Effects of carbon to nitrogen ratio on nitrogen removal in a single-stage microaerobic system: A model-based evaluation

Single-stage microaerobic systems have been proven to be effective for concurrent removal of ammonium and organic carbon from sewage. While mechanistic models derived from activated sludge models (ASMs) have simulated nutrients removal under microaerobic conditions, classic ASMs exhibit limitations in capturing the intricate effects of carbon to nitrogen (C/N) ratio on nitrogen removal performance. To address this issue, a mechanistic model modified from the classic ASMs was proposed to capture the combined inhibitory effects of carbon and ammonium on microaerobic systems. This modified model was established based on experimental data from a single-stage microaerobic reactor encompassing simultaneous nitrification-denitrification and anammox processes. The inhibition coefficient of C/N ratio was integrated into the process rate equations, and its effectiveness was validated through model performance evaluation. Compared to the classic models, the modified one achieved superior predictions for nitrite and nitrate nitrogen concentrations. Simulations revealed that under optimized conditions with a C/N of 4.57 and a dissolved oxygen (DO) of 0.41 mg/L, the system could achieve up to 95.5% of total nitrogen (TN) removal efficiency. Based on the simulation of substrate uptake/production rate, increasing the nitrogen loading rate (NLR) rather than organic loading rate (OLR) was crucial for efficient nitrogen removal. The proposed modified model served as a valuable tool for designing and optimizing similar biological wastewater treatment systems.

Altitudinal and aspect-driven variations in soil carbon storage potential in sub-tropical Himalayan forest ecosystem: assisting nature to combat climate change

Forest soils serve as the greatest sink of terrestrial carbon (C) and have a significant impact on worldwide or regional C cycling. By reducing emissions and enhancing the C storage in forests, the environmental monitoring function of a forest ecosystem may be ensured. The study focused on measuring the densities of major nutrients in soil to gain insight into the C and nitrogen dynamics of the Himalayan sub-tropical forest ecosystem of India besides supplementing the information about the C storage potential of these forest soils. The study examined the physico-chemical properties and nutrient densities across three altitudinal ranges viz., 600-800 m (A1), 800-1000 m (A2) and 1000-1200 m (A3) and two aspects, i.e. Northern (N) and Southern (S) in a randomized complete block design and data collection was done from 24 main sample plots (3 altitudinal ranges × 2 aspects × 4 replications). The soil pH, electrical conductivity, and bulk density observed a decreasing pattern with an increase in altitude, whereas a reverse trend was observed in soil organic C (SOC), total nitrogen and available phosphorus. The SOC and total nitrogen densities ranged from 20.08 to 48.35 Mg ha-1 and 2.56 to 4.01 Mg ha-1, respectively in an increasing trend from A1 to A3. The northern aspect exhibited significantly higher SOC and nitrogen densities than the southern aspects. The C storage potential of forest soils followed the order A1 < A2 < A3 with significantly higher potential (nearly 1.5 times) compared to those on the southern aspect. There was a consistently significant increase in the C:N ratio (CNR) with a maximum value (10.51) at A3 and minimum value (8.37) at A1, however the effect of aspect remained insignificant. This research underscores the importance of considering altitude and aspect when planning forest restoration efforts, as these factors have a substantial influence on soil properties, C storage potential and CNR. Understanding the significance of CNR is critical, as it serves as a key indicator of greenhouse gas (GHG) emissions from forest soils. Ultimately, these findings empower policymakers and conservationists to make informed decisions that can contribute to the sustainable management of Himalayan forests and the global fight against climate change.

Effect of biodrying of lignocellulosic biomass on humification and microbial diversity

By optimizing the carbon to nitrogen (C/N) ratio, this study accomplished an improved level of humification and microbial diversity in the biodrying process of lignocellulosic biomass. The results demonstrated that C/N ratio of 20 accelerated the decomposition of refractory lignocellulose, resulting in lower greenhouse gas emissions and the production of highly mature fertilizer with a germination index of 119.0% and a humic index of 3.2. Moreover, C/N ratio of 20 was found to diversify microbial communities, including Pseudogracilibacillus, Sinibacillus, and Georgenia, which contributed to the decomposition of lignocellulosic biomass and the production of humic acid. Hence, it is recommended to regulate the C/N ratio to 20:1 during the biodrying of biogas residue and wood chips to promote the economic feasibility and bioresource recycling.

