Rhizobia as complex biofertilizers for wheat: Biological nitrogen fixation and plant growth promotion

This article presents the results of the analysis of the process of growth and biological fixation of atmospheric nitrogen, carried out by the cyanobacterium Nostoc punctiforme, cultivated on the nutrient media M.S. Taha (M), Kratz and Myers (C), modified Detmer (De) and Drew (Dr). The highest amount of biomass was attested when cultivating the cyanobacterium on the nutrient medium De, and the lowest on the medium Dr, as well as the values of the reproduction rate and the reproduction coefficient. When cultivating the cyanobacterium on the nutrient media studied, the pH tends to alkalize. The highest amount of fixed atmospheric nitrogen was found when cultivating on the nutrient media De and M, on the sixth day of the experiment, and cultivation on the nutrient medium Dr presented the lowest intensity. Thus, it was found that the biological fixation of atmospheric nitrogen, carried out by N. punctiforme, is subject to the legitimacy of "quantitative nitrogen self-regulation".

Nitrogen is the element most demanded by the soybean crop, and the biological fixation of atmospheric nitrogen is the main means to supply it. In contrast, micronutrients and chemical treatments applied on seeds together with the inoculant can alter the phenomenon of biological fixation of atmospheric nitrogen. This work aimed to evaluate the effect of chemical products, micronutrients, and nitrogen fertilization on the nodulation, development, and yield of soybean. The experiment was developed in a field and a greenhouse in the municipality of Toledo, Brazil. A randomized block with four repetitions was used as an experimental design. This design had eight treatments, namely: T1 - Control (seeds treated with insecticide); T2 - Seeds treated with insecticides and inoculated with Bradyrhizobium; T3 - Untreated seeds inoculated with Bradyrhizobium; T4 Seeds treated with insecticides and cobalt-molybdenum (CoMo), inoculated with Bradyrhizobium; T5 - Seeds with CoMo inoculated with Bradyrhizobium; T6 - Seeds treated with insecticides, inoculated with Bradyrhizobium and with foliar application of CoMo; T7 - Seeds treated with insecticides, inoculated with Bradyrhizobium and with the application of nitrogen in cover; T8 - Seeds treated with nitrogen by broadcast. No significant differences were observed between treatments on the nodules numbers, stem diameter, plant height, root length, the mass of 1000 grains, and yield. The application of nitrogen at the R2 stage (a plant with an open flower in one of the two uppermost nodes of the main stem with a fully developed leaf) and in association with the inoculant + CoMo without seed treatment provided a greater number of nodes, pods, and grains per plant.

Biological soil crusts are important cryptogamic communities covering the sand dunes of the north-western Negev. The biological crusts contain cyanobacteria and other free-living N(2)-fixing bacteria and are hence able to fix atmospheric nitrogen (N). This is why they are considered to be one of the main N input pathways into the desert ecosystem. However, up to now, in situ determinations of the N(2) fixation in the field are not known to have been carried out. We examined the natural (15)N method to determine the biological N(2) fixation by these soil crusts under field conditions. This novel natural (15)N method uses the lichen Squamarina with symbiotic green algae--which are unable to fix N(2)--as a reference in order to determine N(2) fixation. Depending on the sampling location and year, the relative biological fixation of atmospheric nitrogen was estimated at 84-91% of the total N content of the biological soil crust. The cyanobacteria-containing soil lichen Collema had a fixation rate of about 88%. These fixation rates were used to derive an absolute atmospheric N input of 10-41 kg N ha(-1) year(-1). These values are reasonable results for the fixation of atmospheric N(2) by the biological crusts and cyanolichens and are in agreement with other comparable lab investigations. As far as we are aware, the results presented are the first to have been obtained from in situ field measurements, albeit only one location of the Negev with a small number of samples was investigated.

