Polyploidy (the state of having more than two genome copies) is widely distributed in flowering plants and can vary within species, with polyploid races often associated with broad ecological tolerances. Polyploidy may influence within-species variation in seed development, germination and establishment. We hypothesized that interactions between polyploidy and the seed developmental environment would affect subsequent dormancy, germination and early growth traits, particularly in stressful environments.• Using seeds developed in a common garden under ambient and warmed conditions, we conducted germination trials under drought and temperature stress, and monitored the subsequent growth of seedlings. The study species, Themeda triandra, is a widespread, keystone, Australian native grass and a known polyploid complex.• Tetraploid plants produced heavier, more viable seeds than diploids. Tetraploids were significantly more dormant than diploids, regardless of seed developmental environment. Non-dormant tetraploids were more sensitive to germination stress compared to non-dormant diploids. Finally, tetraploid seedlings were larger and grew faster than diploids, usually when maternal plants were exposed to developmental temperatures atypical to the source environment.• Seed and seedling traits suggest tetraploids are generally better adapted to stressful environments than diploids. Because tetraploid seeds of T. triandra are more dormant they are less likely to germinate under stress, and when they do germinate, seedling growth is rapid and independent of seed developmental environment. These novel results demonstrate that polyploidy, sometimes in interaction with developmental environment and possibly also asexuality, can have within-species variation in seed and seedling traits that increase fitness in stressful environments.Plant Biology 22 (2020) 500-513
Context Australia’s tropical montane cloud forests (TMCF) exhibit exceptional species richness and endemism. Determinants of regeneration via seed of these species are next to unknown, limiting our ability to quantify and project their vulnerability to climate change. The ratio of red to far-red light (R:FR) has been shown to influence seed germination of many tropical species. Aims We investigated germination of six previously unstudied TMCF species in relation to the presence or absence of light (light/dark) and light quality (R:FR). We hypothesised that increased R:FR would lead to increased germination and that small-seeded species would be more likely to have a light requirement and be less sensitive to R:FR compared to larger-seeded species. Methods Sunlight and polyester filters were used to create a gradient of R:FR ranging from 0.1 to 1.14. Seeds were also sown in constant darkness. Key results Across species we saw varying germination responses. Three of the four smallest-seeded species exhibited an absolute light requirement for germination and did not discriminate between different R:FR. Germination of the small-seeded TMCF endemic Dracophyllum increased exponentially with increasing R:FR. Germination of the largest-seeded species was inhibited by both low and high R:FR, and germination was higher in constant darkness than diurnal light/dark. All six species were able to germinate at remarkably low R:FR values. Conclusions Light affects seed germination of Australia’s TMCF plant species in a variety of ways. Implications The findings of this study provide insights into plant recruitment in situ, and the acclimation potential of these species under reduced R:FR predicted for the future.
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