Improving the adaptability of rice leaves to high-light under heat stress is essential for maximizing photosynthetic efficiency. This study examined the responses of leaf gas exchange and hydraulic parameters to intense light under heat stress (40 °C) in wild type (Nipponbare) and four genetically modified rice varieties (NAL1-K, NAL1-O, Ghd7.1-K, and Ghd7.1-O) that exhibited significant differences in leaf area (LA). When measured irradiance increased from 1000 to 2000 μmol m-2 s-1 under heat stress, the changes of photosynthetic rate (A2000-A1000) ranged from -2.8 μmol m-2 s-1 in NAL1-O to 14.9 μmol m-2 s-1 in NAL1-K. A negative correlation between A2000-A1000 and LA was observed. The varying responses of A to high-light were primarily associated with stomatal conductance (gs). Enhanced leaf hydraulic conductance (Kleaf) facilitated the gs response to high-light under heat stress conditions. Furthermore, this study revealed that, under high-light and heat stress conditions, Kleaf is predominantly regulated by leaf hydraulic conductance inside the xylem (Kx), and reduced LA can significantly improve Kx. These findings demonstrate that reducing LA can enhance Kleaf, thereby improving the response of A to high-light under heat stress.

Accumulation of stem non-structural carbohydrates (NSC) at heading is crucial for mitigating grain-setting defects in large-panicle rice. While traditional panicle nitrogen fertilizer application at the emergence of the fourth leaf from the flag leaf stage (TL4) may weaken stem sink strength, delaying application to the emergence of the third leaf from the flag leaf stage (TL3) significantly enhances NSC accumulation. This study aimed to elucidate the molecular mechanisms through which TL3 remodels stem sink strength to promote NSC storage. Using two large-panicle rice varieties (Huiliangyou 280 and Yangliangyou 228), we compared stem NSC dynamics under TL4 and TL3 treatments and integrated sugar-related metabolite profiling with transcriptome analysis during the critical NSC accumulation phase. The results showed that TL3 treatment significantly increased stem NSC content and NSC per spikelet at heading, leading to a higher percentage of filled grains. The period from 5 days before heading (DBH) to heading showed the highest NSC accumulation rate. At the molecular level, TL3 treatment specifically up-regulated eight key genes in the sucrose-starch metabolism pathway, increasing the activities of sucrose phosphate synthase, sucrose synthase, and ADP-glucose pyrophosphorylase, and thereby promoting the accumulation of sucrose, trehalose, and D-fructose. In summary, delaying panicle nitrogen application to TL3 enhances stem NSC storage by remodeling sink strength via coordinated regulation of the sucrose-starch metabolic network.

Synergistically enhancing both photosynthetic rate (A) and intrinsic water use efficiency (iWUE) in rice remains a major challenge for achieving high productivity in the future. In this study, 37 cultivated rice (Oryza sativa) varieties with significant variation in stomatal morphological traits were selected for pot experiments. Among these, the two highest and two lowest stomatal density varieties were further subjected to drought treatments. Under well-watered conditions, stomatal density was identified as a key factor coordinating stomatal conductance (gs) and mesophyll conductance (gm) among rice varieties by influencing mesophyll cell arrangement through stomatal development. Although increased stomatal density enhanced A, it did not synergistically improve iWUE. Under water stress, however, stomatal aperture decreased rapidly as drought intensified, gradually diminishing the positive effect of high stomatal density on gs until it disappeared. Notably, varieties with high stomatal density maintained higher gm than those with low stomatal density across the entire range of leaf water potentials measured, enabling simultaneous enhancement of both A and iWUE under drought conditions. Our study demonstrates that high stomatal density can synergistically enhance both A and iWUE under drought conditions, underscoring its potential utility in breeding drought-tolerant rice varieties.

