【Objective】Flooding and drainage in paddy fields strongly influence rice growth, yield formation, and nutrient losses. However, their mechanistic effects on crop productivity and nutrient leaching remain poorly understood. This paper aims to elucidate these mechanisms. 【Method】Experiments were conducted in pots. Sediment contents of 0 kg/m3 (S0), 0.10 kg/m3 (S1) and 0.25 kg/m3 (S2), inundation duration with continuous flooding of 3 days (F1) and 6 days (F2), and water recession for 3 days (D1) and 6 days (D2) were applied during the tasseling and yellow ripening stages of early-season rice and the tillering and jointing stages of mid-season rice. The control (CK) was conventional management used by local farmers. In total, there were 13 treatments. In each treatment, we measured changes in sediment content, total nitrogen (TN), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N) and total phosphorus (TP) concentrations in the effluents, as well as rice yield and yield components.【Result】①Flooding resulted in yield reductions ranging from 11.07% to 69.96%; on average, the F1D1 and F1D2 treatments showed the least yield loss for both early- and mid-season rice. ②Sediment concentration decreased significantly over time during the drainage process and was reduced by more than 50% six days after the onset of drainage. ③TN, NH4⁺-N, NO3--N and TP concentrations increased during both flooding and drainage processes, with early-season rice exhibiting the highest concentrations at the tasseling stage and mid-season rice at the tillering stage. ④TN, NH4⁺-N and TP concentrations in the effluent were negatively correlated with early-season rice yield, while their correlations with mid-season rice yield were not statistically significant.【Conclusion】Flooding and drainage critically influence rice yield and nutrient losses in paddy fields. Our experiment showed that flooding for 3 days followed by a 3-6 day drainage minimized yield loss to 18.67%-50.33% for early-season rice and 32.38%-38.35% for mid-season rice, with TN and TP concentrations in the effluent remaining below 25.82 mg/L and 1.41 mg/L, respectively. These strategies can be used in irrigation and drainage system design.

In recent years, there has been a notable increase in the frequency and intensity of floods and heavy rains, which has resulted in the frequent inundation of rice-growing areas. Flooding during the heading–flowering stages of early rice can result in significant yield losses. To elucidate the response of rice to sediment content, flooding, and drainage processes and their underlying mechanisms, a pot experiment was conducted to investigate the effects of sediment contents (S1: 0, S2: 0.10 kg m−3, and S3: 0.25 kg m−3), flooding time (F1: 3 days and F2: 6 days), and drainage time (D1: 3 days and D2: 6 days) during the heading–flowering stage on the oxidation resistance and grain yield of early rice in the Poyang Lake Region. At the same time, an experimental control group (CK) was set up with no sediment, no flooding, or no drainage treatment. The results showed that the flag leaf area of S1F1D2 treatment was diminished by flooding. The relative chlorophyll content (SPAD) reached its lowest value prior to drainage. The treatment of S2F2D1 showed the greatest decrease in SPAD value of 41.57%, which was only 53.88% of that of the control treatment. The activity of superoxide dismutase (SOD), peroxidase (POD), and the content of malondialdehyde (MDA) were observed to increase during the flooding period in comparison to the control treatment. The maximum values for these parameters were recorded at 5.68, 3.09, and 1.9 times higher than those of the control treatment, respectively. However, a decrease was observed after drainage. Furthermore, the occurrence of flooding during the early rice heading–flowering stage resulted in a notable reduction in the grain number per spike and the fruiting rate, consequently leading to a considerable decline in grain yields, with a decrease ranging from 31.81% to 69.96%. The findings indicate that flooding during the heading–flowering stage resulted in a reduction in early rice grain yield yet enhanced the antioxidant capacity of the leaves. Regression analyses indicated that a prediction model for the actual yield after flooding stress at the heading–flowering stage of early rice could be constructed using SFW as the independent variable. The findings of this study provide a theoretical basis for the formulation of a scientific and reasonable drainage scheme with the objective of reducing yield loss following rice flooding in the southern rice-growing region of China.

