•Compost treated lettuce contain less nitrate than inorganically fertilized ones.•Compost addition improved soil characteristics after two successive lettuce crops.•The use of compost in lettuce ...saves 66kgNha−1 from inorganic sources.•Compost additions increase soil P concentrations and organic C and N pools.
Intensive crop over-fertilization is causing the diffuse contamination of superficial and ground-waters by nitrates in many Mediterranean areas. At the same time this practice is also damaging the soil in the long-term. In this work the feasibility of using composts as total or partial substitutes for conventional inorganic fertilization (CIF) was evaluated in two successive crops of lettuce (Lactuca sativa L.), one of the most consumed vegetables in Europe. The aim was to offer alternative agricultural practices that are more environmentally friendly. Treatments consisting of various rates of inorganic and organic fertilizers (composts) were assayed in quadruplicate on a sandy loam soil classified as Haplic Calcisol in Southern Spain. Macro- and micronutrients and heavy metal concentrations were analysed in soil and plant leaves. Parameters such as soil basal respiration (BR), microbial biomass C (Cmic) and dehydrogenase (DHA) and hydrolase activities, indicators of soil microbial abundance and activity, were also determined after each crop. After the second lettuce crop, certain physical soil properties such as aggregate stability and soil water holding capacity were also determined. In the first crop lettuce yields in the compost-treated soils did not significantly (p≤ 0.05) differ from the yields of CIF-treated soils. In the second crop, however, lettuce yields were higher in organically treated soils than in soils receiving only inorganic fertilization. Organic fertilizers were able to supply sufficient nutrients to achieve similar yields as those obtained with additional inorganic fertilizer. After the second crop, organically treated soils also showed higher C, N, P concentrations and higher Cmic, BR and DHA than soils receiving conventional inorganic fertilization as well as improved physical conditions (a higher percentage of stable soil aggregates and a greater water holding capacity). Also after the second lettuce crop, compost-treated soils showed significantly higher β-glucosidase and phosphatase activity than CIF-treated soils. Furthermore, lettuces grown in compost-treated soils showed significantly lower leaf nitrate concentration than lettuces grown in soil receiving CIF, thus reducing the potential toxicological risks associated with consuming nitrate-rich foods. Moreover, compost fertilization did not increase the concentration of heavy metals in lettuce leaves. Results confirm that manure and sewage sludge composts can be used as an alternative to inorganic fertilization in lettuce crop cultivation, leading to similar or even higher yields and reducing nutrient-leaching risks, while improving soil chemical, physical and microbiological properties.
The phytoremediation potential of 14 different plant species belonging to C3 and C4 carbon fixation pathway for soils spiked with polycyclic aromatic hydrocarbons (PAHs) such as benzoapyrene (BaP) ...and pyrene (PYR) was investigated. A glasshouse experiment was conducted to measure the changes in morphological, physiological, biochemical parameters and the bioaccumulation and biodegradation ability of the plants in soils spiked with 48 and 194 mg kg−1 of BaP and PYR, respectively. The per cent removal efficacy of BaP and PYR by the tested plant species over a period of 50 days was from 6 to 26% and 14 to 40% respectively. The maximum removal of both BaP and PYR was observed in Sudan grass (C4), vetiver (C4), maize (C4), and sunflower (C3). In terms of accumulation in root and shoot, the concentration of PYR was higher in both C3 and C4 plant species when compared to BaP. Overall the results indicated that C4 plants were more efficient than their C3 counterparts in terms of morphological, physiological, biochemical and degradation ability of PAHs.
•Plants tolerant to BaP and pyrene were identified.•C4 plants outperformed C3 plants in remediation of PAH contaminated soils.•The efficiency of plants in dissipating pyrene from soil was higher than BaP.•Residual BaP & pyrene significantly differed between unplanted & planted soils.
