Abstract: A qualitative and quantitative evaluation of pollen concentration in the atmosphere of Abha city, Saudi Arabia with the relation to meteorological parameters is presented. Investigations were undertaken from January to December 2006 using a Burkard 7 day volumetric spore trap. A total of 6,492 pollen grains m-3 belonging to 50 pollen taxa was detected. Poaceae represented 55.1% of total pollen, Leguminosae (11.7%), Compositae (6.1%), Solanaceae (4.6%) and Cupressaceae (4.2%). Pollen grains were found throughout the year. July represented the highest peak of pollen number and also the highest pollen taxa. The monthly variation of pollen taxa and their relationship to meteorological parameters were investigated. It was found that the pollen concentration is positively correlated with temperature and negatively correlated with rainfall, relative humidity and wind velocity. May-September represented the months of highest pollen number (95% of total pollen).
INTRODUCTION
Pollen grains are male reproductive units and are released into the air in huge amounts for the purpose of pollination. The concentration of different pollen types in the atmosphere varies enormously from one country to another, in regions of the same country and even among different cities, because pollen emissions depend on the vegetational structure and meteorological conditions (Kaplan, 2004). A positive correlation of pollen concentration and surrounding vegetation density has been described (Romano et al., 1988) indicating that changes in the floral composition of a given area have a direct influence on its aeropalynological spectrum. Ninety-eight percent of the total pollen grains in the atmosphere are from anemophile plants, whereas 2% are from entemophile plants (Mullins and Emberlin, 1997; Molina et al., 2001).
Generally, meteorological parameters have an important influence on pollen concentration in the air. Aerial transport of pollen may have an important impact on earth life, which increases with economic expansion around the world (Ribeiro et al., 2003).
In other countries, many of aeropalynological studies have been conducted for several years using different types of samplers (Giorato et al., 2000; Villegas and Nolla, 2001; Mishra et al., 2002; Murray et al., 2002; Ballero and Maxia, 2003; Porsbjerg et al., 2003; Rodrfguez-Rajo et al., 2003; Paloma et al., 2004; Hasnain et al., 2005; Tejera and Beri, 2005; Ture and Salkurf, 2005).
In Saudi Arabia, aeropalynological studies are scarce but gaining importance (Hasnain et al., 2005). However, the purpose of this study was to identify pollen grains in the air of Abha city, Saudi Arabia and their relation to meteorological parameters.
MATERIALS AND METHODS
Abha city (18°14` N and longitude 42°39` E, altitude of about 2093 m) lies in the Southwestern part of the Arabian Peninsula about 1100 km from Riyadh, the capital of Saudi Arabia. The city is characterized by moderate climate, heavy rainfall, green pasture and agricultural plateaus. The region abounds in mountains, valleys and fertile plains and surrounded by dense forests.
Pollen sampling was carried out from January to December, 2005 using a Burkard volumetric 7 day spore trap (Burkard Manufacturing Co. Ltd., England). The trap was placed on the roof of the laboratories building at the College of Science, King Khalid University, approximately 15 m above ground level. The Sampler was set for seven day sampling onto Melinex tape which was coated with a thin film of Lubriseal (Levetin, 1991). Tapes were changed weekly, cut into seven daily segments and mounted on microscope slides. Slides were stained with glycerin jelly containing basic fuchsin and examined microscopically at 400X using a single longitudinal traverse. Microscope counts were converted into atmospheric concentrations and expressed as pollen grains m-3. Daily concentrations were summed for cumulative monthly totals. Pollen identification was followed using the books on palynology (Erdman, 1966, 1969; McDonald and O`Driscoll, 1980; Moore et al., 1991).
Meteorological data were kindly obtained from Abha Meteorological Station (No. 41112).
With the help of MINITAB computer programme, non-parametric statistical analysis by Spearman`s rank test was applied to determine whether monthly pollen concentration and meteorological parameters were positively or negatively correlated (MINITAB, 1985). The statistical significance of correlation was studied by student`s-test for paired samples following the methods of Subiza et al. (1992) and Vega-Maray et al. (2003).
RESULTS
During the year of observation, 6,492 pollen grains cm-3 belonging to 50 pollen taxa were found. The highest concentration of pollen was that of Poaceae (55.1%), Leguminosae (11.7%), Compositae (6.1%), Solanaceae (4.6%) and Cupressaceae (4.2%) (Table 1). The total pollen count varied throughout the year with the peak period in July (Fig. 1a). Brassicaceae is the only pollen taxon was found all year round with maximum concentration during October, followed by Compositae (9 months, from January-November) with maximum concentration during July, Poaceae (8 months, from March-December) with maximum concentration during July. Palmae and Crassulaceae were found all year round, except February and March with maximum concentration during June and August, respectively. The highest number of taxa was recorded in June (29 taxa), July (31 taxa) and August (24 taxa), whereas, the lowest number of taxa was recorded in February (5 taxa) (Table 2) which represented also the lowest number of pollen.
In the present investigation, most of pollen number was recorded during five months of the year (May-September) (95% of total pollen). During this period, Poaceae, Leguminosae, Compositae, Solanaceae and Cupressaceae were prevailed.
