E. Laitat et H. Boussard, COMPARATIVE RESPONSE ON GAS-EXCHANGE OF PICEA SPP EXPOSED TO INCREASED ATMOSPHERIC CO2 IN OPEN-TOP CHAMBERS AT 2 TEST SITES, Journal of biogeography, 22(2-3), 1995, pp. 241-248
We took comparative measurements of gas exchange response curves of tw
o species of spruce (Picea abies (L.) Karst and Picea sitchensis (Bong
.) Carr.) exposed to high levels of atmospheric carbon dioxide (CO2) i
n two test stations: Vielsalm (Belgium) and Glendevon (United Kingdom)
. The photosynthetic response of these two species to variations in co
ncentrations of intercellular CO2 and to variations in light intensity
were measured in situ using an integrated transportable differential
CO2 and water vapour exchange measuring system. The response curves we
re adjusted by the Mitscherlich function. The statistical analysis of
our measurements and adjustments reveal similarities in the reaction o
f Picea abies and Picea sitchensis to a doubling of the present level
of atmospheric CO2. Regarding the photosynthesis response curves to in
tercellular CO2 variation, we noted a decrease in the maximum photosyn
thesis rate and the carboxylation rate accompanied by an increased com
pensation point. Regarding the photosynthesis response curves to the l
ight variation, we found that dark respiration and photochemical effic
iency remained unchanged, and the maximum photosynthesis rate was slig
htly higher in an atmosphere enriched in CO2. These experimental conte
xts would seem to indicate that the current and forecast levels of CO2
are not ecological factors limiting primary productivity, and that th
e increase in atmospheric CO2 interacts with other environmental facto
rs.