N2-fixing Bacteria Research Articles

Organic matter and mixed biofertilizer for plant growth and yield of shallot grown in fertile soil

Nowadays, shallot is important horticultural crops in Maluku include in Tual City, Maluku Province. For ensuring the macronutrients level in soil and yield during shallot cultivation, fertilization composed of chemical, organic and bio fertilizer is needed. The objective of field experiment was to evaluate the effect of mixed biofertilizer integrated with organic matter on total nitrogen and available phosphorous in soil as well as shallot yield grown in Vertisols of Tual. The experiment was setup in randomized block design with four treatments of compost and chicken manure amendment with and without biofertilizer containing N-fixing bacteria and P-solubilizing. At the vegetative stage, consortia biofertilizer combined with either compost or chicken manure increased plant height and soil reaction but decreased the available phosphate (P) and didn't change nitrogen (N) total in soil. Chicken manure amendment combined with biofertilizer inoculation increased dry weight of shoots and bulbs even though didn't significantly differ with other treatments. Nonetheles, that treatment resulted in high yield of shallot bulbs up to 14 t/ha.

Inoculation of nitrogen fixing bacteria in conjugation with integrated nitrogen sources induced changes in phenology, growth, nitrogen assimilation and productivity of wheat crop

Numerous strains of plant growth-promoting bacteria are used as biofertilizers to minimize the utilization of synthetic fertilizers, improve nutrients use efficiency, crop productivity and to reduce environmental pollution. This study was planned with the aims to assess the effects of seeds inoculation with different strains of nitrogen (N)-fixing bacteria in conjugation with N fertilization from various combinations of farmyard manure (FYM) and urea on days to anthesis, days to physiological maturity, leaf area duration (LAD), crop growth rate (CGR), net assimilation rate (NAR), physiological N use efficiency (PNUE), apparent N re-translocation (ANR), relative N accumulation rate (RN), N harvest index (NHI) and grain yield of wheat crop under the environmental conditions of Northern Pakistan. The experiment was carried out in RCB design with a factorial arrangement of treatments. Wheat seeds were inoculated with N-fixing bacterial strains viz. Azotobacter sp., Azospirillum ER-20, Rhizobium SK-8 and Pseudomonas K-1, and N were applied from three different combinations of FYM and urea i.e. 100% urea, 75% FYM and 25% urea, and 50% FYM and 50% urea. The results showed that days to anthesis (122), days to physiological maturity (162), CGR (10.31 g. m −1 . day −1 ), grain yield (4016 kg ha −1 ), PNUE (43.1 kg grain kg −1 N uptake), ANR (9.1 g kg −1 DM), NHI (79.4) and RN (0.1046 day −1 ) were increased (P < 0.05) by Azospirillum Er-20 and Pseudomonas K-1 inoculation, while maximum (P < 0.05) LAD (76 m. day −1 ) and NAR (0.19 g. m −1 . day −1 ) were attained on Rhizobium SK-8 inoculation with N from 50% FYM and 50% urea, as compared to control. The grain yield revealed a significant (P < 0.001) correlation with CGR (0.76), NHI (0.72) and PNUE (0.68). The regression analysis exhibited a good estimate for grain yield (R 2 = 0.83) and CGR (R 2 = 0.57) in response to soil mineral N content. In conclusion, bacterial inoculation in conjugation with an equal ratio of N from the integrated sources improved the phenological and growth traits as well as N assimilation and grain yield of wheat crop. Therefore, it is suggested to plan long-term experiments to explore the potential of N-fixing bacteria in conjugation with integrated N-sources under different agronomic conditions for attaining sustainability in the wheat cropping systems.

Soil fertility interactions with Sinorhizobium-legume symbiosis in a simulated Martian regolith; effects on nitrogen content and plant health.

