Root Nodule Bacteria Research Articles

Role of biostimulants (ascorbic acid and fulvic acid) to synergize Rhizobium activity in pea (Pisum sativum L. var. Meteor)

Biostimulants such as ascorbic acid (AA) and fulvic acid (FA)can enhance the efficiency of root-nodulating bacteria. This study investigates optimum concentration of these two biostimulants to maximize the Rhizobium activity and increase root size, nodulation capability, NPK uptake, yield and quality. Interaction with nitrogenase enzyme through molecular docking was also studied by using both AA and FA as ligands to better understand their inhibitory role in excess amounts. The findings of the study suggest: the combined application of both FA and AA at 200 ppm concentrations proved to be more effective than the individual application. Excellent vegetative growth was noticed which translated into an increased reproductive growth i.e statistically significant increase in number of pods per plant, fresh and dry weight of pods per plant, number of seeds per pod, total chlorophyll, carotenoids and chemical constituents of pea seeds i.e. N (16.17%), P (40.47%), K (39.96%) and protein (16.25%). These findings were substantiated by molecular docking of nitrogenase enzyme with ascorbic acid and fulvic acid. The XP docking score of ascorbic acid (−7.07 kcal mol-1) and fulvic acid (−6.908 kcal mol-1) exhibited that the optimum doses (200 ppm) should be used as higher dose or their excess amount can hinder the Rhizobium activity of nitrogen fixation by interacting with the nitrogenase enzyme.

Bacillus velezensis S141, a soybean growth-promoting bacterium, hydrolyzes isoflavone glycosides into aglycones.

Bacillus velezensis S141, a plant growth-promoting rhizobacteria (PGPR), was isolated from a soybean field in Thailand. Previous studies demonstrated that S141 enhanced soybean growth, stimulating nodulation for symbiotic nitrogen fixation with soybean root nodule bacteria, including Bradyrhizobium diazoefficience USDA110. Isoflavone glycosides are produced in soybean roots and hydrolyzed into their aglycones, triggering nodulation. This study revealed that S141 efficiently hydrolyzed two isoflavone glycosides in soybean roots (daidzin and genistin) to their aglycones (daidzein and genistein, respectively). However, S141, Bacillus subtilis 168, NCIB3610, and B. velezensis FZB42 hydrolyzed isoflavone glucosides into aglycones. A BLASTp search suggested that S141 and the other three strains shared four genes encoding β-glucosidases corresponding to bglA, bglC, bglH, and gmuD in B. subtilis 168. The gene inactivation analysis of B. subtilis 168 revealed that bglC encoded the major β-glucosidase, contributing about half of the total activity to hydrolyze isoflavone glycosides and that bglA, bglH, and gmuD, all barely committed to the hydrolysis of isoflavone glycosides. Thus, an unknown β-glucosidase exists, and our genetic knowledge of β-glucosidases was insufficient to evaluate the ability to hydrolyze isoflavone glycosides. Nevertheless, S141 could predominate in the soybean rhizosphere, releasing isoflavone aglycones to enhance soybean nodulation.

Morphological, Physiological and Biohchemical Identification of Nitrogen Fixing Mesorhizobium in Chickpea

Chickpea is the world’s second most important legume, and it can be nodulated with a variety of rhizobial species to generate root nodules. The current study investigated the isolation, cultural, and biochemical characterization of several strains of root nodulating bacteria from different locations of Yavatmal districts. The serial dilution approach was used for isolation. Bacterium Mesorhizobium is a gram- negative, aerobic, non-spore producing, motile rods with circular, convex, whitish pink, and glistering colonies with an entire edge. The biochemical characterization of five different strains of bacteria revealed that the catalase, methyl red, urease, and triple sugar iron and citrate utilization test yielded positive results. Based on morphological, biochemical, and physiological characters most of the characteristics were found like the Mesorhizobium spp. The physical and biochemical properties of five different isolates of bacteria were analyzed to determine their taxonomic position, and the authentication test revealed that the strain of rhizobium bacteria is Mesorhizobium spp.

