Nodule Biomass Research Articles

Ionomic and proteomic changes highlight the effect of silicon supply on the nodules functioning of Trifolium incarnatum L.

IntroductionNumerous studies have reported the beneficial effects of silicon (Si) in alleviating biotic or abiotic stresses in many plant species. However, the role of Si in Fabaceae facing environmental stress is poorly documented. The aim of this study is to investigate the effect of Si on physiological traits and nodulation efficiency in Trifolium incarnatum L.MethodsSi was supplied (1.7 mM in the form of Na2SiO3) plants inoculated with Rhizobium leguminosarum bv trifolii and plant physiological traits and nodule ionomic and molecular traits were monitored over 25 days.ResultsSi supply promoted shoot biomass, the quantity of both Si and N in roots and shoots, and the number, biomass and density of nodules and their nitrogenase abundance which contribute to better dinitrogen (N2) fixation. Ionomic analysis of nodules revealed that Si supply increased the amount of several macroelements (potassium, phosphorus and sulfur) and microelements (copper, zinc and molybdenum) known to improve nodulation efficiency and N2 fixation. Finally, comparative proteomic analysis (+Si versus -Si) of nodules highlighted that Si modulated the proteome of both symbionts with 989 and 212 differentially accumulated proteins (DAPs) in the infected host root cells and their symbiont bacteria, respectively.DiscussionAmong the DAPs, the roles of those involved in nodulation and N2 fixation are discussed. For the first time, this study provides new insights into the effects of Si on both nodular partners and paves the way for a better understanding of the impact of Si on improving nodule function, and more specifically, on the nodules’ N2-fixing capacity.

Assessing the combined impacts of microplastics and nickel oxide nanomaterials on soybean growth and nitrogen fixation potential

The excessive presence of polystyrene microplastic (PS-MPx) and nickel oxide nanomaterials (NiO-NPs) in agriculture ecosystem have gained serious attention about their effect on the legume root-nodule symbiosis and biological nitrogen fixation (BNF). However, the impact of these contaminants on the root-nodule symbiosis and biological N2-fixation have been largely overlooked. The current findings highlighted that NiO-NMs at 50 mg kg−1 improved nodule formation and N2-fixation potential, leading to enhanced N2 uptake by both roots and shoots, resulting in increased plant growth and development. While single exposure of PS-MPx (500 mg kg−1) significantly reduced the photosynthetic pigment (8–14 %), phytohormones (9–25 %), nodules biomass (24 %), N2-related enzymes (12–17 %) that ultimately affected the N2-fixation potential. Besides, co-exposure of MPx and NiO at 100 mg kg−1 altered the nodule morphology. Additionally, single and co-exposure of MPx and NiO-NMs at 100 mg kg−1 reduced the relative abundance of Proteobacteria, Gemmatimonadota, Actinobacteria, Firmicutes, and Bacteroidetes is associated with N2-cycling and N2-fixation potential. The findings of this study will contribute to understanding the potential risks posed by MPx and NiO-NMs to leguminous crops in the soil environment and provide scientific insights into the soybean N2-fixation potential.

Effects of warming and parasitism on root traits and the root economics space

Abstract Plants infected by parasitic species might be further stressed by climate warming as both factors can influence the host plant's nutrient acquisition and growth. The root economics space, defined by root functional traits, reflects a plant's nutrient acquisition strategy. However, the combined effects of warming and parasitism on root functional traits and their positions within the root economics space have not been extensively studies. We grew soybean plants in pot cultures outdoor in the absence or presence of parasitism by Cuscuta gronovii and with or without simulated climate warming using infrared heater lamps. We measured various root functional traits of soybean, including root morphological traits, symbiosis with arbuscular mycorrhizal fungi (AMF) and rhizobia and enzyme activity. Correlations among these traits were analysed, and principal component analysis was used to determine the position of the plants in the root economics space. Parasitism significantly reduced AMF colonization rate, nodule biomass, root tissue density (RTD) and phosphatase activity in the rhizosheath, while increasing root nitrogen concentration (RN). Nodule biomass was positively correlated with AMF colonization, indicating an ‘outsourcing’ strategy for nutrient foraging. Parasitized soybeans occupied a trait space with higher RN and lower RTD, indicative of a ‘fast’ nutrient acquisition strategy. Warming did not significantly affect root functional traits or the plants' positions in the root economics space, regardless of parasitism presence. This study is the first to demonstrate that rhizobial colonization, similar to AMF colonization, is part of the ‘outsourcing’ strategy and that parasitism shifts host plants from a ‘slow’ to a ‘fast’ nutrient uptake strategy. These findings provide new insights into plant below‐ground strategies under warming and parasitism. Read the free Plain Language Summary for this article on the Journal blog.

