Global distributions of diazotrophs abundance, biomass and nitrogen fixation rates - Gridded data product (NetCDF) - Contribution to the MAREDAT World Ocean Atlas of Plankton Functional Types

The MAREDAT atlas covers 11 types of plankton, ranging in size from bacteria to jellyfish. Together, these plankton groups determine the health and productivity of the global ocean and play a vital role in the global carbon cycle. Working within a uniform and consistent spatial and depth grid (map) of the global ocean, the researchers compiled thousands and tens of thousands of data points to identify regions of plankton abundance and scarcity as well as areas of data abundance and scarcity. At many of the grid points, the MAREDAT team accomplished the difficult conversion from abundance (numbers of organisms) to biomass (carbon mass of organisms). The MAREDAT atlas provides an unprecedented global data set for ecological and biochemical analysis and modeling as well as a clear mandate for compiling additional existing data and for focusing future data gathering efforts on key groups in key areas of the ocean. This is a gridded data product about diazotrophic organisms . There are 6 variables. Each variable is gridded on a dimension of 360 (longitude) * 180 (latitude) * 33 (depth) * 12 (month). The first group of 3 variables are: (1) number of biomass observations, (2) biomass, and (3) special nifH-gene-based biomass. The second group of 3 variables is same as the first group except that it only grids non-zero data. We have constructed a database on diazotrophic organisms in the global pelagic upper ocean by compiling more than 11,000 direct field measurements including 3 sub-databases: (1) nitrogen fixation rates, (2) cyanobacterial diazotroph abundances from cell counts and (3) cyanobacterial diazotroph abundances from qPCR assays targeting nifH genes. Biomass conversion factors are estimated based on cell sizes to convert abundance data to diazotrophic biomass. Data are assigned to 3 groups including Trichodesmium, unicellular diazotrophic cyanobacteria (group A, B and C when applicable) and heterocystous cyanobacteria (Richelia and Calothrix). Total nitrogen fixation rates and diazotrophic biomass are calculated by summing the values from all the groups. Some of nitrogen fixation rates are whole seawater measurements and are used as total nitrogen fixation rates. Both volumetric and depth-integrated values were reported. Depth-integrated values are also calculated for those vertical profiles with values at 3 or more depths.

Biological nitrogen fixation and nutrient release from litter of the guachapele leguminous tree under pure and mixed plantation with eucalyptus.

A Pseudosamanea guachapele (guachapele), leguminosa arbórea fixadora de nitrogênio, é uma alternativa para plantios florestais mistos nos trópicos. Como são escassas as informações sobre a espécie em plantios mistos de eucalipto em condições edafoclimáticas brasileiras, foi conduzido um experimento no qual objetivou-se avaliar a contribuição da fixação biológica de nitrogênio para a guachapele e a velocidade de decomposição e de liberação de nutrientes de folhas senescentes de eucalipto e guachapele (oriundas dos plantios puros e consorciado). A porcentagem de N derivado da atmosfera (% Ndfa) foi estimada comparando-se a abundância natural de 15N ( 15N, ) nos tecidos da guachapele com a observada nos tecidos do Eucalyptus grandis, espécie não fixadora, ambas com sete anos de idade. A constante de decomposição (k) e a meia-vida (t1/2) de serapilheira foram estimadas utilizando-se o modelo exponencial aplicado aos dados oriundos de coletas de litterbags. A estimativa da %Ndfa para guachapele, em condições de plantio puro, variou de 17 a 36%, enquanto que, em condições de plantio consorciado, foi de 35 a 60 %. A concentração de N nas folhas senescentes estava positivamente relacionada com a taxa de decomposição, sendo essa decrescente da guachapele para o eucalipto. A t1/2 dos resíduos diferiu significativamente (p < 0.05), sendo de 148, 185 e 218 dias para as folhas de guachapele, mistura das duas espécies e eucalipto, respectivamente. A liberação dos nutrientes (principalmente N, K e Mg) das folhas seguiu a mesma ordem da t1/2 devido à qualidade inicial das mesmas. Os resultados indicam que a guachapele pode beneficiar o plantio misto pela adição de N e por meio da intensificação da decomposição da serapilheira.

