Seasonal variation in δ13C and δ18O of cellulose from growth rings of Pinus radiata

Seasonal variation in delta(13)C and delta(18)O of cellulose (delta(13)C(c) and delta(18)O(c)) was measured within two annual rings of Pinus radiata growing at three sites in New Zealand. In general, both delta(13)C(c) and delta(18)O(c) increased to a peak over summer. The three sites differed markedly in annual water balance, and these differences were reflected in delta(13)C(c) and delta(18)O(c). Average delta(13)C(c) and delta(18)O(c) from each site were positively related, so that the driest site had the most enriched cellulose. delta(13)C(c) and delta(18)O(c) were also related within each site, although both the slope and the closeness of fit of the relationship varied between sites. Supporting the theory, the site with the lowest average relative humidity also had the greatest change in delta(18)O(c) per % change in delta(13)C(c). Specific climatic events, such as drought or high rainfall, were recorded as a peak or a trough in enrichment, respectively. These results suggest that seasonal and between-site variation in delta(13)C(c) and delta(18)O(c) are driven by the interaction between variation in climatic conditions and soil water availability, and plant response to this variation.