Responses of biofilm communities in a hybrid moving bed biofilm reactor-membrane bioreactor system to sulfadiazine antibiotic exposure

Antibiotics in wastewater can affect the structures and functions of bacterial communities, subsequently influencing how well a biological process performs. Therefore, the characteristics of bacterial community were investigated in a hybrid moving bed biofilm reactor-membrane bioreactor system when treating domestic wastewater containing sulfadiazine (SDZ). Results indicated total nitrogen removal reduced by 10.2%, 9.1%, 2.7% and 2.9%, respectively, with increasing carbon to nitrogen (C/N) ratios (2.5, 4, 6 and 9) when SDZ was present (0.5 mg/L). The microbial communities' analysis revealed that the abundance of nitrogen removal-related bacteria increased with C/N. Specifically, the abundance of ammonia-oxidizing bacteria (0.46%-0.90%) was low, and the nitrite-oxidizing bacteria (2.16%-7.13%) and denitrifying bacteria showed a significant increase (Hyphomicrobium: 0.57%-3.54%) when C/N ratio increased. The abundance of denitrifying bacterial declined by 4.82-8.56% at different C/N ratios, while nitrifying bacterial rose by 0.70-5.67%. Interestingly, the denitrifying bacteria Enterobacter, Sphingomonas and Gemmatimonas acted as mutualistic bacteria that stabilized denitrification.

Effects of the chromium content on anaerobic fermentation of chrome shaving collagen and rice straw juice

This thesis investigated the effects of different chromium contents on the gas production characteristics of anaerobic fermentation by mixing the collagen solution obtained from the hydrolysis of chromium tannin chips by alkali-enzyme combination with rice stalk hydrolysate and the changes of system pH, VFA concentration, SCOD concentration, ammonia nitrogen concentration, and chromium concentration during anaerobic fermentation. The experimental results show that the highest total gas production and cumulative methane production are 1531.0 mL/gVS and 761.2 mL/gVS, respectively, with a Cr content of 5 mg/L, and the methane content reaches 49.7%. The best SCOD removal rate is 54.54% at a C/N ratio of 20:1. The increase in SCOD concentration is decreased with increasing chromium content, but there is no significant change in ammonia nitrogen concentration. The highest rate of SCOD degradation is achieved with a chromium content of 5 mg/L. The results of this thesis provide data support and theoretical guidance for the resource recovery of chromium leather shavings.

Tailoring and optimizing fatty acid production by oleaginous yeasts through the systematic exploration of their physiological fitness

Background

The use of palm oil for our current needs is unsustainable. Replacing palm oil with oils produced by microbes through the conversion of sustainable feedstocks is a promising alternative. However, there are major technical challenges that must be overcome to enable this transition. Foremost among these challenges is the stark increase in lipid accumulation and production of higher content of specific fatty acids. Therefore, there is a need for more in-depth knowledge and systematic exploration of the oil productivity of the oleaginous yeasts. In this study, we cultivated Cutaneotrichosporon oleaginosus and Yarrowia lipolytica at various C/N ratios and temperatures in a defined medium with glycerol as carbon source and urea as nitrogen source. We ascertained the synergistic effect between various C/N ratios of a defined medium at different temperatures with Response Surface Methodology (RSM) and explored the variation in fatty acid composition through Principal Component Analysis.

Results

By applying RSM, we determined a temperature of 30 °C and a C/N ratio of 175 g/g to enable maximal oil production by C. oleaginosus and a temperature of 21 °C and a C/N ratio of 140 g/g for Y. lipolytica. We increased production by 71% and 66% respectively for each yeast compared to the average lipid accumulation in all tested conditions. Modulating temperature enabled us to steer the fatty acid compositions. Accordingly, switching from higher temperature to lower cultivation temperature shifted the production of oils from more saturated to unsaturated by 14% in C. oleaginosus and 31% in Y. lipolytica. Higher cultivation temperatures resulted in production of even longer saturated fatty acids, 3% in C. oleaginosus and 1.5% in Y. lipolytica.

