Latitudinal trends in growth, reproduction and defense of an invasive plant

Invasive plants often occupy an array of habitats along wide latitudinal scales which differ considerably in climatic conditions and herbivory. Variation in plant traits across latitude may play an important role in invasion success, yet few studies have tested whether there is a latitudinal pattern in invasive plant traits. Here, we sampled individuals of the invasive plant Phytolacca americana at 15 field sites spanning 10 degrees of latitude from 25.72 degrees to 36.15 degrees N in central and southern China. We measured traits related to growth (plant height, canopy width, number of branches and stem diameter), reproduction (fruits per raceme and racemes per plant) and anti-herbivory defense (leaf, stem, root and fruit saponin). Overall, we found no latitudinal patterns for plant size, reproductive output or defense in growth tissues. However, growth architecture was significantly related to latitude: number of stems increased, while stem diameter decreased with increasing latitude. Reproductive architecture was also significantly related to latitude: with increasing latitude, plants produced fewer fruits per raceme, but more racemes per plant. We also found defense in reproductive tissue (fruit saponin) increased with increasing latitude. These findings provide an important latitudinal perspective for resource allocation and adaptive strategy in invasive P. americana that may aid in management recommendations at regional scales.