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Biological desert crusts are relatively common in the arid deserts of the Sultanate of Oman; however, little is known about their microbial community composition and role in soil fertilization. We compared three crusts from geographically different locations for their soil texture, bacterial community structure, pigment composition and nitrogenase activity. The crusts were growing on alkaline (pH 7.6-8.7) loamy sand and silty loam soils. Microscopically, Microcoleus vaginatus was the most abundant cyanobacterium, but Nostoc and Scytonema types dominated in cultures. The 16S rRNA gene sequences showed close similarities in the crusts' bacterial composition, with 77-81% of the total clones belonging to cyanobacteria and the rest distributed among Alpha- and Deltaproteobacteria, Bacteriodetes, Gemmatimonas and Planctomycetes. Thirty-seven percent of the cyanobacterial clones were affiliated with heterocystous types such as Nostoc, Scytonema, Brasilonema and Petalonema. Chlorophyll a concentrations suggest a similar abundance of phototrophs in all crusts. High levels of the UVA sunscreen scytonemin were detected in the exposed crusts. The three crusts exhibited comparable acetylene reduction rates in the light and in the dark, with a maximum rate of 58.5±2.6 μmol C₂H₂ reduced m⁻² h⁻¹. We conclude that the crusts, regardless of their geographical location, were rich in heterocystous cyanobacteria that can fix nitrogen and could possibly improve soil stability and productivity.

We used a physiological approach to investigate the effect of sulfur dioxide (SO₂) on Alnus sieboldiana Matsum. (A. sieboldiana) and symbiotic Frankia spp. in Miyakejima Island, which was devastated by volcanic action in July of 2000. In April of 2008, three study sites were chosen in the forest of Miyakejima Island, and were categorized as high, medium, or low in relation to their sulfur dioxide concentration (volcanic gas). Nine A. sieboldiana trees were selected from naturally regenerated forest at each site. The higher the SO₂ concentration at the study site, the lower was the photosynthetic rate and the maximum photochemical efficiency of PSII (F ᵥ/F ₘ) of A. sieboldiana and its apparent quantum yield. The acetylene reduction rate of the Frankia spp. symbiotic with A. sieboldiana was significantly less at the high SO₂ concentration (p<0.05). The nitrogen concentration in their leaves remained high, however. There was no significant difference in the chlorophyll concentration (Chl a + b) in leaves from the three sites. The photosynthetic nitrogen use efficiency decreased significantly in sites with a high SO₂ concentration, however. As a result, A. sieboldiana regenerated at the sites with high or medium SO₂ concentration underwent approximately 50–70 % less growth than at the site with a low SO₂ concentration.

Background Nitrogen-fixing prokaryotes (diazotrophs) contribute substantially to nitrogen input in mangrove sediments, and their structure and nitrogen fixation rate (NFR) are significantly controlled by environmental conditions. Despite the well-known studies on diazotrophs in surficial sediments, the diversity, structure, and ecological functions of diazotrophic communities along environmental gradients of mangrove sediment across different depths are largely unknown. Here, we investigated how biological nitrogen fixation varied with the depth of mangrove sediments from the perspectives of both NFR and diazotrophic communities. Results Through acetylene reduction assay, nifH gene amplicon and metagenomic sequencing, we found that the NFR increased but the diversity of diazotrophic communities decreased with the depth of mangrove sediments. The structure of diazotrophic communities at different depths was largely driven by salinity and exhibited a clear divergence at the partitioning depth of 50 cm. Among diazotrophic genera correlated with NFR, Agrobacterium and Azotobacter were specifically enriched at 50–100 cm sediments, while Anaeromyxobacter , Rubrivivax , Methylocystis , Dickeya , and Methylomonas were more abundant at 0–50 cm. Consistent with the higher NFR, metagenomic analysis demonstrated the elevated abundance of nitrogen fixation genes ( nifH/D/K ) in deep sediments, where nitrification genes ( amoA/B/C ) and denitrification genes ( nirK and norB ) became less abundant. Three metagenome-assembled genomes (MAGs) of diazotrophs from deep mangrove sediments indicated their facultatively anaerobic and mixotrophic lifestyles as they contained genes for low-oxygen-dependent metabolism, hydrogenotrophic respiration, carbon fixation, and pyruvate fermentation. Conclusions This study demonstrates the depth-dependent variability of biological nitrogen fixation in terms of NFR and diazotrophic communities, which to a certain extent relieves the degree of nitrogen limitation in deep mangrove sediments. BxKuS27-gQH4xs4TJqgBb7 Video Abstract

