title: 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.
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D002244:Carbon / Q000378:metabolism*; D017753:Ecosystem; D007313:Insecta; D009584:Nitrogen / Q000378:metabolism*; D063245:Plant Development; D010944:Plants / Q000737:chemistry; D010945:Plants, Edible; D013634:Tannins / Q000378:metabolism
chemical_list: D013634:Tannins; D002244:Carbon; D009584:Nitrogen