Abstract
ABSTRACT Salinity affects growth and quality of ornamental plants, but studies on mechanisms of salt tolerance in these plants are scarce, particularly under tropical climate conditions. Thus, the morphophysiological leaf responses of four tropical ornamental species were studied, in order to identify the mechanisms involved in the tolerance to salinity and their potentials to be irrigated with brackish water. The research was conducted in a greenhouse using a completely randomized block design, in a 10 x 4 factorial scheme, with four repetitions. The treatments consisted of ten levels of electrical conductivity of irrigation water (0.5; 1.0; 2.0; 3.0; 4.0; 5.0; 6.0; 8.0; 10.0 and 12.0 dS m-1) and four ornamental tropical species (Catharanthus roseus, Allamanda cathartica, Ixora coccinea, and Duranta erecta). At 30 and 60 days after the beginning of saline treatments (DAST), measurements of leaf gas exchange and chlorophyll index were performed. At 60 DAST, leaf area, specific leaf area, leaf area ratio, leaf succulence, Na+ and proline concentrations were measured. The physiological and morphophysiological responses of the leaves indicate that I. coccinea species has high capacity to grow under irrigation with saline water. Its higher tolerance to salinity is related to the lower concentration of Na+ in the leaves. Conversely, the sensitivity of D. erecta was associated with high Na+ and proline concentrations in leaves. The leaf concentration of proline showed to be an indicator more related to the sensitivity of ornamental plants to salt stress; however this relationship should not be generalized for all ornamental species studied.
Highlights
The worth of the world production of ornamental plants and cut flowers is about 50 billion Euros, corresponding to a high global consumption annually
It can be observed that the species C. roseus stands out with highest values of gs (Figures 1A and B), A (Figures 1C and D) and E (Figures 1E and F) under low-salinity conditions, whereas the species I. coccinea showed the lowest values under these same conditions
When comparing the effects of salinity on leaf gas exchanges, it becomes evident that at 30 days after the beginning of saline treatments (DAST) the species I. coccinea was little influenced by the stress, while the rates observed for D. erecta were close to zero at the highest levels of salinity (Figures 1A, C and E)
Summary
The worth of the world production of ornamental plants and cut flowers is about 50 billion Euros, corresponding to a high global consumption annually. In Brazil, the cultivation of ornamental plants is an important economic activity due to the climatic diversity (wet, semi-arid, hot, cold) and strategic points for their marketing. High salinity compromises the development of crops, especially in dry climates (Munns & Tester, 2008). Physiological processes and plant growth (Lacerda et al, 2006a; Acosta-Motos et al, 2015; Taiz et al, 2015). Salt stress can affect the visual quality, a relevant characteristic in the commercialization (Niu et al, 2012; Neves et al, 2018; Oliveira et al, 2018)
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