The two commonly applied methods to assess dinitrogen (N(2)) fixation rates are the (15)N(2)-tracer addition and the acetylene reduction assay (ARA). Discrepancies between the two methods as well as inconsistencies between N(2) fixation rates and biomass/growth rates in culture experiments have been attributed to variable excretion of recently fixed N(2). Here we demonstrate that the (15)N(2)-tracer addition method underestimates N(2) fixation rates significantly when the (15)N(2) tracer is introduced as a gas bubble. The injected (15)N(2) gas bubble does not attain equilibrium with the surrounding water leading to a (15)N(2) concentration lower than assumed by the method used to calculate (15)N(2)-fixation rates. The resulting magnitude of underestimation varies with the incubation time, to a lesser extent on the amount of injected gas and is sensitive to the timing of the bubble injection relative to diel N(2) fixation patterns. Here, we propose and test a modified (15)N(2) tracer method based on the addition of (15)N(2)-enriched seawater that provides an instantaneous, constant enrichment and allows more accurate calculation of N(2) fixation rates for both field and laboratory studies. We hypothesise that application of N(2) fixation measurements using this modified method will significantly reduce the apparent imbalances in the oceanic fixed-nitrogen budget.

Corn silage is an important feed for intense ruminant production, but the growth of corn relies heavily on the use of chemical fertilizers. Sustainable crop production requires careful management of all nutrient sources available on a farm, particularly in corn-based cropping systems. Experiments were conducted to determine the appropriate technique of corn-legume intercropping in conjunction with the supplemental use of chemical fertilizers, organic manure, and biofertilizers (BFs). Acetylene reduction assays (ARAs) were also performed on corn and soybean roots. Combining chemical fertilizers with chicken manure (CM) in a 50:50 ratio and applying 50% NPK+50% CM+BF produced fresh forage and dry matter (DM) yields that were similar to those produced in the 100% nitrogen (N), phosphorus (P), potassium (K) treatment. Among the lone fertilizer treatments, the inorganic fertilizer (100% NPK) treatment produced the highest DM yield (13.86 t/ha) of forage and outyielded the 100% CM (9.74 t/ha) treatment. However, when CM was combined with NPK, the resulting DM yield of forage (13.86 t/ha) was the same as that resulting from 100% NPK (13.68 t/ha). Compared with CM applications alone, combinations of NPK and CM applications resulted in increased plant height, crop growth rates (CGRs) and leaf area index (LAI), but the values of these parameters were similar to those resulting from 100% NPK application. Fertilizers in which the ratio was 50% CM+50% NPK or 50% CM+50% NPK+BF resulted in protein yields that were similar to those resulting from conventional fertilizers. Similarly, the CP content did not significantly differ between applications of the 100% NPK and 50% CM+50% NPK fertilizers. The use of BFs had no significant impact on improving either the yield or quality of forage fertilized with inorganic or organic fertilizer. Lactic acid responded differently to different fertilizer applications and was significantly higher in the fertilized plots than in the unfertilized plots. Compared with treatments of lone chemical and lone organic manure fertilizers, treatments involving applications of BF and a combination of BF and NPK or CM resulted in higher ARA values. There is no simple and easy approach to increase biological nitrogen fixation (BNF) in grain legumes grown as part of a cropping system under realistic farm field conditions. Overall, evidence recorded from this study proves that, compared with corn monocrops combined with CM and chemical fertilizers, corn-soybean intercrops could increase forage yields and quality, produce higher total protein yields, and reduce the need for protein supplements and chemical fertilizers.

