Institute of Ecology, Ecosystem Functions, Leuphana University of Lüneburg, Lüneburg, Germany.
Agroecology, DNPW, University of Göttingen, Göttingen, Germany.
Plant Biol (Stuttg). 2022 Jan;24(1):134-144. doi: 10.1111/plb.13343. Epub 2021 Oct 7.
Floral nectar is considered the most important floral reward for attracting pollinators. It contains large amounts of carbohydrates besides variable concentrations of amino acids and thus represents an important food source for many pollinators. Its nutrient content and composition can, however, strongly vary within and between plant species. The factors driving this variation in nectar quality are still largely unclear. We investigated factors underlying interspecific variation in macronutrient composition of floral nectar in 34 different grassland plant species. Specifically, we tested for correlations between the phylogenetic relatedness and morphology of plants and the carbohydrate (C) and total amino acid (AA) composition and C:AA ratios of nectar. We found that compositions of carbohydrates and (essential) amino acids as well as C:AA ratios in nectar varied significantly within and between plant species. They showed no clear phylogenetic signal. Moreover, variation in carbohydrate composition was related to family-specific structural characteristics and combinations of morphological traits. Plants with nectar-exposing flowers, bowl- or parabolic-shaped flowers, as often found in the Apiaceae and Asteraceae, had nectar with higher proportions of hexoses, indicating a selective pressure to decelerate evaporation by increasing nectar osmolality. Our study suggests that variation in nectar nutrient composition is, among others, affected by family-specific combinations of morphological traits. However, even within species, variation in nectar quality is high. As nectar quality can strongly affect visitation patterns of pollinators and thus pollination success, this intra- and interspecific variation requires more studies to fully elucidate the underlying causes and the consequences for pollinator behaviour.
花卉蜜液被认为是吸引传粉者最重要的花卉报酬。它除了含有可变浓度的氨基酸外，还含有大量的碳水化合物，因此是许多传粉媒介的重要食物来源。然而，其营养成分和组成在植物物种内和之间可能会有很大的差异。导致花蜜质量变化的因素在很大程度上仍不清楚。我们研究了 34 种不同草原植物物种中花卉蜜液宏量营养素组成的种间变异的因素。具体来说，我们测试了植物的系统发育亲缘关系和形态与碳水化合物 (C) 和总氨基酸 (AA) 组成以及蜜液 C:AA 比之间的相关性。我们发现，花蜜中的碳水化合物和 (必需) 氨基酸组成以及 C:AA 比在种内和种间都有显著差异。它们没有明显的系统发育信号。此外，碳水化合物组成的变化与科特异性的结构特征和形态特征的组合有关。具有暴露花蜜的花朵、碗状或抛物状花朵的植物，如伞形科和菊科中常见的花朵，其花蜜中含有更高比例的己糖，表明通过增加花蜜渗透压来减缓蒸发的选择性压力。我们的研究表明，花蜜营养成分的变化除其他外，还受到科特异性的形态特征组合的影响。然而，即使在同种内，花蜜质量的变化也很大。由于花蜜质量会强烈影响传粉者的访问模式，从而影响传粉的成功率，因此这种种内和种间的变异需要更多的研究来充分阐明其潜在原因及其对传粉者行为的影响。
