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Nitrogen is an essential macronutrient required for plant growth. In this study, the relationships between plant growth, photosynthetic capability, chlorophyll fluorescence characteristics and nitrogen forms in response to low-nitrogen stress were studied in tomato grafted with different nitrogen-use-efficiency tomato seedlings. Using tomato plants grafted with different rootstocks, we found that, under low-nitrogen stress, plant growth, chlorophyll contents, net photosynthetic rate (Pn), maximal photochemical efficiency (Fv/Fm), the total nitrogen (TN) concentration, and nitrate reductase (NR) activity were significantly inhibited but that the ammonium-nitrogen (NH4+-N) content in the roots significantly increased. High-nitrogen-use-efficiency tomato grafted plants exhibited significantly enhanced plant growth but reduced Pn, Fv/Fm, TN content and NR activity under low-nitrogen conditions compared to the grafted seedlings of the low-nitrogen-use-efficiency genotype. In addition, tomato plants grafted onto high-nitrogen efficient rootstock presented reduced damage caused by excessive accumulation of NH4+-N in the roots under low-nitrogen stress. Our results indicate that tomato plants grafted onto high-nitrogen efficient rootstock presented enhanced absorption and utilization of nitrogen and maintained growth by promoting the use efficiency of light energy under low-nitrogen stress.

Background The optimized illumination of plants using light-emitting diodes (LEDs) is beneficial to their photosynthetic performance, and in recent years, LEDs have been widely used in horticultural facilities. However, there are significant differences in the responses of different crops to different wavelengths of light. Thus, the influence of artificial light on photosynthesis requires further investigation to provide theoretical guidelines for the light environments used in industrial crop production. In this study, we tested the effects of different LEDs (white, W; blue, B; green, G; yellow, Y; and red, R) with the same photon flux density (300 μmol/m 2 ·s) on the growth, development, photosynthesis, chlorophyll fluorescence characteristics, leaf structure, and chloroplast ultrastructure of Welsh onion ( Allium fistulosum L.) plants. Results Plants in the W and B treatments had significantly higher height, leaf area, and fresh weight than those in the other treatments. The photosynthetic pigment content and net photosynthetic rate ( P n ) in the W treatment were significantly higher than those in the monochromatic light treatments, the transpiration rate ( E ) and stomatal conductance ( G s ) were the highest in the B treatment, and the intercellular CO 2 concentration ( C i ) was the highest in the Y treatment. The non-photochemical quenching coefficient (NPQ) was the highest in the Y treatment, but the other chlorophyll fluorescence characteristics differed among treatments in the following order: W > B > R > G > Y. This includes the maximum photochemical efficiency of photosystem II (PSII) under dark adaptation (Fv/Fm), maximum photochemical efficiency of PSII under light adaptation (Fv′/Fm′), photochemical quenching coefficient (qP), actual photochemical efficiency (ΦPSII), and apparent electron transport rate (ETR). Finally, the leaf structure and chloroplast ultrastructure showed the most complete development in the B treatment. Conclusions White and blue light significantly improved the photosynthetic efficiency of Welsh onions, whereas yellow light reduced the photosynthetic efficiency.

Soil salinization has become an increasingly serious ecological problem, which limits the quality and yield of crops. As an important economic vegetable in winter, however, little is known about the response of Chinese cabbage to salt, alkali and salt–alkali stress in photosynthetic characteristics and chloroplast ultrastructure. Thus, two Chinese cabbage cultivars, ‘Qinghua’ (salt-tolerant–alkali-sensitive) and ‘Biyu’ (salt-sensitive–alkali-tolerant) were investigated under stresses to clarify the similarities and differences between salt tolerance and alkali tolerance pathways in Chinese cabbage. We found that the root of Qinghua, the leaf ultrastructure and net photosynthetic rate (Pn), stomatal conductance (Gs), water use efficiency (WUE), maximum photochemical quantum yield of PSII (Fv/Fm) and nonphotochemical quenching (NPQ) were not affected by salt stress. However, Biyu was seriously affected under salt stress. Its growth indexes decreased by between 60 and 30% compared with the control and the photosynthetic indexes were also seriously affected under salt stress. This indicated that the salt-tolerant cultivar Qinghua improved the photosynthetic fluorescence ability to promote the synthesis of organic matter resulting in salt tolerance. In contrast, under alkali treatment, the root of Biyu was affected by alkali stress, but could still maintain good growth, and root and leaf structure were not seriously affected and could maintain the normal operations. Biyu improved its tolerance by improving the water use efficiency, regulating the synthesis of organic acids and carbohydrates, ensuring the synthesis of organic matter and ensured the normal growth of the plant.