N2 fixation associated with the bryophyte layer is suppressed by low levels of nitrogen deposition in boreal forests

Nitrogen Fixation by Epiphylls in a Tropical Rainforest

7 - Nitrogen Fixation

7 - Nitrogen Fixation

Aims Several local varieties of wheat (Triticum aestivum) developed by Northwest Institute of Plateau Biology, Chinese Academy of Sciences, are widely cultivated in the agricultural regions in Qinghai-Xizang Plateau. These varieties are well adapted to multiple environmental stresses such as low temperature, strong solar radiation, and drought. The objective of this study was to determine the responses of PSII photochemical efficiency to high solar irradiance in leaves of four wheat varieties. We examined whether photo-inhibition was appeared in wheat varieties and analysed variations of quantum yield of quenching due to light-induced and non-light-induced. Methods Field experiments were conducted on the farmland of Xiangride, which is located in the eastern side of Caidamu Basin, Qinghai Province. Four local wheat varieties were used during the heading stage in 2013. Measurements of photochemical efficiency and quantum yield were made on the abaxial surface of flag leaves facing the Sun by using a FMS-2 fluorometer, and the content of photosynthetic pigments and specific leaf weight (SLW) were concurrently determined. Pulse-modulated in-vivo chlorophyll fluorescence technique was used to obtain rapid information on photosynthetic processes. The maximum quantum efficiency of PSII photochemistry (Fv/Fm) was determined at 8:30, 12:00 and 16:30 on clear days after allowing for 20 min dark adaptation with leaf clips. The PSII maximal and actual photochemical efficiency (Fv′/Fm′ and ΦPSII), the PSII photochemical and non-photochemical quenching coefficient (qP and NPQ) were analyzed between morning and afternoon using inner actinic light with photosynthetically active photon flux density at 1 120 μmol photons·m·s. Furthermore, along with analysis of the fraction of PSII reaction centers that are opened (qL), the quantum yield of quenching due to light-induced processes (ΦNPQ) and non-light-induced processes (ΦNO) were explored. Important findings There were significant differences in the content of photosynthetic pigments and SLW among the four wheat varieties. Under conditions of clear days, the flag leaves exhibited marked depressions in 376 植物生态学报 Chinese Journal of Plant Ecology 2014, 38 (4): 375–386 www.plant-ecology.com Fv/Fm at three typical times when determined after 20 min dark adaptation. At a given light intensity, the values of Fv′/Fm′ were significantly reduced in the afternoon due to influences by long-lasting high-light irradiation, and ΦPSII showed little differences among the four wheat varieties and no difference between morning and afternoon. There were almost similar variations in qP and NPQ among the four wheat varieties, suggesting that qP and NPQ belong to instinct property and are influenced by the accumulative stresses of high-light intensity. The fractions of ΦNPQ were higher than that of ΦNO in the four wheat varieties and the up-regulatory of ΦNPQ in the afternoon indicated that the photosynthetic apparatus in these wheat varieties had already acclimated to strong solar irradiation in agricultural regions of Qinghai-Xizang Plateau.

The micronutrients, such as zinc, iron, copper, and boron play an important role in the physiological processes of plants. This experiment evaluate the impact of organic (GA3, Seaweed extract solid/liquid) and inorganic (Nitrobenzene and micronutrients- Zn, Fe, B, Cu) plant growth promoters on the growth indices and yield of wheat varieties. The experiment was laid out in Split Plot Design with three replications. Three timely shown wheat varieties (DBW-187, K-1006, and K-607) allocated in the main plots and plant growth promoters (Nitrobenzene, Gibberellic acid, Seaweed extract, and a mixture of micronutrients-Zn, Fe, Cu, B) in the sub-plots comprised of 18 treatment combinations. The results revealed that significant variations in the response of wheat varieties to the different plant growth promoters. The highest growth and yield viz., plant height (85.50cm), number of tillers (451.75 m-2), fresh weight (86.83 g plant-1), dry weight (23. 39 g plant-1), crop growth rate, test weight (40.67g) and grain yield (4764.67 kg ha-1) was recorded in wheat varieties DBW-187 followed by K-1006 and minimum in variety K-607. Among plant growth promoters, the mixture of micronutrients (Zn, Fe, Cu, B) @ 0.5% foliar spray at tillering stage, show significant result in growth and yield viz., plant height (86.21cm), number of tillers (459.63 m-2), fresh weight (86.96 g plant-1), dry weight (23.92 g plant-1), crop growth rate, test weight (41.87g) and grain yield (4813.67 kg ha-1) as compared to all other treatment. The Gibberellic acid @ 2000 ppm and Seaweed extract liquid @ 625 ml ha-1 show significant result also. The maximum growth and yield was obtained by the variety DBW-187 and mixture nutrients (Zn, Fe, Cu, and B). The interaction effects were found non-significant.

