| Elevation of atmospheric carbon dioxide (CO2) is an important aspect of global climate change, which affects plant populations and communities. Many studies have investigated the effects of CO2 on plants, from molecular to community level. However, how population differentiation in ecotypes of a particular species influences the responding potential of ecotypes to elevated CO2 is unclear. Stellaria longipes is a good model species for such studies. Through three sets of experiments, using three ecotypes (alpine, prairie and sand dune) of S. longipes , this aspect was investigated. In the first set of experiments, phenotypic plasticity and phenotypic integration were studied in the alpine and prairie ecotypes grown at 365, 750 and 1000 PPM CO2. The two ecotypes showed differences in the amount and/or pattern of plasticity in some traits. Divergence between trait means and patterns of plasticity revealed that trait means responded to elevated CO2, but patterns of plasticity remained stable. In both ecotypes, elevated CO2 altered phenotypic integration. In the second set of experiments, ontogenetic trajectories of morphological traits and ethylene production rate were determined during the exponential growth phase in the alpine and prairie ecotypes grown at 365 and 1000 ppm CO2. A moderate acceleration of growth under elevated CO2 conditions was more common in alpine than in prairie. In both ecotypes, ethylene production rate was unaffected by elevated CO2. In the third set of experiments, biomass partitioning and physiological processes in all three ecotypes grown at 365 and 1000 PPM CO2 were studied. Modifications of biomass partitioning in the ecotypes grown at elevated CO 2 were likely due to ontogenetic plasticity rather than direct effects of elevated CO2 on allocation. In all ecotypes grown at elevated CO2, photosynthesis and water use efficiency increased while transpiration and chlorophyll concentration and content decreased. Overall, the magnitude of the effects of elevated CO2 on the morphology and physiology of the three ecotypes was influenced by inherent differences in growth rate and phenotypic plasticity of the ecotypes. Ecotypic differentiation of the alpine ecotype and reduced genetic variation of the sand dune ecotype limit the responding ability of these two ecotypes to elevated CO2. |
