dominant factor mediating diazotrophs during biocrust succession.展开更多
Many insects feed on a low‐nitrogen diet,and the origin of their nitrogen supply is poorly understood.It has been hypothesized that some insects rely on nitrogen‐fixing bacteria(diazotrophs)to supplement their diets...Many insects feed on a low‐nitrogen diet,and the origin of their nitrogen supply is poorly understood.It has been hypothesized that some insects rely on nitrogen‐fixing bacteria(diazotrophs)to supplement their diets.Nitrogen fixation by diazotrophs has been extensively studied and convincingly demonstrated in termites,while evidence for the occurrence and role of nitrogen fixation in the diet of other insects is less conclusive.Here,we summarize the methods to detect nitrogen fixation in insects and review the available evidence for its occurrence(focusing on insects other than termites).We distinguish between three aspects of nitrogen fixation investigations:(i)detecting the presence of potential diazotrophs;(ii)detecting the activity of the nitrogen‐fixing enzyme;and(iii)detecting the assimilation of fixed nitrogen into the insect tissues.We show that although evidence from investigations of the first aspect reveals ample opportunities for interactions with potential diazotrophs in a variety of insects,demonstrations of actual biological nitrogen fixation and the assimilation of fixed nitrogen are restricted to very few insect groups,including wood‐feeding beetles,fruit flies,leafcutter ants,and a wood wasp.We then discuss potential implications for the insect's fitness and for the ecosystem as a whole.We suggest that combining these multiple approaches is crucial for the study of nitrogen fixation in insects,and argue that further demonstrations are desperately needed in order to determine the relative importance of diazotrophs for insect diet and fitness,as well as to evaluate their overall impact on the ecosystem.展开更多
Soil heterotrophic respiration during decomposition of carbon(C)-rich organic matter plays a vital role in sustaining soil fertility.However,it remains poorly understood whether dinitrogen(N_(2))fixation occurs in sup...Soil heterotrophic respiration during decomposition of carbon(C)-rich organic matter plays a vital role in sustaining soil fertility.However,it remains poorly understood whether dinitrogen(N_(2))fixation occurs in support of soil heterotrophic respiration.In this study,^(15)N_(2)-tracing indicated that strong N_(2)fixation occurred during heterotrophic respiration of carbon-rich glucose.Soil organic ^(15)N increased from 0.37 atom%to 2.50 atom%under aerobic conditions and to 4.23 atom%under anaerobic conditions,while the concomitant CO_(2)flux increased by 12.0-fold under aerobic conditions and 5.18-fold under anaerobic conditions.Soil N_(2)fixation was completely absent in soils replete with inorganic N,although soil N bioavailability did not alter soil respiration.High-throughput sequencing of the 16S rRNA gene further indicated that:i)under aerobic conditions,only 15.2%of soil microbiome responded positively to glucose addition,and these responses were significantly associated with soil respiration and N_(2)fixation and ii)under anaerobic conditions,the percentage of responses was even lower at 5.70%.Intriguingly,more than 95%of these responses were originally rare with<0.5%relative abundance in background soils,including typical N_(2)-fixing heterotrophs such as Azotobacter and Clostridium and well-recognized non-N_(2)-fixing heterotrophs such as Sporosarcina,Agromyces,and Sedimentibacter.These results suggest that only a small portion of the soil microbiome could respond quickly to the amendment of readily accessible organic C in a fluvo-aquic soil and highlighted that rare phylotypes might have played more important roles than previously appreciated in catalyzing soil C and nitrogen turnovers.Our study indicates that N_(2)fixation could be closely associated with microbial turnover of soil organic C when available in excess.展开更多
Diazotrophic bacteria applied as a seed inoculant can improve the grain yield of several crops including maize. The current study aimed to test the agronomic efficiency and contribution of biological nitrogen fixation...Diazotrophic bacteria applied as a seed inoculant can improve the grain yield of several crops including maize. The current study aimed to test the agronomic efficiency and contribution of biological nitrogen fixation(BNF) of the endophytic diazotroph Herbaspirillum seropedicae strain ZAE94 to maize under field conditions. Eighteen field assays were conducted in four different locations during consecutive years on two hybrids and two varieties of maize in a random block design with four replicates using a peat-based inoculant. The inoculant containing the ZAE94 strain