Deltamethrin's Effect on Nitrogen-Fixing Nodules in Medicago truncatula.

Deltamethrin is used against plant pests (e.g., mites and ants) and, in farm animals, against biting insects because of its acaricidal and repellent effects against ticks, thus protecting the sheep and cattle from the transmission of pathogens. However, its impact on the environment still needs to be fully evaluated. This study evaluates the impact of this pyrethroid on the nitrogen-fixing nodules in Medicago truncatula, a model legume. This research compares nodular biomass and root weight between a deltamethrin-treated section and an untreated control section of this legume. Our results indicate a significant reduction in the biomass of nitrogen-fixing nodules in the treated grove, suggesting that deltamethrin negatively affects the symbiotic relationship between M. truncatula and nitrogen-fixing bacteria. This reduction in nodule formation can impair soil fertility and plant growth, highlighting an ecological risk associated with pyrethroid's use in livestock farming. These findings underscore the need for a shift towards Green Veterinary Pharmacology (GVP), which promotes environmentally sustainable practices in managing livestock health. By minimizing our reliance on harmful chemical treatments, GVP offers viable solutions to protect and enhance ecosystem services such as biological nitrogen fixation that are essential for maintaining soil health and agricultural productivity.

Evolutionary history and root trait coordination predict nutrient strategy in tropical legume trees.

Plants express diverse nutrient use and acquisition traits, but it is unclear how trait combinations at the species level are constrained by phylogeny, trait coordination, or trade-offs in resource investment. One trait - nitrogen (N) fixation - is assumed to correlate with other traits and used to define plant functional groups, despite potential confounding effects of phylogeny. We quantified growth, carbon metabolism, fixation rate, root phosphatase activity (RPA), mycorrhizal colonization, and leaf and root morphology/chemistry across 22 species of fixing and nonfixing tropical Fabaceae trees under common conditions. Belowground trait variation was high even among closely related species, and most traits displayed a phylogenetic signal, including N-fixation rate and nodule biomass. Across species, we observed strong positive correlations between physiological traits such as RPA and root respiration. RPA increased ~ fourfold per unit increase in fixation, supporting the debated hypothesis that N-fixers 'trade' N for phosphatases to enhance phosphorus acquisition. Specific root length and root N differed between functional groups, though for other traits, apparent differences became nonsignificant after accounting for phylogenetic nonindependence. We conclude that evolutionary history, trait coordination, and fixation ability contribute to nutrient trait expression at the species level, and recommend explicitly considering phylogeny in analyses of functional groupings.

Synchrotron tomography of magnetoprimed soybean plant root system architecture grown in arsenic-polluted soil.

