Abstract
The dynamics of flowering and pollen release in anemophilous plants and the length of the particular phases depend largely on the geobotanical features of a region, its climate, meteorological factors, biological characteristics of vegetation, and abundance of pollen resources. The aim of the study was to determine the relationship between the flowering phases in eight <i>Alnus</i> taxa and the dynamics of occurrence and abundance of airborne pollen grains as well as the meteorological factors (maximum and minimum temperature, relative air humidity, maximum wind speed, and precipitation). The flowering phenophases and pollen seasons were studied in 2008–2011. Phenological observations of flowering were conducted in the Maria Curie-Skłodowska University Botanical Garden in Lublin and they involved the following taxa: <i>Alnus crispa</i> var. <i>mollis</i>, <i>A. glutinosa</i>, <i>A. incana</i>, <i>A. incana</i> ‘Aurea’, <i>A. incana</i> ‘Pendula’, <i>A. maximowiczii</i>, <i>A. rubra</i> and <i>A. subcordata</i>. Spearman’s r correlation coefficients were calculated in order to determine the relationship between the dynamics of inflorescence development and meteorological conditions. Aerobiological monitoring using the gravimetric method was employed in the determination of <i>Alnus</i> pollen content in the air. The annual phenological cycles in 2008-2011 varied distinctly in terms of the time of onset of successive flowering phases in the <i>Alnus</i> taxa studied, which depended largely on the taxonomic rank and meteorological factors. The following flowering sequence was revealed in the 2008-2011 growing seasons: <i>A. subcordata</i> (December or January), <i>A. incana</i> ‘Pendula’, <i>A. incana</i>, <i>A. maximowiczii</i>, <i>A. rubra</i>, <i>A. glutinosa</i>, <i>A. incana</i> ‘Aurea’ (February or March), and <i>A. crispa</i> var. <i>mollis</i> (April). The study demonstrated that the pollen of the taxa persisted in the air, on average, from mid-December to early May. The mean length of the flowering period, which coincided with various phases of the pollen season, was 17 days. The <i>Alnus</i> pollen season in 2008 started at the end of January and lasted until mid-March. In 2009, 2010, and 2011, the beginning of the pollen season was recorded in the first week of March and the end in the first week of April. The maximum concentration of airborne <i>Alnus</i> pollen was found at the full bloom stage of mainly <i>A. glutinosa</i> and <i>A. rubra</i>. Inflorescence development was most closely related to temperature and relative air humidity; there was a weaker relationship with wind speed and precipitation.
Highlights
35 Alnus species are known to occur primarily in the cool temperate climatic zone of the northern hemisphere
Flowering was observed in the Maria Curie-Skłodowska University Botanical Garden in Lublin and it involved eight taxa (Table 1 and Fig. 1)
There were A. glutinosa naturally growing in the humid valley of the Garden and A. incana introduced as seedlings into the Garden from the Bieszczady Mountains
Summary
35 Alnus species are known to occur primarily in the cool temperate climatic zone of the northern hemisphere. In the wild, they are found in humid forests, along streams, in river valleys and on the shores of lakes, ponds, and other water bodies. They are found in humid forests, along streams, in river valleys and on the shores of lakes, ponds, and other water bodies They are monoecious, dioecious, anemophilous trees or shrubs. Male inflorescences are clustered in pendulous cylindrical inflorescences – catkins (Szafer et al 1986; Seneta and Dolatowski, 2008). They are formed in the summer of the year preceding flowering (Rodkiewicz et al 1996). One stamen produces an average of 8,420 pollen grains, whereas one inflorescence 19,534,000. Alder pollen grains are classified as small; they mostly have 5, sometimes 4 or 6 pores with the characteristic
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