Salt-affected soils severely decrease agricultural productivity by reducing the uptake of water and nutrients by plants, toxic ions accumulation and soil structure degradation. The sustainable synthesis of hybrid nanospheres through green approaches has emerged as an effective strategy to enhance crop productivity and improve tolerance to abiotic stress. However, the defensive functions and fundamental mechanisms of green synthesized calcium-doped carbon nano-spheres in protecting maize against salt stress remain elusive. Thus, calcium-doped carbon nanospheres were innovatively synthesized by doping calcium oxide nanoparticles (CaO NPs) with lignin nanoparticles (LNPs) which were further analyzed using Fourier Transform Infrared Spectroscopy (FT-IR), Energy Dispersive X-Ray Spectroscopy (EDX), Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM). These analyses validated the successful doping of Ca@CNs, elucidating the purity and morphology of the hybrid nanospheres. More importantly, the effect of Ca@CNs on maize plants under NaCl stress, unreported so far, was examined. Results of the current study showed that treating salt-stressed plants with Ca@CNs significantly improved maize growth and biomass accumulation by enhanced absorption of minerals and improved photosynthetic efficiency. Furthermore, Ca@CNs application has also reduced NaCl-induced oxidative damage by enhancing antioxidant defense mechanisms and maintaining cellular integrity, resulting in improved resistance to salt stress. Moreover, Ca@CNs substantially up-regulated the expression of salt-tolerant genes ZmNHX3, CBL, ZmHKT1, and MAPK1, as well as genes involved in lignin biosynthesis such as 4CL2, PAL1, CCR, and COMT, in both shoot and root tissues. Conversely, the expression levels of genes Zm00001d003114, Zm0001d026638, Zm00001d028582 and Zm00001d051069 associated with Ca2 +-responsive SOS3 pathway were all down-regulated under NaCl treatment, while up-regulated in the presence of Ca@CNs along with NaCl. The observed changes in transcript levels of these genes highlight the potential of Ca@CNs in alleviating NaCl toxicity. These results demonstrated that the green synthetic Ca@CNs can significantly alleviate salt stress and promote plant growth in saline environments, which will provide a new strategy for the utilization of nanoparticles in agriculture to maintain sustainable agriculture and improve crop yield.

Backround The utilization of high-quality water in agriculture is increasingly constrained by climate change, affecting availability, quality, and distribution due to altered precipitation patterns, increased evaporation, extreme weather events, and rising salinity levels. Salinity significantly challenges salt-sensitive vegetables like lettuce, particularly in a greenhouse. Hydroponics water quality ensures nutrient solution stability, enhances nutrient uptake, prevents contamination, regulates pH and electrical conductivity, and maintains system components. This study aimed to mitigate salt-induced damage in lettuce grown via the floating culture method under 50 mM NaCl salinity by applying biostimulants. Results We examined lettuce's physiological, biochemical, and agronomical responses to salt stress after applying biostimulants such as amino acids, arbuscular mycorrhizal fungi, plant growth-promoting rhizobacteria (PGPR), fulvic acid, and chitosan. The experiment was conducted in a greenhouse with a randomized complete block design, and each treatment was replicated four times. Biostimulant applications alleviated salt's detrimental effects on plant weight, height, leaf number, and leaf area. Yield increases under 50 mM NaCl were 75%, 51%, 31%, 34%, and 33% using vermicompost, PGPR, fulvic acid, amino acid, and chitosan, respectively. Biostimulants improved stomatal conductance (58-189%), chlorophyll content (4-10%), nutrient uptake (15-109%), and water status (9-107%). They also reduced MDA content by 26-42%. PGPR (1.0 ml L-1), vermicompost (2 ml L-1), and fulvic acid (40 mg L-1) were particularly effective, enhancing growth, yield, phenol, and mineral content while reducing nitrate levels under saline conditions. ConclusionsBiostimulants activated antioxidative defense systems, offering a sustainable, cost-effective solution for mitigating salt stress in hydroponic lettuce cultivation.

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 center dot L-1 5-aminolevulinic acid (5-ALA) (A treatment), and CK + 30 mg center dot 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.

This study aimed to investigate whether presoaking with hemin (5 mu mol center dot L-1) could alleviate NaCl stress during rapeseed seedlings' growth and its role in the regulation of photosynthesis. In this experiment, 'HUAYOUZA 62 (HYZ 62)' and 'HUAYOUZA 158R (158R)' were used as materials for pot experiments to study the morphology, photosynthetic characteristics, antioxidant activity, and osmoregulatory factors of seedlings under different salt concentrations, as well as the regulatory effects of hemin-presoaked seeds. Our findings revealed that, compared the control, NaCl stress inhibited the growth of two rapeseed varieties, decreased the seedling emergence rate, and increased the content of malondialdehyde (MDA), the electrolyte leakage rate (EL) and antioxidant enzyme activity. Hemin soaking alleviated the adverse effects of salt stress and increased plant height, root elongation and dry matter accumulation. Compared with all NaCl treatments, hemin significantly enhanced photosynthetic indexes, including a percent increase of 12.99-24.36% and 5.39-16.52% in net photosynthetic rate (Pn), 17.86-48.08% and 8.6-23.44% in stomatal conductivity (Gs), and 15.42-37.94% and 11.09-19.08% in transpiration rate (Tr) for HYZ62 and 158R, respectively. Moreover, hemin soaking also increased antioxidant enzyme activities, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX), reducing the malondialdehyde, and thus resulting in the alleviation of oxidative damage caused by NaCl stress. Furthermore, hemin stimulated the formation of soluble protein, which effectively regulated the osmo-protective qualities. The current findings strongly elucidate that hemin soaking could effectively alleviate the negative impacts of NaCl stress by regulating the morphological, photosynthetic, and antioxidant traits. This study provides a new idea regarding the effect of Hemin on the salt tolerance of rapeseed, and provides a basis for the practical application of Hemin in saline-alkali soil to improve the salt tolerance of cultivated rapeseed.