Transport, storage and mobilization of nitrogen by trees and shrubs in the wet/dry tropics of northern Australia

Xylem sap from woody species in the wet/dry tropics of northern Australia was analyzed for N compounds. At the peak of the dry season, arginine was the main N compound in sap of most species of woodlands and deciduous monsoon forest. In the wet season, a marked change occurred with amides becoming the main sap N constituents of most species. Species from an evergreen monsoon forest, with a permanent water source, transported amides in the dry season. In the dry season, nitrate accounted for 7 and 12% of total xylem sap N in species of deciduous and evergreen monsoon forests, respectively In the wet season, the proportion of N present as nitrate increased to 22% in deciduous monsoon forest species. These results suggest that N is taken up and assimilated mainly in the wet season and that this newly assimilated N is mostly transported as amide-N (woodland species, monsoon forest species) and nitrate (monsoon forest species). Arginine is the form in which stored N is remobilized and transported by woodland and deciduous monsoon forest species in the dry season. Several proteins, which may represent bark storage proteins, were detected in inner bark tissue from a range of trees in the dry season, indicating that, although N uptake appears to be limited in the dry season, the many tree and shrub species that produce flowers, fruit or leaves in the dry season use stored N to support growth. Nitrogen characteristics of the studied species are discussed in relation to the tropical environment.

Nitrogen cycling in degraded Leucaena leucocephala-Brachiaria decumbens pastures on an acid infertile soil in south-east Queensland, Australia

A grazing trial was conducted to quantify N cycling in degraded Leucaena leucocephala (leucaena)-Brachiaria decumbens (signal grass) pastures grown on an acid, infertile, podzolic soil in south-east Queensland. Nitrogen accumulation and cycling in leucaena-signal grass pastures were evaluated for 9 weeks until all of the leucaena on offer (mean 600 kg edible dry matter (EDM)/ha, 28% of total pasture EDM) was consumed. Nitrogen pools in the grass, leucaena, soil, cattle liveweight, faeces and urine were estimated. The podzolic soil (pH 4.8-5.9) was found to be deficient in P, Ca and K. Leucaena leaf tissues contained deficient levels of N, P and Ca. Grass tissues were deficient in N and P. Grazing was found to cycle 65% of N on offer in pasture herbage. However, due to the effect of the plant nutrient imbalances described above, biological N fixation by leucaena contributed only 15 kg/ha N to the pasture system over the 9-month regrowth period, of which 13 kg/ha N was cycled. Cattle retained 1.8 kg/ha N (8% of total N consumed) in body tissue and the remainder was excreted in dung and urine in approximately equal proportions. Mineral soil N concentrations did not change significantly (-3.5 kg/ha N) over the trial period. The ramifications of grazing and fertiliser management strategies, and implications for pasture rundown and sustainability are discussed.

Inoculation with Azospirillum, associated with nitrogen fertilization in maize

The biological nitrogen fixation is an alternative to supply the nitrogen needed for maize. The objective of this study was to evaluate the development and yield of maize in response to inoculation with Azospirillum associated with nitrogen fertilization. We conducted two field experiments in the summer harvest, the first in the 2000/2001 crop year in the region of Marechal Cândido Rondon, under conventional tillage, and second in the 2002/2003 agricultural year in the region of Cascavel, under no tillage. The experimental design in both experiments was a randomized complete block, with four replications, 2x2x2 factorial, with two levels of nitrogen at sowing (zero and 20 kg ha-1), two levels of inoculum (zero and 200 g ha-1) and two levels of nitrogen in topdressing (zero and 100 kg ha-1). There was evaluated the height of ear insertion, total plant height, leaf N content, shoot dry biomass and grain yield. The height of ear insertion and total plant height were not influenced by the factors under study. Nitrogen fertilization at sowing increased the leaf N content, causing the opposite effect when combined with inoculation. Inoculation with Azospirillum in the absence of nitrogen, provide productivity increases of 15.4% and 7.4% for 2000/2001 and 2002/2003 crops, respectively. The inoculation provided productivity similar to that obtained with 100 kg ha-1 in topdressing in crop 2000/2001, while in association with the topdressing, reduced productivity and shoot dry biomass in crop 2002/2003.

