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Abstract
The effect of elevated CO
2 and O
3 on apparent quantum yield (ø), maximum photosynthesis (P
max), carboxylation efficiency (V
cmax) and electron transport capacity (J
max) at different canopy locations was studied in two aspen (
Populus tremuloides) clones of contrasting O
3 tolerance. Local light climate at every leaf was characterized as fraction of above-canopy photosynthetic photon flux density (%PPFD). Elevated CO
2 alone did not affect ø or P
max, and increased J
max in the O
3-sensitive, but not in the O
3-tolerant clone. Elevated O
3 decreased leaf chlorophyll content and all photosynthetic parameters, particularly in the lower canopy, and the negative impact of O
3 increased through time. Significant interaction effect, whereby the negative impact of elevated O
3 was exaggerated by elevated CO
2 was seen in Chl, N and J
max, and occurred in both O
3-tolerant and O
3-sensitive clones. The clonal differences in the level of CO
2 x O
3 interaction suggest a relationship between photosynthetic acclimation and background O
3 concentration.
Citation
Noormets, Asko; Kull, Olevi; Sober, Anu; Kubiske, Mark E.; Karnosky, David F. 2010. Elevated CO
2 response of photosynthesis depends on ozone concentration in aspen. Environmental Pollution 158: 992-999.
