Phenology and growth in four annual species grown in ambient and elevated CO2

摘要

The objectives of this study were (i) to test the hypothesis that changes in phenology with CO2are a function of the effect of CO2upon growth and (ii) to determine if CO2-induced changes in phenology can influence competitive outcome. We examined the effect of 350, 525, and 700ensp;mu;L∙Lminus;1CO2onGuara brachycarpa,Gailardia pulchella,Oenothera laciniata, andLupinus texensis. Plants were grown as individuals in 150-, 500-, or 1000-mL pots and in competition in 1000-mL pots. Growth and development were monitored at twice-weekly intervals by recording the number of leaves and noting the presence or absence of stem elongation, branching, flower buds, and open flowers. Elevated CO2affected both growth and phenology, but the direction and magnitude of effects varied with species and soil volume. Elevated CO2did not appear to affect development through its effect on growth. Those treatments in which there were significant effects of CO2on growth were generally different from those treatments in which CO2affected phenology. Rather than affecting phenology by changing plant size, CO2appeared to affect phenology by modifying the size at which plants switched from one stage to the next. The level of CO2changed competitive outcome; the importance ofLupinusincreased whereas that ofOenotheradecreased with increased CO2. These changes were more closely related to the effect of CO2on growth than its effect on phenology.Key words: time of flowering, size at flowering, competition, photoperiod, rate of developmen