BACKGROUND:Early indica rice frequently encounters high temperature damage during grain-filling period in the Yangtze River basin, China induced by later sowing date, decreasing grain yield and qualities. Nitrogen panicle fertilizer application (NPF) positively mitigates the adverse effects; however, the specific details remain unclear. A field experiment using poor or high-quality early indica rice cultivars was conducted over 2 years to investigate rice yield, grain qualities and starch related traits subjected to slightly natural warming (W) under different NPF levels (Low NPF, LN; Middle NPF, MN; High NPF, HN) through delaying sowing date, with normal sowing date as the control. RESULTS:The result showed that under W, compared to LN, elevated NPF (HN and MN) significantly increased the grain yield of the rice cultivars by 11.7-21.0%, which was mainly attributed to the high effective panicle and spikelets. Elevated NPF increased the protein and amino acid contents, especially for the HN treatment, resulting in the high nutritional qualities of rice grain, at the same time as demonstrating increased hardness and stickiness, as well as decreased breakdown and amylose content, negatively affecting the eating and textural qualituies of cooking rice. Notably, compared with HN and LN, MN treatment totally enhanced the processing qualities under W in 2 years. However, HN significantly deteriorated the rice appearance qualities in the temperature treatments. These results might be a result of the unordered arrangement and irregular surface of starch granules, particular high-quality rice cultivar. CONCLUSION:The results suggest that optimizing NPF under slightly warming at grain-filling stage synergistically improve grain yield and processing qualities of early indica rice. © 2026 Society of Chemical Industry.

[Objective]Long-term direct returning of straw to the field improves the physical and chemical properties of the soil and is conducive to soil carbon and nitrogen retention.However,there are differences among various soil layers.This study aimed to clarify the variation characteristics of soil organic carbon,nutrients and structure at different soil depths.[Method]The study was based on a long-term straw returning experiment established in 2009,with a double rice system as the research object.Four treatments were set up:no straw returning and no fertilizer control(CK),chemical fertilizer only(F),straw burning and returning(SBR),and full returning(SR).In 2021,samples were taken to analyze the physical properties of the soil,aggregate structure,the content of carbon,nitrogen and available nutrients in each soil layer,and the formation of double-cropping rice yield.[Result]Compared with CK,all fertilization treatments could improve soil physical and chemical properties and carbon and nitrogen contents.Compared with SBR and F treatments,SR significantly increased the soil moisture content and total porosity of double-cropping paddy fields,while reducing soil bulk density,with a decrease of 12.0％-17.3％in early rice and 10.7％-16.0％in late rice.SR treatment significantly increased the content of large aggregates(＞2 mm)and the average mass diameter and geometric diameter of soil in the 0-15 cm layer of double-cropping paddy fields,which was conducive to promoting the formation and stability of large aggregates,and the effect was the most significant in the 0-5 cm layer of soil.SR treatment also significantly increased the organic carbon content in each soil layer of 0-30 cm and promoted the increase of total nitrogen content in the 10-30 cm layer of soil,while there was no significant difference in organic carbon and total nitrogen between SBR and F treatments.At the same time,SR treatment significantly increased the content of available nutrients,such as ammonium nitrogen,alkali-hydrolyzable nitrogen and available phosphorus in the 0-10 cm layer of soil,but the nitrate nitrogen content only significantly increased in the 0-10 cm layer of soil in the early rice season.In addition,compared with F treatment,SR significantly increased the content of slow-release potassium in each soil layer in the late rice season,thereby significantly increasing the yield of late rice.[Conclusion]Overall,direct straw returning to the field was beneficial to increase the content of large soil aggregates in the 0-15 cm soil layer of double-cropping rice fields,promote the increase of available nutrients in the 0-10 cm soil and the content of organic carbon,total nitrogen and slow-release potassium in deep soil,and achieve stable and high yields.

