Biochemical, Physiological and Anatomical Mechanisms of Adaptation of Callistemon citrinus and Viburnum lucidum to NaCl and CaCl2 Salinization

Abstract

Callistemon citrinus and Viburnum lucidum are appreciated and widespread ornamental shrubs for their abundant flowering and/or brilliant foliage. The intrinsic tolerance to drought/salinity supports their use in urban areas and in xeriscaping. Despite adaptive responses of these ornamental species to sodium chloride (NaCl) have been extensively explored, little is known on the effects of other salt solution, yet iso-osmotic, on their growth, mineral composition and metabolism. The present research was aimed to assess responses at the biochemical, physiological and anatomical levels to iso-osmotic salt solutions of NaCl and CaCl 2 to discriminate the effects of osmotic stress and ion toxicity. The two ornamental species developed different salt-tolerance mechanisms depending on the salinity sources. The growth parameters and biomass production decreased under salinization in both ornamental species, independently of the type of salt, with a detrimental effect of CaCl 2 on C. citrinus. The adaptive mechanisms adopted by the two ornamental species to counteract the NaCl salinity were similar, and the decline in growth was mostly related to stomatal limitations of net CO 2 assimilation rate, together with the reduction in leaf chlorophyll content (SPAD index). The stronger reduction of C. citrinus growth compared to V. lucidum , was due to an exacerbated reduction in net photosynthetic rate, driven by both stomatal and non stomatal limitations. In similar conditions, V. lucidum exhibited other additional adaptive response, such as modification in leaf functional anatomical traits, mostly related to the reduction in the stomata size allowing plants a better control of stomata opening than in C. citrinus . However, C. citrinus plants displayed an increased ability to retain higher Cl - levels in leaves than in roots under CaCl 2 salinity compared to V. lucidum , thus, indicating a further attempt to counteract chloride toxicity through an increased vacuolar compartmentalization and to take advantages of them as chip osmotica.

Morphological and Physiological Responses Induced by Protein Hydrolysate-Based Biostimulant and Nitrogen Rates in Greenhouse Spinach

“…The effectiveness of cluster heat map analysis for simultaneously analyzing and interpreting multiple morpho-functional traits has been reported previously in a series of research papers [4,52,60]. This was the case in the current study, since this analysis has introduced important information on the differences between all treatments.…”

Growth, Visual Quality, and Morphological Responses of 12 Viburnum Taxa to Saline Water Irrigation

“…Shoot dry weight of Coleus blumei (coleus) treated with saline solution reduced when NaCl concentration increased from 0 to 60 mM (Ibrahim et al, 1990). Viburnum lucidum watered with 80 mM NaCl or 53.3 mM calcium chloride (CaCl 2 ) had a 28% reduction in shoot dry weight, but there was no significant change in the root dry weight compared with no salt treatment (Cirillo et al, 2019). When the salinity level of irrigation water increased to 200 mM NaCl (20.5 dS • m -1 ), the shoot and root dry weight of V. lucidum dropped by 37% and 29%, respectively, compared with the control (1.6 dS • m -1 ) (Cassaniti et al, 2009).…”

“…Plant shoot growth is more sensitive to salinity stress than root growth, and an increased root-to-shoot (R/S) ratio is expected in response to salinity stress (Hanin et al, 2016). Cirillo et al (2019) determined that the R/S ratio increased from 0.49 to 0.61 in V. lucidum and from 0.37 to 0.46 in C. citrinus when the EC of irrigation water increased from 2.0 to 11.0 dS • m -1 . Acosta-Motos et al (2015) also observed an increasing R/S ratio in Myrtus communis (common myrtle) plants irrigated with NaCl solution at an EC of 8.0 dS • m -1 for 1 month.…”

Effects of Water Stress on Gas Exchange, Water Relations and Leaf Structure in Two Ornamental Shrubs in the Mediterranean Area

“…The species is considered as a low water-use plant [28,29] and is able to grow in regions with mild winters [30].Both species are widespread in the Mediterranean area of Italy, in gardens and green areas, because of their ornamental value and adaptability to many environmental conditions. Different studies were carried out on Viburnum to investigate on salt stress response [28,31], but little information is available in terms of growth parameters, photosynthetic efficiency, leaf functional anatomical traits in drought stress conditions.These two species were chosen on the basis of our previous studies [32]; Polygala myrtifolia L. and Viburnum tinus L. 'Lucidum' were found, respectively, to be moderately sensitive and sensitive to salinity. Since salinity and drought stresses share important adaptation strategies, this work was carried out to verify if unavailability of water activates the same adaptation strategy observed under salinity stress.…”

“…Both species are widespread in the Mediterranean area of Italy, in gardens and green areas, because of their ornamental value and adaptability to many environmental conditions. Different studies were carried out on Viburnum to investigate on salt stress response [28,31], but little information is available in terms of growth parameters, photosynthetic efficiency, leaf functional anatomical traits in drought stress conditions.…”