Biodegradable mulch films improve yield of winter potatoes through effects on soil properties and nutrients.

Biodegradable mulch films are recognized as a promising substitute of polyethylene (PE) films to alleviate the "white pollution". Biodegradable mulch films with optimum degradation rates increase crop yield even compared to PE films. However, the mechanisms underlying this yield-increasing effect remains elusive. In this study, three biodegradable film treatments (BFM1, BFM2 and BFM3) and one PE film treatment (PFM) were used to evaluate their effects on soil and winter potatoes, and a partial least squares path model (PLS-PM) was constructed to investigate their relationships. The degradation rates of films under different treatments were ranked as BFM3 > BFM2 >BFM1 > PFM, and presented distinctive effects on soil properties and nutrients, structure of soil bacterial community, and yield traits of winter potatoes. The PLS-PM showed that mulch treatments affected potato yield through effects on soil properties (soil water and temperature) and soil nutrients (TOC, DOC, TN and NO3--N). The disintegration of the biodegradable films decreased soil water content and temperature, and reduced the loss of soil nutrients in the topsoil at the later growth stage of winter potatoes compared to PE films. Additionally, the elevated content of soil TN and NO3--N under treatment BFM1 may play a key role in its yield-increasing effect on potatoes compared to treatments PFM and BFM2. Thus, biodegradable mulch films with proper degradation rates regulate soil TN and NO3--N through their effects on soil water and temperature, and subsequently improve the yield of winter potatoes compared to PE mulch films.

Cr(VI) Reduction and Fe(II) Regeneration by Penicillium oxalicum SL2-Enhanced Nanoscale Zero-Valent Iron.

Nanoscale zero-valent iron (nZVI) faces significant challenges in Cr(VI) remediation through aggregation and passivation. This study identified a Cr(VI)-resistant filamentous fungus (Penicillium oxalicum SL2) for nZVI activation and elucidated the synergistic mechanism in chromium remediation. P. oxalicum SL2 and nZVI synergistically and effectively removed Cr(VI), mainly by extracellular nonenzymatic reduction (89.1%). P. oxalicum SL2 exhibited marked iron precipitate solubilization and Fe(II) regeneration capabilities. The existence of the Fe(II)-Cr(V)-oxalate complex (HCrFeC4O9) indicated that in addition to directly reducing Cr(VI), iron ions generated by nZVI stimulated Cr(VI) reduction by organic acids secreted by P. oxalicum SL2. RNA sequencing and bioinformatics analysis revealed that P. oxalicum SL2 inhibited phosphate transport channels to suppress Cr(VI) transport, facilitated iron and siderophore transport to store Fe, activated the glyoxylate cycle to survive harsh environments, and enhanced organic acid and riboflavin secretion to reduce Cr(VI). Cr(VI) exposure also stimulated the antioxidative system, promoting catalase activity and maintaining the intracellular thiol/disulfide balance. Cr(VI)/Fe(III) reductases played crucial roles in the intracellular reduction of chromium and iron, while nZVI decreased cellular oxidative stress and alleviated Cr(VI) toxicity to P. oxalicum SL2. Overall, the P. oxalicum SL2-nZVI synergistic system is a promising approach for regenerating Fe(II) while reducing Cr(VI).

Impact of plastic film mulching on microplastic in farmland soils in Guangdong province, China.

