INVESTIGATIONS ABOUT THE SEASONAL DYNAMICS IN THE URBAN ENVIRONMENT ON PLANTAGO MAJOR

Abstract

This paper presents an ecophysiological study on Plantago major in the urban environment. The study followed the variations which appear at leaf level depending on season of vegetation, gathering zone, stage of development and the differences between healthy leaves and the ones affected by pathogens or diseases. The analyzed parameter was LRWC -leaf relative water content. The leaf relative water content decreased as the seasons passed regardless of the leaf development stage, being more pronounced for the juvenile samples. At leaf level the most variations were observed in the plants gathered during autumn.

Headnote

ABSTRACT

This paper presents an ecophysiological study on Plantago major in the urban environment. The study followed the variations which appear at leaf level depending on season of vegetation, gathering zone, stage of development and the differences between healthy leaves and the ones affected by pathogens or diseases. The analyzed parameter was LRWC -leaf relative water content. The leaf relative water content decreased as the seasons passed regardless of the leaf development stage, being more pronounced for the juvenile samples. At leaf level the most variations were observed in the plants gathered during autumn.

KEY WORDS: Plantago major, leaf relative water content (LRWC), urban environment

INTRODUCTION

Studies on Plantago species in the natural environment were related to studies addressing to its ecology (Clauss & Venable, 2000; Lacey & Herr, 2000; Sanderson & Elwinger, 2000; Ianovici et al, 2010), the manifestation of allelopathy (Newman & Rovira, 1975), relations with insects (Bowers & Stamp, 1993), interactions with bacteria, viruses and micoritic fungi (Blaszkowski et al, 2006), pollutants (Siegel & Siegel, 1984), ozone (Tonneijck et al, 2004), nutritional aspects (Den Hertog et al., 1996) and salt stress (Koyro, 2006). In other studies, experiments have been carried out on plants in greenhouses and controlled condition growing rooms (Reynolds et al, 2005). On the other hand, micropropagation techniques were applied to in vitro cultures of Plantago (Jasrai et al, 1993) in order to increase knowledge on the phenolic profile (Budzianowska et al, 2004), to study how the process of biotransformation correlates with the metabolism of polyphenolic compounds (Fons et al, 2008), to select hybrids with high resistance to stress / salt, or with a high content of bio-active compounds (Li & Li, 2005). The Plantago genus was a very interesting subject for evolutionary studies due to the wide range of mating systems (Hale & Wolff, 2003).

In 2010, a review synthetized the Romanian specialty literature in regards to Plantago species (Ianovici et al, 2010). The first studies about quantifying the degree of colonization by the vesicular-arbuscular mycorrhizas were realized on the species of the Plantago genus (Ianovici et al, 2009a; Ianovici, 2010a; Ianovici, 2010b). Anatomical particularities and ecological adaptations of healthy leaves were compared in Plantago species from Romania (Ianovici et al, 2011). Differences between healthy and non-healthy leaves were studied on Plantago schwarzenbergiana (Ianovici, 2011b). The fact that the stomatal density of an alpine plant (Plantago atrata) varies with altitude was confirmed by another study. The nutritional status of the plant was not seriously affected by the altitude change, fact suggested by lamina thickness (Ianovici, 2012). The seasonal dynamics of the airborne Plantago pollen from Timisoara was presented in several scientific articles (Ianovici, 2007a; Ianovici, 2007b; Ianovici et al, 2008a). The investigations made on the pollen of Plantago lanceolata and Plantago major from the urban environment revealed the fact that it can be used as an ambiental bioindicator (Ianovici et al, 2008b). The changes of the anatomical foliar parameters in an urban environment were studied on Plantago lanceolata and Plantago major (Ianovici et al, 2009).

Water content is a useful indicator of water balance in plants (Yamasaki & Rebello Dillenburg, 1999; Farhat et al, 2008; Lugojan & Ciulca, 2011; Rahimi et al, 2010; Ganji Arjenaki et al, 2012; Juneau & Tarasoff, 2012), and it can differ significantly among cultivars exposed to the same period of water exclusion (Lafitte, 2002). Several studies have focused on developing appropriate techniques for measuring RWC (Weatherley, l950; Harms & McGregor, l962; Turner, 1981; Bannister, 1986; Klar, 1988). The temperature may be a major factor involved in measuring RWC, fact suggested by several authors (Barrs & Weatherley, 1962; Millar, 1966; Slatyer, 1967; Catsky, l969). The reliability of RWC measurements is pretty good using widely available equipment. The variation of the results depends on the rehydration method used (Lafitte, 2002). RWC determination is commonly done on leaf tissue (Smart, 1974). The water status in the leaves is closely related to several physiological variables such as turgor, growth, stomatal conductance, transpiration, photosynthesis and respiration (Kramer & Boyer, 1995).

The first study on LRWC variations made in Romania was on Plantago maritima species (Ianovici, 2011a).

