A large number of dead seedlings can occur in saline soils, which seriously affects the large-scale cultivation of rice. This study investigated the effects of plant growth regulators (PGRs) and nitrogen application on seedling growth and salt tolerance (Oryza sativa L.), which is of great significance for agricultural production practices. A conventional rice variety, “Huang Huazhan”, was selected for this study. Non-salt stress treatments included 0% NaCl (CK treatment), CK + 0.05 g N/pot (N treatment), CK + 40 mg·L⁻¹ 5-aminolevulinic acid (5-ALA) (A treatment), and CK + 30 mg·L⁻¹ diethylaminoethyl acetate (DTA-6) (D treatment). Salt stress treatments included 0.3% NaCl (S treatment), N + 0.3% NaCl (NS treatment), A + 0.3% NaCl (AS treatment), and D + 0.3% NaCl (DS treatment). When 3 leaves and 1 heart emerged from the soil, plants were sprayed with DTA-6 and 5-ALA, followed by the application of 0.3% NaCl (w/w) to the soil after 24 h. Seedling morphology and photosynthetic indices, as well as carbohydrate metabolism and key enzyme activities, were determined for each treatment. Our results showed that N, A, and D treatments promoted seedling growth, photosynthesis, carbohydrate levels, and the activities of key enzymes involved in carbon metabolism when compared to the CK treatment. The A treatment had the most significant effect, with increases in aboveground dry weight and net photosynthetic rates (Pn) ranging from 17.74% to 41.02% and 3.61% to 32.60%, respectively. Stomatal limiting values (Ls) significantly decreased from 19.17% to 43.02%. Salt stress significantly inhibited seedling growth. NS, AS, and DS treatments alleviated the morphological and physiological damage of salt stress on seedlings when compared to the S treatment. The AS treatment was the most effective in improving seedling morphology, promoting photosynthesis, increasing carbohydrate levels, and key enzyme activities. After AS treatment, increases in aboveground dry weight, net photosynthetic rate, soluble sugar content, total sucrose synthase, and amylase activities were 17.50% to 50.79%, 11.39% to 98.10%, 20.20% to 80.85%, 21.21% to 33.53%, and 22.17% to 34.19%, respectively, when compared to the S treatment. In summary, foliar sprays of 5-ALA, DTA-6, and additional nitrogen fertilizer enhanced rice seedling growth, increased photosynthesis, lowered Ls values, and improved seedling salt tolerance. Spraying two regulators, 5-ALA and DTA-6, quantitatively increased the effect of nitrogen fertilizer, with comparable effects on NaCl stress regulation. This study provides the basis for efficient agricultural production.

The aim of this experiment was to investigate the effects of exogenous sprays of 5-aminolevulinic acid (5-ALA) and 2-Diethylaminoethyl hexanoate (DTA-6) on the growth and salt tolerance of rice (Oryza sativa L.) seedlings. This study was conducted in a solar greenhouse at Guangdong Ocean University, where ‘Huanghuazhan’ was selected as the test material, and 40 mg/L 5-ALA and 30 mg/L DTA-6 were applied as foliar sprays at the three-leaf-one-heart stage of rice, followed by treatment with 0.3% NaCl (W/W) 24 h later. A total of six treatments were set up as follows: (1) CK: control, (2) A: 40 mg⋅ L⁻¹ 5-ALA, (3) D: 30 mg⋅ L⁻¹ DTA-6, (4) S: 0.3% NaCl, (5) AS: 40 mg⋅ L⁻¹ 5-ALA + 0.3% NaCl, and (6) DS: 30 mg⋅ L⁻¹ DTA-6+0.3% NaCl. Samples were taken at 1, 4, 7, 10, and 13 d after NaCl treatment to determine the morphology and physiological and biochemical indices of rice roots. The results showed that NaCl stress significantly inhibited rice growth; disrupted the antioxidant system; increased the rates of malondialdehyde, hydrogen peroxide, and superoxide anion production; and affected the content of related hormones. Malondialdehyde content, hydrogen peroxide content, and superoxide anion production rate significantly increased from 12.57% to 21.82%, 18.12% to 63.10%, and 7.17% to 56.20%, respectively, in the S treatment group compared to the CK group. Under salt stress, foliar sprays of both 5-ALA and DTA-6 increased antioxidant enzyme activities and osmoregulatory substance content; expanded non-enzymatic antioxidant AsA and GSH content; reduced reactive oxygen species (ROS) accumulation; lowered malondialdehyde content; increased endogenous hormones GA3, JA, IAA, SA, and ZR content; and lowered ABA content in the rice root system. The MDA, H₂O₂, and O₂₋ contents were reduced from 35.64% to 56.92%, 22.30% to 53.47%, and 7.06% to 20.01%, respectively, in the AS treatment group compared with the S treatment group. In the DS treatment group, the MDA, H₂O₂, and O₂₋ contents were reduced from 24.60% to 51.09%, 12.14% to 59.05%, and 12.70% to 45.20%. In summary, NaCl stress exerted an inhibitory effect on the rice root system, both foliar sprays of 5-ALA and DTA-6 alleviated damage from NaCl stress on the rice root system, and the effect of 5-ALA was better than that of DTA-6.