was applied without nitrogen(N)fertilization or with 40 kg N ha^(-1) and was compared to the application of 40 and 80 kg N ha^(-1) without inoculation. Crop productivity and N accumulation in the grain were evaluated in addition to ^(15)N natural abundance(δ^(15)N) to evaluate BNF in the treatments without N fertilization. Fertilization at 40 kg N ha^(-1) plus bacterial inoculation produced crop yields similar to the treatment with 80 kg N ha^(-1) and increased grain N content, especially in the off-season with 40 kg N ha^(-1). The inoculation treatments showed lower δ^(15)N values than the non-inoculated treatments, which was most evident in the off-season. The BNF contributed about 30% of N accumulated in plants inoculated with ZAE94. On average, 64% of the N fertilized plots showed an increase of the parameters evaluated in the inoculated treatments, compared with the control. Inoculation also increased root length, root volume, and leaf area, and these parameters were positively correlated with plant weight using a hydroponic assay. This study revealed that the application of H. seropedicae inoculant increased the amount of N in plants owing to BNF, and there is a better chance of yield response to inoculation under low N fertilizer application in the off-season.展开更多
Biological nitrogen fixation(BNF)can help replenish available nitrogen(N)in cropland and reduce the use of chemical N fertilizers,with diazotrophs playing an important role.However,the response of diazotroph community...Biological nitrogen fixation(BNF)can help replenish available nitrogen(N)in cropland and reduce the use of chemical N fertilizers,with diazotrophs playing an important role.However,the response of diazotroph community and BNF activity in biochar amendment soil,especially in the deep soil horizon,are poorly understood.In this study,soil samples were collected from topsoil(0-20 cm)and subsoil(20-40 cm)in the field experiment(established in 2013)comprising treatments with no chemical fertilizer(CK),chemical fertilizer(NPK),biochar(BC),and biochar plus chemical fertilizers(BNPK).Here,we investigated the diazotroph community using real-time PCR and high-throughput sequencing of the nifH gene,and assessed the soil N_(2)fixation rate(R_(Nfix))using acetylene reduction assay(ARA).Results showed that in the topsoil,the treatments with biochar significantly increased nifH gene copies and R_(Nfix),which was consistent with the increased soil organic matter(SOM),total carbon-to-nitrogen ratio(C/N),dissolved organic carbon(DOC)and pH.In the subsoil,applying chemical fertilizers(NPK)strongly decreased R_(Nfix),but had no effect on diazotroph abundance;in contrast,biochar application(BC)had no effect on R_(Nfix),but suppressed the growth of bacteria and diazotrophs while increasing the abundance of Rhizobiales order.Diazotroph and bacterial gene copies were significantly and positively correlated in both top-and sub-soil,and they were mainly influenced by SOM and total nitrogen(TN).In addition,soil nitrate nitrogen(NO_(3)^(−)-N)was the major factor in shaping the vertical stratification of diazotroph community structure.Although nifH gene abundance was significantly cor-related with R_(Nfix)in the topsoil,the structure equation modeling(SEM)showed the highest correlation between diazotroph community structure and R_(Nfix).Hence,we suggested that soil carbon and nitrogen sources were the key factors correlated with changes in the vertical pattern of diazotroph abundance.Biochar induced the dominant diazotroph community succes-sion and increased soil carbon content and pH,which contributed to the BNF activity.Changes in the BNF activity were driven by the variation in diazotroph community structure.展开更多
文摘The effect of diazotrophs and chemical fertilizers on yield attributing characters and economics of okra cultivation was evaluated. Application of highest dose of NPK @100% in combination with vermicompost (5 t ha-1) and biofertilizers with FYM increased the fruit yield of okra (cultivar Mahyco-10) considerably with yield varying between 80.00 q ha-1 to 227.13 q ha-1 and 80.49 q ha-1 to 229.62 q ha-1 during 2010 and 2011 respectively. In okra cv. Utkal Gaurav the fruit yield varied from 47.68 q ha-1 to 129.84 q ha-1 in 2010 and 47.27 q ha-1 to 131.35 q ha-1 in 2011. As regards the net return, highest net profit of Rs 87,630 and Rs. 89,370 ha-1 from the okra was realized over an investment of Rs. 71,360 ha-1 during both the years with a benefit cost ratio of 2.23 and 2.25 when 100% NPK integrated with vermicompost @5t ha-1 and biofertilizers with FYM applied in okra cv.Mahyco-10. The highest net return of Rs. 14,350 in 2010 and Rs. 15,260 in 2011 with an investment of Rs. 63,550 each year was found in cultivar Utkal Gaurav under highest level of nutrient application.
