Topdressing at panicle differentiation (PF) according to soil fertility and regularity of rice nutrient absorption is an important agronomic practice used in cultivation of rice cultivars with a long growth duration. We studied the impacts of timing of nitrogen fertilizer application during PF on photosynthesis and yield-related agronomic traits in ‘Y-Liang-You 900’ and ‘Y-Liang-You 6’, which are representative rice cultivars with a long growth duration. Data for two years showed that timing of topdressing application during PF affected panicles per unit area, percentage grain set, spikelets per panicle, and leaf photosynthetic traits during the grain-filling period. Topdressing at the initial stage of flag-leaf extension resulted in higher grain yield (typically by 10.55–19.95%) than in plants without topdressing. Grain yield was significantly correlated with flag leaf photosynthetic rate and leaf SPAD value (r = 0.5640 and r = 0.5589, respectively; p < 0.01) at an advanced grain-filling stage (30 days after heading). Surprisingly, grain yield was not correlated with carbohydrate remobilization from the stem and sheath. For rice cultivars with a long growth duration, nitrogen-fertilizer topdressing must be applied at the initial stage of flag-leaf extension to delay leaf senescence during the grain-filling stage and realize the enhanced yield potential.

Fertilizer application for rice production has increased significantly in southern China to raise yields, but has led to problems with lodging, quality decline and environmental pollution. Therefore, research on fertilizer-saving cultivation technologies for high-yielding rice is necessary. A two-factor experiment was conducted to evaluate the effects of seedling-addition treatment (SAT) and nitrogen-saving treatment (NST) on yield formation and nitrogen absorption of individual plants and plant groups under the seedling-throwing cultivation system. Numbers of spikelets per panicle and filled grains per panicle of individual plants declined under decreased nitrogen application, but was compensated by substantially increased effective panicles number and total number of glumous flowers under SAT. Under the optimal SAT–NST treatments of 18% less N fertilizer and 32% additional seedlings, yield increased 1.79% and 4.29% compared with that of conventional practice (CK) in 2015 and 2016, respectively. The mature-stage individual-plant biomass under SAT–NST treatments decreased by 27.46% and 20.49% compared with CK in 2015 and 2016, but plant-group biomass did not differ significantly (all >16 t ha⁻¹). Under SAT–NST treatments, effective number of panicles was positively correlated with maximum number of seedlings (r = 0.643) and N absorption amount in the tillering stage (r = 0.901).

Rice (Oryza sativa L.) is one of the most significant food crops worldwide. Flooding can significantly impact the survival and emergence of rice seedlings in the direct planting form of rice, leading to a loss of production. This work investigated the critical phase of rice seed germination to the seedling establishment under submergence stress. It also explored the underlying physiological and molecular processes of shoot and root submergence tolerance. Physiological and transcriptomic analysis of flood-tolerant varieties (LS273) and non-flood-tolerant varieties (ZZ39) were performed. Under submergence stress, LS273 showed longer roots, taller shoots than ZZ39, and lower levels of malondialdehyde and GSSG, but a greater level of GSH/GSSG. In response to stress induced by submersion, LS273 produces more auxin than ZZ39. Within shoots, 4285 DEGs specific to LS273 and 4389 DEGs specifics to ZZ39 were found using the RNA-seq technique. There were 3983 specific DEGs in LS273 and 3292 specific DEGs in ZZ39 in the roots. Antioxidants and plant growth hormones were primarily mentioned in the annotations for these DEGs. Overall, our research provides a thorough foundation for investigating the molecular network underlying shoots’ and roots’ resistance to submergence stress in rice seedlings, leading us to hypothesize that the resistance of flood-tolerant rice may be attributed to high levels of oxidation resistance and auxin accumulation.

Super high-yielding rice (SHYR) (>15 t ha⁻¹) plays a crucial role in global food production and security. We hypothesized that the external environment of different ecological regions could improve biomass accumulation in different periods and thus increase the rice yield. Two SHYR varieties, i.e., Xiangliangyou900 (XLY900) and Yliangyou900 (YLY900), were cultivated in the YONGSHENG and LONGHUI ecoregions, China. The results indicated that the average yield of the two SHYRs in the LONGHUI ecological region was 15.27–15.45 t ha⁻¹ and 18.81–20.10 t ha⁻¹ in YONGSHENG. The high grain yield in the YONGSHENG ecoregion was mainly due to the increased number of spikelets per panicle, crop growth rate, and total biomass during the transplanting–heading stage (TP-HS) and heading–maturity stage (HS-MS), and harvest index. The yield of SHYR was significantly correlated with external environment conditions, i.e., average minimum temperature, average daytime, and night-time temperature, and average daily temperature at the TP-HS, HS-MS, and transplanting–maturity (TP-MS) stages. The rice yield was significantly and positively correlated with the cumulative daily radiation. Therefore, it can be concluded that the final yield of super high-yield rice is closely related to the utilization of temperature and radiation resources during the growth process in the ecological environment.

Improving rice productivity remains essential under land constraints and rising food demand. However, spatial yield variation of super hybrid rice across agroecosystems and the mechanisms driving it is not fully resolved. We evaluated how thermal regimes, nitrogen management and genotype jointly shaped yield differences of super hybrid rice across two ecological regions. Field experiments (2021–2022) used three super-hybrid cultivars — Liangyoupeijiu (LYPJ), Y-liangyou-1 (YLY1) and Y-liangyou-900 (YLY900) — under four N rates (0, 150, 240, and 330 kg ha⁻¹) at Longhui and Changsha. Averaged across varieties and years, grain yield in Longhui exceeded Changsha by 16.8% (2021) and 26.7% (2022). These site differences were associated with higher temperatures in Changsha during panicle initiation and grain filling, which were accompanied by reductions in spikelets per panicle (~ 5.6%), total spikelets (~ 7.7%) and seed-setting rate (~ 10.6%). Longhui also exhibited greater leaf area index, dry-matter accumulation, and crop growth rate, supporting superior sink formation and grain filling. Partial least squares path modeling indicated that crop growth rate, total dry weight, and seed-setting rate mediated much of the observed yield gap. Nitrogen at 240 and 330 kg ha⁻¹ narrowed inter-site yield differences by improving yield components and growth traits. Among cultivars, YLY900 achieved the highest yield, while YLY1 showed the greatest cross-site stability. Under the tested conditions, these results suggest that aligning N management with genotype selection relative to local thermal regimes can help reduce temperature-driven yield losses in super hybrid rice.