Due to increasing population growth and declining arable land on Earth, astroagriculture will be vital to terraform Martian regolith for settlement. Nodulating plants and their N-fixing symbionts may play a role in increasing Martian soil fertility. On Earth, clover (Melilotus officinalis) forms a symbiotic relationship with the N-fixing bacteria Sinorhizobium meliloti; clover has been previously grown in simulated regolith yet without bacterial inoculation. In this study, we inoculated clover with S. meliloti grown in potting soil and regolith to test the hypothesis that plants grown in regolith can form the same symbiotic associations as in soils and to determine if greater plant biomass occurs in the presence of S. meliloti regardless of growth media. We also examined soil NH4 concentrations to evaluate soil augmentation properties of nodulating plants and symbionts. Greater biomass occurred in inoculated compared to uninoculated groups; the inoculated average biomass in potting mix and regolith (2.23 and 0.29 g, respectively) was greater than the uninoculated group (0.11 and 0.01 g, respectively). However, no significant differences existed in NH4 composition between potting mix and regolith simulant. Linear regression analysis results showed that: i) symbiotic plant-bacteria relationships differed between regolith and potting mix, with plant biomass positively correlated to regolith-bacteria interactions; and, ii) NH4 production was limited to plant uptake yet the relationships in regolith and potting mix were similar. It is promising that plant-legume symbiosis is a possibility for Martian soil colonization.

Co-cultivation enhanced microbial protein production based on autotrophic nitrogen-fixing hydrogen-oxidizing bacteria

Autotrophic N2-fixing H2-oxidizing communities produced sustainable microbial protein as an alternative to food and feed based on the Haber-Bosch process. Their dynamics and complexity make it challenging to control the composition and evaluate the product safety. Based on the isolates from a previously enriched community and their metabolism, this research studied the potential of binary cocultures for the production of safe protein. Compared to the monocultures of the isolates from Xanthobacter variabilis, i.e. the only N2-fixing H2-oxidizing species in the study, 31% of the 72 cocultures containing X. variabilis and the other isolates were promoted regarding growth due to co-cultivation, while 6% and 63% of the cocultures were inhibited and slightly affected, respectively. For the coculture where the cell count of X. variabilis was improved by 11.4 ± 3.5 times, its growth surpassed that of all monocultures and was high among the cocultures. Besides, the protein content, essential amino acid contents, and biomass yield of this coculture were 24 ± 2%, 28 ± 11% to 1.3 ± 0.3 times, and 26 ± 3% higher, respectively, than those of its X. variabilis monoculture. Compared to the mixed communities, the coculture had a similar biomass yield but superior protein quality. With the low predicted risk from bacterial toxins, the coculture had the potential for safe use and is currently the most suitable protein producer based on N2-fixing H2-oxidizing bacteria. In addition, the coculture independent of centrally synthesized Haber-Bosch nitrogen and its transportation had higher CO2 fixation potential than H2-oxidizing bacteria grown on Haber-Bosch nitrogen producing CO2, converted solar energy more efficiently than agriculture, and can benefit in situ storage of solar and wind power.

Dairy Effluent-Saturated Biochar Alters Microbial Communities and Enhances Bermudagrass Growth and Soil Fertility

Recently, biochar has been proposed for various agronomic applications including improved plant growth and soil fertility. In this study, the effects of dairy effluent-saturated (SBC) and unsaturated wood-derived biochar (UBC) on Bermudagrass (Cynodon spp.) growth, soil fertility and microbial communities were investigated in a greenhouse pot study. SBC and UBC were mixed with sandy loam soil at various loading rates (0, 1, 2, 4, and 8%) to grow Bermudagrass for 10 weeks. Soil physicochemical properties and plant growth measurements were taken, followed by 16S rRNA (V3-V4) amplicon sequencing of soil bacterial communities. Amendment of SBC to soil altered the soil physicochemical properties and increased the concentrations of N and P in the soil at 2 to 8% loading rates compared to UBC treated soil. The addition of SBC to soil also increased the overall plant biomass compared to UBC with more effects on aboveground biomass. Differential abundance analysis of taxa showed enrichment of Proteobacteria in UBC-amended soil, whereas Firmicutes and Nitrospirae were abundant in SBC-amended soil. Interestingly, enrichment of photosynthetic and N-fixing bacteria was observed in both SBC and UBC-amended soils after 10 weeks of treatments. However, oxidative phosphorylation and biotin metabolisms were found to be more abundant in SBC-amended soil compared to UBC-amended soil. Overall, our study suggested that amendment of SBC to soil resulted in enhanced soil nutrients, microbial capacity and Bermudagrass growth than that of UBC. Therefore, application of SBC to soil in field trials would be merited to identify sustainable and effective practices for enhancing plant growth, soil fertility and soil bacterial community.