Alder-induced stimulation of soil gross nitrogen turnover in a permafrost-affected peatland of Northeast China

For the prediction of permafrost nitrogen (N) climate feedbacks, a better process-based understanding of the N cycle in permafrost ecosystems is urgently needed. Therefore, we characterized and quantified soil organic matter, gross soil microbial ammonification and nitrification and soil-atmosphere exchange of nitrous oxide (N2O) of boreal permafrost ecosystems on the southern edge of the Eurasian permafrost area in situ.Soil organic carbon (SOC) and total nitrogen (TN) stocks (top 0.5 m) of tree-free lowland peatland (LP) soils exceeded those of gravel-rich upland forest (UF) soils by an order of magnitude. Nuclear magnetic resonance spectroscopy revealed more recalcitrant organic matter at greater depth and more bioavailable organic matter substrates in upper peat horizons. In line with this result, gross ammonification and nitrification generally decreased with increasing sampling depth. Gross rates of mineral N turnover in active layers were comparable to those of temperate ecosystems. Despite substantial gross ammonification, the low nitrification:ammonification ratios and negligible soil N2O emissions depicted however a closed N cycle at UF and LP characterized by N limitation.In strong contrast, the lowland peat soils underneath alder trees (LA), being associated with diazotrophic bacteria in root nodules, showed an accelerated N turnover with very high gross rates of ammonification (3.1 g N m−2 d−1) and nitrification (0.5 g N m−2 d−1), exceeding those of UF and LP soils by an order of magnitude. This was accompanied by substantial N2O emissions comparable to temperate agricultural systems or tropical forests. The increase in gross soil microbial ammonification and nitrification was most pronounced in the rooted soil layer, where N inputs from biological N fixation almost doubled TN concentrations and halved SOC:TN ratios. The frozen ground of LA contained strongly increased ammonium concentrations that might be prone to release upon thaw via subsequent nitrification. This study shows that alder forests that further expand on permafrost-affected peatlands with global change create hot spots of soil mineral N turnover, thereby potentially enhancing permafrost N climate feedbacks via N2O emissions.

​Effect of Organic and Inorganic Sources of Nutrients on Growth, Yield Attributes and Nutrient Uptake of Soybean in Vertisols of Rajasthan

Background: Soybean [Glycie max (L.) Merril] is a very important oil seed and protein rich crop. It has the specific character to fix atmospheric nitrogen through root nodule bacteria in symbiotic relationship. A field experiment was conducted during kharif, 2019 at ARS farm, College of Agriculture, Ummedganj, Kota (Rajasthan). To find out the effect of organic and inorganic sources of nutrients on growth, yield attributes and nutrient uptake of soybean in Vertisols of Rajasthan. The soil of the experimental field comes under Vertisols with clay loam texture having low to medium fertility status and good porosity. Methods: The experiment consisted of 10 treatments viz. T0- Control (Absolute), T1- RDF (20-40-40), T2- 75% RDF + FYM (2.0 t ha-1), T3- 50% RDF + FYM (4.0 t ha-1), T4- 75% RDF + FYM (2.0 t ha-1) + Rhizobium, T5- 50% RDF + FYM (4.0 t ha-1) + Rhizobium, T6- 75% RDF + Vermicompost (1.0 t ha-1), T7- 50% RDF + Vermicompost (2.0 t ha-1), T8- 75% RDF + Vermicompost (1.0 t ha-1) + Rhizobium, T9- 50% RDF + Vermicompost (2.0 t ha-1) + Rhizobium. The experiment was laid out in randomised block design and was replicated thrice. Result: Among the nutrient management treatment, application of 75% RDF + Vermicompost (1.0 t ha-1) + Rhizobium (T8) resulted into maximum plant height (58.70 cm), branches plant-1 (5.60), chlorophyll content (2.84 mg g-1), total nodules per plant (47.40), effective nodules (31.59) and dry weight (84.20 mg), pods plant-1 (41.90), seeds pod-1 (3.47), grain yield (1380 kg ha-1), haulm yield (1885 kg ha-1), biological yield (3325 kg ha-1), protein (42.25%) and oil content (19.92%), N, P, K content and their uptake, with maximum gross return (53042.71 Rs ha-1), net return (28980.71 Rs ha-1) and B:C ratio (2.20) in soybean crop.

