Direct-seeded rice is a labor-saving and simplified planting pattern, usually accompanied by an increase in lodging risk. Improving the population structure has been demonstrated as an effective approach for solving this problem, and changing the sowing method is the most direct way to construct a reasonable population structure. The objective of this study was to compare the lodging characteristics of rice plants under three sowing or transplanting methods, including drone-ordered hill direct-seeding (DHDS), manual broadcast direct-seeding (MDS), and machine transplanting (MTR). In a two-year field experiment, DHDS significantly reduced the lodging index of the fourth (N4) internode from the top of the rice stem compared with MDS. Over the two years, DHDS and MTR decreased the field lodging rate by an average of 99.3% and 79.2%, respectively. This improvement in lodging resistance was mainly attributed to the enhanced breaking resistance caused by increased internode diameter and culm wall thickness, rather than changes in plant height or bending moment. DHDS also increased the cellulose and starch content of the N4 internode by 17.7% and 50.3% compared to MDS, respectively. Furthermore, there was no significant difference in grain yield among the different treatments. Our results suggest that DHDS can enhance lodging resistance of direct-seeded rice as a feasible sowing method without compromising yield, and it was noninferior to MTR in terms of yield and lodging resistance.

Complex and spatially varying warming impacts on rice yield hinder climate change impact assessments on food security. To address this issue, we compiled a global dataset of field-warming experiments (n = 214) and analyzed stage-specific crop responses to temperature variations. Results show that exposures to high (30° to 35°C) and extreme high (>35°C) temperatures are the dominant drivers of warming-induced rice yield losses, primarily through harvest index reductions. One additional exposure day above 30°C during the reproductive stage reduces rice yields by 1.1 to 1.8%. In contrast, current global gridded crop models underestimate this sensitivity, simulating only 0.1 to 1.3% yield loss per exposure day. After adjusting the model biases, we estimate that global rice yield losses decrease by 8.1% under 1°C of global warming, approximately twice the unadjusted estimates, with South and Southeast Asia being the most vulnerable regions. Our results highlight the critical role of high-temperature exposure in shaping warming impacts on rice yield.

Rice–wheat rotation is a major intensive cropping system in China. Existing research has focused mainly on single-season crop yield, with limited attention to coordinating cultivar duration and sowing schedules between rice and wheat for high annual system productivity. In this study, we combined a regional climatic suitability index (CSI) and a variety-specific annual thermal-radiation proportion (TRP) with annual and daily potential yield and wheat late-sowing loss to evaluate the yield benefits and late-sowing risks across regions. Using well-calibrated crop models by high-yielding experiments, we compared two typical high-yield rice–wheat combinations in these regions: a medium-duration hybrid indica combination and a long-duration hybrid indica–japonica combination. Compared with the medium-duration combination, the long-duration combination had a 5–12 percentage-point higher TRP and increased annual potential yield by 346–1,214 kg ha-1, but reduced daily potential yield by 3–13 kg ha-1 d-1 and shortened the rice harvest-to-wheat sowing interval. The high-CSI zone had the highest potential yield but the shortest, non-overlapping optimal sowing windows and greatest sensitivity to delayed wheat sowing. The medium-CSI zone provided the favorable balance between annual yield gain and wheat establishment risk, whereas the low-CSI zone had longer, substantially overlapping windows but limited benefits from the long-duration combination. Historical climate change generally reduced system yield potential. However, the long-duration combination reversed the decline in the high-CSI zone, mitigated it in the medium-CSI zone, and intensified it in the low-CSI zone. Overall, CSI characterizes regional climatic suitability, whereas TRP quantifies variety-specific thermal-radiation coverage. Their integration provides a system-level framework for evaluating and managing the trade-off between annual yield potential and timely wheat establishment under spatially heterogeneous and changing climates.