Alien invasive plant Amaranthus spinosus mainly altered the community structure instead of the α diversity of soil N-fixing bacteria under drought

Soil N-fixing bacteria (SNFB) may be vital to the invasion process of invasive alien plants (IAPs). Further, SNFB may be altered under drought which can affect the invasion process of IAPs. This study aims to estimate the differences in the α diversity and β diversity of SNFB between the infamous IAP Amaranthus spinosus L. (a spinous annual or perennial herb weed; originates from tropical America) and the native species A. tricolor L. (an annual herb crop) under various degrees of drought (i.e., control, and low, medium, and high degrees of drought, respectively). Drought significantly declines soil pH, water content, and electrical conductivity. Drought significantly rises soil microbial biomass carbon but poses unobvious impacts on the α diversity of SNFB. A. spinosus recruits indistinctive impacts on soil pH, water content, and electrical conductivity as well as the α diversity of SNFB. Drought and A. spinosus significantly affect the β diversity of SNFB. Further, some SNFB taxa have been significantly altered under drought and A. spinosus (i.e., f_Bradyrhizobiaceae under high degree of drought; p_uncultured_bacterium in the rhizosphere soil of monocultural A. spinosus) according to the results of the LEfSe analysis. Thus, drought and A. spinosus are largely changed the community structure of SNFB instead of the α diversity of SNFB.

Organic soil amendments using vermicomposts under inoculation of N2-fixing bacteria for sustainable rice production.

Organic and biological fertilizers are considered as a very important source of plant nutrients. A field experiment was conducted during 2017−2018 in paddy soil to investigate the effect of vermicomposting of cattle manure mixture with Azolla and rice straw on soil microbial activity, nutrient uptake, and grain yield under inoculation of N2-fixing bacteria. Experimental factors consisted of organic amendments at six levels (vermicomposts prepared from manure (VM); manure + rice straw (VRM); manure + Azolla mixture (VAM); manure + rice straw + Azolla mixture (VRAM); raw manure without vermicomposting (M), and a control) and N2-fixing bacteria at three levels (Azotobacter chroococcum, Azospirillum brasilence, and non−inoculation). The results showed that, vermicompost treatments compared to control and raw manure significantly increased the number and biomass−C of soil microorganisms, urease activity, number of tillers hill−1, phosphorus (P) and potassium (K) uptake, and grain and protein yield. Inoculation of plants with N2-fixing bacteria, especially Azotobacter increased the efficiency of organic amendments, so that the maximum urease activity, soil microbial activity, P and N uptake, and grain yield (4,667 (2017) and 5,081 (2018) kg/h) were observed in vermicompost treatments containing Azolla (VAM and VRAM) under inoculation with Azotobacter. The results of the study suggested that, using an organic source along with inoculation with appropriate N2-fixing bacteria for vermicompost has a great effect on enzyme activity, soil biology, nutrient uptake and grain yield has a synergistic interaction on agronomic traits under flooded conditions. Therefore, this nutrient method can be used as one of the nutrient management strategies in the sustainable rice production.

Effect of different long-term fertilizer managements on soil nitrogen fixing bacteria community in a double-cropping rice paddy field of southern China.

Soil microorganism plays an important role in nitrogen (N) fixation process of paddy field, but the related information about how soil microorganism that drive N fixation process response to change of soil phy-chemical characteristics under the double-cropping rice (Oryza sativa L.) paddy field in southern of China is need to further study. Therefore, the impacts of 34-years different long-term fertilization system on soil N-fixing bacteria community under the double-cropping rice paddy field in southern of China were investigated by taken chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method in this paper. The field experiment were set up four different fertilizer treatments: chemical fertilizer alone (MF), rice straw and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and unfertilized as a control (CK). This results showed that compared with CK treatment, the diversity index of cbbLR and nifH genes with OM and RF treatments were significantly increased (p<0.05), respectively. Meanwhile, the abundance of cbbLR gene with OM, RF and MF treatments were increased by 23.94, 12.19 and 6.70×107 copies g-1 compared to CK treatment, respectively. Compared with CK treatment, the abundance of nifH gene with OM, RF and MF treatments were increased by 23.90, 8.82 and 5.40×109 copies g-1, respectively. This results indicated that compared with CK treatment, the soil autotrophic azotobacter and nitrogenase activities with OM and RF treatments were also significantly increased (p<0.05), respectively. There were an obvious difference in features of soil N-fixing bacteria community between application of inorganic fertilizer and organic manure treatments. Therefore, this results demonstrated that abundance of soil N-fixing bacteria community in the double-cropping rice paddy field were increased by long-term applied with organic manure and crop residue managements.