The present study evaluated the repercussions of magnetopriming on the root system architecture of soybean plants subjected to arsenic toxicity using synchrotron radiation source based micro-computed tomography (SR-µCT). This will be used evey where as abbreviation for the technique for three-dimensional imaging. Seeds of soybean were exposed to the static magnetic field (SMF) of strength (200 mT) for 1h prior to sowing. Magnetoprimed and non-primed seeds were grown for 1 month in a soil-sand mixture containing four different levels of sodium arsenate (0, 5, 10, and 50 mg As kg-1 soil). The results showed that arsenic adversely affects the root growth in non-primed plants by reducing their root length, root biomass, root hair, size and number of root nodules, where the damaging effect of As was observed maximum at higher concentrations (10 and 50 mg As kg-1 soil). However, a significant improvement in root morphology was detected in magnetoprimed plants where SMF pretreatment enhanced the root length, root biomass, pore diameter of cortical cells, root hair formation, lateral roots branching, and size of root nodules and girth of primary roots. Qualitative analysis of x-ray micro-CT images showed that arsenic toxicity damaged the epidermal and cortical layers of the root as well as reduced the pore diameter of the cortical cells. However, the diameter of cortical cells pores in magnetoprimed plants was observed higher as compared to plants emerged from non-primed seeds at all level of As toxicity. Thus, the study suggested that magnetopriming has the potential to attenuate the toxic effect of As and could be employed as a pre-sowing treatment to reduce the phytotoxic effects of metal ions in plants by improving root architecture and root tolerance index. This study is the very first exploration of the potential benefits of magnetopriming in mitigating the toxicity of metals (As) in plant roots utilizing the micro-CT technique.

Strong regulation of nitrogen supply and demand in a key desert legume tree

High abundance of legumes in drylands suggests that symbiotic nitrogen fixation provides an advantage in water-limited environments. However, the interactive effect of nitrogen availability and water scarcity on the nitrogen fixation strategies of dryland legumes remain largely unexplained. We conducted two experiments to test the effects of nitrogen availability and drought on symbiotic nitrogen fixation in two drought-adapted Acacia tree species. Seedlings were grown under deficient and sufficient levels of nitrogen and with and without an imposed drought to test the effect of resource availability on nitrogen fixation and plant growth. We found that seedlings that grew in extreme deficiency of nitrogen reached a similar biomass as seedling that grew with a sufficient supply of nitrogen, showing a high nitrogen-use efficiency. Nitrogen fixation was strongly downregulated (reduction of 90% in biomass allocation to nodules) when plants received sufficient nitrogen supply. Under nitrogen deficiency, drought had a slight negative effect on nodule biomass and total biomass. Under sufficient nitrogen, drought reduced nitrogen availability enough to induce an increase in symbiotic nitrogen fixation in the risk-averse A. raddiana but not in the risk-taking A. tortilis. We conclude that strong regulation of nitrogen fixation together with low nitrogen demand, and flexible strategies of carbon and nitrogen allocation, increase the chance of legume tree survival and establishment in dry and unpredictable environments.

Maize/Peanut Intercropping Affects Legume Nodulation in Semi-Arid Conditions

Maize/peanut intercropping is practiced widely to increase land productivity and considered a sustainable way for using and saving resources through peanut’s complementary N source via biological N2 fixation. Our study aims to understand how maize/peanut intercropping affects the nodulation of peanuts under water-limiting conditions and different nitrogen inputs. A two-year micro-plot experiment in 2015–2016 and a two-year field experiment in 2017–2018 were conducted to quantify nodulation in maize/peanut intercropping and sole peanut cropping under four N fertilization rates (N-free, low, medium, and high N) in rain-fed water-limited conditions. In the micro-plot experiment, intercropped peanuts increased nodule biomass compared to sole peanuts. The nodule number of intercropped peanuts was 51.6% (p = 0.001) higher than that of sole cropped peanuts, while nodule weights did not differ at high N fertilization rates and were lower in the no-N fertilization control. However, the results were different in the field experiment. Both the nodule number and single weight of the sole cropped peanut were 48.7% (p = 0.020) and 58.9% (p = 0.014) higher than that of the intercropped peanut. The ratio of the nodule weight to aboveground dry matter at the beginning peg in the dry year of 2017 was lower in intercropping than sole cropping, especially at low N fertilization rates. The potential increase in nodulation found in a well-controlled micro-plot environment might be limited by strong water and light competitions in field conditions. The results could contribute to the understanding of interspecific interactions in cereal/legume intercropping.

Microbiome properties in the root nodules of Prosopis cineraria, a leguminous desert tree.