Nitrogen (N) dynamics critically regulate rice productivity through root-mediated absorption and assimilation processes. This study investigates the differential responses of japonica (Suxiu 867) and indica (Yangxianyou 918) rice to N deficiency and subsequent high-efficiency compensation, integrating metagenomic analysis with physiological assessments of N metabolism. Building on an established high-efficiency N compensation period (18 days after tillering for japonica and 12 days for indica), we demonstrate that optimized N compensation significantly enhances dry matter accumulation and yield in both subspecies through distinct biological mechanisms. Compensation treatment elevated key metabolic indicators including soluble protein content (Cpr), glutamine synthetase (GDH) activity, soil urease (S-UE) activity, glutamate synthase (GOGAT) activity, and glutamine synthetase (GS) activity, collectively enhancing N assimilation efficiency. Rhizosphere microbiome restructuring showed subspecies-specific patterns, with Chloroflexi and Betaproteobacteria abundance positively correlating with N metabolic enzymes in indica, versus Actinomycetia, Deltaproteobacteria associations in japonica. Functional microbial analysis revealed divergent keystone taxa, with Noviherbaspirillum (indica) and Bacillus (japonica) driving N conversion efficiencies through niche-specific community synergies. Notably, indica rice presented a relatively high N absorption capacity and conversion efficiency, while japonica rice presented relatively stable N absorption and distribution mechanisms, and relatively high N fertilizer application significantly increased the abundance of specific microbial communities in japonica rice. These findings elucidate how subspecies-specific root physiology coordinates with rhizosphere microbial ecology to optimize N utilization, providing actionable insights for precision N management strategies tailored to rice genetic types.

The impact of the flooding-draining process on soil ecosystems is complex and dynamic. However, the specific effects of different drainage durations on soil microorganisms and metabolites remain unclear. This study adopted a multi-omics research method. After nontargeted metabolomics analysis of lipids as the main metabolite, microbial diversity analysis and lipidomics analysis were conducted to determine the main influencing factors. Subsequently, correlation analysis was performed with physiological and biochemical data to logically explore the changes in soil microorganisms and metabolites during the drainage process (Day 1 after drainage, R1; Day 2, R2; Day 3, R3; Day 4, R4; and Day 5, R5). The results revealed that S-PPO, S-POD, and S-CAT decreased with prolonged drainage time, whereas the soil redox potential (Eh-mV) and POD increased. Among the various postdrainage comparison groups, lipids and lipid-like molecules were the predominant metabolites. Among lipids, the TG subclass of glycerolipids (GLs) and the Cer subclass of sphingolipids (SPs) were the most abundant. The TG subclass was consistently present in the lipid correlation networks across all comparison groups, with TG (15:0/18:1/18:1) exhibiting significant differences between the R4 and R1 groups. Redox reactions involving lipids were associated mainly with triglycerides, with the most pronounced reduction observed on the second day postdrainage. The most pronounced lipid reduction reaction was observed on the second day after drainage. Notable differences in bacterial abundance were detected between the R4 and R5 groups. At the phylum level, the dominant bacterial communities primarily comprised Actinobacteriota and Chloroflexi, with the bacterial community structure being significantly influenced by drainage. The predominant fungal communities were composed of mainly Ascomycota and Rozellomycota. Actinobacteriota and triglyceride (TG) lipids were the major components affected during the drainage period. Correlations were identified among environmental factors, lipids, and microbial communities, indicating their cooperative interactions. The results of this study indicate that with the increase in water intake time, the redox reactions in soil lipids and the richness of bacterial communities in rice soil significantly increase. At the same time, rapid remodeling can have an impact on soil ecosystems, which helps to better understand the adaptation strategies of rice soil ecosystems under adversity.

