Background/Question/Methods Atmospheric carbon dioxide concentrations ([CO2]) are predicted to rise from 380 ppm (current) to 700 ppm (elevated) within 50-80 years. Plants grown at elevated [CO2] exhibit increases in photosynthetic rates, biomass accumulation, and reproductive output and may exhibit altered flowering times, which has the potential to alter processes at the population, community, and ecosystem levels. Upon surveying the literature, we found that 57% of wild species and 62% of crop species exhibit altered flowering times in response to elevated [CO2] (Springer & Ward, 2007). Moreover, we found intra-specific genetic variation in flowering times of field-collected genotypes of Arabidopsis thaliana grown at elevated relative to current [CO2]. This indicates a potential for natural selection to act on flowering time in future elevated [CO2] environments. Understanding the mechanism(s) responsible for changes in flowering time at elevated [CO2] will help to predict the impact of elevated [CO2] on future ecosystems. Using a Quantitative Trait Loci (QTL) approach to detect genomic regions that may be responsible for controlling flowering time, we utilized 150 RILs (recombinant inbred lines) of Arabidopsis derived from two parental genotypes: Landsberg Erecta (Ler) and Cape Verde Islands (Cvi) developed by Alonso-Blanco and colleagues (1998). We grew 8 replicates of each line at current and elevated [CO2] and found the average flowering time for each RIL based upon individual data. Using QTL CARTOGRAPHER (Basten et al. 1998), we conducted a composite interval mapping analysis using a forward-backward regression with a maximum of 5 background parameters, a window size of 10cM, and an experiment-wise LOD (log of the odd ratio) threshold significance level that was set by computing 1,000 permutations of flowering time. We analyzed flowering time for significant QTL by [CO2] interactions using the JZmapqtl module and detected genomic regions exhibiting QTL by [CO2] interactions for the five Arabidopsis chromosomes. Results/Conclusions We found three similar significant QTLs between plants grown at current and elevated [CO2] on Chromosome 5 and only 1 QTL that differed between plants grown at current and elevated [CO2] on Chromosome 3. Only marker DF.77C on Chromosome 3 had a significant QTL x [CO2] interaction for flowering time. This interaction indicates that the Cvi allele leads to accelerated flowering at elevated [CO2] conditions. Using this data we will identify candidate genes within genomic regions responsible for altered flowering at elevated [CO2]. Identifying candidate genes is key to fully understand the future responses of plants to elevated [CO2].