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Microbial nitrogen cycling on the Greenland Ice Sheet  [PDF]
J. Telling,M. Stibal,A. M. Anesio,M. Tranter
Biogeosciences Discussions , 2011, DOI: 10.5194/bgd-8-10423-2011
Abstract: Microbial nitrogen cycling was investigated along a 79 km transect into the Greenland Ice Sheet (GrIS) in early August 2010. The depletion of dissolved nitrate and production of ammonium (relative to icemelt) in cryoconite holes within 7.5 km of the ice sheet margin suggested microbial uptake and ammonification respectively. Nitrogen fixation (<4.2 μmoles C2H4 m 2 day 1 to 16.3 μmoles C2H4 m 2 day 1) was active in some cryoconite holes at sites up to 5.7 km from the ice sheet margin, with nitrogen fixation inversely correlated to concentrations of inorganic nitrogen. There may be the potential for the zone of nitrogen fixation to progressively extend further into the interior of the GrIS as the melt season progresses as reserves of available nitrogen are depleted. Estimated annual inputs of nitrogen from nitrogen fixation along the transect were at least two orders of magnitude lower than inputs from precipitation, with the exception of a 100 m long marginal debris-rich zone where nitrogen fixation could potentially equal or exceed that of precipitation. The average estimated contribution of nitrogen fixation to the nitrogen demand of net microbial growth at sites along the transect ranged from 0% to 17.5%.
Microbial nitrogen cycling on the Greenland Ice Sheet
J. Telling, M. Stibal, A. M. Anesio, M. Tranter, I. Nias, J. Cook, C. Bellas, G. Lis, J. L. Wadham, A. Sole, P. Nienow,A. Hodson
Biogeosciences (BG) & Discussions (BGD) , 2012,
Abstract: Nitrogen inputs and microbial nitrogen cycling were investigated along a 79 km transect into the Greenland Ice Sheet (GrIS) during the main ablation season in summer 2010. The depletion of dissolved nitrate and production of ammonium (relative to icemelt) in cryoconite holes on Leverett Glacier, within 7.5 km of the ice sheet margin, suggested microbial uptake and ammonification respectively. Positive in situ acetylene assays indicated nitrogen fixation both in a debris-rich 100 m marginal zone and up to 5.7 km upslope on Leverett Glacier (with rates up to 16.3 μmoles C2H4 m 2 day 1). No positive acetylene assays were detected > 5.7 km into the ablation zone of the ice sheet. Potential nitrogen fixation only occurred when concentrations of dissolved and sediment-bound inorganic nitrogen were undetectable. Estimates of nitrogen fluxes onto the transect suggest that nitrogen fixation is likely of minor importance to the overall nitrogen budget of Leverett Glacier and of negligible importance to the nitrogen budget on the main ice sheet itself. Nitrogen fixation is however potentially important as a source of nitrogen to microbial communities in the debris-rich marginal zone close to the terminus of the glacier, where nitrogen fixation may aid the colonization of subglacial and moraine-derived debris.
Advances in functional gene diversity of microorganism in relation to soil nitrogen cycling

ZHANG Jing,LIN Xian-Gui,YIN Rui,
张 晶
,林先贵,尹 睿

中国生态农业学报 , 2009,
Abstract: Soil nitrogen cycling is an important part of biogeochemical cycling. Not only does it influence soil productivity and durative development, but also influences global environmental changes. Terrestrial microorganisms play a vital role in soil nitrogen cycling. They participate in important ecological processes such as nitrogen fixation, ammonification, nitrification and denitrification. With the development of molecular biological technology in recent decades, it is possible to study microbial functional community composition, structure and abundance in relation to soil nitrogen cycling from the point of functional gene. In this paper, advances in functional gene diversity in relation to soil nitrogen cycling are reviewed and future areas of improvement identified.
The characteristics of nitrogen fixation, ammonification, nitrification and denitrification in coastal zones

XU Jirong,WANG Youshao,SUN Song,

生态学报 , 2004,
Abstract: The biogeochemical cycling of nitrogen is a significant factor influencing global climatic change. It is a complex process involving interactions between the atmosphere, seawater, sediments, and microorganisms. Nitrogen cycling is particularly active in estuarine and coastal zones, regions where human activities can impact on the natural process. There are four major processes in biogeochemical cycling: nitrification fixation;organic nitrogen ammonification;nitrification, and denitrification. The mechanism...