We conducted a comprehensive analysis of the total microbiome and transcriptionally active microbiome communities in the roots and root nodules of Prosopis cineraria, an important leguminous tree in arid regions of many Asian countries. Mature P. cineraria trees growing in the desert did not exhibit any detected root nodules. However, we observed root nodules on the roots of P. cineraria growing on a desert farm and on young plants growing in a growth chamber, when inoculated with rhizosphere soil, including with rhizosphere soil from near desert tree roots that had no nodules. Compared to nearby soil, non-nodulated roots were enriched with Actinobacteria (e.g., Actinophytocola sp.), whereas root nodules sampled from the desert farm and growth chamber had abundant Alphaproteobacteria (e.g., Ensifer sp.). These nodules yielded many microbes in addition to such nitrogen-fixing bacteria as Ensifer and Sinorhizobium species. Significant differences exist in the composition and abundance of microbial isolates between the nodule surface and the nodule endosphere. Shotgun metagenome analysis of nodule endospheres revealed that the root nodules comprised over 90% bacterial DNA, whereas metatranscriptome analysis showed that the plant produces vastly more transcripts than the microbes in these nodules. Control inoculations demonstrated that four out of six Rhizobium, Agrobacterium, or Ensifer isolates purified from P. cineraria nodules produced nodules in the roots of P. cineraria seedlings under greenhouse conditions. The best nodulation was achieved when seedlings were inoculated with a mixture of those bacterial strains. Though root nodulation could be achieved under water stress conditions, nodule number and nodule biomass increased with copious water availability. .IMPORTANCEMicrobial communities were investigated in roots and root nodules of Prosopis cineraria, a leguminous tree species in arid Asian regions that is responsible for exceptionally important contributions to soil fertility in these dramatically dry locations. Soil removed from regions near nodule-free roots on these mature plants contained an abundance of bacteria with the genetic ability to generate nodules and fix nitrogen but did not normally nodulate in their native rhizosphere environment, suggesting a very different co-evolved relationship than that observed for herbaceous legumes. The relative over-expression of the low-gene-density plant DNA compared to the bacterial DNA in the nodules was also unexpected, indicating a very powerful induction of host genetic contributions within the nodule. Finally, the water dependence of nodulation in inoculated seedlings suggested a possible link between early seedling growth (before a deep root system can be developed) and the early development of nitrogen-fixing capability.

Sorghum and cowpea intercropping response to woody residue amendments in Sahelian agro-ecosystems of Burkina Faso

In West African agro-ecosystems, soils are inherently low in soil organic carbon decreasing the capacity of soils to sustain crop productivity. Woody Residues instead of being burnt or exported out of the cropping systems, can be managed to optimize soil organic carbon build-up, nutrient cycling and crop productivity. The aim of this study was to determine the effect of woody residue amendments from Piliostigma reticulatum (D.C.) Hochst associated with sorghum-cowpea intercropping on the soil residual property and crop productivity. The investigation was carried out in two experimental sites in the Sudano-Sahelian (Gampela and Kulungu) area of Burkina Faso (West Africa). The experimental design was organized into four replicates consisting of two treatments of woody residue amendments: amended (WR+) and unamended (WR-) soils. The results for both sites showed an overall significant increase in numbers (+ 35%) and biomass (+ 64%) of cowpea nodules. The root and aerial biomasses at the flowering stage of cowpeas were significantly improved in amended soils (WR+) by 26% and 44%, respectively compared to unamended soils (WR-). In addition, the WR+ treatment increase significantly cowpea and sorghum yields by 41% and 25%, respectively, as well as water use efficiency (+ 40% and + 26%, respectively) compared to the WR- treatment. Moreover, our results exhibited a strong correlation (r = 0,95) between cowpea nodular biomass and sorghum grain yields, reflecting more contribution of cowpea ecosystem services (facilitation and complementarity) for associated sorghum productivity. However, despite favorable soil conditions (soil water and organic carbon content) that occurred by WR input, it was not sufficient to improve soil residual total nitrogen and available phosphorus. The woody residue management associated with cereal-legume intercropping is a promising option to sustain crop productivity in Sahelian agro-ecosystems.