Conclusions

In this study, we provided the optimum C/N ratio and temperature for C. oleaginosus and Y. lipolytica by RSM. Additionally, we demonstrated that lipid accumulation of both oleaginous yeasts was significantly affected by the C/N ratio and temperature. Furthermore, we systematically analyzed the variation in fatty acids composition and proved that changing the C/N ratio and temperature steer the composition. We have further established these oleaginous yeasts as platforms for production of tailored fatty acids.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01956-5.

Critical insights into anaerobic co-digestion of wheat straw with food waste and cattle manure: Synergistic effects on biogas yield and kinetic modeling

In this study, four batch assays were performed to ensure the synergic effects of co-digestion and find out the best inoculums to substrate ratio (ISR), carbon to nitrogen ratio (C:N), and total solid (TS) percentage in sequence. The co-digestion of three feedstocks had a 20% higher biogas yield (416 mL/gVS added) than mono-digestion with 21% volatile solids (VS) degradation. The ISR of 2 leads to the highest biogas yield (431 mL/gVS added) and VS removal (30.3%) over other ISRs (0.5, 1.0, 2.5) studied. The lower ISR (<2) tended to have lower pH due to insufficient anaerobes inside the digester. The C:N 35 (with ISR 2) yielded 17.4% higher biogas (443.5 mL/gVS added) than mono-digestion and was the highest among the C:N ratios studied with 36.6% VS removal. The VFA, alkalinity, and pH in C:N 35 assay were more stable than in other C:N assays. In the fourth batch assay, varying TS% (5, 7.5, 10, 12.5) were used with optimized ISR (2) and C:N (35). Higher TS% (10 and 12.5) had some lag phase but later achieved higher biogas production. The 12.5% TS assay achieved 80% higher biogas yield (679 mL/gVS added) over mono-digestion, i.e., highest among the TS% studied, with 48% VS removal. In conclusion, co-digestion of mixed feedstocks with ISR 2, C:N 35, and TS 12.5% could degrade almost half of the substrate available for biodegradation. Further biodegradation may require pretreatment of the recalcitrant WS. Modified Gompertz, first-order, transference, and logistic models were used for kinetic study and curve fitting of experimental data. For the optimized batch assays, the estimated specific rate constants were 0.08, 0.12, 0.083, and 0.084. The data fits well in all the models, with the coefficient of discrimination (R²) ranging from 0.882 to 0.999.

Variations in antibiotic resistance genes and removal mechanisms induced by C/N ratio of substrate during composting

For a comprehensive insight into the potential mechanism of the removal of antibiotic resistance genes (ARGs) removal induced by initial substrates during composting, we tracked the dynamics of physicochemical properties, bacterial community composition, fungal community composition, the relative abundance of ARGs and mobile genetic genes (MGEs) during reed straw and cow manure composting with different carbon to nitrogen ratio. The results showed that the successive bacterial communities were mainly characterized by the dynamic balance between Firmicutes and Actinobacteria, while the fungal communities were composed of Ascomycota. During composting, the interactions between bacteria and fungi were mainly negative. After composting, the removal efficiency of ARGs in compost treatment with C/N ≈ 26 (LL) was higher than that in compost treatment with C/N ≈ 35 (HL), while MGEs were completely degraded in HL and enriched by 2.3% in LL. The large reduction in the relative abundance of ARGs was possibly due to a decrease in the potential host bacterial genera, such as Advenella, Tepidimicrobium, Proteiniphilum, Acinetobacter, Pseudomonas, Flavobacteria and Arcbacter. Partial least-squares path modeling (PLS-PM) revealed that the succession of bacterial communities played a more important role than MGEs in ARGs removal, while indirect factors of the fungal communities altered the profile of ARGs by affecting the bacterial communities. Both direct and indirect factors were affected by composting treatments. This study provides insights into the role of fungal communities in affecting ARGs and highlights the role of different composting treatments with different carbon to nitrogen ration on the underlying mechanism of ARGs removal.