[Context]: Developing direct-seeded ratoon rice (DS-R) offers promising potential for further reducing labor requirements and agricultural inputs in rice production. [Research question]: However, limited information is available on the differences between DS-R and transplanted ratoon rice (TP-R) in grain yield and nitrogen use efficiency (NUE). [Methods]: Field experiments were conducted in 2022 and 2023 to investigate the effects of crop establishment on yield formation and NUE of Fengliangyouxiang1 (FLYX1) and Huiliangyou898 (HLY898) grown under three nitrogen (N) treatments. [Results] Grain yields of the main crop ranged from 5.94 t ha-1 to 9.58 t ha-1 in DS-R, which were 11.4 % lower than those in TP-R, primarily due to a lower grain filling percentage in 2022, fewer spikelets panicle-1 in 2023, and a lower harvest index, total N uptake (TNU), and N recovery use efficiency (RE) in both years. In the ratoon crop, the grain yields of DS-R were 3.54-6.03 t ha-1 for FLYX1, which were comparable to those of TP-R; however, the grain yields of DS-R were 2.61-5.08 t ha-1 for HLY898, which were 9.7 % lower than those of TP-R. Yield reduction in HLY898 was mainly attributed to the decreases in panicle number per m2, ratooning ability, total dry weight, and crop growth rate after heading, which were associated with the reduction in TNU and RE. Overall, N treatments, except zero-N control, did not have a consistent and significant effect on either grain yield or NUE. [Conclusions]: Our results indicated that DS-R reduced grain yield and NUE in the main crop, whereas such reductions could be prevented with FLYX1 in the ratoon crop [Implications]: Given the variety-specific responses of yield and NUE to crop establishment, selecting suitable varieties will be critical for enhancing the grain yield and NUE in DS-R system.

Cadmium (Cd) accumulation in ratoon rice poses significant food-safety risks and complicates the sustainable expansion of ratooning systems. This study elucidates the physiological mechanisms governing Cd accumulation patterns in ratoon rice by comparing two genotypes contrasting in Cd accumulation under controlled Cd exposure. OsNramp5 loss-of-function reduced grain Cd by 39.5-51.2% across the main and ratoon seasons, accompanied by downregulation of OsNramp1 (root uptake) and OsHMA2 (xylem loading) and enhanced leaf Cd chelation. Across the ratoon crop, upper-node tillers accumulated 30.8-59.5% more grain Cd than lower-node tillers, attributable to 13.4-40.4% higher transpiration rates and 41.0-45.5% greater grain-filling rates. Lower-node tillers exhibited late-season Cd accumulation surges coinciding with OsLCT1/OsCCX2 upregulation and peak transpiration rates (7.17-8.38 mmol·m⁻²·s⁻¹). Overall, our findings support OsNramp5 loss-of-function as a practical genetic option to reduce grain Cd in ratoon rice system. Upper-node tillers acted as preferential Cd sinks due to early-season vigor, prolonged grain-filling, and elevated gas-exchange capacity, amplifying ratoon grain contamination risks.

Extremely high temperatures (HT) caused by global warming pose serious threats to rice production. Potassium (K) is critical for plant stress tolerance, but its role in mitigating heat damage remains unclear. This study aimed to elucidate how high panicle K application affects mid-season rice HT tolerance in central China. A two-year field experiment grew two rice cultivars (heat-resistant Shanyou 63, SY63; heat-sensitive Liangyoupeijiu, LYPJ) under varying sowing dates and two K application levels (low K, LK, 50 kg K ha−1; high K, HK, 90 kg K ha−1) at the panicle initiation stage. Sowing date 1 (S1) and sowing date 2 (S2) increased the risk of heat stress exposure. Compared with late sowing (S3) under LK, early sowing reduced the yield in LYPJ by 41.3% (S1) and 51.3% (S2) in 2022, and by 35.4% (S2) in 2023, but did not affect the yield in SY63. Compared with LK in the same sowing date, HK increased yield by 44.7% (S1) and 61.5% (S2) in LYPJ in 2022, and by 30.6% (S2) in 2023, whereas it showed no significant effect on SY63 yield. Structural equation modeling analysis indicated that the yield loss could be primarily attributed to heat intensity at the panicle initiation and maturity stages. HK increased stomatal conductance and improved leaf water potential, thereby reducing canopy temperature by 1.2–1.3 °C at heading and 1.1–2.5 °C at maturity. Concurrently, HK enhanced carbohydrate supply and elevated enzyme activity for sugars utilization in anthers, collectively enhancing pollen viability and spikelet fertility. HK optimized source-sink traits via increasing leaf area index, specific leaf weight, spikelets per unit leaf area, post-anthesis translocation of stem dry matter (47.5%–48.9% in 2022 and 24.0% in 2023), and post-anthesis dry matter accumulation (33.0%–38.2% in 2022 and 19.0% in 2023). The study indicates that early sowing increases the risk of heat stress exposure for mid-season rice in central China, and the increase of panicle K application can mitigate yield loss by lessening canopy temperature and optimizing source-sink relationships.