Altering Nitrogen Sources Affects Growth Carbon Costs in Vachellia nilotica Growing in Nutrient-Deficient Grassland Soils.

Vachellianilotica (L.) Willd. Ex Del. is a multipurpose leguminous tree that is common in grassland and savanna ecosystems in southern and eastern Africa. These ecosystem soils are reported to be acidic and nutrient-limited, specifically with regards to nitrogen (N) and phosphorus (P). The presence of this plant in these terrestrial ecosystems improves soil fertility benefiting the surrounding vegetation due to its ability to fix atmospheric N. This study seeks to understand the N-fixing bacteria symbiosis and physiological adaptations of V. nilotica in these acidic and nutrient-deficient KwaZulu-Natal soils. The soils used for this study were collected from the Ukulinga Grassland Nutrient Experiment located at the Ukulinga research farm of the University of KwaZulu-Natal, Pietermaritzburg, South Africa. Due to long-term soil nutrient addition treatments, these soils offered a diverse nutrient variation for better understanding the effects of acidity and nutrient variation on microbial symbiosis, plant nutrition, and biomass accumulation of V. nilotica. V. nilotica was able to maintain growth by relying on both atmospheric and soil-derived N across all treatments decreasing carbon (C) growth costs. There was an increased reliance on atmospheric-derived N of un-nodulated high N-treated plants. The plants grown in high N + P soils were able to nodulate with various species from the Mesorhizobium genus, which resulted in increased biomass compared to other plants. The results of this study show that V. nilotica can alter N sources to reduce C growth costs. In addition, both nodulating and free-living soil N2 fixing bacteria such as Caulobacter rhizosphaerae, Sphingomonas sp. and Burkholderia contaminans identified in the experimental soils may play an important role under P-deficient conditions.

Tripartite legume-rhizobia-mycorrhizae relationship is influenced by light and soil nitrogen in Neotropical canopy gaps.

Plants and their soil microbial symbionts influence ecosystem productivity and nutrient cycling, but the controls on these symbioses remain poorly understood. This is particularly true for plants in the Fabaceae family (hereafter legumes), which can associate with both arbuscular mycorrhizal fungi (AMF) and nitrogen (N) -fixing bacteria. Here we report results of the first manipulated field experiment to explore the abiotic and biotic controls of this tripartite symbiosis in Neotropical canopy gaps (hereafter gaps). We grew three species of Neotropical N-fixing legume seedlings under different light (gap-full light, gap-shadecloth, and understory) and soil nitrogen (20 g N·m-2 ·yr-1 vs. 0 g N·m-2 ·yr-1 ) conditions across a lowland tropical forest at La Selva Biological Station, Costa Rica. We harvested the seedlings after 4 months of growth in the field and measured percent AMF root colonization (%AMF), nodule and seeding biomass, and seedling aboveground:belowground biomass ratios. Our expectation was that seedlings in gaps would grow larger and, as a result of higher light, invest more carbon in both AMF and N-fixing bacteria. Indeed, seedlings in gaps had higher total biomass, nodule biomass (a proxy for N-fixing bacteria investment) and rates of AMF root colonization, and the three were significantly positively correlated. However, we only found a significant positive effect of light availability on %AMF when seedlings were fertilized with N. Furthermore, when we statistically controlled for treatment, species, and site effects, we found %AMF and seedling biomass had a negative relationship. This was likely driven by the fact that seedlings invested relatively less in AMF as they increased in biomass (lower %AMF per gram of seedling). Taken together, these results challenge the long-held assumption that high light conditions universally increase carbon investment in AMF and demonstrate that this tripartite symbiosis is influenced by soil nutrient and light conditions.