Paddy fields serve as both significant carbon (C) sinks and sources. Straw biochar application has been identified as an effective material for C sequestration and the reduction of greenhouse gas (GHG) emissions. However, comprehensive assessments of crop production, carbon footprint (CF) and net ecosystem economic benefits (NEEB) of incorporating biochar produced from equivalent amounts of straw into double-cropping rice systems remain unclear. A three-year field experiment was conducted with four treatments including conventional fertilization (SF), double-cropping rice straw return (DSR), biochar return after early rice harvest followed by straw return after late rice harvest (BSR), and double-cropping biochar return (DBR). Compared to the SF treatment, DSR significantly increased cumulative CH4 and N2O emissions, thereby raising the global warming potential (GWP). In contrast, DBR consistently reduced GWP by suppressing methanogen abundance and enhancing methanotrophic activity. Although BSR initially increased CH4 emissions during early rice season, it overall mitigated late rice season emissions in the years. DSR, DBR and BSR significantly improved SOC storage compared to SF, with DBR showing the greatest soil C sequestration. Consequently, DBR achieved the largest reduction in net GWP and CF, and also generated the highest NEEB. Notably, BSR obtained the highest grain yield while maintained competitive GHG mitigation and C sequestration benefits. These findings suggest that straw-derived biochar amendment, particularly under the DBR measure, presents a superior strategy for climate change mitigation and economic return, while the BSR strategy offers a viable trade-off for prioritizing grain yield, thereby supporting sustainable rice production.

The practice of returning straw enhances the accumulation of soil organic carbon (SOC), dissolved organic carbon (DOC), and microbial communities. Nonetheless, the mechanisms in which microbes affect the variations in SOC and DOC during rice critical growth stages remain unclear. This research examines SOC, DOC, and microbial communities at panicle initiation (PI), heading (HS), and maturity (MS) stages in a paddy field, 13 years after long-term straw incorporation under no chemical fertilizers application with straw removal (CK), straw removal with only chemical fertilizer application (F), straw burning return with some chemical fertilizer application (SBR), and straw return in situ with some chemical fertilizer application (SR). Compared to CK, the other treatments significantly enhanced SOC levels throughout all growth stages. Notably, SR exhibited an average increase of 37.9% during the early rice season and 41.9% during the late rice season. Compared to F and SBR, SR significantly increased SOC by 7.1% at the PI stage of early rice, and by 9.2% and 10.1% at all late rice growth stages, respectively. SR also significantly enhanced the DOC level at the late growth stages of both rice seasons. Furthermore, SR enhanced microbial diversity at the PI stage in both rice seasons, aiding SOC accumulation. Although DOC had a positive relationship with microbial diversity in the early rice season, this relationship turned negative in the late rice season, likely due to the influence of the phylum Actinobacteria. Moreover, the significant enrichment of Cyanobacteria under SR at all stages of the late rice season was associated with an increase in SOC content. These results highlight the importance of Actinobacteria and Cyanobacteria in promoting the formation of SOC and DOC during key growth periods under long-term straw return. Future research requires the integration of 13C labelling with multi-omics to trace microbial-mediated straw carbon sequestration.

Reduced panicle nitrogen fertilizer (PNF) impacts indica rice grain quality by altering starch and protein composition, but the underlying mechanisms remain unclear. Field and pot experiments involving four PNF treatments (NE: full basal shift; LN: zero panicle nitrogen; DN: 50% reduction in panicle nitrogen; NN: normal panicle nitrogen) showed that, compared to the NN treatment, the NE, LN, and DN significantly increased amylose content while decreasing processing and appearance qualities, and protein content. Meanwhile, the LN and DN treatments decreased the proportion of amylopectin extremely short chains (DP 0-12) and short chains (DP 13-36), large granule starch, and starch gelatinization enthalpy, while increased the amylose extremely long chain, resulted in increasing peak viscosity and breakdown, and decreasing setback, ultimately improving rice eating quality. Furthermore, compared to the NN treatment, both the NE and LN treatments significantly downregulated genes governing nucleic acid processing (endonucleases, phosphodiester hydrolysis), RNA modification, and chloroplast function; and the anabolic substances related to protein, including sphingolipids, amino acids, and purines, thereby impairing grain filling and diminishing the processing, appearance, and nutritional qualities. In contrast, the LN and DN treatments upregulated genes involved in trehalose synthesis, driving the conversion of trehalose to glucose-1-phosphate and thereby facilitating ADP-glucose formation. These metabolic approaches decreased short-chain amylopectin synthesis while increasing long-chain amylose, contributing to the improvement of rice eating quality, especially for high-quality indica rice. Overall, the DN treatment achieves the optimal improvement effect on eating quality while ensuring good agronomic traits of the rice.

