Vivipary, a Reproductive Strategy in Response to Environmental Stress?

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The occurrence of vivipary as a reproductive strategy in arctic and alpine plants is discussed with special reference to the viviparous grasses, and in particular to the ecology of Festuca vivipara (L.) Sm. There are considerable differences between the seeds and plantlets of closely related species of seminiferous and viviparous grasses apart from those of morphology and weight. F. vivipara plantlets had a higher nutrient capital than F. ovina L. seeds, and in contrast to seeds, contained predominantly low molecular weight organic reserves. 25% of the dry weight was in the form of soluble carbohydrates. On germination, the content of the soluble carbohydrate and amino acids changed little, unlike the large changes observed in seeds. Developing plantlets of F. vivipara increased in dry weight throughout the season until culm collapse. In the early stages of growth, the plantlets were non-viable as independent propagules, but 89% of plantlets were non-dormant and capable of germination immediately prior to culm collapse. In contrast Poa bulbosa L. plantlets reached a stable dry weight, and the bulbils were dormant at dehiscence. The establishment of F. ovina and F. vivipara propagules from neighbouring populations in the English Lake District was compared in experiments not involving competition between the two species. Despite the larger weight of the plantlets, a slower initial growth rate of F. vivipara plants resulted in larger plants of F. ovina at the end of the experiments. No such slow initial growth rate was observed with Poa alpina L. var. vivipara L. In a competition experiment the growth of the viviparous species Deschampsia alpina (L.) R + S, Poa alpina var. vivipara and F. vivipara was less adversely affected than that of closely related seminiferous species. F. vivipara plantlets became water-stressed in the field as demonstrated by a large increase in proline content, whereas the leaves of the parent plants did not. Developing plantlets of other viviparous grasses showed similar large increases in proline content, and it is proposed that a major cause of the restriction of these species is the desiccation of both developing and dehisced plantlets. The success of vivipary in arctic and alpine habitats is discussed in terms of the variety of dispersal mechanisms and the problems of establishment and growth in the short, cold growing seasons of these regions.