Evaluating climate signal recorded in tree-ring δ C and δ O values from bulk wood and α-cellulose for six species across four sites in the northeastern US.

RATIONALE

We evaluated the applicability of tree-ring δ C and δ O values in bulk wood - instead of the more time and lab-consuming α-cellulose δ C and δ O values, to assess climate and physiological signals across multiple sites and for six tree species along a latitudinal gradient (35°97'N to 45°20'N) of the northeastern United States.

METHODS

Wood cores (n = 4 per tree) were sampled from ten trees per species. Cores were cross-dated within and across trees at each site, and for the last 30 years. Seven years, including the driest on record, were selected for this study. The δ C and δ O values were measured on two of the ten trees from the bulk wood and the α-cellulose. The offsets between materials in δ C and δ O values were assessed. Correlation and multiple regression analyses were used to evaluate the strength of the climate signal across sites. Finally the relationship between δ C and δ O values in bulk wood vs α-cellulose was analyzed to assess the consistency of the interpretation, in terms of CO assimilation and stomatal conductance, from both materials.

RESULTS

We found offsets of 1.1‰ and 5.6‰ between bulk and α-cellulose for δ C and δ O values, respectively, consistent with offset values reported in the literature. Bulk wood showed similar or stronger correlations to climate parameters than α-cellulose for the investigated sites. In particular, temperature and vapor pressure deficit and standard precipitation-evaporation index (SPEI) were the most visible climate signals recorded in δ C and δ O values, respectively. For most of the species, there was no relationship between δ C and δ O values, regardless of the wood material considered.

CONCLUSIONS

Extraction of α-cellulose was not necessary to detect climate signals in tree rings across the four investigated sites. Furthermore, the physiological information inferred from the dual isotope approach was similar for most of the species regardless of the material considered.