Rice Fields In China Research Articles

A Trp-574-Leu mutation in acetolactate synthase confers imazamox resistance in barnyardgrass (Echinochloa crus-galli) from China

Abstract Barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] is increasingly infesting imidazolinone-tolerant (IMI-T) rice fields in China, imazamox resistance of E. crus-galli has become the major concern for weed management in IMI-T rice fields. In this study, the susceptible population JLGY-3 (S) and the suspected resistant population JHXY-2 (R) collected from IMI-T rice fields were used as research subjects. When treated with imazamox, JHXY-2 (R) population showed a high level of herbicide resistance with a resistance index (RI) of 31.2. JHXY-2 (R) was cross-resistant to all five acetolactate synthase (ALS) inhibitors from different chemical families, but sensitive to herbicides inhibiting acetyl-CoA carboxylase (ACCase). In order to understand the reason why JHXY-2 (R) was resistant to imazamox, we performed experiments to characterize potential TSR and NTSR mechanisms. A trp-574-leu amino acid mutation in ALS and low imazamox ALS sensitivity were the main mechanism underlying imazamox resistance in this JHXY-2 (R) population. There was no significant difference in ALS gene expression and ALS protein abundance between R and S populations. High-performance liquid chromatography-tandem mass spectrometry analysis showed enhanced metabolism of imazamox in JHXY-2 (R), which was in contrast to the results of pretreatment with a metabolic enzyme inhibitor. Treatments with the P450/GST inhibitors did not alter the resistance level of JHXY-2 (R) against imazamox. To further clarify the NTSR mechanism of JHXY-2 (R), transcriptome sequencing showed that there was almost no significant difference in the expression of P450 and GST metabolic enzyme genes between R and S populations, and only GST-U1 showed a significant induction in R population. In conclusion, amino acid mutation and higher enzyme activity of ALS are the main causes of imazamox resistance in JHXY-2 (R). However, given the differences in imazamox residues in the leaves of the E. crus-galli, there may still be undetectable NTSR that are causing imazamox resistance in the R population.

Diverse mechanisms confer bensulfuron-methyl resistance in Schoenoplectiella juncoides (Roxb.) lye

The effectiveness of bensulfuron-methyl in controlling Schoenoplectiella juncoides (Roxb.) Lye has significantly decreased in rice fields in China. Hence, a bensulfuron-methyl-resistant S. juncoides population (W15) was collected from Dandong City, Liaoning Province, China, to investigate the underlying resistance mechanisms. Whole-plant dose-response experiments and ALS activity assay confirmed that W15 has evolved high-level resistance to bensulfuron-methyl compared with the susceptible S. juncoides population (W4). Molecular analysis revealed a Pro-197-Ser mutation in ALS1, while there was no significant difference in the relative ALS gene expression between W15 and W4. LC-MS/MS analysis showed W15 metabolized bensulfuron-methyl more rapidly than W4. Furthermore, bensulfuron-methyl resistance in W15 was significantly alleviated by malathion and 4-chloro-7-nitrobenzoxadiazole (NBD-Cl). Glutathione S-transferase activity was higher in W15 than in W4. Meanwhile, W15 displayed cross-resistance to halosulfuron-methyl and multi-resistance to MCPA-Na. In summary, these findings demonstrated for the first time that both target- and non-target-site resistance are relevant in the resistance of S. juncoides to bensulfuron-methyl.

Lime Application Reduces Methane Emissions Induced by Pig Manure Substitution from a Double-Cropped Rice Field

Abstract: The substitution of chemical fertilizers with organic manure plays a critical role in sustainable crop production. Nevertheless, organic amendments promote the global warming potential (GWP) in rice paddies due to increased methane (CH4) emissions. Increasing evidence shows that lime application can reduce CH4 emissions from acidic paddy soils; however, it is still not clear whether liming can reduce the GWP in rice fields under organic manure substitution. A two-year field experiment was conducted to investigate the impacts of pig manure substitution and lime application on grain yield, CH4 and nitrous oxide (N2O) emissions in a subtropical double-cropped rice field in China. The experiment consisted of three treatments: CF (100% chemical nitrogen fertilizer), 1/2N + M (50% of the applied nitrogen substituted by pig manure, M represents manure), and 1/2N + M + L (lime amendment with 50% of the applied nitrogen substituted with pig manure, L represents lime). On average, 1/2N + M reduced rice yield by 5.65% compared to CF, while the lime application had no effect on rice yield. Mean cumulative CH4 emissions were 218.8% higher in 1/2N + M than in CF, whereas 1/2N + M + L reduced CH4 emissions by 36.6% compared to 1/2N + M. Neither pig manure substitution nor lime application affected N2O emissions. Consequently, 1/2N + M increased the GWP and greenhouse gas intensity (GHGI) by 214.6% and 228.3%, respectively, compared to CF. In contrast, 1/2N + M + L reduced the GWP and GHGI by 36.4% and 36.5% compared to 1/2N + M. Lime application can mitigate CH4 emissions and GWP induced by pig manure amendment in double-cropped rice fields.