Cold stress (CS) severely limits the growth and productivity of rice (Oryza sativa L.), particularly in temperate regions where abrupt temperature declines frequently occur during early developmental stages. In recent years, nanoparticle (NP) application has emerged as a promising approach for alleviating CS; however, systematic comparisons of different NPs across multiple growth stages remain unclear. This study evaluated the effectiveness and physiological mechanisms of four NPs (Fe2O3, ZnO, TiO2, and CeO2) in enhancing CS tolerance of rice seedlings using four cultivars with contrasting cold tolerance: two conventional cultivars (ZJZ-17, cold-sensitive; XZX-6, cold-tolerant) and two hybrid cultivars (LLY-7108, cold-tolerant; LLY-32, cold-sensitive). Seedlings were subjected to CS (14 °C day/10 °C night) for 5 days at three developmental stages (14, 21, and 28 days after emergence), followed by a 7-day recovery period under optimal conditions. CS markedly reduced plant height (34.8%), fresh weight (57.2%), dry weight (50.0%), and chlorophyll a and b contents (48%) following recovery. Foliar application of NPs significantly mitigated the adverse effects of CS, with Fe2O3 and ZnO showing the highest effectiveness. Fe2O3 treatment increased plant height, fresh weight, and dry weight by 25.6%, 43.5%, and 40.6%, respectively, relative to cold-stressed plants, while chlorophyll a and b contents increased by 41.6% and 42.2%. NPs application alleviated oxidative damage by reducing reactive oxygen species (up to 67.4%), malondialdehyde (up to 51.2%), and proline accumulation (up to 60.4%). Enhanced antioxidant defense was evidenced by increased activities of superoxide dismutase (66.6%), peroxidase (59.6%), and catalase (34.3%) under Fe2O3 treatment. Yield-related traits also showed significant recovery, with Fe2O3 increasing tiller number, spikelets per panicle, and grain yield per plant. The hybrid cultivar LLY-7108 consistently exhibited greater CS tolerance than conventional cultivars, while the cold-sensitive cultivar ZJZ-17 showed the greatest susceptibility. CS imposed at later growth stages (28-day-old seedlings) caused less damage and allowed greater recovery than early-stage stress (14-day-old seedlings). Overall, NP-mediated enhancement of photosynthesis and antioxidant capacity significantly improves CS tolerance and yield performance in rice, with Fe2O3 NPs emerging as a promising strategy for mitigating CS. These findings provide practical insights for rice cultivation in regions prone to chilling events and contribute to the development of nanoparticle-based approaches for rice production under climate stress.

The poor filling of inferior spikelets (IS) compared with superior spikelets (SS) constitutes a major constraint on rice yield potential, yet the underlying physiological mechanisms remain inadequately understood. In this study, field experiments were conducted to examine phloem unloading patterns in SS and IS. We combined microscopic observation of rachis vascular bundles, symplastic tracer (carboxyfluorescein) transport assays, gene expression of key sucrose-transport and starch-synthesis components, and protein expression profiling of sucrose transporters (SUTs). Results indicated that SS exhibited superior grain filling performance relative to IS, which corresponded to its more developed phloem structure, larger vascular bundle and phloem areas, and a higher density of plasmodesmata at the intercellular interfaces within the dorsal vascular bundles. Carboxyfluorescein (CF) fluorescence signals were more intense in the vascular bundles of SS, suggesting an enhanced capacity for symplastic transport. SS exhibited higher transcript levels of genes encoding sugars will eventually be exported transporters (SWEET), SUTs, and cell wall invertase (CWI). Correspondingly, the protein abundance of SUT and CWI, along with CWI activity, was elevated in SS. These findings collectively indicate that SS possesses an enhanced capacity for phloem unloading through apoplastic and symplastic pathways. RNA-Seq analysis revealed that, compared to IS, SS exhibited upregulated expression of most genes involved in starch and abscisic acid biosynthesis, while genes for ethylene synthesis were downregulated. These results underscore the critical roles of phloem-unloading and phytohormonal regulation in determining grain filling, thereby providing an integrative explanation for the differential filling patterns between SS and IS in rice.