Phytoremediation of heavy metal-contaminated soils is often limited by phytotoxicity and metal availability. This study evaluated the phytoremediation potential of Astragalus sinicus L. and its symbiotic rhizobia. A nationwide soil survey revealed significantly lower arsenic (As) in planted versus unplanted soils, and key factors governing metal retention were attenuated in planted soils, indicating plant-mediated interference. Pot experiments confirmed that A. sinicus L. cultivation significantly reduced soil cadmium (Cd) (33.33%), lead (Pb, 39.73%), copper (Cu, 12.92%), and As (23.70%). Among rhizobial isolates, Mesorhizobium sp. XS6-2 exhibited the highest heavy metal tolerance. Inoculation with XS6-2 increased plant biomass and specifically enhanced chromium (Cr) and Pb remediation. Microbiome analysis showed that XS6-2 reshaped the rhizosphere community and strengthened microbial interactions. Our findings demonstrate a potent plant-microbe synergy that alleviates phytotoxicity and increases metal availability, offering an effective strategy to advance phytoremediation.

The impacts of whole-growth-duration warming on grain yield and quality in a double rice cropping system remain largely unknown. In this study, a 2-year field whole-growth-duration warming experiment was conducted with two inbred indica rice cultivars (Zhongjiazao 17 and Xiangzaoxian 45) for early season and two hybrid indica rice cultivars (Wanxiangyouhuazhan and Tianyouhuazhan) for late season, respectively. The results showed that whole-growth-duration warming did not affect early rice yield but significantly decreased late rice yield, which was caused by the decreased grain weight that may be related to the reduced translocation of dry matter accumulated during the pre-heading phase under warming. Whole-growth-duration warming improved the milling quality of late rice but decreased that of early rice; however, the chalky rice rate and chalkiness degree were increased by 20.7% and 33.9% for early rice, and 37.6% and 51.6% for late rice under warming, respectively. We found that the crude protein content of milled rice was significantly increased by warming in both early and late rice, which would result in the deterioration of eating quality. Besides, compared with the control treatment, the setback of late rice was significantly reduced by 17.8% under warming, while that of early rice was not significantly affected by warming. These results suggest that the negative impacts of whole-growth-duration warming on grain quality varied between early rice and late rice to some extent. In summary, adaptation in both rice breeding and agronomic practices is needed to alleviate climate warming on the production of the double rice cropping system.