Symbiotic Effectiveness of Acid Tolerant Nodulating Rhizobia on Growth, Yield and Nutrient Uptake of Pigeon pea (Cajanus cajan L.) in Acidic Alfisols

The symbiotic association between root nodulating bacteria viz. Rhizobium and pulses enhance the crop agronomic characteristics, productivity and quality depending upon the symbiotic effectiveness of the bacterial strain. To evaluate this effectiveness, a study was conducted during December, 2019−April, 2020 (rabi) at Central Farm of Odisha University of Agriculture and Technology, Bhubaneswar- 751003, Odisha aimed at evaluating the efficiency of seven isolated rhizobial strains of pigeon pea viz. BRP-2, BRP-4, BRP-8, BRP-20, BRP-28, BRP-56 and a local strain CHRS-7 in a randomized block design with four replications. The pigeon pea cv PRG-176 was used for study. The results revealed that seed inoculation with different Rhizobium strains enhanced the plant height (41.84–90.09 cm), relative growth rate (0.410−0.898 mm day-1), nodular characteristics, nodular nitrogen (3.11 to 4.11%), pod and seed characteristics in pigeon pea. In addition to that the potentiality of pigeon pea producing only 408 kg seed ha-1 without any seed inoculation could be enhanced to produce 888 kg seed ha-1 by seed inoculation in a coastal agroecosystem. The findings also revealed a better uptake of nutrients by the crop in Rhizobium inoculated practices that performed in the order Control <BRP-20<BRP-8<BRP-4<BRP-56<BRP-28<BRP-2<CHRS-7. The performance of local isolated rhizobial strain (CHRS-7) was better over other strains and it gives cardinal importance for the enhancement of pigeon pea growth, productivity and economics in a coastal acidic Alfisols.

Phylogenetic diversity and plant growth-promoting activities of rhizobia nodulating fenugreek (Trigonella foenum-graecum Linn.) cultivated in different agroclimatic regions of India.

Fenugreek (Trigonella foenum-graecum Linn.), is an extensively cultivated legume crop used as a herb, spice, and traditional medicine in India. The symbiotic efficiency and plant growth-promoting potential of fenugreek rhizobia depend on the symbiont strain and environmental factors. We isolated 176 root-nodulating bacteria from fenugreek cultivated in different agroclimatic regions of India. MALDI-TOF MS-based identification and phylogenetic analyses based on 16S rRNA and five housekeeping genes classified the fenugreek-rhizobia as Ensifer (Sinorhizobium) meliloti. However, the strains represent separate sub-lineages of E. meliloti, distinct from all reported sub-lineages across the globe. We also observed the spatial distribution of fenugreek rhizobia, as the three sub-lineages of E. meliloti recorded during this study were specific to their respective agroclimatic regions. According to the symbiotic gene (nodC and nifH) phylogenies, all three sub-lineages of E. meliloti harboured symbiotic genes similar to symbiovar meliloti; as with the housekeeping genes, these also revealed a spatial distribution for different clades of sv. meliloti. The strains could nodulate fenugreek plants and they showed plant growth-promoting potential. Significant differences were found in the plant growth parameters in response to inoculation with the various strains, suggesting strain-level differences. This study demonstrates that fenugreek rhizobia in India are diverse and spatially distributed in different agro-climatic regions.

Fungus Applications on Growth and Yield of Dena-1 Soybean Varieties

This study aims to determine the response of black soybean variety Dena-1 that has been inoculated with Rhyzobium indigenous bacteria to the activity of Trichoderma and Glomus spp fungi given as soil treatment. The experiment was arranged in a completely randomized design with effective fungal application treatment consisting of without application, T. esperellum, Glomus spp., and both types of fungi. All treatments were repeated five times. Observations were made on plant stem height and diameter, dry weight of the stover, number of pods, number of grains, grain weight, and weight of 100 grains. Data were analyzed by ANOVA and HSD test with a significance level of 5%. Trichoderma and Glomus application had no effect in increasing plant growth and production. The simultaneous application of these two fungi resulted in a decrease in dry weight of stover, number of pods, number of grains, grain weight, and weight of 100 soybeans respectively 15.41, 22.50, 30.87, 69.95, and 49.03%. This indicates that there is competition in the use of resources between the root nodule bacteria and the two biological agent fungi.

