How do soil nutrients affect within-plant patterns of herbivory in seedlings of Eucalyptus nitens?

Abstract

This study assessed how the palatability of leaves of different age classes (young, intermediate and older) of Eucalyptus nitens seedlings varied with plant nutrient status, based on captive feeding trials with two mammalian herbivores, Red-bellied Pademelons (Thylogale billardierii), and Common Brushtail Possums (Trichosurus vulpecula). Seedlings were grown under three nutrient treatments (low, medium and high) and we determined how palatability was related to chemical and physical characteristics of the leaves. Pademelons ate more older leaves than young and intermediate leaves for all treatments. This pattern was best explained by sideroxylonals (formylated pholoroglucinol compounds known to deter herbivory by other marsupials), and/or essential oil compounds that were in lower concentrations in older leaves. In the low nutrient treatment, possums also ate more of the older leaves. However, in the medium and high nutrient treatments, possums ate more intermediate leaves than older leaves and showed a behavioural preference for young leaves (consuming younger leaves first) over intermediate and older leaves, in spite of high levels of sideroxylonals and essential oils. The young leaves did, however, have the highest nitrogen concentration of the leaf age classes. Thus, either sideroxylonals and essential oils provided little or no deterrent to possums, or the deterrent was outweighed by other factors such as high nitrogen. This study indicates that mammalian herbivores show different levels of relative use and damage to leaf age classes at varying levels of plant nutrient status and, therefore, their impact on plant fitness may vary with environment.

Quantitative trait loci for foliar terpenes in a global eucalypt species

“…In contrast, we did not find similar co-location of QTL for these compounds (Freeman et al 2008) despite significant correlation between their levels in the present and past studies in eucalypts (e.g. Andrew et al 2005;Loney et al 2006), consistent with the fact that sideroxylonal A does not have a terpene moiety.…”

Native plant/herbivore interactions as determinants of the ecological and evolutionary effects of invasive mammalian herbivores: the case of the common brushtail possum

“…The brushtail possum in Australia thus co-exists with a eucalypt flora with a very wide range of plant chemical defenses. Studies have demonstrated the importance of terpenes (Wiggins et al 2003), tannins (Marsh et al 2003;O'Reilly-Wapstra et al 2005) and FPCs (Wallis et al 2002;O'Reilly-Wapstra et al 2004;Loney et al 2006) in deterring feeding by this species. These latter compounds (found only in the eucalypt subgenus Symphyomyrtus) have been shown to influence the feeding preference of many arboreal marsupial folivores ) including the Box 1 The brushtail possum in New Zealand and the influence of 'generic' invasive factors New Zealand provides an interesting case study to examine the success and impacts of introduced herbivores.…”

“…For example, field and captive studies by Scott et al (2002) demonstrated clear feeding preferences by the brushtail possum for Eucalyptus gunnii over Eucalyptus globulus, but when feeding on E. globulus this species showed clear preferences for certain populations over others (O'Reilly-Wapstra et al 2002, 2007. Within plants (seedlings), brushtail possums tend to preferentially consume younger leaves (top of the seedling) compared to the older lower leaves on the plant (Loney et al 2006). Thus this species is capable of exhibiting clear hierarchical feeding preferences at all patch levels (species down to individual plant parts).…”

Water Stress and Afforestation: A Contribution to Ameliorate Forest Seedling Performance During the Establishment

“…Similarly, the young foliage of E. nitens seedlings that receive medium and high levels of nutrient regime was intensively consumed. High levels of N in young leaves outweighed the presence of sideroxylonals and essential oils that generally act as deterrents to herbivores (Loney et al, 2006). In contrast, low nutritional quality seems to be a plant defence against herbivores.…”