Context: The effects of root traits and aboveground agronomic traits on net CH4 emissions from paddy fields differ across rice growth stages. High-yielding rice varieties have double-peak CH4 reduction potential during tillering and heading, but the underlying mechanisms remain unclear. Methods: Four high-yield low-CH4-emission (HyLc) and four low-yield high-CH4-emission (LyHc) rice varieties, including indica and japonica subtypes, were tested over two field seasons (2022-2023). Aboveground agronomic traits, root traits, root exudates, and rhizosphere microbial communities were analyzed. Results: Compared to LyHc varieties, HyLc indica and japonica rice achieved yield increases of 27.5% and 32.6%, respectively, over 2 years. They reduced CH4 emissions by 51.8% and 43.6% during the tillering stage and by 47.8% and 71.1% during the heading stage, resulting in overall CH4 emission reductions of 49.0% and 52.4%, respectively. Path analysis of partial least square path modeling (PLS-PM) revealed that aboveground agronomic traits were the primary contributing factors influencing CH4 emissions during the tillering stage (path coefficient: 0.72). Reducing the LAI, number of tillers, and SPAD during the tillering stage decreased the number of transmission pathways, thereby lowering CH4 emissions. Root traits were the primary negative contributors to CH4 emissions during the heading stage (path coefficient: -0.63). Increasing the root diameter (RD) and root dry weight (RDW) during heading enhanced the root oxygen release potential, thereby reducing CH4. Additionally, HyLc varieties increased the relative abundance of CH4-oxidizing bacteria (Methylomicrobium, Methylomonas) and reduced the relative abundance of CH4-producing archaea (Methanosaeta, Methanobacterium, Methanoregula) in the rhizosphere soil during heading, which synergistically promoted CH4 oxidation and reduced CH4 production. This is associated with the increased stearic acid content in root exudates, regardless of indica and japonica subtypes. Conclusions: Overall, the reduction in CH4 emission from HyLc varieties during tillering was primarily associated with reduced aboveground agronomic traits, whereas the reduction during heading was associated with enhanced root traits, as well as stearic acid-mediated microbial regulation. Implications: Reducing early nitrogen and applying precise panicle nitrogen to match HyLc variety production may further increase rice yield and reduce CH4 emissions from paddy fields.

High-temperature stress during the flowering stage, exacerbated by climate change, has become a major abiotic constraint on global rice production. This study aimed to identify effective mitigation strategies by systematically evaluating the physiological effects of exogenous compound agents on rice under high-temperature stress at flowering. A heat-tolerant cultivar (N22) and a heat-sensitive cultivar (YR343) were subjected to high-temperature stress during flowering, and 17 different formulations comprising calcium chloride (CaCl2), salicylic acid (SA), abscisic acid (ABA) and potassium dihydrogen phosphate (KH2PO4) were applied. The results showed that high-temperature stress significantly reduced pollen viability, the net photosynthetic rate (P n), and the activities of peroxidase (POD) and catalase (CAT), while increasing malondialdehyde (MDA) content, ultimately leading to significant decreases in the seed-setting rate and yield. In contrast, exogenous compound treatments effectively alleviated this physiological damage. Among them, the ternary formulations ABC (CaCl2 + SA + ABA) and ABD (CaCl2 + SA + KH2PO4) were the most effective. The underlying physiological mechanisms involve the synergistic regulation of three key processes: first, improving anther carbohydrate metabolism and increasing pollen stainability, thereby stabilising the seed-setting rate; second, slowing chlorophyll degradation and maintaining a higher P n to ensure photosynthetic productivity; and finally, synergistically enhancing the activities of antioxidant enzymes (POD, CAT) and promoting the accumulation of osmotic regulators (e.g., soluble sugars and proteins), thereby reducing oxidative damage and maintaining cell membrane stability. This study demonstrates that foliar application of ABC or ABD can systematically enhance thermotolerance during flowering through multi-target synergistic effects. These findings not only elucidate the physiological mechanisms of crop responses to high temperature but also propose a feasible agronomic strategy to mitigate heat-induced yield losses.