In the present investigation, the influence of meteorological factors on the pollen concentration was studied (Fig. 1a-c and 2a-c). Here, a positive and statistically significant correlation was found between the air temperature and pollen concentration. Conversely, a negative correlation was observed between rainfall, relative humidity and wind velocity and pollen concentration (Table 3).
Maximum concentration of pollen grains was found mostly between June-September (Fig. 1a), probably due to moderately high temperature, low relative humidity, moderately low wind velocity and low rainfall. The count became very low during January-April and October-December may be due to high wind velocity. Thus the pollen concentration depends upon the climatic factors and this has been statistically supplemented. A correlation was made between the monthly total pollen count (Table 3) and meteorological parameters through statistical analysis. From the value of the correlation coefficient (r), it was found that pollen concentration was positively correlated with temperature and negatively correlated with rainfall, relative humidity and wind velocity during the year (Table 3). The level of significance was also determined from the statistical table. In case of temperature, the level of significance was below 0.1, while it was between 0.1-0.05 for rainfall and between 0.01-0.001 for relative humidity and below 0.1 for wind velocity.
| Fig. 1: | Relationship between pollen number (a) rainfall (b) and wind velocity (c) during the year of study |
| Table 1: | Monthly pollen taxa found in the air of Abha city from January (1) December (12), 2006 |
| Table 2: | Monthly number of pollen taxa recorded during the period of study |
| Table 3: | Correlation between meteorological parameters and monthly
total pollen count (coefficient of correlation (r) values) |
| Degree of Freedom (DF) (12-2 = 10) | |
| Fig. 2: | Relationship between pollen number (a), temperature
(b) and relative humidity (c) during the year of study |
DISCUSSION
The frequency of pollen differs from place to another due to the difference in geographical position, local vegetation and other environmental conditions (Subiza et al., 1992; Frenze, 2000; Vega-Maray et al., 2003). Frenze (2000) demonstrated that airborne pollen concentrations exhibit spatial variability, as pollens from nearby vegetation exert a profound local influence. Moreover, the size of source area represented by a pollen sampler depends on the distance between the sampler and the nearest vegetation. The present results support the view of Frenze (2000), because of high incidence of Poaceae, Leguminosae, Compositae, Solanaceae and Cupressaceae pollens was probably due to the presence of a large area of such vegetation and grass loan, in and around the sampling site.
Magnitude and quality of annual pollen load in the atmosphere varies significantly. Meteorological parameters like temperature, rainfall, relative humidity, wind velocity are responsible for fluctuations in pollen concentration (Anderson, 1980; Bricchi et al., 1992).
In the present investigation, the influence of meteorological factors on the pollen concentration was studied. Here, a positive and statistically significant correlation was found between the air temperature and the pollen concentration. Conversely, a negative correlation was observed between rainfall, relative humidity and wind velocity and pollen concentration. The present results are consistent with previous observations in different countries (Puc and Wolski, 2002; Vega-Maray et al., 2003; Boral et al., 2004).
Apart from rhythm of plant pollination, meteorological conditions are considered the most important factors determining the dispersion and content of pollen in the air (Subiza et al., 1992; Puc and Wolski, 2002). Subiza et al. (1992) have shown that humidity and rainfall appear to be the predominant factors in determining the grass pollen potential for the season. It is evidenced that temperature is the factor that exerts the greatest influence on the release of pollen grains in the atmosphere (Puc, 2003; Vega-Maray et al., 2003). Rainfall and relative humidity yielded negative correlations since water droplets wash away pollen particles (Vega-Maray et al., 2003). Puc and Wolski (2002) showed a positive and statistically significant correlation between the air temperature and the Betula pollen concentration, while a similar but negative correlation was found for Populus pollen. A relationship was established between the airborne ragweed pollen concentration and the macrosynoptic weather situation (Feher and Jarai-Komlodi, 1996).
Therefore, the aerobiological survey in relation to meteorological parameters has proved that weather factors have great influence on the occurrence and distribution of pollen grains in the atmosphere.
Fifty airborne pollen taxa have been identified from Abha city. Poaceae, Leguminosae, Compositae, Solanaceae and Cupressaceae recorded the highest pollen number throughout the year of investigation. July represented the highest peak of pollen number and also the highest pollen taxa. A positive correlation was found between pollen concentration and air temperature, while a negative correlation of pollen concentration was observed with rainfall, relative humidity and wind velocity.
| Fig. 3: | One-year (2006) pollen calendar of Abha city |
This study gives an idea about the airborne pollen types present in the Abha atmosphere and gives also an indication of their main flowering seasons (Fig. 3). It can be concluded that Abha receives a large pollen concentration from grasses, weeds, ornamental trees and shrubs found around the city. However, an aeropalynological study of 1 year is not sufficient to analyze seasonal variations of airborne pollen. It would be necessary to extend these studies to more years and to other strategically placed areas to achieve a global pollen calendar for the city and to improve the knowledge of flowering and pollen dynamics and its relation to the meteorological parameters.
ACKNOWLEDGMENTS
This study was financially supported by SABEC Company, Saudi Arabia. The author is grateful to the Department of Biology, College of Science, King Khalid University for providing the facilities of this study.