Tradeoffs in non-native plant herbivore defenses enhance performance

To compare herbivore pressure on a wide range of non-native and native species under natural conditions, we conducted a field survey in abandoned agricultural fields at 28 sites in northern China.  We conducted a common garden experiment at Henan University, Kaifeng, China. We selected the 12 most common non-native herbaceous species in the field survey and compared herbivory on these species and 12 co-planted native congeners.  We used the same species as in the common garden to assess constitutive and induced defenses.  To quantify constitutive defenses, which can inhibit insect growth, we measured larval weight gain when fed on undamaged leaves harvested from undamaged plants.  To quantify induced defenses, we measured larval weight gain on undamaged leaves that were harvested from plants possessing other leaves previously damaged by herbivores.  We measured total phenolics and total triterpenoids in leaves harvested from undamaged and herbivore-damaged plants for same species as described above in the common garden.  To evaluate the relationship between the strength of induced defenses and plant growth, we measured the absolute growth rate for the species in the common garden.