Effect of creating a fed-batch like condition using carbon to nitrogen ratios on lipid accumulation in Rhodosporidium toruloides-1588

Utilizing the undetoxified wood hydrolysate to accumulate maximum lipids in Rhodosporidium toruloides under optimum conditions has been regarded as a renewable and cost-effective strategy. The current investigation aims to identify the best carbon to nitrogen (C/N 20, 70, and 120) ratio for maximum lipid accumulation in R. toruloides-1588 using wood hydrolysate. Additionally, a fed-batch-like condition was employed, where C/N ratios were maintained during the fermentation that inherently decreases in batch fermentation. The C/N ratio 70 has been identified as the best condition with 3 times higher lipid accumulation (43% w/w) than the control. Additionally, >95% and 70% of glucose and xylose consumption were observed, respectively. Moreover, 50% increase in polyunsaturated fatty acids compared to the control media reinforced the potential of R. toruloides-1588 to thrive on undetoxified hydrolysate, high lipid productivity (3.8 mg/g of dry weight per hour) and produce high value monosaturated and polyunsaturated fatty acids.

Soil type regulates carbon and nitrogen stoichiometry and mineralization following biochar or nitrogen addition

Most studies on the effects of biochar and fertilizer on soil carbon (C) and nitrogen (N) mineralization, and microbial C and N content, are restricted to a single soil type, limiting our understanding of the interactions between these factors and microbial functions. To address this paucity in knowledge, we undertook a 3-year experiment using four contrasting soils to assess the role of peanut shell biochar and fertilizer on C and N mineralization, microbial C and N, and N stoichiometry. Across all four soils, biochar significantly (P < 0.05) increased soil carbon mineralization (C_min) and nitrogen mineralization (N_min) over three years compared to fertilizer and the control. Biochar also increased total C (C_soil) across the four soils in year 1, with the Fluvisol recording greater total C in year 2 and Phaeozem having greater total C in year 3. Biochar resulted in a higher microbial biomass C (C_mic), total N (N_soil) and microbial biomass N (N_mic); the degree of change was closely related to C_soil and N_soil. There was a positive correlation between C_mic:N_mic and C_soil:N_soil; while C_soil and C_mic increased following amendment with biochar, which reduced the soil C and N stoichiometric imbalance (N_imb) caused by the increase in the C to N ratio. However, fertilizer exacerbated the imbalance of soil C and N stoichiometry. Fertilizer also reduced the C_soil:N_soil and C_mic:N_mic ratios. Soil pH had a positive correlation with C_soil, C_mic, N_mic, C_min, N_min, C_soil:N_soil, C_mic:N_mic, and biochar increases this correlation. The soil pH was negatively correlated with C_imb:N_imb and N_soil. Fertilizer was positively correlated C_imb:N_imb and N_soil. In contrast, fertilizer N application lowered microbial biomass C:N. We conclude that biochar reduces the imbalance of soil C and N stoichiometry, whereas fertilizer increased this imbalance. Biochar had a greater impact on C and N in soils with a lower pH.

C/N ratio and carbon source-dependent lipid production profiling in Rhodotorula toruloides

Microbial oils are lipids produced by oleaginous microorganisms, which can be used as a potential feedstock for oleochemical production. The oleaginous yeast Rhodotorula toruloides can co-produce microbial oils and high-value compounds from low-cost substrates, such as xylose and acetic acid (from hemicellulosic hydrolysates) and raw glycerol (a byproduct of biodiesel production). One step towards economic viability is identifying the best conditions for lipid production, primarily the most suitable carbon-to-nitrogen ratio (C/N). Here, we aimed to identify the best conditions and cultivation mode for lipid production by R. toruloides using various low-cost substrates and a range of C/N ratios (60, 80, 100, and 120). Turbidostat mode was used to achieve a steady state at the maximal specific growth rate and to avoid continuously changing environmental conditions (i.e., C/N ratio) that inherently occur in batch mode. Regardless of the carbon source, higher C/N ratios increased lipid yields (up to 60% on xylose at a C/N of 120) but decreased the specific growth rate. Growth on glycerol resulted in the highest specific growth and lipid production (0.085 g lipids/gDW*h) rates at C/Ns between 60 and 100. We went on to study lipid production using glycerol in both batch and fed-batch modes, which resulted in lower specific lipid production rates compared with turbisdostat, however, fed batch is superior in terms of biomass production and lipid titers. By combining the data we obtained in these experiments with a genome-scale metabolic model of R. toruloides, we identified targets for improvements in lipid production that could be carried out either by metabolic engineering or process optimization.