Genetic diagnosis of some root nodule bacteria isolated from leguminous Plants in Nineveh Governorate

The importance of atmospheric nitrogen-fixing bacteria The study aimed to isolate bacteria from the roots of plants From four areas of the city of Mosul the winter agriculture, season 2020-2021 and using biochemical tests and phenotypic and agricultural characteristics to diagnose bacterial isolates and study sensitivity and resistance of bacterial isolates to ten antibiotics. if the results showed that the highest percentage of resistance was to the two antibiotics, Trimethoprim, and streptomycin, at 100%, while The least resistance was to the two antivirals Gentamycin and Rifampicin by 20%. In addition to Studying The sensitivity and resistance of bacterial isolates to four heavy Metals, namely Mercury chloride (HgCl), Cobalt chloride (CoCl), Cadmium Chloride (CdCl), and nickel chloride (NiCl). The resistance was high with Cadmium chloride salt (CdCl) and the lowest salt Mercury Chloride (HgCl). PCR techniques were used to diagnose samples based on 16S rRNA sequence analysis and comparison of sequences resulting from DNA amplification with standard isolates within NCBI to detect new bacterial isolates

Functional Specificity of the nifA Gene Product within the Group of Root Nodule Bacteria

Functional Specificity of the nifA Gene Product within the Group of Root Nodule Bacteria

Nitrogen Fixation and Diazotrophs – A Review

Nitrogen fixation involves formation of ammonium from N2, which needs a high input of energy. Biological nitrogen fixation utilizes the enzyme nitrogenase and ATP to fix nitrogen. Nitrogenase contains a Fe-protein and a Mo-Fe-protein and other metal cofactors. Soil diazotrophs possess the function of fixing atmospheric N2 into biologically available ammonium in ecosystems. In Aechaea, nitrogen fixation has been reported in some methanogens such as Methanobacteriales, Methanococcales, and Methanosarcinales. Community structure and diversity of diazotrophic are correlated with soil pH. All known organisms which involve in nitrogen-fixing which are called diazatrophs are prokaryotes, and both bacterial and archaeal domains are responsible for that. Diazotrophs are categorized into two main groups namely: root-nodule bacteria and plant growth-promoting rhizobacteria. Diazotrophs include free living bacteria, such as Azospirillum, Cupriavidus, and some sulfate reducing bacteria, and symbiotic diazotrophs such Rhizobium and Frankia. Two important parameters which may affect diazotroph communities are temperature and soil moisture in different seasons. To have sustainable agriculture, replacing expensive chemical nitrogen fertilizers with environmentally friendly ways is the most accepted practice.

Soybean Productivity Depending On The Elements Of Organic Cultivation Technology In The Short-Term Crop Rotation Of Ukrainian Polissia

Over the past decades, intensive farming has operated under conditions of progressive degradation of the soil cover, maintaining production levels only at the expense of inadequate expenditure of non-renewable energy resources. The soils have acquired irreversible excessive compaction in the sub-arable part of the profile, and the dehumification has acquired a threatening status. The humus content in the soils of Ukraine decreased by almost 25%, and the average annual losses amount to 0.6-0.7 t/ha. Therefore, the search for ways to guarantee the reproduction of soil organic matter, reliable control and restoration of the optimal humus status is extremely relevant. The purpose of the study is to activate natural nitrogen-fixing systems using a mix of green manure and by-products of agricultural crops of short-term leguminous crop rotation. Field experiments were conducted on light grey soils during 2018-2020 in the experimental field of Polissia National University in a leguminous short-term rotation system. This study uses general scientific methods to establish the area of research, plan and lay experiments, conduct observations and analysis; visual – during the implementation of phenological observations; field – to study the relationship with abiotic factors; physiological – to determine the symbiotic effectiveness of preparations of biological origin. The technology of growing agricultural crops in leguminous crop rotation, which ensures the supply of raw materials of organic origin and the accumulation of air nitrogen by root nodule bacteria, has been theoretically substantiated and improved. It is established that one hectare of crop rotation area receives 6.8 tonnes of dry organic raw materials, which corresponds to 78.3 kg/ha of biological nitrogen. It is found out that inoculation of soybean seeds with a preparation of biological origin – Optimise 400, and treatment of soybean crops at BBCH microstages 60-63 with a complex microfertiliser on a chelated basis Nanovit Super+Magnesium Sulphate contributes to the active development of nodule bacteria, the number and weight of which is 81-89 pcs per plant and 510-572 kg/ha. Thus, the active symbiotic potential was 34.2-38.9 thousand kg/day. It is proved that during the growing season soybeans generate 357-400 kg/ha of biological nitrogen in the air, which provides a seed yield of 2.96-2.64 t/ha and leaves 117-160 kg/ha of nitrogen in the soil. The practical value of this study lies in the possibility of enriching the soil with organic matter and the biological form of nitrogen