Efek Inokulasi Konsorsium Mikroba dan Aplikasi Nutrisi terhadap Populasi Azotobacter spp, Serapan N, Pertumbuhan Tanaman dan Hasil Tomat (Solanum lycopersicum L.) pada Sistem Hidroponik

Hydroponic system is an alternative agricultural cultivation technology and a potential system to overcome the decreasing availability of land. Tomato production with this system has its own market segment. Balanced nutrient management combined with inoculation of functional microbial consortium (N-fixing bacteria and phosphate solubilizers) is one of the efforts to increase tomato production in a hydroponic system. This experiment aimed to examine the effect of microbial consortium and hydroponic nutrition on tomato plant growth, Azotobacter spp. population, N uptake and tomato yield. The research design used was a factorial randomized block design (RBD) consisted of two factors. The first factor was the dose of the microbial consortium, consisting of three levels (0 mL/polybag, 5 mL/polybag, and 10 mL/polybag. The second factor was the nutritional dose consisting of three levels (0 mL, 250 mL, and 500 mL). The experimental results showed that there was no interaction between the microbial consortium treatment nutrients on hydroponic plants’ height, N uptake, Azotobacter spp. population and tomato yield. Increased nutrient dose significantly increased N uptake, with the highest yield at 500 ml/pot. But the increased nutrients dose did not lead to significantly different tomato yields. Inoculation of the microbial consortium did not significantly increase all tested parameters.

Diversity of non-symbiotic nitrogen-fixing bacteria and their potential in andisols affected by the eruption of Mount Sinabung, North Sumatra, Indonesia

Abstract. Sembiribg M, Sabrina T. 2021. Diversity of non-symbiotic nitrogen-fixing bacteria and their potential in andisols affected by the eruption of Mount Sinabung, North Sumatra, Indonesia. Biodiversitas 22: 3539-3544. Nitrogen is the main macro-nutrient that is very important for plant growth. Nitrogen is absorbed by plants in the form of NO3-or NH4+ ions from the soil. The andisols affected by the eruption of Mount Sinabung alter the chemical, physical and biological characteristics of the soil. As a result, the population of beneficial microbes in the soil decreased, so soil fertility also decreased. The aim of this research is to determine the diversity of nitrogen-fixing microbes in andisol soil affected by the Mt. Sinabung eruption. The soil samples used in this research were collected from andisols affected by the eruption of Mount Sinabung. The isolation of non-symbiotic nitrogen-fixing bacteria was carried out using a nitrogen-free Jensen medium. The results showed that five non symbiotic N-fixing bacteria can increase the N content in andisols affected by Mount Sinabung eruption. Enterobacter cloacae can increase soil N by 111.76% as compared to without microbial application.

Abundance and potency of Non-Symbiotic Nitrogen-Fixing Bacteria in Padang Sapu-sapu, Pejem Village, Bangka

Padang sapu-sapu soil is similar with post-tin mining soil in its white sand texture and poor nutrient. One factor causes the disturbed land in Bangka Belitung islands is tin mining activity. One method to rehabilitate marginal soil is by utilizing the potential nonsymbiotic N2-fixing bacteria, which are able to fertilize the soil and is able to provide macro nutrient. This study aims to measure the abundance and potency of non-symbiotic N2-fixing bacteria in padang sapu-sapu, Pejem Village, Bangka. The site selection is determined by purposive sampling method and interviews and the samples were collected randomly. Isolation used selective media Ashby'`s Monitol Agar and Azospirillum media. Morphological characterization was conducted on isolates and a series selective test was carried out, i.e. hipersentivity test, hemolysis test, IAA phytohormone test and nitrogenase test. The study of the abundance population of non-symbiotic N2-fixing bacteria of two different locations showed that the total bacterial population in padang sapusapu is very small compared to its lowland forest. Isolate Azotobacter sp. TH105(a) from the lowland forests is potential as natural fertilizer.