Resistance patterns and molecular basis to ACCase-inhibiting herbicides

Abstract Digitaria ciliaris var. chrysoblephara (Fig. & De Not.) R.R. Stewart is an annual xeromorphic weed that severely infests direct-seeded rice fields in China. Herbicide resistance is emerging in D. ciliaris var. chrysoblephara owing to extensive and recurrent use of the acetyl-CoA carboxylase (ACCase)-inhibiting herbicide metamifop. In this study, a total of 53 D. ciliaris var. chrysoblephara populations randomly sampled from direct-seeded rice fields across Jiangsu Province were investigated for metamifop resistance and potential resistance-endowing mutations. Single-dose assays revealed that 17 (32.1%) populations evolved resistance to metamifop and 5 (9.4%) populations were in the process of developing resistance. The resistance index (RI) of metamifop-resistant populations ranged from 2.7 to 32.1. Amino acid substitutions (Ile-1781-Leu, Trp-2027-Cys/Ser, and Ile-2041-Asn) in ACCase genes were detected in resistant D. ciliaris var. chrysoblephara plants and caused various cross-resistance patterns to ACCase-inhibiting herbicides. All of four resistant populations (YC07, YZ09, SQ03, and HA06), with different ACCase mutations, exhibited cross-resistance to the aryloxyphenoxypropionate (APP) herbicides cyhalofop-butyl (RI values: 10.0 to 19.9), fenoxaprop-P-ethyl (RI values: 53.7 to 132.8), and haloxyfop-P-methyl (RI values: 6.2 to 62.6), and the phenylpyrazoline (DEN) pinoxaden (RI values: 2.3 to 5.4), but responded differently to the cyclohexanedione (CHD) herbicides clethodim and sethoxydim. It is noteworthy that four postemergence herbicides used for rice cropping, including bispyribac-sodium, pyraclonil, quinclorac, and anilofos, showed poor control effect against D. ciliaris var. chrysoblephara, suggesting few alternations for managing this weed in rice fields except ACCase inhibitors. In conclusion, this work demonstrated that the D. ciliaris var. chrysoblephara had developed resistance to ACCase-inhibiting herbicides in rice cultivation of China, and target-site amino acid substitutions in ACCase were primarily responsible for metamifop resistance.

Rice Stripe Virus Infection Facilitates the Reproductive Potential of Laodelphax striatellus

The rice stripe virus (RSV) is transmitted by the small brown planthopper Laodelphax striatellus in a persistent and circulative–propagative manner. During the last few decades, RSV has caused serious disease outbreaks in rice fields in China. The results of long-term coevolution have led to complex and diverse relationships between viruses and vector insects, and understanding these interactions is critical for the management of diseases and vector organisms. In this study, three groups of comparative experiments were performed to investigate the effects of RSV infection on the reproductive parameters, vitellogenin (Vg), and Vg receptor (VgR) expressions of L. striatellus. The results showed that RSV infection promoted the fecundity, hatchability, and Vg and VgR expressions of L. striatellus but had no effect on the preoviposition period and oviposition period. Furthermore, the RNA interference of the nucleocapsid protein (CP) gene and the injection of the CP antibody in RSV-viruliferous L. striatellus reduced the fecundity, hatchability, and Vg and VgR expressions, further strengthening the hypothesis that RSV may manipulate the reproductive behavior of insect vectors to promote its own transmission. The results of this study can further reveal the interaction mechanism of virus–vector insects in reproduction and virus transmission, and provide new insights for the control of insect-borne viruses.