Compensatory effects are common biological phenomena in nature. In this study, we investigated the changes in root nitrogen uptake, root morphological and physiological responses, and changes in the rhizosphere soil microbial communities of indica and japonica rice during a nitrogen deficiency-sensitive period and an effective compensation period with double the nitrogen supply. We conducted a bucket experiment using Suxiu 867 (a japonica rice variety) and Yangxian You 918 (an indica rice variety). Treatments included CK (constant distribution of nitrogen fertilizer at each growth stage, represented by CK867 and CK918) and NDC (nitrogen deficiency in the tillering stage, double nitrogen application in the ear differentiation stage to compensate, represented by NDC867 and NDC918) variations. Both varieties presented the highest delta N-15 and N-15 abundances and Ndff (refers to the proportion of nitrogen in a plant's body that comes directly from the fertilizer applied.) in rice under the NDC treatment. Metagenomic sequencing of rhizospheric soil showed that the dominant bacterial groups at the phylum level among each treatment were Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, and Nitrospirae. The rhizosphere of indica rice was more enriched with the microbial communities involved in nitrogen metabolism, which contributed to higher nitrogen utilization efficiency. A correlation-based network was constructed and provides insights into the formation of nitrogen deficiency compensation effects and contributes to the enhancement of nitrogen uptake and utilization efficiency in rice production.

Designing appropriate nitrogen (N) application rates and planting densities is crucial for ensuring high-yield and high-quality rice production. The effects of N fertilizer and planting density on the soil microbial community composition and abundance and on root N uptake mechanisms were investigated. In this study, high-nitrogen low-density (HNLD), medium-nitrogen medium-density (MNMD) and low-nitrogen high-density (LNHD) experiments were conducted via the bucket planting method, and plant physiology, dry matter mass and N uptake, root enzyme activities and rhizosphere soil microbial communities were examined via metagenomic sequencing and isotope tracing. The HNLD treatment exhibited the highest N absorption and utilization capacity. Compared to those in the other treatments, the δ15N values and abundance increased by 52.96–63.45

Exploring the growth and physiological response mechanisms of rice under continuous drought stress circumstances can provide a significant scientific foundation and technological assistance for meeting drought difficulties, improving drought resistance and rice (Oryza sativa L.) output, and ensuring food security. In this study, a rice field experiment was conducted under a rain shelter with five different treatments set up: P1 (drought stress from tillering stage), P2 (drought stress from jointing–booting stage), P3 (drought stress from heading–flowering stage), P4 (drought stress from grain filling stage), and CK (adequate water management throughout the growth stage). Continuous drought stress from different growth stages with four levels (mild, medium, moderate, and severe). The results showed that the effects of different drought stress treatments on rice growth varied significantly. Compared with the CK treatment, plant height was reduced by 12.10%, 8.14%, 3.83%, and 1.06% in the P1, P2, P3, and P4 treatments, respectively, and the number of tillers was reduced by 23.83%, 18.91%, 13.47%, and 8.68%, respectively. With the increase in drought stress levels, SPAD values and Rubisco activity of rice leaf continued to decrease; SOD activity showed a decreasing trend, but the decreasing trend of POD and CAT activities was not significant, while MDA content showed an increasing trend. For yield components, continuous drought stress significantly reduced spike length of rice by an average of 3.5%, effective number of spikes by 18.9%, thousand grain weight by 3.7%, grain number per spike by 11.6%, and fruiting rate by 1.8%, respectively, compared to CK treatments during the growth period. In general, continuous drought stress during the early growth period affected the effective spike number and the grain number per spike. Continuous drought stress after the grain filling stage had the least effect on yield (17.62% of yield reduction), and water use efficiency (1.76 kg m−3) was much higher than other treatments. These researchers’ findings provide insight into how rice physiology and growth react to continuous drought stress, which is significant for agricultural operations.

