How wind affects the photosynthetic performance of trees: quantified with chlorophyll a fluorescence and open-top chambers

Meteorological parameters inside and outside an open-top chamber (OTC) fumi gation facility were recorded and the primary photosynthetic response of fo ur tree species measured with chlorophyll (Chl) a fluorescence emission. Pa rameters extracted from the Chi a fluorescence transient were used to calcu late photosynthetic activity of the leaves using a performance index. Measu rements were made during the night throughout a single growing season. The seasonal primary photosynthetic performance in all species was significantl y altered by growth in the OTCs, and the degree of response was dependent u pon the species. Wind was an important effectual component of the altered e nvironment. The average temperature was consistently 1.94+/-0.70 degreesC h igher within the OTCs, whereas wind speed fluctuated substantially more bet ween inside and outside the OTCs (0 to 8 m s(-1)). There was a correlation between the photosynthetic performance index and wind speed in Fagus sylvat ica, Fraxinus excelsior, and Prunus serotina. The response to wind was also particular to each species: the photosynthetic performance of F. sylvarica increased with wind speed (1 to 7 m s(-1)), decreased with F. excelsior (0 to 6.5 m s(-1)) and P. serorina (0 to 5.5 m s(-1)). Abies alba, in contras t, was almost insensitive to wind. A model was proposed and tested for the conversion of the photosynthetic performance values collected in OTCs to pr edict the photosynthetic performance outside OTCs. The wide variety of resp onses to wind and temperature of the four species conformed to linear funct ions that describe the relationship of the wind speed and temperature respo nses with the difference in photosynthetic performance between the OTC and open environments. Specific coefficients for wind and temperature were prop osed. The photosynthetic response to wind of each species depends on its ec ophysiological specialisation.