FLOWERING PHENOLOGY AND POLLEN SEASONS OF Corylus spp . IN LUBLIN ( POLAND ) , 2008-2011

In the years 2008-2011, phenological observations of flowering of male inflorescences were carried out in seven taxa from the genus Corylus: C. americana, C. avellana, C. avellana ‘Contorta’, C. avellana ‘Pendula’, C. × colurnoides, C. cornuta, C. maxima, grown in the Maria Curie-Skłodowska University Botanical Garden in Lublin. Simultaneously, the hazel pollen seasons in the atmosphere of Lublin were analysed using a Durham sampler. The aim of the work was to assess the flowering in seven Corylus taxa in relation to selected meteorological elements and to describe the pollen seasons in the years 2008-2011. During the study years, the annual phenological cycles in the studied Corylus taxa differed markedly in terms of timing of the onset of the successive flowering phases. During the four years of observations, the earliest beginning of hazel flowering was found at the end of January, whereas the latest – at the end of March. The earliest full bloom took place in the first decade of February, and the latest – in the first decade of April. The end of flowering was reported in February or in the first or second decade of April. Each year, C. avellana was the first to produce flowers and it was subsequently followed by C. americana, C. × colurnoides, C. maxima, C. avellana ‘Pendula’, C. avellana ‘Contorta’, and C. cornuta. The pollen seasons in the study period began at the end of January, in the second decade of February, or in the first decade of March. The end of the pollen seasons most frequently took place in the first or second decade of April. The length of the pollen seasons ranged from 38 to 49 days, while the length of the flowering periods in the individual taxa was 22 days on average. During the four study years, the onset of flowering in C. avellana and the beginning of the pollen season coincided on the same day, whereas the onset of flowering in the other taxa was usually reported after the beginning of the pollen seasons. The flowering period of C. avellana ‘Contorta’ and C. cornuta lasted from 5 to 16 days after the pollen season. The development of inflorescences was most closely related to maximum temperature and relative air humidity.


INTRODUCTION
Phenological studies are employed in many branches of natural sciences and widely applied in practice.Records of the dynamics of seasonal changes occurring in the plant or animal world are used in environmental sciences for studying the interactions between living organisms and their environment.Phenology is also an important branch of science for meteorological research, especially in climatology and biometeorology.Phenological events may serve as good indicators in assessment of potential trends in climate change, which is important in various branches of eco- Corylus avellana is a characteristic plant for the early spring growing period.Hazel plants in Poland bloom at the turn of February and March.Male inflorescences are clustered in pendulous cylindrical inflorescences -catkins (S z a f e r et al. 1986).During flowering, the inflorescence axis becomes elongated, thereby making the flowers less compact, which facilitates pollen release from the anther.One inflorescence comprising on average 240 flowers releases approximately 8 736 000 pollen grains sized 24.6 × 22.0 μm The aim of the work was to assess flowering in seven Corylus taxa grown in the Maria Curie-Skłodowska University Botanical Garden in Lublin in the years 2008-2011 in relation to selected meteorological elements and to describe the pollen seasons.The results obtained may be helpful in cultivation of hazel nuts (C.avellana) and their ornamental varieties as well as in acclimation of foreign taxa.Additionally, they may facilitate answering the question whether the prevailing climatic conditions are suitable for cultivation of these plants in our country.

Flowering phenophases
The phenological observations of flowering were carried out on seven Corylus taxa grown in the Maria Curie-Skłodowska University Botanical Garden in Lublin in the years 2008-2011.1).The study specimens grow amongst trees and shrubs in insolated localities in the north-eastern part of the garden.The distances between them range from 20 to 400 m (Fig. 1).All the specimens were adult (Table 1), in good condition, and fully acclimatized.The plants were identified in accordance with the papers of K r ü s s m a n n (1976), R e h d e r (1977), W a l t e r s (1980), S e n e t a and D o l a t o w s k i (2008).
The phenological observations of the flowering stages of the seven Corylus taxa were carried out twice a week between 12.00 and 1.00 p.m. 10 inflorescences in each specimen were observed.The following stages of plant development were assessed: loose inflorescences, flowers with closed anthers (phase 0); inflorescences with a few open pollen-releasing anthers (phase 1); inflorescences with several empty anthers (phase 2); inflorescences with open pollen-releasing anthers and with empty anthers (phase 3); inflorescences with empty anthers only (phase 4).
The flowering onset was defined as a moment when several open anthers in the inflorescence started releasing pollen (phase 1); the period when the majority of anthers in the inflorescence released pollen was regarded as full bloom (phase 2 and 3); the end of flowering was defined as a moment when all anthers were empty (phase 4).
Spearman's analysis was employed to determine the relationships between the dynamics of development of male inflorescences in the seven Corylus taxa and the meteorological conditions: maximum temperature, relative air humidity, maximum wind speed, and precipitation from January to April in the years 2008-2011.Spearman's r correlation coefficients were calculated with the use of the version 7.1 of the STA-TISTICA programme (StatSoft Inc. 2007).The data were obtained from the weather station of the UMCS Institute of Meteorology and Climatology situated 3 km from the sampling site.

