In an attempt to investigate the cause of change in the competitive ability between monocots and dicots in a pastureland in Farnham, Quebec under CO2 enrichment, I chose to study the response of Plantago major (dicot) and Poa pratensis (monocot) grown in ambient and elevated CO2 chambers, hypothesizing that a large increase in root biomass of dicots would be observed under elevated CO 2. A transient stimulation of root biomass of Plantago major was found during the first month of CO2 exposure but disappeared later. / The second objective of this study was to examine the effect of 5 years of CO2 enrichment both on root biomass and on total C and N content of roots and soil in the pasture. The largest belowground growth was recorded for Taraxacum officinale. Plantago major responded by achieving the highest aboveground growth. / N content of CO2 enriched roots was reduced. This change in the elemental composition of root tissues might negatively affect the process of decomposition and therefore, the nutrient availability to soil microbes and plants. The observed reduction of NO3 in CO2 enriched soil maybe due to greater N immobilization caused by the expected increase in microbial populations.

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