A FIELD-STUDY OF THE EFFECTS OF ELEVATED CO2 ON CARBON ASSIMILATION, STOMATAL CONDUCTANCE AND LEAF AND BRANCH GROWTH OF PINUS-TAEDA TREES

A study was conducted in 21-year-old loblolly pine (Pinus taeda L.) tr ees growing in plantation in north central Georgia, USA, The experimen t used branch chambers to impose treatments of ambient, ambient+165 an d ambient+ 330 mu mol mol(-1) CO2. After one growing season there was no indication of acclimation to elevated CO2. In August and September, carbon assimilation, measured by two different methods, was twice as high at ambient +330 mu mol mol(-1) CO2 than at ambient, Dark respirat ion was suppressed by 6% at ambient+l65 and by 14% at ambient+330 mu m ol mol(-1) CO2. This suppression was immediate, and not an effect of e xposure to elevated CO2 during growth, since respiration was reduced b y the same amount in all treatments when measured at a high CO2 concen tration, Elevated CO2 increased the growth of foliage and woody tissue , It also increased instantaneous transpiration efficiency, but it had no effect on stomatal conductance, Since the soil at the study site h ad low to moderate fertility, these results suggest that the growth po tential of forests on many sites may be enhanced by global increases i n atmospheric CO2 concentration.