Response of Potted Australian Ornamental Plants to Different Soil Water Conditions

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1 Response of Potted Australian Ornamental Plants to Different Soil Water Conditions B. De Lucia University of Bari Department of Science of Vegetable Crops Via Amendola 165/A Bari Italy Keywords: plant performance, stress conditions, container-grown Eremophila species Abstract Knowledge of plant performance under reduced irrigation has the potential to reduce drastically the amounts of the applied container irrigation water, but there is still a lack of information about growth and eco-physiological behaviour relative to potted ornamentals grown under limited water availability. Australian ornamental plants show many positive characteristics, such as unusual flower shapes and colours and the presence of species interesting as potted plants and landscaping. Therefore, the main objective of this work was to study the response to water stress conditions by evaluating bio-morphological parameters (plant height and diameter, number of shoots and leaves, leaf area, total fresh and dry weights, dry matter content) of two Australian ornamental shrubs. This research was carried out, under Mediterranean conditions in an iron glasshouse, from March to May 2006 in the experimental field of the Faculty of Agriculture of Bari (Italy), on Eremophila glabra (R. Br) Ostenf and E. nivea Chinnock. Container-grown plants were irrigated with a drip-system: the compared water regimes planned the restitution of 100% (control: optimal regime), 50% and 0% (reduced regimes: stress) of the evapo-transpired water, determined by differential weightings at intervals of six days, in conditions of full water satisfaction. Survival rate was higher in E. glabra (100%) than in E. nivea (64%); the two species show significant differences in all the studied parameters. The response of E. nivea and E. glabra to water stress has not been the same. The visual appearance was more affected, however, in E. nivea than in E. glabra. On the whole, the obtained results suggest that E. glabra could be considered a useful potted species in landscaping and xerogardening, due to its tolerance to severe water stress. Irrigation values close to 50% of ET0 would be enough to maintain the ornamental values of plants: in this way, a considerable saving in water could be promoted, which is one of the most important negative environmental factors for plant productivity under Mediterranean conditions. INTRODUCTION The demand for potted ornamental plants having a low water requirement is increasing, especially in regions having a dry Mediterranean climate. The success of this trend depends on appropriate plant selection (De Lucia, 2003). As researchers, we develop opinions about the relative ability of various crops to withstand drought, but little has been published regarding the actual dehydration tolerance of ornamental plants (Araújo-Alves et al., 2000). Recently, some Australian species such as Leptospermum, Grevillea, Chamelacium, Callistemon, have provoked great interest for the innovations of the ornamental production. In spite of their intense introduction process, there are still many vegetal species which could contribute to enlarge the product range of the ornamental horticulture. Genus Eremophila belongs to the Myoporaceae family and it consists of small to medium shrubs or small trees (Brooks, 1961). All Eremophila species are endemic to Australia and they produce fleshy fruits which are often eaten by birds and animals; they are also known as "poverty bushes" because of the ability of many of them to survive in very dry and inhospitable environments. In the use of Eremophila species for Proc. IS on Prot. Cult. Mild Winter Climate Eds.: Y. Tüzel et al. Acta Hort. 807, ISHS