Straw return has demonstrated significant potential for enhancing carbon (C) sequestration and nitrogen (N) uptake while concurrently promoting plant productivity. However, the specific transport and distribution of C produced by photosynthesis and exogenous N within the rice plant-soil system under straw return remains unclear. A longterm straw return pot trial experiment was conducted in a double cropping rice system, incorporating treatments of inorganic fertilizer application with straw removal (F), straw burning and ash return with reducing inorganic fertilizers (SBR), and straw return with reducing inorganic fertilizers (SR) to investigate C sequestration and exogenous N uptake using 13C pulse and 15N isotope tracer techniques. The SR treatment had significantly higher soil 13C abundance, by 24.4 and 25.4%, respectively, 13C concentrations in aboveground plant parts, by 18.4 and 35.8% respectively, and 15N concentrations in rice panicles, by 12.8 and 34.3% than the SBR and F treatments. This enhancement contributed to a higher total organic C concentration and increased rice grain yield in the SR treatment. Furthermore, the SR treatment had significantly higher photosynthetic C, by 9.8%, which was directly transferred to soil C. The SR treatment had a higher distribution of photosynthetic C in the leaves and stems, but a lower distribution in the panicle compared to the SBR treatment. This finding is advantageous for sequestering photosynthetic C into the soil through straw return; conversely, opposite trends were observed in 15N distribution. In addition, rice plants in the SR treatment had increased N uptake from urea and soil N sources, enhancing N recovery by 9.2 and 12.5%, respectively, and reducing soil N residues. Correlation analysis showed that the SR treatment increased the concentrations of 13C in leaves and roots while decreasing the 15N abundance in all rice organs, thereby contributing to an increase in rice yield. The partial least square path model suggested that the increase in rice yield under the SR treatment was primarily linked to 13C accumulation within the rice plant-soil system. The results suggest that straw return increases the sequestration of photosynthetic C and exogenous N in the rice plant-soil system and increases N utilization efficiency, which subsequently improves both rice and soil productivity.

While nitrogen is essential for rice production, excessive application promotes lodging, threatening yield stability. In this study, we evaluated the impact of three nitrogen application rates (105, 165, and 225 kg ha−1) on yield formation and lodging resistance in two elite late-season indica rice varieties—Meixiangzhan 2 (MXZ2) and Taiyou 871 (TY871). Our findings demonstrate that (1) elevated nitrogen increased productive panicle number but reduced grains per panicle and percentage of filled grains. (2) High nitrogen inputs substantially elevated the lodging risk, with the lodging index increasing by 20.4% and 45.7% in MXZ2, and by 15.4% and 38.3% in TY871, at 165 and 225 kg ha−1, respectively. (3) Reduced mechanical strength—associated with impaired morphological structure (e.g., increased plant height and height of gravity center), diminished structural carbohydrate content in sheaths and culms, and expanded pith cavity area—collectively contributed to the increased lodging susceptibility with elevated nitrogen. (4) MXZ2, though lower-yielding, exhibited greater lodging resistance than TY871, owing to its superior culm anatomy and sheath strength. (5) Interannual climate variation—particularly low temperature and light intensity in 2020—amplified the negative effects of high nitrogen. Our results provide insights into nitrogen-driven trade-offs between yield and lodging, supporting tailored nitrogen management strategies for indica rice under varying environmental conditions.

The underlying mechanisms of warming effects on rice protein content have not been thoroughly investigated in the double rice cropping system. Here, a 2-year field experiment was conducted to clarify the physiological mechanisms related to nitrogen (N) uptake and assimilation under warming. The results showed that warming significantly increased albumin (16.7%), globulin (2.9%), and glutelin (26.1%) contents in early rice, while it increased prolamin (6.3%) and glutelin (13.4%) contents in late rice. The increased protein content under warming was associated with the elevated N concentration in the panicle, which was partly caused by the enhanced N uptake in early rice but not in late rice. A 15N pot experiment demonstrated that warming improved total N uptake from soil in both early and late rice; however, N uptake from fertilizer was increased and decreased by warming in early and late rice, respectively, resulting in improved total N uptake in early rice but not in late rice. Additionally, our results confirmed that increased soil net N mineralization rate and root activity contributed to the increased N uptake from soil under warming for both early and late rice. Furthermore, the activities of key enzymes, including glutamine synthetase, glutamate synthase, glutamic-oxaloacetic transaminase, and glutamate-pyruvate transferase, were increased, while protein hydrolysis was suppressed by warming in both early and late rice. Our findings indicate that the increase in protein components under warming conditions is due to improved N uptake in early rice and increased protein synthesis in both early and late rice.

