Paederus fuscipes is a general predator in rice fields and a non-target organism of chlorantraniliprole, an effective insecticide for insect-pest control in paddy fields. Pesticide hazards to non-target organisms have been a growing global problem for decades. This study was designed to evaluate the toxicity of chlorantraniliprole at lethal and sublethal levels against P. fuscipes larvae and adults. The LC₅₀ of chlorantraniliprole against P. fuscipes adults and larvae were respectively 535.49 and 111.24 mg a.i. L⁻¹, which is higher than the dosage recommended for use in the field (59.38 mg a.i. L⁻¹), but the LC₃₀ and LC₁₀ for larvae are lower than the recommended field dose which showed that the sublethal effects on immature stages are inevitable. Treatment at larval stage with LC₃₀ of chlorantraniliprole significantly elongated the pre-imaginal developmental and pre-oviposition periods. Also, adults exposed directly to chlorantraniliprole oviposited significantly less number of eggs in both LC₁₀ and LC₃₀ treatments. Furthermore, the larval predation efficiency and female bodyweight were also reduced due to exposure to sublethal doses. Meanwhile, the activities of antioxidant (SOD, POD and CAT) and detoxification (P450, AChE and GST) enzymes were also significantly affected by the exposure to these sublethal concentrations. These findings showed that sublethal doses of chlorantraniliprole adversely influenced P. fuscipes development and physiology, and therefore its use as part of integrative pest management should be given further considerations.

Decision-making related to nitrogen (N) fertilization is a crucial step in agronomic practices because of its direct interactions with agronomic productivity and environmental risk. Here, we hypothesized that soil apparent N balance could be used as an indicator to determine the thresholds of N input through analyzing the responses of the yield and N loss to N balance. Based on the observations from 951 field experiments conducted in rice (Oryza sativa L.) cropping systems of China, we established the relationships between N balance and ammonia (NH₃) volatilization, yield increase ratio, and N application rate, respectively. Dramatical increase of NH₃ volatilizations and stagnant increase of the rice yields were observed when the N surplus exceeded certain levels. Using a piecewise regression method, the seasonal upper limits of N surplus were determined as 44.3 and 90.9 kg N ha⁻¹ under straw-return and straw-removal scenarios, respectively, derived from the responses of NH₃ volatilization, and were determined as 53.0–74.9 and 97.9–112.0 kg N ha⁻¹ under straw-return and straw-removal scenarios, respectively, derived from the maximum-yield consideration. Based on the upper limits of N surplus, the thresholds of N application rate suggested to be applied in single, middle-MLYR, middle-SW, early, and late rice types ranged 179.0–214.9 kg N ha⁻¹ in order to restrict the NH₃ volatilization, and ranged 193.3–249.8 kg N ha⁻¹ in order to achieve the maximum yields. If rice straw was returned to fields, on average, the thresholds of N application rate could be theoretically decreased by 17.5 kg N ha⁻¹. This study provides a robust reference for restricting the N surplus and the synthetic fertilizer N input in rice fields, which will guide yield goals and environmental protection.

Mixed pollution due to heavy metals (HMs), especially cadmium (Cd), lead (Pb), and arsenic (As), seriously endangers the safety of food produced in paddy soil. In the field experiments, foliar application of 2,3-dimercaptosuccinic acid (DMSA) at the flowering stage was found to significantly reduce the levels of Cd, Pb, total As, and inorganic As (iAs) in rice grains by 47.95%, 61.76%, 36.37%, and 51.24%, respectively, without affecting the concentration of metallonutrients, including Mn, K, Mg, Ca, Fe, and Zn. DMSA treatment significantly reduced the concentrations of Cd, Pb, and As in the panicle node, panicle neck, and rachis, while those in the flag leaves were significantly increased by up to 20.87%, 49.40%, and 32.67%, respectively. DMSA application promoted the transport of HM from roots and lower stalks to flag leaves with a maximum increase of 34.55%, 52.65%, and 46.94%, respectively, whereas inhibited the transport of HM from flag leaves to panicle, rachis, and grains. Therefore, foliar application of DMSA reduced Cd, Pb, and As accumulation in rice grains by immobilizing HMs in flag leaves. Thus, this strategy could act as a promising agronomic measure for the remediation of mixed HM contamination in paddy fields.