2 flowered pots, one of the most perceived problems is the species sensibility toward water stress. Even if its duration is quite kept down, this stress is frequent or possible during the growing period, above all in mediterranean environment. A previous research (De Lucia and Cocozza-Talia, 2007) provided information for E. glabra (R. Br) Ostenf. and E. nivea Chinnock about the productive performances and aesthetic qualities obtained according to the growing media and the fertilisation. Therefore, the main objective of this work was to study the response to water stress conditions by evaluating bio-morphological parameters of two potted Australian ornamental shrubs. MATERIALS AND METHODS Two different trials were carried out, from March to May 2007, for 75 days, in the experimental farm of the Department of Science of vegetable crops of the Faculty of Agriculture (Bari University in Apulia - South Italy: ,79 N; ,44 E; 3,35 m above sea level). Ten months year-old plants from rooted cuttings of Eremophila glabra (R. Br) Ostenf. (1 st trial) and E. nivea Chinnock (2 nd trial) were transplanted into pots (24 cm of diameter and height) filled with a peat perlite (1:1, v:v) substrate and placed on benches in an east west greenhouse with iron structure and glass cover. Plants were irrigated with a drip-system and weekly fertilized with a soluble fertilizer (12:18:27 +MgO with microelements) at a final concentration of 1.8 g 1-1 (ph 5.5, EC 1.1 ms cm -1 ). The main morpho-biological traits of the examined species in a spontaneous state are shown in Table 1. Plants were subjected to three different water regimes that planned the restoration of 100% (control: optimal regime), 50% and 0% (reduced regimes: stress) of the evapo-transpired water, determined by differential weightings at intervals of six days, in conditions of full water satisfaction. For each water regime 45 plants/pots divided into three replicates have been considered: the determinations have been done singly. Data recorded at the end of the experiment included: plant height and diameter; number and length of lateral shoots, leaf area, number of flowers, dry and fresh plant weights and dry matter content. Dry weight was obtained after drying the samples in an oven at 70 C for 48hr. The climatic parameters of outdoor and confined temperature and air relative humidity in the glasshouse were determined. Treatments were arranged in a randomized complete-block design with three replicates. The significance of the result was tested by the analysis of variance (F test) and the treatment means were compared by the Student Newman Keuls (S.N.K.) at the P 0.01, using a specific software (CoStat Co-hort Software Inc.). RESULTS AND DISCUSSION Survival rate was higher in E. glabra (100%) than in E. nivea (74%); both species show significant differences in all the studied parameters. Eremophila glabra The Table 2 shows the results of three different levels of ET0 restoration on some visual quality traits: a significant difference between 50% and 0% treatments was not registered for height, diameter, number of lateral shoots and fresh plant weight. As expected, all stressed plants showed a significant decrease in the total length of the lateral shoots with respect to the control plants. The stress effects once again appeared more clearly in the total leaf area: in the 50% level of ET0 restoration the reduction has been of the 68%, proving that the water stress effect reflects above all on the differentiation of new leaves and on the processes of blade stretching and leaf fall. The defoliation and reduction of growth in E. glabra did not prevent the plant from blooming in the 50% of the ET0 (Data not shown). The reduction of the dry weight due to the evapo-transpired water restoration has been respectively of the 41 and 60% in the 50% and 0% levels. With regard to the dry matter, the higher value has been reached in the 0% restoration volume. 278

3 Eremophila nivea The Table 3 shows the results of three different levels of ET0 restoration on some morphological parameters. The variation registered for the visual quality traits due to the restitution volume of the 0% of the evapo-transpired water has been even more sensible. Once again the stress effects have appeared more with reference to the plant height and diameter. The number of lateral shoots varied of the 28% between the 100 and 50% treatments while it suffered a sharp decrease in those plants which, during the whole testing period, could not enjoy water. The registered reduction of the total leaf area due to water stress has been of the 27 and 55% respectively in the 50 and 0% treatments. The fresh weight value, which in the control plants has been of 132 g, has significantly reduced, consolidating itself respectively at 83 and 66 g in the 50% and 0% water regimes. The reductions were 31 and 49% with regard to the dry weight. For the dry matter parameter the higher percentage value has been reached with the 0% restoration volume showing reductions of the 17 and 25% for the 50 and 100% treatments. The linkage between water availability and growth is well known and documented in a wide range of species; drought stress is one of the major stress factors limiting plant growth (Boyer, 1982), but few data are available for Australian ornamental shrubs. Previous studies (Romano et al., 2003) suggest that a high water availability represents the major factor for improving growth parameters in Grevillea plants. The knowledge about how aesthetic and functional characteristics are influenced by water stress may help too in the landscape design process (García-Navarro et al., 2004). In this case, the growth of Eremophila was affected by reduced irrigation. The visual appearance was more affected, however, in E. nivea than in E. glabra. The reduction of the leaf area under drought stress can be considered as an avoidance mechanism minimising water losses when the stomata are closed, which happens to many species under osmotic stress (Savé et al., 1995; Ruiz-Sánchez et al., 2000). By and large, the obtained results suggest that E. glabra could be considered a useful potted species in landscaping and xerogardening, due to its tolerance to severe water stress in the irrigation water. CONCLUSION Irrigation usually improves significantly plant productivity and, in this essay, the ornamental value of plants. This study agrees with the results obtained in other Australian species (Romano et al., 2003) and with the perspective that irrigation values close to 50% of ET0 would be enough in order to maintain the ornamental values of plants used in xerogardening (Sachs and Shaw, 1993). In this way, it could promote considerable savings in water, which is one of the most important negative environmental factors for plant productivity under Mediterranean conditions. ACKNOWLEDGEMENTS This research was financed by the University of Bari (Athenaeum Fund, ). Literature Cited Araújo-Alves, J.P.L., Torres-Pereira, J.M., Biel, C., de Herralde, F. and Savé, R Effects of minimum irrigation technique on ornamental parameters of two mediterranean species used in xerogardening and landscaping. Acta Hort. 541: Boyer, J.S Plant productivity and environment. Science 218: Brooks, A.E Australian native plants for cultivation. Lothian Publishing, Melbourne: 139. De Lucia, B Il giardino mediterraneo luogo ideale per lo xeriscaping. Linea Verde. vol. 3, pp ISSN: (in italian). De Lucia, B. and Cocozza - Talia, M.A Growing medium and fertilisation affect visual quality characteristics of Eremophila potted plants. Proceedings VI 279