基金The National Natural Science Foundation of China under contract Nos 41890802 and 42076153。
文摘Dinitrogen(N_(2))fixed by a group of prokaryotes(diazotrophs)is the dominant process adding bioavailable nitrogen into the ocean.Although it has been intensively studied how N_(2) fixation is controlled by resources(bottom-up factors),it is unclear whether the grazing(top-down control)effectively impacts growth and distribution of different diazotroph groups.In this study,we evaluate this question by conducting log-log regression of diazotroph biomass onto corresponding N_(2) fixation rates in the global ocean.The slope of the regression for Trichodesmium is~0.8,indicating that a small portion of the increase in N_(2) fixation does not accumulate as its biomass.This leads to a conclusion that Trichodesmium is under a substantial top-down control,although bottom-up control still dominates.We also analyze the residuals of the regression in the North Atlantic,concluding that free trichomes of Trichodesmium are subject to stronger top-down control than its colonies.The weak correlation between the biomass and N_(2) fixation of unicellular cyanobacterial diazotrophs indicates that the degree of top-down control on this type of diazotrophs varies greatly.The analyses obtain unrealistic results for diatom-diazotroph assemblages due to complicated nitrogen sources of these symbioses.Our study reveals the variability of top-down control among different diazotroph groups across time and space,suggesting its importance in improving our understandings of ecology of diazotrophs and predictions of N_(2) fixation in biogeochemical models.Measurements of size-specific N_(2) fixation rates and growth rates of different diazotroph groups can be useful to more reliably analyze the top-down control on these key organisms in the global ocean.
文摘Enhancement of nitrogen fixation in the rhizo-sphere of cereals has attracted a wide interestin biological and agricultural research,insteadof chemicals,for supplying higher plants withcombined nitrogen.Bacteria in association withrice plant.s were sensitive to the surroundingfactors in the soil,such as NH~+ or O,whichrepressed associative nitrogen fixation between
基金supported by the National Natural Science Foundation of China(41771293,41630751,31670503)Chinese Academy of Sciences(XXH13503-03-106,XDB15010303)+1 种基金Open Fund of Key Laboratory of Environmental and Applied Microbiology CAS(KLCAS-2017-3,KLCAS-2016-03)China Biodiversity Observation Networks(Sino BON).
文摘Mountain systems are unique for studying the responses of species distribution and diversity to environmental changes along elevational gradients.It is well known that free-living diazotrophic microorganisms are important to nitrogen cycling in mountain systems.However,the elevational patterns of free-living diazotrophs and the underlying ecological processes in controlling their turnover along broader gradients are less well documented.Here,we investigated the pattern of diazotrophic diversity along the elevational gradient(1800 m-4100 m)in Mount Gongga of China.The results showed that the α-diversity of diazotrophs did not change with the elevation from 1800 m to 2800 m,but decreased at elevations above 3000 m.Such diversity pattern was driven mainly by soil total carbon,nitrogen,and plant richness.Various diazotrophic taxa showed differential abundance-elevation relationships.Ecological processes determining diazotrophic community assemblage shift along the elevations.Deterministic processes were relatively stronger at both low and high elevations,whereas stochastic processes were stronger at the middle elevation.This study also suggested a strong relationship among aboveground plants and diazotrophs,highlighting their potential interactions,even for free-living diazotrophs.
基金Supported by the State Key Basic Research and DevePopment Plan of China （001CB1089-06） and the NationaP NaturaP Science Foundation of China （30270296）.