Influence of carbon type and carbon to nitrogen ratio on the biochemical methane potential, pH, and ammonia nitrogen in anaerobic digestion

Organic waste used as a feedstock in the anaerobic digestion (AD), it includes carbon and nitrogen. Carbon and nitrogen have an effect on the various digestive characteristics during AD, however, the study is rare about those of the interaction. This study investigates the influence of carbon type and carbon to nitrogens (C/N ratios) on the AD characteristics of organic waste. Experimental treatments involved a combination of three carbon types with three C/N ratios. The AD tests were carried out using a 125-mL serum bottle at a constant temperature of 37°C and moisture 95% for 18 days. Degradation pattern shows the difference among three-carbon treatments, the starch group was faster than other groups. Maximum methane production date was similar between starch (9.96 ± 0.05 day) and xylan group (10.0 ± 0.52 day), those of the cellulose group (14.6 ± 1.80 day) was slower than other groups (p < 0.05). The lag phase was only affected by the carbon type (p < 0.05). Ammonia nitrogen was mainly affected by nitrogen concentration regardless of carbon type (p < 0.05). This study showed that xylan is useful as feedstock in order to decrease the lag phase, and it showed that ammonia was independently affected by the nitrogen concentration.

Impact of carbon to nitrogen ratio on the performance of aerobic granular reactor and microbial population dynamics during aerobic sludge granulation

Carbon to nitrogen (C/N) ratio is one of the most important factor affecting aerobic granular sludge (AGS) growth and pollutant removal in aerobic granular sludge sequencing batch reactor (AGSBR). For stability of sludge granulation process, AGSs were domesticated in five sequence batch reactors (SBRs) with different C/N ratios (6, 7, 8, 9, and 10), which the ammonia nitrogen concentration of influent was 165 mg/L. The effects of C/N ratio on morphology and property of AGS were studied. The results showed that stable AGS was yielded with good settleability, high pollutant removal efficiency and rich microbial diversity when C/N ratio was 8. AGS yielded had stable structure due to higher protein in extracellular polymeric substances (EPS). High throughput 16S rDNA gene analysis revealed the microbial community diversity increased in AGS under the C/N ratio. The dominant microbes changed at the phylum, class and family three levels with the increasing operation time.

Synergistic co-digestion of wastewater grown algae-bacteria polyculture biomass and cellulose to optimize carbon-to-nitrogen ratio and application of kinetic models to predict anaerobic digestion energy balance

This study investigated enhancing methane production from algal-bacteria biomass by adjusting the C/N ratio through co-digestion with a nitrogen-poor co-substrate - cellulose. A biomethane potential test was used to determine cumulative biogas and methane production for pure and co-digested substrates. Four kinetic models were evaluated for their accuracy describing experimental data. These models were used to estimate the total energy output and net energy ratio (NER) for a scaled AD system. Increasing the algal C/N ratio from 5.7 to 20-30 (optimal algae:cellulose feedstock ratios of 35%:65% and 20%:80%) improved the ultimate methane yield by >10% and the first ten days production by >100%. The modified Gompertz kinetic model demonstrated highest accuracy, predicting that co-digestion improved methane production by reducing the time-lag by ∼50% and increasing rate by ∼35%. The synergistic effects increase the AD system energy efficiency and NER by 30-45%, suggesting potential for substantial enhancements from co-digestion at scale.

