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Keywords:

  • canopy scale;
  • elevated CO2;
  • emission modeling;
  • global climate change;
  • growth modeling;
  • isoprene emission;
  • leaf scale

Summary

  • Effects of elevated atmospheric [CO2] on plant isoprene emissions are controversial. Relying on leaf-scale measurements, most models simulating isoprene emissions in future higher [CO2] atmospheres suggest reduced emission fluxes. However, combined effects of elevated [CO2] on leaf area growth, net assimilation and isoprene emission rates have rarely been studied on the canopy scale, but stimulation of leaf area growth may largely compensate for possible [CO2] inhibition reported at the leaf scale. This study tests the hypothesis that stimulated leaf area growth leads to increased canopy isoprene emission rates.
  • We studied the dynamics of canopy growth, and net assimilation and isoprene emission rates in hybrid aspen (Populus tremula × Populus tremuloides) grown under 380 and 780 μmol mol−1 [CO2]. A theoretical framework based on the Chapman–Richards function to model canopy growth and numerically compare the growth dynamics among ambient and elevated atmospheric [CO2]-grown plants was developed.
  • Plants grown under elevated [CO2] had higher C : N ratio, and greater total leaf area, and canopy net assimilation and isoprene emission rates. During ontogeny, these key canopy characteristics developed faster and stabilized earlier under elevated [CO2]. However, on a leaf area basis, foliage physiological traits remained in a transient state over the whole experiment.
  • These results demonstrate that canopy-scale dynamics importantly complements the leaf-scale processes, and that isoprene emissions may actually increase under higher [CO2] as a result of enhanced leaf area production.