文摘Nitrogenase is a metalloprotein complex that catalyses the reaction of biological nitrogen fixation. At least three genetically distinct nitrogenase systems have been confirmed in diazotrophs, namely Nil, Vnf, and Anf, in which the active-site central metals are Mo, V, and Fe, respectively. The present review summarizes progress on the genetic, structural, and functional investigations into the three nitrogenases and discusses the possibility of the existence of other novel nitrogenases.
文摘Biological nitrogen fixation is a very valuable alternative to nitrogen fertilizer. This process will be discussed in the “Biological Nitrogen Fixation” book. A wide array of free-living and associative nitrogen fixing organisms (diazotrophs) will be covered. The most extensively studied and applied example of biological nitrogen fixation is the symbiotic interaction between nitrogen fixing “rhizobia” and legume plants. While legumes are important as major food and feed crops, cereals such as wheat, maize and rice are the primary food crops, but do not have this symbiotic nitrogen fixing interaction with rhizobia. It has thus been a “holy grail” to transfer the ability to fix nitrogen to the cereals and this topic will be also addressed in these books.
文摘Three soils with different Electrolytic Conductivity (EC) from the former Lake Texcoco (soil with low EC 1.2 dS·m<sup>-1</sup>, medium with EC 83.1 - 107.8 dS·m<sup>-1</sup>, and high with EC 137.3 - 152.5 dS•m<sup>-1</sup>) were used to isolate nitrogen-fixing bacterial strains through enrichment cultures in nitrogen-free media. The medium and high EC in the soil affected negatively the nitrogen-fixing activity, which was generally ten times lower compared to the activity in the soil with low EC. Twenty-one bacterial strains were isolated, identified and characterized for their nitrogen fixation capacity. The diazotrophic genetic potential of all isolates was confirmed by amplification and sequencing of partial nifH and nifD genes and diazotrophic activity quantified by the acetylene reduction assay. Azospirillum brasilense, and several species of Paenibacillus (P. fujiensis, P. durus, P. borealis, P. graminis, P. massiliensis and P. wynnii) were identified. Isolates belonging to the Paenibacillus genus were found in the three soils. Paenibacillus fujiensis and P. durus showed a high nitrogenase activity. The phylograms based on nifH and nifD gene sequences were consistent with 16S rRNA gene phylogeny.
基金The National Basic Research Program of China under contract No.2015CB452903the Foundation of China Ocean Mineral Resources R&D Association under contract No.DY135-E2-2-03+1 种基金the Science and Technology Basic Resources Investigation Program of China under contract No.2017FY201403the National Natural Science Foundation of China under contract Nos 41676174,41206104 and 41876198
文摘In the present study, we report N2 fixation rate(15N isotope tracer assay) and the diazotroph community structure(using the molecular method) in the western tropical North Pacific Ocean(WTNP)(13°–20°N, 120°–160°E). Our independent evidence on the basis of both in situ N2 fixation activity and diazotroph community structure showed the dominance of unicellular N2 fixation over majority of the WTNP surface waters during the sampling periods.Moreover, a shift in the diazotrophic composition from unicellular cyanobacteria group B-dominated to Trichodesmium spp.-dominated toward the western boundary current(Kuroshio) was also observed in 2013. We hypothesize that nutrient availability may have played a major role in regulating the biogeography of N2 fixation.In surface waters, volumetric N2 fixation rate(calculated by nitrogen) ranged between 0.6 and 2.6 nmol/(L·d) and averaged(1.2±0.5) nmol/(L·d), with <10 μm size fraction contributed predominantly(88%±6%) to the total rate between 135°E and 160°E. Depth-integrated N2 fixation rate over the upper 200 m ranged between 150 μmol/(m^2·d)and 480 μmol/(m^2·d)average(225±105) μmol/(m^2·d). N2 fixation can account for 6.2%±3.7% of the depthintegrated primary production, suggesting that N2 fixation is a significant N source sustaining new and export production in the WTNP. The role of N2 fixation in biogeochemical cycling in this climate change-vulnerable region calls for further investigations.
