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To investigate the mechanisms by which g-C 3 N 4 alleviates metal(loid)-induced phytotoxicity, rice seedlings were exposed to 100 and 250 mg/kg graphitic carbon nitride (g-C 3 N 4 ) with or without coexposure to 10 mg/kg Cd and 50 mg/kg As for 30 days. Treatment with 250 mg/kg g-C 3 N 4 significantly increased shoot and root fresh weight by 22.4-29.9%, reduced Cd and As accumulations in rice tissues by 20.6-26.6%, and elevated the content of essential nutrients (e.g., K, S, Mg, Cu, and Zn) compared to untreated controls. High-throughput sequencing showed that g-C 3 N 4 treatment increased the proportion of plant-growth-promoting endophytic bacteria, including Streptomyces , Saccharimonadales , and Thermosporothrix , by 0.5-3.30-fold; these groups are known to be important to plant nutrient assimilation, as well as metal(loid) resistance and bioremediation. In addition, the population of Deinococcus was decreased by 72.3%; this genus is known to induce biotransformation As(V) to As(III). Metabolomics analyses highlighted differentially expressed metabolites (DEMs) involved in the metabolism of tyrosine metabolism, pyrimidines, and purines, as well as phenylpropanoid biosynthesis related to Cd/As-induced phytotoxicity. In the phenylpropanoid biosynthesis pathway, the increased expression of 4-coumarate (1.13-fold) and sinapyl alcohol (1.26-fold) triggered by g-C 3 N 4 coexposure with Cd or As played a critical role in promoting plant growth and enhancing rice resistance against metal(loid) stresses. Our findings demonstrate the potential of g-C 3 N 4 to enhance plant growth and minimize the Cd/As-induced toxicity in rice and provide a promising nanoenabled strategy for remediating heavy metal(loid)-contaminated soil.

This present study investigated pork bone-derived biochar as a promising amendment to reduce Cd accumulation and alleviate Cd-induced oxidative stress in rice. Micro/nanoscale bone char (MNBC) pyrolyzed at 400 °C and 600 °C was synthesized and characterized before use. The application rates for MNBCs were set at 5 and 25 g·kg -1 and the Cd exposure concentration was 15 mg·kg -1 . MNBCs increased rice biomass by 15.3-26.0% as compared to the Cd-alone treatment. Both types of MNBCs decreased the bioavailable Cd content by 27.4-54.8%; additionally, the acid-soluble Cd fraction decreased by 10.0-12.3% relative to the Cd alone treatment. MNBC significantly reduced the cell wall Cd content by 50.4-80.2% relative to the Cd-alone treatment. TEM images confirm the toxicity of Cd to rice cells and that MNBCs alleviated Cd-induced damage to the chloroplast ultrastructure. Importantly, the addition of MNBCs decreased the abundance of heavy metal tolerant bacteria, Acidobacteria and Chloroflexi, by 29.6-41.1% in the rhizosphere but had less impact on the endophytic microbial community. Overall, our findings demonstrate the significant potential of MNBC as both a soil amendment for heavy metal-contaminated soil remediation and for crop nutrition in sustainable agriculture., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Microplastics (MPs, <5 mm) are enriched in paddy ecosystems as emerging environmental pollutants. Biochar (BC) is a controversial recalcitrant carbon product that poses potential environmental risks. The presence of these two exogenous organic substances has been demonstrated to have impacts on soil nitrogen cycling and crop production. However, the after-effects of MPs and BC on soil ammonia (NH 3 ) volatilization and rice yield after field aging remain unexplored. In this study, two common MPs, including polyethylene (PE) and polyacrylonitrile (PAN), and BC were selected for rice growing season observations to study the impacts on soil NH 3 volatilization and rice yield after field aging. The results showed that the reduction of cumulative soil NH 3 losses by MPs was around 45% after one-year field aging, which was within the range of 40-57% in the previous rice season. Abatement of NH 3 volatilization by MPs mainly occurred in basal fertilization and was related to floodwater pH. Besides, the reduction rate of NH 3 volatilization by BC and MPs + BC was enhanced after field aging (63% and 50-57%) compared to that in the previous rice season (5% and 11-19%), with the abatement process occurring in the first supplementary fertilization. There was a significant positive correlation between cumulative NH 3 volatilization and soil urease activity. Notably, field aging removed the positive effect of MPs and MPs + BC in reducing yield-scale NH 3 losses in the previous rice season (∼62%). Furthermore, despite BC affecting rice yield insignificantly after field aging, the presence of MPs led to a significant 17-19% reduction in rice yield. Our findings reveal that differences in the after-effects of BC and MPs in field aging emerge, where the negative impacts of MPs on soil NH 3 abatement and crop yield are progressively becoming apparent and should be taken into serious consideration., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Microplastics (MPs) are verified to affect the fate of ammonia (NH 3 ) in agricultural soils. However, the impacts and mechanisms of MPs coupled with biochar (BC), a widely used agricultural conditioner, on NH 3 losses are mostly untapped. The aim of this study was to investigate the mechanisms of common MPs (i.e., polyethylene, polyester, and polyacrylonitrile) and straw-derived BC on NH 3 volatilization in rice-wheat rotation soils. Results showed that BC alone and MPs with BC (MPs + BC) reduced 5.5 % and 11.2-26.6 % cumulative NH 3 volatilization than the control (CK), respectively, in the rice