Differential growth response to atmospheric carbon dioxide enrichment in seedlings of Cedrusatlantica and Pinusnigra ssp. Laricio var. Corsicana

Abstract

Nine-months-old seedlings of Cedrus atlantica Manetti and Pinus nigra Arn. ssp. Laricio var. Corsicana were transplanted in parallelepipedal containers permitting root growth observations (minirhizotrons) and in 6 L pots and were then transferred into two polyethylene tunnels in a greenhouse, where they were submitted to atmospheric CO2 concentrations of 350 (normal) and 800 .mu.mol .cntdot. mol-1 (enriched) for their 2nd growth year. At the end of the enrichment period, the biomass of the enriched plants was 66 (C. atlantica) and 30% (P. nigra) higher than those of the plants grown at normal CO2 concentrations. The root:shoot biomass ratio remained unaffected by enrichment in both species. Height and diameter growth were 20 (C. atlantica) and 10% (P. nigra) higher in the enriched treatment. At the end of the enrichment period, the CO2 assimilation rate was no longer stimulated in the enriched C. atlantica plants as compared with the normal treatment, but remained slightly stimulated in the P. nigra seedlings. The differential growth response to elevated CO2 appears to be related to the distinct genetic growth pattern of the two species, namely to their different patterns of root growth before bud break and during early aerial growth.