Interspecific variation and elevated CO2 influence the relationship between plant chemical resistance and regrowth tolerance

To understand how comprehensive plant defense phenotypes will respond to global change, we investigated the legacy effects of elevated CO2 on the relationships between chemical resistance (constitutive and induced via mechanical damage) and regrowth tolerance in four milkweed species (Asclepias). We quantified potential resistance and tolerance tradeoffs at the physiological level following simulated clipping/mowing, which are relevant to milkweed ecology and conservation. We examined the legacy effects of elevated CO2 on four hypothesized tradeoffs between: 1) plant growth rate and constitutive chemical resistance (foliar cardenolide concentrations), 2) plant growth rate and mechanically induced chemical resistance, 3) constitutive resistance and regrowth tolerance, and 4) regrowth tolerance and mechanically induced resistance. We observed support for one tradeoff between plant regrowth tolerance and mechanically induced resistance traits that was, surprisingly, independent of CO2 expo...