Plastic mulch film is often believed to be a significant contributor to microplastic pollution in farmland soil, however, its direct impact in areas with high human activities remains unclear due to the presence of multiple pollution sources. This study aims to address this knowledge gap by investigating the impact of plastic film mulching on microplastic pollution in farmland soils in Guangdong province, China's largest economic province. The macroplastic residues in soils were investigated in 64 agricultural sites, and the microplastics were analyzed in typical plastic film mulched and nearby non-mulched farmland soils. The average concentration of macroplastic residues was 35.7 kg/ha and displayed a positive correlation with mulch film usage intensity. Contrarily, no significant correlation was found between macroplastic residues and microplastics, which exhibited an average abundance of 22,675 particles/kg soil. The pollution load index (PLI) model indicated that the microplastic pollution level was category I and comparatively higher in mulched farmland soils. Interestingly, polyethylene accounted for only 2.7% of the microplastics, while polyurethane was found to be the most abundant microplastic. According to the polymer hazard index (PHI) model, polyethylene posed a lower environmental risk than polyurethane in both mulched and non-mulched soils. These findings suggest that multiple sources other than plastic film mulching primarily contribute to microplastic pollution in farmland soils. This study enhances our understanding of microplastic sources and accumulation in farmland soils, offering crucial information on potential risks to the agroecosystem.

Oxalic acid enhances bioremediation of Cr(VI) contaminated soil using Penicillium oxalicum SL2.

Oxalic acid is the most abundant low molecular weight organic acid (LMWOA) in many environments and offers enormous prospects for treating Cr(VI) contamination. In this study, laboratory batch experiments were conducted to estimate the roles of oxalic acid in Cr(VI) removal by Penicillium oxalicum SL2. Oxalic acid changed the initial pH and provided a suitable condition for the growth of strain SL2 when the penicillium was applied to bioremediation of Cr(VI) contamination in alkaline soil. Gompertz model analysis indicated that initial pH affected the lag time of the growth curve of strain SL2. Scanning electron microscopy and scanning transmission X-ray microscopy analysis showed strain SL2 sufficiently contacted with contaminated soil and reduced Cr(VI) to Cr(III) in the hyphae. The results suggested that oxalic acid could enhance the bioremediation efficiency of strain SL2 though improving chromium bioleaching from the contaminated soil and strengthening Cr(VI) removal in the leaching solution. This study provided oxalic acid as a green reagent for stimulating Cr(VI) removal by strain SL2 and would expand knowledge on the roles of LMWOA in Cr(VI) bioremediation.

Integrated effects of residual plastic films on soil-rhizosphere microbe-plant ecosystem.

Intensive application of low-density polyethylene mulch films has resulted in substantial accumulation of residual plastics in agricultural soil. Although considerable concerns have been raised on the residual plastic pollution, their impacts on the soil-rhizosphere microbe-plant ecosystem have not been fully elucidated. In this study, we used a pot experiment to determine the effects of residual plastic films with different sizes (La, Ma, Mi and Mx) on properties, enzyme systems and nutrients of soil, composition of rhizosphere microbial community, and physiology, growth and stress response of rice plants. Residual plastic films significantly decreased soil bulk density and increased soil porosity, leading to the alteration of extracellular enzyme activities, and accumulation of dissolved nitrogen (NO3-N + NH4-N). The structures of both bacterial and fungal communities were significantly changed by residual plastic films with rhizosphere microbes more sensitive to small-sized plastics. Plant growth was inhibited to different extents by residual plastic films with different sizes. The weighted gene co-expression network analysis (WGCNA) showed that photosynthesis and carbon fixation of rice plants were repressed by residual plastic films, due to the reduced chlorophyll content and rubisco activity. In addition, the endogenous jasmonic acid and antioxidant enzyme system were induced to activate tolerant responses in rice plants to the stress imposed by residual plastic films. The partial least squares path models (PLS-PMs) revealed that residual plastic films had direct and/or indirect effects on the soil-rhizosphere microbe-plant system.

Effects of biodegradable and polyethylene film mulches and their residues on soil bacterial communities.

