Secondary invasion of Acer negundo: the role of phenotypic responses versus local adaptation

Abstract

During plant species invasions, the role of adaptive processes is particularly of interest in later stages of range expansion when populations start invading habitats that initially have not been disposed to invasions. The dioecious tree Acer negundo, primarily invasive in Europe in wet habitats along riversides and in floodplains, has increased its abundance in dry habitats of industrial wasteland and ruderal sites during the last decades in Eastern Germany. We chose 21 invasive populations from wet and from dry habitats in the region of Halle, Saxony-Anhalt, Germany, to test whether Acer negundo exhibits a shift in life-history strategy during expansion into more stressful habitats. We analyzed variables of habitat quality (pH, soil moisture, exchangeable cations, total C and N content) and determined density, sex ratio and regeneration of the populations. In addition, we conducted germination experiments and greenhouse studies with seedlings in four different soil moisture environments. Local adaptation was studied in a reciprocal transplant experiment. We found habitat type differentiation with lower nutrient and water supply at the dry sites than at the moist sites and significant differences in the number of seedlings in the field. In accordance, seeds from moist habitats responded significantly faster to germination treatments. In the transplant experiment, leaf life span was significantly larger for populations originating from dry habitat types than from moist habitats. This observed shift in life history strategy during secondary invasion of A. negundo from traits of establishment and rapid growth towards traits connected with persistence might be counteracted by high gene flow among populations of the different habitat types. However, prolonged leaf life span at dry sites contributed remarkably to the invasion of less favourable habitats, and, thus, is a first indication of ongoing adaptation.

Phenotypic variation of 38 European Ambrosia artemisiifolia populations measured in a common garden experiment

“…Time of flowering may also vary strongly between populations (Dickerson and Sweet 1971;Hodgins and Rieseberg 2011). Phenotypic variation between populations may occur in terms of clines especially along large latitudinal or other environmental gradients (Erfmeier et al 2013) which we also observed in this study. Whether this variability results from phenotypic plasticity as a response to environmental conditions at the respective site of origin or from genetic adaptation has not yet been evaluated.…”

Killing it Softly: Girdling as an Efficient Eco-friendly Method to Locally Remove InvasiveAcer negundo

“…Although this control method has been demonstrated in wet and nutrient-rich ecosystems, it can be applied on A. negundo invading dry and resource-poor environments corresponding to its secondary invasive habitats (Erfmeier et al 2011). When healing development is observed, it only requires repeated girdling for a few years to lead to exhaustion of A. negundo below-ground systems and to tree death.…”

Potenziale und Risiken eingeführter Baumarten

“…arizonicum und var. californicum) unterschieden, die auch als geografisch getrennte Klimarassen bezeichnet werden können (Overton 1990 (Nybom und Rogstad 1990, Erfmeier et al 2011. Neuere Untersuchungen weisen allerdings auch darauf hin, dass physiologische und phänotypische Anpassungsmechanismen ebenso bedeutsam sind (Saccone et al 2010, Porté et al 2011, Lamarque et al 2013).…”

“…In der Hördter Rheinaue kommt A. negundo nur selten und nicht dominierend vor (Vor und Schmidt 2008). Seit zwei Jahrzehnten breitet sich der Eschenahorn auch auf trockenen, oft ruderalen Standorten aus (Erfmeier et al 2011). Dies trifft auch für innerstädtische Bereiche zu, in denen es häufig wärmer ist als in den umliegenden Regionen (Sukopp und Wurzel 2004).…”

“…Die in jüngster Zeit vermehrte Ausbreitung auf trockenen und nährstoffar-men Standorten ) deutet auf die Fähigkeit einer lokalen Adaption aufgrund einer breiten genetischen Variabilität hin, die z. B. dazu führt, dass unterschiedlich hohe Mengen an Blättern und Samen produziert werden (Erfmeier et al 2011). Der wichtigste Konkurrenzfaktor des Eschenahorns im Jungwuchsstadium liegt hauptsächlich in der Beschattung lichtbedürftigerer Pflanzenarten.…”