Cadmium (Cd) is a toxic heavy metal that initiates diverse chronic diseases through food chains. Developing a biotechnology for manipulating Cd uptake in plants is beneficial to reduce environmental and health risks. Here, we identified a novel epigenetic mechanism underlying Cd accumulation regulated by an uncharacterized metallochaperone namely Heavy Metal Responsive Protein (HMP) in rice plants. OsHMP resides in cytoplasm and nucleus, dominantly induced by Cd stress and binds directly to Cd ions. OsHMP overexpression enhanced the rice growth under Cd stress but accumulated more Cd, whereas knockout or knockdown of OsHMP showed a contrasting effect. The enhanced Cd accumulation in the transgenic lines was confirmed by a long-term experiment with rice growing at the environmentally realistic Cd concentration in soil. The bisulfite sequencing and chromatin immunoprecipitation assessments revealed that Cd stress reduced significantly the DNA methylation at CpG (Cytosine-Guanine) and histone H3K9me2 marks in the upstream of OsHMP. By identifying a couple of mutants defective in DNA methylation and histone modification (H3K9me2) such as Osmet1 (methylatransfease1) and Ossdg714 (kryptonite), we found that the Cd-induced epigenetic hypomethylation at the region was associated with OsHMP overexpression, which consequently led to Cd detoxification in rice. The causal relationship was confirmed by the GUS reporter gene coupled with OsHMP and OsMET1 whereby OsMET1 repressed directly the OsHMP expression. Our work signifies that expression of OsHMP is required for Cd detoxification in rice plants, and the Cd-induced hypomethylation in the specific region is responsible for the enhanced OsHMP expression. In summary, this study gained an insight into the epigenetic mechanism for additional OsHMP expression which consequently ensures rice adaptation to the Cd-contaminated environment.

Rice paddies are one of the largest greenhouse gases (GHGs) facilitators that are predominantly regulated by nitrogen (N) fertilization. Optimization of N uses based on the yield has been tried a long since, however, the improvement of the state-of-the-art technologies and the stiffness of global warming need to readjust N rate. Albeit, few individual studies started to, herein attempted as a systematic review to generalize the optimal N rate that minimizes global warming potential (GWP) concurrently provides sufficient yield in the rice system. To satisfy mounted food demand with inadequate land & less environmental impact, GHGs emissions are increasingly evaluated as yield-scaled basis. This systematic review (20 published studies consisting of 21 study sites and 190 observations) aimed to test the hypothesis that the lowest yield-scaled GWP would provide the minimum GWP of CH₄ and N₂O emissions from rice system at near optimal yields. Results revealed that there was a strong polynomial quadratic relationship between CH₄ emissions and N rate and strong positive correlation between N₂O emissions and N rate. Compared to control the low N dose emitted less (23%) CH₄ whereas high N dose emitted higher (63%) CH₄ emission. The highest N₂O emission observed at moderated N level. In total GWP, about 96% and 4%, GHG was emitted as CH₄ and N₂O, respectively. The mean GWP of CH₄ and N₂O emissions from rice was 5758 kg CO₂ eq ha⁻¹. The least yield-scaled GWP (0.7565 (kg CO₂ eq. ha⁻¹)) was recorded at 190 kg N ha⁻¹ that provided the near utmost yield. This dose could be a suitable dose in midseason drainage managed rice systems especially in tropical and subtropical climatic conditions. This yield-scaled GWP supports the concept of win–win for food security and environmental aspects through balancing between viable rice productivity and maintaining convincing greenhouse gases.