Effect of varieties and applications of clove oil on growth, productivity, and pest and disease resilience of soybean

Efforts to increase soybean productivity are carried out in various ways, including improving cultivation technology and applying pest and disease control technologies for soybeans. In addition to chemical pesticides, pest and disease control can use botanical pesticides or biopesticides, including those made from clove oil. This study aimed to determine the effect of varieties and clove oil on the growth, production, and pest-disease resilience of soybean. The study was conducted at Majalengka Regency, West Java, Indonesia from April to July 2021. The research used a factorial randomized complete block design with four replications. The first factor was soybean genotypes: Dena 1, Dega 1, and Anjasmoro. The second factor was the concentration and interval of application of clove oil: control, 3 mL L-1 with an interval of 10 days, 3 mL L-1 with an interval of 15 days, 5 mL L-1 with an interval of 10 days, and 5 mL L-1 with an interval of 15 days. The results showed that the Dena 1 variety had the highest plant height, number of branches, number of pods per plant, and dry weight per plant. The Dega 1 variety produced the highest weight of plant dry mass, dry pod shell weight, and 100-grain. Anjasmoro variety had the highest root length and number of nodules per plant. The Anjasmoro was more resistant to leaf caterpillar attacks, while the Dena 1 was more resistant to leaf rust disease. Botanical pesticides derived from clove oil affected various aspects of soybean growth including plant height at 60 days after planting, weight of dry biomass, root length and number of root nodules per plant, dry pod shell weight, dry seed weight, and 100-grains weight.
 Keywords: botanical pesticide; clove oil; Glycine max; root nodulation; variety

Co-existence of halo-tolerant Pseudomonas fluorescens and Enterococcus hirae with multifunctional growth promoting traits to ameliorate salinity stress in Vigna radiata

Soil salinization has become a prominent obstacle in diverse arid and semi-arid region damaging agricultural productivity globally. From this perspective, present investigation was aimed to compare the potential compatible consortium of bio-inoculants for improving Plant Growth Promoting (PGP) attributes, anti-oxidative enzymes, grain yield and profitability of Vigna radiata in saline soil conditions. A total of 101 rhizobacterium isolated from salt affected regions of Punjab, India were screened for their ability to induce salt tolerance, multifunctional PGP traits and antagonistic activities. The 16S rRNA sequencing identified the strains LSMR-29 and LSMRS-7 as Pseudomonas flourescens and Enterococcus hirae, respectively. In-vitro compatible halo-tolerant dual inoculant (LSMR-29 + LSMRS-7) as bio-inoculants mitigated salt stress in Vigna radiata (spring mungbean) seedling with improved seed germination, biomass and salt tolerance index together with the presence of nifH, acds, pqq and ipdc gene under salinity stress as compared to single inoculants. Further, the potential of single and dual bio-inoculants were also exploited for PGP attributes in pot and field experiments. Results indicated that a significant improvement in chlorophyll content (2.03 fold), nodulation (1.24 fold), nodule biomass (1.23 fold) and leghemoglobin content (1.13 fold) with dual inoculant of LSMR-29 + LSMRS-7 over the LSMR-29 alone. The concentrations of macro & micronutrients, proline, soil enzyme activities i.e. soil dehydrogenase, acid & alkaline phosphatases and antioxidant enzymes such as superoxide dismutase, catalase and peroxidase also found to be high for LSMR-29 + LSMRS-7 as compared to un-inoculated control. The high grain yield thereby leading to Benefit: Cost (B: C) ratio at field scale was indicative of the commercial use bio-inoculants under salt affected Vigna radiata (spring mungbean) to improvement of productivity and soil health. The current finding reveals a co-inoculation of halo-tolerating Pseudomonas fluorescens and Enterococcus hirae containing ACC deaminase could prove to be novel approach for inducing salt tolerance and improving productivity of Vigna radiata (spring mungbean).

