植物-环境间的长期相互作用驱动着植物表型及次生代谢物的变异。随着海拔梯度的变化, 环境中的非生物因子会发生变化, 但它们如何影响植物的表型以及次生代谢物的组成和含量, 以及植物不同组织器官的次生代谢物是否存在差异, 目前有关这方面的研究还较少。本文选取3个不同海拔中的柳条杜鹃(Rhododendron virgatum)和大白杜鹃(R. decorum) (大理苍山居群)及红棕杜鹃(R. rubiginosum) (老君山居群)为研究对象, 测定不同海拔的环境因子(温度、相对湿度和相对光照强度), 测量和分析了不同海拔植物的表型性状, 花蜜体积、糖浓度及花蜜中糖成分(HPLC分析方法), 以及植株的茎、叶、花瓣、花粉、花蜜中次生代谢物组成及含量(UPLC-Qtof分析法)。结果表明: 随着海拔升高, 温度、相对湿度和相对光照强度降低, 杜鹃的植株高度、花冠大小和花药体积显著减小, 而枝条直径、雌蕊和雄蕊长度显著增大。3种杜鹃在海拔C的花蜜体积和糖浓度均显著高于海拔A和海拔B, 海拔C中花蜜的蔗糖成分也显著增多。杜鹃属植物主要含黄酮类、甾体类、苯丙素类、萜类和生物碱类等次生代谢物, 随着海拔的变化, 这5类次生代谢物质的相对含量没有显著变异, 但是它们两两之间存在显著的相关性。杜鹃属植物不同组织中次生代谢物的含量有明显差异, 整体来说, 花粉和花蜜中次生代谢物的种类和含量要显著低于其他组织。主成分分析结果显示, 海拔A和海拔B中杜鹃的表型和化学特征比较相似, 海拔C杜鹃的黄酮类物质组成和含量与海拔A和海拔B具有显著差异。本研究表明, 随着海拔及其环境因子的变化, 杜鹃属植物的表型特征和化学性状都存在一定程度的适应性变异, 但表型特征的变异程度远大于次生代谢物的组成和相对含量。相对于植物内在的次生代谢物, 环境因子的差异更容易影响植物的表型特征。

Aims: Interactions between plants and the environment drive the diversity of plant phenotypes and secondary metabolites. Abiotic factors in the environment are known to vary with altitude, but it remains unclear how this variation affects plant characters and secondary metabolite composition, including whether secondary metabolites differ among different tissues and organs within a plant.

Methods: We took samples of Rhododendron virgatum, R. decorum, and R. rubiginosum from three different altitudes. We measured environmental factors at each altitude, including temperature, relative humidity, and relative light intensity. We also measured vegetative traits, characteristics of plants’ reproductive organs, and nectar features (nectar volume, sugar concentration, nectar components). We used UPLC-Qtof methods to analyze the levels and composition of secondary metabolites in the stems, leaves, petals, pollen, and nectar of populations from different altitudes.

Results: As altitude increased, the temperature, relative humidity, and relative light intensity decreased. The heights, corolla sizes, and anther volumes of the sampled plants decreased significantly, while the branch diameters and pistil and stamen lengths increased significantly. The floral nectar volume and sugar concentration at the highest altitude (altitude C) were significantly higher than at altitudes A and B, the lowest and middle altitudes. The nectar sucrose content in Rhododendron was also significantly higher at altitude C than at the lower altitudes. The secondary metabolites of the Rhododendron samples did not differ significantly at different altitudes—at every altitude, the plants were dominant in flavonoids, steroids, terpenoids, phenylpropanoids, and alkaloids, and there were significant correlations among these components. However, the secondary metabolites did vary between different organs of the plants: nectar and pollen had significantly lower levels of metabolites than branches, leaves, and petals. Additionally, PCA results showed that Rhododendron plants at altitudes A and B were relatively similar in character and metabolites. It also revealed that the flavonoid components of plants at altitude C were different from those at altitudes A and B.

Conclusion: Our results reveal a degree of adaptive variation in phenotypic characteristics and metabolite composition of Rhododendron plants at different altitudes. However, phenotypic traits vary much more than the composition and relative contents of secondary metabolites. We conclude that environmental factors present at different altitudes are much more likely to shape the external characteristics of plants than to change their internal metabolic profile.