[Objective]To explore the effect characteristics of irrigation and planting methods on nitrogen loss and water utilisation in rice fields.[Method]We selected four planting methods:hand-transplanting(HT),seedling throwing(ST),machine-transplanting(MT)and direct seeding(DS),and two irrigation modes:flooding irrigation(FI)and intermittent irrigation(II),and carried out a plot experiment on late rice to analyse and evaluate the characteristics of paddy rice field water balance,water-use efficiency,and nitrogen runoff and leaching loss under different irrigation and planting modes.[Result]The results showed that:the water use efficiency of different irrigation modes was higher in intermittent irrigation,and the water use efficiency of different planting modes was HT(ST)>MT>DS.The water quantity,water consumption,leakage,and evapotranspiration were reduced by 9.87%-22.11%,9.65%-21.49%,1.46%-3.64%,and 11.18%-27.15%,respectively,for the treatments of each cropping method under the intermittent irrigation pattern as compared to the flooded irrigation pattern.Planting method and irrigation pattern had a greater impact on nitrogen runoff and leaching loss,which accounted for 0.02%-0.17%and 2.33%-3.53%of the applied fertiliser,respectively.Under the same irrigation pattern,the nitrogen surface runoff loss and leaching loss of different planting treatments were DS>MT>ST>HT.The leaching amount and nitrogen leaching loss of different treatments varied in each fertility period under the influence of irrigation pattern and planting method,among which the loss was higher in seedling and pre-tiller stage,which accounted for the proportion of the whole fertility period,respectively,43.35%-53.79%and 6.67%.53.79%,and 6.67%-22.38%,respectively.With the combined irrigation pattern and planting method,the yield and water use efficiency of different treatments were the highest in HT-II and the lowest in DS-FI,while the nitrogen leaching loss was the lowest in HT-II and the highest in DS-FI.[Conclusion]Intermittent irrigation is beneficial to improve rice yield and water use efficiency,water consumption and nitrogen loss of direct seeding rice are higher than that of transplanted rice,and hand-planting with intermittent irrigation is beneficial to improve water use efficiency of rice and reduce nitrogen loss from paddy fields.In the production practice of double-season late rice,the environmental effect of paddy field can be improved by strengthening the water management at seedling and pre-tiller stages to reduce paddy leaching and nitrogen leaching loss.

Differences in main nutritional components in relation to biomarkers of metabolites in purple rice grains at different fillings stages have not been determined previously. This study measured the contents of amino acids, several nutritional indicators, and mineral elements in purple rice grains at five stages following the filling stage. The results revealed that the amino acid, ascorbic acid, total sugar, carotenoid, vitamin B9, cyanidin-3-O-glucoside, peonidin 3-glucoside and seven minerals were highest in the final stage of grain filling. Citric acid, L-isoleucine, trigonelline, and L-glutamate are key metabolites in the metabolic pathway and exhibit strong correlations with various nutritional indicators. Hence, this research preliminarily suggested that trigonelline, L-isoleucine, L-glutamate, and citric acid could be potential biomarkers of nutritional components in purple rice grains during various postfilling stages.

Colored rice is richer in nutrients and contains more nutrients and bioactive substances than ordinary white rice. Moderate consumption of black (purple) rice has a variety of physiological effects, such as antioxidant effects, blood lipid regulation, and blood sugar control. Therefore, we utilized nontargeted metabolomics, quantitative assays for flavonoid and phenolic compounds, and physiological and biochemical data to explore the correlations between metabolites and the development of antioxidant characteristics in pigmented rice seeds. The findings indicated that, among Yangjinnuo 818 (YJN818), Hongnuo (HN), Yangchannuo 1 hao (YCN1H), and Yangzi 6 hao (YZ6H), YZ6H exhibited the highest PAL activity, which was 2.13, 3.08, and 3.25 times greater than those of YJN818, HN, and YCN1H, respectively. YZ6H likewise exhibited the highest flavonoid content, which was 3.8, 7.06, and 35.54 times greater than those of YJN818, HN, and YCN1H, respectively. YZ6H also had the highest total antioxidant capacity, which was 2.42, 3.76, and 3.77 times greater than those of YJN818, HN, and YCN1H, respectively. Thus, purple rice grains have stronger antioxidant properties than other colored rice grains. Receiver operating characteristic (ROC) curve analysis revealed that trans-3,3',4',5,5',7-hexahydroxyflavanone, phorizin, and trilobatin in the YZ6H, HN, and YCN1H comparison groups all had area under the curve (AUC) values of 1. Phlorizin, trans-3,3',4',5,5',7-hexahydroxyflavanone, and trilobatin were recognized as indices of antioxidant capability in colored rice in this research. This research adds to the understanding of antioxidant compounds in pigmented rice, which can increase the nutritional value of rice and promote the overall well-being of individuals. This type of information is of immense importance in maintaining a balanced and healthy diet.

