Polyploidy Improves Photosynthesis Regulation Within The Ranunculus Auricomus Complex (Ranunculaceae)

Simple Summary Genome duplication or multiplication, polyploidy, has contributed substantially to the evolutionary success of plants. Polyploidy is often connected to a higher resilience to environmental stress. We have chosen the goldilocks, the Ranunculus auricomus complex, to study effects of light stress. In this species complex, diploid (2x), tetraploid (4x), and hexaploid (6x) cytotypes occur in Central Europe in both shaded and sun-exposed habitats. In this study, we exposed them to different photoperiods in climate growth chambers to explore how the efficiency of photosynthesis varied between the various ploidies (2x, 4x, and 6x). We used fluorescence experiments exploring the proportion of light that is captured for photosynthesis and the resulting energy fluxes. In addition, quenching coefficients can be calculated that inform about the capability of a plant to deal with excess light. We found that the polyploids can quench excess light better, which concurs with their adaptation to open habitats and their predominantly asexual mode of reproduction that is probably favored by low stress levels in the reproductive tissues. Polyploidy has substantially contributed to successful plant evolution, and is often connected to a higher resilience to environmental stress. We test the hypothesis that polyploids tolerate light stress better than diploids. The Ranunculus auricomus complex comprises diploid (2x), tetraploid (4x), and hexaploid (6x) cytotypes, the former of which occur in shaded habitats and the latter more in open, sun-exposed habitats in Central Europe. In this study, we experimentally explored the effects of ploidy and photoperiod extension on the efficiency of photosystem II in the three cytotypes in climate growth chambers. Quantum yields and various coefficients that can be calculated from light curve, Kautsky curve, and fluorescent transient OJIP experiments provided support for the hypothesis that, in comparison to diploids, the improved regulation of excess light by more efficient photochemical and non-chemical quenching in polyploids might have facilitated the adaptation to unshaded habitats. We suggest how lower stress levels in reproductive tissues of polyploids might have favored asexual reproduction.