Comparison of individual and combined effects of salinity and deficit irrigation on physiological, nutritional and ornamental aspects of tolerance in Callistemon laevis plants

Abstract

SummaryThe effect of water deficit, salinity and both applied simultaneously on several physiological and morphological parameters in the ornamental plant Callistemon laevis was studied to identify the tolerance mechanisms developed by this species to these sources of stress and to evaluate their adaptability to such conditions. C. laevis plants were grown in pots outdoors and subjected to four irrigation treatments lasting ten months: control (0.8 dS m -1 , 100% water holding capacity), water deficit (0.8 dS m -1 , 50% of the amount of water supplied in control), saline (4.0 dS m -1 , same amount of water supplied as control) and saline water deficit (4.0 dS m -1 , 50% of the water supplied in the control). Water and saline stress when applied individually led to a reduction of 12 and 39% of total biomass, respectively, while overall plant quality (leaf color and flowering) was unaffected. However, saline water deficit affected leaf color and flowering and induced an excessive decrease of growth (68%) due to leaf tissue dehydration and a high leaf Cl and Na concentration. Biomass partitioning depended no only on the amount of water applied, but also on the electrical conductivity of the water. Water stress induced active osmotic adjustment and decreased leaf tissue elasticity. Although both Na and Cl concentrations in the plant tissues increased with salinity, Cl entry through the roots was more restricted. In plants submitted to salinity individually, Na tended to remain in the roots and stems, and little reached the leaves. However, plants simultaneously submitted to water and saline stress were not able to retain this ion in the woody parts. The decrease in stomatal conductance and photosynthesis was more marked in the plants submitted to both stresses, the effect of which decreased photosynthesis, and this together with membrane damage, could delay plant recovery. The results show that the combination of deficit irrigation and salinity in C. laevis is not recommended since it magnifies the adverse effects of either when applied individually.Keywords: Gas exchange; Ion uptake; Ornamental potted plant; Water relations; Water use efficiency; Elastic modulus.Abbreviations: C, control; C*, chroma; DW, dry weight; EC, electrical conductivity; gs, stomatal conductance; hº, hue angle; J, absorption rate of ions by the root system; L*, lightness; P, significance; Pn, net photosynthesis rate; P-V, pressure-volume; RWCtpl, relative water content at turgor loss point ; S, saline treatment; W, deficit irriation treatment; WUE, water use efficiency of production; W+S, simultaneous saline and water stress treatment.; Ψl, leaf water potential; Ψs, stem water potential; Ψ100s, leaf osmotic potential at full turgor; Ψtpl, leaf water potential at turgor loss point. ε; bulk modulus of elasticity.3

Plant Responses to Salt Stress: Adaptive Mechanisms

“…Also, these changes, induced by salinity, have the potential to improve crop quality by reducing excessive vigour and promoting a more compact habit [49]. However, the level of soil salinity is important, and irrigation with high salt concentrations provokes a decrease in this ratio (leaf area/plant height) due to a reduction in both components which could negatively affect the commercial quality of plants [93,95].…”

“…Depending on the ability of plants to grow in saline environments, they are classified as either glycophytes or euhalophytes, and their response to salt stress differs in terms of toxic ion uptake, ion compartmentation and/or exclusion, osmotic regulation, CO 2 assimilation, photosynthetic electron transport, chlorophyll content and fluorescence, reactive oxygen species (ROS) generation, and antioxidant defences [11][12][13][14]. Most salinity adaptive mechanisms in plants are Callistemon citrinus 4 dS·m −1 NaCl 56 days Leaf DW, stem DW, stem diameter, root DW, total DW, root:shoot DW ratio, total leaf area, plant height, root morphology parameters, RGR [42] Lawsonia inermis L. 75, 150 mM NaCl 53 days Total FW, shoot:root DW ratio, RGR [94] Myrtus communis L. 4, 8, 12 dS·m −1 NaCl 30 days Leaf DW, stem DW, root DW, root:shoot DW ratio [28] Eugenia myrtifolia 4, 8, 12 dS·m −1 NaCl 30 days Leaf FW, leaf DW, total leaf area, leaf water content, stem DW, root DW, root:shoot DW ratio [29] Callistemon laevis 4 dS·m −1 NaCl 300 days Leaf DW, leaf area, stem DW, root DW, plant height, root:shoot DW ratio, plant compactness (leaf area/ height) [95] Myrtus communis L. 2.0, 5 dS·m −1 10.0 dS·m −1 RW NaCl 90 days Leaf DW, stem DW, root DW, total DW, root:shoot DW ratio [6] Viburnum lucidum Callistemon citrinus 200 mM NaCl 103 days Leaf number, leaf area, shoot DW, apical shoot length, lateral shoot length, lateral shoots, plant height, root DW, root:shoot DW ratio [8] Verbana bonariensis L. 200 mM NaCl 2013-2014 Total plant height, FW of aboveground part, visual score [96] Gómez-Bellot et al [45] reported increases in the root to shoot ratio in E. japonica plants irrigated with an NaCl solution with an electric conductivity (EC) of 4 dS m −1 . The use of saline water in C. citrinus plants also slightly decreased aerial growth, increased the root to shoot ratio and improved the root system (increase in root diameter and root density) [42].…”

Plant Responses to Salt Stress: Adaptive Mechanisms

“…Also, these changes, induced by salinity, have the potential to improve crop quality by reducing excessive vigour and promoting a more compact habit [49]. However, the level of soil salinity is important, and irrigation with high salt concentrations provokes a decrease in this ratio (leaf area/plant height) due to a reduction in both components which could negatively affect the commercial quality of plants [76,77].…”

Response of Mediterranean Ornamental Plants to Drought Stress

“…The effect of drought stress on plant growth and dry matter has been noticed in numerous ornamental species-for example, Pistacia [12], Spiraea, Pittosporum [19], Bougainvillea [20], Callistemon [21], Laurus, and Thunbergia [22] (Table 1). Since the photosynthetic pathways strongly influence the response to water stress, only the responses of C3 plants are presented in Table 1.…”

“…2-year-old rooted cuttings Total biomass (−); plant height (−); osmotic adjustment (−), leaf tissue elasticity (−) [21] Viburnum opulus L. and Photinia x fraseri 'Red Robin' bushy shrubs…”