And Alnus Glutinosa (L.) Gaertn
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ACTA AGROBOTANICA Vol. 61 (1): 33–39 2008 ECOLOGICAL FEATURES OF FLOWERS AND THE AMOUNT OF POLLEN RELEASED IN CORYLUS AVELLANA (L.) AND ALNUS GLUTINOSA (L.) GAERTN. Krystyna Piotrowska Department of Botany, University of Life Sciences, Akademicka 15, 20-095 Lublin, Poland e-mail: [email protected] Received: 15.03.2008 Summary from black alder pollen are often greenish-yellow (Maurizio and Grafl, 1969) or grey-green col- Hazel and alder bloom as one of the fi rst plants in climatic conditions of Poland. In the present study, detailed observations oured (L i p i ń ski, 1982; J a b ł o ń ski, 1998). were made of the structure of fl owers of Corylus avellana L. and Corylus and Alnus pollen grains contain one of Alnus glutinosa (L.) Gaertn. Pollen yield of the abovementioned the strongest allergens in terms of their effects on hu- species was determined. The number of pollen grains in the theca, mans. In the early-spring period, they cause allergy in anther, fl ower and infl orescence was calculated. A comparison was sensitive persons. Hazel pollen allergens exhibit cross made of the number of pollen grains of these taxa recorded during reactions with allergens contained in alder and birch pol- the atmospheric pollen seasons analysed over a period of 8 years len (Mattiesen et al. 1991; Spieksma and F ren- in the conditions of Lublin. The study demonstrates that pollen guelli, 1991; Knox and Suphioglu, 1996). yield of the common hazel infl orescence was 66 mg, whereas for An analysis of black alder (Alnus glutinosa) and black alder it was 120 mg. It was found that the number of pollen common hazel (Corylus avellana) distribution in Poland grains produced by the alder infl orescence was 2.2 times higher demonstrates that they are evenly distributed across the than by the hazel infl orescence. The atmospheric pollen season country (Z a j ą c and Z a j ą c , 2001). of the studied plant taxa was recorded at similar dates, but alder The aim of the study was to determine pollen pollen was in much larger concentrations. yield and the amount of pollen released in the above- mentioned plant species in the conditions of Lublin and Key words: Corylus avellana, Alnus glutinosa, fl ower features, to compare these results with annual sums of pollen pollen yield, number of pollen grains, pollen season grains obtained from detailed analyses of atmospheric pollen seasons over a period of 8 years. INTRODUCTION MATERIALS AND METHODS Hazel and alder are an important source of fresh The research material consisted of common hazel pollen for bees in early spring, since pollen fl ows from (Corylus avellana L.) shrubs growing in a line at a sunny other plants are still unavailable. The pollen shedding in site and black alder (Alnus glutinosa (L.) Gaertn.) trees these plants usually starts in the second half of January occurring individually on the bank of the Czechówka during sunny, not very cool days. The several-year-long River. Observations were made in Lublin, in the western studies show that the maximum pollen release by hazel part of the city (51o14’ N and 22o32’ E). and alder in Lublin falls on different days of March or at In the present study, pollen yield of the studied the beginning of April (Weryszko-Chmielews- species was calculated based on the weight difference k a and Piotrowska, 2006). The most effi cient of 25 infl orescences before pollen shedding and after pollen shedding takes place at a temperature of 15-18oC pollen release. The method of Wa r akomska (1972) (Suszka, 1980). Hazel pollen is collected by bees in was used to determine the pollen weight. The average the form of medium-sized pollen pellets. These pellets number of fl owers per infl orescence was determined can have different shades, as shown by data reported based on investigations of 30 infl orescences sampled by different authors: bright yellow (Maurizio and from different plants. The number of infl orescences per Grafl, 1969), olive-yellow (L i p i ń ski, 1982) or plant was estimated in accordance with the recommen- grey-yellow (J a b ł o ń ski, 1998). But pellets formed dations of D e mianowicz and Hł y ń (1960). 