Quantitative effects of enhanced CO₂ on jasmonic acid induced plant volatiles of lima bean (<em>Phaseolus lunatus</em> L.)

Abstract

Globally rising CO₂ has been predicted to affect plant biochemistry and in consequence the interaction of plants with multiple associated organisms. While CO₂ mediated effects on nutritive compounds and direct anti-herbivore defenses appear to be well studied for many plant species, the importance of altered atmospheric CO₂ concentrations on indirect defenses is only little understood. In this study, we analyzed the effects of enhanced CO₂ on the release of volatile organic compounds (VOCs) using jasmonic acid (JA) as a natural hormone-like inductor. We cultivated lima bean plants (Phaseolus lunatus L.) under different CO₂ concentrations (ambient, 500, 700, and 1000 ppm) and quantified the release of VOCs using GC-MS. The total release of VOCs significantly increased in response to higher CO₂ concentrations. However, the quantitative emission of individual compounds was differently affected. Nine out of twelve VOCs were released at significantly higher levels (cis-3-hexenylacetate, cis-ocimene, linalool, cis-3-hexenyl butyrate, methyl salicylate, cis-jasmone, β-caryophyllene, trans-geranylacetone, and methyl jasmonate) at enhanced CO₂, whereas two were not affected (2-ethylhexan-1-ol, cis-3-hexenyl isovalerate) and the release of indole decreased. Shifts in VOCs release under elevated CO(2) likely affect efficacy of plants' resistance to herbivores, as a range of the affected compounds are of central importance in defense-associated plant-plant and within-plant signaling. Given the importance of plant-herbivore interactions in terrestrial ecosystems, CO₂ mediated changes in defense-associated VOCs might have implications on agricultural and natural ecosystem functions.