Isotope discrimination and photosynthesis of vegetation growing in the Bossoleto CO2 spring

The Bossoleto CO2 spring emits CO2 which has a stable carbon isotopic ratio (~5~3C= - 8%o). We determined ~3C on leaves of several individual species growing in Bossoleto and in a nearby control site at ambient CO,.. ~5t3Cwas 6% more negative in leaves of species collected from the grassland community of Bossoleto, indicating increased discrimination (A) against the heavy carbon isotope. No such changes were found in ruderal species growing in the same spring, suggesting that photosynthetic capacity was much less affected. A was substantially increased under elevated CO2 in leaves of Quercus pubescens but not in Quercus ilex, which also did not show any increase in non-structural carbohydrates. Gas-exchange measurements made on Plantagolanceolata, supportedtheviewthatphotosyntheticcapacityisdecreasedinplantsgrownunderelevatedCO:andon poor soils. ©1998 Elsevier Science Ltd