To investigate the effects of plastic film mulches and their residual films after use on soil bacterial communities, mulching experiment and the subsequent residual film experiment were conducted on winter-planting potato field in two locations. During mulching experiment, treatments biodegradable film mulch (BM) and PE film mulch (PM) reduced soil nutrient regarding available nitrogen and available potassium, as well as microbial biomass carbon (MBC), but increased urease activity, as compared to treatment no film mulch (NM). Soil moisture was significantly elevated by mulching practices and correlated with more microbial phyla than the other tested soil properties, indicating its important role in shaping soil bacterial communities. In addition, mulching practices increased alpha diversity of soil bacteria, although location heterogeneity was observed. Network analyses showed that both treatments BM and PM promoted the interrelations within bacterial communities and harbored more keystone taxa than treatment NM. During residual film experiment, residual films from BM and PM were incorporated into soil after harvest of potato. Treatment residual biodegradable film (RBF) significantly increased the content of MBC and activity of ß-glucosidase (BG) as compared to treatments residual PE film (RPF) and no residual film (NRF), and BG had the most correlations with microbial phyla among all the tested soil properties. Treatments RBF and RPF increased the relative abundance of some dominant bacterial phyla, including Bacteroidetes, Actinobacteria, and Chlorofexi, and enhanced the interrelations within bacterial community, whereas more keystone taxa were harbored by treatment RBF, due to the increase of keystone taxa in phyla Acidobacteria, Actinobacteria, Bacteroidetes, and Proteobacteria. These results indicate that the indirect effects of biodegradable and PE film mulch as a soil surface barrier on soil are similar, whereas their direct effects via incorporation into soil as residual films show specificity.

Green Production of Biodegradable Mulch Films for Effective Weed Control.

Biodegradable mulch films are supposed to be a prospective substitute for poly(ethylene)-based mulch films in the field of sustainable agriculture. Among them, weeding mulch films play significant roles. However, the large-scale production of weeding mulch films through the traditional high-temperature film blowing process would often cause serious pollution due to the diffusion of herbicides in the surroundings. Herein, a green and facile coating approach is developed to produce biodegradable weeding mulch films. In our strategy, a herbicide was added into a poly(vinyl alcohol) aqueous solution with dopamine in it. After the subsequent low-temperature coating procedure on a biodegradable poly(butylene adipate-co-terephthalate)/poly(lactic acid) film, effective weeding mulch films were obtained. The morphology, structure, and mechanical property test results revealed the robustness and stability of the coating, and the pot experiments clearly demonstrated the effective weed suppression ability of the obtained weeding films. Evidently, this strategy to produce biodegradable weeding mulch films is green and facile, exhibiting great prospects in the large-scale production of weeding mulch films and other functional biodegradable mulch films.

Rapid and Green Fabrication of Carbon Dots for Cellular Imaging and Anti-Counterfeiting Applications.

Carbon dots (CDs) with plenty of favorable properties have been extensively investigated in diverse areas including bioimaging, biomedicine, sensor, energy storage, anti-counterfeiting, photocatalysis, and optoelectronic devices. Herein, a simple, rapid, and green sonochemical-assisted method for fabricating nitrogen-doped CDs has been developed. In this approach, the nitrogen-doped CDs can be obtained through irradiation by intensive ultrasonic waves from ultrasonic probes in 30 min. The achieved CDs exhibit excellent water dispersibility, which can be ascribed to their high functionalization. Importantly, the CDs also demonstrate remarkable fluorescent properties, high photostability, and low cytotoxicity, which can be utilized for multicolor cellular imaging and anti-counterfeiting applications. As far as we know, the sonochemical-assisted method for rapidly synthesizing nitrogen-doped CDs from gelatin has never been reported before. Significantly, the sonochemical-assisted approach to rapidly fabricate CDs is versatile for the facile construction of fluorescent CDs, and the obtained CDs can be potentially used in various areas including bioimaging and anti-counterfeiting.

Cr(VI) removal by Penicillium oxalicum SL2: Reduction with acidic metabolites and form transformation in the mycelium.

