Ontogenetic changes in anti‐herbivore defensive traits in leaves of four Mediterranean co‐occurring Quercus species

Abstract

Investment in anti‐herbivore defence in tree species has been one of the priority research topics in plant terrestrial ecology during the last decades. However, despite considerable experimental effort, interspecific differences in the ontogenetic trends in the investment in defence are still a matter of debate, as to date experimental evidence is contradictory. In the present work, insect herbivory levels were measured in seedlings and mature trees of four co‐occurring Mediterranean Quercus species with differing leaf life spans, as well as several leaf characteristics that can determine herbivore preference. The measured leaf traits included nitrogen (N), fibre (cellulose, hemicellulose and lignin), total phenolic contents, leaf mass per unit area (LMA) and leaf thickness. The leaves of seedlings had a lower LMA and leaf thickness and lower concentrations of N and cellulose, but higher concentrations of lignin and phenols than those of mature trees. However, the loss of leaf area tended to be more severe for seedlings than for mature trees, although the differences were only significant for deciduous species. This constitutes a confirmation of the strong effects of physical traits on herbivore preferences. The greater resource limitations for defensive mechanisms in seedlings with respect to mature trees would explain that at intraspecific level we do observe a compromise between chemical and physical defences. As a result, seedlings rely on chemical rather than on physical defences.

Top-down factors contribute to differences in insect herbivory between saplings and mature trees in boreal and tropical forests

“…To test this prediction, we measured the damage imposed by chewing insect herbivores and the attack rates on model prey on mature and juvenile trees at two study sites located in tropical and boreal forests. Finally, we controlled for potential effects of ontogenetic changes in plant quality on herbivory by measuring the specific leaf area (SLA), which, along with other mechanical leaf properties, is a better predictor of field herbivory than are concentrations of plant defensive compounds or leaf nutrients (Caldwell et al 2016;Mediavilla et al 2018).…”

Revisiting the Functional Basis of Sclerophylly Within the Leaf Economics Spectrum of Oaks: Different Roads to Rome

“…Dash line represents the correlation (r 2 = 0.39, p < 0.001) for temperate deciduous species. Data from literature [6,[120][121][122][123][124] and personal measurements…”

“…In this sense, leaf herbivory by insects has been the most common mechanical stress factor studied in the literature [127,129,130]. Generally, insects avoid eating sclerophyllous (high-LMA) leaves, both under laboratory [41] and field experiments [121,131]. Accordingly, Quercus species with lower LMA suffer a higher percentage of leaf area lost per branch due to insect herbivory (see supplementary material Figure 1).…”

The green thorns of Ulex europaeus play both defensive and photosynthetic roles: consequences for predictions of the Enemy Release Hypothesis

“…Simulated trampling damage increased stem resistance to bending and rupture in shrub species (Xu et al 2013). Plant physical defenses may change with plant ontogeny: due to limitations on resource acquisition, seedlings often show less investment in physical defenses than mature plants (Boege and Marquis 2005;Hanley et al 2007;Mediavilla et al 2018; but see Clark and Burns 2015). Nonetheless, physical defenses in seedlings are effective against vertebrate and invertebrate herbivores but costly (Cooper and Ginnett 1998;Boege and Marquis 2005;Cash and Fulbright 2005;Barton and Hanley 2013).…”