Seeking to understand the mechanisms of tolerance of melon plants under water deficit, this study aimed to evaluate the biochemical behavior of melon cultivars and the allocation of biomass under water deficit. Two experiments were conducted in a shaded environment in the experimental area of the State University of Bahia, Juazeiro / BA; the first was carried out in 2015 and the second in 2016. The experimental design was in randomized blocks, replicated three times, with subdivided plots; the plots consisted of four water application rates (50, 75, 100 and 125% of the crop evapotranspiration), the subplots of two melon cultivars 'Yellow' and 'Piel de Sapo'. The sub-subplots were the sampling periods: 15; 30 and 45 days after transplantation. In the first experiment it was evaluated: total soluble sugars, reducing sugars, total proteins. In the second experiment, in addition to biochemical analyzes, the allocation of biomass of leaves, branches, roots, fruits and root / shoot ratio was evaluated. At the end of both experiments, root proline and aerial part were evaluated. Both cultivars showed similar biochemical behavior, except for the accumulation of proline obtained in the cultivar 'Piel de sapo', which allowed greater biomass allocation to the fruit than the cultivar 'Amarelo'.

Climate-change-driven elevation of atmospheric CO₂ (e[CO₂]) disrupts rice physiology by impairing nitrogen use efficiency (NUE) and leaf carbon balance. This study investigated how sodium chloride (NaCl) amendment modulates these processes in upland rice (Oryza sativa L. cv. CMG 2085) under current (400 μmol mol⁻¹) and elevated (700 μmol mol⁻¹) CO₂ concentrations. Using a randomized block design with factorial treatments (CO₂ × NaCl), we analyzed leaf nutrients, gas exchange, chlorophyll fluorescence, and yield parameters. Our findings revealed that 3 mmol L⁻¹ NaCl under ambient CO₂ (1) reduced photorespiration by half, (2) increased grain yield, and (3) enhanced leaf area despite lower leaf N content, indicating improved NUE. Conversely, under e[CO₂], NaCl supplementation decreased rice yield by 15%, demonstrating CO₂-dependent reversal of sodium benefits. Photosynthetic modeling showed higher Vcmax and J values at ambient CO₂, while e[CO₂] increased J/Vcmax, suggesting altered nitrogen allocation to photosynthetic reactions. These results demonstrate that applying low-dose NaCl (3 mmol L⁻¹) can optimize carbon and nitrogen economy under current CO₂ concentrations, although its efficacy diminishes under e[CO₂]. These findings support climate-resilient cultivation strategies for upland rice in tropical and subtropical regions where mild salinity can be used to enhance nitrogen use efficiency and yield under present-day atmospheric conditions.