Herbivory changes biomass allocation but does not induce resistance among ramets of an invasive plant

Authors: BECKER, ZOE - Colorado State University; ODE, PAUL - Colorado State University; West, Natalie; PEARSE, IAN - Us Geological Survey (USGS)

Submitted to: Arthropod-Plant Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2022
Publication Date: 5/4/2022
Citation: Becker, Z.Q., Ode, P.J., West, N.M., Pearse, I.S. 2022. Herbivory changes biomass allocation but does not induce resistance among ramets of an invasive plant. Arthropod-Plant Interactions. 16:297-307. https://doi.org/10.1007/s11829-022-09897-x.
DOI: https://doi.org/10.1007/s11829-022-09897-x

Interpretive Summary: Many invasive weeds are clonal plants, and this can complicate our predictions of how vulnerable a weed population might be to management. For instance, clonal connections might carry signals that benefit (e.g., induce defense compound production) or cost (e.g., regrowth of a damage shoot fueled by a neighbor's stored resources) connected plants in response to management. We conducted a greenhouse experiment with hoary cress (Lepidium draba) to determine whether feeding by a generalist or specialist herbivore on one clone induces a defense response or biomass shift in a neighboring connected clone. We found that, though herbivory induced a local defense response, this response did not affect the neighboring clone. However, feeding by the specialist, though not the generalist, herbivore resulted in a shift in biomass allocation from neighbors that fueled compensatory regrowth of damaged clones. This response was found regardless of intact physical connections, suggesting there may be volatile signaling among clones. Such data will be valuable in anticipating how effective management with insect herbivores, such as through classical biocontrol programs, might be for controlling this problematic weed.

Technical Abstract: Inducible responses to herbivores can be either localized or spread systemically throughout a plant. The ways in which clonal plants integrate their response to herbivores among clonal ramets is not well understood. Yet, this is important to understand the impacts that herbivores may have on clonal plants. We conducted a factorial experiment to determine whether resistance is induced among clones and how biomass allocation changes among clones following herbivore damage to one of them. We manipulated the presence of two herbivores, Pieris rapae and Trichoplusia ni, and the root connection of ramets of the clonal invasive weed, Lepidium draba. We found evidence for local inducible resistance towards subsequent herbivory on the ramet where an herbivore fed, but not in neighboring clones. Biomass allocation shifted in response to herbivores, but in an herbivore-specific way. Feeding by the specialist caterpillar P. rapae decreased allocation to roots and increased regrowth of neighboring ramets, resulting in greater tolerance to aboveground damage for the neighboring ramet. On the other hand, the generalist T. ni had no effect on regrowth potential or biomass allocation of either local or neighboring ramet. Interestingly, the change in biomass allocation to roots of the neighboring clone occurred irrespective of whether ramets shared a root connection, suggesting some form of volatile communication between neighboring ramets. Feeding by herbivores did not induce systemic resistance among clones of L. draba, but the specialist did alter how neighboring clones allocate biomass. This observation will be important in anticipating how insect herbivores affect the control and success of this problematic invasive plant.