Diverse symbiovars nodulating cowpea (Vigna unguiculata L. Walp.) in highly adaptable agro-ecological zones in Mozambique

The presence of effective microsymbionts in the soil and their compatibility with the host plant are the key determinants to the N2 fixation process. In Sub-Saharan Africa, nitrogen fixation in locally adapted cowpea and the distribution of their symbiovars are not well understood. The Aim of the study was to assess the distribution and symbiotic phylogenetic position of cowpea microsymbionts. Root nodules were sampled from various cowpea genotypes planted in Agro-Ecological Zone 7 and 8 (AEZ 7 and AEZ 8). Root-nodule bacteria were isolated and their molecular characterization was conducted. Physicochemical properties of soil were recorded. Enterobacterial Repetitive Intergenic Consensus (ERIC) distribution patterns in rhizobial genomes resulted in genetically diverse rhizobial population in Northern Mozambique. Principal component analysis showed that location-specific soil environment determined the presence of particular microsymbionts. Based on 16S rRNA and symbiotic gene analysis many diverse symbiovars were found in Mozambican soils. With few discrepancies, the results further confirmed the coevolution of the nifH, nodD, nodC and nodY/K genes, which was indicative of natural events such as vertical/horizontal gene transfer. The results suggested that ecological and phylogenetic studies of the microsymbionts are necessary to better reflect symbiovar identification and the ecological adaptation of the cowpea-nodulating rhizobial community.

Archaea, bacteria and termite, nitrogen fixation and sustainable plants production

Certain bacteria and archaea are responsible for biological nitrogen fixation. Metabolic pathways usually are common between archaea and bacteria. Diazotrophs are categorized into two main groups namely: root-nodule bacteria and plant growth-promoting rhizobacteria. Diazotrophs include free living bacteria, such as Azospirillum, Cupriavidus, and some sulfate reducing bacteria, and symbiotic diazotrophs such Rhizobium and Frankia. Three types of nitrogenase are iron and molybdenum (Fe/Mo), iron and vanadium (Fe/V) or iron only (Fe). The Mo-nitrogenase have a higher specific activity which is expressed better when Molybdenum is available. The best hosts for Rhizobium legumiosarum are Pisum, Vicia, Lathyrus and Lens; Trifolium for Rhizobium trifolii; Phaseolus vulgaris, Prunus angustifolia for Rhizobium phaseoli; Medicago, Melilotus and Trigonella for Rhizobium meliloti; Lupinus and Ornithopus for Lupini, and Glycine max for Rhizobium japonicum. Termites have significant key role in soil ecology, transporting and mixing soil. Termite gut microbes supply the enzymes required to degrade plant polymers, synthesize amino acids, recycle nitrogenous waste and fix atmospheric nitrogen. The positive effects of Arbuscular mycorrhizal (AM) fungi such as growth promotion, increased root length, leaf area, stem diameter, transplant performance and tolerance to stresses have been reported previously.