Paddy fields are complex ecosystems that both emit CH4 and absorb CO2, which plays an important role in the global water-carbon cycle and carbon budget. In this study, the CH4 fluxes and CO2 fluxes of double-cropping direct-seeded rice fields in 2020 in the Poyang Lake Plain were obtained using the eddy covariance method, and the variation characteristics, accumulation in the whole growth period, and comprehensive greenhouse effects of two greenhouse gases were quantitatively revealed. The results showed that, the double-cropping direct-seeded rice field in Poyang Lake Plain was the source of CH4 emission, and the emission during the whole growth period was 52.6 g·m-2, with an average daily emission of 0.208 g·(m2·d)-1. CH4 emission and daily average emission in the early rice season were 20.7 g·m-2 and 0.188 g·(m2·d)-1, respectively, which were lower than the emissions of 31.9 g·m-2 and 0.255 g·(m2·d)-1 in the late rice season. CH4 flux had significant seasonal variation characteristics. The strong emission period (emission peak) of CH4 was concentrated in the middle growth stage of early rice and the early growth stage of late rice. A total of 85.5% of CH4 in the early rice season and 92.1% of CH4 in the late rice season were released during the strong emission periods, and seasonal peak values were 0.638 g·(m2·d)-1 and 1.282 g·(m2·d)-1, respectively. The diurnal variation characteristics of CH4 flux showed three types:obvious unimodal type, non-obvious unimodal type, and irregular type. The strong emission period was mainly the unimodal type, and the peak values of 0.453 μmol·(m2·s)-1 in the early rice season and 0.977 μmol·(m2·s)-1 in the late rice season appeared at 14:00-15:00 and maintained a high emission rate at 12:30-16:00. The CO2 accumulation in the whole growth period of early rice and late rice was -990.4 g·m-2 and -1156.6 g·m-2, respectively, and the total was -2147.0 g·m-2. The comprehensive greenhouse effect of CH4 emission and CO2 exchange in the double-cropping paddy field was -673.6 g·m-2 (calculated using the CO2 equivalent), which showed a cooling effect. Excluding CH4 emissions when evaluating the greenhouse effect of the paddy field, the CO2 equivalent emission of 1473.4 g·m-2 would be underestimated, accounting for 68.6% of the net CO2 absorption. Considering CH4 emissions, CO2 exchanges, and carbon emissions caused by rice harvest, the two-season direct seeding paddy field in Poyang Lake Plain was the source of greenhouse gas emissions.

The normal methods of agricultural production worldwide have been strongly affected by the frequent occurrence of drought. Rice rhizosphere microorganisms have been significantly affected by drought stress. To provide a hypothetical basis for improving the drought resistance and N utilization efficiency of rice, the study adopted a barrel planting method at the heading stage, treating rice with no drought or drought stress and three different nitrogen (N) levels. Untargeted metabolomics and 16S rRNA gene sequencing technology were used to study the changes in microorganisms in roots and the differential metabolites (DMs) in rhizosphere soil. The results showed that under the same N application rate, the dry matter mass, N content and N accumulation in rice plants increased to different degrees under drought stress. The root soluble protein, nitrate reductase and soil urease activities were improved over those of the no-drought treatment. Proteobacteria, Bacteroidota, Nitrospirota and Zixibacteria were the dominant flora related to N absorption. A total of 184 DMs (98 upregulated and 86 downregulated) were identified between low N with no drought (LN) and normal N with no drought (NN); 139 DMs (83 upregulated and 56 downregulated) were identified between high N with no drought (HN) and NN; 166 DMs (103 upregulated and 63 downregulated) were identified between low N with drought stress (LND) and normal N with drought stress (NND); and 124 DMs (71 upregulated and 53 downregulated) were identified between high N with drought stress (HND) and NND. Fatty acyl was the metabolite with the highest proportion. KEGG analysis showed that energy metabolism pathways, such as D-alanine metabolism and the phosphotransferase system (PTS), were enriched. We conclude that N-metabolism enzymes with higher activity and higher bacterial diversity have a significant effect on drought tolerance and nitrogen uptake in rice.