•Pioneering application of Mn2+-based catalytic ozonation conditioning to in-situ sludge reduction.•Doubled the MLSS reduction rate in sludge and a 19% decrease in observed sludge yield.•Significant ...increase in peak dehydrogenase activity from 143.83 to 176.41 mg TF/g TSS·hr.•An 18% promotion in the maximum utilization of carbon sources by microorganisms.•Enhancement of sludge reduction and solubilization dominated by Defluviicoccus and Ferruginibacter.
To improve the sludge conditioning efficiency without increasing the ozone dose, an in-situ sludge reduction process based on Mn2+-catalytic ozonation conditioning was proposed. Using ozone conditioning alone as a control, a lab-scale sequencing batch reactor coupled with ozonated sludge recycle was evaluated for its operating performance at an ozone dose of 75 mg O3/g VSS and 1.5 mmol/L Mn2+ addition. The results showed a 39.4% reduction in MLSS and an observed sludge yield of 0.236 kg MLSS/kg COD for the O3+Mn2+ group compared to the O3 group (15.3% and 0.292 kg MLSS/kg COD), accompanied by better COD, NH4+-N, TN and TP removal, improved effluent SS and limited impact on excess sludge properties. Subsequently, activity tests, BIOLOG ECO microplates and 16S rRNA sequencing were applied to elucidate the changing mechanisms of Mn2+-catalytic ozonation related to microbial action: (1) Dehydrogenase activity reached a higher peak. (2) Microbial utilization of total carbon sources had an elevated effect, up to approximately 18%, and metabolic levels of six carbon sources were also increased, especially for sugars and amino acids most pronounced. (3) The abundance of Defluviicoccus under the phylum Proteobacteria was enhanced to 12.0% and dominated in the sludge, they had strong hydrolytic activity and metabolic capacity. Denitrifying bacteria of the genus Ferruginibacter also showed an abundance of 7.6%, they contributed to the solubilization and reduction of sludge biomass. These results could guide researchers to further reduce ozonation conditioning costs, improve sludge management and provide theoretical support.
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Labile fractions of soil organic matter (SOM) have been used as indicators for land use induced changes in soil quality. Differences in soil C pools under row crop production and uncultivated soils ...may provide information about soil C sequestration. The impact of agroforestry consisting of poplar with wheat, rice–wheat, maize–wheat and sugarcane agro-ecosystems on total organic carbon (TOC) and labile pools, viz. water-extractable (WEOC), hot water-soluble (HWC), KMnO4-oxidizable, microbial biomass and mineralizable C; and organic C fractions of different oxidizability was studied at 22-sites for each land use. Cultivation resulted in decrease in TOC (21–36%) and dehydrogenase activity (by 2.8–3.4mgkg−1soilh−1) compared to uncultivated soils. Labile C pools, except WEOC, were correlated (P<0.05), though the amount extracted by different methods varied considerably suggesting that each method enumerated different fractions of TOC. Agroforestry and sugarcane systems were characterized by very labile C compared with uncultivated soils and the soils under rice–wheat and maize–wheat systems. Conversely, uncultivated soils and the soils under maize–wheat and rice–wheat held greater proportion of organic C in recalcitrant fractions. Results suggest that soil organic C (SOC) pools in agroforestry and sugarcane systems could be decomposed under land use alterations. However, no single soil C pool alone was suitable as a sensitive indicator for land use induced changes in SOM. A composite of soil indicators encompassing labile C, KMnO4-oxidizable C, non-labile and recalcitrant C, mineralizable C, basal soil respiration, and dehydrogenase activity could distinguish different land use systems.
•Cultivation of undisturbed soils results in decline in soil organic carbon stocks.•Land-use influences the quality of soil organic matter.•Agroforestry and sugarcane systems are characterized by labile carbon pool.•Maize–wheat and rice–wheat soils show predominance of recalcitrant carbon pool.•No single C pool can serve as indicator of land-use changes on soil organic matter.
