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Effects of elevated CO2 concentration and climate-warming on photosynthesis during winter in Lolium perenne
Authors:Nijs  I; Impens  I
Abstract:Long-term effects of atmospheric carbon dioxide concentration(ambient or 700 µmol mol–1) and air temperature(simulation of field conditions or + 4 C) on leaf photosyntheticrate were examined in Lolium perenne L. cv. Vigor, exposed tonatural illumination during winter. Photosynthetic capacitywas compared over a range of air temperatures and photon fluxdensities of photosynthetically active radiation which wererepresentative of winter climate (5–15 C and 0–500µmol m–2s–1), with CO2 level during measurementsimilar to that during the experimental period. Long-term exposureto increased air temperature reduced leaf CO2 fixation capacityby 23% (averaged over all measurement conditions), resultingfrom a decline in lightsaturated uptake rate, but not in incident-lightquantum efficiency. CO2- stimulation was largely absent in plantsgrown in ambient temperature, but pronounced in plants grownunder +4 C, where it compensated for two-thirds of the 23%drop. This enhancing effect of elevated CO2 level on leaf CO2uptake rate observed in the warmer treatment, was strongly dependenton measurement temperature, increasing from 5% at 5 C, to upto 32% at 15 C. Measurements of chlorophyll fluorescence anddry matter corresponded with the observed changes in assimilationcapacity, which could not be attributed to a deteriorated nitrogenstatus of the leaves as there was a similar N content on anarea basis. Several hypotheses are considered to explain theobserved CO2-temperature interactions. Key words: Acclimation, chlorophyll fluorescence, elevated CO2 level, global warming, low temperature
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