Generalities in the growth, allocation and leaf quality responses to elevated CO2 in eight woody species

This paper reports general patterns of relative growth rate and related tra its in response to elevated atmospheric CO2 in eight woody species ranging widely in life form, leaf habit, taxonomy and ecology. Young plants of thes e species, all of comparable ontogenetic phases, R-ere grown simultaneously in large containers with favourable nutrient and water availability in tra nsparent outdoor chambers at 350 and 700 mu l l(-1) CO2 for one growing sea son. We found the following consistent responses. (1) All species grew fast er at elevated CO2, whereas the following leaf and allocation traits were c onsistently lower in CO2-enriched environments: specific leaf area (quotien t of leaf area and leaf weight), leaf area ratio (quotient of total leaf ar ea and plant weight), weight-based foliar N concentration and, to a smaller extent, leaf weight fraction (quotient of leaf weight and plant weight). ( 2) There was important interspecific variation in the magnitude of the resp onse of relative growth rate to CO2. Specific leaf area at ambient CO2 expl ained 88% of the variation in relative growth rate response to CO2 among th e eight species. At ambient CO2, relative growth rate itself, was significa ntly correlated with the relative growth rate response to CO2 only if the l eafless species Ulex gallii was excluded from analysis. (3) The four decidu ous species had a significantly stronger relative growth rate response to C O2 than the four evergreens. This corresponded with their generally higher specific leaf area. (4) Specific leaf area and leaf habit might be useful f or scaling up exercises, as easy-to-measure substitutes for growth response s of (woody) vegetation to elevated CO2. However, the usefulness of such tr aits in this contest needs to be tested in realistic, longer-term manipulat ive experiments in real ecosystems.