Responses to elevated atmospheric CO2 concentration and nitrogen supply ofQuercus ilex L-seedlings from a coppice stand growing at a natural CO2 spring

Quercus ilex acorns were collected from a population of trees with a lifeti me exposure to elevated atmospheric CO2 concentration (CO2), and after germ ination seedlings were exposed at two [CO2] (370 or 520 mu mol mol(-1)) in combination with two soil N treatments (20 and 90 mu mol mol(-1) total N) i n open-tap chambers for 6 months. Increasing [CO2] stimulated photosynthesi s and leaf dark respiration regardless of N treatment. The increase in phot osynthesis and leaf dark respiration was associated with a moderate reducti on in stomatal conductance, resulting in enhanced instantaneous transpirati on efficiency in leaves of seedlings in CO2-enriched air. Elevated [CO2] in creased biomass production only in the high-N treatment. Fine root/foliage mass ratio decreased with high-N treatment and increased with CO2 enrichmen t. There was evidence of a preferential shift of biomass to below-ground ti ssue at a low level of nutrient addition. Specific leaf area (SLA) and leaf area ratio (LAR) decreased significantly in leaves of seedlings grown in e levated [CO2] irrespective of N treatment. Leaf N concentration decreased s ignificantly in elevated [CO2] irrespective of N treatment. As a result of patterns of N and carbon concentrations, C/N ratio generally increased with elevated [CO2] treatment and decreased with high nutrient supply. Afternoo n starch concentrations in leaves did not increase significantly with incre asing [CO2], as was the case for morning starch concentrations at low-N sup ply. Starch concentrations in leaves, stem and roots increased with elevate d [CO2] and decreased with nutrient addition. The concentration of sugars w as not significantly affected by either CO2 or N treatments. Total foliar p henolic concentrations decreased in seedlings grown in elevated [CO2] irres pective of N treatment, while nutrient supply had less of an effect. We con clude that available soil N will be a major controlling resource for the es tablishment and growth of Q. ilex in rising [CO2] conditions. (C) 1999 Edit ions scientifiques et medicales Elsevier SAS.