Grass Pollen Affects Survival and Development of Larval Anopheles arabiensis (Diptera: Culicidae)

Nutrients in breeding sites are critical for the survival and development of malaria mosquitoes, having a direct impact on vectorial capacity. Yet, there is a limited understanding about the natural larval diet and its impact on the individual fitness of mosquitoes. Recent studies have shown that gravid Anopheles arabiensis Patton (Diptera: Culicidae) are attracted by and oviposit in grass-associated habitats. The pollen provided by these grasses is a potential source of nutrients for the larvae. Here, we assess the effect of Typha latifolia L. (Poales: Typhaceae), Echinochloa pyramidalis Lamarck, Pennisetum setaceum Forsskål, and Zea mays L. pollen on larval survival and rate of development in An. arabiensis under laboratory conditions. In addition, we characterize the carbon to nitrogen ratio and the size of pollen grains as a measure of diet quality. Carbon-rich pollen with a small grain size (T. latifolia and P. setaceum; 9.7 ± 0.3 × 103 and 5.5 ± 0.2 × 104 µm3, respectively) resulted in enhanced rates of development of An. arabiensis. In contrast, the larva fed on the nitrogen-rich control diet (TetraMin) was slower to develop, but demonstrated the highest larval survival. Larvae fed on carbon-rich and large-grained Z. mays pollen (4.1 ± 0.2 × 105 µm3) survived at similar levels as those fed on the control diet and also took a longer time to develop compared with larvae fed on the other pollens. While males and females did not appear to develop differently on the different pollen diets, males consistently emerged faster than their female counterparts. These results are discussed in relation to integrated vector management.

Enhancing rock phosphate integration rate for fast bio-transformation of cow-dung waste-paper mixtures to organic fertilizer

Rock phosphate (RP) addition in cow-dung waste-paper mixtures at rates above 2% P has been reported to increase the rate of bio-transformation and humification of organic waste mixtures during vermicomposting to produce organic fertilizer for organic farming. However, the optimization of RP for vermicomposting was not established. The objective of this study was to determine the optimal amount of RP integration rates for effective bio-transformation of cow-dung waste-paper mixtures. Arrays of RP integration degrees (0, 0.5, 1, 1.5, 2, and 4% P as RP) were thoroughly mixed with cow- dung waste-paper mixtures to achieve an optimized C:N ratio of 30 and allowed to vermidegrade following the introduction of earthworms at a stocking mass of 12.5 g-worms kg⁻¹. The bio-transformation of the waste mixtures was examined by measuring C:N ratios and humification index (HI) and per cent ash and volatile solids. Application of 1% P as RP resulted in fast bio-transformation and maturation of cow-dung waste-paper mixtures. A scanning electron microscopy (SEM) was used to evaluate the morphological properties of the different vermicomposts affected by rates of RP showing the degree of degradation of initial compacted aggregates of cellulose and protein fibres in the mixtures at maturity. A germination test was used to further determine phytotoxicity of the final composts and microbial biomass assessment. The final vermicompost (organic fertilizer) had a C:N ratio of 7, MBC of 900 mg kg⁻¹ and HI of 27.1%. The RP incorporation rate of 1% P of RP investigated is therefore, recommended for efficient vermidegradation and humification of cow-dung waste-paper mixtures. However, higher rates of RP incorporation should be considered where greater P enrichment of the final vermicompost (organic fertilizer) is desired.

Effects of adjacent land-use types on the distribution of soil organic carbon stocks in the montane area of central Taiwan

BACKGROUND

Soil organic carbon (SOC) stocks can be altered through reforestation and cropping. We estimated the effects of land use on SOC stocks after natural deciduous forests replaced by crops and coniferous plantations by examining the vertical distribution of SOC stocks at different depth intervals in an adjacent Oolong tea (Camellia sinensis L.) plantation, Moso bamboo (Phyllostachys pubescens) forest, Japanese cedar (Cryptomeria japonica) forest, and Taiwania (Taiwania cryptomerioides) forest in central Taiwan. The main soil characteristics, soil nitrogen (N) content, and soil carbon to nitrogen (C/N) ratio were also determined.

