Influence of air temperature and CO₂ concentration on C3 plants

Adaptation ability of C3 plants was verified with regard to the expected climate changes. The measurement of carbon dioxide exchange was carried out and net photosynthesis (PN) was calculated in C3 species of white goosefoot (Chenopodium album L., Chenopodiaceae). The tested plants were grown in plant growth chambers (Sanyo MLR 350) with controlled temperature (20°C), light length (14 hours day) and illuminance (20000 lx). While testing, the air temperature was increased stepwise from 5 to 40°C. Similarly, CO₂ concentration was changed in leaf cuvette from 200 – 1500 ppm by built-in removable CO₂ regulator. Considering the assumed climatic changes relating a raise of the air temperature and CO₂ concentration, the values of carbon dioxide concentration based on the climate scenarios ECHAM4 (Germany) and HadCM3 (G. Britain) were classified as well. Optimistic carbon dioxide emissions scenario B1 assumed the CO₂ concentration to be 467 ppm and pessimistic one A2 to 535 ppm.
   The exchange of carbon dioxide was measured after the plant adaptation on certain temperature and CO₂ concentration in the light as well as under dark conditions. The adaptation to the given temperature and CO₂ concentration took approximately 45 minutes. Except for the carbon dioxide concentration and air temperature setting, in the clamp-on chamber the photosynthetically active radiation (PAR) value was programmed to automatically control light intensity at the level of 500 μmol m^-2 s^-1 being the optimum for C3 plants. Measurements were taken with the CIRAS2 (PPSystems, UK) supplied with universal leaf cuvette type U RICE having the measured leaf area of 1.7 cm².
   The C3 plants examined are best adapted to temperature ranging from 20 to 25°C in light. Nevertheless, at high concentration of CO₂ the C3 plants have proven to cope better with higher temperatures than with low ones. At 5°C the calculated values of PN achieved approximately 4 μmol m^-2 s^-1 regardless the carbon dioxide concentration. Conversely, at 40°C the influence of CO₂ concentration was more significant. Therefore, we suppose that with increasing CO₂ concentration C3 plants are able to tolerate rise in temperature. Net photosynthesis rate at 1000 ppm CO₂ reached at least the value of 10 μmol m^-2 s^-1. When dark adapted, there is a better ability to cope with a higher CO₂ concentration at lower temperatures. In the dark the PN values were often negative, because the energy required for plant survival exceeds the energy amount obtained by photosynthesis.
   Considering these facts, the climate changes will have significant influence on C3 plants. As a response to the rising CO₂ levels and air temperature, the rate of photosynthesis will increase and plants will accumulate more aboveground biomass. It can be assumed that climate changes will influence the competition ability of crops as well as weeds. Additionally, climate changes could influence the ecosystems composition and plant morphology.