Germination requirements of invasive and non-invasive Atriplex species: a comparative study

Abstract

Summary Atriplex sagittata , A. hortensis , A. tatarica and A. rosea are annual heterocarpic early succesional species not native in Central Europe. All of them inhabit predominantly urban areas, road margins, dumps or railways. Whereas A. sagittata and A. tatarica are relatively frequent species in warmer areas where they are highly invasive, A. hortensis and A. rosea are relatively rare species. Hence, the four closely related species constitute two natural invasive and non-invasive pairs, i.e. A. sagittata – A. hortensis and A. tatarica – A. rosea . Using comparative ecology I have tried to find differences in germination requirements of the two pairs of species and searched for attributes contributing to their invasiveness. Thus, both species pairs were compared in relation to the role of heterocarpy, dormancy breaking mechanism and germination requirements under different nitrate and salinity levels. All the Atriplex species tested possess a remarkable heterocarpy with a similar dormancy pattern, i.e. one type of fruit is non-dormant and one (in case of A. tatarica and A. rosea ) or two (in case of A. sagittata and A. hortensis ) fruit types showed different dormancy levels. The main result of this study is that in a comparison of germination requirements of the two species pairs, the germinability pattern is clearly different. In the A. sagittata – A. hortensis group the species differed in dormancy level and germinability of particular seed types. Invasibility of A. sagittata could be explained as the ability to time germination and consequently extend the germination period over several years. In contrast, the invasive A. tatarica and the non-invasive A. rosea did not show much difference, despite having very different distributions in the Czech Republic and the explanation of invasibility probably lies in other life history traits such as competitive ability, resource allocation to reproductive structures, relative growth rate, ability to spread in space or resistance to predators.