Photosynthetic characteristics of three ploidy levels of Allium oleraceum L. (Amaryllidaceae) differing in ecological amplitude

To elucidate the mechanisms of the adaptive advantages of polyploidy, there is a need to identify physiological traits that participate in the success of polyploids. We studied selected photosynthetic characteristics, stomatal density, and specific leaf area of three ploidy levels (2n = 4x, 5x, 6x) of the geophyte Allium oleraceum that partially differ in their ecological niches. Although the cytotypes were on average similar with regard to most of the measured photosynthetic traits, the hexaploids showed more rapid initial photosynthetic induction and a tendency for a higher maximum photosynthetic rate per unit area. The stomatal density was not affected by ploidy, though the specific leaf area was reduced for the hexaploids compared to the other cytotypes. A lower intracytotype variation was found for most of the studied photosynthetic and anatomical traits for the hexaploids compared to the large variation found within other cytotypes. A comparison of the photosynthetic traits between the cytotypes showed that the ecological differentiation between cytotypes is only weakly related to the characteristics of their photosynthetic apparatus. However, contrasting ranges of variability in the measured traits between the cytotypes can be related to previously observed differences between cytotypes with regard to the ranges of intracytotype genetic variation, genome size variation, and niche breadth. A higher variability of photosynthetic traits in tetraploids and pentaploids may be related to the existence of a spectrum of types adapted to different environmental conditions. Hexaploids may represent a recently formed cytotype adapted to open environmental conditions.