Drought is a common stress in crop growth that limits plant growth, development and yield. Therefore, we explored the feasibility of bio-saving water for tomato production by grafting with drought-tolerant seedlings. In this experiment, we carried out grafting on different drought-tolerant tomato seedlings to study the effects of grafting on root growth and plant nutrient uptake under drought stress. We measured the effects of grafting on root growth, nutrient uptake, carbohydrate content and organic acids in tomato leaves and roots under drought stress. The growth and vigor of roots as well as the concentration of N, P, K, Ca and Mg of the plant were significantly inhibited by drought. The nutrient content was significantly decreased in leaves, and the content of carbohydrates and organic acids was increased in both leaves and roots under drought conditions. Treatment with drought-tolerant tomato seedlings significantly enhanced root growth and increased the element content under water deficit conditions compared to those grafted with drought-susceptible seedlings. In the plants grafted with drought-tolerant seedlings, the contents of carbohydrates and organic acids increased. Our results indicated that the grafted tomato seedlings showed beneficial root growth because drought-tolerant seedlings increased in inorganic and organic osmotic adjustment substances that helped the plants absorb more water and promoted plant growth.

Salt stress and alkali stress are major factors that affect the growth and production of Chinese cabbage. To explore their tolerant mechanism to salt and alkali stress, three salinity levels (0, 50, 100 mmol/L NaCl) and three different pH levels (pH6.5, pH7.5, pH8.5) were interactively applied on Qinghua (salt-tolerant–alkali-sensitive) and Biyu (salt-sensitive–alkali-tolerant) cultivars; the root morphology, ion content and antioxidant enzymes were determined. The results showed that the root morphology and root water content of Qinghua under S0pH7.5 and S0pH8.5 were seriously affected, and the content of H2O2 and MDA increased by 143%, 190% and 234%, 294%, respectively, compared with S0pH6.5; when Biyu was under S50pH6.5 and S100pH6.5 stress, the content of H2O2 and MDA increase to 152%, 208% and to 240%, 263%, respectively, but the activities and genes expression of SOD, POD, CAT, AAO, APX, DHAR and MDHAR did not change. The root and the contents of H2O2 and MDA were not affected when Qinghua was treated with salt and Biyu was treated with alkali, but the activities of the antioxidant enzymes increased to 150–200%, and their relative expression was overexpressed and 2.5–3.5-fold of the S0pH6.5. The increase of Na+ in Qinghua was limited under salt stress, Mg2+ in Biyu increased significantly under alkali stress. These all indicated that the adaptability of roots could reflect the degree of tolerance; Chinese cabbage with high salt and alkali tolerance enhanced the regulation of their absorption of ions and increased the relative expression and activities of related antioxidant enzymes.

We used ‘Shannong No.1’ experimental material to simulate higher salt concentration in ginger and analyzed the physiological responses of different parts of ginger seedlings under salt stress. The results showed that salt stress led to a significant decrease in fresh and dry weight of ginger, lipid membrane peroxidation, increased sodium ion content and enhanced activity of antioxidant enzymes. Compared with the control, the overall plant dry weight of ginger under salt stress decreased by about 60%, and the MDA content in roots, stems, leaves, and rhizomes increased by 372.27%, 184.88%, 291.5%, and 171.13%, respectively, and the APX content increased by 188.85%, 165.56%, 195.38%, and 40.08%, respectively. After analysis of the physiological indicators, it was found that the roots and leaves of ginger were the most significantly changed parts. We analyzed the transcriptional differences between ginger roots and leaves by RNA-seq and found that they jointly initiated MAPK signaling pathways in response to salt stress. By combining physiological and molecular indicators, we elucidated the response of different tissues and parts of ginger to salt stress during the seedling stage.

