Direct seeding of rice has attracted attention because of its simplicity and rapidity compared with traditional cultivation methods. However, the geographical location of the rice region in Southwest China is complex, and the common characteristics of high yield of direct seeding hybrid indica rice and the law of nutrient absorption and accumulation are still unclear. This study results demonstrated that the mean yield of high‐yield varieties (HYV) in the two ecological points increased by 17.68%–19.98% and 17.37%–27.06%, respectively, compared with low‐yield varieties (LYV). The high tillering ability and effective tillering rate of HYV promoted a large leaf area index (LAI) and a strong photosynthetic capacity and stimulated the accumulation of aboveground biomass and nitrogen, phosphorus, and potassium nutrients in rice plants, which were finally transported and allocated to the grains to maintain high yields. Correlation analysis indicated that yield and its components were closely related to spatial population structure and nutrient accumulation and allocation. In particular, LAI at the full heading stage, net photosynthetic rate, aboveground biomass from jointing to maturity stage, and nitrogen, phosphorus, and potassium accumulation and distribution from jointing to full heading stage have the strongest correlation with yield and its components. Therefore, improving the effective tillering rate and LAI, as well as the accumulation and distribution of aboveground biomass, nitrogen, phosphorus, and potassium of rice plants from jointing to full heading stage, are the common laws for the formation of high yield of direct seeding hybrid rice in different ecological areas.

Low-temperature and anaerobic conditions are two major limiting factors in the germination of direct-seeded rice. Sixteen hybrid Indica rice varieties were screened and subjected to two different temperatures and oxygen levels. The results revealed that relative to anaerobic conditons, low-temperature is the key limiting factor for seed germination. For all varieties, relative to normal temperature (30°C) and aerobic conditions (89.0% germination), the germination percentages when seeds were germinated under anaerobic (normal temperature), low-temperature (15°C) or combined anaerobic and low-temperature conditions were 64.0, 46.0 and 23.2%, respectively. Under the three latter treatments, the soluble sugar (SS) and gibberellin (GA) was significantly decreased, the abscisic acid (ABA) had significantly increased by 14.6–251.8%, and the superoxide dismutase (SOD) initially increased by 30.2–49.7% and decreased thereafter by 34.7%. Seeds of ‘Shen 9 you 28’ and ‘Jingliangyou 534’ performed better than seeds of the other varieties, with high germination percentages, SS, SOD, GA and low ABA. Correlation analysis revealed that the germination percentages were significantly correlated with the SS, SOD, GA, ABA and GA/ABA. Elevated SS, GA and SOD, as well as reduced ABA content were thought to account for the high germination of rice varieties resistant to combined low-temperature and anaerobic stress.

Zinc (Zn) is essential for human health, but rice often lacks sufficient amounts. Leaf senescence is a vital developmental stage during which nutrients are redistributed to other organs. However, Zn retransfer during deficiency is often overlooked. In this hydroponic experiment, we studied the effect of Zn deficiency on rice seedlings, specifically focusing on the fourth leaf under control and deficient conditions. Growth phenotype analysis showed that the growth of rice nodal roots was inhibited under Zn deficiency, and the fourth leaf exhibited accelerated senescence and increased Zn ion transfer. We conducted transcriptome analysis on the fourth leaf at two time points. The fourth leaf at the second time point under control conditions was used as the control and compared to when Zn ion content markedly decreased under control and deficiency conditions. Analyzing differentially expressed genes showed that Zn deficiency regulates more ZIP family genes involved in Zn ion retransfer in the leaves. OsZIP3 upregulation under Zn-deficient conditions may not be induced by Zn deficiency, whereas OsZIP4 is only induced during Zn deficiency. Gene Ontology enrichment analysis showed that Zn-deficient leaves mobilized more biological pathways (BPs) during aging, and the enrichment function differed from that of normal aging leaves. The most apparent “zinc ion transport” BP was stronger than that of normal senescence, possibly due to Zn-deficient leaves mobilizing large amounts of BP related to lipid metabolism during senescence. These results provide a basis for further functional analyses of genes and the study of trace element transfer during rice leaf senescence.