Effect of Co-Inoculation of Multi-Traits Bacteria Based Bio-Formulations on the Growth, Yield and Enzyme Activities of Tea

The objective of this study was to evaluate possible effects of mineral fertilizer (NPK), one commercial and three N2-fixing, P-solubilizing and/or ACC deaminase-containing bacteria based bio-fertilizers in triple strains combinations (BF9: Bacillus megaterium 47/9+ Paenibacillus macquariensis RC696 + Pseudomonas fluorescens 9/7; BF10: Bacillus megaterium RC665+ Paenibacillus macquariensis RC382 + Pseudomonas fluorescens 9/7; BF11: Bacillus simplex RC64 + Pseudomonas putida 3/10 + Burkholderia pyrrocinia RC134) were evaluated for their growth and enzyme activities of tea under acidic soil conditions, in three years. The experiment was conducted in a completely randomized design with six treatments and four replicates (each having five tea bushes). Bio-fertilizers formulations stimulated overall plant growth, including leaf area, green leaf yield, chlorophyll content and enzyme activities in tea. In addition, inoculation with bacterial formulation, activities of the different enzymes like glutathione reductase, glutathione S-transferase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, polyphenol oxidase, peroxidase, urease, 5-dehydroshikimate reductase, and alcohol dehydrogenases also changed. The selected effective acid-tolerant multi-traits bacteria based bio-formulations could play an important role in understanding the plant tolerance and adaptation to stress, processing technology, and may contribute to the concept of the quality of tea products. This study shows that these indigenous beneficial rhizobacteria isolates have the potential to be used as microbial inoculation or bio fertilizer to stimulate tea crop growth and are promising for sustainable tea cultivation.

A private channel of nitrogen alleviates interspecific competition for an annual legume.

The way resource availability predictably alters interspecific interactions and may favor one resource-acquisition strategy over another is critical for understanding context dependency. The ubiquity of nitrogen (N) limitation across terrestrial environments is a driver of plant competition and the association of some plants with N-fixing bacteria (rhizobia) may alleviate competition with nonfixing plants. Conversely, when available soil N is elevated, competitive advantages imparted by rhizobia are hypothesized to decline because nonfixing species are able to acquire those nutrients readily. We manipulated competition, soil N, and soil microbial inoculation, employing the ground bean Amphicarpaea bracteata, a native annual N-fixing legume, and jewelweed Impatiens capensis, a native co-occurring nonfixing annual. We found that legume performance was negatively impacted by interspecific competition, but less so under lower soil N in both the greenhouse and field. The legume invested a greater proportion of resources in rhizobia when competing, but only under low N. Also consistent with predictions, a competition-by-microbial-inoculation interaction demonstrated that negative effects of competition were alleviated by rhizobia. Finally, we detected an interaction between inoculation and fertilization, whereby N addition resulted in increased performance for uninoculated legumes, but a small decline in performance for inoculated plants, the latter likely representing a cost of mutualism. Thus, several lines of evidence point to the legume-rhizobia mutualism being more beneficial under competition and limited soil N. Competing I. capensis, in contrast, benefited from N addition regardless of the addition of soil microbes. In a survey of natural populations, legume and rhizobia growth were positively correlated at population edges (where interspecific competition is expected to be higher, the mutualism is stronger), whereas at population centers we found no association. Isotopic evidence confirmed a higher degree of rhizobial N-fixation at population edges compared to centers. Taken together, our results demonstrate an important role for the largely private channel of nitrogen in legume competitive performance, but with the benefits imparted by rhizobia being predictably weaker at higher soil fertility. We speculate that alleviation of competitive impacts through resource partitioning is an important and yet largely overlooked aspect of the evolutionary ecology of legume-rhizobia interactions.