Research on biological nitrogen fixation began in Western Europe during the nineteenth century, under conditions where a mere increase in nitrogen fertilization inevitably increased yields: it was the beginning of the triumphal era of fertilizers. In the thirties began the era of legume inoculation: and this again was due to a very simplistic situation in Western countries: the absence of bacterial symbionts adapted to crops such as soybeans. Biological nitrogen fixation (BNF) appeared as an extension of nitrogen fertilization, with the same effects on farmers’ incomes. The amount of nitrogen available was the limiting factor of the farmer’s income, whatever its origin: mineral nitrogen from soil or fertilizers as well as nitrogen derived from biological fixation. In a way, this very clear-cut situation allowed for the rapid development of our knowledge about BNF, and its use by farmers. Nevertheless, when the time came to extrapolate to tropical countries, some difficulties arose. Some were due to a lack of knowledge about BNF systems in warm countries. Other difficulties were due to the interference of many yield-limiting factors other than nitrogen. But the main difficulty resulted from a misunderstanding about the objectives: the goal of developing BNF is not to achieve the maximum nitrogen input, it is really to achieve the maximum income (money and/or food) for farmers. In many tropical countries, the farmer’s income is not directly proportional to nitrogen availability. We, as scientists, are confined to scientific objectives (maximum nitrogenase activity) whereas countries, such as Bangladesh, must aim at a maximum farming efficiency, biological science being largely secondary to other disciplines such as sociology or economics.

It is unanimously admitted that the chemical fertilizers and pesticides used in modern agriculture create a real environmental and public health problems. One of the promising solutions to substitute these agrochemicals products is the use of bio-resources, including plant growth promoting rhizobacteria (PGPR). The PGPR focused more and more scientific attention in recent decades. These rhizospheric bacteria colonize actively the root system of plants and improve their growth and yield. The PGPR use different mechanisms of action to promote plant growth. These mechanisms were grouped into three clusters according to the PGPR effects on plant physiology. These groups are as follow: (i) biofertilization including biological fixation of atmospheric nitrogen, phosphate solubilization, siderophores production and exopolysaccharides production; (ii) phytostimulation including production of indole acetic acid, gibberellins, cytokinins and ethylene; and (ii) biocontrol including induction of systemic resistance, competition for iron, nutrient and space, production of antibiotics, lytic enzymes, hydrogen cyanide and volatile compounds. In view of the latest advances in PGPR biotechnology, this paper proposes to do the review on PGPR in rhizosphere and describes the different mechanisms used by PGPR to promote the plants growth and health. In prospect to a healthy and sustainable agriculture, respectful of environment, the PGPR approach revealed as one of the best alternatives. Keywords: Rhizosphere, plant growth promoting rhizobacteria (PGPR), root colonization, biofertilization, biocontrol, biostimulation, interaction plant-microorganisms, sustainable agriculture

Salinity tolerance during germination and early seedling growth was evaluated of four wheat varieties under four salinity (NaCl) levels that included Control (distilled water) 0, 9, 12 and 16 dSm-1. The seeds of four wheat varieties including Imdad-2005, Mahran-89, TJ-83 and TD-1 were sown under various NaCl levels in Petri dishes. The trial was performed at Seed Testing Laboratory, Department of Agronomy, Sindh Agriculture University, Tandojam Pakistan, following completely randomized design with three replications. The results showed that different salt stress (NaCl) levels had significant effects on germination (%), shoot and root length (cm), shoot and root water content (%), shoot and root fresh weight (g) and shoot and root dry weight (g) of wheat varieties. Among varieties, Imdad-2005 showed tolerance against salt stress for all parameters as compared to other varieties. The Imdad-2005 produced maximum mean germination (93.7%), shoot and root length (14.8 cm and 9.3 cm), shoot and root RWC (80.1 % and 86.2%), shoot and root fresh weight (2.3 g and 1.5 g) and heaviest shoot and root dry weight (0.28 g and 0.13 g). However, for NaCl levels, maximum germination (96.2 %), shoot and root length (15.5 cm, 10.7 cm), shoot and root water content (86.4 %, 87.0%), shoot and root fresh weight (2.3 and 1.5 g) and highest shoot and root dry weight (0.28 g and 0.13 g) was noted at control, where seeds were on sown by using distilled water. Keywords: Germination; NaCl Tolerance; Seedling growth; Salinity levels; Wheat (Triticum aestivum L.) http://dx.doi.org/10.19045/bspab.2018.700223