Biopolymer as an additive for effective biochar-based rhizobial inoculant

Biochar is an efficient and inexpensive carrier for bacteria that stimulate plant development and growth. In this study, different biopolymer additives (cellulose, xanthan gum, chitin and tryptone) were tested with different addition ratios (1:0.1, 1:0.5 and 1:1) on further enhancing biochar capacity for supporting the growth and activity of Bradyrhizobium japonicum (CB1809). We utilized pine wood biochar (PWBC) pyrolyzed at 400 °C as the base inoculum carrier. The shelf life and survival rate of CB1809 were counted using the colony-forming unit (CFU) method for up to 120 days. Peat served as a standard reference material against which all treatments were compared. Subsequent experiments evaluated the ability of carrier inoculants to promote Glycine max L. (soybean) plant growth and nodulation under different watering regimes, i.e., 55 % water holding capacity (WHC) (D0), 30 % WHC (D1) and, 15 % WHC (D2) using sandy loam soil. Results revealed that among different additives; xanthan gum with 1:0.5 to PWBC [PWBC-xanthan gum(1:0.5)] was observed as a superior formulation in supporting rhizobial shelf life and survival rate of CB1809. In pot experiments, plants with PWBC-xanthan gum(1:0.5) formulation showed significant increase in various physiological characteristics (nitrogenase activity, chlorophyll pigments, membrane stability index, and relative water content), root architecture (root surface area, root average diameter, root volume, root tips, root forks and root crossings), and plant growth attributes (shoot/root dry biomass, shoot/root length, and number of nodules). Additionally, a reduced enrichment of isotopic signatures (δ13C, δ15N) was observed in plants treated with PWBC-xanthan gum(1:0.5), less enrichment of δ15N indicates an inverse link to nodulation and nitrogenase activity, while lower δ13C values indicates effective water use efficiency by plants during drought stress. These results suggest that biopolymers supplementation of the PWBC is useful in promoting shelf life or survival rate of CB1809.

Consequences of excess urea application on photosynthetic characteristics and nitrogen metabolism of Robinia pseudoacacia seedlings

Urea is the most frequently used nitrogen (N) fertilizer worldwide. However, the mechanisms in plants to cope with excess urea are largely unknown, especially for woody legumes that can meet their N demand by their own N2-fixation capacity. Here, we studied the immediate consequences of different amounts of urea application and exposure duration on photosynthesis, N metabolism, and the activity of antioxidative enzymes of Robinia pseudoacacia seedlings. For this purpose, seedlings were grown for 3 months under normal N availability with rhizobia inoculation and, subsequently, 50 mg N kg−1 was applied to the soil twice with urea as additional N source. Our results show that excess urea application significantly promoted photosynthesis, which increased by 80.3% and 84.7% compared with CK after the 1st and 2nd urea applications, respectively. The increase in photosynthesis translated into an increase in root and nodule biomass of 88.7% and 82.0%, respectively, while leaf biomass decreased by 4.8% after the first application of urea. The N content in leaves was 92.6% higher than in roots, but excess urea application increased the N content of protein and free amino acids in roots by 25.0%, and 43.3%, respectively. Apparently, enhanced root growth and N storage in the roots constitute mechanisms to prevent the negative consequences of excess N in the shoot upon urea application. Nitrate reductase (NR) activity of leaves and roots increased by 74.4% and 26.3%, respectively. Glutathione reductase (GR) activity in leaves and roots was enhanced by 337% and 34.0%, respectively, but then decreased rapidly to the initial level before fertilization. This result shows that not only N metabolism, but also antioxidative capacity was transiently promoted by excess urea application. Apparently, excess urea application initially poses oxidative stress to the plants that is immediately counteracted by enhanced scavenging of reactive oxygen species via enhanced GR activity.

Silicon Supply Improves Nodulation and Dinitrogen Fixation and Promotes Growth in Trifolium incarnatum Subjected to a Long-Term Sulfur Deprivation.

