Nectar and pollen production in Arabis procurrens Waldst. & Kit. and Iberis sempervirens L. (Brassicaceae)

Ecological environment in urban areas is specific in many aspects. There are evidences that ornamental plants cultivated in local urban gardens may help in conservation of pollinators. In this study, the flowering pattern, the abundance of flowering, nectar and pollen production as well as insect visitation in Arabis procurrens Waldst. & Kit. and Iberis sempervirens L. were investigated. The species were grown in the UMCS Botanical Garden in Lublin, southeastern Poland. Arabis procurrens bloomed from the middle of April until middle of May and I. sempervirens from the end of April until middle of June. In both species, most flowers opened in the morning hours (40–45% of total were opened by 8:00 h GMT + 2 h). The average sugar yield of A. procurrens was ca. 53% lower compared to I. sempervirens (mean = 1.08 g/m2 and 2.32 g/m2, respectively). In both species, considerable differences in the amount of produced sugars were noted between years. The mass of pollen produced in the flowers of A. procurrens was approx. 35% lower compared to that of I. sempervirens (mean = 0.06 mg and 0.09 mg per flower, respectively). Pollen produced per unit area was correlated with the number of flowers. On average, the species produced 1.46 g (A. procurrens) and 2.54 g (I. sempervirens) of pollen per 1 m2. The flowers of A. procurrens attracted mainly dipterans (56.3% of total visitors), while I. sempervirens lured chiefly solitary bees (47.4% of total visitors), however in both cases, honeybees, bumblebees and lepidopterans were also recorded. The A. procurrens and I. sempervirens due to flowering in early spring period may be promoted for use in small gardens (rock or pot gardens) for both aesthetic value and as plants that support insect visitors in nectar and pollen rewards.