Interpreting species-specific variation in tree-ring oxygen isotope ratios among three temperate forest trees

Abstract

Although considerable variation has been documented in tree-ring cellulose oxygen isotope ratios (δ¹⁸O_cell) among co-occurring species, the underlying causes are unknown. Here, we used a combination of field measurements and modelling to investigate the mechanisms behind variations in late-wood δ¹⁸O_cell (δ¹⁸O_lc) among three co-occurring species (chestnut oak, black oak and pitch pine) in a temperate forest. For two growing seasons,we quantified among-species variation in δ¹⁸O_lc, as well as several variables that could potentially cause the δ¹⁸O_lc variation. Data analysis based on the δ¹⁸O_cell model rules out leaf water enrichment (Δ¹⁸O_lw) and tree-ring formation period (Δt), but highlights source water δ¹⁸O (δ¹⁸O_sw) as an important driver for the measured difference in δ¹⁸O_lc between black and chestnut oak. However, the enriched δ¹⁸O_lc in pitch pine relative to the oaks could not be sufficiently explained by consideration of the above three variables only, but rather, we show that differences in the proportion of oxygen exchange during cellulose synthesis (p_ex) is most likely a key mechanism. Our demonstration of the relevance of some species-specific features (or lack thereof) to δ¹⁸O_cell has important implications for isotope based ecophysiological/paleoclimate studies.

Citation

Song, Xin; Clark, Kenneth S.; Helliker, Brent R. 2014. Interpreting species-specific variation in tree-ring oxygen isotope ratios among three temperate forest trees. Plant, Cell & Environment. 37(9): 2169-2182.