In this study, we investigated the nectar of twelve native plant species. Our focus was the quantity of nectar secretion and its chemical composition (sugars, amino acids, and phenolic compounds). We further examined the influence of diurnal variation on nectar production, as well as the effects of abiotic factors, including air and soil temperature, soil and air humidity, and UVB radiation. Nectar samples were collected using both the capillary method and flower washing under natural field conditions in Ljubljana and its surroundings. We evaluated the reliability and applicability of both sampling techniques for flowers of varying corolla depths and determined that the capillary method is generally more reliable, with certain limitations in shallow flowers. Our results indicate that the time of day significantly affects both the quantity of nectar secreted and the concentrations of compunds. All examined abiotic factors were also found to influence nectar secretion and, to some extent, the concentration of individual compounds. Additionally, we observed species- and family-level differences in nectar composition, with the most pronounced variation observed in nectar secretion rates, which were largely driven by diurnal and abiotic factors. Based on these findings, we can infer which plant species represent more valuable forage for pollinators.
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