WITHIN-RING DELTA-C-13 SPATIAL VARIABILITY AND INTERANNUAL VARIATIONSIN WOOD CELLULOSE OF 2 CONTRASTING PROVENANCES OF PINUS-PINASTER

The carbon isotope composition (delta(13)C) of cellulose extracted fro m wood samples was measured on 26-year-old maritime pine trees (Pinus pinaster Ait,) of the mesic French provenance Landes and of the drough t-resistant Moroccan provenance Tamjoute, all growing at the same loca tion in France. Analysis of spatial variability revealed that intra-ri ng delta(13)C values varied over a range of about 0.5 parts per thousa nd (mean SD = 0.12 parts per thousand) for circumference and of about 1 parts per thousand (mean SD = 0.22 parts per thousand) for height an d that interannual variability of delta(13)C was 3 parts per thousand. The successive year-to-year delta(13)C values on four trees (from 197 2 to 1991) were found to roughly parallel the variations of a water st ress index, calculated by taking into account climatic variables as we ll as the level of the water table in the soil: delta(13)C increased w ith drought. The two provenances (30 trees per provenance) were compar ed at a juvenile stage (old rings) and at a mature stage (recent rings ). The drought-resistant provenance (Tamjoute) presented lower delta(1 3)C values, independent of ring age. Relationships between delta(13)C and tree height are discussed both at the within- and between-provenan ce levels.