Water-saving and drought-resistant rice (WDR) achieves drought resistance and stable yield by maintaining high photosynthetic potential in leaves under severe drought. We speculated that the sheath organ serving as a photosynthetic source can contribute to a positive response to drought in WDR. However, the synergetic photosynthetic adaptation mechanisms of leaf and sheath organs to drought remain unknown. In this study, a pot experiment was conducted to investigate the WDR of Hanyou73 (HY73) and its parents, Hanhui3 (HH3) and Huhan7A (HH7A). All varieties were subjected to drought at heading with -100 kPa soil water potential. The results demonstrated that chlorophyll content, relative water content, photosynthesis-related parameters, and sugar contents of leaf and sheath organs were significantly reduced during drought across three varieties. However, the activities of catalase and peroxidase and the contents of proline, hydrogen peroxide, and abscisic acid increased during drought treatment in leaf and sheath organs of all varieties. The stomatal conductance changed less in the sheath organ than in the leaf organ under drought stress. Further analyses revealed that stomatal conductance in leaf and sheath organs was mainly regulated by large stomatal apertures among anatomical structural characteristics of stomata across varieties and treatments. For HY73, high drought resistance was associated with a high sucrose-supplying capacity, resulting from high photosynthetic potential in leaf and sheath organs, which was achieved by improving stomatal aperture compared to its parents. This study provides a theoretical basis for the mechanism of photosynthetic adaptation of leaf and sheath organs, synergistically improving drought resistance in rice.

Nitric oxide (NO) positively contributes to maintaining a high photosynthetic rate in waterlogged-wheat plants by maintaining high stomatal conductance (gs), mesophyll conductance (gm), and electron transport rates in PSII (J). However, the molecular mechanisms underlying the synergistic regulation of photosynthetic characteristics during wheat waterlogging remain unclear. Pot experiments were conducted with two cultivars: Yangmai15 (YM15: high waterlogging-tolerance capacity) and Yangmai24 (YM24: conventional waterlogging-tolerance capacity). The 2 cm waterlogging depth treatment (WL), exogenous spraying of NO every two days in the WL treatment (WLsnp), and suitable soil water content treatment (CK) were established during the flowering stage for eight consecutive days. RNA-seq, weighted gene co-expression network analysis (WGCAN), and protein interaction analysis were performed on the 8th day to screen key genes that maintain high photosynthetic performance in waterlogged-wheat plants. The results indicated that cultivar YM24 and YM15 contained 10411 and 10582 differentially expressed genes (DEGs), respectively. The WL treatment had obviously higher DEGs than the WLsnp treatment compared to the CK treatment. Based on the WGCAN method, the DEGs were clustered into eight modules and correlated significantly with the four photosynthetic parameters mentioned above (P < 0.05). Only the DEGs in the ivory module (571) enriched the photosynthetic pathways among the eight modules. In the ivory module, 10 hub genes, including TaB1274F11.29-1, TaT6H20.190, TaOSNPB_100100300, TaLHCB, TaPSAG, TaCAP10B, TaFAD7A-1, TaCAB3C, TaT27G7, and TaF24G24.140, were screened using the co-expression network method because the genes exhibited similar variation trends with gs, gm, or J across the three water treatments and both cultivars. TaLHCB and TaCAP10B exhibited significant linear relationships with the three parameters of gs, gm, and J (P < 0.05). Consequently, TaLHCB and TaCAP10B genes are defined as waterlogging-resistance genes due to the synergistic regulation of photosynthetic characteristics in waterlogging. Both genes were significantly down-regulated in the WL treatment compared to CK treatment in both cultivars. However, there was no significant difference between WLsnp and CK treatments for the genes in the cultivar YM15. These results suggest that the positive effects of spraying NO with high waterlogging resistance capacities are linked to maintaining high expression levels of key genes and obtaining high photosynthetic characteristics during waterlogging, particularly for cultivars with high waterlogging resistance.

