Phosphorus Increases K+ in the Shoot and Improves Salinity Tolerance in Sweetsop Seedlings

The use of brackish waters is an alternative for the cultivation of fruit-bearing plants in semi-arid regions; nonetheless, sweetsop trees ( Annona squamosa L.) are sensitive to these types of waters. However, phosphate fertilization can be a technique used to mitigate the harmful effects of salinity. Thus, our objective was to evaluate the application of phosphorus to mitigate the salinity in irrigation water. The experiment was conducted in a randomized block design, with six treatments S1 (2.5 dS m −1 ) S2 = (4 dS m −1 ), SP1 (2.5 dS m −1 + 1.35 g dm −3 of P 2 O 5 ), SP2 = (4 dS m −1 + 1.35 g dm −3 of P 2 O 5 ), T (control), and P (1.35 g dm −3 of P 2 O 5 ). After 78 days of transplantation, the seedlings were evaluated for the total dry weight (TDW), leaf area (LA), salt tolerance index (STI), water use efficiency (WUE), Na + and K + levels in the shoot and root, chlorophylls a and b , maximum (Fm) and variable (Fv) chlorophyll fluorescence, quantum efficiency of photosystem II (Fv/Fm), total soluble sugar (TSS), total free amino acids (TFAA), proline, and glycine betaine (GB). It was observed that plants treated with SP1 and SP2 show higher results of TDW, LA, STI, WUE, and K in the shoot, Chl a, Chl b, Fm, Fv, Fv/Fm, TFAA, proline, GB, and TSS in relation to S1 and S2. The presence of phosphorus under salinity conditions increased the K + concentration in the shoot, which was responsible for the improvement of pigments as well as increasing the quantum efficiency of photosystem II and carbohydrates, maintaining the growth and, consequently, the salinity tolerance of the sweetsop seedlings.