Against the background of increasing global soil salinity, exogenous salicylic acid (SA) and melatonin (MT) have attracted much attention for their potential in regulating plant stress tolerance and have become an important research direction for the development of green and sustainable agriculture. In this study, the alleviating effects of different concentrations of SA (100–900 μM) and MT (100–900 μM) on salt stress (50 mM NaCl) and their physiological mechanisms were systematically investigated using the Tianjin specialty rice, Xiaozhan rice, as the research object. The results showed that salt stress significantly inhibited the germination and seedling growth of the two varieties, in which the salt-sensitive variety Jinchuan No. 1 showed significantly higher decreases in root length, plant height, and biomass (54.7–69.1%) than the salt-tolerant variety Jindao 919 (4.0–28.9%). Exogenous SA and MT were effective in mitigating salt stress injury, but there were genotypic differences in their pathways of action. For the first time in japonica rice, the genotype specificity of the SA/MT response was clearly revealed: SA dominated the response of salt-tolerant varieties by enhancing antioxidant defences, whereas MT optimized the overall performance of the salt-sensitive varieties through scavenging of reactive oxygen species, and in addition, it was further determined that SA and MT exhibited optimal mitigating effects on both varieties in the 300–700 μM concentration range, showing the best mitigation effect for both varieties. This finding provides an important theoretical basis and technological paradigm for precision stress tolerance cultivation of saline rice, and the application of appropriate concentrations of SA/MT according to genotype specificity to reduce the dependence on agrochemicals is of practical value in promoting green and sustainable production in saline agriculture.

Salt stress severely impairs rice (Oryza sativa L.) germination and seedling establishment. Exogenous spermidine (Spd) has been shown to regulate stress tolerance in plants, but whether it acts during rice germination and seedling establishment under salt stress remains unclear. Here, rice seeds (cv. Jindao 919) were exposed to 75 mM NaCl with different Spd concentrations (0–1.4 mM), and physiological, biochemical, and transcriptomic responses were evaluated. The findings showed that salt stress had a pronounced inhibitory effect on both seed germination and seedling development. Exogenous Spd effectively alleviated these negative effects, with the most significant improvements observed at 1.0–1.2 mM: germination rate increased by 3.98–8.52%, seedling root length increased by 17.74–37.68%, soluble sugar content increased by 29.83–230%, and SOD and POD activities increased by 29.81–40.3% and 18.45–44.0%, respectively, while MDA content decreased by 36.28–40.3%. Further transcriptomic analysis identified a total of 1835 differentially expressed genes (DEGs). KEGG enrichment analysis revealed these genes were concentrated in key pathways including terpenoid biosynthesis, phenylpropanoid biosynthesis, and amino sugar and nucleotide sugar metabolism, thus alleviating the negative impact of salt stress on rice germination and seedling development. These pathways are closely related to gibberellin metabolism, lignin biosynthesis, and amino sugar metabolism, further revealing the regulatory role of Spd. Overall, 1.0–1.2 mM Spd was most effective in alleviating salt stress by synergistically regulating antioxidant defense, osmoregulation, and metabolic reprogramming, enhancing rice’s overall stress tolerance. This study provides theoretical guidance for precise regulation of Spd concentration to improve rice performance in saline-alkaline soils, and reveals the sustained promoting effects of Spd across various developmental stages of rice and its underlying molecular mechanisms.

Rice yield improvement depends on the coordinated optimization of plant architecture and physiological performance. In this study, an F8 indica–japonica recombinant inbred line (RIL) population derived from ‘Zhongyouzao8’ × ‘Toyonishiki’ was evaluated in a single field environment to examine how heading progression, flag-leaf SPAD dynamics around heading, and upper-leaf architecture were associated with grain yield. A total of 159 RILs and the two parents were phenotyped for grain yield, initial heading date, full heading date, pre-heading SPAD (SPAD1), post-heading SPAD at the onset of grain filling (SPAD2), flag leaf angle, plant height, and flag leaf traits. Substantial phenotypic variation and evident transgressive segregation were observed for most traits. Grain yield ranged from 2.62 to 9.88 t ha ^- ¹, and several traits showed moderate to high broad-sense heritability. Correlation, regression, principal component analysis, and high- versus low-yielding group comparisons suggested that, under the conditions evaluated, grain yield variation was more closely associated with upper-leaf architecture than with heading progression itself, whereas SPAD dynamics provided complementary but weaker information. However, the regression model explained only a limited proportion of yield variability, indicating that additional unmeasured yield components may also have contributed substantially to grain yield. Several preliminary candidate lines carrying relatively high grain yield and favorable combinations of flag leaf morphology and SPAD-related phenotypic profiles were identified from the single-environment screening. These findings are exploratory and require multi-environment validation before these trait combinations can be used as stable selection criteria in rice breeding.

In order to explore the response mechanism of heavy metal content in Oryza sativa L. fields under winter green manure. In this study, through field experiments, the changes of soil chemical properties and heavy metal content in Brassica napus L. and Oryza sativa L. at different growth stages were analyzed. The results are as follows: the pH value in Brassica napus L. harvest stage is higher than that before sowing, while the pH value in Oryza sativa L. harvest stage is lower than that before sowing. Eh of Brassica napus L. soil is positive during the whole growth period, showing a fluctuating upward trend. Eh of soil decreased to negative value during the whole growth period of Oryza sativa L. The contents of As, Hg, Pb, Cd and Cr in the soil decreased gradually in the whole growth period of Brassica napus L., and decreased to the lowest level in the harvest period. During the whole growth period of Oryza sativa L., the content of Hg and Cd decreased, while the content of Pb and Cr increased in the harvest period compared with before sowing. Therefore, planting green manure Brassica napus L. in winter is beneficial to alleviate heavy metal pollution in soil.