High temperatures during the rice panicle initiation stage can easily lead to yield loss. Although exogenous trehalose has been shown to significantly improve plant tolerance to abiotic stresses, its application in rice remains limited. Therefore, in this study, pot experiments were conducted using two rice varieties with differing heat tolerance to investigate whether exogenous trehalose could alleviate heat stress during the panicle initiation stage and to elucidate the underlying physiological mechanisms. The results demonstrated that exogenous trehalose significantly increased rice yield under high-temperature conditions. In the experiment in 2023, the maximum yield increases for N22 and YR343 were 89.5% and 110.3%, respectively, while in 2024, the increases were 89.2% and 111.6%, respectively. The optimal concentration for exogenous trehalose application was found to be 15 mmol L-1. The yield improvement was primarily attributed to the synergistic effects of exogenous trehalose, which not only enhanced leaf photosynthetic capacity but also improved the activity of key carbohydrate metabolism enzymes, up-regulated the expression of sucrose transporter genes, and enhanced sucrose utilisation in young panicles. Additionally, it elevated endogenous trehalose levels, increased the accumulation of osmoregulatory compounds, and enhanced antioxidant enzyme activity, while reducing membrane lipid peroxidation. Furthermore, the regulation of hormone metabolism contributed to improved high-temperature tolerance in rice. In conclusion, the application of trehalose may provide an effective strategy for mitigating high-temperature damage during the rice panicle initiation stage.

Enhancing rice photosynthesis is essential for increasing yield, yet the specific leaf morphological characteristics associated with high photosynthetic efficiency remain unclear. This study aims to investigate how reducing leaf width (LW) influences photosynthetic rate (A) and water-use efficiency (iWUE) in rice. Pot experiments were performed using 14 cultivated rice genotypes exhibiting considerable LW variations and genetically modified rice lines carrying the NARROW LEAF 1 (NAL1) gene. We observed a significant negative correlation between LW and A among the 14 cultivated rice varieties. Simultaneously, a 48.2% reduction in the LW of NAL1-K was accompanied by a 49.9% significant increase in A. Narrower leaves increased leaf hydraulic conductance and stomatal density, thereby synergistically augmenting stomatal conductance (gs). Furthermore, increased stomatal density enhances mesophyll conductance (gm) by facilitating airspace formation and less resistance to CO2 transfer. Reduced LW also increased leaf nitrogen content and enhanced the maximum carboxylation rate of RuBisCO (Vcmax). Although reduced LW synergistically increased gs, gm, Vcmax, and ultimately A, it did not concurrently achieve a coordinated improvement in iWUE. Our findings provide valuable insights into the physiological mechanisms underlying photosynthetic efficiency in rice, suggesting that optimizing LW may be a potential strategy for enhancing A without necessarily improving iWUE.

BACKGROUND:Appropriate nitrogen (N) fertilizer practices can be used to improve rice grain quality without compromising yield formation. The aim of this study is to investigate the performance of phenological N status in predicting rice grain yield and eating scores, and provide N fertilizer management recommendations. Two indica rice cultivars were selected for 3-year field experiments with multiple N application rates. The correlation between N diagnostic indicators [nitrogen nutrition index (NNI) and integrated NNI (NNIinte)] derived from two critical nitrogen dilution curves (CNDCs) based on shoot dry matter (DM) and leaf area index (LAI) with relative yield (RY) and relative eating score (RE) will be investigated. The optimal N fertilizer application rate obtaining high-yield and superior-quality (RY and RE ≥ 0.900) were recommended by the optimized phenological N status. RESULTS:NNI and NNIinte based on DM and LAI CNDC at each growth stage were significantly correlated with the RY and RE. The single-stage estimation performance of the NNIinte at the tillering stage were improved. The accumulated NNIinte (from transplanting to jointing) was better for estimating RY and RE than single-stage NNI and NNIinte. The LAI-CNDC can comprehensively and accurately estimate RY and RE. The optimal N fertilizer application rate was recommended as 126-209 kg ha-1, for rice to obtain high yield and good eating quality. CONCLUSIONS:This finding demonstrated the potential N diagnostic tool for estimating rice yield and eating quality in precision farming system, and NNIinte can be used to determine N requirement for rice high-yield and superior-quality. © 2025 Society of Chemical Industry.