Replacing the oxygen evolution reaction with more thermodynamically favourable organic oxidation reactions (OORs) can enable energy-efficient hydrogen evolution and hydrogenation. However, cathodic reduction rates are limited by sluggish OORs. Herein, we report a decoupled electrolysis strategy using a solid redox reservoir (RR) to realize an optimized hydrogen evolution reaction (HER) paired with valuable chemical synthesis. The decoupled system with a rechargeable capability features a HER coupled with RR oxidation for electricity storage, which is followed by the conversion of OORs (e.g., ethylene glycol, glycerol) into value-added chemicals coupled with the reduction of the oxidized RR to generate electricity. The fast kinetics of RR oxidation and membrane-free cell operation optimize the HER rate. The value-added chemicals and electricity are cocreated during the discharge process, offering more economic benefits. This decoupling design is universally applicable to other OORs-paired reduction systems (e.g., acetylene-to-ethylene semihydrogenation) to synthesize various chemicals for electricity storage and generation, paving a sustainable avenue for H 2  production/hydrogenation and chemicals manufacturing. Using thermodynamically favourable organic oxidations instead of oxygen evolution enables energy-efficient cathodic reactions, but rates are limited by slow anodic kinetics. Here, the authors report decoupled charge‒discharge electrolysis using a solid redox reservoir to overcome this limitation.

AbstractThe biological activity of eutrophic peat soils on the floodplain of the Poros River located in the paleovalley of the Tom River (Tomsk oblast, Western Siberia) was studied. Microbial biomass, respiration intensity, methanogenesis, nitrogen fixation, and denitrification were determined in soils of native and long-drained areas on the left-bank and right-bank floodplain. Microbial biomass stock in the 1-m layer of the studied soils ranged from 240 to 1068 g/m2, and basal respiration rate ranged from 87 to 351 μg CO2/(g per day). Nitrogen cycle activity indicators were characterized by low values: 3–12 ng C2H4/(g per day) for nitrogen fixation estimated by the acetylene reduction method and 0.1 to 8 μg N2O/(g per day) for denitrification. It was found that 27 years of the floodplain drainage by a network of open channels contributed to a 2–4.5-fold increase in the total microbial biomass (owing to the fungal component in the upper eutrophic peat horizon and the bacterial component in the underlying peat layer) and in the respiratory and nitrogenase activities. At the same time, the activities of methanogenesis and denitrification decreased. The negative effect of the long-term drainage—the loss of up to 45% of carbon and 50% of nitrogen stocks—manifested itself in the surface eutrophic peat TE horizon (0–25 cm).

Nitrogen is a crucial element for the growth and development of insects, but herbivorous insects often suffer from nitrogen nutrition deficiencies in their diets. Some symbiotic microorganisms can provide insect hosts with nitrogen nutrition through nitrogen fixation. Extensive research has clearly demonstrated the process of nitrogen fixation by symbiotic microorganisms in termites, while evidence supporting the occurrence and significance of nitrogen fixation in the diets of the Hemiptera is less conclusive. In this study, we isolated a strain of R. electrica from the digestive tract of a leafhopper, R. dorsalis, and found that it had nitrogen-fixing capabilities. Fluorescence in situ hybridization results showed that it was located in the gut of the leafhopper. Genome sequencing revealed that R. electrica possessed all the genes required for nitrogen fixation. We further evaluated the growth rate of R. electrica in nitrogen-containing and nitrogen-free media and measured its nitrogenase activity through an acetylene reduction assay. The findings of these studies could shed light on how gut microbes contribute to our understanding of nitrogen fixation.