In order to clarify the effect of reducing nitrogen application on Yield and water and nitrogen utilization efficiency of doubleseason rice under the combined application mode of Chinese milk vetch and straw returning, five treatments, including non-returning with no fertilizer（S0N0）, non-returning with total nitrogen fertilizer（S0N3）, Chinese milk vetch and straw returning with no fertilizer（S1N0）, Chinese milk vetch and straw returning with reduced nitrogen fertilizer（S1N1） and Chinese milk vetch and straw returning with reduced nitrogen fertilizer（S1N2） were set in this study. Nitrogen content and accumulation in plants of double-season rice in different growth stages were determined, and water and nitrogen utilization efficiency, yield and yield components of double-season rice were analyzed. The results showed that compared with S0N0 treatment, nitrogen content and accumulation, water and fertilizer utilization efficiency and yield of S1N0were improved without nitrogen application. S1N2 treatment had the highest nitrogen content and nitrogen uptake in two-season rice at heading stage and yellow maturity stage. At early rice stage, the yield of early rice was the highest under conventional nitrogen application S0N3 treatment, and the yield of early rice under nitrogen reduction treatment S1N1 and S1N2 decreased by 7.43% and 1.68% respectively,while that of late rice increased by 0.68% and 2.35% respectively, but there was no significant difference. Compared with conventional nitrogen application（S0N3）, reducing nitrogen application（treatment S1N1, S1N2） could reduce irrigation water, drainage and field water consumption of double-season rice, significantly improving water use efficiency by 5.24% and 25.86% respectively in late rice period, and significantly improving nitrogen use efficiency by 6.23% and 13.74% respectively. Therefore, based on comprehensive consideration of water and fertilizer utilization efficiency and yield, it was appropriate to reduce the amount of nitrogen fertilizer for early and late rice by 15% and 10% respectively under the way of returning aster and straw to field.

In order to clarify the application effect of the intelligent irrigation system in double-cropping rice field, a comparison experiment between intelligent irrigation system and conventional irrigation with water layer in the double-cropping rice field was carried out in Jiangxi province for 4 consecutive years and 8 rice seasons from 2017 to 2020,and the influences of different irrigation methods on the rice yield and quality, water use efficiency and environment of double-cropping rice were compared and analyzed.The results showed that, compared with conventional irrigation, the intelligent irrigation system of double-cropping rice field could carry out precise irrigation according to the irrigation rules formulated by soil moisture and weather variables combined with the water requirement law of double-cropping rice, which increased the yield of double-cropping rice by 6.4%-14.3%,slightly improved the quality of rice, especially the appearance quality, and reduced the chalkiness rate and degree of chalkiness significantly in some years.At the same time, the irrigation water and drainage can be significantly reduced, the irrigation water reduction rate is 14.1%-90.8%,the water reduction rate is 56.1%-100%,the water use efficiency can be improved by 0.07-0.59 kg/m~3,the total nitrogen emission in runoff water can be reduced by 47.3%-100%,the total phosphorus emission in runoff water can be reduced by 44.5%-100%.It is worth popularizing and applying in double cropping rice area in south China.