Background Leaf water content (LWC) significantly affects rice growth and development. Real-time monitoring of rice leaf water status is essential to obtain high yield and water use efficiency of rice plants with precise irrigation regimes in rice fields. Hyperspectral remote sensing technology is widely used in monitoring crop water status because of its rapid, nondestructive, and real-time characteristics. Recently, multi-source data have been attempted to integrate into a monitored model of crop water status based on spectral indices. However, there are fewer studies using spectral index model coupled with multi-source data for monitoring LWC in rice plants. Therefore, 2-year field experiments were conducted with three irrigation regimes using four rice cultivars in this study. The multi-source data, including canopy ecological factors and physiological parameters, were incorporated into the vegetation index to accurately predict LWC in rice plants. Results The results presented that the model accuracy of rice LWC estimation after combining data from multiple sources improved by 6–44% compared to the accuracy of a single spectral index normalized difference index (ND). Additionally, the optimal prediction accuracy of rice LWC was produced using a machine algorithm of gradient boosted decision tree (GBDT) based on the combination of ND (1287,1673) and crop water stress index (CWSI) (R 2 = 0.86, RMSE = 0.01). Conclusions The machine learning estimation model constructed based on multi-source data fully utilizes the spectral information and considers the environmental changes in the crop canopy after introducing multi-source data parameters, thus improving the performance of spectral technology for monitoring rice LWC. The findings may be helpful to the water status diagnosis and accurate irrigation management of rice plants.

Water-saving and drought-resistant rice (WDR) coupled with alternate wetting and drying irrigation (AWDI) possesses a high photosynthetic potential due to higher mesophyll conductance (g(m)) under drought conditions. However, the physiological and structural contributions to the g(m) of leaves and their mechanisms in WDR under AWDI are still unclear. In this study, WDR (Hanyou 73) and drought-sensitive rice (Huiliangyou 898) were selected as materials. Three irrigation patterns were established from transplanting to the heading stage, including conventional flooding irrigation (W1), moderate AWDI (W2), and severe AWDI (W3). A severe drought with a soil water potential of -50 kPa was applied for a week at the heading stage across all treatments and cultivars. The results revealed that severe drought reduced gas exchange parameters and g(m) but enhanced antioxidant enzyme activities and malondialdehyde content in the three treatments and both cultivars. The maximal photosynthetic rate (A(max)) of HY73 in the W2 treatment was greater than that in the other combinations of cultivars and irrigation patterns. The contribution of leaf structure (54%) to g(m) (g(m)-S, structural g(m)) was higher than that of leaf physiology (46%) to g(m) (g(m)-P, physiological g(m)) in the W2 treatment of Hanyou 73. Additionally, g(m)-S was significantly and linearly positively correlated with g(m) under severe drought. Moreover, both the initial and apparent quantum efficiencies were significantly and positively with g(m) in rice plants (p < 0.05). These results suggest that the improvements in photosynthesis and yield in the WDR combined with moderate AWDI can mainly be attributed to the enhancement of g(m)-S under severe drought conditions. Quantum efficiency may be a potential factor in regulating photosynthesis by cooperating with the g(m) of rice plants under severe drought conditions.