基金Funding:This work was supported by the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico(CNPq grant number 310030/2015-3)and MCSB obtained a scholarship from Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior(CAPES).
文摘Endophytic bacteria may influence agricultural production in several ways, including promoting plant growth. Two experiments were conducted in order to evaluate the combination of endophytic bacteria from the Brazilian Northeast region aims at the commercial introduction of the inoculation of these bacteria in micropropagated sugarcane plants using a temporary immersion bioreactor. One experiment was done in tubes with sterile commercial substrate, and the other was done in pots with soil;both were installed in a greenhouse. A mixed inoculation was performed in six inoculated endophytic diazotrophic bacteria in micropropagated sugarcane plants, variety RB92579. In the experiment with soil, the mixed inoculation significantly increased the shoot dry matter of plants without the addition of nitrogen fertilizer. However, the accumulation of total-N in the tissues showed no significant differences between treatments with and without nitrogen fertilization. The evaluation of micropropagated seedlings showed no increases in the parameters tested. The results showed that the response of inoculation in temporary immersion bioreactor micropropagation is possible, and that the application of homologous strains may have contributed to a better response by the interaction of endophytic bacteria with sugarcane RB92579. Further studies should be conducted to improve the methodology, which indicates a great potential to optimize this process on a commercial scale.
基金the special fund at Henan Agricultural University
文摘Maize(Zea mays)requires substantial amounts of nitrogen,posing a challenge for its cultivation.Recent work discovered that some ancient Mexican maize landraces harbored diazotrophic bacteria in mucilage secreted by their aerial roots.To see if this trait is retained in modern maize,we conducted a field study of aerial root mucilage(ARM)in 258 inbred lines.We observed that ARM secretion is common in modern maize,but the amount significantly varies,and only a few lines have retained the nitrogen‐fixing traits found in ancient landraces.The mucilage of the high‐ARM inbred line HN5‐724 had high nitrogen‐fixing enzyme activity and abundant diazotrophic bacteria.Our genome‐wide association study identified 17 candidate genes associated with ARM across three environments.Knockouts of one candidate gene,the subtilase family gene ZmSBT3,confirmed that it negatively regulates ARM secretion.Notably,the ZmSBT3 knockout lines had increased biomass and total nitrogen accumulation under nitrogen‐free culture conditions.High ARM was associated with three ZmSBT3 haplotypes that were gradually lost during maize domestication,being retained in only a few modern inbred lines such as HN5‐724.In summary,our results identify ZmSBT3 as a potential tool for enhancing ARM,and thus nitrogen fixation,in maize.
基金the National Natural Science Foundation of China(32071548,31670503,42077206)the National Key Research and Development Program of China(2018YFE0107000)+2 种基金the 13th Five-year Informatization Plan of Chinese Academy of Sciences(XXH13503-03-106)the National Science Fund for Distinguished Young Scholars(41925028)China Biodiversity Observation Networks(Sino BON).
文摘The diazotrophic community in biological soil crusts(biocrusts)is the key supplier of nitrogen in dryland.To date,there is still limited information on how biocrust development influences the succession of diazotrophic community,and what are the most important factors mediating diazotrophic communities during biocrust succession.Using the high throughput nifH amplicon sequencing,the diazotrophs in soils at different developmental stages of biocrust were comparatively studied.The results evidenced the decreases of TOC/TN ratio and pH value with biocrust development.Nostoc and Scytonema were the most dominant diazotrophic genera at all biocrust stages,while Azospirillum and Bradyrhizobium were abundant only in bare soil.Diazotrophic co-occurrence networks tended to be less complex and less connected with biocrust succession.The soil TOC/TN ratio was the most dominant factor mediating diazotrophic diversity,community composition and assembly processes,while diazotrophic-diversity and NO3–-N/NH4+-N ratio were positively correlated with the nitrogenase activity during biocrust succession.This study provided novel understandings of nitrogen fixation and succession patterns of diazotrophic community,by showing the effects of biocrust succession on diazotrophic diversity,community composition,community assembly and co-occurrence networks,and recognizing TOC/TN ratio as the most dominant factor mediating diazotrophs during biocrust succession.
