Tolerance responses to simulated herbivory in the seagrass Cymodocea nodosa

Abstract

Herbivory causes both direct and indirect damage to plants, with negative consequences for plant performance and fitness. Plants have thus evolved strategies to counteract or mitigate such negative effects. The strategies used by aquatic plants to cope with herbivore pressure are of key importance to better understand ecological and evolutionary processes. However, little is known about such strategies. To help fill this gap, and to better understand induced responses to herbivory in aquatic plants, we simulated grazing at various intensities in the seagrass Cymodocea nodosa for ca. 4 mo, and measured plant responses in terms of shoot density, aboveground biomass, leaf growth, total nitrogen and carbon content in tissues, total non-structural carbohydrates in rhizomes and total phenolic content in leaves. Most of these plant attributes showed changes under both low and high simulated herbivory at the end of the experiment, indicating that C. nodosa is able to change a suite of plant traits to compensate for biomass losses. At least 3 tolerance strategies were involved in this process: growth compensation and overcompensation, increased nitrogen content (either from uptake or through reclamation from rhizome pools) and remobilization of carbohydrates stored in the rhizomes. Phenolic content decreased in the low-intensity treatment but was similar to control plants in the high-intensity herbivore treatment, indicating the role of phenolic compounds in the tolerance response.