The biological characteristics of crop roots are closely related to the efficient utilization of nitrogen and have become a research hotspot in agricultural cultivation and breeding in recent years. The root system and root microbiota play a crucial role in both the basic and the plastic growth and development of plants in response to external environmental changes. Nitrogen is an indispensable nutrient element for crop growth, and the efficient utilization of nitrogen is the key to achieving the high yield and quality of crops and establishing environmentally friendly agricultural production. The nitrogen absorbed and utilized by rice mainly enters the aboveground part of the plant through the root system from within the soil. This process is explored from the perspective of root biology (root morphology, physiological and biochemical characteristics, root growth and development process and regulation, rhizosphere microorganisms, and their symbiotic systems), which is in line with the directions of "less investment, increased production, environmental protection, and sustainable development" in China. Based on the research status in this field at present, this article explored the interaction mechanism between crop root biology and nitrogen absorption and utilization, and looks forward to the future research directions for root biology. This study provides a theoretical basis for reducing nitrogen fertilizer application, optimizing nitrogen-efficient cultivation management techniques, and selecting nitrogen-efficient varieties.

针对膜设备在农村分散式饮用水处理上的应用,总结国内外相关研究成果,以膜处理技术为对象,分析膜处理技术在农村分散式饮用水中的应用现状,探讨膜处理技术在今后的应用前景,为今后膜处理技术在农村分散式饮用水中的应用提供实践指导.

Water stress can affect rice yield and its growth.To enhance the adaptability of rice to adversity and examine the associ-ated physiological mechanisms,experiments focused on investigating the effects of drought exercise at the tillering stage on the for-mation of rice yield per plant and physiological adaptation to subsequent drought or submergence at the jointing-booting stage were performed.The results showed that the rice yield per plant of drought exercise treatment at the tillering stage combined with joint-ing-booting stage drought exercise treatment(D+D)was increased by 10.92％compared with that of the rice yield per plant of no drought exercise treatment at the tillering stage combined with jointing-booting stage drought exercise treatment(ND+D)without significant difference.The rice yield per plant of drought exercise treatment at the tillering stage combined with jointing-booting stage submergence treatment(D+S)was also increased by 19.91％compared with that of the rice yield per plant of no drought ex-ercise at the tillering stage combined with jointing-booting stage submergence treatment(ND+S)without a significant difference.The net photosynthetic and transpiration rates of the rice plants of the D+S treatments were increased by 10.6％and 26.69％,com-pared with the ND+S treatments,respectively.The ratio of variable fluorescence to the maximum fluorescence(Fv/Fm)of the rice plants with the ND+D treatment was less significant and decreased by 3.67％compared with the D+D treatment,the soluble sugar content of D+D treatment was decreased by 9.36％compared with ND+D treatment without any significant difference,and the solu-ble sugar content of the D+S treatment was 21.41％higher than the ND+S treatment.The subjection to drought exercise at the tille-ring stage along with subsequent drought and submergence treatments at the jointing-booting stage increased the activities of superox-ide dismutase(SOD),peroxidase(POD),catalase(CAT),and total antioxidant capacity while decreased malondialdehyde(MDA)and H202 contents for the rice plants to protect themselves from injury.Therefore,the study demonstrated that the drought exercise at the tillering stage was helpful for the rice plants in forming the tolerance to water stress at subsequent jointing-booting stage,and the results can provide guidance for the rice production practices in drought or flood disasters.

The aim of this study was to explore the differences in metabolites related to rice quality formation under different nitrogen (N) fertilizers and planting densities. In this study, Yangnongxiang 28 was used as the experimental material with the following conditions: high nitrogen and low density (HNLD; high nitrogen: 360 kg·hm−2, low density: the row spacing of rice plants was 16 cm × 30 cm), medium nitrogen and medium density (MNMD; medium nitrogen: 270 kg·hm−2, medium density: the row spacing of rice plants was 13 cm × 30 cm), and low nitrogen and high density (LNHD; low nitrogen: 270 kg·hm−2, high density: the row spacing of rice plants was 10 cm × 30 cm). The rice quality indexes, including the processing quality, amylose content, and taste value, were compared under different treatments, and we analyzed their relationship with the metabolites. The results show that the milled rice rate of HNLD was 13.85% and was 1.89% higher than that of LNHD and MNMD, respectively. The head milled rice rate of HNLD was 32.45% and 6.39% higher than that of LNHD and MNMD, respectively. The milled rice rate and head milled rice rate of HNLD and MNMD were significantly higher than those of LNHD. This study identified 22 differential metabolites (DMs) in HNLD and LNHD, 38 DMs in HNLD and MNMD, and 23 DMs in LNHD and MNMD. Most of the identified differential metabolites were lipid metabolites, which were mainly enriched in the lipid metabolic pathways and amino acid metabolic pathways. The correlation analysis showed that the lipid metabolite physapubescin was significantly negatively correlated with the taste value. The lipid metabolites 2-undecen-1-ol, lucidenic acid F, and 8-deoxy-11,13-dihydroxygrosheimin were significantly positively correlated with the taste value. Lipids may be important substances that lead to differences in taste under different nitrogen fertilizer and density treatments.