Early indica rice in Southern China frequently experiences high temperatures (HT) and strong light (SL) during grain filling, which accelerates grain maturity. In this study, two indica rice cultivars with different grain qualities under control (CK), HT, and HT + SL treatments to investigate their impacts on starch structure and physicochemical properties. The results demonstrated that HT and HT + SL treatments increased the amylopectin average chain length, long chain, relative crystallinity, large granule, and protein content (40.9 %-41.6 %), while decreasing amylose content (15.4 %-21.6 %) and branching degree compared to CK. This was due to a reduction in granule-bound starch synthase, soluble starch synthase, and starch branching enzymes, along with an increase in debranching enzyme activity, which altered the starch fine structure and diminished thermal stability and gelatinization viscosity. The HT + SL treatment exhibited a more pronounced impact, increasing the amylopectin middle chain (fb1) and relative crystallinity, while decreasing the branching degree and amylopectin short-chain length, indicating that SL exacerbated the deterioration of starch structure. Nevertheless, the starch physicochemical properties of high-quality cultivar were relatively less affected by the HT + SL conditions, suggesting a potential for improved utilization of starch in high-quality early indica rice in food processing.

Straw return has demonstrated significant potential for enhancing carbon (C) sequestration and nitrogen (N) uptake while concurrently promoting plant productivity. However, the specific transport and distribution of C produced by photosynthesis and exogenous N within the rice plantu2013soil system under straw return remains unclear. A long-term straw return pot trial experiment was conducted in a double cropping rice system, incorporating treatments of inorganic fertilizer application with straw removal (F), straw burning and ash return with reducing inorganic fertilizers (SBR), and straw return with reducing inorganic fertilizers (SR) to investigate C sequestration and exogenous N uptake using 13C pulse and 15N isotope tracer techniques. The SR treatment had significantly higher soil 13C abundance, by 24.4 and 25.4%, respectively, 13C concentrations in aboveground plant parts, by 18.4 and 35.8% respectively, and 15N concentrations in rice panicles, by 12.8 and 34.3% than the SBR and F treatments. This enhancement contributed to a higher total organic C concentration and increased rice grain yield in the SR treatment. Furthermore, the SR treatment had significantly higher photosynthetic C, by 9.8%, which was directly transferred to soil C. The SR treatment had a higher distribution of photosynthetic C in the leaves and stems, but a lower distribution in the panicle compared to the SBR treatment. This finding is advantageous for sequestering photosynthetic C into the soil through straw return; conversely, opposite trends were observed in 15N distribution. In addition, rice plants in the SR treatment had increased N uptake from urea and soil N sources, enhancing N recovery by 9.2 and 12.5%, respectively, and reducing soil N residues. Correlation analysis showed that the SR treatment increased the concentrations of 13C in leaves and roots while decreasing the 15N abundance in all rice organs, thereby contributing to an increase in rice yield. The partial least square path model suggested that the increase in rice yield under the SR treatment was primarily linked to 13C accumulation within the rice plantu2013soil system. The results suggest that straw return increases the sequestration of photosynthetic C and exogenous N in the rice plantu2013soil system and increases N utilization efficiency, which subsequently improves both rice and soil productivity.

Rice growth and yield performance are closely related to climate variables and soil water regimes. Therefore, in this study, normal humidity (NH) and high humidity (HH) treatments of rice canopy were performed and combined with continuous flooding (CF), alternate wetting and drying (AWD), and drought cultivation (DC). The changes in crop physiology were monitored in a 2-year artificial intelligence greenhouse experiment. Creating HH lowered the seed setting rate, grains per panicle and yield relative both under AWD and CF, but was rather beneficial under DC. The HH decreased the soil plant analysis development (SPAD) parameter and net photosynthetic rate while leaf surface temperature, antioxidant enzyme activity and malondialdehyde (MDA) level got increased. Additionally, HH increased the contents of abscisic acid (ABA), gibberellin (GA3) and jasmonic acid (JA) and the activities of key starch synthase, increasing the grain filling rate while shortening the active filling duration. The rice yield of AWD treatment under HH condition was the highest, mainly because the net photosynthetic rate, pollen viability and key starch synthase activity were maintained at a higher level. The AWD measures can be adopted to maintain high rice yields under high humidity conditions, while yields can be improved by increasing canopy humidity under persistent drought conditions.