Hazard or Non-Hazard Flood: Post Analysis for Paddy Rice, Wetland, and Other Potential Non-Hazard Flood Extraction from the VIIRS Flood Products

VIIRS flood products have been widely used by the National Weather Service (NWS) for river flood monitoring, and by the Federal Emergency Management Agency (FEMA) and the International Charter Program for rescue and relief efforts. However, some water bodies, like irrigated or flooded paddy rice fields, and water in seasonal wetlands, are detected as floodwater instead of permanent, seasonal, controlled, or normal water in the VIIRS flood products. Because these kinds of floodwater don’t cause any severe disasters, they should be delineated as non-hazard floods to differentiate from real hazardous floods, the latter of which generally pose a significant risk and damage to human life, property, and the environment. Hazardous floods are usually caused by intensive rainfall, rapid snowmelt, or ice jams, they appear accidentally and tend to be short-term events. Non-hazard floodwaters generally result from tides, wetlands, agricultural irrigation, and other human activities, and thus they appear regularly and often stand for a longer time. Therefore, non-hazard floodwaters are some kind of standing water and usually have much larger long-time flood frequency or probability than hazardous floods. Based on this feature, it’s possible to combine long-time flood frequency calculated as the ratio of total flooding days over total clear days, including both flooding and no-flooding days, from VIIRS flood products with some additional information, such as agriculture statistics and land cover and land use map, to identify non-hazard floodwater in paddy rice fields and wetland. In this study, non-hazard floodwater bodies are classified into four types: paddy rice fields, wetlands, riparian and coastal tidal flooding, and other non-hazard floods, including possible fishing ponds. In this study, we selected several examples, such as the 2023 California flood event and some large paddy rice fields in China, to demonstrate how to identify water in paddy rice fields. The Florida flood event due to Hurricane Ian in 2022 is used to demonstrate how to separate wetlands from real hazardous floods. In addition to non-hazard floodwaters in wetlands, some coastal tidal flooding in Florida is also detected. The non-hazard floodwaters extracted from the proposed methods are compared with change detection analysis and good agreement is found. The paddy rice fields obtained from this study are compared and evaluated with the rice distribution data from the USDA. The quantitative evaluation results from the confusion matrix calculation demonstrate that the accuracy is 99.96%, recall is 83.69%, precision is 61.57%, and the F1-score is 70.95%. The high accuracy indicates that the method developed in this study for paddy rice field extraction from the VIIRS flood products is feasible.

Propyrisulfuron plus cyhalofop butyl as one-shot herbicides provide high weed control efficiency and net economic performance in mechanically transplanted rice.

Propyrisulfuron is a novel pyrimidinylsulfonylurea herbicide with good activity for controlling annual weed in rice fields. To evaluate the economic performance of propyrisulfuron, a field study was conducted in 2021 and 2022 on a farm of the Jiangsu Academy of Agricultural Sciences, China. Eight different herbicide treatments were employed, including CB (cyhalofop butyl), Py (propyrisulfuron), CBPy (cyhalofop butyl plus propyrisulfuron), PrBe 3, PrBe 10, and PrBe 3+PrBe 10 (pretilachlor plus bensulfuron applied at different times [at 3 (PrBe 3) and 10 (PrBe 10) d] or sequentially, respectively), 2PrBe+PeCBBz (pretilachlor plus bensulfuron [applied sequentially] followed by penoxsulam plus cyhalofop butyl plus bentazone), 2PrBe+MeCBBz (pretilachlor plus bensulfuron [applied sequentially] followed by metamifop plus cyhalofop butyl plus bentazone), along with weed-free and nontreated weedy check treatments. Herbicide treatments did not cause visual phytotoxicity to rice, and bending and leaf rolling were not observed. Only the two propyrisulfuron treatments had temporary negative effects on rice height, but rice recovered quickly. Compared with the weed-free treatment, CBPy did not affect rice tiller number or dry matter accumulation. Compared with the nontreated weedy check, herbicide treatments reduced total weed density by 29.4% to 99.1% and dry biomass by 32.2% to 98.7%. The CBPy treatment provided the best weed control, reducing weed density and biomass by 96.7% and 95.9% in 2021 and 97.4% and 95.6% in 2022, respectively. Rice grain yield was not significantly different between CBPy and the weed-free treatment in either year. Economic analysis showed that CBPy provided the highest net profit, followed by that in 2PrBe+PeCBBz and 2PrBe+MeCBBz, with the lowest net profit in the nontreated weedy check. Thus, CBPy provides good weed control and could be promoted in mechanically transplanted rice fields in China.