The goals of this study are the following:

- finding the differences between LRWC of Plantago major from urban area (U) and LWRC of the same species from urban green area (UG);

- finding the differences between the LRWC of mature leaves and the LRWC of juvenile ones;

- finding the differences between the LRWC of the affected leaves and the LRWC of the non-affected ones.

MATERIAL AND METHOD

The main area for the research was the city of Timisoara. The Plantago major plants are found in the entire urban environment. The gathering was realized during three vegetation seasons from unflowered plants, flowered plants and plants in the fructification phenophase.

In this study, I focused on two main areas: urban (U) and urban green (UG). The U area was considered Pestalozzi and Cuvin streets and UG area was constituted from the Justitiei park, Cathedral park, Rozelor park and Central park.

Visible damage was assessed on a five-point scale for the following features: chlorosis, necrosis and withered leaves (Dimitrova & Ninova, 1998; Ianovici et al, 2012). The scale includes: Level I - intact leaves (0% of leaf area affected), level II - slightly affected leaves (up to 25%), level III - moderate affected leaves (up to 50%), level IV - considerably affected leaves (up to 75%) and level V heavily affected leaves (over 75%), including dead leaves.

Leaf relative water content (LRWC) was determined by starting with measuring the fresh weight of the leaves (FW) for 59 samples, distributed to summer, autumn and spring. Each sample contained 3 leaves: one healthy, one affected by pathogens or diseases and one juvenile.

In order to obtain the turgid weight (TW), each leaf was kept floating in distilled water inside a closed Petri dish for 2 hours in fluctuating conditions of light and temperature. The samples were oven dried at 100°C for 2 hours to determine the dry weight (DW). LRWC was calculated using the formula:

LRWC = [(F.W - D.W) / (T.W - D.W)] × 100 (Ianovici, 2011a).

For the considered parameter (LRWC) several types of variations were monitored. Significant differences were determined in Microsoft Office Excel 2007 by using the t test.

RESULTS AND DISCUSSIONS

The relative water content technique, formerly known as relative turgidity, has been widely accepted as a reproducible and meaningful index of the plant's water status.

First the differences of LRWC between the two main zones were analyzed. The mean value of LRWC for the leaves from U zone was 87.67 %, significantly higher (p=0.0022) than the one corresponding to the UG zone, 84.13 % respectively. The seasonal dynamics of LRWC for the two investigated zones can be observed in Fig. 1 for U and in Fig. 2 for UG. Significantly higher values (p =0.0001) of this parameter, only for autumn harvested samples, were obtained for U zone to the detriment of UG zone, after applying the t test. The lowest values, in both cases, were observed for the autumn samples.

Further, the differences which may appear between the LRWC of the mature leaves and LRWC of the juvenile ones were investigated. The mean value of LRWC for the mature samples from all the seasons was 86.3458% and the mean for the juvenile ones was 82.1082%. A significant increase in LRWC (p= 0.0060) of the mature samples was observed after applying the t test. Mean values of LRWC for the mature samples can be observed in Fig. 3. The LRWC of the mature samples decreases as the seasons pass. Significantly lower values of this parameter were observed for the autumn samples as against the spring (p= 0.0003) and summer (p=0.0016) ones.

A decrease of LRWC for juvenile leaves appeared with the coming of autumn, fact which can be observed in Fig. 4. A significant decrease of LRWC in autumn gathered juvenile leaves was observed as against the LRWC in the summer (p= 0.0070) gathered ones and the LRWC in the spring (p= 0.0016) gathered ones. The results are in accordance with the ones obtained by Ianovici (2011a), respectively that the juvenile leaves exhibit an increased capacity of imbibition.

Further, differences between the LRWC in the affected samples and the LRWC in the non-affected ones were searched. The identified necrosis was only of levels II, III and IV. Overall, in the LRWC of the two types of leaves analyzed, no significant difference was found. Mean values of LRWC for the two types of samples, depending on the season of vegetation, can be observed in Fig. 5. An increase of LRWC in the healthy samples from spring and summer appeared. On the other hand, a significant increase of LRWC (p= 0.0020) in the affected leaves as against the healthy ones exists for the autumn. Further studies are needed to clarify this matter.

CONCLUSIONS

The LRWC in all the samples analyzed decreases as the seasons pass.The samples from UG area had a higher LRWC in spring and summer, than those from U area. In contrast, it has been found an increase of this parameter for the samples gathered during autumn in the U area, probably due to environmental adaptations. For the non-affected spring and summer gathered samples, increases in LRWC were found, but for the affected autumn gathered samples significant increases in this parameter were observed, thing which needs further investigation. As against the mature leaves, the juvenile leaves have an increased imbibition capacity. On Plantago major, during the autumn, the leaves from the U area, the mature leaves and those affected seem "to learn" how to conserve the water in their tissues.

ACKNOWLEDGEMENTS

The author wishes to thank Dr. Nicoleta Ianovici for her valuable suggestions to evaluate the results.

References

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