In many crops species, sulfur (S) deprivation negatively affects growth, seed yield quality and plant health. Furthermore, silicon (Si) is known to alleviate many nutritional stresses but the effects of Si supply on plants subjected to S deficiency remain unclear and poorly documented. The objective of this study was to evaluate whether Si supply would alleviate the negative effects of S deprivation on root nodulation and atmospheric dinitrogen (N2) fixation capacity in Trifolium incarnatum subjected (or not) to long-term S deficiency. For this, plants were grown for 63 days in hydroponic conditions with (500 µM) or without S and supplied (1.7 mM) or not with Si. The effects of Si on growth, root nodulation and N2 fixation and nitrogenase abundance in nodules have been measured. The most important beneficial effect of Si was observed after 63 days. Indeed, at this harvest time, a Si supply increased growth, the nitrogenase abundance in nodules and N2 fixation in S-fed and S-deprived plants while a beneficial effect on the number and total biomass of nodules was only observed in S-deprived plants. This study shows clearly for the first time that a Si supply alleviates negative effects of S deprivation in Trifolium incarnatum.

“Alperujo” Compost Improves Nodulation and Symbiotic Nitrogen Fixation of Soybean Inoculated with Bradyrhizobium diazoefficiens

The utilization of compost to enhance plant productivity and symbiotic nitrogen fixation (SNF) has been recognized as an effective alternative to synthetic nitrogen fertilizers. This environmentally sustainable method is readily accessible to farmers. This study investigated the effect of olive pomace (“alperujo”, AL) compost on the nodulation and SNF of soybeans (Glycine max L.) and their natural symbiont (Bradyrhizobium diazoefficiens). For that, soybean plants were subjected to several doses of AL compost under controlled greenhouse conditions. At the end of the experiment, the dry weight of plant biomass (aerial part and roots), the number and fresh weight of nodules, and nitrogen and leghaemoglobin contents were analyzed. The application of AL compost significantly improved soybean growth, as demonstrated by an increase in both plant biomass and height. Furthermore, nodular leghaemoglobin content and nitrogen content were found to be enhanced by the addition of AL compost (7 and 40%, respectively), indicating an increase in nodule effectiveness and symbiotic efficiency. Our results provide clear evidence of the synergetic effect of AL compost on the soybean-B. diazoefficiens association, probably due to AL-compost improved soybean roots development, and rhizospheric organic matter and nutrients assimilation by rhizobia.

Nodulation alleviates the stress of lower water availability in Vachellia sieberiana

The genus Vachellia (Fabaceae) has a pan-tropical distribution and numerous Vachellia species are currently observed to be expanding their indigenous ranges and/or are invasive. Most Vachellia species have the capacity to enhance nitrogen uptake via an N2-fixing rhizobial mutualism that manifests in specialized root nodule structures enabling the catalysis of atmospheric N2 into a plant useable form. Improved understanding of nodulation may provide new insight to the changing patterns of ecological success of Vachellia species. Here, we investigated how the seedling growth, allometry and nodulation of two common Vachellia species, the arid Vachellia erioloba and the mesic Vachellia sieberiana, responded to varied levels of water availability. Seedlings were grown at 4%, 8% and 16% soil moisture content (SMC) for four months. The seedling growth and allometry of V. erioloba was unresponsive to changing water availability, and no nodulation was observed. The allometry of V. sieberiana was responsive to changing water availability and nodulation was observed; with the highest nodule biomass and growth rate recorded at 4% SMC. These patterns suggest that V. erioloba does not require the rhizobial mutualism, possibly due to lower competitive interactions between woody plants and grass in the arid savanna. Whereas, due to the competitive vegetation interactions typical in the mesic savanna, N2- fixation via nodule development could provide V. sieberiana a competitive advantage over grass not only in limited N conditions, but also during periods of lower water availability.

Nitrogen and light regulate symbiotic nitrogen fixation by a temperate forest tree.