RESULTS

Different land uses resulted in significantly higher bulk density, lower cation exchange capacity, SOC, soil N, soil C/N ratio, and SOC stocks in croplands compared to forestlands. Due to the long-term application of chemical fertilizers, a significantly lower soil pH was found in the tea plantation. Croplands had a lower soil C/N ratio because of less C input into the soil and a higher mineralization rate of organic carbon during cultivation. Similar SOC stocks were found in Taiwania and Japanese cedar forests (148.5 and 151.8 Mg C ha^-1, respectively), while the tea plantation had comparable SOC stocks to the bamboo forest (101.8 and 100.5 Mg C ha^-1, respectively). Over 40% of SOC stocks was stored in croplands and over 56% was stored in forestland within the upper 10 cm of soil.

CONCLUSIONS

Coniferous plantations can contribute to a higher SOC stock than croplands, and a significant difference can be found in the top 0-5 cm of soil.

Changes in light quality alter physiological responses of soybean to thiamethoxam

MAIN CONCLUSION

The interaction between neighboring weed-induced far-red enriched light and thiamethoxam can significantly alter soybean seedling morphology, nodulation, isoflavone levels, UV-absorbing phenolics, and carbon and nitrogen content. Neonicotinoid insecticides that are widely used on major crop plants can enhance plant growth and yield. Although the underlying mechanism of this enhanced growth and yield is not clear, recent studies suggest that neonicotinoids such as thiamethoxam (TMX) may exert their effects at least in part via signals that involve salicylic acid (SA) and jasmonic acid (JA). In the current research, effects of TMX on morphological and physiological responses of soybean have been compared under far-red-depleted (FR-D) and far-red-enriched (FR-E) light reflected by neighboring weeds. TMX significantly enhanced shoot and root growth but did not prevent stem elongation under FR-E light. Also, TMX did not prevent reductions in shoot carbon content and shoot carbon to nitrogen ratio under FR-E light. Despite similarities between these TMX effects in soybean and those known for SA and JA in other plant species, TMX significantly enhanced root-nodule numbers per plant and levels of root isoflavones malonyl-daidzin and malonyl-genistin under FR-E light only. These results suggest that the combined effect of FR-E light and TMX triggers a mechanism that operates concomitantly to enhance root isoflavones and nodulation in soybean.

Biological nitrate removal using a food waste-derived carbon source in synthetic wastewater and real sewage

The production of volatile fatty acids (VFAs) from food waste to improve biological nutrient removal has drawn much attention. In this study, acidogenic liquid from food waste was used as an alternative carbon source for synthetic wastewater treatment. C/N ratios of 5 and 6 were suitable for denitrification, and the change in acidogenic liquid composition had no negative effect on denitrification. The denitrification rates using optimal carbon-to-nitrate ratios of acidogenic liquid were more than 25 mg NO3-N/(gVSS·h). At the same time, acidogenic liquid was used to improve nutrient removal from summer and winter sewage. C/N ratios of 5 and 6 were acceptable for summer sewage treatment. Total nitrogen in the final effluent was less than 7 mg/L. Two additional hours were required for winter sewage treatment, and the C/N ratio had to be >6.

Physicochemical profile of microbial-assisted composting on empty fruit bunches of oil palm trees

This study was carried out to investigate the physicochemical properties of compost from oil palm empty fruit bunches (EFB) inoculated with effective microorganisms (EM∙1™). The duration of microbial-assisted composting was shorter (∼7 days) than control samples (2 months) in a laboratory scale (2 kg) experiment. The temperature profile of EFB compost fluctuated between 26 and 52 °C without the presence of consistent thermophilic phase. The pH of compost changed from weak acidic (pH ∼5) to mild alkaline (pH ∼8) because of the formation of nitrogenous ions such as ammonium (NH4 (+)), nitrite (NO2 (-)), and nitrate (NO3 (-)) from organic substances during mineralization. The pH of the microbial-treated compost was less than 8.5 which is important to prevent the loss of nitrogen as ammonia gas in a strong alkaline condition. Similarly, carbon mineralization could be determined by measuring CO2 emission. The microbial-treated compost could maintain longer period (∼13 days) of high CO2 emission resulted from high microbial activity and reached the threshold value (120 mg CO2-C kg(-1) day(-1)) for compost maturity earlier (7 days). Microbial-treated compost slightly improved the content of minerals such as Mg, K, Ca, and B, as well as key metabolite, 5-aminolevulinic acid for plant growth at the maturity stage of compost. Graphical Abstract Microbial-assisted composting on empty fruit bunches.