The cultivation strategy of 'postponed nitrogen with increased panicle fertilization (PNIPF)' boosts rice yield but the balance between lodging remains unclear. We evaluated three panicle nitrogen ratios (0%, 20% and 40% of total 165 kg N ha-1) in two late indica rice varieties (Meixiangzhan 2 and Taiyou 871) to assess this trade-off. Results demonstrated that: (1) Compared to R0, PNIPF to 20% showed no difference on yield, while R4 raised grain yield by 4.84% and 8.69% but increased lodging index by 30.5% and 35.8% in TY871 and MXZ2. (2) Relative to R0, R4 induced taller plants with elevated center of gravity, reduced culm diameter, diminished culm mechanical strength, and decreased structural carbohydrate content (cellulose -29.2%, lignin -23.8%). The effect of R2 is weaker than R4 on plant morphology. (3) Compared to R0, R4 manifested more profound anatomical deterioration than R2. (4) Significant variety differences existed; PNIPF exhibited a more profound impact on MXZ2 than TY871 by inferior morphological, physiological and anatomical traits. We recommend limiting panicle nitrogen to below 20% to achieve synergistic improvement of yield and lodging resistance in high-quality late indica rice production.

Climate warming affects rice seed vigor during ripening, which plays a crucial role in seed quality. However, the actual response of rice seed vigor to warming is still unclear. In this study, seeds after warming treatment in a double rice cropping system were used to determine seed vigor and related physiological traits during germination. Warming treatment significantly improved the germination index (GI), seed vigor index (VI), and seedling dry weight (SDW) for the late-season rice seeds but had no effect on hull thickness, grain weight, and starch and protein contents for both early- and late-season rice seeds, and these parameters were highly associated with germination rate, GI, VI, and SDW. Warming treatment increased gibberellin content and α-amylase and β-amylase activities in endosperm and coleoptile in both seasons during the later stage of germination, reaching a significant level on the 7th d. Moreover, IAA content of the coleoptile was consistently increased but decreased in the endosperm in response to warming, and warming did not affect zeatin content. These results suggest that future global warming will improve rice seed vigor by regulating the synthesis of endogenous hormones and amylases, especially in the late-season rice.

Post-heading high temperatures occurred frequently in late indica rice regions in southern China recently, but the effects of high post-heading temperature on rice yield and quality under nitrogen application including nitrogen management (NM) and panicle fertilizer (NPF) were still unclear. Therefore, the grain yield and quality of late indica rice cultivars were compared in 2020 (ambient temperature) to 2019 (warming 2.3 degrees C) and 2021 (warming 3.5 degrees C). The results showed that moderate NPF can increase the yield, protein content (PC) and brown rice rate, and reduce the chalkiness and amylose content (AC) under naturally high temperatures. The proportion and application of NPF values higher than 22.5%, 36 kg center dot ha(-1) effectively improved grain yield, processing and appearance qualities, and PC, while reducing AC of late indica rice under natural warming. The temperature parameters, AC and PC during the total growth period could explain 81.7%, 90.7% and 89.6% of the variation in rice processing qualities, appearance qualities and gel consistency, respectively. The finding demonstrated that the optimum T-mean of improving rice yield and quality was 29.0 degrees C before heading and 21.1 degrees C after heading under NM, and 28.6 degrees C before heading, and 22.9 degrees C after heading under NPF. This study suggested that optimizing nitrogen management strategies under future climate warming conditions can synergistically increase indica rice yield and quality.