基金We thank Tamir Rosenberg for technical support.We thank Shimon Rachmilevitch,Martin Kaltenpoth,and Itamar Gilady for discussions and comments on earlier versions of the manuscript.We thank the Daniel E.Koshland Fund,the Sol Leshin Program for BGU-UCLA Academic Cooperation,and the Israel Science Foundation(Award No.364/16)for supporting this work.This is publication number 1032 of the Mitrani Department of Desert Ecology。
文摘Many insects feed on a low‐nitrogen diet,and the origin of their nitrogen supply is poorly understood.It has been hypothesized that some insects rely on nitrogen‐fixing bacteria(diazotrophs)to supplement their diets.Nitrogen fixation by diazotrophs has been extensively studied and convincingly demonstrated in termites,while evidence for the occurrence and role of nitrogen fixation in the diet of other insects is less conclusive.Here,we summarize the methods to detect nitrogen fixation in insects and review the available evidence for its occurrence(focusing on insects other than termites).We distinguish between three aspects of nitrogen fixation investigations:(i)detecting the presence of potential diazotrophs;(ii)detecting the activity of the nitrogen‐fixing enzyme;and(iii)detecting the assimilation of fixed nitrogen into the insect tissues.We show that although evidence from investigations of the first aspect reveals ample opportunities for interactions with potential diazotrophs in a variety of insects,demonstrations of actual biological nitrogen fixation and the assimilation of fixed nitrogen are restricted to very few insect groups,including wood‐feeding beetles,fruit flies,leafcutter ants,and a wood wasp.We then discuss potential implications for the insect's fitness and for the ecosystem as a whole.We suggest that combining these multiple approaches is crucial for the study of nitrogen fixation in insects,and argue that further demonstrations are desperately needed in order to determine the relative importance of diazotrophs for insect diet and fitness,as well as to evaluate their overall impact on the ecosystem.
基金financially supported by the National Science Foundation of China(Nos.91751204,41530857,and 41471205)the National Basic Research Program of China(No.2015CB150501)the Strategic Priority Research Program of Chinese Academy of Sciences(CAS)(No.XDB15040000)。
文摘Soil heterotrophic respiration during decomposition of carbon(C)-rich organic matter plays a vital role in sustaining soil fertility.However,it remains poorly understood whether dinitrogen(N_(2))fixation occurs in support of soil heterotrophic respiration.In this study,^(15)N_(2)-tracing indicated that strong N_(2)fixation occurred during heterotrophic respiration of carbon-rich glucose.Soil organic ^(15)N increased from 0.37 atom%to 2.50 atom%under aerobic conditions and to 4.23 atom%under anaerobic conditions,while the concomitant CO_(2)flux increased by 12.0-fold under aerobic conditions and 5.18-fold under anaerobic conditions.Soil N_(2)fixation was completely absent in soils replete with inorganic N,although soil N bioavailability did not alter soil respiration.High-throughput sequencing of the 16S rRNA gene further indicated that:i)under aerobic conditions,only 15.2%of soil microbiome responded positively to glucose addition,and these responses were significantly associated with soil respiration and N_(2)fixation and ii)under anaerobic conditions,the percentage of responses was even lower at 5.70%.Intriguingly,more than 95%of these responses were originally rare with<0.5%relative abundance in background soils,including typical N_(2)-fixing heterotrophs such as Azotobacter and Clostridium and well-recognized non-N_(2)-fixing heterotrophs such as Sporosarcina,Agromyces,and Sedimentibacter.These results suggest that only a small portion of the soil microbiome could respond quickly to the amendment of readily accessible organic C in a fluvo-aquic soil and highlighted that rare phylotypes might have played more important roles than previously appreciated in catalyzing soil C and nitrogen turnovers.Our study indicates that N_(2)fixation could be closely associated with microbial turnover of soil organic C when available in excess.
