Impact of autopolyploidy on leaf structure and photosynthesis in Saxifraga oppositifolia L.

Abstract

Polyploidization can be a rapid path to speciation and is considered an important evolutionary mechanism. Some predict that all plants have undergone a polyploidization event during their evolutionary history, and the frequency of polyploid species increases with latitude. The Arctic-Alpine Saxifraga oppositifolia, an autopolyploid, has two polyploids that have successfully established themselves in the high Arctic archipelago of Svalbard, Norway. It can be found in a growth form gradient spanning from prostrate form to dense cushions. This gradient, as well as differences in habitat preferences and reproductive strategy have later been linked to its polyploid nature. As the most likely route for polyploid long-term establishment is linked to niche differentiation, I investigated several plant physiological traits both in in situ and in vivo settings to gain an insight into its success story, but also provide insight into the effect of autopolyploidization and the psychological effects of polyploidy. Two under-researched aspects of polyploidization. In general, polyploids can be seen to have higher photosynthetic rates and stress tolerance and previous studies on S. oppositifolia would suggest that its polyploids have higher rate of growth and photosynthesis. I hypothesized that polyploids displayed physiological characteristics related to this. In this study I found polyploids to have higher leaf mass per area (LMA) than diploids. Tetraploids showed weak evidence of higher efficiency of photosystem II (PSII) through the proxy measurement of electron transfer rate, and higher stress tolerances through higher efficiency of non-photochemical quenching (NPQ). Nitrogen-to-carbon content did not change with polyploidy, but leaf relative water content could be influenced by polyploidy. As higher PSII efficiency was only seen in measurements in tetraploid re-rooted cuttings of S.oppositifolia, I suggest that this efficiency increase is an adaptation to quickly grow to successfully establish themselves as a new individuals. The higher LMA seen in both polyploids, and higher NPQ seen in the tetraploid, are linked to higher stress tolerances, probably related to drought stress.