Identifying the adverse impacts of pesticide exposure is essential to guide regulations that are protective of wildlife and human health. Within rice ecosystems, amphibians are valuable indicators because pesticide applications coincide with sensitive reproductive and developmental life stages. We conducted two experiments using wild cane toads (Rhinella marina) to test 1) whether environmentally relevant exposure to a commercial formulation of butachlor, an acetanilide herbicide used extensively in rice, affects amphibian development and 2) whether cane toad tadpoles are capable of acclimatizing to sub-lethal exposure. First, we exposed wild cane toads to 0.002, 0.02, or 0.2 mg/L of butachlor (Machete EC), during distinct development stages (as eggs and hatchlings, as tadpoles, or continuously) for 12 days. Next, we exposed a subset of animals from the first experiment to a second, lethal concentration and examined survivorship. We found that cane toads exposed to butachlor developed slower and weighed less than controls, and that development of the thyroid gland was affected: exposed individuals had smaller thyroid glands and thyrocyte cells, and more individual follicles. Analyses of the transcriptome revealed that butachlor exposure resulted in downregulation of transcripts related to metabolic processes, anatomic structure development, immune system function, and response to stress. Last, we observed evidence of acclimatization, where animals exposed to butachlor early in life performed better than naïve animals during a second exposure. Our findings indicate that the commercial formulation of butachlor, Machete EC, causes thyroid endocrine disruption in vertebrates, and suggest that exposure in lowland irrigated rice fields presents a concern for wildlife and human health. Furthermore, we establish that developmental assays with cane toads can be used to screen for adverse effects of pesticides in rice fields.

Initial Cadmium (Cd) isotope fractionation studies in cereals ascribed the retention of Cd and its light isotopes to the binding of Cd to sulfur (S). To better understand the relation of Cd binding to S and Cd isotope fractionation in soils and plants, we combined isotope and XAS speciation analyses in soil-rice systems that were rich in Cd and S. The systems included distinct water management (flooded vs. non-flooded) and rice accessions with (excluder) and without (non-excluder) functional membrane transporter OsHMA3 that transports Cd into root vacuoles. Initially, 13% of Cd in the soil was bound to S. Through soil flooding, the proportion of Cd bound to S increased to 100%. Soil flooding enriched the rice plants towards heavy isotopes (δ¹¹⁴/¹¹⁰Cd = −0.37 to −0.39%) compared to the plants that grew on non-flooded soils (δ¹¹⁴/¹¹⁰Cd = −0.45 to −0.56%) suggesting that preferentially light Cd isotopes precipitated into Cd sulfides. Isotope compositions in CaCl₂ root extracts indicated that the root surface contributed to the isotope shift between soil and plant during soil flooding. In rice roots, Cd was fully bound to S in all treatments. The roots in the excluder rice strongly retained Cd and its lights isotopes while heavy isotopes were transported to the shoots (Δ¹¹⁴/¹¹⁰Cdₛₕₒₒₜ₋ᵣₒₒₜ 0.16–0.19‰). The non-excluder rice accumulated Cd in shoots and the apparent difference in isotope composition between roots and shoots was smaller than that of the excluder rice (Δ¹¹⁴/¹¹⁰Cdₛₕₒₒₜ₋ᵣₒₒₜ −0.02 to 0.08‰). We ascribe the retention of light Cd isotopes in the roots of the excluder rice to the membrane transport of Cd by OsHMA3 and/or chelating Cd–S complexes in the vacuole. Cd–S was the major binding form in flooded soils and rice roots and partly contributed to the immobilization of Cd and its light isotopes in soil-rice systems.

