THE INFLUENCE OF ELEVATED CO2 ON SPECIES PHENOLOGY, GROWTH AND REPRODUCTION IN A MEDITERRANEAN OLD-FIELD COMMUNITY

We studied the effects on the phenology, growth and reproduction of 19 Mediterranean species, of elevating the atmospheric CO2 concentration ([CO2]) to twice-ambient. Intact monoliths were taken from an old-fie ld and put, during a six month growing season, into growth chambers in which external climatic conditions were mimicked and [CO2] was regula ted. Fruit set time was significantly changed in six species under ele vated [CO2] and leaf and branch senescence accelerated in most species . Grasses had fewer leaves and legumes were more branched at peak prod uction under elevated [CO2] than under ambient. Plant seed number was not significantly changed under elevated [CO2], whereas the reproducti ve effort of grasses was significantly depressed. Reproductive and veg etative characteristics showed related responses to [CO2], as species with enhanced biomass had a hastened fruit set time, a higher number o f fruits per plant and a higher reproductive biomass under elevated [C O2] than under ambient conditions, while species with depressed biomas s had a delayed fruit set time, a lower number of fruits per plant and a lower reproductive biomass. Our results also show a high interspeci fic variability in [CO2] response, but some trends emerged at the fami ly level: the production of vegetative and reproductive modules were d epressed in grasses and slightly stimulated in legumes.