Quantitative assessment and mitigation strategies of greenhouse gas emissions from rice fields in China: A data-driven approach based on machine learning and statistical modeling

The accurate prediction of greenhouse gas (GHG) emissions from paddy fields is critical for developing mitigation strategies to reduce emissions, while realizing the large-scale prediction of GHG emissions from paddy fields remains to be a challenge. Here, we established machine learning models to predict the GHG emissions from Chinese paddy systems using a dataset including 782 CH4 and 679 N2O emission observations based on 118 published studies across China. Our results identified XGBoost was the most suitable model with the outstanding efficiency and accuracy for predicting both CH4 (R2 = 0.754, RMSE = 0.485 kg ha−1) and N2O emissions (R2 = 0.762, RMSE = 0.423 kg ha−1) from rice fields in China. We found mineral and organic fertilizer rate, irrigation mode, straw returned proportion and tillage depth were key factors in regulating GHG emissions. Specifically, CH4 emissions trended to increase first and then decrease with increasing mineral nitrogen fertilizer rate, with the inflection point delayed under the application of organic fertilizer. On the other hand, N2O emissions continued to increase until the N fertilizer rate reached approximately 150 kg ha−1. The use of organic fertilizer, tillage, straw return in half and full quantity increased global warming potential (GWP) by 80.3 %, 33.8 %, 25.2 % and 111.6 %, respectively. Frequent drainage (FD) was identified as the most promising water management mode, with a higher potential for GHG emission mitigation of 39.5 % compared to continuous flooding, followed by mid-season drainage at 18.4 %. We found the combination of a mineral nitrogen fertilizer rate of 128 kg ha−1, FD water management, without straw, tillage, and organic fertilizer could achieve the most effective GHG emission mitigation, with a GWP of 3.13 Mg CO2 equivalent ha−1. Our findings provided a new insight for predicting GHG emissions from rice fields on a large scale, and offered guidance for mitigating GHG emissions from rice production in China.

First Report of Fusarium proliferatum Associated with Leaf Yellow on Alternanthera philoxeroides in China.

Alternanthera philoxeroides (Mart.) Griseb is a highly invasive weed commonly found in rice fields in China. In May 2021, leafyellowing was observed on this weed (about 10 ha) in Zhanjiang (21°19'N, 110°20'E), Guangdong Province, China. Disease incidence was approximately 20% (n = 100 investigated plants). Ten yellow leaves from 10 plants were sampled, surface-sterilized with 75% ethanol for 30 s, followed by 2% NaClO for 5 min. The leaves were rinsed three times in sterile distilled water and four sections of each leaf were placed onto potato dextrose agar (PDA). Pure cultures were obtained by transferring hyphal tips to new PDA plates. Twenty-two isolates of Fusarium ssp. (69% of the isolates) were obtained from 55% of the leaf samples. Three representative single-spore isolates (APF-1, APF-2, and APF-3) were used for further study. Colonies were white to pink on PDA. Conidiogenous cells were monophialidic or polyphialidic. Macroconidia were slightly curved, tapering apically with three to five septa, and measured from 32.5-55.8 μm × 2.5-5.1 μm in size (n=50). The morphological features of these fungi were noted to be in line with those ofFusariumproliferatum(Leslie and Summerell, 2006). For molecular identification, a colony PCR method (Lu et al. 2012) was used to amplify the internal transcribed spacer (ITS) and portions of elongation factor 1-α (EF1-α), RNA polymerase II largest subunit (RPB1), and RNA polymerase II second largest subunit (RPB2) genes using primers ITS1/ITS4, EF1-728F/EF1-986R,RPB1-R8/RPB1-F5, and RPB2-7CF/fRPB2-11aR, respectively (O'Donnell et al. 1998; O'Donnell et al. 2010). The sequences were submitted to GenBank under accession numbers MZ026797-MZ026799 (ITS) and MZ032209-MZ032217 (RPB1, RPB2, EF1-α). The sequences of the three isolates were 100% identical (ITS, 537/537 bp; RPB1, 1606/1606 bp; RPB2, 770/770 bp and EF1-α, 683/683 bp) with those of F. proliferatum (accession nos. MT378328, MN193921, MH582196, and MH582344) through BLAST analysis. Analysis of the sequences revealed a 99.87 - 100% identity with the isolates of theF. proliferatum (F. fujikuroi species complex, Asian clade) by polyphasic identification using theFUSARIUM-ID database (Yilmaz et al. 2021). The sequences were also concatenated for phylogenetic analysis by the maximum likelihood method. The isolates clustered withF. proliferatum. Pathogenicity was tested through in vivo experiments. The inoculated and control plants (n = 5, 30 days old) were sprayed with a spore suspension (1 × 105 per mL) of the three isolates individually and sterile distilled water, respectively, until run-off (Feng and Li. 2019). The test was performed three times. The plants were grown in pots in a greenhouse at 25 °C to 28 °C, with relativehumidity of approximately80%. Yellowing was observed on the inoculated plants after 7 days, while the control plants remained healthy. The pathogen re-isolated from all the inoculated plants was identical to the inoculated isolates in terms of morphology and ITS sequences. No fungi were isolated from the control plants. To the best of our knowledge, this study is the first to report F. proliferatum causing yellow symptoms on A. philoxeroides. The fungus has some potential biological control properties, but its host range needs to be further determined.

