DECORATIVE VALUES AND THE NUTRITIONAL STATUS OF SOME Magnolia L. SPECIES UNDER THE CLIMATIC CONDITIONS OF LUBLIN (POLAND) PART. I. DECORATIVE VALUES OF THE PLANTS

Six species of Magnolia L., growing in the Botanical Garden of the Maria Curie-Sk ł odowska University in Lublin which is located on the north-western outskirts of the city of Lublin, were studied during the period 2006-2008. The aim of this study was to determine the dynamics of leaf and flower development in these Magnolia species under the climatic and soil conditions of Lublin as well as to evaluate the size of their leaves and long shoots. The present study included the following species: M. acuminata L., M. kobus DC, M. liliiflora Desr., M. salicifolia Siebold et Zuch, M. x soulangiana Soul.--Bod., and M. tripetala L. The magnolia trees were planted in 1968-1989 on grey-brown podzolic soil derived from loess. The study area is affected by the continental climate which is characterized by large annual amplitude of temperatures, long summers as well as long and cold winters. The long-term average annual air temperature for this region is 8.1 o C, while the long-term average annual rainfall reaches 541.6 mm. The obtained results showed that, among the Magnolia species studied, M. salicifolia flowered earliest under the climatic and soil conditions of Lublin, while M. tripetala was the last to bloom . Full leaf development, on average for the study period, was recorded earliest in M. salicifolia and M. liliiflora , whereas it occurred latest in M. tripetala . The leaves of M. tripetala were characterized by the greatest length and width, while the smallest leaves were recorded in M. kobus . M. liliiflora was found to show the smallest annual shoot increments and the lowest number of leaves .


INTRODUCTION
The genus Magnolia includes about 80 tree and shrub species growing in the wild in the eastern part of North America and in south-eastern Asia (C a l l aw a y , 1994; C z e k a l s k i , 2007). In this group, there are both low trees and shrubs growing up to a height of 60 m which produce impressive flowers from early spring until mid-summer (W e a v e r , 1987; M a t ys i a k , 2002). The great popularity of these plants in park and garden plantings is attributable to their precious decorative values -the varied form and growth habit of trees, characteristic different coloured flowers as well as interesting foliage. The species flowering in early spring before leaf development are exceptionally attractive visually (D i r r , 1990; T u m i ł o w i c z , 2005). Many authors stress the important role that magnolias play in the maintenance of the biodiversity of ecosystems that they inhabit. Y a s u k a w a et al. (1992) draw attention to the importance of magnolia flowers in the biology of pollinating insects, whereas C a l l a w a y (1994) reports that magnolia fruits can be food for numerous animal species. The latest research shows new possibilities of using these valuable plants.
The reports of L i u (2008) and Z h e n h o n g (2011) confirm the usefulness of essential oils obtained from various Magnolia species in pharmacology and aromatherapy.
The aim of the present study was to compare the decorative values of six Magnolia species on the basis of their flowering phenology and leaf development under the climatic and soil conditions of Lublin as well as to evaluate some morphological characters of their leaves and shoots.

MATERIALS AND METHODS
The study was conducted in 2006-2008 on six Magnolia species growing in the Botanical Garden of the Maria Curie-Skłodowska University in Lublin, central-eastern Poland. This garden is located on the north-western outskirts of the city of Lublin in the Czechówka River valley, at an altitude of 200 m a.s.l. The garden area includes a part of the river valley, a slope cut by three loess gullies, and a part of a plateau. The elevation difference is about 40 m. The study area is clearly affected by the continental climate which is characterized by large annual amplitude of temperatures, long summers as well as long and cold winters. The long-term average annual air temperature for this region is 8.1 o C, while the long-term average annual rainfall reaches 541.6 mm. Grey-brown podzolic soils derived from less are predominant in the garden area, on the slopes there are eroded brown soils, whereas alluvial soils are found in the depressions in the land surface. Varied locations with the following characteristics were selected for the investigations: The characteristics of meteorological conditions prevailing during the present study were made based on the data obtained from the Weather Station of the Maria Curie-Skłodowska University located in the Botanical Garden.

RESULTS AND DISCUSSION
Plan growth and development during the growing season is closely correlated with weather conditions prevailing in a given area (K l u z a and Z i e nt a r s k a , 1999). According to the climatic regionalization used for the selection of ornamental trees and shrubs in Poland, the Lublin Upland is situated in the eastern zone (III) that provides less favourable conditions for growing magnolias (C z e k a l s k i , 2007). The analysis of the meteorological data for the Botanical Garden in Lublin showed that average monthly temperatures for the study area were higher in all study years compared to the long-term average ( Table 1). The highest average temperature throughout the entire study period was recorded in 2006 (17.2 o C) and the lowest one in 2008 (16.1 o C). The average monthly distribution of rainfall during the successive years of the study much differed from the long-term average. The highest rainfall total was recorded in 2006 (402.9 mm) and the lowest one in 2008 (346.3 mm).
Observations of the development of flower buds and of the flowering pattern in the selected Magnolia species carried out throughout the study years showed that, under the climatic and soil conditions of Lublin, M. salicifolia produced flower buds and bloomed earliest, whereas M. tripetala was the last to flower (Fig. 1) One of important characters that determine decorative values of plants are foliage size and colour (C a l l a w a y , 1994). The analysis of the biometric measurements made in the present study showed that, among the magnolia species under evaluation, M. tripetala produced the longest (33.5-38.2 cm) and at the same time widest leaves (14.4-14.9 cm). These results are consistent with the views of some other authors who report that the length of leaves of this magnolia can even reach 50-65 cm (W e e k s , 2003; G u y , 2006; C z e k a l s k i , 2007). In the opinion of these authors, M. tripetala produces the largest leaves among all known Magnolia species. The shortest leaves (8.2-9.1 cm) were recorded in the case of M. kobus. C z e k a l s k i (2007) reports that this species produces leaves with a length of 5-15 cm. In this study, the narrowest leaves were noted in M. salicifolia (4.8-5.2 cm) and in M. kobus (4.7-5.3 cm.).
Magnolia liliiflora was characterized by the smallest length of annual increments (long shoots). At the same time, this species was found to have the lowest number of leaves per long shoot (on average 6-7). The obtained results can be related to the nutritional status of the studied plants. The leaves of the purple lily magnolia (M. liliiflora) were shown to have the significantly lowest amount of total nitrogen and calcium (M i c h a ł o j ć et al. in press). Significantly worse nitrogen supply to the plants of M. liliiflora, compared to the other species under evaluation, was probably the reason for reduced elongation growth of their long shoots. It is known that the nutritional status largely determines vegetative plant development (N u r z y ń s k i , 2003). The longest long shoots were found in M. acuminata (on average 24.4 cm) and in M. tripetala (on average 23.7 cm).