Given the rapidly increasing use of metal oxide nanoparticles in agriculture as well as their inadvertent addition through sewage sludge application to soils, it is imperative to assess their ...possible toxic effects on soil functions that are vital for healthy crop production. In this regard, we designed a lab study to investigate the potential toxicity of one of the most produced nanoparticles, i.e. zinc oxide nanoparticles (nZnO), in a calcareous soil. Microcosms of 80 g of dry-equivalent fresh soils were incubated in mason jars for 64 days, after adding 100 or 1000 mg of biogenically produced nZnO kg
soil. Moreover, we also added rice-straw derived biochar at 1 or 5% (w: w basis) hypothesizing that the biochar would alleviate nZnO-induced toxicity given that it has been shown to adsorb and detoxify heavy metals in soils. We found that the nZnO decreased microbial biomass carbon by 27.0 to 33.5% in 100 mg nZnO kg
soil and by 39.0 to 43.3% in 1000 mg nZnO kg
soil treatments across biochar treatments in the short term i.e. 24 days after incubation. However, this decrease disappeared after 64 days of incubation and the microbial biomass in nZnO amended soils were similar to that in control soils. This shows that the toxicity of nZnO in the studied soil was ephemeral and transient which was overcome by the soil itself in a couple of months. This is also supported by the fact that the nZnO induced higher cumulative C mineralization (i.e. soil respiration) at both rates of addition. The treatment 100 mg nZnO kg
soil induced 166 to 207%, while 1000 mg nZnO kg
soil induced 136 to 171% higher cumulative C mineralization across biochar treatments by the end of the experiment. However, contrary to our hypothesis increasing the nZnO addition from 100 to 1000 mg nZnO kg
soil did not cause additional decrease in microbial biomass nor induced higher C mineralization. Moreover, the biochar did not alleviate even the ephemeral toxicity that was observed after 24d of incubation. Based on overall results, we conclude that the studied soil can function without impairment even at 1000 mg kg
concentration of nZnO in it.
Most current models of soil C dynamics predict that climate warming will accelerate soil C mineralization, resulting in a long‐term CO2 release and positive feedback to global warming. However, ...ecosystem warming experiments show that CO2 loss from warmed soils declines to control levels within a few years. Here, we explore the temperature dependence of enzymatic conversion of polymerized soil organic C (SOC) into assimilable compounds, which is presumed the rate‐limiting step of SOC mineralization. Combining literature review, modelling and enzyme assays, we studied the effect of temperature on activity of enzymes considering their thermal inactivation and catalytic activity. We defined the catalytic power of enzymes (Epower) as the cumulative amount of degraded substrate by one unit of enzyme until its complete inactivation. We show a universal pattern of enzyme's thermodynamic properties: activation energy of catalytic activity (EAcat) < activation energy of thermal inactivation (EAinact). By investing in stable enzymes (high EAinact) having high catalytic activity (low EAcat), microorganisms may maximize the Epower of their enzymes. The counterpart of such EAs’ hierarchical pattern is the higher relative temperature sensitivity of enzyme inactivation than catalysis, resulting in a reduction in Epower under warming. Our findings could explain the decrease with temperature in soil enzyme pools, microbial biomass (MB) and carbon use efficiency (CUE) reported in some warming experiments and studies monitoring the seasonal variation in soil enzymes. They also suggest that a decrease in soil enzyme pools due to their faster inactivation under warming contributes to the observed attenuation of warming effect on soil C mineralization. This testable theory predicts that the ultimate response of SOC degradation to warming can be positive or negative depending on the relative temperature response of Epower and microbial production of enzymes.
While most current models of soil C dynamics predict that climate warming will accelerate soil CO2 release, ecosystem warming experiments show that soil CO2 loss declines to control levels within a few years. We re‐analysed the temperature dependence of biological processes (e.g. soil C degradation) by focusing on an overlooked process, the thermal inactivation of enzymes. We show a universal pattern of enzyme's thermodynamic properties leading to decrease in enzymes catalytic power with temperature. Our findings can explain the attenuation with time of warming effect on soil respiration and provide new insights for understanding organism's response to their thermal environment.
