PLANT-RESPONSES TO ATMOSPHERIC CARBON-DIOXIDE ENRICHMENT - INTERACTIONS WITH SOME SOIL AND ATMOSPHERIC CONDITIONS

In general, C3 plant species are more responsive to atmospheric carbon dioxide (CO2) enrichment than C4-plants. Increased relative growth rate at elevated CO2 primarily relates to increased Net Assimilation Rate (NAR), and enhancement of net photosynthesis and reduced photorespiration. Transpiration and stomatal conductance decrease with elevated CO2, water use efficiency and shoot water potential increase, particularly in plants grown at high soil salinity. Leaf area per plant and leaf area per leaf may increase in an early growth stage with increased CO2, after a period of time Leaf Area Ratio (LAR) and Specific Leaf Area (SLA) generally decrease. Starch may accumulate with time in leaves grown at elevated CO2, Plants grown under salt stress with increased (dark) respiration as a sink for photosynthates, may not show such acclimation to increased atmospheric CO2 levels. Plant growth may be stimulated by atmospheric carbon dioxide enrichment and reduced by enhanced UV-B radiation but the limited data available on the effect of combined elevated CO2 and ultraviolet B (280-320 nm) (UV-B) radiation allow no general conclusion. CO2-induced increase of growth rate can be markedly modified at elevated UV-B radiation. Plant responses to elevated atmospheric CO2 and other environmental factors such as soil salinity and UV-B tend to be species-specific, because plant species differ in sensitivity to salinity and UV-B radiation, as well as to other environmental stress factors (drought, nutrient deficiency). Therefore, the effects of joint elevated atmospheric CO2 and increased soil salinity or elevated CO2 and enhanced UV-B to plants are physiologically complex.