Effect of volcanic rock dust and Fe-EDTA on the root nodule bacteria and the growth and yield of broad bean plants

The experiment was conducted during the 2018 season at the research station of the College of Agriculture and Forestry (University of Mosul, Iraq) to investigate the effect of volcanic rock dust (VRD) (0, 125, 250 g m-2) and the fertilizer chelated Iron Fe-EDTA (0, 100, 200 mg L-1) on the bacteria Rhizobium fabae, and the growth and yield of two broad bean (Vicia faba L.) varieties, Histal and Aquadulce. A randomized complete block design was used with three replicates and least significant difference (LSD) to compare means at a significance level of 0.05. Results showed that VRD 250 g m-2 obtained the highest significant mean for the following traits: leaf area index (LAI), number of branches per plant, leaf contents of chlorophyll and total iron, number of effective bacteria nodules per plant, 100-seed weight, plant yield, and percentage of protein in the seeds. On the other hand, 200 mg L-1 Fe-EDTA obtained the highest significant mean of all the traits for both varieties, except for LAI and number of branches per plant. The application of Fe-EDTA per plant had no significant effect on the leaf content of chlorophyll for both varieties and the percentage of protein in the seeds for variety Aquadulce. The interaction of VRD 250 g m-2 with 200 mg L-1 Fe-EDTA achieved the highest significant average for all the traits, except for plant height.

The impact of intra-specific diversity in the rhizobia-legume symbiosis.

Rhizobia - nitrogen-fixing, root-nodulating bacteria - play a critical role in both plant ecosystems and sustainable agriculture. Rhizobia form intracellular infections within legumes roots where they produce plant accessible nitrogen from atmospheric nitrogen and thus reduce the reliance on industrial inputs. The rhizobia-legume symbiosis is often treated as a pairwise relationship between single genotypes, both in research and in the production of rhizobial inoculants. However in nature individual plants are infected by a high diversity of rhizobia symbionts. How this diversity affects productivity within the symbiosis is unclear. Here, we use a powerful statistical approach to assess the impact of diversity within the Rhizobium leguminosarum - clover symbiosis using a biodiversity-ecosystem function framework. Statistically, we found no significant impact of rhizobium diversity. However this relationship was weakly positive - rather than negative - indicating that there is no significant cost to increasing inoculant diversity. Productivity was influenced by the identity of the strains within an inoculant; strains with the highest individual performance showed a significant positive contribution within mixed inoculants. Overall, inoculant effectiveness was best predicted by the individual performance of the best inoculant member, and only weakly predicted by the worst performing member. Collectively, our data suggest that the Rhizobium leguminosarum - clover symbiosis displays a weak diversity-function relationship, but that inoculant performance can be improved through the inclusion of high performing strains. Given the wide environmental dependence of rhizobial inoculant quality, multi-strain inoculants could be highly successful as they increase the likelihood of including a strain well adapted to local conditions across different environments.

Effect of rosR Gene Overexpression on Biofilm Formation by Rhizobium leguminosarum

The regulatory protein encoded by the rosR gene is involved in the processes of adaptation of root nodule bacteria Rhizobium leguminosarum to changes in environmental conditions. It affects the expression of a number of genes associated with the synthesis of exopolysaccharides, which play a critical role in formation of bacterial biofilms on various surfaces. The goal of this work was to study the effect of overexpression of the rosR gene on formation of R. leguminosarum biofilms on inert surfaces and roots of heterologous plant hosts by obtaining recombinant strains with an additional copy of the rosR gene under the control of the Pm promoter. Our analysis of recombinant strains showed that additional expressed copies of the rosR gene allowed rhizobia to overcome the inhibitory effect on biofilm formation caused by low calcium concentrations in the medium, the effect of proteases and detergents, and to form biofilms more efficiently on the surface of tomato and clover roots. The results obtained open up prospects for using rosR as a tool both for increasing the efficiency of endosymbiosis of rhizobia with legumes, and for the formation of stable associative interactions with other agricultural crops.

Diversity of Root Nodule-Associated Bacteria of Diverse Legumes Along an Elevation Gradient in the Kunlun Mountains, China.

