A possible ontogenetic trade-off between defense and tolerance in response to simulated herbivory in seedlings and saplings of Araucaria angustifolia

Abstract

When facing herbivory, plants can defend themselves and/or tolerate the inflicted damage. Unlike defense, tolerance does not prevent herbivory, but enables plants to compensate for damage. Resource allocation theories assume that plants have a limited pool of resources and that those allocated to one function or structure cannot be used by another. Also, due to their limited photosynthetic area and root biomass, seedlings are expected to invest less in defenses than later plant stages. Seedlings of the conifer species Araucaria angustifolia (Brazilian pine) were shown to be quite tolerant to shoot damage, but their ability to defend themselves from herbivores is not yet known. In the present study we tested whether the species is equally tolerant to shoot damage at the seedling and early sapling stages. We also looked for a possible ontogenetic trade-off between tolerance and defense along early plant ontogeny, and compared the allocation of starch reserves between those two developmental stages in response to the inflicted damage. To simulate herbivory, we severed the shoots from seedlings and saplings (~80 % of shoot mass removed). Shoot replacement by sprouting was observed in both groups, although the number of sprouts produced in saplings was greater than in seedlings. Damage resulted in increased mobilization of seed starch in seedlings. In saplings, underground reserves were apparently deployed in response to simulated herbivory. While seedlings had a greater ability to compensate for tissue loss, saplings were more able to chemically defend themselves, suggesting a possible ontogenetic trade-off between tolerance and defense.