The purpose of this study is to determine the effect of light quality on growth, carbon and nitrogen metabolism, and antioxidant defense system of rice seedlings. Six light conditions were employed, including white (W), red (R), blue (B), combined LED of R and B at 3:1 (R3B1), combined LED of R and B at 1:1 (R1B1), as well as combined LED of R and B at 1:3 (R1B3). Combined application of red light and blue light could promote the growth of rice seedling leaves and roots under low light stress to varying degrees, increase the photosynthetic area by increasing the leaf area, improve the root characteristics by increasing the root volume, and increase the dry matter accumulation of rice seedlings. In addition, the combination of red light and blue light could increase carbon and nitrogen metabolites in rice seedling leaves, regulate the expression of genes related to carbon and nitrogen metabolism and enzyme activity, and enhance the antioxidant enzyme activity of rice seedlings. These results indicate that red light and blue light directly have synergistic effects which can regulate the carbon and nitrogen metabolism of rice seedlings, promote the morphogenesis of rice seedlings under low light stress, and promote growth, which has never been reported in previous studies. This study is a new discovery in the application of light quality in crop production and provides new avenues to enhance crop stress resistance. However, further study is needed to explore the physio-biochemical and molecular mechanisms of light quality in crop production.

The purpose of this study is to determine the effects of red and blue lights on the photomorphogenesis and photosynthetic traits of rice seedlings. The rice seedlings were cultured with red light (R), blue light (B), combined red and blue lights (R3B1/R1B1/R1B3), and white light (CK) as the control. The combined application of red and blue lights could promote the growth of rice seedlings to varying degrees; enhance photosynthesis by increasing the seedling leaf area, chlorophyll content, and chlorophyll fluorescence; improve root characteristics by increasing root number, root volume, and root activity; and thus increase the dry matter accumulation of rice seedlings. In addition, the combination of red and blue lights could regulate the expression of genes related to photosynthesis in rice leaves, affect the activity of the Rubisco enzyme, and then affect the photosynthesis of rice seedlings. These results indicate that red and blue lights have direct synergistic effects, which can regulate the growth of rice seedlings and promote the morphogenesis of rice seedlings. The combined application of red and blue lights can be used to supplement the light in rice-factory seedling raising.

High‐density planting is a strategy employed to save resources in crop production, particularly in environmentally friendly double‐season rice (Orvza sativa L.) cropping, where it promotes high grain yield and reduces required nitrogen (N) input. We conducted a field experiment in 2014–2018 to detect the combined effect of increased seedling density and reduced N input on early rice grain yield and N use efficiency (NUE). The higher basic seedling with low N input treatment (T2) had an average grain yield of 7.01 t ha⁻¹, which was 16.3% greater than that of the control (CK). There was a strong linear relationship between grain yield and panicles m⁻² (R² = .82, P < .001). Grain yield increased significantly with above‐ground biomass before the full‐heading stage (R² = .79, P < .001), which in turn promoted an increase in panicles m⁻² (R² = .85, P < .001). Mean agronomic efficiency (AE) in the T2 treatment was 34.3 kg kg⁻¹ N, which was 48.1% higher than that in the CK treatment. Therefore, increasing seedling density from 62.5 to 176 seedlings number m⁻² while reducing inorganic N input in the early season resulted in significantly higher grain yield in hand‐transplanted rice production. Our results indicate that dense planting with N reduction could improve early rice grain yield and enhance NUE.

In present study, sodium salt of α-naphthalene acetic acid (NA), potassium salt of fulvic acid (KF) and their combinations were applied to the growth substrates of tomato seedlings (Solanum lycopersicum L.) under chilling stress. The changes in aboveground biomass, root attributes, pigment contents, chlorophyll fluorescence, photosynthesis, osmotic regulation substances, and antioxidant enzymes activity of the tomato seedlings in response to NA and KF were investigated. The application of NA, KF and their combination could promote the growth of plant height and stem diameter of tomato seedlings under chilling stress to varying degrees, and improve root characteristics by increasing root volume, root length and root activity, and increase dry matter accumulation. In addition, the combined use of NA and KF improved the seedling leaf chlorophyll content, qP, Fv/Fm, ΦPSII , Pn and increased the activity of antioxidant enzymes in the tomato plants. The above results suggested a synergistic effect between NA and KF to stimulate the seedlings growth and to enhance the ROS scavenging ability of tomato, which has never been reported in previous research before. However, further researches are needed to explore the physiological and molecular mechanism underlying the synergistic effect between NA and KF.

Gibberellic acid (GA₃) application after anthesis is an important practice in hybrid rice seed production, and it plays diverse roles in seed quality and seed yield. The main objective of this study was to determine (1) the effects of GA₃ application after anthesis on seed vigor and (2) the optimal GA₃ dosage applied to Indica hybrid rice seed production. Field experiments of different GA₃ dosages (15 g hm⁻² and 30 g hm⁻², respectively) after anthesis were conducted in 2016 and 2017, and seed vigor parameters, stigma vigor index, and seed yield were determined. We found that significant differences in seed vigor parameters by a standard germination test and a cool germination test were observed among different GA₃ dosages after anthesis. Compared with the water spraying treatment, the germination percentage (GP) increased by 2.5–6.3%, and the vigor index (VI) increased by 8.9–19.8% from GA₃ application after anthesis, respectively. Moreover, the stigma vigor index of the female parent was enhanced with an increasing GA₃ dosage, and there were significant increases (7.5–16.0%) between the water spraying treatment and GA₃ spraying treatments. There were positive significant relationships between the VI and stigma vigor index. Additionally, the seed yield of the GA₃ application with 30 g hm⁻² was 3.9% higher on average than that of the water spraying treatment. Therefore, our study suggests that seed vigor can be increased by GA₃ application after anthesis, and GA₃ application should be applied at a rate of 30 g hm⁻² to improve seed vigor and maintain seed yield in Indica hybrid rice seed production.