Symbiotic nitrogen fixation in the reproductive structures of a basidiomycete fungus

Nitrogen (N) fixation is a driving force for the formation of symbiotic associations between N2-fixing bacteria and eukaryotes.1 Limited examples of these associations are known in fungi, and none with sexual structures of non-lichenized species.2-6 The basidiomycete Guyanagaster necrorhizus is a sequestrate fungus endemic to the Guiana Shield.7 Like the root rot-causing species in its sister genera Armillaria and Desarmillaria, G.necrorhizus sporocarps fruit from roots of decaying trees (Figures 1A-1C),8 and genome sequencing is consistent with observations that G.necrorhizus is a white-rotting decomposer. This species also represents the first documentation of an arthropod-dispersed sequestrate fungus. Numerous species of distantly related wood-feeding termites, which scavenge for N-rich food, feed on the mature spore-bearing tissue, or gleba, of G.necrorhizus. During feeding, mature spores adhere to termites for subsequent dispersal.9 Using chemical assays, isotope analysis, and high-throughput sequencing, we show that the sporocarps harbor actively N2-fixing Enterobacteriaceae species and that the N content within fungal tissue increases with maturation. Untargeted proteomic profiling suggests that ATP generation in the gleba is accomplished via fermentation. The use of fermentation-an anaerobic process-indicates that the sporocarp environment is anoxic, likely an adaptation to protect the oxygen-sensitive nitrogenase enzyme. Sporocarps also have a thick outer covering, possibly to limit oxygen diffusion. The enriched N content within mature sporocarps may offer a dietary inducement for termites in exchange for spore dispersal. These results show that the flexible metabolic capacity of fungi may facilitate N2-fixing associations, as well as higher-level organismal associations.

Poor Competitiveness of Bradyrhizobium in Pigeon Pea Root Colonization in Indian Soils.

ABSTRACTPigeon pea, a legume crop native to India, is the primary source of protein for more than a billion people in developing countries. The plant can form symbioses with N2-fixing bacteria; however, reports of poor crop nodulation in agricultural soils abound. We report here a study of the bacterial community associated with pigeon pea, with a special focus on the symbiont population in different soils and vegetative and non-vegetative plant growth. Location with respect to the plant roots was determined to be the main factor controlling the bacterial community, followed by developmental stage and soil type. Plant genotype plays only a minor role. Pigeon pea roots have a reduced microbial diversity compared to the surrounding soil and select for Proteobacteria, especially for Rhizobium spp., during vegetative growth. While Bradyrhizobium, a native symbiont of pigeon pea, can be found associating with roots, its presence is dependent on plant variety and soil conditions. A combination of 16S rRNA gene amplicon survey, strain isolation, and co-inoculation with nodule-forming Bradyrhizobium spp. and non-N2-fixing Rhizobium spp. demonstrated that the latter is a much more successful colonizer of pigeon pea roots. Poor nodulation of pigeon pea in Indian soils may be caused by a poor Bradyrhizobium competitiveness against non-nodulating root colonizers such as Rhizobium. Hence, inoculant strain selection of symbionts for pigeon pea should be based not only on their nitrogen fixation potential but, more importantly, on their competitiveness in agricultural soils.

Effects of arbuscular mycorrhizal fungi inoculation and crop sequence on root-associated microbiome, crop productivity and nutrient uptake in wheat-based and flax-based cropping systems

Arbuscular mycorrhizal fungi (AMF) inoculation and preceding crop identity have been widely reported to affect crop performance and root-associated microbiomes. However, the underlying relationship between the resulting crop performance and the dynamics of root-associated microbiomes is still poorly explored. In this study, the interaction of AMF inoculant and preceding crop was tested in wheat (Triticum aestivum L.) and flax (Linum usitatissimum L.) based rotation systems under three fertilization levels. Effects on agronomic traits, root-associated microbiome, and the relationship between root-associated microbiome and crop productivity were investigated. Higher crop yields were produced following a pulse crop (i.e., Fabaceae harvested for dry seed) than a canola crop. Better yields were at least partially due to higher plant N and P uptake, possibly mediated by certain taxa of the root-associated microbiome, such as N2-fixing and H2-oxidizing bacteria. Some differential rhizosphere zOTUs between canola and pulse crops were significantly related to succeeding crop yield. The structure of the communities of AMF, fungi and bacteria responded differently to the influence of geographical location, plant identity and microecological zone (i.e. root and rhizosphere). Results showed that the microbial communities in belowground microecological zones have specific patterns of sensitivity to driving factors, and the dynamics of certain taxa belonging to some N2-fixing and H2-oxydizing bacterial groups may be involved in the effect of crop rotation on the productivity of wheat and flax.