34 Krystyna Piotrowska The number of pollen grains produced per anther were observed in the second half of June. At the begin- was also determined. Mature stamens were sampled ning of September, when their average length was 1.4 for the investigations before anther dehiscence. Pollen cm, pollen grains were found to be already fully devel- grains were washed out of the thecae with 70% alcohol oped. In the period which immediately preceded pollen onto a microscope slide using a stereoscopic microscope, shedding, the infl orescences reached the length of 3.6 and then they were counted exactly. The obtained results cm, on the average. During fl owering, the infl orescence were recalculated per fl ower and per infl orescence. Six extended by over 100%, it became slender, susceptible replications were made for each species. to wind blasts. The bracts were characteristically bent The occurrence of airborne pollen was recorded back, forming in its upper part a bowl-shaped hollow using a Lanzoni VPPS 2000 pollen trap, located on (Fig. 4) in which a part of pollen settled from the higher a building roof at a height of 18 m above ground. Pollen located anthers; it is favourable for the pollen dispersal monitoring was conducted in the years 2001-2008. by wind and, at the same time, facilitates pollen collec- tion by bees. RESULTS Hazel male fl owers are composed of four stamens subtended by bracts (Fig. 5). The stamen fi lament is di- Hazel and alder belong to plants with unisexual vided as far as the base, and two thecae are not joined fl owers, arranged monoeciously. They form male Amen- by the connective (Fig. 3), which is a special adaptation tifl orae-type infl orescences with a long, slender axis, the to anemophily. The bracts which enclose the stamens so-called base. exhibit a roof-tile-like arrangement and they are cov- Catkin male infl orescences of Corylus avellana ered with numerous hairs (Fig. 2). One outer bract and grow on shoots in clusters, most frequently grouping two inner bracts – with total dimensions of 3.22 mm x 3-4 of them. Flowers are arranged spirally on the axis 2.45 mm – are fused together. In the examined material, and initially they form a rigid, relatively compact ar- the thecae reached the average length and width dimen- rangement (Figs 1, 2). They are formed in the summer sions of 1.16 mm x 0.61 mm. Initially, the fi lament was of the previous year. The fi rst–formed fl ower primordia short – 0.2 mm, but during pollen shedding it extended Table 1 Characteristics of male infl orescences and fl owers of Corylus avellana and Alnus glutinosa. Traits investigated Corylus avellana Alnus glutinosa Number of infl orescences per plant 2430 7370 Number of fl owers per infl orescence 240 580 Number of stamens per fl ower 4 4 Length [mm] 1.16 0.92 Theca Width [mm] 0.61 0.52 Theca 4550 4210 Anther 9100 8420 Number of pollen grains Flower 36 400 33 680 produced by: Infl orescence 8 736 000 19 534 000 Pollen weight per infl orescence [mg] 66 120 Ecological features of fl owers and the amount of pollen released in Corylus avellana (L.) and Alnus glutinosa (L.) Gaertn. 35 Fig. 1. Male infl orescence of Corylus avellana. Fig. 2. Male infl orescence fragment before pollen shedding with visible haired bracts, x 28. Fig. 3. Schematic diagram of the structure of the stamen with separated thecae, x 14. Fig. 4. Male infl orescence fragment during pollen shedding with bowl-shaped bent bracts (arrows), x 9. Fig. 5. Single male fl ower with 4 stamens and bracts (arrows), x 27. Fig. 6. Pollen grain in polar view (P), x 1200. Fig. 7. Pollen grain in equatorial view (E), x 1200. 36 Krystyna Piotrowska Fig. 8. Male infl orescences of Alnus glutinosa before pollen shedding, next to them female infl orescences (arrow). Fig. 9. Cyme with three male fl owers, x 30. Fig. 10. Schematic diagram of the stamen structure, x 16. Fig. 11. Cymes enclosed by claret-coloured bracts, x 10. Fig. 12. Single male fl ower with 4-segmented perianth (arrow heads) and four stamens with the expanded connective (double arrow), x 32. Fig. 13. Pollen grain in polar view (P), x 1100. Fig. 14. Pollen grain in equatorial view (E), x 1100. Ecological features of fl owers and the amount of pollen released in Corylus avellana (L.) and Alnus glutinosa (L.) Gaertn. 37 Corylus Alnus Average Average Fig. 15. Annual sums of Corylus and Alnus pollen grains in the air of Lublin in the years 2001-2008. Fig. 16. The pattern of Corylus and Alnus pollen seasons in Lublin (means from the years 2001-2008). its length up to about 1 mm. In the apical portion of the Alnus glutinosa male infl orescences grow at the thecae, tufts of hairs were observed with the length of top of twigs in clusters of 3–5. Their dark brown-claret col- 0.2-0.3 mm, forming a characteristic little beard (Fig. our is given by the fused bracts: the outer bract, two inner 3). bracts and two bracteoles, from underneath of which bright Average pollen yield of the common hazel infl o- yellow stamens come out (Fig. 8).