Ecophysiology of soursop seedlings fertilized with calcium silicate under different irrigation frequencies

Propose: The soursop tree ( Annona muricata L.) is a tropical fruit tree cultivated in the semi-arid region of Brazil; however, it is sensitive to water deficit. The application of calcium silicate can promote plant growth and development under water stress. Therefore, the objective was to evaluate the ecophysiological and biochemical changes in soursop seedlings fertilized with calcium silicate under different irrigation frequencies. Methods: The experiment was conducted in a greenhouse using a randomized block design with a 4 × 2 factorial scheme and four replications. The treatments consisted of four irrigation frequencies: TR1 – daily irrigation; TR2 – irrigation every two days; TR3 – irrigation every four days; TR4 – irrigation every six days, combined with the presence or absence of calcium silicate (CaSiO₃), applied via soil, at a dose of 3.5 g plant⁻¹. Results: Soursop seedlings subjected to TR3 associated with CaSiO₃ showed improved gas exchange, including transpiration, stomatal conductance, and photosynthetic rate. Fertilization with CaSiO₃ regulated proline synthesis, increased leaf biomass and silicon and calcium content in leaf tissues, conferring greater tolerance to water deficit. Treatments TR2 and TR3 were similar to TR1 in plant height, number of leaves, leaf area, biomass accumulation, chlorophyll a fluorescence, chlorophyll content, and total soluble sugars, whereas TR4 significantly reduced these variables, regardless of CaSiO₃ fertilization. Conclusions: The application of CaSiO₃ under moderate stress (TR3) increases soursop seedlings' tolerance to deficit irrigation regimes.