Impactos da salinidade e da luminosidade no crescimento, fisiologia e qualidade visual de Euphorbia milii e Zamioculcas zamiifolia

Abstract

Brazil is going through a major economic crisis, affecting considerable sectors of its economy; with the return of activities, the floriculture sector should resume growth in line with the global trend. The Northeast region has favorable climatic conditions for the development of floriculture; however, water scarcity and salinization of part of its water sources act as an obstacle to this activity. Furthermore, little is known about the tolerance of ornamental plants to salt stress, when they are grown in full sun or under different levels of shading. In this context, the objective was to evaluate the effects of irrigation water salinity and different light conditions on growth, gas exchange and visual quality of two ornamental species: Euphorbia milii and Zamioculcas zamiifolia. The research was carried out at the Center for Teaching and Research in Urban Agriculture (NEPAU) of the Federal University of Ceará – UFC, in Fortaleza – CE. The experimental design was in randomized blocks in a split-plot scheme, with five replications, with the plots being determined by the different cultivation environments (full sun and shading of 30%, 50% and 70%), the subplots corresponding to the salinity levels in the irrigation water ECa (0.5; 2.0; 3.5; and 5.0 dS m-1), and the sub-plots to the species Euphorbia milii and Zamioculcas zamiifolia, with two plants per repetition, totaling 320 experimental units. Biometric measures of growth (height, stem diameter, number of branches and leaf area), biomass production and partition, leaf macronutrient and sodium contents, leaf gas exchange, salinity tolerance and qualitative sensory analysis were evaluated. Shading had a greater impact on qualitative variables than on salinity tolerance based on the results of the quantitative variables. The 30% shaded environment is the most favorable for the cultivation of E. milii when using water with low to moderate salinity. Shading reduces direct radiation damage to Z. zamiifolia leaves and improves the visual quality of this species under high salinity. The high luminosity condition stimulated greater biomass partition to the aerial part in relation to the root system of the Euphorbia milii species. The species Zamioculcas zamiifolia, in turn, allocated a greater fraction of biomass to the root+rhizome group. Leaf gas exchange and sodium (Na) and macronutrient nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S) contents in both species were influenced by the effect of the shading and salinity of the irrigation water. Shaded environments provided taller plants, with greater leaf area, greater accumulation of dry matter in shoots and flowers, and a greater number of flowers, these last two variables being inherent only to Euphorbia milii.