“Biological Nitrogen Fixation” Book Summary  [PDF]
Frans J. de Bruijn
Advances in Microbiology (AiM) , 2016, DOI: 10.4236/aim.2016.66040
Abstract: 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.
Prospects of Nitrogen Fixation in Rice  [PDF]
Parvez Sofi,Shafiq Wani
Asian Journal of Plant Sciences , 2007,
Abstract: Global agriculture relies heavily on fertilizers which are ecologically as well as economically expensive. Nitrogen which is undoubtedly the most important nutrient input required for rice production, is most frequently also a limiting factor. In a world facing acute energy crisis at global level and unpredictable spurs in world crude oil process due to political turmoil’s and lack of dependable alternative energy resources, it is imperative to develop the system of rice production which, without compromising on yield out-put, lowers dependability on chemical N-fertilizers besides being ecologically compatible. Nitrogen fixation in rice seems to be an efficient prospective system that is compatible with principles of resource conservation and ecological security. The dream project of BNF rice was started in 1992 based on expert recommendations which involve improving endophytic associations between rice and N2 fixing bacteria, engineering of rice plants capable of forming legume like symbiosis and nodules with rhizobia, transforming rice to ensure expression of nitrogenase and protect nitrogenase system from oxygen damage and enhancing N-use efficiency of rice. A large number of diazotropic microorganisms have been found to be associated with rice roots. Among these endophytic diazotropes, Alcaligenes, Azoarcus, Serratia marcesscens and Azorhizobium caulinodons have received major attention. Though most of the aspects of rice-diazotroph interaction and nitrogen fixation have been elucidated both at genetic as well as molecular level, the engineering of an autonomous nitrogen fixing rice plants is undoubtedly a long term endeavor. A large number of endophytic diazotrophs have been found to be associated with rice and factors encouraging bacterial colonization have been characterized but certain critical differences in rice-rhizobial interaction relative to root nodule symbiosis in legumes have to become a reality. It will require a series of genetic manipulation of nodulation genes from plants and nif genes from bacteria to realize the dream of developing a biologically nitrogen fixing rice.
Biological nitrogen fixation in grass  [cached]
, Julierme Zimme rBarbosa; Rangel Consalter; , Antonio Carlos Vargas Motta
Evidência : Ciência e Biotecnologia - Interdisciplinar , 2012,
Abstract: Biological nitrogen fixation in grassAbstractNitrogen (N) due to their role in plant metabolism is the nutrient that most limits crop production. It ispresent in large quantities in air, primarily as di-nitrogen, but unfortunately the plants are not able to 8 Evidência, Joa aba v. 12 n. 1, p. 7-18, janeiro/junho 2012directly use the nutrient in that form, requiring it to be fixed in the form of ammonia. In soil, the fixed N isconverted to nitrate by nitrification process (mediated by Nitrossomonas sp. and Nitrobacter sp. bacteria),thus becomes available for plants. The N fixation may occur via atmospheric, biological and industrial, andthe last was and still is a pillar in the construction and maintenance of modern agriculture. The biologicalnitrogen fixation (BNF) provides economic and environmental advantages, being characterized asan important tool in achieving a more sustainable crop production. Plants of the family Fabaceae (legumes)has the efficiency in the process of BNF known and consecrated, however, four more crops produced inthe world (sugar cane, corn, rice and wheat) are of the family Poaceae (grass), and exploitation of BNF inplants of this family is a recent possibility, with relatively low efficiency, however, the optimization ofthese processes can bring significant benefits, since plants of this family are of paramount importance inproducing food, fiber and energy. Based on the above, this review summarizes knowledge regarding theprocess and efficiency of non-nodulating diazotrophs in Poaceae, in order to assess the state of the scienceof BNF this plants family.
