The resource economics of chemical and structural defenses across nitrogen supply gradients

Abstract

In order to better understand the role of nutrient supplies in determining the prevalence of plant defense types, we investigated the theoretical relationships between ecosystem N supply and the net C gain of shoots that were undefended or defended in one of three ways: (1) by N-free chemical compounds, (2) by N-containing chemical compounds, or (3) by structural defenses. By extending economic models of shoot resource balance to include the relative value of C and N, depreciation, and amortization, we were able to show that the relative net C gain of the three defense types were similar to changes in their generally understood abundance along an N supply gradient. At low N supply, the additional C acquired when investing C in defense is much higher than investing N in defenses. Only at high N supply is it better to invest large quantities of N in defense rather than additional photosynthesis. In a sensitivity analysis, net C gain of shoots was most sensitive to factors that affect the relative value of C and N and the rate of herbivory. Although there is support for the relative value of C and N influencing defense strategies, more research is necessary to understand why tannins are not more prevalent at high N supply and why moderate amounts of N-based defenses are not used at low N supply.

The Growth–defense Trade-Off and Habitat Specialization by Plants in Amazonian Forests

“…We predicted that the impact of herbivory would be greater in a white-sand forest, because it is more difficult for plants to replace the nitrogen lost to herbivores (Coley 1987b, Craine et al 2003. This prediction was supported by the fact that all plants transplanted into white-sand forest had significantly higher mortality when defoliated than those transplanted into clay forest (Fig.…”

Root and leaf traits reflect distinct resource acquisition strategies in tropical lianas and trees

“…A particular suite of root traits may facilitate the rapid acquisition of belowground resources, but result in poor structural integrity, leading to fast root turnover (Eissenstat 1992;Ryser 1996;Eissenstat and Yanai 1997;Eissenstat et al 2000;Craine et al 2003). For example, high specific root length (SRL; root length per unit of dry mass, cm g −1 ), low average root diameter, low tissue density (g cm −3 ), high N and P concentrations, and high branching intensity (forks cm −1 ) are commonly associated with a resource acquisitive strategy with short root life spans, and vice versa (Comas and Eissenstat 2004;Roumet et al 2006;Holdaway et al 2011;McCormack et al 2012).…”

Quantitative Chemical Defense Traits, Litter Decomposition and Forest Ecosystem Functioning

“…For example, in the savannas of southern Africa, infertile miombo woodlands and savannas on soils derived from highly weathered granites have trees whose leaves are defended by www.intechopen.com tannins, while on nearby savannas on higher-nutrient soils such as shales and young volcanic soils, plants are defended by spines. The prevalence of chemical defenses depends on ecosystem nutrient supply (Craine et al, 2003). Fig.…”