The growth and development and metabolism of plants have different physiological responses to different light qualities. To study the influence of light qualities on green onions, the impacts of LED light treatment on the growth and development as well as the nutritional components and flavor substances in green onions were studied under controlled conditions. Leaf area, plant height, dry matter accumulation, Dickson’s quality index (DQI), nutritional content, and volatile compounds under different light quality treatments were determined. The results indicated that the white and blue combined light (W/B: 3/1) treatment was the most beneficial to growth and nutrient accumulation and led to higher levels of sulfur compounds in the green onions than the other treatments. This shows that it is possible to control the contents of compounds that affect consumer preferences by adjusting the lighting conditions and to thereby increase the value and quality of seasoning vegetables.

Salt is the most important limiting factor in plant yield and quality. Different Chinese cabbage cultivars appeared different salt tolerances, but there are few studies attempting to elucidate the mechanism underlying this phenomenon. In this study, 100 mmol L –1 NaCl was found to be the most suitable treatment concentration according to a sprouting bag test of 39 Chinese cabbage cultivars, and through comprehensive comparison and analysis, the relative values of fresh weight and electrolyte leakage in leaves proved to be convenient indicators for the identification of salt tolerance in Chinese cabbage. We analyzed the physiological responses of Qinghua45 (salt-tolerant) and Biyuchunhua (salt-sensitive) in terms of the growth indexes, ion homeostasis and Photosynthesis, the results indicated that Qinghua45 could ensure osmotic regulation, ion homeostasis and photosynthesis under salt stress. Next, we compared the transcriptome dynamics of the two cultivars. Overall, 2,859 differentially expressed genes (DEGs) were identified, and the number of DEGs in Qinghua45 was significantly less than that in Biyuchunhua. VDAC promoted the release of Ca 2+ , which indirectly promoted the transport of Na + to vacuoles through the SOS 2 pathway. Cation/H (+) antiporter 17 and V-H + -ATPase improve the exchange of Na + and H + and maintain Na + in the vacuoles, thereby reducing the injury affected by salt stress. Increases in galactinol synthase and soluble protein synthesis helped relieve osmotic stress caused by salt, together, they regulated the Na + content and chlorophyll biosynthesis of the plant and enabled the plant to adapt to salt stress over time.

We investigated the effects of low pH on the photosynthesis, chlorophyll fluorescence, and mineral contents of the leaves of ginger plants under salt stress. This experiment involved four treatments: T1 (pH 6, 0 salinity), T2 (pH 4, 0 salinity), T3 (pH 6, 100 mmol L −1 salinity) and T4 (pH 4, 100 mmol L −1 salinity). This study showed that photosynthesis (Pn, Gs, WUE and Tr) and chlorophyll fluorescence (qP, Φ PSII, and Fv/Fm) significantly decreased under salt stress; however, all the parameters of the ginger plants under the low-pH treatment and salt stress recovered. Moreover, low pH reduced the content of Na and enhanced the contents of K, Mg, Fe and Zn in the leaves of ginger plants under salt stress. Taken together, these results suggest that low pH improves photosynthesis efficiency and nutrient acquisition and reduces the absorption of Na, which could enhance the salt tolerance of ginger.

The active regulation of the plant growth environment is a common method for optimizing plant yield and quality. In horticulture today, light quality control is carried out using photo-selective nets or membranes to improve the yield and quality of cultivated plants. In the present study, with natural light as the control (CK), we tested different photo-selective nets (white, WN; blue, BN; green, GN; yellow, YN; and red, RN) with 30% shade for characteristics of growth, development, quality, yield, photosynthesis, and chlorophyll fluorescence, considering the antioxidant system, as well as the influence of element absorption and transformation of green onion ( Allium fistulosum L.) plants at different growth stages. We found that plants under BN and WN have greater height and fresh weight than those of plants under the other nets. Plants under the BN treatment had the highest quality, yield, photosynthetic pigment content, net photosynthetic rate, transpiration rate, and stomatal conductance, whereas the intercellular CO 2 concentration was the highest in plants in the YN treatment. The photosynthesis noon break phenomenon was significantly lower in plants with covered photo-selective nets than in CK plants. NPQ was the highest in the YN treatment, and Fv/Fm, ΦPSII, and qP among the plants in the other treatments were different; from highest to lowest, they were as follows: BN > WN > CK > RN > GN > YN. The active oxygen content of green onion leaves in the BN treatment was significantly lower than that in the other treatments, and their key enzyme activity was significantly increased. BN also improved the absorption and transformation of elements in various organs of green onion.