I. Nijs et I. Impens, EFFECTS OF ELEVATED CO2 CONCENTRATION AND CLIMATE-WARMING ON PHOTOSYNTHESIS DURING WINTER IN LOLIUM-PERENNE, Journal of Experimental Botany, 47(300), 1996, pp. 915-924
Long-term effects of atmospheric carbon dioxide concentration (ambient
or 700 mu mol mol(-1)) and air temperature (simulation of field condi
tions or +4 degrees C) on leaf photosynthetic rate were examined in Lo
lium perenne L. cv. Vigor, exposed to natural illumination during wint
er. Photosynthetic capacity was compared over a range of air temperatu
res and photon flux densities of photosynthetically active radiation w
hich were representative of winter climate (5-15 degrees C and 0-500 m
u mol m(-2) s(-1)), with CO2 level during measurement similar to that
during the experimental period, Long-term exposure to increased air te
mperature reduced leaf CO2 fixation capacity by 23% (averaged over all
measurement conditions), resulting from a decline in light-saturated
uptake rate, but not in incident-light quantum efficiency, CO2-stimula
tion was largely absent in plants grown in ambient temperature, but pr
onounced in plants grown under +4 degrees C, where it compensated for
two-thirds of the 23% drop. This enhancing effect of elevated CO2 leve
l on leaf CO2 uptake rate observed in the warmer treatment, was strong
ly dependent on measurement temperature, increasing from 5% at 5 degre
es C, to up to 32% at 15 degrees C. Measurements of chlorophyll fluore
scence and dry matter corresponded with the observed changes in assimi
lation capacity, which could not be attributed to a deteriorated nitro
gen status of the leaves as there was a similar N content on an area b
asis. Several hypotheses are considered to explain the observed CO2-te
mperature interactions.