Deep fertilization improves rice productivity and reduces ammonia emissions from rice fields in China; a meta-analysis

Deep fertilization (DF) has been introduced to rice production systems in China to improve rice productivity with minimum nitrogen (N) losses, however, the effects of DF on rice yield and ammonia (NH 3 ) emissions were never analyzed systematically. In the present study, we evaluated the impact of DF on rice productivity and NH 3 emissions via a meta-analysis based on 1023 observations collected from 144 studies. Data interpretation showed that DF can significantly increase yield by 8.6% (95% confidence interval (CI): 7.3–10.0%), N use efficiency by 16.7% (95% CI: 14.5–18.9%) and reduce NH 3 emissions by 78.1% (95% CI: 71.3–81.3%), respectively compared to broadcast fertilizer (BF). Variation in the effects of DF was mainly due to climate factors, soil properties, and agronomic practices whereas optimization of agronomic practices can improve the rice productivity under DF. The optimal depth of DF ranges between 7 and 13 cm, which coincides with the distribution of the majority of the rice root system. Reducing the fertilizer application rate to the range of 150–250 kg/ha coupled with split fertilization can improve rice yield and reduce NH 3 emissions. Importantly, the DF could significantly increase the total output and net economic benefits compared to the BF. In conclusion, the DF can significantly increase rice productivity and reduce ammonia emissions, however, large-scale adoption of the DF in rice systems are constrained by the availability of well-equipped machinery, good fertilizer products, and skilled farmers and labor. • Effects of deep fertilization (DF) on rice yield and NH 3 emissions were assessed. • Variations in the effects of DF were mainly due to agronomic practices. • Site-specific optimizations are needed to improve the performance of DF.

Periphytic biofilms function as a double-edged sword influencing nitrogen cycling in paddy fields.

It remains unclear whether periphytic biofilms are beneficial to N cycling in paddy fields. Here, based on a national-scale field investigation covering 220 rice fields in China, the N accumulation potential of periphytic biofilms was found to decrease from 8.8 ± 2.4 to 4.5 ± 0.7g/kg and 3.1 ± 0.6g/kg with increasing habitat latitude and longitude, respectively. The difference in abundant and rare subcommunities likely accounts for their geo-difference in N accumulation potential. The N cycling pathways involved in periphytic biofilms inferred that soil N and N2 were two potential sources for N accumulation in periphytic biofilms. Meanwhile, some of the accumulated N may be lost via N2 , N2 O, NO, or NH3 outputs. Superficially, periphytic biofilms are double-edged swords to N cycling by increasing soil N through biological N fixation but accelerating greenhouse gas emissions. Essentially, augmented periphytic biofilms increased change of TN (ΔTN) content in paddy soil from -231.9 to 31.9mg/kg, indicating that periphytic biofilms overall benefit N content enhancement in paddy fields. This study highlights the contribution of periphytic biofilms to N cycling in rice fields, thus, drawing attention to their effect on rice production and environmental security.

Differences in the Mode of Action of Florpyrauxifen-Benzyl between Barnyardgrass and Yerbadetajo