Faba bean is an important leguminous winter crop in warm temperate and subtropical areas that has been cultivated for more than 10,000 years as a source of protein in human and livestock diets. It is also grown to enhance yields of other crops. Faba bean provides nitrogen in agricultural systems through the unique process of biological fixation of atmospheric nitrogen by symbiosis with Rhizobium bacteria. This substantially reduces the need for nitrogen fertilizers, which contribute to both carbon dioxide and nitrous oxide emissions. This 2-page fact sheet written by D.C. Odero provides weed control recommendations. Published by the UF Department of Agronomy, April 2011. SS-AGR-345/AG355: Weed Control for Winter Faba Bean Cover Crop in South Florida (ufl.edu)

Diazotrophic cyanobacteria are important components of marine ecosystems, where they contribute to primary production and provide a source of fixed nitrogen (N). During biological fixation of atmospheric nitrogen (N2), hydrogen is produced as an obligate by-product. The present study investigated the potential contribution of 4 marine diazotrophs to the pool of dissolved H2 in the oceans. N2 fixation, as measured by acetylene reduction, and H2 production rates were monitored throughout the diel period in cultures of the filamentous Trichodesmium erythraeum strain IMS101, and the unicellular organisms Cyanothece sp. strain ATCC 51142 and Crocosphaera watsonii strains WH8501 and WH0002. H2 production coincided with diel variations in N2 fixation for each strain regardless of whether N2 fixation peaked during the day or night. Chlorophyll-normalized rates of H2 production ranged 100-fold from a maximum of 3 nmol µg chl a -1 h -1 in T. erythraeum IMS101 cul- tures to 0.03 nmol µg chl a -1 h -1 in Crocosphaera watsonii WH0002. Overall, the ratio of net H2 pro- duced to N2 fixed varied from 0.05 to 0.003 in the unicellular cyanobacteria, compared to 0.3 in the filamentous T. erythraeum IMS101, indicating that unicellular cyanobacteria produce less, or alterna- tively, re-assimilate more of the H2 produced during N2 fixation. Crocosphaera watsonii has recently been identified as a significant source of fixed N in the marine environment, and an efficient recy- cling of H2 would provide a valuable source of energy to their respiratory electron transport chain. Furthermore, the magnitude of H2 produced by T. erythraeum IMS101 strongly implicates this organism in the production of H2 in the upper ocean.

The biological fixation of atmospheric nitrogen (N) is a major pathway for available N entering ecosystems. In N-limited boreal forests, a significant amount of N2 is fixed by cyanobacteria living in association with mosses, contributing up to 50% to the total N input. In this review, we synthesize reports on the drivers of N2 fixation in feather moss-cyanobacteria associations to gain a deeper understanding of their role for ecosystem-N-cycling. Nitrogen fixation in moss-cyanobacteria associations is inhibited by N inputs and therefore, significant fixation occurs only in low N-deposition areas. While it has been shown that artificial N additions in the laboratory as well as in the field inhibit N2 fixation in moss-cyanobacteria associations, the type, as well as the amounts of N that enters the system, affect N2 fixation differently. Another major driver of N2 fixation is the moisture status of the cyanobacteria-hosting moss, wherein moist conditions promote N2 fixation. Mosses experience large fluctuations in their hydrological status, undergoing significant natural drying and rewetting cycles over the course of only a few hours, especially in summer, which likely compromises the N input to the system via N2 fixation. Perhaps the most central question, however, that remains unanswered is the fate of the fixed N2 in mosses. The cyanobacteria are likely to leak N, but whether this N is transferred to the soil and if so, at which rates and timescales, is unknown. Despite our increasing understanding of the drivers of N2 fixation, the role moss-cyanobacteria associations play in ecosystem-N-cycling remains unresolved. Further, the relationship mosses and cyanobacteria share is unknown to date and warrants further investigation.