Activity of phosphatases and microbial phosphorus under various tree species growing on reclaimed technosols

Tree species forming a symbiosis with N-fixing bacteria (N-fixing plants) may alleviate P deficiency in afforested technosols by increasing activities of phosphatases. The objective of this study was to compare the effect of rhizobial and actinorhizal N-fixing tree species and non-N-fixing species on the activity of phosphatases in various technosols. Soil samples were taken at two depths (0 – 5 cm and 5 – 20 cm) under black locust (Robinia pseudoaccaccia), black alder (Alnus glutinosa), silver birch (Betula pendula) and Scots pine (Pinus sylvestris) stands growing on technosols developing from Quaternary sands, fly ashes after lignite combustion as well as acidic and alkaline Miocene clays. The samples were measured for the contents of organic carbon (Corg), total nitrogen (Nt) and total phosphorus (Pt), texture and pH in H2O and KCl. Microbial analyses included determination of microbial biomass carbon (Cmic) and phosphorus (Pmic), basal respiration rate (RESP) as well as activities of acid and alkaline phosphatase and inorganic pyrophosphatase. Enzyme activities were expressed per soil dry (AcdPho, AlkPho, PyroPho for acid phosphatase, alkaline phosphatase and and inorganic pyrophosphatase, respectively) and per unit of Cmic as specific enzyme activities (AcdPhoSP, AlkPhoSP and PyroPhoSP for acid, alkaline and inorganic pyrophosphatase, respectively). The soils under black locust and alder exhibited higher AcdPho than the soils under non-N-fixing trees. The soils under black locust had also higher AcdPhoSP, AlkPhoSP and PyroPhoSP values and the soils under alder AcdPhoSP compared with the soils under pine and birch. The high Nt content was the major factor positively affecting absolute activities of phosphatases. However, high values of specific activities suggest a strong competition for soil P between N-fixing plants and soil microorganisms. In particular, the high P demand of black locust resulted in more intense microbial release of phosphatases and greater retention of P in microbial biomass. Our study indicated that both N-fixing tree species affected microbial release of enzymes involved in P cycling but the influence of rhizobial black locust was stronger than the influence of actinorhizal alder.

Life on the Rocks: First Insights Into the Microbiota of the Threatened Aquatic Rheophyte Hanseniella heterophylla.

Little is known about microbial communities of aquatic plants despite their crucial ecosystem function in aquatic ecosystems. Here, we analyzed the microbiota of an aquatic rheophyte, Hanseniella heterophylla, growing at three areas differing in their degree of anthropogenic disturbance in Thailand employing a metabarcoding approach. Our results show that diverse taxonomic and functional groups of microbes colonize H. heterophylla. Proteobacteria, Actinobacteria, Dothideomycetes, and Sordariomycetes form the backbone of the microbiota. Surprisingly, the beneficial microbes reported from plant microbiomes in terrestrial habitats, such as N-fixing bacteria and ectomycorrhizal fungi, were also frequently detected. We showed that biofilms for attachment of H. heterophylla plants to rocks may associate with diverse cyanobacteria (distributed in eight families, including Chroococcidiopsaceae, Coleofasciculaceae, Leptolyngbyaceae, Microcystaceae, Nostocaceae, Phormidiaceae, Synechococcaceae, and Xenococcaceae) and other rock biofilm-forming bacteria (mainly Acinetobacter, Pseudomonas, and Flavobacterium). We found distinct community compositions of both bacteria and fungi at high and low anthropogenic disturbance levels regardless of the study areas. In the highly disturbed area, we found strong enrichment of Gammaproteobacteria and Tremellomycetes coupled with significant decline of total bacterial OTU richness. Bacteria involved with sulfamethoxazole (antibiotic) degradation and human pathogenic fungi (Candida, Cryptococcus, Trichosporon, and Rhodotorula) were exclusively detected as indicator microorganisms in H. heterophylla microbiota growing in a highly disturbed area, which can pose a major threat to human health. We conclude that aquatic plant microbiota are sensitive to anthropogenic disturbance. Our results also unravel the potential use of this plant as biological indicators in remediation or treatment of such disturbed ecosystems.