Leaf defense syndromes in tropical ferns

Abstract

Vascular plants exhibit defense syndromes, a variety of interdependent defensive traits against herbivores, which may considerably differ between plant groups. Although ferns are an abundant component of tropical forest understories, studies of fern–herbivore interactions are scarce, and none has focused on the underlying defense syndromes. To examine the potential defense syndromes of 34 species of tropical ferns of Brazilian forests, we measured ten leaf traits and examined their correlation with parallelly assessed leaf damages. The first three components of categorical PCA were related (1) with SLA, water content, nitrogen, and phosphorus (33.2% of variance); (2) with tannins and saponins, but negatively with trichome density (22.5%); and (3) with phenol concentrations (16.1%). We identified three groups of fern species with similar leaf damages but different defense syndromes: (I) 14 species were of high nutritional quality (= high SLA, N and water content), but a variable trichome density; (II) 4 species were of low nutritional quality, but had high phenol concentrations, and often a high trichome density; and (III) 16 species were of intermediate nutritional quality and had a low trichome density or were glabrous. Most species (groups I and III) including tree ferns used chemical defenses to protect their highly valuable, nutritious leaves. Group II, exemplified by bracken fern, combined however a low nutritional quality with a powerful chemical defense, including high phenol concentrations, and many trichomes. Because leaf damages did not differ significantly among groups, we conclude that each defense syndrome provides species with a similar resistance against their herbivores.