【Objective】 The plum rainy season from May to July in southern China is a period where rice accumulates nutrients. The purpose of this paper is to explore the effects of onset, duration of flooding and recession of waterlogging in this period on oxidation resistance and yield of rice in the catchment of Poyang Lake. 【Method】 Pot experiments with Semilate rice as the model plants were conducted when the crop was in the elongation stage. Sediment contents of the surface water was 0 kg/m3 (S0), 0.10 kg/m3(S1) and 0.25 kg/m3 (S2), respectively. For each sediment content, there were two waterlogging treatments with the duration of surface-flooding being 3d (F1) and 6 d (F2) respectively. For each sediment and waterlogging combination, there were two drainages with the duration of the surface water receding being 3 d (D1) and 6 d (D2) respectively. The control was without taking interferences (CK). In each treatment, we measured the SPAD, activity of antioxidant enzymes in the flag leaves and the rice yield. We then analyzed the response of the rice to waterlogging and its associated recession. 【Result】 ①The SPAD decreased with the increase in sediment content, duration of flooding and its recession; it peaked prior to the onset of the drainage. The greatest SPAD fall was in S2+F2+D2, decreasing by 46.20% compared to the CK. ②The activities of SOD and POD, as well as MDA content increased first followed by a decline as the waterlogging recessed; they all peaked prior to the starting of the drainage. ③Waterlogging reduced the 1 000-grain weight and hence the grain yield significantly, compared to the CK (P<0.05), especially S0+F2+D2 and S2+F2+D2 whose yield was down by 52.22% and 52.00%, respectively, than the CK. 【Conclusion】 The enhanced oxidation resistance in semilate rice leaves due to waterlogging at the elongation stage reduced the grain yield. Among the three factors we investigated, duration of flooding and flooding recession affected the rice yield more. To alleviate yield reduction, the duration of the waterlogging and the time it takes to drain the flooding should be less than six days.

为探究不同种植方式下双季稻田水肥利用、流失及其环境效应,以中嘉早17和H优518为试验材料,采用大田对比试验方法,通过设置手工插秧(HT)、抛秧(ST)、机插(MT)、直播(DS)4种种植方式,研究种植方式对双季稻产量、水分利用效率、氮磷利用与流失、稻田温室气体排放及温室效应的影响.结果表明,不同种植方式下,早晚稻产量、水分利用效率、氮磷内部利用效率和收获指数的变化趋势均表现为HT>ST(或MT)>DS,径流氮磷排放量、CH4和CO2排放量以及双季累计的全球增温潜势和温室气体排放强度均表现为DS>ST(或MT)>HT;DS处理较HT处理双季平均减产12.35％,水分利用效率和氮、磷养分内部利用效率双季平均分别下降19.50％、6.73％、6.29％,而径流总氮排放量、径流总磷排放量、CH4排放量、CO2排放量、全球增温潜势和温室气体排放强度双季累计分别增加24.05％、41.40％、6.67％、14.47％、6.74％、21.37％.由此可见,手工插秧在降低农田径流氮磷流失、减少温室气体排放和温室效应、促进水肥利用和水稻增产方面效果最优,而直播方式的生态效应相对较差.