Thermomyces lanuginosus is the dominant fungus in maize straw composts

The microbial community composition and function of three self-heating maize straw composts were compared by integrated meta-omics. The results revealed that the fungal communities were primarily dominated by the phylum Ascomycota (>90%) regardless of different nitrogen sources, which were exclusively composed of the Thermomyces, a genus of hemicellulose degraders. The bacterial community composition was affected by the addition of nitrogen sources, as the abundance of the Actinobacteria increased, while the Proteobacteria and Bacteroidetes decreased. Various hemicellulases and cellulases were detected in the composts, and the major xylanase secreted by Thermomyces lanuginosus was always present, revealing that it was the dominant fungus in hemicellulose hydrolysis and that bacteria and fungi might synergistically degrade lignocellulose. Thus, microbial communities in composts may develop a simple and stable structure of a dominant fungal species and limited numbers of bacterial species under the selective pressure of high temperature and maize straw as starting materials.

Alkyl polyglucose enhancing propionic acid enriched short-chain fatty acids production during anaerobic treatment of waste activated sludge and mechanisms

Adding alkyl polyglucose (APG) into an anaerobic treatment system of waste activated sludge (WAS) was reported to remarkably improve the production of short-chain fatty acids (SCFAs), especially propionic acid via simultaneously accelerating solubilization and hydrolysis, enhancing acidification, inhibiting methanogenesis and balancing carbon to nitrogen (C/N) ratio of substrate. Not only the production of SCFAs, especially propionic acid, was significantly improved by APG, but also the feasible operation time was shortened. The SCFAs yield at 0.3 g APG per gram of total suspended solids (TSS) within 4 d was 2988 ± 60 mg chemical oxygen demand (COD) per liter, much higher than that those from sole WAS or sole WAS plus sole APG. The corresponding yield of propionic acid was 1312 ± 25 mg COD/L, 7.9-fold of sole WAS. Mechanism investigation showed that during anaerobic treatment of WAS in the presence of APG both the solubilization and hydrolysis were accelerated and the acidification was enhanced, while the methanogenesis was inhibited. Moreover, the activities of key enzymes involved in WAS hydrolysis and acidification were improved through the adjustment of C/N ratio of substrates with APG. The abundance of microorganisms responsible for organic compounds hydrolysis and SCFAs production was also observed to be greatly enhanced with APG via 454 high-throughput pyrosequencing analysis.

Ecological correlates of seed mass variation in Phoradendron juniperinum, a xylem-tapping mistletoe

We investigated several ecological correlates of seed mass variation in the hemiparasitic, xylemtapping mistletoe, Phoradendron juniperinum. Mean seed mass varied two-fold among plants between the ages of 4 and 14 years old and was positively correlated with parental plant age. Both the standard deviation and the coefficient of variation in mean seed mass decreased with increasing plant age demonstrating that, on average, younger plants produced seed with more variable mass. Nitrogen concentrations (mg nitrogen per gram of seed) of both the seed and "fruit" (pericarp) were not correlated with mass or the age of the parent plant from which the seed was taken. However, the nitrogen content per seed (mg nitrogen per seed) was positively correlated with the mean seed dry mass and the age of the seed parent, suggesting that the carbon to nitrogen ratio of individual seeds remained relatively constant as seed mass increased and plants grew older. Seed germination ranged between 20% and 86% and was positively correlated with mass and parental plant age. Heavier seeds (seeds from older plants) also had the highest root radicle growth rates. Furthermore, the final root radicle length after 76 d of growth was positively correlated with seed dry mass. When grown on a medium containing an extract prepared from the host plant foliage, all seeds showed lower germination, grew more slowly and had shorter overall root radicles, but had significantly greater development of the haustorial "disks" (the holdfast which forms the host-parasite junction in Phoradendron) than seeds grown on a control medium. Our results suggest that, on average, seeds of greater mass produced by older plants have a greater total resource pool per propagule (fruit + seed). This resource pool may be important in conferring a greater potential for dispersal (fruit), survival, colonization, and establishment.