Nitrogen Fixation in Denitrified Marine Waters  [PDF]
Camila Fernandez,Laura Farías,Osvaldo Ulloa
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0020539
Abstract: Nitrogen fixation is an essential process that biologically transforms atmospheric dinitrogen gas to ammonia, therefore compensating for nitrogen losses occurring via denitrification and anammox. Currently, inputs and losses of nitrogen to the ocean resulting from these processes are thought to be spatially separated: nitrogen fixation takes place primarily in open ocean environments (mainly through diazotrophic cyanobacteria), whereas nitrogen losses occur in oxygen-depleted intermediate waters and sediments (mostly via denitrifying and anammox bacteria). Here we report on rates of nitrogen fixation obtained during two oceanographic cruises in 2005 and 2007 in the eastern tropical South Pacific (ETSP), a region characterized by the presence of coastal upwelling and a major permanent oxygen minimum zone (OMZ). Our results show significant rates of nitrogen fixation in the water column; however, integrated rates from the surface down to 120 m varied by ~30 fold between cruises (7.5±4.6 versus 190±82.3 μmol m?2 d?1). Moreover, rates were measured down to 400 m depth in 2007, indicating that the contribution to the integrated rates of the subsurface oxygen-deficient layer was ~5 times higher (574±294 μmol m?2 d?1) than the oxic euphotic layer (48±68 μmol m?2 d?1). Concurrent molecular measurements detected the dinitrogenase reductase gene nifH in surface and subsurface waters. Phylogenetic analysis of the nifH sequences showed the presence of a diverse diazotrophic community at the time of the highest measured nitrogen fixation rates. Our results thus demonstrate the occurrence of nitrogen fixation in nutrient-rich coastal upwelling systems and, importantly, within the underlying OMZ. They also suggest that nitrogen fixation is a widespread process that can sporadically provide a supplementary source of fixed nitrogen in these regions.
The Role of Nitrogen Fixation in Cyanobacterial Bloom Toxicity in a Temperate, Eutrophic Lake  [PDF]
Lucas J. Beversdorf, Todd R. Miller, Katherine D. McMahon
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0056103
Abstract: Toxic cyanobacterial blooms threaten freshwaters worldwide but have proven difficult to predict because the mechanisms of bloom formation and toxin production are unknown, especially on weekly time scales. Water quality management continues to focus on aggregated metrics, such as chlorophyll and total nutrients, which may not be sufficient to explain complex community changes and functions such as toxin production. For example, nitrogen (N) speciation and cycling play an important role, on daily time scales, in shaping cyanobacterial communities because declining N has been shown to select for N fixers. In addition, subsequent N pulses from N2 fixation may stimulate and sustain toxic cyanobacterial growth. Herein, we describe how rapid early summer declines in N followed by bursts of N fixation have shaped cyanobacterial communities in a eutrophic lake (Lake Mendota, Wisconsin, USA), possibly driving toxic Microcystis blooms throughout the growing season. On weekly time scales in 2010 and 2011, we monitored the cyanobacterial community in a eutrophic lake using the phycocyanin intergenic spacer (PC-IGS) region to determine population dynamics. In parallel, we measured microcystin concentrations, N2 fixation rates, and potential environmental drivers that contribute to structuring the community. In both years, cyanobacterial community change was strongly correlated with dissolved inorganic nitrogen (DIN) concentrations, and Aphanizomenon and Microcystis alternated dominance throughout the pre-toxic, toxic, and post-toxic phases of the lake. Microcystin concentrations increased a few days after the first significant N2 fixation rates were observed. Then, following large early summer N2 fixation events, Microcystis increased and became most abundant. Maximum microcystin concentrations coincided with Microcystis dominance. In both years, DIN concentrations dropped again in late summer, and N2 fixation rates and Aphanizomenon abundance increased before the lake mixed in the fall. Estimated N inputs from N2 fixation were large enough to supplement, or even support, the toxic Microcystis blooms.
Factors Affecting the Efficiency of Symbiotic Nitrogen Fixation by Rhizobium  [PDF]
Abdullah M. K. Al-Falih
Pakistan Journal of Biological Sciences , 2002,
Abstract: Recent reports pointed to a decline in agricultural dependence on symbiotic nitrogen fixation, and in the use of rhizobial inoculants. The aim of the present review was to study the environmental factors that affect the efficiency of symbiotic nitrogen fixation by Rhizobium in soil. These factors included pH, salinity, moisture, temperature, microorganisms, organic matter and soil texture. The overall conclusion is that symbiotic nitrogen fixation by Rhizobium is a critical biological process. Environmental stresses are generally the limiting factors of the symbiotic nitrogen fixation. With the selection of the appropriate legume and rhizobial inoculant, nitrogen fixation can be increased and concomitantly food production can be improved even under environmentally stressed conditions.
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