The growth of rice (Oryza sativa L.) depends on various physiological and metabolic activities of the leaves. The decrease in photosynthesis and carbohydrate metabolism of rice flag leaves under high temperature stress at the flowering stage is an important cause of the loss of rice yields. The addition of exogenous trehalose has a significant effect on alleviating this loss of yields under high temperature stress at the flowering stage. It is highly important to elucidate the physiological reasons for the development of the management of heat-resistant rice. In this study, the heat-resistant rice variety Nagina22 (N22) and the heat-sensitive rice variety YR343 were used as the test varieties. The rice in a pot experiment were treated with high temperature (38 °C) and normal temperature (32 °C) during the flowering stage, and different concentrations of exogenous trehalose were added before the temperature treatment. The research results showed that under high temperature stress during the flowering stage, the seed setting rate of N22 and YR343 decreased by 42.1 and 82.2

[Objective]In order to explore the common agronomic and physiological characteristics of good taste and high yield type japonica rice in the lower reaches of the Yangtze River,the study could provide theoretical basis and technical support for realizing synergistic improvement of rice yield and quality in this region.[Method]The cultivar screening tests were conducted in 2018 and 2022 using 14 and 13 conventional japonica rice cultivars,respectively,to systematically compare the yield and composition,taste quality and textural characteristics,as well as agronomic and physiological indicators such as biomass,stem non-structural carbohydrates(NSC),and leaf area duration(LAD)among the different cultivars.[Result]The taste value and yield varied across the different cultivars,so through clustering by taste value and yield,they can be further divided into three types:medium taste and low yield(ML),medium taste and high yield(MH),good taste and high yield(GH).The average taste value and yield of GH in two years were 68.5 and 10.2 t·hm-2,respectively,which were 6.8%higher in taste value and 14.6%higher in yield than MH and ML.In terms of performance for yield and quality traits,GH showed the highest grain filling percentage and taste scores compared to MH and ML.In terms of the dry matter accumulation,GH increased the proportion of dry matter accumulation at the early stage of grain filling stage,and showed the highest dry matter accumulation from heading stage to 15 days after heading stage.Further analysis of the causes of dry matter accumulation at this stage revealed that GH significantly increased the NSC remobilization rate while steadily increasing LAD.Correlation analyses showed highly significant positive correlations between grain filling percentage and taste,dry matter accumulation and LAD from heading stage to 15 days after heading stage,and NSC remobilization rate.[Conclusion]While maintaining a high LAD from heading stage to 15 days after heading stage(100.4 m2·m-2·d),further increasing NSC remobilization rate during grain filling stage(79.9%)to promote the initiation of grain filling,increasing the dry matter accumulation from heading stage to 15 days after heading stage(3.6 t·hm-2),then improving the grain filling percentage(95.4%),and taste(9.6),which are the common characteristics of good taste and high yield type japonica rice in this region.In addition,the development of water and fertilizer management techniques targeting the enhancement of NSC remobilization at the grain filling stage and NSC accumulation at heading stage is expected to further exploit the yield and taste quality potential of the above good taste and high yield type japonica rice.

The reserve of stem nonstructural carbohydrates (NSC) at heading can enhance the sink strength and improve the grain-filling ability of large-panicle rice, which is beneficial to realizing its high-yield potential. Delaying panicle nitrogen (N) application is expected to increase stem NSC accumulation, but the relevant technical parameters and their impact on the yield of large-panicle rice remain unclear. Two-year field experiments were conducted in 2021 and 2022 with two large-panicle rice cultivars (HLY280 and YLY228) and five panicle N treatments: panicle N application at emergence of 4th leaf from flag leaf (TL4), 3rd leaf from flag leaf (TL3), 2nd leaf from flag leaf (TL2), flag leaf (TL1), and no panicle N application (CK) as the control, to study the effect of different panicle N treatments on the accumulation and translocation of stem NSC, as well as their impact on rice yield and its components. The results showed that the panicle N treatments significantly influenced rice yield. Among the panicle N application treatments, TL3 showed the highest yield for both cultivars over two years. Compared with TL4, TL3 significantly increased the percentage of filled grains and grain weight while maintaining a similar number of spikelets per panicle, which increased the yield of HLY280 and YLY228 by 10.1–13.6% and 12.4–12.7%, respectively. Among the panicle N application treatments, TL3 significantly increased the translocation of stem mass (net output of stem mass) and stem NSC (∆NSC) from heading to 15 days after heading (DAH), which led to the highest dry matter accumulation during the initiation of grain filling from heading to 15 DAH. The higher ∆NSC of TL3 was mainly due to the higher stem NSC at heading, which was contributed by the higher stem NSC accumulation from 5 days before heading (DBH) to heading. Additionally, the higher stem NSC accumulation under TL3 from 5 DBH to heading was significantly positively correlated with the higher leaf area duration (LAD) in this period. These results suggest that delaying panicle N application to TL3 can significantly increase the yield of large-panicle rice compared with TL4 by increasing the percentage of filled grains and grain weight, which is the result of increased stem NSC accumulation.