Enzymes are potent catalysts that increase biochemical reaction rates by several orders of magnitude. Flavoproteins are a class of enzymes whose classification relies on their ability to react with ...molecular oxygen (O2) during catalysis using ionizable active site residues. Pseudomonas aeruginosa D-arginine dehydrogenase (PaDADH) is a flavoprotein that oxidizes D-arginine for P. aeruginosa survival and biofilm formation. The crystal structure of PaDADH reveals the interaction of the glutamate 246 (E246) side chain with the substrate and at least three other active site residues, establishing a hydrogen bond network in the active site. Additionally, E246 likely ionizes to facilitate substrate binding during PaDADH catalysis. This study aimed to investigate how replacing the E246 residue with leucine affects PaDADH catalysis and its ability to react with O2 using steady-state kinetics coupled with pH profile studies. The data reveal a gain of O2 reactivity in the E246L variant, resulting in a reduced flavin semiquinone species and superoxide (O2•ˉ) during substrate oxidation. The O2•ˉ reacts with active site protons, resulting in an observed nonstoichiometric slope of 1.5 in the enzyme’s log (kcat/Km) pH profile with D-arginine. Adding superoxide dismutase results in an observed correction of the slope to 1.0. This study demonstrates how O2•ˉ can alter the slopes of limbs in the pH profiles of flavin-dependent enzymes and serves as a model for correcting nonstoichiometric slopes in elucidating reaction mechanisms of flavoproteins.
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•A novel approach for utilization of fly ash was adopted.•Studied feasibility of fly ash as an additive in composting of organic wastes.•Fly ash was found a suitable additive for ...in-vessel composting of organic wastes.•Combination of 80% organic waste and 20% fly ash showed better enzymatic activity.•Jaggery was used as an additional carbon source for enhancing microbial activity.
In the present study, fly ash was used as an additive for the rapid composting of biomass and kitchen waste with jaggery as an activator. The in-vessel composting experiments were carried out in ten plastic vessels of 15 L capacity containing varying amounts of fly ash, biomass waste, and kitchen waste. The effect of fly ash on the microbial and enzymatic activity of the composting system was also ascertained. The compost in Vessel No. 10 having a combination of 50% biomass waste, 30% kitchen waste, and 20% fly ash seemed to have a significant effect on the compost quality. Statistical analysis revealed Vessel No. 10 as significantly separated from other vessels whereas microbial activity (342.67 CFU 108/g), pH (8.15), temperature (48.50 °C), and heavy metals, such as Ni (0.1239 mg kg−1), Ba (0.6109 mg kg−1), Cd (0.0004 mg kg−1) were the most influential variables for the separation.
Frequent periods of low rainfall accompanying climate change are expected to affect many aspects of agricultural production and greenhouse gas emissions. In this work, we conducted field experiments ...on soil CO2 efflux and soil microbial activity using two precipitation treatments and two crop management technologies. While the control treatment was exposed to natural precipitation, the reduced water availability was induced during the early stages of crop growth using rain-exclusion shelters within the water deficit treatment. We aimed to test the difference in the response to water deficit between two management technologies: conventional tillage (CT - ploughed without cover crops) and adaptation technology (AT - no-till with species rich cover crops). After a month of simulated water deficit, the soil CO2 efflux under a regime of adaptation technology was essentially the same as that under the conventional technology, and the decrease in soil CO2 efflux ranged between 22 % and 55 %. The water deficit had a technology-specific effect on microbes. While no effect on the microbial carbon under CT was observed, the water deficit decreased Cmic under AT. In contrast, the opposite pattern was observed for DHA. When a normal soil water regime was restored, CO2 efflux recovered rapidly while recovery of microbial biomass and dehydrogenase activity was more variable. Generally, the soil microbial biomass and activity recovered better under AT. The results show that while the reduction in Rs during water deficit and its recovery after the restoration of the ambient precipitation regime were not affected by the technology, the response of microbial biomass and activity to water deficit depended on the technology with better recovery under AT.
