DOI: 10.2478/jas-2013-0021 J. APIC. SCI. Vol. 57 No. 2 2013 J. APIC. SCI. Vol. 57 No. 2 2013 Original Article Flowering dynamics and pollen production oF laburnum anagyroides med. under the conditions oF south-eastern poland Ernest Stawiarz Anna Wróblewska University of Life Sciences in Lublin, Department of Botany, Akademicka 15, 20-950 Lublin, Poland *corresponding author: [email protected] Received: 08 April 2013; accepted 05 November 2013 a b s t r a c t a study on the flowering biology and pollen production of the common laburnum (laburnum anagyroides med.) was conducted under the conditions of lublin during the period 2004 - 2006. the flowering of this species began in the second 10-day period of may and lasted for 2.5 - 4 weeks. the flowers of common laburnum are borne in showy golden-yellow pendulous racemes. they develop successively, starting from the base and moving to the tip of an inflorescence. during the growing season, one shrub produces 800 to 3200 racemes, with 14 to 35 flowers in a single raceme. on average, the flowering duration for a raceme was 12.8 days and 8.7 days for a single flower. throughout the study years, the shrubs proved to be most attractive in the third 10-day period of may when they reached full bloom. the average weight of pollen produced was 6.08 mg per 10 flowers of laburnum anagyroides, 14.02 mg per raceme, and 26.0 g per shrub. pollen grains reached average dimensions of 24.01 µm × 24.26 µm. Keywords: flowering, laburnum anagyroides, pollen forage, pollen grain morphology. INTRODUCTION Numerous studies conducted in different countries relate to the poisonous and medicinal The genus Laburnum comprises four species properties of this taxon (Greinwald et al. 1990; of low trees or shrubs of the family Fabaceae, Szentesi and Wink, 1991). subfamily Faboideae, tribe Genisteae (Lewis In a few papers, Laburnum anagyroides is and Schrire, 2003; Wojciechowski, 2003). In the mentioned as a species that can be used in wild, they are found in western Poland as well beekeeping (Bodnarčuk et al. 1993; Pritsch, as in central and south-western Europe, and in 2007; Kozłowski et al. 2011). Its entomophilous Central Asia (Scheller, 1974; Krüssmann, 1984; flowers, devoid of nectaries, only provide floral Pritsch, 2007; Johnson and More, 2009; Seneta pollen to bees (Szklanowska and Dąbska, 1993; and Dolatowski, 2012; Tokarska-Guzik et al. Lipiński, 2010). This raw material is a source of 2012). protein food for insects, and its abundance near The common laburnum (Laburnum anagyroides an apiary is necessary in the spring during the Med. also known as Cytisus laburnum L.) is development of bee families. often planted in many European countries as The aim of the present study was first, to an attractive ornamental species intended for determine the time, dynamics and abundance park plantings as well as for gardens and slopes of flowering of Laburnum anagyroides under (Bodnarčuk et al. 1993; Wasson, 2001; Pritsch, the conditions of Lublin; second, to estimate the 2007; Tokarska-Guzik et al. 2012). In the British weight of floral pollen as a source of forage for Isles, this species was also grown in the past for insects; and third, to determine the morphologi- wood fuel and was commonly used as a hedge cal characteristics of pollen grains, which can be plant (Chater, 1992; Johnson and More, 2009). useful for their identification in bee products. 103 stawiarz and Wroblewska Flowering and Pollen production of Laburnum anagyroides MATERIAL and methods flowering stage, morphological measurements of the flowers were made, including their length Flowering observations and width, the dimensions of petals measured The study on flowering and flower production from the base to the tip of the corolla, and the of the common laburnum (Laburnum anagy- dimensions of the banner. roides Med.) was conducted in urban plantings in Lublin (51°14’ N and 22°34’ E), Poland, during investigation of the rate of pollen release the period 2004 - 2006. The flowering duration and pollen morphological characters of this taxon as well as its inflorescences Pollen production of this species was studied and flowers was determined. Flowering time using ether extraction and weight measure- was defined as the number of days from the ment following the modified method described beginning of flowering to the end of flowering, by Warakomska (1972). Mature stamens, and was measured on the same several-year- just before anther dehiscence, were sampled old shrubs in the successive years. Detailed separately for the flowers located at the base, observations of the flowering dynamics of this in the middle part, and in the apical part of the species were carried out over two growing inflorescence. Anther heads from 10 flowers seasons (in the period 2004 - 2005). They (100 stamens) were placed on individual watch were started when the first flower appeared glasses in 6 replications for each region