Divergent seed production responses of white and blue flowers of Gentiana leucomelaena (Gentianaceae) to warming and watering

Abstract

Background: The adaptation, evolution and function of flower colour diversity in response to changing environments are one of the oldest puzzles in plant ecology. It is logical that comparative studies on fitness of flower colour would be the most meaningful if they were conducted on the same genotype. Aims: We used Gentiana leucomelaena, which produces both white and blue flowers on different tillers of the same individual, as a model species to test adaption and fitness differences of contrasting flowers in contrasting environments. Methods: We examined seed production by white and blue flowers in response to increased temperatures (28 °C/2 °C vs. 12 °C/2 °C; 12 h light/12 h dark) in a climate chamber study and to watering in the field (+1.5 l m−2 d−1 vs. control with no supplementary irrigation). Results: For white and blue flowers warming decreased but watering increased seed number. Increased temperature and watering increased the size of seeds from white flowers, but neither warming nor watering significantly changed seed size of blue flowers. Seed size was significantly negatively correlated with seed number in the temperature treatments but positively correlated in watering treatments. The positive correlation was strong in white flowers, but the negative correlation was stronger in blue than in white flowers. Conclusions: Water availability and low temperature confer an advantage to white flowers, while warming and dry habitats favour blue flowers. These divergent responses may influence total plant fitness and thus help explain the adaptive value and evolution of flower colour diversity.