Bacteria in root nodules of legumes play important roles in promoting plant growth. In this study, we investigated root nodule-associated bacteria isolated from leguminous plants along an elevation gradient on the northern slope of the Kunlun Mountains, China, using a cultivation approach. In total, 300 isolates were obtained from seven legume species within six ecological zones. Isolates were identified based on 16S rRNA gene phylogenetic analysis and potential rhizobia were further identified using a recA gene phylogeny. Among the isolates, Bacillales (particularly Bacillus) were the dominant isolates from all host legumes and all elevations (63.5%), followed by Rhizobiales (13%) and Pseudomonadales (11.7%). Less than 3% of the isolates belonged to Burkholderiales, Paenibacillales, Enterobacteriales, Actinomycetales, Sphingomonadales, Xanthomonadales, Chitinophagales, Brevibacillales, Staphylococcales, or Mycobacteriales. A few elevation-specific patterns emerged within the Bacillales and Pseudomonadales. For example, isolates related to the psychrotroph Bacillus psychrosaccharolyticus were only isolated from the highest elevation sites (>3,500 m) whereas those related to the mesophile Bacillus endophyticus were only isolated from lowest elevation sites (1,350 m), suggestive of a role of soil temperature in their distribution. Similarly, isolates related to Pseudomonas brassicacearum were the dominant Pseudomonadales isolates, but they were only isolated from middle and low elevations (<3,200 m). A total of 39 isolates belonged to the Rhizobiales, 36 of which were confirmed to the genus level using the recA gene. In all, Rhizobiales isolates were obtained from five different host legumes spanning the entire elevation gradient. Those from the low-elevation Qira Desert-Oasis Transition Zone (1,350–1,960 m) suggested some patterns of host preference. For example, most isolates from Albizia julibrissin formed a monophyletic group related to Rhizobium lemnae and most from Alhagi sparsifolia were closely related to Ensifer kummerowiae. In general, this study shows that most bacteria associated with root nodules of legumes are widely distributed in distinct ecological zones within a single geographic region but suggests that both climate and host interactions may influence their distributions.

The Dynamic of Nitrogen Uptake from Different Sources by Pea (Pisum sativum L.)

Nitrogen uptake from various sources by plants capable of biological reduction of N2 in symbiotic systems with root nodule bacteria is influenced by many factors. The aim of the study was to examine the influence of the development stage and variety of pea (Pisum sativum L.) cultivated in years with different temperature and precipitation conditions on the dynamics of nitrogen uptake from the atmosphere (Ndfa), fertilizer (Ndff), and soil (Ndfs). Pre-sowing nitrogen fertilization with the 15N isotope and the isotope dilution method were used in the research. The highest rate of Ndfa uptake was noted between the three-internode stage and the stage of the first visible flower buds outside the leaves, while Ndff and Ndfs uptake was highest between the 4-leaf stage and the 3-internode stage. The lowest rate of Ndfa uptake was noted from sowing to the four-leaf stage, while Ndff and Ndfs uptake was lowest between the stage when 50% of pods were of typical length and full maturity. Nitrogen uptake from all sources was similar for all pea cultivars, but significantly depended on the variable temperature and precipitation conditions (years of the study).

Mechanism and application of Sesbania root-nodulating bacteria: an alternative for chemical fertilizers and sustainable development.

Chemical fertilizers are used in large-scale throughout the globe to satisfy the food and feed requirement of the world. Demanding cropping with the enhanced application of chemical fertilizers, linked with a decline in the recycling of natural or other waste materials, has led to a decrease in the organic carbon levels in soils, impaired soil physical properties and shrinking soil microbial biodiversity. Sustenance and improvement of soil fertility are fundamental for comprehensive food security and ecological sustainability. To feed the large-scale growing population, the role of biofertilizers and their study tends to be an essential aspect globally. In this review, we have emphasized the nitrogen-fixing plants of Sesbania species. It is a plant that is able to accumulate nitrogen-rich biomass and used as a green manure, which help in soil amelioration. Problems of soil infertility due to salinity, alkalinity and waterlogging could be alleviated through the use of biologically fixed nitrogen by Sesbania plants leading to the conversion of futile land into a fertile one. A group of plant growth-promoting rhizobacteria termed as "rhizobia" are able to nodulate a variety of legumes including Sesbania. The host-specific rhizobial strains can be used as potential alternative for nitrogenous fertilizers as they help the host plant in growth and development and enhance their endurance under stressed conditions. The review gives the depth understanding of how the agriculturally important microorganisms can be used for the reduction of broad-scale application of chemical fertilizers with special attention to Sesbania-nodulating rhizobia.