Symbiotic nitrogen fixation (SNF) is a critical mechanism of ecosystem recovery, and in forests of the eastern United States, the most common tree species that supports SNF is black locust (Robinia pseudoacacia L.). Despite its prevalence, black locust's fixation strategy-whether it maintains fixation at a constant rate (obligate fixation) or reduces its fixation rate (facultative fixation)-is unknown. Here, we examined how nitrogen and light control SNF by black locust, by growing seedlings under two nitrogen levels and across four levels of light. Seedlings were harvested after 12weeks to determine biomass changes, nodule activity, and photosynthetic rates. Black locust seedlings increased biomass growth with increasing light, but only in the absence of nitrogen addition, while seedling root:shoot (biomass) modestly declined with increasing light regardless of nitrogen level. We found that black locust behaved like a facultative fixer, and regulated fixation by excising or maintaining nodules, and by controlling nodule biomass and activity. Specifically, nitrogen addition reduced seedling investment in nodule biomass (g g-1) by 63%, and reduced seedling allocation to nitrogen fixation (µmol C2H4 g-1h-1) by 66%. In contrast, light affected nitrogen fixation through two indirect pathways. First, light increased plant growth, and hence nitrogen demands, which caused an increase in nitrogen fixation proportional to biomass. Second, light increasd photosynthetic activity, which was positively associated with nodule activity, but only in the absence of nitrogen addition. Our findings for how black locust regulates SNF can improve predictions of ecosystem SNF under the changing environmental conditions.

Sex-Related Ecophysiological Responses of Hippophae rhamnoide Saplings to Simulate Sand Burial Treatment in Desertification Areas

(1) Background: In recent years, Hippophae rhamnoides has been used extensively to prevent desertification in China due to its nitrogen (N) fixation and sand stabilization abilities. However, as a dioecious species, few studies have focused on the sexual dimorphism of H. rhamnoides in response to sand burial, which frequently presents in desertification areas. (2) Methods: In this paper, we explored the ecophysiological responses of female and male saplings of H. rhamnoides under unburied treatment (control) and different sand burial depths (denoted as T33, T67, T90 and T133, corresponding to sand burial depths of 33, 67, 90 and 133 percent of the mean initial height of the saplings, respectively). (3) Results: Compared with unburied controls, the T33 treatment significantly promoted biomass accumulation and photosynthetic capacity, whereas T67 and T90 treatments inhibited biomass and physiological parameters of the two sexes. Deeper sand burial treatments, i.e., T90 and T133, significantly decreased the survival rates of the two sexes. Furthermore, the sex-specific responses of the two sexes of H. rhamnoides were affected by different depths of sand burial. Males had higher levels of stem starch and root sucrose and exhibited a larger increase in root nodule biomass under the T33 treatment, indicating better carbohydrate utilization and N fixation, whereas females showed lower total biomass and fewer root nodules, as well as more inhibition of photosynthetic and chlorophyll fluorescence parameters, water potential and root carbohydrates, indicating more negative effects on females than males under the T67 treatment. (4) Conclusions: We conclude that sex-related response and adaptation to sand burial depths may potentially affect the colonization, sex ratio and ecological function of the two sexes of H. rhamnoides in desertification areas.

Phytoremediation of isoproturon-contaminated sites by transgenic soybean.

The widespread application of isoproturon (IPU) can cause serious pollution to the environment and threaten ecological functions. In this study, the IPU bacterial N-demethylase gene pdmAB was transferred and expressed in the chloroplast of soybean (Glycine max L. 'Zhonghuang13'). The transgenic soybeans exhibited significant tolerance to IPU and demethylated IPU to a less phytotoxic metabolite 3-(4-isopropylphenyl)-1-methylurea (MDIPU) invivo. The transgenic soybeans removed 98% and 84% IPU from water and soil within 5 and 14 days, respectively, while accumulating less IPU in plant tissues compared with the wild-type (WT). Under IPU stress, transgenic soybeans showed a higher symbiotic nitrogen fixation performance (with higher total nodule biomass and nitrogenase activity) and a more stable rhizosphere bacterial community than the WT. This study developed a transgenic (TS) soybean capable of efficiently removing IPU from its growing environment and recovering a high-symbiotic nitrogen fixation capacity under IPU stress, and provides new insights into the interactions between rhizosphere microorganisms and TS legumes under herbicide stress.