Seasonal variations in the stable oxygen isotope ratio of wood cellulose reveal annual rings of trees in a Central Amazon terra firme forest

Title
Seasonal variations in the stable oxygen isotope ratio of wood cellulose reveal annual rings of trees in a Central Amazon terra firme forest

Author
Shinta Ohashi , Flávia M. Durgante , Akira Kagawa , Takuya Kajimoto , Susan E. Trumbore , Xiaomei Xu , Moriyoshi Ishizuka , Niro Higuchi

Oecologia 2016 v.180 no.3 pp. 685-696

Abstract

In Amazonian non-flooded forests with a moderate dry season, many trees do not form anatomically definite annual rings. Alternative indicators of annual rings, such as the oxygen (δ¹⁸Owc) and carbon stable isotope ratios of wood cellulose (δ¹³Cwc), have been proposed; however, their applicability in Amazonian forests remains unclear. We examined seasonal variations in the δ¹⁸Owc and δ¹³Cwc of three common species (Eschweilera coriacea, Iryanthera coriacea, and Protium hebetatum) in Manaus, Brazil (Central Amazon). E. coriacea was also sampled in two other regions to determine the synchronicity of the isotopic signals among different regions. The annual cyclicity of δ¹⁸Owc variation was cross-checked by ¹⁴C dating. The δ¹⁸Owc showed distinct seasonal variations that matched the amplitude observed in the δ¹⁸O of precipitation, whereas seasonal δ¹³Cwc variations were less distinct in most cases. The δ¹⁸Owc variation patterns were similar within and between some individual trees in Manaus. However, the δ¹⁸Owc patterns of E. coriacea differed by region. The ages of some samples estimated from the δ¹⁸Owc cycles were offset from the ages estimated by ¹⁴C dating. In the case of E. coriacea, this phenomenon suggested that missing or wedging rings may occur frequently even in well-grown individuals. Successful cross-dating may be facilitated by establishing δ¹⁸Owc master chronologies at both seasonal and inter-annual scales for tree species with distinct annual rings in each region.

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