High yield, good eating quality, and high nitrogen (N) use efficiency present challenges in cultivating medium hybrid indica rice. We hypothesized that balanced source-sink relationships are key traits for achieving high yield, good eating quality, and high N use efficiency in medium hybrid indica rice under suitable N management regimes. Three field experiments were conducted with two medium hybrid indica rice cultivars. Five distinct N application levels, designated as N0, N75, N150, N225, and N300, were used to investigate varying source-sink characteristics and their impact on yield, eating quality, and N use efficiency. The results indicated that the ratio of dry matter at the heading stage to the number of spikelets per unit area (DM/Spik. R) exhibited a significant decrease with increasing N application rates in both cultivars over three years, except for the cultivar HLY898 in 2021. Conversely, an increase in N application rates generally increased the ratios of accumulated N rate and leaf area at the heading stage to the number of spikelets per unit area (AN/Spik. R and LA/Spik. R) across the cultivars and experimental years. Only AN/Spik. R showed significant relationships with yield, eating score, and N partial factor productivity (PFPN). In addition, significant differences were observed among the three study years for DM/Spik. R and LA/Spik. R, but no significant difference was found for AN/Spik. R across the three study years. Moreover, both N concentration and nitrogen nutrition index (NNI) at heading had significant and linear relationships with AN/Spik. R. Further analysis revealed that the highest yield and maximum eating scores, constituting 92 % of the total, were achieved when AN/Spik. R reached 3.65 mg per spikelet. Correspondingly, the NNI was recommended as 0.93 at heading when 90 % of the highest yield and maximum eating scores were harvested. Additionally, 79 % of the highest yield and maximum PFPN were obtained when AN/Spik. R and NNI were approximate to 2.58 mg per spikelet and 0.78 at heading, respectively. These results suggest that moderate AN/Spik. R corresponding to mild N deficiency at heading could be a key source-sink indicator for the integrated regulation of high yield, good eating quality, and high N use efficiency in medium hybrid indica rice.

The effects of nitric oxide (NO) on the photosynthetic adaptation mechanisms of wheat plants in waterlogging during the flowering stage are poorly understood. Field and pot experiments using two cultivars were conducted with three treatments: waterlogging (WL), waterlogging plus NO donor sodium nitroprusside (WLsnp), and adequate water (CK). The results indicated that the WLsnp and CK treatments exhibited significantly higher 1000-kernel weight and yield than the WL treatment because of high photosynthetic potential(P<0.05). We found that the photosynthetic performance, including photosynthetic rate (P-n), stomatal conductance (g(s)), mesophyll conductance (g(m)), carbon dioxide concentration at the carboxylation site (C-c), maximum carboxylation rate (V-cmax), maximum electron transfer rate (J(max)), actual electron transfer rate (J), actual PSII efficiency (Phi(PSII)) and potential maximum efficiency in PSII (F-v/F-m), was significantly improved in the WLsnp treatment compared to the WL treatment, both during waterlogging and after de-waterlogging. Little difference was observed in the photosynthetic performance between the WLsnp and CK treatments during waterlogging for cultivar YM15 and after de-waterlogging for cultivar YM24. Further analysis indicated that g(s), g(m) and J were identified as key physiological indicators that synergistically regulate P-n of waterlogged wheat plants. Overall, the improvement of wheat's waterlogging resistance capacity after spraying NO is mainly related to high g(s), great g(m), and high J.