Double-season late indica rice frequently experiences low temperature accompanying with low light stress during the grain filling stage in southern China, which alters the carbon and nitrogen metabolism of the rice grains, thereby impacting both grain yield and quality. However, the physiological mechanism is still unclear. A pot experiment using two late indica rice cultivars (high-quality and common-quality rice cultivars) was conducted under control (CK), low temperature (LT) and low temperature and light (LT+LL) to investigate the grain filling, photosynthetic characteristics, carbon and nitrogen metabolic enzymes and related gene expression. The results indicated that both LT and LT+LL treatments primarily reduced grain weight in the two cultivars compared to CK. This effect was particularly pronounced for LT+LL, which showed a significant difference in both superior and inferior grains of the common-quality rice cultivar. This reduction in grain weight was attributed to an average decrease in the photosynthetic rate of rice leaves by 23.5%, a decrease in Fv/Fm by 6.2%, and a decrease in the original grain filling rate by 10.3%. LT and LT+LL treatments decreased the activities of soluble starch synthase (SSS), granules bound starch synthetase (GBSS) and starch branch enzyme (SBE) in the early grain filling stage, and its related gene expression including OsAGPL2, OsAGPS2b, OsGBSSI and OsSSIIIa, and the influence degree was intensified by LT+LL, compared with LT. For nitrogen metabolism, the activity of glutamic oxalic aminotransferase (GOT) also significantly decreased by LT and LT+LL during grain filling in the cultivars, which was relatively lower under LT+LL, and only decreased the glutamic pyruvic transaminase (GPT) in the early grain filling stage but increased in the later period. However, the related gene expressions of OsGOT1B and OsGS1;3 were enhanced significantly by LT and LT+LL treatments, and reached the highest level under LT+LL treatment, implying the disordered process of nitrogen metabolism. The results suggest that low temperature decreased photosynthetic traits to hinder grain filling in the cultivars, mainly derived from the worsened carbon and nitrogen metabolism, and LT+LL combined stress aggravated the damage degree.

The southern rice-growing region plays a crucial role in ensuring national food security in China. However, rice production in this area is often affected by unfavorable weather conditions such as rainy and dim days, which significantly impact rice yield. Therefore, we conducted two field experiments to explore and compare the effects of climate variations and simulated shading on rice yield and quality. The results indicated that (a) both interannual climate variation and simulated shading had adverse effects on rice yield and quality, (b) the impact of interannual climate variation on yield was less severe compared with simulated shading, but it had a more significant negative effect on rice quality, and (c) different cultivars/quality groups of rice exhibited variations in response to weak solar radiation, with high-quality rice being more susceptible. The findings suggest that in the production of high-quality rice, it is important to select cultivars that are resilient to interannual climate variation and to develop supporting cultivation techniques to cope with growing incidence of weakened solar radiation in the future. Breeders can try to tap into potential weak-light-resistance genes and cultivators can try to use different cultivation methods to determine the optimal water and fertilizer regimes.

This study conducted a two-year field artificial intelligence (AI) greenhouse rice planting experiment with different canopy humidity (normal humidity, NH; high humidity, and HH) and irrigation regimes (continuous flooding, CF; drought cultivation, DC; alternate wetting-drying, AWD) to test whether high canopy humidity from heading to maturity deteriorates rice grain quality, whether appropriate water management can alleviate these adverse effects, and the related mechanisms. The results showed that compared with NH, HH significantly decreased the head rice rate while increasing the protein, amino acid, amylopectin, amylose, and chalkiness. Moreover, HH significantly decreased the peak viscosity, breakdown, and number of small starch granules, while increasing the setback, number of large starch granules, relative crystallinity, gelatinization temperature, and enthalpy. Under NH and HH, AWD treatment resulted in a higher head rice rate, peak viscosity, breakdown, key enzyme activities of starch synthesis, amylose, amylopecan, relative crystallinity, small starch granules, gelatinization temperature, and enthalpy than DC and CF treatments, while lower chalkiness, setback, protein, amino acid, and large starch granules were observed. HH increased the chalkiness by promoting the formation of large starch granules, thus reducing the milling quality. The increase in amylose and relative crystallinity further causes HH to deteriorate the cooking and eating quality. AWD could alleviate the deterioration of rice grain milling, appearance, and eating quality caused by HH by improving starch granules.