Enhanced cadmium (Cd) uptake in lower-node tillers increases the contamination risk in ratoon rice. Using OsNramp5 mutants and seasonal Cd treatments, we quantified the contributions of stubble-redistributed Cd and newly soil-derived Cd to ratoon tillers at different nodal positions. OsNramp5 loss-of-function reduced grain Cd content by 55.4%-66.8% in the ratoon season by decreasing Cd uptake and translocation to grains. Compared with their wild-type, the mutants exhibited 16.3%-26.3% lower grain Cd concentrations at lower nodes than at upper nodes under exogenous Cd treatment. Upper-node tillers accounted for 84.0%-97.7% of the stubble-redistributed Cd, whereas soil-derived Cd preferentially accumulated in lower-node tillers, increasing their share of Cd accumulation by 12.4-26.0 percentage points relative to stubble-redistributed Cd. The expression levels of OsNramp1, OsHMA2, and OsHMA3 were also downregulated in mutant adventitious roots, suggesting a possible feedback response associated with reduced Cd transport. Overall, OsNramp5 loss-of-function reduces both Cd uptake and translocation, thereby providing a genetic strategy for mitigating Cd contamination in ratoon rice systems.

To elucidate the relationship between leaf color-changing and stem NSC translocation during grain filling and their impact on yield formation, two indica-japonica hybrid varieties with distinct leaf color change patterns were planted under three N fertilizer dosages (LN 0 kg ha−1; MN 150 kg ha−1; HN 300 kg ha−1). Leaf color change characteristics, photosynthetic productivity, stem NSC translocation, yield and harvest index were analyzed. The results showed that CY927 (slow leaf color change) achieved 10.45%−21.81% higher yields than YY1540 (fast leaf color change) under high-temperature conditions. Compared to YY1540, CY927 delayed the onset of leaf color-changing (T0) by 2.1−4.1 d, enhanced the final leaf color indicator at maturation (CIf) by 16.79−52.25%, contributing to 10.56−42.77% greater aboveground biomass accumulation through higher photosynthetic capacity, but significantly limited stem NSC remobilization, reduced total NSC translocation by 23.78−33.19% and NSC translocation ratio by 14.65−22.19%, resulting in a 2.66−8.43% lower harvest index. N application increased rice yield via a delay in leaf color-changing onset (T0), a reduced color-changing rate (Rm), a shortened color-changing duration (T100), and an improved final color index (CIf). This retardation of senescence enhanced photosynthetic capacity, which was associated with elevated sucrose content and sucrose synthase activity. However, N reduced stem α-amylase activity (14.83−62.07%) and NSC translocation ratio (5.44−16.30%) in both varieties. Correlation analysis revealed significant positive relationships between T0 and aboveground biomass (P<0.001), and between T100 and stem NSC translocation (P<0.001). In conclusion, rice variety and N application indirectly regulate the dynamic balances between leaf photosynthetic carbon metabolism and stem NSC translocation by influencing the leaf color-changing dynamic, ultimately affecting yield and resource use efficiency. This integrative framework, connecting leaf color-changing, carbon allocation, and yield performance, provides scientific guidance for optimizing rice cultivars and N fertilization strategies.

