Seasonal and interannual variations in carbon isotope discrimination in a maritime pine (Pinus pinaster) stand assessed from the isotopic compositionof cellulose in annual rings

Stable carbon isotope composition (delta; parts per thousand) was measured on cellulose extracted from maritime pine (Pinus pinaster Mr.) tree rings t o investigate inter-tree and interannual variability (7 trees, 20 rings per tree, each ring divided into early and late wood). A model of stand primar y production coupled to water balance was used to calculate the stand, annu al, intrinsic water-use efficiency. Inter-tree variability in discrimination (maximum 2.88 parts per thousand i n late wood in 1989, 2.69 parts per thousand in early wood in 1983) was as large as interannual variation (maximum 2.72 parts per thousand in late woo d, 2.05 parts per thousand in early wood). Tree size did not explain these differences. Relationships were found between annual discrimination and cli mate variables such as annual rainfall, summer temperature and vapor pressu re deficit. Higher correlations were found with late wood discrimination. E arly wood discrimination was shown to be related to previous-year late wood discrimination. Late wood discrimination was also related to soil water av ailability. Stand, annual, intrinsic water-use efficiency was only weakly r elated to tree ring carbon discrimination.