Photosynthetic acclimation of beech seedlings to full sunlight following a major windstorm event in France

The effect of natural disturbance (windthrow of mature forests) on photosynthetic acclimation of shade-grown beech (Fagus sylvatica L.) seedlings seas studied at a northeastern France location near Nancy in the Lorraine Region after a major windstorm event in December 1999. Treatments consisted of shaded and full sun plots prior to the storm, and plots where beech seedlings were released from shading by the storm. In 2000. beech in released and full sun plots were characterized by similar photosynthesis, transpiration, mesophyll conductance, and water use efficiencies, which were generally 2-fold higher than those for beech in shaded plots. Additionally, photosynthetic saturation curves did not differ for released and full sun treatments, but did differ from the shade treatment. However, stomatal conductance values for shaded and released beech did not differ, and were lower than those for full sunlight seedlings. Acclimation continued in 2001, but remained incomplete, as evidenced by similar intrinsic water use efficiency values for released and shade treatments, which were lower than the mean value for the full sun treatment. Plant water potential remained highest for shaded seedlings in both years. These findings suggest that full acclimation is a gradual process, occurring over successive growing seasons. We speculate that full acclimation may be directly related to future development of greater root biomass in released seedlings.