The change in leaf color during the later reproductive period of rice is directly related to photoassimilate accumulation and nutrient reuse, and it ultimately affects grain filling and yield. This study aimed to explore an assessment model that depicts the leaf color change process, and extract parameters that can precisely distinguish differences in leaf color changes among different treatments and varieties. A total of 31 rice varieties were selected as the field experiment materials in 2019 and 2023. The SPAD values of the flag, 2nd and 3rd leaves were measured after heading, and they were normalized to the leaf color index (CI). A functional model for the variation of leaf CI with time (t) in the late reproductive stage of rice was established based on CI=at2+bt+c, and seven color change parameters were extracted for the quantitative comparison and assessment of leaf color changes, including three time related parameters for color change (onset time, T0; midpoint time, T50; and color change duration, T100); one leaf color index (final value of CI, CIf); and three parameters related to the color change rate (the rate during T0-T50, R1; the rate during T50-T100, R2; and the mean color change rate, Rm). In 2023, Chunyou 927 (CY927) with a dark leaf color and Yongyou 1540 (YY1540) with a normal leaf color were used as materials, and three N fertilizer amounts were applied to explore the effects of N fertilizer on the leaf color change process through the established assessment system. The T0 of the flag leaf was delayed by 2.6-3.0 d compared to the 2nd and 3rd leaves. The CIf of the flag leaf was 12.12 and 21.15% higher than those of 2nd and 3rd leaves, respectively. In addition, the R1, R2 and Rm of the 3rd leaf were 10.75-19.82%, 17.99-20.09% and 18.23-11.61% higher than the flag and 2nd leaves, respectively. Rice yield was significantly positively correlated with T0, positively correlated with T50 and T100, and negatively correlated with R1, R2 and Rm. The average T0, T50, and T100 of rice varieties with yields higher than 8,000 kg ha-1 were 6.8, 22.2, and 31.8 d, respectively, with a CIf of 0.563 and an Rm of 0.015 d-1. N applications delayed T0 by 4.5-6.2 d, reduced Rm by 30.06-32.33%, and increased CIf by 35.78-39.69%. The established leaf color change model and extracted parameters quantitatively depicted the leaf color change process during the later reproductive period. They also effectively distinguished the differences in leaf color change among leaf positions, rice varieties and N treatments. This approach is valuable for selecting and cultivating high-yield and nutrient-efficient rice varieties, as well as for analyzing the underlying mechanisms.

High nighttime temperatures (HNT) tend to diminish rice quality by disrupting assimilate translocation and grain filling process in rice (Oryza sativa L.). However, there is controversy remains regarding whether source or sink limitation are the primary driver under HNT during grain filling period. Additionally, the physiological mechanisms underlying the genotypic variation in the response of grain protein content to HNT and its effect on rice quality have been less explored. To address whether nitrogen remobilization from leaves to grains during grain filling determines genotypic differences in grain quality under high night temperature, two cultivars - HHZ (Huanghuazhan, an indica inbred line) and YY4949 (Yongyou4949, an indica-japonica hybrid) - were treated with 30/22°C (day/night, CK) and 30/27°C (HNT) over two consecutive years. Significant genotypic variation in the response of grain storage substances to HNT was observed between the two cultivars. Under HNT, YY4949 exhibited a significant increase in grain protein content and glutelin/prolamin ratio, and this shift negatively impacted rice eating and cooking quality. Notably, the protein/amylose ratio exhibited a stronger correlation with chalkiness degree and pasting characteristics of rice flour. Under HNT, accelerated nitrogen remobilization from leaves to grains in YY4949 - driven by enhanced chloroplast degradation and upregulated expression of nitrogen metabolism-related enzymes and transporters exacerbated source limitation to rice quality and disrupted the balance between starch and protein in grains. Collectively, these findings suggest that genetic modulation of nitrogen remobilization could facilitate the breeding of climate-resilient rice cultivars with superior grain quality.

Ratoon-based cropping systems have re-emerged as a strategy to enhance productivity and resource use efficiency in crop production; however, the mechanisms governing regeneration across harvest cycles remain poorly understood, resulting in highly variable and unpredictable performance. Ratoon yield depends on two tightly coupled components: the establishment of reproductive tillers that form yield-bearing units and the productivity of each unit, which were determined by organ differentiation and biomass accumulation. Here, we propose Ratoon Biology as a conceptual framework that redefines ratooning as a continuous, whole-plant developmental process that extends across seasons. We identify five interacting dimensions that jointly regulate ratoon productivity. First, ratoon buds determine regenerative potential through their meristem viability, dormancy status, and competitive competence. Second, stubble functions provide the structural and metabolic foundation for regeneration by maintaining vascular continuity, supplying carbon and nitrogen reserves, and integrating systemic signals. Third, root-shoot coordination enables the rapid re-establishment of hydraulic, nutritional, and hormonal coupling between residual roots and emerging shoots, thereby supporting early tiller vigor. Fourth, tiller regeneration and establishment represent a selective developmental process shaped by nodal competition, spatial heterogeneity, and unequal access to internal resources, together determining which buds survive to become productive tillers. Fifth, inter-seasonal continuity reflects the developmental and physiological legacy linking the main crop to subsequent ratoon performance through structural, metabolic, and regulatory carry-over effects, including persistent plant-microbe interactions. By framing ratooning as an integrated, cross-seasonal biological system, Ratoon Biology establishes a roadmap for future research that targets key mechanistic gaps and provides a conceptual basis for next-generation breeding and management strategies aimed at improving multi-season productivity.

