Elevated [CO(2)] magnifies isoprene emissions under heat and improves thermal resistance in hybrid aspen

Isoprene emissions importantly protect plants from heat stress, but the emissions become inhibited by instantaneous increase of [CO(2)], and it is currently unclear how isoprene-emitting plants cope with future more frequent and severe heat episodes under high [CO(2)]. Hybrid aspen (Populus tremula x Populus tremuloides) saplings grown under ambient [CO(2)] of 380 μmol mol(−1) and elevated [CO(2)] of 780 μmol mol(−1) were used to test the hypothesis that acclimation to elevated [CO(2)] reduces the inhibitory effect of high [CO(2)] on emissions. Elevated-[CO(2)]-grown plants had greater isoprene emission capacity and a stronger increase of isoprene emissions with increasing temperature. High temperatures abolished the instantaneous [CO(2)] sensitivity of isoprene emission, possibly due to removing the substrate limitation resulting from curbed cycling of inorganic phosphate. As a result, isoprene emissions were highest in elevated-[CO(2)]-grown plants under high measurement [CO(2)]. Overall, elevated growth [CO(2)] improved heat resistance of photosynthesis, in particular, when assessed under high ambient [CO(2)] and the improved heat resistance was associated with greater cellular sugar and isoprene concentrations. Thus, contrary to expectations, these results suggest that isoprene emissions might increase in the future.