Gas exchanges in Handroanthus impetiginosus seedlings under artificial shading and irrigation with brackish water

Abstract

The Caatinga biome has peculiar climate and soil conditions. Although native vegetation has mechanisms of adaptation to conditions imposed by the environment, little is known about the development of forest species under the influence of abiotic factors. Thus, the objective of the present work was to evaluate the effects of irrigation with brackish water on the leaf gas exchange of Handroanthus impetiginosus seedlings grown in different types of artificial shading. The experiment was conducted at the Center of Education and Research in Urban Agriculture of the Federal University of Ceará, under a randomized blocks design with four repetitions. The plots were composed of four levels of shading, formed by black shading screen of the sombrite type: 0 (full sun), 30, 50 and 70% and the subplots were formed by five increasing levels of electrical conductivity of the irrigation water: 0.4, 1.6, 2.8, 4.0, and 5.2 dS m-1. At 60 days after sowing (DAS) net photosynthesis rates, transpiration, stomatal conductance, internal CO2 concentration, and water use efficiency were determined. The higher electrical conductivities of the water (4.0 and 5.2 dS m-1) caused damage to the photosynthetic apparatus of Handroanthus impetiginosus seedlings, however, the use of artificial shading attenuated the harmful effects of salinity, and the black shading screen with 50% shade was the one that most favored leaf gas exchange, allowing tolerance of up to 2.8 dS m-1.