Seasonal and interannual variations in carbon isotope discrimination in a maritime pine (Pinus pinaster) stand assessed from the isotopic composition of 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 to investigate inter-tree and interannual variability (7 trees, 20 rings per tree, each ring divided into early and late wood). A model of stand primary production coupled to water balance was used to calculate the stand, annual, intrinsic water-use efficiency. Inter-tree variability in discrimination (maximum 2.88 parts per thousand in 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 wood, 2.05 parts per thousand in early wood). Tree size did not explain these differences. Relationships were found between annual discrimination and climate variables such as annual rainfall, summer temperature and vapor pressure deficit. Higher correlations were found with late wood discrimination. Early wood discrimination was shown to be related to previous-year late wood discrimination. Late wood discrimination was also related to soil water availability. Stand, annual, intrinsic water-use efficiency was only weakly related to tree ring carbon discrimination.