THE IMPACT OF ELEVATED CO2 ON GROWTH AND PHOTOSYNTHESIS IN AGROSTIS-CANINA L SSP MONTELUCCII ADAPTED TO CONTRASTING ATMOSPHERIC CO2 CONCENTRATIONS

The aim of this study was to characterise growth and photosynthetic ca pacity in plants adapted to long-term contrasting atmospheric CO2 conc entrations (C-a). Seeds of Agrostis canina L. ssp. monteluccii were co llected from a natural CO2 transect in central-western Italy and plant s grown in controlled environment chambers at both ambient and elevate d CO2 (350 and 700 mu mol mol(-1)) in nutrient-rich soil. Seasonal mea n C-a at the source of the plant material ranged from 610 to 451 mu mo l CO2 mol(-1), derived from C-4 leaf stable carbon isotope discriminat ion (delta(13)C). Under chamber conditions, CO2 enrichment stimulated the growth of all populations. However, plants originating from elevat ed C-a exhibited higher initial relative growth rates (RGRs) irrespect ive of chamber CO2 concentrations and a positive relationship was foun d between RGR and C-a at the seed source. Seed weight was positively c orrelated with C-a, but differences in seed weight were found to expla in no more than 34% of the variation in RGRs at elevated CO2. Longer-t erm experiments (over 98 days) on two populations originating from the extremes of the transect (451 and 610 mu mol CO2 mol(-1)) indicated t hat differences in growth between populations were maintained when pla nts were grown at both 350 and 700 mu mol CO2 mol(-1). Analysis of lea f material revealed an increase in the cell wall fraction (CWF) in pla nts grown at elevated CO2, with plants originating from high C-a exhib iting constitutively lower levels but a variable response in terms of the degree of lignification. In vivo gas exchange measurements reveale d no significant differences in light and CO2 saturated rates of photo synthesis and carboxylation efficiency between populations or with CO2 treatment. Moreover, SDS-PAGE/LISA quantification of leaf ribulose bi sphosphate carboxylase/oxygenase (Rubisco) showed no difference in Rub isco content between populations or CO2 treatments. These findings sug gest that long-term adaptation to growth at elevated CO2 may be associ ated with a potential for increased growth, but this does not appear t o be linked with differences in the intrinsic capacity for photosynthe sis.