The widespread use of lead (Pb) has led to serious environmental and human health problems worldwide. The application of oxide nanoparticles (CeO₂ NPs) in alleviating abiotic stress in plants has received extensive attention. In this study, 50 mg·L⁻¹ CeO₂ NPs can improve Pb resistance and promote rice growth. Specifically, this study observed that CeO₂ NPs increased the activity of antioxidant enzymes peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), but the difference did not reach a significant level. At the same time, CeO₂ NPs upregulated antioxidant metabolites alpha-linolenic acid, linoleic acid, ferulic acid, and kaempferol under Pb stress. In addition, CeO₂ NPs upregulated multiple defense response-related genes, such as OsOPR1 and OsPR10a; RPR10a, and improved rice carbon flow and energy supply by upregulating sucrose and D-glucose. The results of this study provided technical support for alleviating Pb stress in rice.

Salt stress is a vital environmental stress that severely limits plant growth and productivity. Prohexadione-calcium (Pro-Ca) has been extensively studied to regulate plant growth, development, and stress responses. However, the constructive role of Pro-Ca in alleviating damages and enhancing rice tillers’ morph-physiological characteristics under salt stress remains largely unknown. The results showed that Pro-Ca significantly improved Changmaogu’s (CMG’s) productive tillering rate and the total yield per plant by 17.1% and 59.4%, respectively. At tillering stage, the results showed that Pro-Ca significantly improved the morph-physiological traits, i.e., leaf area, and photosynthetic traits of the rice variety with salt tolerance, under NaCl stress. Pro-Ca significantly increased the seedling index of the main stem and tiller by 10.3% and 20.0%, respectively. Pro-Ca significantly increased the chlorophyll a (chl a), chlorophyll b (chl b) and carotenoid contents by 32.8%, 58.4%, and 33.2%, respectively under NaCl stress. Moreover, Pro-Ca significantly enhanced the net photosynthetic rate (A) by 25.0% and the non-photochemical (NPQ) by 9.0% under NaCl stress. Furthermore, the application of Pro-Ca increased the activities of antioxidant enzymes by 7.5% and 14.7% in superoxide dismutase (SOD), 6.76% and 18.0% in peroxidase (POD), 26.4% and 58.5% in catalase (CAT), 11.0% and 15.9% in ascorbate peroxidase (APX), and Pro-Ca reduced the membrane damage index by 10.8% and 2.19% in malondialdehyde (MDA) content, respectively, for main stem and tiller leaves under NaCl stress. Pro-Ca significantly enhanced the soluble protein content of the main stem and tiller leaves by 2.60% and 6.08%, respectively. The current findings strongly suggested that exogenous application of Pro-Ca effectively alleviated the adverse impact of NaCl stress on the main stem and tillers by enhancing the photosynthetic capacity and antioxidant enzyme activity, and ultimately increased the productive tillering rate and grain yield.

Against the backdrop of a changing global climate, the soil environment may undergo significant changes, directly affecting agricultural productivity and exacerbating global food security issues. Three different substrates were set up in this study, namely, S (high sand and low nutrient content), T (medium sand and medium nutrient content), and TT (low sand and high nutrient content). The results showed that the root/shoot ratio increased as the sand content increased (nutrient content decreased). Rice in different substrates had various degrees of dependence on antioxidant enzymes and antioxidants. For example, seedlings in TT treatment may depend more on ascorbic acid (AsA) compared to T. In addition, compared with S and T, the photosynthetic activity of rice in the optimized substrate (TT) was the highest; the net photosynthetic rate (Pn) of TT seedlings was significantly higher than that of T. This study also detected that the change in substrates affected the gas exchange parameters of rice leaves. The transpiration rate (Tr) and stomatal conductance (Gs) of the TT treatment were higher than those of the T treatment. The results of this study may provide a scientific basis for formulating agricultural management strategies.

The impact of substrates with different physicochemical properties on the response of rhizosphere fungi in rice to salt stress has not been fully explored. The purpose of this study is to reveal the adaptation characteristics of fungal colonies to salt stress under different substrate conditions and the relationship between different properties of substrates and fungal colonies. Four different substrates were set by adjusting the sand, peat moss, and laterite ratio, with different bulk density, total porosity, and nutrient content. The same dose of sodium chloride solution was added to each substrate, and water was used as the control. The results showed that salt stress did not cause significant changes in the diversity and richness of fungal communities in different substrates. This study found that the responses of Ascomycota and Penicillium to salt stress varied depending on the substrate. The abundance of Penicillium was significantly positively correlated with total porosity (saline or non-saline conditions), but that of Acrostalagmus was significantly negatively correlated with total porosity under non-saline conditions. In addition, Lefse multi-level species difference discrimination analysis identified biomarkers in different treatments and revealed the core communities in response to substrate changes or salt stress. The results of this study contribute to a deeper understanding of the ecological functions of fungi.