Cold stress significantly impairs the rice (Oryza sativa L.) growth and yield, particularly in temperate regions where abrupt temperature fluctuations often occur during the early growth stages. Given the need for novel strategies to improve crop cold tolerance, we evaluated the efficacy of iron oxide nanoparticles (Fe2O3) in enhancing rice cold stress resilience. The reported mechanisms involve promoting plant growth and development, alleviating oxidative stress and inducing defense responses. Using RNA-seq, we analyzed the physiological and transcriptomic responses of rice to cold stress and Fe2O3 treatment. Under cold stress, the NPs elicited a strong antioxidant response-elevating superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, which led to a marked reduction in oxidative damage, as shown by decreased ROS and MDA levels. Transcriptomic analysis further revealed that NP treatment modulated key pathways related to carbohydrate metabolism, photosynthesis, hormone signaling, and antioxidant metabolism. Collectively, our findings establish that Fe2O3 nanoparticles ameliorate cold stress by preserving chloroplast structure, stomatal architecture, reduce oxidative stress marker, enhancing antioxidant defense system and stabilize photosystem and providing a promising nanozyme-based approach for rice protection against cold induce damage.

Early seedling vigor is a key determinant of rapid canopy establishment and early biomass production in rice, yet its physiological and morphological drivers remain incompletely understood. Rapid growth is often assumed to result from enhanced leaf-level photosynthetic capacity, but this assumption has rarely been tested explicitly. Here, we examined growth dynamics, biomass allocation, leaf morphology, and photosynthetic traits in newly developed rice lines exhibiting strong early vigor and compared them with the elite cultivar HHZ. The new lines accumulated biomass more rapidly than HHZ and exhibited non-exponential growth patterns, with higher absolute and relative growth rates. Despite lower leaf photosynthetic rates and lower leaf nitrogen content, the new lines showed significantly greater early biomass accumulation and larger canopy leaf area than HHZ. Canopy expansion was driven mainly by increased leaf width, rather than leaf length or leaf number per tiller, together with a greater allocation of biomass to leaves relative to roots during early growth. These results demonstrate that rapid early growth can be achieved through a canopy expansion strategy that prioritizes leaf morphological development and biomass allocation over photosynthetic efficiency per unit leaf area. This observation entails clear trade-offs, including nitrogen dilution and reduced photosynthetic biochemical capacity, yet it results in greater whole-plant biomass accumulation during early establishment. Our findings challenge the conventional assumption that early vigor is necessarily associated with higher leaf photosynthesis and highlight alternative physiological pathways for improving early growth and competitiveness in rice.

Rice (Oryza sativa L.) root characteristics are closely associated with nitrogen (N) uptake, root growth and development are greatly influenced by ethylene. In this study, a hydroponic experiment was conducted using four rice genotypes [Shanyou 63 (SY63) and Zhonghua 11 (ZH11) with well-developed aerenchyma; Yangdao 6 (YD6) and mutant rcn1 from ZH11 with less-developed aerenchyma] to investigate the effects of exogenous ethephon (Eth) on root characteristics, N uptake, dry matter distribution, and clarify the underlying relationship. Compared with YD6 and rcn1, SY63 and ZH11 had higher N accumulation, higher root aerenchyma area to cortex area ratio (ACR), higher NH4+ uptake via the apoplasmic pathway and root-to-shoot NH4+ translocation under no ethephon application (NEth) and Eth treatment, and elevated expression of the three genes (OsAMT1;2, OsAMT2;2, and OsAMT4;1) for ammonium transporters under Eth treatment. Eth treatment increased shoot N and dry matter accumulation, decreased the total root length and root diameter, and increased ACR and the expression of OsAMT genes in four genotypes. In summary, Eth could increase N accumulation via modifying root characteristics in rice, particularly by enlarging root aerenchyma and thinning the roots. The findings provide implications for development of elite rice varieties and green rice production with higher N efficiency. (c) 2025 Crop Science Society of China and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