Bioremediation of Cr(VI) contamination using microorganisms is a promising method for reducing its environmental risks. The objective of this study was to clarify Cr(VI) removal by Penicillium oxalicum SL2 in terms of indirect Cr(VI) reduction by metabolites, interaction sites, and form transformation of chromium. Strain SL2 could sequentially remove Cr(VI) in the bioreactor. Oxalic acid produced by the fungus contributed to Cr(VI) reduction. Scanning transmissiony X-ray microscop (STXM) analysis suggested strain SL2 could partly reduce Cr(VI) to Cr(III) in the cell. Amine, carboxyl, and phosphate groups were related to Cr(VI) removal. Chromium K-edge X-ray absorption near edge structure (XANES) analysis implied Cr(III)-Cys potentially acted as an intermediate for the formation of chromium oxalate complexes during the process of treatment. This study would support the application of strain SL2 in Cr(VI) bioremediation and expand knowledge on the interaction of chromium with fungus.

Simultaneous removal of multiple heavy metals from soil by washing with citric acid and ferric chloride.

The remediation of soil contaminated with multiple heavy metals is a matter of great concern due to its serious threat to the ecosystem and human health. Batch and slurry reactor soil washing experiments were conducted to explore the removal of Cd, Cr, Pb and Zn using 7 agents. Citric acid (CA) and ferric chloride (FeCl3) exhibited an obvious synergistic effect on the removal of heavy metals. Furthermore, the concentration of heavy metals in different soil particle size fractions was closely related to the soil element concentrations. Fine sand (0.05-0.25 mm) had a strong adsorption capacity for Cr and Pb because of the high Mn concentration. Notably, heavy metals in smaller-size soil particles could be efficiently removed by CA and FeCl3. After remediation, the bioavailability of heavy metals in soil decreased. The potential ecological risk of heavy metals in soil reduced from an extremely high level to a low level. Moreover, some elements (e.g. Al, Mn and Fe) and organic matter in soil were dissolved by CA and FeCl3, which accelerated the desorption of heavy metals from the soil. In a slurry reactor experiment, the removal efficiencies of Cd, Cr, Pb and Zn were 94.8%, 79.5%, 92.7% and 97.2%, respectively. The combination of CA and FeCl3 is a feasible practice to remediate soil contaminated by multiple heavy metals.

Ca2+ and SO42- accelerate the reduction of Cr(VI) by Penicillium oxalicum SL2.

Some ions in soils may affect the growth and metabolism of microorganisms and subsequently alter the remediation efficiency of Cr(VI). Here, the effects of different Ca2+ and SO42- levels on the reduction of Cr(VI) by Penicillium oxalicum SL2 were investigated. The results showed that Cr(VI) reduction by P. oxalicum SL2 in potato dextrose liquid (PDL) medium was accelerated by the presence of exogenous Ca2+ and SO42-. The Cr(VI) reduction rates were increased by 52.5% (200 mg L-1 Ca2+ treated) and 55.9% (2000 mg L-1 SO42- treated), respectively. High concentration of Ca2+ in medium resulted in the production of calcium oxalate crystals, which was contributed to the adsorption of chromium. In addition, X-ray absorption near-edge spectroscopy (XANES) analysis showed that P. oxalicum SL2 could reduce the toxicity of Cr(VI) by synthesizing cysteine (Cys) and reduced glutathione (GSH). The decrease of thiol compounds (Cys and GSH) in P. oxalicum SL2 mycelia treated with SO42- proved the alleviation of oxidative stress. In conclusion, exogenous Ca2+ could reduce the damage of Cr(VI) to P. oxalicum SL2 by maintaining the integrity of cell wall, and the addition of SO42- alleviated the Cr(VI) toxicity to P. oxalicum SL2, thus accelerating the reduction of Cr(VI).

Investigation of lead bioimmobilization and transformation by Penicillium oxalicum SL2.