season. The increased nitrate concentration and soil cation exchange capacity were dominant contributors to the reduced soil NH 3 volatilization in the rice season. BC and MPs + BC persistently reduced 44.5 % and 60.0-62.6 % NH 3 losses than CK in the wheat season as influenced by pH and nitrate concentration. Moreover, BC and MPs + BC increased humic acid-like substances in soil dissolved organic matter by an average of 159.1 % and 179.6 % than CK, respectively, in rice and wheat seasons. The increased adsorption of soil NH 4 + and the promotion of crop root growth were the main mechanisms of NH 3 reduction. Our findings partially revealed the mechanisms of the coexistence of MPs and BC on NH 3 mitigation in rice-wheat rotational ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Microplastics (MPs), as an emerging pollutant, may cause deleterious changes to the nitrogen cycle in terrestrial ecosystems. However, single impact of MPs and synergistic effects of MPs with hydrochar on ammonia (NH 3 ) volatilization and soil microbiome in paddy fields has been largely unexplored. In this study, polyethylene (PE), polyacrylonitrile (PAN) and straw-derived hydrochar (HBC) were selected for observations in an entire rice cycle growth period. Results showed that under the condition of 0.5% (w/w) MPs concentration, presence of MPs alone and co-existence of MPs and HBC (MPs + HBC) unexpectedly mitigated cumulative NH 3 volatilization from paddy soil compared with the control with no MPs or HBC addition. MPs + HBC increased NH 3 volatilization by 37.8-46.2% compared with MPs alone, indicating that co-existence of MPs and HBC weaken the mitigation effect of MPs on NH 3 volatilization. Additionally, results of nitrogen cycle related microorganisms closely related to NH 3 volatilization demonstrated that MPs + HBC altered the bacterial community structure and species diversity. These findings provide an important opportunity to advance our understanding of the impacts of MPs in agricultural environment and soils, and provide a sound theoretical basis for rationalizing the application of HBC in soil with MPs., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Microplastic (MP) contamination is ubiquitous in agricultural soils. As a cost-effective soil amendment, biochar (BC) often coincides with MP exposure. However, little research has been conducted regarding the independent and combined effects of MPs and BC on the soil microbiome and N 2 O/CH 4 emissions. Therefore, in this study, polyethylene terephthalate (PET) and wheat straw-derived BC were used, respectively, as representative MP and BC during an entire rice growth period. The high-throughput sequencing results showed that PET alone lowered bacterial diversity by 26.7%, while PET and BC co-existence did not induce apparent change. The relative abundances of some microbes (e.g., Cyanobacteria, Verrucomicrobia, and Bacteroidetes) that are associated with C and N cycling were changed at the phylum and class levels by all the treatments. In comparison with the control, the treatment of BC, PET, and their co-existence reduced the cumulative CH 4 emissions by 50%, 53%, and 61%, respectively. The higher mitigation by BC + PET may be the result of higher soil Eh and a consequently lower methanogenesis functional gene mcrA abundance in the treated soils. In addition, BC and PET alone, as well as their combined treatment, increased the abundance of nitrification genes, enhancing the soil nitrification process. However, the relative contribution of the nitrification process to N 2 O emission was possibly lower than that of denitrification, in which the N 2 O reductase gene nosZ was found to be the primary gene regulating N 2 O emissions. BC alone increased nosZ abundance by 42.3%, thereby showing the potential in suppressing N 2 O emission. In contrast, when BC was co-added with PET, the nosZ abundance lowered possibly because of increased soil aeration, and thus its cumulative N 2 O emission was 38% higher than the BC treatment. Overall, these results demonstrated that BC and PET function differently in soil ecosystems when they coexisted., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The importance of hydrochar properties for soil application is well known, but the effects of natural aging on hydrochar properties remain ambiguous. The present study aimed to determine the shift patterns in the physicochemical properties of hydrochar through a 16-month soil column aging experiment conducted in a rice-wheat rotation system with hydrochars derived from a wheat straw at 220 °C and 260 °C. Obvious decreasing hydrophilic/polarity indices and increasing porosity, ash content, and stability occurred in aged hyrdrochar, which were due to the dissolved organic matter (DOM) leaching and the interaction with mineral content and fertilizer during the 16-month aging process. Besides, fewer C-OH, slightly more CO, and higher aromaticity (C-C/CC) in aged hydrochar were observed. Meanwhile, the relative abundance of the compounds containing only C, H, and O atoms in water extract of aged hydrochar decreased, while that of the compounds containing C, H, O, and N atoms increased during aging; these findings were attributed to the less labile DOM and microbial degradation and the retention of some plant-derived dissolved organic carbon, respectively. This study provided 16-month aging characterization data regarding alteration in hydrochar physicochemical properties, which was conducive to make a better understanding of the use of hydrochars as sustainable soil amendments from agroecosystems and environmental perspective., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)