Soybean response to starter nitrogen and Bradyrhizobium inoculation on a Cerrado oxisol under no-tillage and conventional tillage systems

In Brazil, Bradyrhizobium inoculation has successfully replaced the use of N fertilizer on soybean [Glycine max (L) Merr.] crops. However, with the expansion of no-tillage cropping systems in the Cerrados region, the idea that it is necessary to use small N rates at the sowing to overcome problems related with N immobilization has become widespread, mainly when soybean is cultivated after a non-legume crop. In this study we examined soybean response to small rates of N fertilizer under no-tillage (NT) and conventional tillage (CT) systems. Four experiments (a completely randomized block with five replicates) were carried out in a red yellow oxisol, during the periods of 1998/1999 and 1999/ 2000, under NT and CT. The treatments consisted of four urea rates (0, 20, 30 and 40 kg ha-1 N). All treatments were inoculated with Bradyrhizobium japonicum strains SEMIA 5080 and SEMIA 5079, in the proportion 1 kg of peat inoculant (1,5 x 10(9) cells g-1) per 50 kg of seeds. In both experiments, soybean was cultivated after corn and the N fertilizer was band applied at sowing. In all experiments, N rates promoted reductions of up to 50 % in the nodule number at 15 days after the emergence. Regardless of the management system, these reductions disappeared at the flowering stage and there was no effect of N rates on either the number and dry weight of nodules or on soybean yields. Therefore, in the Brazilian Cerrados, when an efficient symbiosis is established, it is not necessary to apply starter N rates on soybean, even when cultivated under notillage systems.

Exopolysaccharides produced by the symbiotic nitrogen-fixing bacteria of leguminosae

The process of biological nitrogen fixation (BNF), performed by symbiotic nitrogen fixing bacteria with legume species, commonly known as α and β rhizobia, provides high sustainability for the ecosystems. Its management as a biotechnology is well succeeded for improving crop yields. A remarkable example of this success is the inoculation of Brazilian soybeans with Bradyrhizobium strains. Rhizobia produce a wide diversity of chemical structures of exopolysaccharides (EPS). Although the role of EPS is relatively well studied in the process of BNF, their economic and environmental potential is not yet explored. These EPS are mostly species-specific heteropolysaccharides, which can vary according to the composition of sugars, their linkages in a single subunit, the repeating unit size and the degree of polymerization. Studies have showed that the EPS produced by rhizobia play an important role in the invasion process, infection threads formation, bacteroid and nodule development and plant defense response. These EPS also confer protection to these bacteria when exposed to environmental stresses. In general, strains of rhizobia that produce greater amounts of EPS are more tolerant to adverse conditions when compared with strains that produce less. Moreover, it is known that the EPS produced by microorganisms are widely used in various industrial activities. These compounds, also called biopolymers, provide a valid alternative for the commonly used in food industry through the development of products with identical properties or with better rheological characteristics, which can be used for new applications. The microbial EPS are also able to increase the adhesion of soil particles favoring the mechanical stability of aggregates, increasing levels of water retention and air flows in this environment. Due to the importance of EPS, in this review we discuss the role of these compounds in the process of BNF, in the adaptation of rhizobia to environmental stresses and in the process of soil aggregation. The possible applications of these biopolymers in industry are also discussed.

Effect of 15n-labeled hairy vetch and nitrogen fertilization on maize nutrition and yield under no-tillage¹

This study evaluated the effect of hairy vetch (Vicia villosa Roth) as cover crop on maize nutrition and yield under no tillage using isotope techniques. For this purpose, three experiments were carried out: 1) quantification of biological nitrogen fixation (BNF) in hairy vetch; 2) estimation of the N release rate from hairy vetch residues on the soil surface; 3) quantification of 15N recovery by maize from labeled hairy vetch under three rates of mineral N fertilization. This two-year field experiment was conducted on a sandy Acrisol (FAO soil classification) or Argissolo Vermelho distrófico arênico (Brazilian Soil Classification), at a mean annual temperature of 18 ºC and mean annual rainfall of 1686 mm. The experiment was arranged in a double split-plot factorial design with three replications. Two levels of hairy vetch residue (50 and 100 % of the aboveground biomass production) were distributed on the surface of the main plots (5 x 12 m). Maize in the sub-plots (5 x 4 m) was fertilized with three N rates (0, 60, and 120 kg ha-1 N), with urea as N source. The hairy vetch-derived N recovered by maize was evaluated in microplots (1.8 x 2.2 m). The BFN of hairy vetch was on average 72.4 %, which represents an annual input of 130 kg ha-1 of atmospheric N. The N release from hairy vetch residues was fast, with a release of about 90 % of total N within the first four weeks after cover crop management and soil residue application. The recovery of hairy vetch 15N by maize was low, with an average of 12.3 % at harvest. Although hairy vetch was not directly the main source of maize N nutrition, the crop yield reached 8.2 Mg ha-1, without mineral fertilization. There was an apparent synergism between hairy vetch residue application and the mineral N fertilization rate of 60 kg ha-1, confirming the benefits of the combination of organic and inorganic N sources for maize under no tillage.