Barnyardgrass (a monocotyledon) and yerbadetajo (a dicotyledon) are the most troublesome weeds in rice fields in China. The synthetic auxin herbicide florpyrauxifen-benzyl can effectively control both weeds. The objective of this research was to clarify modes of action of florpyrauxifen-benzyl in barnyardgrass and yerbadetajo. Our results showed that yerbadetajo was more sensitive to florpyrauxifen-benzyl than barnyardgrass: the 50% growth rate inhibition in barnyardgrass and yerbadetajo was 4.14 and 0.38 g a.i. ha−1, respectively. Florpyrauxifen-benzyl induced the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and abscisic acid (ABA) in yerbadetajo within 24 h, while in barnyardgrass, the highest production occurred at 12 h and decreased at 24 h. ACC and ABA levels in yerbadetajo at 24 h of treatment were significantly higher than those in barnyardgrass at any time. There were less differentially expressed genes related to ethylene and ABA synthesis in barnyardgrass than in yerbadetajo. There were five genes induced to increase by florpyrauxifen-benzyl in barnyardgrass and eleven genes in yerbadetajo. More ACC oxidase genes (ACO) were induced in barnyardgrass and more ACC synthesis genes (ACS) in yerbadetajo, especially three ACS3 (>30 fold). We speculated that differences in gene expression caused differences in ethylene and ABA production, leading to differences in phytotoxicity.

Model the Relationship of NH3 Emission with Attributing Factors from Rice Fields in China: Ammonia Mitigation Potential Using a Urease Inhibitor

Substantial ammonia (NH3) losses from rice production result in poor nitrogen (N) use efficiency and environmental damage. A data synthesis using the published literature (127 studies with 700 paired observations), combined with an incubation experiment using 50 paddy soils from across China, were conducted to improve the current understanding of the NH3 loss from paddy rice and its drivers. The efficacy of the urease inhibitor Limus® for reducing NH3 losses was also evaluated. The mean loss of N, through NH3 volatilization, was 16.2% of the urea-N applied to paddy rice. The largest losses were from double rice cropping systems, and losses increased with the N application rate, surface application of N, unstable N types (ammonium bicarbonate and urea), and high floodwater pH. Under simulated flooded conditions, urea amended with Limus® reduced NH3 loss by 36.6%, compared to urea alone, but floodwater pH had a significant effect on inhibitor efficacy. Key driving factors were air temperature, N application rate, and floodwater pH. The effectiveness and limitations of the inhibitor in NH3 emission mitigation was examined, as well as its basis as one means of N pollution control in paddy rice cropping systems.

Update of a biogeochemical model with process-based algorithms to predict ammonia volatilization from fertilized cultivated uplands and rice paddy fields

Abstract. Accurate simulation of ammonia (NH3) volatilization from fertilized croplands is crucial to enhancing fertilizer-use efficiency and alleviating environmental pollution. In this study, a process-oriented model, CNMM–DNDC (Catchment Nutrient Management Model–DeNitrification–DeComposition), was evaluated and modified using NH3 volatilization observations from 44 and 19 fertilizer application events in cultivated uplands and paddy rice fields in China, respectively. The major modifications for simulating NH3 volatilization from cultivated uplands were primarily derived from a peer-reviewed and published study. NH3 volatilization from cultivated uplands was jointly regulated by wind speed, soil depth, clay fraction, soil temperature, soil moisture, vegetation canopy, and rainfall-induced canopy wetting. Moreover, three principle modifications were made to simulate NH3 volatilization from paddy rice fields. First, the simulation of the floodwater layer and its pH were added. Second, the effect of algal growth on the diurnal fluctuation in floodwater pH was introduced. Finally, the Jayaweera–Mikkelsen model was introduced to simulate NH3 volatilization. The results indicated that the original CNMM–DNDC not only performed poorly in simulating NH3 volatilization from cultivated uplands but also failed to simulate NH3 volatilization from paddy rice fields. The modified model showed remarkable performances in simulating the cumulative NH3 volatilization of the calibrated and validated cases, with drastically significant zero-intercept linear regression of slopes of 0.94 (R2 = 0.76, n = 40) and 0.98 (R2 = 0.71, n = 23), respectively. The simulated NH3 volatilization from cultivated uplands was primarily regulated by the dose and type of the nitrogen fertilizer and the irrigation implementation, while the simulated NH3 volatilization from rice paddy fields was sensitive to soil pH; the dose and depth of nitrogen fertilizer application; and flooding management strategies, such as floodwater pH and depth. The modified model is acceptable to compile regional or national NH3 emission inventories and develop strategies to alleviate environmental pollution.