of the on the shrubs and were continued until the last inflorescence. Anthers on the glasses were flowers faded. Observations of the flowering dried in a drying oven at a temperature of 30oC. pattern were recorded every day according to The pollen released from the anthers was first the recommendations of Łukasiewicz (1984). washed with 70% alcohol then washed several The following flower development stages were times with ether until the pollen grains were recorded: beginning of flowering, that is, when completely washed out of the anthers, which the first flowers open; full flowering when was carefully checked with a MSZ 200T ster- 50 - 75% of the flowers are in bloom; and eoscopic microscope. After the pollen grains the end of flowering when nearly 100% of the were completely washed out and the anther flowers had faded. walls were removed, the glasses with pollen The flowering of inflorescences was observed were weighed and pollen production per flower, at full bloom of the taxon in each year of the raceme, and shrub were calculated. study on 10 randomly selected racemes located The extracted pollen was used to prepare glyc- on different shrubs. Each day, the number of erol-gelatin coated microscope slides. The pollen open flowers on the flowering racemes was sampled from the flowers located at the base, determined on individual days of bloom. the middle part, and the apical parts of the in- The flowering duration of single flowers was -in florescence were fixed on separate slides. Two vestigated several times during the successive replications for each region of the inflorescence seasons under varying weather conditions. The were done. Subsequently, measurements of observations were started at bud burst, and the pollen grains were taken to determine the bud development was observed until petal fall. length of their polar and equatorial axes using The particular stages of flower development a Nikon Eclipse E 600 light microscope at were recorded using the phenological signs of a magnification of 40 × 15. Fifty pollen grains Krotoska (1958). These were as follows: bud were measured on each slide. stage, beginning of flowering, full flowering, and Statistical analysis of the study results was end of flowering. performed based on analysis of variance Measurements of the inflorescence rachis (ANOVA) and Tukey’s multiple t-tests at a signif- length were made and the number of flowers icance level of α = 0.05. Calculations were done per inflorescence was determined. At full using Statistica 6.0 software. 104 of of Under the conditions of Lublin, the biology flowering Flowering RESULTS Table 1. this season, the shrubs blossomed the flowering earliest (10 May). During period was the study, of the year In the first 2.5 - 4 weeks. the second 10-day period of May and lasted for Flowering of Laburnum anagyroides under the conditions in Lublin Laburnum Flowering Inflorescence length Number of flowers Length of flowering (days) Year time (cm) in inflorescence Flower Inflorescence (days) anagyroides Mean ± SD Range Mean ± SD Range Mean ± SD Range Mean ± SD Range 10.05 - 07.06 2004 13.9 ± 2.86a 9 - 18 27.8 ± 5.14b 18 - 35 10.8 ± 2.66c 7 - 13 16.2 ± 1.93c 14 - 20 (29) 15.05 - 02.06 a a a a 2005 16.7 ± 4.22 9 - 23 21.7 ± 4.45 14 - 28 6.4 ± 0.97 5 - 8 8.5 ± 0.71 7 - 9 started during the (19) 19.05 - 11.06 2006 16.3 ± 2.36a 13 - 19 22.9 ± 6.15ab 14 - 33 8.8 ± 1.03b 8 - 10 13.8 ± 1.13b 12 - 16 (24) Mean - 15.6 - 24.1 - 8.7 - 12.8 - Abbreviations: SD - standard deviation. Mean values in column followed by the same letter do not differ significantly atα ≤0.05. Table 2. pendulous delicate, very loose, golden-yellow, in borne are laburnum common the of flowers The (Fig. 1). occurred during the first 10-day periodof June 10-day period of May and the end of flowering The shrubs reached full bloom during the third 19 days in 2005 and 24 days in 2006 1). (Tab. flowering time was shorter, with a durationof longest, lasting 29 days. In the next years, the Mean air temperatures and total rainfall during the decade of the study period relative to the long-term means 2004 2005 2006 Meteorological Month Decade Decade Decade 1951 - 2005 factor Mean Mean Mean I II III I II III I II III April 5.2 8.8 9.8 7.9 9.0 10.9 7.4 9.1 6.2 7.7 12.3 8.7 7.4 J. APIC.SCI.Vol.57No.22013 Temperature May 13.6 10.8 11.4 11.9 10.8 10.5 18.0 13.1 13.5 14.6 12.8 13.6 13.0 (oC) June 15.7 15.8 16.1 15.8 13.4 17.2 17.4 16.0 11.6 17.9 21.1 16.9 16.2 April 24.6 10.4 3.1 38.1 0.2 4.0 14.4 18.6 19.4 10.5 0.4 30.3 40.2 Precipitation May 10.1 11.3 16.6 38.0 32.8 65.0 0.2 98.0 9.0 18.4 32.2 59.5 57.7 (mm) June 3.7 25.9 20.3 49.9 47.1 7.4 1.4 55.9 28.4 0.0 9.5 37.9 65.7 105 stawiarz and Wroblewska Flowering and Pollen production of Laburnum anagyroides 200 180 2004 2005 160 140 120 100 80 60 Number of flowering racemes per shrub shrub per racemes flowering Numberof 40 20 0 8 10 12 14 16 18 20 22 24 26 28 30 1 3 5 7 May June Fig.