Fungi Penicillium oxalicum SL2 was applied for Pb2+ bioremediation in aqueous solution in this study. After 7 days of incubation at different initial concentrations of Pb2+ (0, 100, 500 and 2500 mg L-1), most of Pb2+ were removed (90, 98.3, and 86.2%), the maximum Pb content in mycelium reached about 155.6 mg g-1 dw. Meanwhile, the formation of extracellular secondary minerals and intracellular Pb-complex were observed and identified, the speciation of Pb in mycelium was also detected by X-ray absorption near-edge structure (XANES) spectroscopy, i.e., Pb-oxalate, Pb-citrate, Pb-hydrogen phosphate and Pb-glutathione analogues. In addition, content of glutathione and oxidized glutathione was increased under the exposure of Pb2+, which implied that glutathione might play a key role in Pb immobilization and detoxification in P. oxalicum SL2. This study elucidated partial mechanisms of Pb immobilization and speciation transformation of this strain, providing an alternative biomaterial in the bioremediation of Pb-contaminated wastewater.

Characterization of Penicillium oxalicum SL2 isolated from indoor air and its application to the removal of hexavalent chromium.

Removal of toxic Cr(VI) by microbial reduction is a promising approach to reducing its ecotoxicological impact. To develop bioremediation technologies, many studies have evaluated the application of microorganisms isolated from Cr(VI)-contaminated sites. Nonetheless, little attention has been given to microbes from the environments without a history of Cr(VI) contamination. In this study, we aimed to characterize the Cr(VI) tolerance and removal abilities of a filamentous fungus strain, SL2, isolated from indoor air. Based on phenotypic characterization and rDNA sequence analysis, SL2 was identified as Penicillium oxalicum, a species that has not been extensively studied regarding Cr(VI) tolerance and reduction abilities. SL2 showed high tolerance to Cr(VI) on solid and in liquid media, facilitating its application to Cr(VI)-contaminated environments. Growth curves of SL2 in the presence of 0, 100, 400, or 1000 mg/L Cr(VI) were well simulated by the modified Gompertz model. The relative maximal colony diameter and maximal growth rate decreased as Cr(VI) concentration increased, while the lag time increased. SL2 manifested remarkable efficacy of removing Cr(VI). Mass balance analysis indicated that SL2 removed Cr(VI) by reduction, and incorporated 0.79 mg of Cr per gram of dry biomass. In electroplating wastewater, the initial rate of Cr(VI) removal was affected by the initial contaminant concentration. In conclusion, P. oxalicum SL2 represents a promising new candidate for Cr(VI) removal. Our results significantly expand the knowledge on potential application of this microorganism.

Spatial and temporal variations of nitrogen pollution in Wen-Rui Tang River watershed, Zhejiang, China.

Water quality has degraded dramatically in Wen-Rui Tang River watershed, Zhejiang, China, especially due to rapid economic development since 1995. This paper aims to assess spatial and temporal variations of the main pollutants (NH⁺4-N, TN, BOD(5), COD(Mn), DO) of water quality in Wen-Rui Tang River watershed, using the geographic information system, cluster analysis (CA) and principal component analysis (PCA). Results showed that concentrations of BOD(5), COD(Mn), NH⁺4-N, and TN were significantly higher in tertiary rivers than in primary and secondary rivers. From April 2006 to March 2007, the concentrations of NH⁺ 4-N (2.25-57.9 mg/L) and TN (3.78-70.4 mg/L) in all samples exceeded Type V national water quality standards (≥2 mg/L), while 5.3% of all COD(Mn) (1.83-27.5 mg/L) and 33.6% of all BOD(5) (0.34-50.4 mg/L) samples exceeded Type V national water quality standards (COD(Mn) ≥ 15 mg/L, BOD(5) ≥ 10 mg/L). Monthly changes of pollutant concentrations did not show a clear pattern, but correlation analysis indicated that NH⁺4-N and TN in tertiary rivers had a significant negative correlation with 5-day cumulative rainfall and monthly rainfall, while there were no significant correlations in primary and secondary rivers. The results of CA and spatial analysis showed that the northern part of Wen-Rui Tang River watershed was the most seriously polluted. This region is characterized by the high population density and industrial and commercial activities. The PCA and spatial analysis indicated that the degraded water quality is caused by anthropogenic activities and poor wastewater management.