Current status of carbon neutrality in Chinese rice fields (2002–2017) and strategies for its achievement

China has pledged to achieve carbon neutrality by 2060 to address global climate change, and achieving carbon neutrality in rice fields is a vital component of this commitment. However, the current status of carbon neutrality in rice fields in China is unclear, and there are few feasible strategies to achieve its successful implementation. Therefore, this study calculated the net carbon sequestration rate (NCSR, i.e., carbon sequestration minus carbon emissions) of rice fields in China from 2002 to 2017 to clarify the carbon neutrality status of Chinese rice fields. Furthermore, the effects of field management measures, rice sown area, and rice yield on NCSR were analyzed to identify suitable carbon neutralization pathways in Chinese rice fields. Our findings indicated that the annual carbon sequestration rate in rice fields was lower than the carbon emissions, resulting in continuous net emissions of 195.49 Tg CO2-eq yr−1. The NCSR of paddy fields increased first and then decreased with increases in rice sown area and yield. Meta-analysis indicated that management measures such as water conservation and biochar significantly increased NCSR by ~5766.50 kg CO2-eq ha−1 yr−1 and 22,296.62 kg CO2-eq ha−1 yr−1, respectively. Our findings suggests that proper control of rice sown area and the adoption of reasonable field management measures (water conservation and biochar) can promote carbon neutrality in Chinese rice fields.

A novel Phe‐206‐Leu mutation in acetolactate synthase confers resistance to penoxsulam in barnyardgrass (Echinochloa crus‐galli (L.) P. Beauv)

Barnyardgrass (Echinochloa crus-galli (L.) P. Beauv) has evolved resistance to the acetolactate synthase (ALS) inhibitor penoxsulam which is used to control weeds in rice fields in China. The present study is conducted to identify the target-site resistance (TSR) mechanisms conferring resistance in a penoxsulam-resistant population. The ALS sensitivity in vitro of the resistant population was sixfold lower to penoxsulam than that of the sensitive population. ALS sequencing revealed that no known mutation conferring ALS herbicide resistance was detected. However, a novel mutation Phe-206-Leu was identified in the ALS gene. Additionally, ALS gene expression level of the resistant population was lower than that of the sensitive population. Therefore, the penoxsulam resistance was not due to the overexpression of ALS gene. Molecular docking revealed that this mutation may change the interaction of the penoxsulam-ALS binding and weaken its mutual affinity by approximately 10%. Arabidopsis thaliana transformed with mutant ALS had fourfold greater resistance to penoxsulam and varied cross-resistance to other ALS herbicides than those transformed with sensitive ALS. Mutant and sensitive ALS proteins expressed by the baculovirus system exhibited different in vitro penoxsulam sensitivity levels. Mutant ALS had eightfold lower sensitivity to penoxsulam than sensitive ALS. This report provides clear evidence that the ALS mutation at position 206 (Phe-206-Leu) confers penoxsulam resistance in barnyardgrass. Phe-206 was confirmed to be the ninth amino acid residue related to ALS herbicide resistance in weeds. © 2022 Society of Chemical Industry.

Effect of soil degradation on the carbon concentration and retention of nitrogen and phosphorus across Chinese rice paddy fields

Soil degradation is a multi-factorial process that threatens crop production and the environment. According to the classification method of Pieri et al. (1992), soils are classified into different degradation classes by calculating the soil structural stability index (SSI). Soil nitrogen, phosphorus, labile organic carbon, mineral N and available-P concentration and stoichiometry under different degrees of degradation in rice fields in China were determined and analyzed. The results showed that 47% of the soil in China's rice fields had degradation problems. As the soil gradually degraded, soil N, P, AP concentrations were found to significantly decline (p < 0.05). Soils with lower organic matter levels and higher degrees of degradation were typically found in wetter and hotter climates. Furthermore, soil salinity, pH and bulk density in Chinese paddy fields were 65.7%, 12.3%, and 12.0% higher in the soils with low risk of degradation compared to the degraded soils. Nutrient stoichiometric ratios were found to significantly vary between different stages of soil degradation. Moreover, as the soil degraded, the rate of soil carbon loss was found to be greater than for nitrogen, and alluded a decoupling of soil carbon and nitrogen cycles. Soil degradation also effected other physical and chemical properties, including pH, organic matter, porosity and bulk density. Restraining annual cropping frequencies and adopting sustainable rice farming practises should safeguard against further soil degradation in China.

