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要旨:
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.
