Bożena Denisow
Pollen production of selected ruderal plant species in the Lublin area
Introduction. As a consequence of multi-directional civilization changes the diversity and population size of wild Apoidea pollinators and the number of honey bee colonies have drastically declined [Banaszak 1983, 1995, Pawlikowski and Celary 2006, Moroń et al. 2009, Topolska et al. 2010]. Among others the possible reason for decline is the transformation of forage flora and the deficiencies of pollen resources. The lack of comprehensive studies on the usefulness of synanthropic vegetation for pollinators, caused the decision: 1) to determine the pollen production of the species and the total pollen yield from the patches of the distinguished phytocoenoses, including the effect of the dynamics of vegetation on variations in pollen forage between growing seasons; 2) to evaluate (based on the phenology of flowering and pollen output) the seasonal distribution of pollen resources in the ruderal patches; 3) to investigate factors affecting the pollen amount in anthers and flowers; 4) to verify, whether and to what extent, the amount of pollen provided and the selected qualitative characteristics of pollen influenced pollinator preferences and the composition of pollinators.
Material and methods. The studies were carried out in 2002–2006 in Lublin, in south eastern Poland. The location of 14 study sites is given in Fig. 1. The detailed study on flowering biology, pollen production and the pollinator preferences covered 66 plant species of the angiosperms (Angiospermae = Magnoliophytina), from the dicotyledonous class (Dicotyledoneae). The phytocoenoses were distinguished according to the Braun-Blanquet method [1964]. Pollen production was determined using the method of Warakomska [1972], modified by Szklanowska [1995]. The homogeneity of the plant species in relation to the plant-pollinator connections was evaluated by Ward’s dendrite method, with the Euclidean distance as a measure of similarity [Caliński and Harabasz 1974].
Results.Ruderal phytocoenoses represent different phytosociological classes and succession stages (Tab. 3). This determines their floristic diversity, the diversity of pollen sources and the total pollen yield. 
The flowering season for forage species in the ruderal flora lasts from April until the middle of October (Tabs 4, 5, Fig. 2). The main factors determining the mass of pollen produced in flowers include anther size, the proportion of pollen in anther biomass, pollen viability and the number of anthers developed in flowers (Fig. 4, Tabs 8, 11). The productivity of the archesporial tissue shows phylogenetic correlations and it ranges from 9.42 (Euphorbiaceae) to 54.62% (Resedaceae) (Tabs 7, 8). The mass of pollen produced in anthers significantly depends on environmental factors (Tab. 9). The flowers of Papaver rhoeas (77.7 mg of pollen per 10 flowers) and the capitula of Onopordum acanthium (49.5 mg per inflorescence) were characterised by the highest pollen production (Tab. 10).
Depending on the year and phytocoenosis, the total annual pollen resources of ruderal patches may range from 45.3 (Bunietum orientalis) to 590.2 kg·ha-1 (community with Cenaturea scabiosa) (Fig. 7). The spectrum of flowering of the ruderal flora affects the seasonal distribution of pollen forage. Early spring pollen forage is provided by few perennial herbaceous species and trees (Tab. 4). This is short-term forage, and the pollen resources of the patches are small – a mean ranged from 0.7 to 7.9 kg·ha-1 (Tab. 13, Fig. 8). The maximum pollen flow occurs from the first decade of June until the end of July when the flowering periods of most of species overlap. In the early summer period the mean pollen yield of ruderal patches is 41.6 kg·ha-1, in the full summer period – 83.1 kg·ha-1, and in the late summer period – 34.9 kg·ha-1.
The input of particular taxa into the total pollen resources of the phytocoenoses depends both on the species frequency of occurrence and pollen production. The representatives of Asteraceae provide the main mass of pollen (ca. 40% of total), most of them are perennials; as much as 15% of the total pollen amount is provided by Papaveraceae members, in spite of their low frequency, due to their high pollen yield (mean = 109.8 kg·ha-1); a major contribution is also provided by the representatives of Fabaceae and Brassicaceae (Fig. 9).   
The pollen of the ruderal species is generally a good source of protein (mean = 26.8%) (Tabs 14, 15). The protein content ranging from 15.0% (Polygonaceae) to 48.5% (Scrophulariaceae) does not affect foraging preferences of pollinating insects. The presence of starch in pollen grains influences the foraging preferences of pollinators (Tab. 16). Solitary bees, Diptera and Syrphidae eagerly visit the plant species which contain starch in pollen grains, whereas species of the genus Bombus avoid starchy pollen. Pollen is not an important source of energy for Apis mellifera, either.The honey beeshows significant preferences to the plant species with an even small amount of pollen produced in flowers, compensated by an abundance of flowers resulting in a high pollen yield per unit area over a short period of time (Figs 10, 11, 12). Other Apoidea also eagerly collect pollen forage when the species bloom less abundantly and their pollen yield is low. Generally, at the ruderal sites the food spectrum of the Apoidea includes ca. 98% of dicotyledonous species. 
Conclusion. The obtained results may be of practical importance when selecting species intended for the enrichment of bee pastures. Tussilago farfaraPrunus spinosaCardaria drabaBerteroa incanaRorippa austriacaMelilotus albaPapaver rhoeasCentaurea cyanus, C. scabiosa, Onopordum acanthiumOriganum vulgare, Solidago giganteaS. canadensis and Helianthus tuberosus, among others, belong to the species of ruderal habitats which show good prospects for improvement of the pollen base around apiaries. They combine both appropriate time of flowering in the season and a high pollen yield (from 29.7 to 202.5 kg·ha-1) as well as the high intensity of Apis mellifera foraging activity and a concurrent presence of pollen collectors on flowers.  
In conclusion, pollen forage for wild bee pastures can be enriched by recommending most of the species of the ruderal habitats. However, the propagation of invasive species, e.g. Bunias orientalisSolidago canadensis and S. gigantea, should be avoided in natural and semi-natural habitats, in spite of the fact that they provide attractive pollen forage to the Apoidea.