Germination performance of native and non-native Ulmus pumila populations

Heidi Hirsch,Karsten Wesche,Henrik Von Wehrden,Isabell Hensen,Daniel Renison,Catherina Wypior

doi:10.3897/neobiota.15.4057

Abstract

Germination is a crucial step for invasive plants to extend their distribution under different environmental conditions in a new range. Therefore, information on germination characteristics of invasive plant species provides invaluable knowledge about the factors which might contribute to the invasion success. Moreover, intra-specific comparisons under controlled conditions will show if different responses between non-native and native populations are caused by evolutionary changes or by phenotypic plasticity towards different environmental influences.This paper focuses on the germination of native and non-native Ulmus pumila populations. We expected that non-native populations would be characterized by their higher final germination percentage and enhanced germination rate, which might indicate an influence due to corresponding climatic conditions.Germination experiments with a moderate and a warm temperature treatment did not reveal significant differences in final germination percentage. However, seeds from the North American non-native range germinated significantly faster than native seeds (p < 0.001). Additionally, mean time to germination in both ranges was significantly negatively correlated with annual precipitation (p = 0.022). At the same time, this relationship is stronger in the native range whereas mean time to germination in non-native populations seems to be less influenced by climatic conditions.Different germination responses of the North American populations could be caused by a fast evolutionary change mediating a higher tolerance to current climatic conditions in the non-native range. However, our findings could also be caused by artificial selection during the introduction process and extensive planting of U. pumila in its non-native range. Nevertheless, we assume that the faster germination rate of non-native populations is one potential explanation for the invasion success of U. pumila in its new range since it might provide a competitive advantage during colonization of new sites.

Highlights

Introduced species often face different environmental conditions in their new range compared to their range of origin
Several studies have shown that plant species can exhibit differing germination responses which are related to differing habitats or biotic influences (e.g. Giménez-Benavides et al 2007, Jorritsma-Wienk et al 2007, Grondahl and Ehlers 2008)
Our study addresses the comparison of germination responses between native and non-native Ulmus pumila L. (Ulmaceae) populations

Summary

Introduction

Introduced species often face different environmental conditions in their new range compared to their range of origin. Even after becoming established in the new range, there are consistent characteristics which can alter the ongoing invasion spread. Germination is crucial for dispersal and to establish populations in new sites in order to expand in range (Theoharides and Dukes 2007, Donohue et al 2010). Data about shifts in germination characteristics could provide valuable information to predict the success of an invading species. Differing germination characteristics can be caused by evolutionary changes mediated by corresponding environmental conditions. Shifts in the germination performance towards different environmental conditions can be an important factor during range expansion in the course of invasion. Enhanced germination percentages and rates of invaders compared to their native congeners or competitors have been associated with increased colonization success of the invaders (Burke and Grime 1996, Muñoz and Ackerman 2011)

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Conclusion