Potassium humate supplementation improves photosynthesis and agronomic and yield traits of foxtail millet.

Foxtail millet is a highly nutritious crop, which is widely cultivated in arid and semi-arid areas worldwide. Humic acid (HA), as a common plant growth regulator, is used as an organic fertilizer and feed additive in agricultural production. However, the impact of potassium humate KH on the photosynthetic rate and yield of foxtail millet has not yet been studied. We explored the effects of KH application on the morphology, photosynthetic ability, carbon and nitrogen metabolism, and yield of foxtail millet. A field experiment was performed using six concentrations of KH (0, 20, 40, 80, 160, and 320 kg ha-1) supplied foliarly at the booting stage in Zhangza 10 cultivar (a widely grown high-yield variety). The results showed that KH treatment increased growth, chlorophyll content (SPAD), photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs). In addition, soluble protein content, sugar content, and nitrate reductase activity increased in KH-treated plants. With increased KH concentration, the effects became more evident and the peak values of each factor were achieved at 80 kg ha-1. Photosynthetic rate showed significant correlation with SPAD, Tr, Gs, and soluble protein content, but was negatively correlated with intercellular CO2 concentration. Compared to that of the control, the yield of foxtail millet under the T2, T3, T4, and T5 (40, 80, 160, and 320 kg ha-1 of KH) treatments significantly increased by 6.0%, 12.7%, 10.5%, and 8.6%, respectively. Yield exhibited a significant positive correlation with Tr, Pn, and Gs. Overall, KH enhances photosynthetic rate and yield of foxtail millet, therefore it may be conducive to stable millet production. These findings may provide a theoretical basis for the green and efficient production of millet fields.

Synergistic influence of selenium and silicon supplementation prevents the oxidative effects of arsenic stress in wheat.

Influence of supplementation of selenium (Se, 1 and 5 µM) and silicon (Si, 0.1 and 0.5 mM) was investigated in wheat under arsenic (30 µM As) stress. Plants grown under As stress exhibited a significant decline in growth parameters however, Se and Si supplementation mitigated the decline significantly. Treatment of Se and Si alleviated the reduction in the intermediate components of chlorophyll biosynthesis pathway and the content of photosynthetic pigments. Arsenic stressed plants exhibited increased reactive oxygen species accumulation and the NADPH oxidase activity which were lowered significantly due to Se and Si treatments. Moreover, Se and Si supplementation reduced lipid peroxidation and activity of lipoxygenase and protease under As stress. Supplementation of Se and Si significantly improved the antioxidant activities and the content of cysteine, tocopherol, reduced glutathione and ascorbic acid. Treatment of Se and Si alleviated the reduction in nitrate reductase activity. Exogenously applied Se and Si mitigated the reduction in mineral elements and reduced As accumulation. Hence, supplementation of Se and Si is beneficial in preventing the alterations in growth and metabolism of wheat under As stress.

Alleviation of Adverse Effects of Drought Stress on Growth and Nitrogen Metabolism in Mungbean (Vigna radiata) by Sulphur and Nitric Oxide Involves Up-Regulation of Antioxidant and Osmolyte Metabolism and Gene Expression.

The influence of drought induced by polyethylene glycol (PEG) and the alleviatory effect of nitric oxide (50 µM) and sulphur (S, 1 mM K2SO4) were studied in Vigna radiata. Drought stress reduced plant height, dry weight, total chlorophylls, carotenoids and the content of nitrogen, phosphorous, potassium and sulphur. The foliar applications of NO and sulphur each individually alleviated the decline, with a greater alleviation observed in seedlings treated with both NO and sulphur. The reduction in intermediates of chlorophyll synthesis pathways and photosynthesis were alleviated by NO and sulphur. Oxidative stress was evident through the increased hydrogen peroxide, superoxide and activity of lipoxygenase and protease which were significantly assuaged by NO, sulphur and NO + sulphur treatments. A reduction in the activity of nitrate reductase, glutamine synthetase and glutamate synthase was mitigated due to the application of NO and the supplementation of sulphur. The endogenous concentration of NO and hydrogen sulphide (HS) was increased due to PEG; however, the PEG-induced increase in NO and HS was lowered due to NO and sulphur. Furthermore, NO and sulphur treatments to PEG-stressed seedlings further enhanced the functioning of the antioxidant system, osmolytes and secondary metabolite accumulation. Activities of γ-glutamyl kinase and phenylalanine ammonia lyase were up-regulated due to NO and S treatments. The treatment of NO and S regulated the expression of the Cu/ZnSOD, POD, CAT, RLP, HSP70 and LEA genes significantly under normal and drought stress. The present study advocates for the beneficial use of NO and sulphur in the mitigation of drought-induced alterations in the metabolism of Vigna radiata.

The role of root size and root efficiency in grain production, and water-and nitrogen-use efficiency in wheat.