Climate and land-use changes modify plant rooting depth, signifying that organic matter with long residence times in deep soil layers can be exposed to rhizospheres and associated microbial ...activities. The presence of roots in soils stimulates mineralization of native soil C, via a process termed the rhizosphere priming effect (RPE), which may in consequence lead to loss of soil C. By growing a deep rooting grass, Festuca arundinacea, on soil columns and under continuous dual labelling (13C- &14C-CO2), we show that root penetration up to 80 cm into a soil profile stimulated mineralization of ∼15,000 year-old soil C. The RPE, after normalization with root biomass, was similar along the soil profile indicating that deep C is as vulnerable to priming as surface C. The RPE was strongly correlated with respiration of plant-derived C, and a PLFA marker representative of saprophytic fungi (18:2ɷ6c) across all soil layers. Moreover, experimental disruption of soil structure further stimulated soil C mineralization. These findings suggest that the slow soil C mineralization in deep layers results from an impoverishment of energy-rich plant C for microorganisms (especially for saprophytic fungi), combined with a physical disconnection between soil C and microorganisms. Based on our results, we anticipate higher mineralization rates of deep millennia-old SOM in response to deeper root penetration which could be induced by changes in agricultural practices and climate.
•The vulnerability of deep C to mineralization was assessed in a mesocosm experiment.•A deep rooting grass was cultivated on soil columns with under dual (13C &14C-CO2) labelling.•Deep roots stimulated microbial mineralization of ∼15,000 years old C.•Deep C is as vulnerable to rhizosphere-induced mineralization as the surface C.
In this study, a pre-isolated dye-decolorizing bacterium,
Pseudomonas aeruginosa
ZM130, was tested to explore its potential for the treatment of synthetic and real textile wastewaters in aerobic and ...anaerobic bench-scale sequencing batch bioreactors (SBRs) as well as in constructed soil columns. The decolorizing ability of strain ZM130 against reactive black-5 (RB5) was optimized following a response surface methodology (RSM)-based approach, and this strain was observed to effectively decolorize RB5 even in presence of a substantial quantity of NaCl salt along multi-metal mixture including Cr
6+
, Pb
2+
, Cd
2+
, and Zn
2+
. In the SBR containing the immobilized cells of the strain ZM130, more than 80% of the RB5, hexavalent chromium Cr(VI), and chemical oxygen demand (COD) were removed from the textile wastewater under partially anaerobic condition using yeast extract as an additional carbon co-substrate. Furthermore, while studying the bioremediating ability of strain ZM130 in constructed soil columns, the maximum color removal (> 90%), Cr(VI) removal (> 95%), and COD removal (> 90%) were achieved in the soil columns bioaugmented with ZM130 together with either sludge or yeast extract. Interestingly, it was further noticed that soil columns augmented with
P. aeruginosa
ZM130 also showed maximum color removal from real textile wastewater in vertical columns filled with sterilized (> 87%) and non-sterilized soil (> 91%). Based on the results of the present research work, it can be concluded that
P. aeruginosa
ZM130 can serve as an excellent potential candidate for treatment of textile wastewaters in bioreactors as well as in soils.
Discharge of untreated textile wastewaters loaded with dyes is not only contaminating the soil and water resources but also posing a threat to the health and socioeconomic life of the people. Hence, ...there is a need to devise the strategies for effective treatment of such wastewaters. The present study reports the catalytic potential of biogenic ZnO nanoparticles (ZnO NPs) synthesized by using a bacterial strain
Pseudochrobactrum
sp. C5 for degradation of dyes and wastewater treatment. The catalytic potential of the biogenic ZnO NPs for degradation of dyes and wastewater treatment was also compared with that of the chemically synthesized ones. The characterization of the biogenic ZnO NPs through FT-IR, XRD, and field emission scanning electron microscopy (FESEM) indicated that these are granular agglomerated particles having a size range of 90–110 nm and zeta potential of −27.41 mV. These catalytic NPs had resulted into almost complete (> 90%) decolorization of various dyes including the methanol blue and reactive black 5. These NPs also resulted into a significant reduction in COD, TDS, EC, pH, and color of two real wastewaters spiked with reactive black 5 and reactive red 120. The findings of this study suggest that the biosynthesized ZnO NPs might serve as a potential green solution for treatment of dye-loaded textile wastewaters.
Azo dyes are one of the largest classes of synthetic dyes being used in textile industries. It has been reported that 15-50% of these dyes find their way into wastewater that is often used for ...irrigation purpose in developing countries. The effect of azo dyes contamination on soil nitrogen (N) has been studied previously. However, how does the azo dye contamination affect soil carbon (C) cycling is unknown. Therefore, we assessed the effect of azo dye contamination (Reactive Black 5, 30 mg kg
dry soil), bacteria that decolorize this dye and dye + bacteria in the presence or absence of maize leaf litter on soil respiration, soil inorganic N and microbial biomass. We found that dye contamination did not induce any change in soil respiration, soil microbial biomass or soil inorganic N availability (
> 0.05). Litter evidently increased soil respiration. Our study concludes that the Reactive Black 5 azo dye (applied in low amount, i.e., 30 mg kg
dry soil) contamination did not modify organic matter decomposition, N mineralization and microbial biomass in a silty loam soil.
