Growth, dry weight partitioning and wood properties of Pinus radiata D. Don after 2 years of CO₂ enrichment

Advanced selections (families 20010 and 20062) of P. radiata D. Don were exposed to either 340 or 660 μmol CO 2 mol 1 for 2 years to establish if growth responses to high CO 2 would persist during the development of woody tissues. The experiment was carried out in glasshouses and some of the trees at each CO 2 concentration were subjected to phosphorus deficiency and to periodic drought. CO 2 enrichment increased whole‐plant dry matter production irrespective of water availability, but only when phosphorus supply was adequate. The greatest increase occurred during the exponential period of growth and appeared to be tied to increased rates of photosynthesis, which caused accelerated production of leaf area. The increase in whole‐plant dry matter production was similar for both families; however, family 20010 partitioned larger amounts of dry weight to the trunks than family 20062. which favoured the roots and branches. Wood density was generally increased by elevated CO 2 and for family 20010 this increase was due to thickening of the tracheid walls. Tracheid length was similar at both CO 2 levels but differed between families. These results suggest that, as the atmospheric CO 2 concentration rises, field‐grown P. radiata should produce more dry weight at sites where phosphorus is not acutely deficient, even where drought limits growth; however, increases in wood production are likely only for genotypes which continue to partition at least the same proportion of dry weight to wood in the trunk.