Erhöhte Frosttoleranz und vorteilhafte Keimeigenschaften in europäischen Ambrosia artemisiifolia Populationen

Die Keimeigenschaften und die Frosttoleranz von Keimlingen sind Parameter, die für die Etablierung und den Invasionserfolg von Pflanzen entscheidend sind. Wir haben Keimraten und Keimgeschwindigkeit von europäischen und nordamerikanischen Ambrosia artemisiifolia Populationen experimentell unter einem Temperaturgradienten untersucht. Mithilfe der gemessenen Werte wurden minimale, optimale und maximale Temperaturen für die Keimung berechnet. Weiterhin wurde die Frosttoleranz von Ambrosia-Keimlingen für europäische und nordamerikanische Populationen untersucht. Die europäischen Populationen wiesen im Vergleich mit den nordamerikanischen höhere Keimraten, eine höhere Keimgeschwindigkeit und auch ein breiteres Temperaturfenster, unter dem Keimung stattfinden kann, auf. Hierbei besaßen die europäischen Populationen sowohl niedrigere Werte für die minimale Keimtemperatur als auch höhere Werte für die maximale Keimtemperatur. Auch die Frosttoleranz der Keimlinge war in den europäischen Populationen signifikant höher. Die hohen Keimraten und Keimgeschwindigkeiten der europäischen Populationen dürften ein Grund für die erfolgreiche Invasion der Art in Europa sein. Die erhöhte Frosttoleranz der europäischen Populationen kann, in Kombination mit den niedrigeren minimalen Keimtemperaturen, eine frühere Keimung im Jahr ermöglichen. Dies kann aufgrund der hierdurch verlängerten Vegetationsperiode zu einer höheren Biomasseakkumulation führen. Die hieraus resultierende größere Menge an produzierten Pollen und Samen könnte die in Europa existierenden Probleme mit der Art weiter verschärfen.Stichwörter: EICA-Hypothese, Etablierung, Gebietserweiterung, invasive Art, Neophyt, TemperaturIncreased frost tolerance and advantageous germination traits in European Ambrosia artemisiifolia populationsGermination characteristics and frost tolerance of seedlings are crucial parameters for establishment and invasion success of plants. Within this study, we investigated germination characteristics of Ambrosia artemisiifolia L. populations from native and invasive ranges. We determined germination rates and speed under different temperature conditions. From these parameters we calculated minimal, optimal, and maximal temperature for germination. We also investigated the frost tolerance of seedlings. The European populations were characterized by a higher fitness with higher germination rates and germination speed, increased biomass and higher frost tolerance of seedlings. Furthermore, the temperature niche width for germination was significantly broader for the European populations. The increased frost tolerance of the European populations might allow germination earlier in the year which may subsequently lead to higher biomass allocation – due to a longer growing period – and result in higher pollen and seed production. The increase in germination rates, germination speed and seedling frost tolerance might result in a higher fitness of the European populations which may facilitate further successful invasion and sharpen the existing problems.Keywords: EICA hypothesis, establishment, invasive species, neophyte, range expansion, temperatur

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

The knowledge of phenotypic variation in the European range of the highly allergenic Ambrosia artemisiifolia L. (common ragweed) is not entirely complete, even though it is an invasive species of utmost concern. We hypothesized the prevalence of phenotypic differentiations between common ragweed populations in the introduced range, and we assumed that those differentiations were related to environmental conditions at the points of origin. Using a common garden experiment, we investigated biomass allocation, growth rates, and flowering phenology of 38 European common ragweed populations originating from a major geographical gradient. We observed considerable phenotypic variation in growth parameters and flowering phenology, e.g. mean aboveground biomass varied from 23.3 to 47.3 g between the populations. We were able to relate most measured traits with environmental parameters prevailing at the points of origin. For example, early growth of ruderal populations was highly correlated with temperature and precipitation at the point of origin. Late growth and flowering phenology were highly correlated with latitude, i.e. individuals from northern populations grew smaller and flowered and dispersed their pollen and seeds up to 5 weeks earlier than individuals from southern populations. We also found a longitudinal gradient in flowering phenology which has not yet been described. The existence of such a high variability in the introduced range may facilitate further range expansion. We suggest that the correlation with environmental variables rests upon genetic variation possibly due to adaptations to the respective environment. To clarify if such adaptation results from multiple events of introduction or as evolutionary response after introduction, genetic investigations are needed

Germination and seedling frost tolerance differ between the native and invasive range in common ragweed

Germination characteristics and frost tolerance of seedlings are crucial parameters for establishment and invasion success of plants. The characterization of differences between populations in native and invasive ranges may improve our understanding of range expansion and adaptation. Here, we investigated germination characteristics of Ambrosia artemisiifolia L., a successful invader in Europe, under a temperature gradient between 5 and 25 °C. Besides rate and speed of germination we determined optimal, minimal and maximal temperature for germination of ten North American and 17 European populations that were sampled along major latitudinal and longitudinal gradients. We furthermore investigated the frost tolerance of seedlings. Germination rate was highest at 15 °C and germination speed was highest at 25 °C. Germination rate, germination speed, frost tolerance of seedlings, and the temperature niche width for germination were significantly higher and broader, respectively, for European populations. This was partly due to a higher seed mass of these populations. Germination traits lacked evidence for adaptation to climatic variables at the point of origin for both provenances. Instead, in the native range, seedling frost tolerance was positively correlated with the risk of frosts which supports the assumption of local adaptation. The increased frost tolerance of European populations may allow germination earlier in the year which may subsequently lead to higher biomass allocation—due to a longer growing period—and result in higher pollen and seed production. The increase in germination rates, germination speed and seedling frost tolerance might result in a higher fitness of the European populations which may facilitate further successful invasion and enhance the existing public health problems associated with this species