Background
A pot experiment was conducted to evaluate the phytotoxic thresholds of zinc oxide (ZnO NPs), iron oxide (FeO NPs), copper (Cu NPs), and silver nanoparticles (Ag NPs) on cotton. All the ...nanoparticles were biosynthesized from
Conocarpus erectus
L. leaf extract. They were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transmission infrared spectroscopy (FTIR). Five concentrations (0, 25, 50, 75, and 100 ppm) of all the biosynthesized nanoparticles were foliar applied thrice over the duration of cotton growth. Five cotton seeds were sown in 5 kg soil pot and harvested after 6 weeks. SPAD values were evaluated before harvesting while physical growth parameters, physiological parameters biochemical, and oxidative stress parameters were measured after harvesting.
Results
The value of all parameters, except oxidative stress, increased by 13–47% in response to ZnO NPs application up to 100 ppm. However, phytotoxic threshold of iron oxide nanoparticles (FeO NPs) and copper nanoparticles (Cu NPs) was only 50 ppm as plant growth was increased by 7.9–24.3%. Above 50 ppm plant growth and biomass were decreased by 6.7–16.2%. Silver nanoparticles (Ag NPs) showed maximum growth (3.7 to 9.12% increased) at 25 ppm concentration. At higher concentrations than 25 ppm, the application of Ag NPs decreased the growth due to toxicity. Foliar application of different biosynthesized nanoparticles showed the different range of threshold value for cotton crop. Threshold value of iron oxide and copper nanoparticles for cotton was 50 ppm, whereas, it was 25 ppm for silver nanoparticles. Since the ZnO NPs application continued increasing the growth till its maximum concentration used i.e., 100 ppm, we cannot say that this is its threshold value.
Conclusion
On the basis of obtained results, it can be concluded that nanoparticles should be used within threshold to avoid adverse effects on crops. Application of nanoparticles within threshold optimum concentration, increased plant biomass and antioxidant system.
Graphical Abstract
Nanoparticles play a vital role in environmental remediation on a global scale. In recent years, there has been an increasing demand to utilize nanoparticles in wastewater treatment due to their ...remarkable physiochemical properties.
In the current study, manganese oxide nanoparticles (MnO-NPs) were synthesized from the
strain and characterized by UV/Vis spectroscopy, X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy.
The objective of this study was to evaluate the potential of biosynthesized MnO-NPs to treat wastewater. Results showed the photocatalytic degradation and adsorption potential of MnO-NPs for chemical oxygen demand, sulfate, and phosphate were 79%, 64%, and 64.5%, respectively, depicting the potential of MnO-NPs to effectively reduce pollutants in wastewater. The treated wastewater was further utilized for the cultivation of wheat seedlings through a pot experiment. It was observed that the application of treated wastewater showed a significant increase in growth, physiological, and antioxidant attributes. However, the application of treated wastewater led to a significant decrease in oxidative stress by 40%.
It can be concluded that the application of MnO-NPs is a promising choice to treat wastewater as it has the potential to enhance the growth, physiological, and antioxidant activities of wheat seedlings.
Sustainable food security is a major challenge in today’s world, particularly in developing countries. Among many factors, environmental stressors, i.e., drought, salinity and heavy metals are major ...impediments in achieving sustainable food security. This calls for finding environment-friendly and cheap solutions to address these stressors. Plant growth-promoting rhizobacteria (PGPR) have long been established as an environment-friendly means to enhance agricultural productivity in normal and stressed soils and are being applied at field scale. Similarly, pyrolyzing agro-wastes into biochar with the aim to amend soils is being proposed as a cheap additive for enhancement of soil quality and crop productivity. Many pot and some field-scale experiments have confirmed the potential of biochar for sustainable increase in agricultural productivity. Recently, many studies have combined the PGPR and biochar for improving soil quality and agricultural productivity, under normal and stressed conditions, with the assumption that both of these additives complement each other. Most of these studies have reported a significant increase in agricultural productivity in co-applied treatments than sole application of PGPR or biochar. This review presents synthesis of these studies in addition to providing insights into the mechanistic basis of the interaction of the PGPR and biochar. Moreover, this review highlights the future perspectives of the research in order to realize the potential of co-application of the PGPR and biochar at field scale.
Graphical Abstract
PDF