Corylus pollen seasons
During the study years, the pollen seasons were identified based on the analysis of pollen fall performed by the gravimetric method using a Durham sampler (D u r h a m , 1964) that was located on a building roof at a height of ca. 5 m in the western part of Lublin (220 m a.s.l.; 51 o 16`N, 22 o 30`E).The building was located in the north-western part of the botanical garden.The surroundings of the garden consist of a compact detached housing area and blocks of flats.The north--western part borders a green belt composed mainly of maple, birch, ash, hazel as well as other ornamental and fruit trees and shrubs.The garden comprises 68 naturally growing several-year-old flowering C. avellana specimens (Fig. 1).The C. avellana species is common in the area of Lublin and Lubelszczyzna (Z a j ą c and Z a j ą c , 2001).The area of Lublin is dominated by west and south-west winds (L o r e n c , 2005).
The pollen fall was expressed as the number of pollen grains •1cm -2 slide collected per two days.The length of the hazel pollen season was determined by the 98% method, which regards the day when 1% of the cumulative annual sum of pollen was recorded as the beginning of the season; in turn, 99% of the recorded pollen denoted the end of the season (E m b e r l i n et al. 1993).

Flowering periods
The average length of male inflorescences in the Corylus taxa observed before flowering was 8-35 mm; C. cornuta exhibited the shortest inflorescences (Table 1 and Fig. 2).During full bloom, the inflorescence axis became elongated by 50% on average (Table 1).During the flowering period, C. americana inflorescences were lemon colour and the others were yellow (Fig. 2).The phenological observation indicates that the timing of the consecutive flowering phases in the selected Corylus taxa is not a constant phenomenon (Table 2 and Fig. 3   who claim that the pollen season begins, on average, 4-18 days after the onset of flowering and continues for even a month after the end of the latter.In general, Corylus pollen grains appear in the air within a few days after the onset of flowering and they remain in the air for several weeks after its end, which is related to long-term transport of pollen from remote regions (Szczepanek, 2003).On average, the highest concentration of airborne pollen was found when the flowering of Corylus began to decrease (R i z z i L o n g o and P i z z u l i n S a u l i , 2010).
During the four years of the study, the date of flowering of hazel and appearance of its pollen in the air were clearly correlated with temperature and relative air humidity.This has been confirmed in investigations conducted by other authors (W i e l g o l a s k i ,

CONCLUSIONS
1.The timing of the phenological events studied, i.e.
the onset of flowering, full bloom, and the end of flowering, was not constant in the selected Corylus taxa.The appearance of the individual flowering phases was dependent on the prevailing thermal and humidity conditions as well as the biological features of the taxa.2. The onset of the Corylus pollen season as well as its length and abundance of airborne pollen grains in Lublin differed considerably between the study years.
nomy (L i e t h , 1974; S o k o ł o w s k a , 1980; K r am e r , 1994; T o m a s z e w s k a and R u t k o w s k i , 1999; M e n z e l et al. 2006; S t u d e r et al. 2007; S c h l e i p et al. 2008).Investigations of flowering phenology facilitate interpretation of aerobiological research results and ensure more precise allergy forecasts.This is especially important in forecasting the concentration of airborne pollen allergens (H ä n n in e n , 1983; L a t t o r e , 1999; J a t o et al. 2002; K as p r z y k , 2003; E s t r e l l a et al. 2006; S t a c h et al. 2006; K a s p r z y k and W a l a n u s , 2007; W er y s z k o -C h m i e l e w s k a et al. 2010).The time of appearance of the characteristic vegetation phases (phenophases), e.g.flowering and unfolding, is closely related to the climate of the study areas.Spring phenophases in the temperate climate zone are dependent on thermal conditions prevailing in the current year and the year preceding flowering (W i e l g o l a s k i , 1999; P u c , 2007; D ą b r o ws k a , 2008; P i o t r o w s k a and K a s z e w s k i , 2009; R i z z i L o n g o and P i z z u l i n S a u l i , 2010; V e r a i a n k a i t et al. 2010; W e r y s z k o --C h m i e l e w s k a et al. 2010; Č r e p i n š e k et al. 2011; Š k v a r e n i n o v á et al. 2011).Phenological phenomena are often modified by individual meteorological elements, e.g.air humidity, solar radiation, draught, and soil properties (K r a m e r , 1994; W i e lg o l a s k i , 1999).