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•One-month simulated drought resulted in a decrease in soil CO2 efflux by 22–55 %.•CO2 efflux recovered after the end of the water deficit period.•Response of microbial carbon and DHA to water deficit depended on the tillage.•Adaptation tillage technology showed better post-drought recovery of soil activity.
•The start-up time of anammox process was reduced 26.9% with RGO addition (100mg/L).•The TN removal rate of R2 with RGO addition was enhanced 27.4% on day 229.•The HDH activity of R2 enhanced 42% ...compared with that of control on day 200.•FISH analysis showed the percentage of anammox bacteria was 62.9% in R2 on day 200.
In this study, two upflow column reactors were built up to investigate the effects of reduced graphene oxide (RGO) on the startup of anammox process. Continuous experiments indicated that the start-up period of anammox process with RGO addition could be shortened from 67 to 49days. The further investigation proved that the anammox reactor with RGO addition possessed relatively higher anammox bacteria activity and stronger stability even against the high nitrogen loading rate (NLR) impacting. After 220days cultivation, the nitrogen removal rate of R2 (RGO addition) reached 1.08×103g-N/(m3d), which was 27.4% higher than 0.846×103g-N/(m3d) of the R1 (the control). The hydrazine dehydrogenase (HDH) activity increased dramatically with RGO addition, which could be the trigger of fast anammox start-up. Compared with the control reactor, the quantity of anammox bacteria in R2 increased during the whole operation period by quantitative PCR and fluorescence in situ hybridization analysis.
This study proposes the phytoremediation of a pyrene (PYR)-contaminated soil by Cannabis sativa L. The experimental campaign was conducted along a 60 days period using three different initial PYR ...concentrations (i.e., 50, 100 and 150 mg kg TS−1 of soil) in 300 mL volume pots under greenhouse conditions (18–25 °C and 45–55% humidity). After 60 days of hemp growth and flourishing, the highest PYR removal reached approximately 95% in planted soil, 35% higher than in the unplanted control. PYR accumulation was observed in both roots and aerial parts of the plant, with a higher PYR uptake at increasing initial PYR concentrations in soil. The initial PYR concentration affected the growth and, thus, the phytoremediation potential of C. sativa L., which was the result of different removal mechanisms. Overall, the lowest initial PYR concentration was the one that resulted in the highest PYR removal. The interaction between the plant roots and microorganisms in rhizosphere was likely associated with PYR removal in this study. The highest DHO activity of 66.26 μg INTF g−1 TS−1 was observed in the soil spiked with 50 mg PYR·kg TS−1.
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•Phytoremediation of pyrene (PYR)-contaminated soil by C. sativa L. was investigated.•A PYR removal of 95% was achieved at a PYR concentration of 50 mg kg TS−1 of soil.•Growth of C. sativa L. biomass was negatively affected at higher PYR concentrations.•Dehydrogenase activity was a good indicator of PYR degradation in planted soil.•Proteobacteria and Firmicutes were the most abundant PYR-degrading phyla.
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Bacteria able to produce biosurfactants can use petroleum-based hydrocarbons as a carbon source. Herein, four biosurfactant-producing Pseudomonas aeruginosa strains, isolated from ...oil-contaminated saline soil, were combined to form a bacterial consortium. The inoculation of the consortium to contaminated soil alleviated the adverse effects of salinity on biodegradation and increased the rate of degradation of petroleum hydrocarbon approximately 30% compared to the rate achieved in non-treated soil. In saline condition, treatment of polluted soil with the consortium led to a significant boost in the activity of dehydrogenase (approximately 2-fold). A lettuce seedling bioassay showed that, following the treatment, the soil's level of phytotoxicity was reduced up to 30% compared to non-treated soil. Treatment with an appropriate bacterial consortium can represent an effective means of reducing the adverse effects of salinity on the microbial degradation of petroleum and thus provides enhancement in the efficiency of microbial remediation of oil-contaminated saline soils.
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