基金funded by Brazilian Agriculture Research Corporation—Embrapa,the National Research Council (CNPq),Brazil (No.465133/2014-2)Newton Fund “Understanding and Exploiting Biological Nitrogen Fixation for Improvement of Brazilian Agriculture” (No.B/N012476/1)+2 种基金the Biotechnology and Biological Sciences Research Council (BBSRC),Brazilthe Brazilian National Council for State Funding Agencies (CONFAP)the Coordination of Improvement of Higher Education Personnel (CAPES),Brazil (No.001)。
文摘Diazotrophic bacteria applied as a seed inoculant can improve the grain yield of several crops including maize. The current study aimed to test the agronomic efficiency and contribution of biological nitrogen fixation(BNF) of the endophytic diazotroph Herbaspirillum seropedicae strain ZAE94 to maize under field conditions. Eighteen field assays were conducted in four different locations during consecutive years on two hybrids and two varieties of maize in a random block design with four replicates using a peat-based inoculant. The inoculant containing the ZAE94 strain was applied without nitrogen(N)fertilization or with 40 kg N ha^(-1) and was compared to the application of 40 and 80 kg N ha^(-1) without inoculation. Crop productivity and N accumulation in the grain were evaluated in addition to ^(15)N natural abundance(δ^(15)N) to evaluate BNF in the treatments without N fertilization. Fertilization at 40 kg N ha^(-1) plus bacterial inoculation produced crop yields similar to the treatment with 80 kg N ha^(-1) and increased grain N content, especially in the off-season with 40 kg N ha^(-1). The inoculation treatments showed lower δ^(15)N values than the non-inoculated treatments, which was most evident in the off-season. The BNF contributed about 30% of N accumulated in plants inoculated with ZAE94. On average, 64% of the N fertilized plots showed an increase of the parameters evaluated in the inoculated treatments, compared with the control. Inoculation also increased root length, root volume, and leaf area, and these parameters were positively correlated with plant weight using a hydroponic assay. This study revealed that the application of H. seropedicae inoculant increased the amount of N in plants owing to BNF, and there is a better chance of yield response to inoculation under low N fertilizer application in the off-season.
基金the National Natural Science Foundation of China(Grant No.31972511)the National Key R&D Program of China(Grant No.2018YFD0201001)China Agriculture Research System of MOF and MARA(CARS-13).
文摘Biological nitrogen fixation(BNF)can help replenish available nitrogen(N)in cropland and reduce the use of chemical N fertilizers,with diazotrophs playing an important role.However,the response of diazotroph community and BNF activity in biochar amendment soil,especially in the deep soil horizon,are poorly understood.In this study,soil samples were collected from topsoil(0-20 cm)and subsoil(20-40 cm)in the field experiment(established in 2013)comprising treatments with no chemical fertilizer(CK),chemical fertilizer(NPK),biochar(BC),and biochar plus chemical fertilizers(BNPK).Here,we investigated the diazotroph community using real-time PCR and high-throughput sequencing of the nifH gene,and assessed the soil N_(2)fixation rate(R_(Nfix))using acetylene reduction assay(ARA).Results showed that in the topsoil,the treatments with biochar significantly increased nifH gene copies and R_(Nfix),which was consistent with the increased soil organic matter(SOM),total carbon-to-nitrogen ratio(C/N),dissolved organic carbon(DOC)and pH.In the subsoil,applying chemical fertilizers(NPK)strongly decreased R_(Nfix),but had no effect on diazotroph abundance;in contrast,biochar application(BC)had no effect on R_(Nfix),but suppressed the growth of bacteria and diazotrophs while increasing the abundance of Rhizobiales order.Diazotroph and bacterial gene copies were significantly and positively correlated in both top-and sub-soil,and they were mainly influenced by SOM and total nitrogen(TN).In addition,soil nitrate nitrogen(NO_(3)^(−)-N)was the major factor in shaping the vertical stratification of diazotroph community structure.Although nifH gene abundance was significantly cor-related with R_(Nfix)in the topsoil,the structure equation modeling(SEM)showed the highest correlation between diazotroph community structure and R_(Nfix).Hence,we suggested that soil carbon and nitrogen sources were the key factors correlated with changes in the vertical pattern of diazotroph abundance.Biochar induced the dominant diazotroph community succes-sion and increased soil carbon content and pH,which contributed to the BNF activity.Changes in the BNF activity were driven by the variation in diazotroph community structure.
