The response of CO2 exchange rate to photosynthetic photon flux density for several Populus clones under laboratory conditions.

No significant differences were found between four mathematical equations describing the response of CO2 exchange rate to photosynthetic photon flux density in seven poplar clones under laboratory conditions. Choice of an optimal equation for poplar may be based on the contemplated aims. High significant differences (at p<0.001) were found among the clones.