Abbreviations -A, net photosynthetic assimilation rate; APX, ascorbate peroxidase; CAT, catalase; Chl a, chlorophyll a; Chl b, chlorophyll b; Chl a/Chl b, ratio between Chl a and Chl b; E, transpiration rate; ETR, electron transport rate; ETR/A, electron transport to oxygen molecules; F0, initial fluorescence; Fv/fm, potential quantum yield of photosystem II; g s , stomatal conductance; H 2 O 2 , hydrogen peroxide; HS, hydrogen sulphide; LDM, leaf dry matter; MDA, malondialdehyde; MWHC, maximum water holding capacity; NPQ, non-photochemical quenching coefficient; POX, peroxidase activity; PP, potassium phosphite; RDW, root dry weight; REL, rate of electrolyte leakage; RWC, relative water content; SDM, shoot dry matter; SOD, superoxide dismutase; TDM, total dry matter; WD, water deficit; WUEg, intrinsic water use efficiency; WW, well-watered; ZS, zinc sulphate; Ψ s , osmotic potential; Ψ w , water potential; Φ PSII , effective quantum yield of photosystem II.

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Thermal stress reduces plant growth and development, resulting in considerable economic losses in crops such as soybeans. Nitric oxide (NO) in plants is associated with tolerance to various abiotic stresses. Nevertheless, there are few studies of the range of observed effects of NO in modulating physiological and metabolic functions in soybean plants under high temperature. In the present study, we investigated the effects of sodium nitroprusside (SNP, NO donor), on anatomical, physiological, biochemical, and metabolic processes of soybean plants exposed to high temperature. Soybean plants were grown in soil: sand (2:1) substrate in acclimatized growth chambers. At developmental V3 stage, plants were exposed to two temperatures (25 °C and 40 °C) and SNP (0 and 100 μM), in a randomized block experimental design, with five replicates. After six days, we quantified NO concentration, leaf anatomy, gas exchange, chlorophyll a fluorescence, photosynthetic pigments, lipid peroxidation, antioxidant enzyme activity, and metabolite profiles. Higher NO concentration in soybean plants exposed to high temperature and SNP showed increased effective quantum yields of photosystem II (PSII) and photochemical dissipation, thereby maintaining the photosynthetic rate. Under high temperature, NO also promoted greater activity of ascorbate peroxidase and peroxidase activity, avoiding lipid peroxidation of cell membranes, in addition to regulating amino acid and organic compound levels. These results suggest that NO prevented damage caused by high temperature in soybean plants, illustrating the potential to mitigate thermal stress in cultivated plants.

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The production of high-quality seedlings and their use in commercial planting reduce pressure on natural areas. Eugenia dysenterica DC is a native fruit tree from the Brazilian Cerrado, whose nutritional requirements are still unclear. This study aimed to evaluate the effects of nitrogen (N) and phosphorus (P) supplementation on the physiology, growth and nutrient uptake, and use efficiencies of E. dysenterica seedlings grown in glasshouse conditions. The following rates were used in separate experiments: 0, 50, 100, 200, and 400 mg dm−3 N and 0, 100, 200, 400, and 600 mg dm−3 P. The experiment was conducted in a randomized block with four replications. The lowest N rate (50 mg dm−3) increased the stomatal conductance (gS) and, consequently, resulted in the highest transpiration (E), electron transport (ETR), and photosynthetic (A) rates. Also, rates of 50 mg dm−3 and 100 mg dm−3 N increased the Root Uptake Efficiency (RUE) and plant Nutrient Use Efficiency (NUE) for macronutrients and the RUE for micronutrients, stimulating plant growth. Phosphorous fertilization resulted in the maximum values for photosynthesis, electron transport rate, total dry mass, and NUE at the 200 mg dm−3 rate. The results of this study suggest that fertilization with 50 mg dm−3 N and 200 mg dm−3 P is suitable for the development of E. dysenterica seedlings.

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