Integrated mosquito management in rice field in China

Rice cultivation is important in China with over 29.33 million hm2 of rice fields, producing 28.9% of rice yields worldwide. Rice fields are mass breeding sites for mosquitoes with approximately 40 mosquito species found breeding amongst them. Anopheles sinensis, Anopheles lesteri, and Culex tritaeniorhynchus are the three main species that are found breeding in rice fields. An. sinensis and An. lesteri are important vectors of malaria in flat areas of China, and Cx. tritaeniorhynchus is a main vector of Japanese B encephalitis. This review provides the principles of mosquito control used to target the species of mosquitoes breeding in rice fields, as well as some main approaches that have been tested and implemented for mosquito control in the past 70 years. The irrigation management of rice fields is included, such as intermittent irrigation, wet irrigation, controlled irrigation, and rotation of rice fields and dry fields. Biocontrol measures and agents, including rice-fish coculture, Azolla, Bacillus thuringiensis israelensis (Bti), and Bacillus sphaericus, for mosquito control are discussed. These control methods benefit the prevention and control of mosquito-borne disease, especially malaria elimination in China.

The phytotoxicity mechanism of florpyrauxifen-benzyl to Echinochloa crus-galli (L.) P. Beauv and weed control effect

Weeds infest rice causing high yield losses, leading to the increasing use of herbicides for weed control. However, many weeds have evolved resistance to common commercial herbicides, including penoxsulam, metamifop and quinclorac. This study investigated the weed control effect and the phytotoxicity mechanism of florpyrauxifen-benzyl, a novel synthetic auxin herbicide registered for weed management in rice fields in China. The greenhouse study showed that florpyrauxifen-benzyl was highly efficient (GR50 < 6 and GR90 < 15 g a.i ha−1) at controlling 10 weed species commonly found in rice fields, including penoxsulam- and quinclorac- resistant(R) biotypes of Echinochloa Beauv. and bensulfuron-methyl-R biotype of Ammannia arenaria. The typical plant hormone content showed that following florpyrauxifen-benzyl treatment, indole-3-acetic acid (IAA) production changed only slightly at 12 h, while abscisic acid (ABA) production increased with time in the treated group, whose content was significantly higher than that of the control. Besides, ethylene biosynthesis was stimulated by florpyrauxifen-benzyl, ethylene production, 1-aminocyclopropane-1-carboxylic acid (ACC) content, and 1-aminocyclopropane-1-carboxylate synthase (ACS) and 1-aminocyclopropane-1-carboxylate oxidase (ACO) activities, which evidently increased in the treated group, and ethylene peaked at 36 h. For the antioxidant enzyme activities and malondialdehyde (MDA) content in the treated group, results showed that MDA content continuously increased with time and was greater than that in the untreated group at 48 h and 72 h, superoxide dismutase (SOD) activity changed with exposure time and was significantly higher in the treatment group than the control at 48 h. A similar phenomenon was observed in peroxidase (POD) activity, which reached a peak at 48 h, and no distinct difference in catalase (CAT) activity was observed among groups except for the higher activity in the treated groups than control at 36 h and 48 h. Our results showed that that the stimulation ethylene biosynthesis and accumulation of ABA and reactive oxygen species (ROS) play important roles in the phytotoxicity mechanism of florpyrauxifen-benzyl in plants. Our findings demonstrate the potential of florpyrauxifen-benzyl to provide an alternative weed management strategy for rice fields.

Molecular basis of resistance to bensulfuron-methyl and cross-resistance patterns to ALS-inhibiting herbicides in Ludwigia prostrata

AbstractLudwigia prostrata is a problematic weed in rice fields in China, where acetolactate synthase (ALS)-inhibiting herbicides (e.g., bensulfuron-methyl) are widely used for the management of broadleaf weeds. Recently, an L. prostrata biotype (JS-R) that failed to be controlled with ALS-inhibiting herbicides was found in Jiangsu Province, China. This study aims to determine the level and molecular mechanism of resistance to bensulfuron-methyl in this JS-R biotype and to evaluate its spectrum of cross-resistance to other ALS-inhibiting herbicides. The dose–response assays indicated that the JS-R L. prostrata biotype had evolved 21.2-fold resistance to bensulfuron-methyl compared with the susceptible biotype (JS-S). ALS gene sequencing revealed that a nucleotide mutation (CCA to TCA) at codon 197, resulting in a Pro-197-Ser mutation, was detected in the resistant plants. Moreover, while the JS-R biotype contained the Pro-197-Ser resistance mutation and showed cross-resistance to pyrazosulfuron-ethyl (12.0-fold), it was sensitive to penoxsulam, bispyribac-sodium, and imazethapyr, which may serve as alternative herbicides to control the resistant L. prostrata biotype. This is the first confirmation of an L. prostrata biotype resistant to bensulfuron-methyl due to a Pro-197-Ser resistance mutation in the ALS gene.