BACKGROUND: The root system is the major plant organ involved in water and nutrient acquisition, influencing plant growth and productivity. However, the relative importance of root size and uptake efficiency remains undetermined. A pot experiment was conducted using two wheat varieties with different root sizes to evaluate their capacity for water and nitrogen (N) uptake and their effects on grain production, water-use efficiency (WUE), and N-use efficiency (NUE) under two water treatments combined with three N levels. RESULTS: The leaf water potential and root exudates of changhan58 (CH, small root variety) were higher or similar to those of changwu134 (CW, large root variety) under water/N treatment combinations, indicating that small roots can transport enough water to above the ground. The addition of N improved plant growth, photosynthetic traits, and WUE significantly. There were no significant differences in WUE or grain production between the two cultivars under well-watered conditions. However, they were significantly higher in CH than in CW under water deficit stress. Nitrogen uptake per unit root dry weight, glutaminase, and nitrate reductase activities were significantly higher in CH than in CW, regardless of moisture conditions. Root biomass was positively correlated with evapotranspiration, while the root/shoot ratio was negatively correlated with WUE (P < 0.05) but not with NUE. CONCLUSION: In a pot experiment, water and N uptake were more strongly associated with resource uptake availability than root size. This may provide guidance in wheat breeding programs for drought-prone regions. © 2023 Society of Chemical Industry.

Genetic variation in nitrogen-use efficiency and its associated traits in dryland winter wheat (Triticum aestivum L.) cultivars released from the 1940s to the 2010s in Shaanxi Province, China.

BACKGROUND: Improving the nitrogen-use efficiency (NUE) of wheat can help mitigate the problems of poor soil fertility under dryland conditions. We conducted field experiments using three nitrogen (N) fertilization levels (0, 120, and 180 kg ha-1 ) applied to eight dryland wheat cultivars to assess NUE and its associated traits. RESULTS: The grain yield significantly increased with the improvement in variety, mainly as a result of a substantial increase in 1000-grain weight and harvest index. Modern wheat varieties have stabilized at an optimal plant height and exhibited improved performance in terms of NUE, partial N productivity, N harvest index, and grain protein content compared to older varieties. The NUE of wheat gradually increased with variety replacement. The net photosynthesis rate of the flag leaves in the filling stage improved with the year of cultivar release; Increasing soil-plant analysis development (SPAD) values of flag leaves in the flowering and filling stages were observed over time, with the flag leaves of modern varieties showing a high chlorophyll content in the filling stage. Additionally, the principal component analysis showed that the SPAD value, grain number per unit area, transpiration rate, leaf area, and grain protein content positively contributed to the clustering of the N180 and modern cultivars (from the 2000s to 2010s). CONCLUSION: Overall, high levels of N application did not significantly improve the NUE of wheat. However, modern wheat varieties can optimize N distribution, increase flag leaf photosynthetic capacity, and improve photosynthesis ability, thus enhancing NUE to achieve high yields under a suitable level of N supply. © 2022 Society of Chemical Industry.

Exogenous calcium promotes growth of adzuki bean (Vigna angularis Willd.) seedlings under nitrogen limitation through the regulation of nitrogen metabolism.

Plants exhibit lower nitrogen use efficiency (NUE) under N-limitation conditions. Although the function of calcium (Ca) has been widely studied in plants, it remains to be explored whether regulation of nitrate uptake and reduction is needed. A hydroponics experiment on adzuki beans (Vigna angularis Willd.) was used as a test material to determine the interactions between Ca and three levels of nitrogen supply. The height of the plant, the leaf area per plant, the biomass of the plant, the morphology of the roots, the hydraulic conductivity of the roots, the level of gas exchange, and the level of N metabolism of the adzuki beans were evaluated. Furthermore, RT-qPCR was conducted to explore the expression of genes related to nitrate transporter responses to Ca under N-limitation stress conditions. The rate of accumulation of N in plant tissue increased with the application of Ca. However, plant biomass, photosynthetic parameters, and root activity peaked for Ca2+ supply under N-marginal conditions. Further investigation revealed that the activities of nitrate reductase and glutamine synthetase were relatively high. The transcription of the nitrate transporter (VaNRT1.1; VaNRT2.5) was up-regulated in the roots of the Ca-treated plants. Both N-marginal conditions and N deficiency inhibit N absorption and utilization. The favorable effects of Ca on seedling growth and N metabolism under N-marginal conditions were more significant than those under N-deficiency conditions. The supply of Ca2+ is optimal, as it increases NUE by enhancing photosynthesis, N-metabolizing enzyme activities, and NO3 uptake and transport under N-marginal conditions.

Lanthanum nitrate improves phosphorus-use efficiency and tolerance to phosphorus-deficiency stress in Vigna angularis seedlings.

Here, we examined the effects of La3+ on growth, photosynthetic ability, and phosphorus-use efficiency (PUE) in various organs of adzuki bean (Vigna angularis) seedlings. La3+ substantially alleviated P-deficiency symptoms. Treatment of young seedlings with La3+ at 150 mg L-1 effectively improved PUE in roots, stems, and leaves via the regulation of root elongation and activation of root physiological responses to P-deficiency, e.g., root activity and acid phosphatase (APase) activity. Root hydraulic conductivity (Lp) was also examined to elucidate the role of La3+ in the relationship between water and nutrition transport. We confirmed that La3+ increased the level of antioxidant protective enzymes, including superoxide dismutase (SOD) and peroxidase (POD), while it significantly decreased malondialdehyde (MDA) content. The use of La3+ to reduce photosynthesis damage under P-deficiency was examined. The negative effects of P-deficiency on net photosynthetic rate (Pn), transpiration rate (Tr), maximum photochemical efficiency (Fv/Fm), and chlorophyll content in leaves were alleviated by La3+ treatment. These results clarify the regulatory functions of La3+ in stress tolerance and P utilization in adzuki bean seedlings.