High temperature events have occurred frequently in recent years under global warming conditions. High temperature during panicle initiation (PI) poses significant negative impacts on rice grain yield. Alternate wetting and drying irrigation (AWD) is widely adopted in rice cultivation. Here, to investigate the alleviating effect of AWD on heat damage to rice (Oryza sativa L.), we selected four rice varieties with different high-temperature resistance (Liangyoupeijiu, IR64, Huanghuazhan, Shanyou 63), two irrigation treatments at the tillering stage including AWD and continuous flooding (CF) and two temperature treatments at the PI stage (high daytime temperature, HDT; and control temperature, CK) were applied. HDT significantly reduced the yield of all four varieties except for Shanyou 63, primarily by decreasing the spikelet fertility and spikelet number, while AWD significantly improved the two traits under HDT. Moreover, HDT reduced the photosynthetic rate, increased the starch content in leaves and stems, and decreased the transport of sucrose to panicles. AWD reduced the panicle temperature, promoted sucrose synthesis in leaves, increased sucrose content and sucrose hydrolase activity in panicles under HDT. HDT also increased the content of abscisic acid and decreased that of cytokinins (CTKs), indole-3-acetic acid (IAA), and gibberellins (GAs) in panicles under CF. AWD increased the expression of CTK biosynthesis genes (IPT, CYP735A, LOG) and decreased that of CTK degradation gene CKX in roots and panicles under HDT, while enhanced the xylem sap flow rate and contents of CTKs, IAA, and GAs in panicles. Furthermore, AWD exhibited a more pronounced alleviating effect on HDT damage in heat-sensitive varieties than in heat-tolerant varieties. In summary, AWD leads to lower panicle temperature and higher photosynthetic rate, sucrose content, and CTK level in panicles, which together enhance the heat tolerance at the PI stage, and therefore is a sustainable and feasible strategy to mitigate heat-induced yield loss in rice.

Rice–rapeseed, one of the most important cropping systems in the Yangtze River Valley (YRV), plays a vital role in ensuring both staple food and vegetable oil security in China. Since the 1960s, the system has undergone a rapid area expansion in YRV, with the total area relatively stable in the last two decades while experiencing a spatial shift towards the upper and middle reaches of YRV. Meanwhile, system yield growth has shown a slowing trend, primarily due to the stagnant rice yield and rapid decrease in rapeseed relative yield gain. However, the system production still has considerable room to increase because of the large relative yield gap of more than 50% in rapeseed season and extensive winter fallow fields that can expand rapeseed planting in YRV. To increase system yield, major yield-limiting factors and optimal agronomic management practices were identified, focusing on the aspects of crop establishment, variety selection, fertilizer application, residue return, and water management. We then thoroughly summarized the environmental impacts of carbon footprint and greenhouse gas emissions, as well as possible benefits and adverse effects of climate change. Furthermore, the challenges of enhancing mechanization and economic profits and perspectives of future research directions were discussed to promote the long-term sustainability and productivity of the rice-rapeseed cropping system.

Context: Ratoon rice is resource-efficient and environmentally friendly but faces challenges under climate-induced water scarcity. While water-saving irrigation and water-saving and drought-resistant varieties offer promise, their effects on yield and water productivity in ratoon rice system remain unclear. Objective: To evaluate the effects of water-saving irrigation and drought-resistant rice varieties on yield, yield components, water use, and water productivity in both main and ratoon crops. Methods: Field experiments were conducted using a split-plot design with two water regimes (continuous flooding [CF] and water-saving [WS]) as main plots and six rice varieties (three water-saving and drought-resistance rice [WDR] and three ordinary paddy rice [OPR] varieties) as subplots in Qichun and Xishui (Hubei, China) in 2023. Results: Yields were similar between CF and WS across sites, but WS reduced irrigation water use by 76.1-84.6 %, increasing water productivity by 16.3-140.0 %. Main crop yield was comparable between WDR and OPR, but WDR yielded 16.1-30.1 % less in the ratoon crop, resulting in lower water productivity. As a result, water productivity of WDR was significantly lower than that of OPR in ratoon crop but not in main crop. The lower ratoon crop yield of WDR was attributed to reduced total dry weight and a decreased number of panicles per unit area, which was associated with fewer panicles at the lower nodes. Significance: Water-saving irrigation maintained yield while reducing water input. To improve WDR performance in ratoon systems, future efforts should target enhancing ratoon biomass and promoting tillering from lower nodes.