Data from: A native plant competitor mediates the impact of above- and belowground damage on an invasive tree

Plant competition may mediate the impacts of herbivory on invasive plant
species through effects on plant growth and defense. This may predictably
depend on whether herbivory occurs above- or belowground and on relative
plant competitive ability. We simulated the potential impact of above- or
belowground damage by biocontrol agents on the growth of a woody invader
(Chinese tallow tree, Triadica sebifera) through artificial herbivory,
with or without competition with a native grass, little bluestem
(Schizachyrium scoparium). We measured two defense responses of Triadica
through quantifying constitutive and induced extrafloral nectar production
and tolerance of above- and belowground damage (root and shoot biomass
regrowth). We examined genetic variation in plant growth and defense
across native (China) and invasive (US) Triadica populations. Without
competition, aboveground damage had a greater impact than belowground
damage on Triadica performance, whereas with competition, above- and
belowground damage impacted Triadica similarly. Whole plant tolerance to
damage belowground was negatively associated with tolerance to grass
competitors indicating tradeoffs in the ability to tolerate herbivory
versus compete. Competition reduced investment in defensive extrafloral
nectar (EFN) production. Aboveground damage inhibited rather than induced
EFN production while belowground plant damage did not impact aboveground
nectar production. We found some support for the evolution of increased
competitive ability hypothesis for invasive plants as US plants were
larger than native China plants and were more plastic in their response to
biotic stressors than China plants (they altered their root to shoot
ratios dependent on herbivory and competition treatments). Our results
indicate that habitat type and the presence of competitors may be a larger
determinant of herbivory impact than feeding mode and suggest that
integrated pest management strategies including competitive dynamics of
recipient communities should be incorporated into biological control agent
evaluation at earlier stages.