One-time application of mixed fertilizer formed by the compounding of two controlled-release nitrogen fertilizers (CRUs) with targeted N supply during the periods from transplantation (TS) to panicle initiation (PI) and from PI to heading (HS) is expected to synchronize the double-peak N demand of rice. However, its effects on the yield and N use efficiency (NUE) of labor-intensive double-cropping rice were unknown. Two targeted CRU (CRUA and CRUB) were compounded in five ratios (CRUA: CRUB = 10:0, 7:3, 5:5, 3:7, and 0:10) to form five mixed fertilizers (BBFs): BBF1–5. A field experiment was performed to investigate the characteristics of N supply in early and late seasons under different BBFs and their effects on N uptake, yield, and ammonia volatilization (AV) loss from paddy fields of double-cropping rice. Conventional high-yield fertilization (CK, three split applications of urea) and zero-N treatments were established as controls. The N supply dropped significantly with the increased compound ratio of CRUB during the period from TS to PI, but increased during the period from PI to HS. With the exception of the period from TS to PI in the late rice season, the N uptake of early and late rice maintained close synchronicity with the N supply of BBFs during the double-peak periods. Excessive N supply (BBF1 and BBF2) in the late rice season during the period from TS to PI increased N loss by AV. The effect of BBF on grain yield increase varied widely between seasons, irrespective of year. Among the BBFs, the BBF2 treatment of early rice not only stabilized the spikelets per panicle but also ensured a high number of effective panicles by promoting N uptake during the period from TS to PI and a high grain-filling percentage by appropriately reducing the N supply at the later PI stage, resulting in the highest rice yield. While stabilizing the effective panicle number, the BBF4 treatment of late rice increased the number of spikelets per panicle by promoting N uptake during the period from PI to HS, resulting in the highest rice yield. The two-year average yield and apparent N recovery efficiency of the BBF2 treatment during the early rice season were 9.6 t ha−1 and 45.3%, while those of late rice in BBF4 were 9.6 t ha−1 and 43.0%, respectively. The yield and NUE indexes of BBF2 in early rice and BBF4 in late rice showed no significant difference from those of CK. The AVs of BBF2 during the early rice season and of BBF4 during the late rice season were 50.0% and 76.8% lower, respectively, than those of CK. BBF2 and BBF4 could effectively replace conventional urea split fertilization in early and late rice seasons, ensuring rice yield and NUE and reducing AV loss in paddy fields.

In recent years, heat stress has become a serious threat to rice production in China. It is well documented that nitrogen forms can regulate the heat tolerance of plants. However, its effect on the rice plants has not been described before. In this study, a pot experiment was performed with two restorer lines of indica rice, heat-tolerant 996 (HT 996) and heat-sensitive 343 (HS 343), to investigate whether nitrogen forms could mitigate heat stress at flowering stage and their physiological mechanism. The experiment received five treatments: (1) NN0: natural temperature level (32 ℃) with urea-N; (2) HN0: high temperature level (38 ℃) with urea-N; (3) HN1: high temperature level with NH4+-N; (4) HN2: high temperature level with mixed N [NH4+: NO3− at 50: 50 (w:w)]; and (5) HN3: high temperature level with NO3−-N, respectively. The results showed that heat stress reduced seed setting, photosynthetic characteristics, leaf nitrogen content and antioxidant enzyme activities of rice. However, the application of mixed N significantly increased the 1000-grain weight and seed setting rate under heat stress, thus increasing yield. The increased yield was mainly caused by higher leaf N content, photosynthetic rate, transpiration rate and stomatal conductance, which led to a reduction in panicle and leaf temperatures. Meanwhile, the application of mixed N also improved the activities of antioxidant enzymes, and reduced the amount of reactive oxygen species, thereby mitigating the damage caused by exposure to high temperature. In conclusion, the application of mixed N can effectively alleviate the adverse consequences of high temperature, and could be further applied to provide strategies for the prevention and control of high temperature-prone areas during the rice flowering period.