Key messageThe black locust is adapted to elevated [CO2] through changes in nitrogen allocation characteristics in leaves.AbstractThe black locust (Robinia pseudoacacia L.) is an invasive woody legume within Japan. This prolific species has a high photosynthetic rate and growth rate, and undergoes symbiosis with N2-fixing micro-organisms. To determine the effect of elevated CO2 concentration [CO2] on its photosynthetic characteristics, we studied the chlorophyll (Chl) and leaf nitrogen (N) content, and the leaf structure and N allocation patterns in the leaves and acetylene reduction activity after four growing seasons, in R. pseudoacacia. Our specimens were grown at ambient [CO2] (370 μmol mol−1) and at elevated [CO2] (500 μmol mol−1), using a free air CO2 enrichment (FACE) system. Net photosynthetic rate at growth [CO2] (Agrowth) and acetylene reduction activity were significantly higher, but maximum carboxylation rate of RuBisCo (Vcmax), maximum rate of electron transport driving RUBP regeneration (Jmax), net photosynthetic rate under enhanced CO2 concentration and light saturation (Amax), the N concentration in leaf, and in leaf mass per unit area (LMA) and ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCo) content were significantly lower grown at elevated [CO2] than at ambient [CO2]. We also found that RuBisCo/N were less at elevated [CO2], whereas Chl/N increased significantly. Allocation characteristics from N in leaves to photosynthetic proteins, NL (Light-harvesting complex: LHC, photosystem I and II: PSI and PSII) and other proteins also changed. When R. pseudoacacia was grown at elevated [CO2], the N allocation to RuBisCo (NR) decreased to a greater extent but NL and N remaining increased relative to specimens grown at ambient [CO2]. We suggest that N remobilization from RuBisCo is more efficient than from proteins of electron transport (NE), and from NL. These physiological responses of the black locust are significant as being an adaptation strategy to global environmental changes.

PurposeThe objective of the study was to explore the effect of pristine (rice husk-derived biochar produced at 500 ℃ by a Japanese company, JBC) and FeCl3-modified biochar (JBC-Fe) and its application rate on denitrification and N2O emission in calcareous arable soil and the potential mechanisms.MethodsAfter biochar preparation and characterization, JBC or JBC-Fe was thoroughly mixed with the soil at the mass ratio of 2% or 5%, which were defined as JBC-2%, JBC-5%, JBC-Fe-2%, and JBC-Fe-5%, respectively, and a control treatment without any biochar addition was also arranged. After 7-day preincubation, an 8-day microcosm incubation experiment was carried out consecutively under the condition of facilitating denitrification. N2O and N2O + N2 emission rates were determined, and the distribution pattern of N2O and N2, as the end products of denitrification, was distinguished by the acetylene inhibition method. The dynamic changes of soil physicochemical properties and the activities of nitrate reductase and nitrite reductase during incubation were also explored.ResultsResults showed that both JBC and JBC-Fe promoted soil cumulative N2O + N2 and N2O emission during the 8-day incubation. Compared with JBC-2%/JBC-5%, the cumulative N2O + N2 emission of JBC-Fe-2%/JBC-Fe-5% significantly increased by 9.83%/41.21% and the cumulative N2O emission significantly increased by 465.98%/147.68%, respectively (p < 0.05), indicating that JBC-Fe promoted soil NO3− reduction and inhibited N2O reduction compared to JBC. Compared with 2% biochar addition, 5% biochar addition increased soil C/N ratio, decreased the bioavailability of nitrogen and inhibited soil nitrate reductase activity, and subsequently decreased the cumulative N2O + N2 emission. Moreover, 5% biochar addition also inhibited soil N2O reductase activity, resulting in the increase of cumulative N2O emission.ConclusionsJBC-Fe did not show the greenhouse gas mitigation benefits, but increased N2O emission from the calcareous arable soil under the condition of facilitating denitrification (e.g., after heavy rainfall, irrigation, and fertilization). The study provides a theoretical basis to functional biochar production and its engineering application in calcareous arable soil.