Physiological responses in sugar apple seedlings under irrigation with saline water and foliar nitrogen

Abstract

Irrigation water salinity is one of the most limiting factors to agriculture in the Northeast region of Brazil, compromising photosynthesis in most crops, especially in the early growth phase, thus requiring the development of research to mitigate its harmful effects. In this context, this study aimed to evaluate the effects of nitrogen fertilization for the mitigation of the salinity on the physiology of sugar apple seedlings. The experimental design was in randomized blocks, using five levels ??of electrical conductivity of irrigation water (0.5; 1.15; 2.75; 4.35 and 5.0 dS m^-1) and five nitrogen levels via foliar application (0.0; 0.33; 1.15; 1.97 and 2.3 g L^-1) in four replications and two plants per plot, totaling nine combinations generated by the Box Central Composite Design. Despite stimulating chlorophyll formation 70 DAS, saline water inhibits the fluorescence of chlorophyll a in photosystem II. Foliar nitrogen fertilization at the level of 1.62 g L^-1 mitigates the effects of salinity on the gas exchange properties of sugar apple seedlings. The fluorescence activity and chlorophyll indices show positive responses to foliar nitrogen fertilization in sugar apple seedlings 70 DAS.