(
2006).In southern Europe, hazel begins flowering the earliest, and in the north of Europe -the latest.In the north-east of Italy, the onset of hazel flowering is recorded in the third decade of January, while the pollen season starts at the turn of January and February (R i z z i L o n g o and P i z z u l i n S a u l i , 2010).In the north-east of Slovenia (Č r e p i n š e k et al. 2011) and northern Croatia (P e t e r n e l et al. 2005), the onset of flowering and pollen release were recorded in the first decade of February.In central Slovakia, hazel begins to flower, on average, on March 2, and the pollen season starts 4 days later (Š k v a r e n i n o v á et al. 2011).In the West Midlands, UK, the pollen season of Corylus begins, on average, in mid-January (E mb e r l i n et al. 2007).In Lithuania, the onset of hazel flowering was recorded at the turn of March and April (V e r a i a n k a i t et al. 2010).In western Norway, in turn, the flowering period starts in the first decade of April (W i e l g o l a s k i , 1999).The results obtained by the above-mentioned authors indicate that the time span between the dates of flowering onset of C. avellana in Europe is 10 weeks.In southern Europe, C. avellana flowering begins at the turn of January and February, in the central part -in early March, and in the north -at the turn of March and April.The results obtained in the present study partly correspond to the data provided by other authors (L a t t o r e , 1999; K a s p r z y k , 2003; P e t e r n e l et al. 2005; E mb e r l i n et al. 2007; Š k v a r e n i n o v á et al. 2011), 1999; P u c , 2007; D ą b r o w s k a , 2008; P i o t r o ws k a and K a s z e w s k i , 2009; R i z z i L o n g o and P i z z u l i n S a u l i , 2010; V e r a i a n k a i t et al. 2010; W e r y s z k o -C h m i e l e w s k a et al. 2010; Č r e p i n š e k et al. 2011; Š k v a r e n i n o v á et al. 2011).The long periods of flowering of the Corylus taxa in 2009 were the consequence of slight frost, which led to a pause followed by re-flowering.In 2010-2011, the meteorological conditions delayed the flowering, which contributed to the shortening of the flowering periods.These phenomena are typical of early spring plants from the temperate climate zone.The modifying effect of meteorological factors on the appearance of successive phenophases has been reported by many authors (W i e l g o l a s k i , 1999; R i z z i L o n g o and P i z z u l i n S a u l i , 2010; V e r a i a n k a i t et al. 2010; W e r y s z k o -C h m i e l e w s k a et al. 2010; Č r e p i n š e k et al. 2011; Š k v a r e n i n o v á et al. 2011).
.). C. avellana.Among the taxa studied, C. avellana was the first to bloom each year.The earliest onset of flowering was recorded on January 26, 2008, and the latest on March 4, 2011.The earliest full bloom period was reported onFebruary 5-11, 2008.In the other study years, full bloom was found between March 20 and 28.The earliest end of flowering was observed on February 22, 2008; during the next three years it took place between April 2 and 6.In 2009 C. avellana flowering was halted by unfavourable weather conditions on February 11 and it was continued on March 3.During the four years of study, C. avellana was characterized by the longest flowering periods lasting from 28 to 58 days (Table2).C. americana.January 26, 2008, was the onset of flowering for both C. americana and C. avellana.In the other years, C. americana bloomed in March.Its earliest full bloom was recorded on February 4-8, 2008, and the latest on March 26-30 in 2009-2010.The earliest end of flowering for this species was recorded on February 18, 2008.In the other years, the end of flowering was recorded in similar periods on April 10 and 13.The length of the flowering periods ranged between 22 and 34 days (Table2).C. × colurnoides.During the four years, the earliest flowering was recorded in 2008 (February 3), and the latest in 2010 (March 23).The earliest full bloom period for this taxon was reported on February 14 and 18, 2008.During the last three years of the study, full bloom was recorded on March 26-31.The length of the longest flowering periods (30 days) was reported during the first two years (Table2).C. maxima.The earliest flowering of C. maxima began on February 14, 2008.That year, the earliest end of flowering was observed as well(March 7, 2008).In the years 2009-2011, the flowering onset was reported between March 14 and 30, and it ended between April 9 and 11 (Table2).C. avellana 'Pendula'.The earliest onset of flowering of this taxon was reported on February 26, 2008.In the other years of the study, the flowering onset was recorded in the second and third decades of March.In 2008 full bloom was recorded at the turn of February and March, and in late March in the other years.The earliest end of flowering was reported on March 17, 2008, whereas in the other years of the study it was recorded in the first decade of April (Table2).C. avellana 'Contorta'.The earliest onset of flowering was recorded on March 13, 2008, and the latest on April 1, 2011.The earliest full bloom was reported on March 27-29, 2008.In the other years, the full bloom period ranged between April 7 and 11.The flowering of this taxon ended in the first or second decade of April (Table2).Geographic distribution and short characteristics of seven Corylus taxa in the collection of the Maria Curie-Skłodowska University Botanical Garden in Lublin.
* The plant has been growing naturally since 1995.

Table 2
Flowering dates of male inflorescences of seven Corylus taxa, with the identification of three phenological phases.Spearman's r correlation coefficients for the growth of male inflorescences of seven Corylus taxa and the weather parameters(2008)(2009)(2010)(2011).