4 International Symposium on New Floricultural Crops ISHS Madeira, Portugal (June 11-15, 2007). Acta Hort. (in press). García-Navarro, M.C., Evans, R.Y and Savé M.R Estimation of relative water use among ornamental landscape species. Scientia Horticulturae 99: Romano, D., Li Rosi, A., Paratore, A. and Salerno, G Risposta allo stress idrico in Grevillea. In Florovivaismo tra innovazione e novità : (in italian). Ruiz-Sánchez, M.C., Domingo, R., Torrecillas, A. and Pérez-Pastor, A Water stress preconditioning to improve drought resistance in young apricot plants. Plant Sci. 156: Sachs, R.M. and Shaw, D.A Avoidance of drought injury and minimum irrigation in Mediterranean climate: the requirement for acclimatized (hardened) plants. J. Arbor. 19(2): Savé, R., Biel, C., Domingo, R., Ruiz-Sánchez, M.C. and Torrecillas, A Some physiological and morphological characteristics of citrus plants for drought resistance. Plant Sci. 110:

5 Tables Table 1. Main morpho-biological traits of the examined species in a spontaneous state. Eremophila nivea Chinnock: silky eremophila. Small shrub about m high; hairy stems and foliage give the plant a very distinctive silvery appearance. Linear lance-shaped leaves approximately 30 mm long and 4 mm wide. Lilac flowers 20 mm long and tubular in shape, from late winter to early summer. It is listed as Endangered under the EPBC Act. Eremophila glabra (R. Br) Ostenf. common emu bush. Prostrate form: a shrub spreading up to 0.3 m; conspicuously hairy egg-shaped leaves, yellow flowers, from late autumn to early spring. Table 2. Effect of different levels of ET0 restoration on some visual quality traits of E. glabra plants. Levels of Plant Plant Lateral Lateral s. Total leaf Fresh Dry Dry ET0 height diameter shoots total length area plant plant matter Restoration (cm) (cm) (n) (cm) (cm 2 ) weight weight content (%) (g) (g) (g) A 87.9 A 41.3 A A A A 62.0 A 31.3 B B 77.0 B 31.7 B B B B 36.7 B 35.6 A B 69.6 B 25.6 B C 87.8 C 78.5 B 24.8 C 38.2 A Within the same column and for a single parameter, different letters mark values significantly different at P=0.01 P according to S.N.K. test. 281

6 282 Table 3. Effect of different levels of ET0 restoration on some visual quality traits of E. nivea plants. Levels of Plant Plant Lateral Lateral s. Total leaf Fresh Dry Dry ET0 height diameter shoots total length area plant plant matter Restoration (cm) (cm) (n) (dm) (cm 2 ) weight weight content (%) (g) (g) (g) A 83.3 A 79.0 A A 2044 A A 39.3 A 29.7 C B 69.2 B 57.0 B B 1487 B 83.3 B 27.3 B 32.8 B C 51.4 C 23.0 C 92.3 C 1120 C 66.8 C 19.9 C 39.4 A Within the same column and for a single parameter, different letters mark values significantly different at P=0.01 P according to S.N.K. test.