Biochar is often applied to paddy soils as a soil improver, as it retains nutrients and increases C sequestration; as such, it is a tool in the move towards C-neutral agriculture. Nitrogen (N) fertilizers have been excessively applied to rice paddies, particularly in small farms in China, because N is the major limiting factor for rice production. In paddy soils, dynamic changes in iron (Fe) continuously affect soil emissions of methane (CH₄) and carbon dioxide (CO₂); however, the links between Fe dynamics and greenhouse gas emissions, dissolved organic carbon (DOC), and rice yields following application of biochar remain unclear. The aims of this study were to examine the effects of two rates of nitrogen (N)-enriched biochar (4 and 8 t ha⁻¹ y⁻¹) on paddy soil C emissions and storage, rice yields, and Fe dynamics in subtropical early and late rice growing seasons. Field application of N-enriched biochar at 4 and 8 t ha⁻¹ increased C emissions in early and late rice, whereas application at 4 t ha⁻¹ significantly increased rice yields. The results of a culture experiment and a field experiment showed that the application of N-enriched biochar increased soil Fe²⁺concentration. There were positive correlations between Fe²⁺concentrations and soil CO₂, CH₄, and total C emissions, and with soil DOC concentrations. On the other way around, these correlations were negative for soil Fe³⁺concentrations. In the soil culture experiment, under the exclusion of plant growth, N-enriched biochar reduced cumulative soil emissions of CH₄ and CO₂. We conclude that moderate inputs of N-rich biochar (4 t ha⁻¹) increase rice crop yield and biomass, and soil DOC concentrations, while moderating soil cumulative C emissions, in part, by the impacts of biochar on soil Fe dynamics. We suggest that water management strategies, such as dry-wet cycles, should be employed in rice cultivation to increase Fe²⁺ oxidation for the inhibition of soil CH₄ and CO₂ production. Overall, we showed that application of 4 t ha⁻¹ of N-enriched biochar may represent a potential tool to improve sustainable food production and security, while minimizing negative environmental impacts.

Supplemental activated biochar pellet fertilizers (ABPFs) were evaluated as a method to sequester carbon and reduce greenhouse gas (GHG) emissions, and improve rice production. The evaluated treatments were a control (standard cultivation method, no additives applied), activated rice hull biochar pellets with 40% of N (ARHBP-40%), and activated palm biochar pellets with 40% of N (APBP-40%). The N supplied by the ARHBP-40% and APBP-40% treatments reduced the need for supplemental inorganic nitrogen (N) fertilizer by 60 percent. The ARHBP-40% treatment sequestered as much as 1.23 tonne ha⁻¹ compared to 0.89 tonne ha⁻¹ in the control during the rice-growing season. In terms of greenhouse gas (GHG) emissions, CH₄ emissions were not significantly different (p > 0.05) between the control and the ARHBP-40%, while the lowest N₂O emissions (0.002 kg ha⁻¹) were observed in the ARHBP-40% during the crop season. Additionally, GHG (CO₂-equiv.) emissions from the ARHBP-40% application were reduced by 10 kg ha⁻¹ compared to the control. Plant height in the control was relatively high compared to others, but grain yield was not significantly different among the treatments. The application of the ARHBP-40% can mitigate greenhouse gas emissions and enhance carbon sequestration in crop fields, and ABPFs can increase N use efficiency and contribute to sustainable agriculture.

Cadmium (Cd) and lead (Pb) are toxic heavy metals that impact human health and biodiversity. Removal of Cd/Pb from contaminated soils is a means for maintaining environmental sustainability and biodiversity. In this study, we applied a newly modified material fly ash (NA), zeolite (ZE), and fly ash (FA) to the paddy soils and evaluated the effects of Cd/Pb accumulation in rice via a one-year field experiment. The results showed that the application of NA and ZE enhanced the soil pH and nutrients to a large extent and reduced the availability of Cd/Pb in soil. The Cd and Pb concentrations in rice grains decreased by 32.8% and 62.9%, respectively, with the NA treatments. Similarly, the application of ZE reduced the Cd and Pb concentrations in rice grains by a factor of 27.9% and 63.5%, respectively, which indicates that the amendments can promote the transfer of Cd and Pb from acid-exchangeable fraction to oxidizable and residual fractions. The Cd/Pb showed a significant positive correlation to other metal ions and a negative correlation to the nutrients. Generally, the application of NA and ZE was effective in reducing Cd/Pb accumulation and improving rice yield. Moreover, the NA was more cost-effective than ZE. Hence, this study proves that NA may be a better amendment for remediation of Cd/Pb contaminated soils.