Wood isotope variation (δ18O and δ13C) suggest new insights on growth
rhythms in trees from the neotropical rainiest forest
Abstract
The drivers of tree growth are one critical question in forest ecology
and conservation. However, the measurement of tree growth is a difficult
task that requires novel methods to improve accuracy and broaden the
understanding of the effect of climate on tree metabolism and carbon
accumulation. In this context, isotopes variation along woody tissues is
a strong tool that provides new information about tree metabolism,
growth rate, and the effect of climatic variation on these processes at
high temporal resolution. Here, we obtained woody samples of two tree
species two individuals per species (n = 4) from the Biogeographic
Choco; Region in Colombia, one of the most humid regions of the planet
without dry periods (mean annual temperature 25.9C and rainfall over
7200 mm). We measured 18O and 13C on these samples across some rings in
each one to obtain intra-annual variation. Using these data, we assessed
if isotopes variation in wood is correlated with climatic variation,
explicitly precipitation regimen indicators employing Pearson
correlation and linear mixed effect models. We found that both isotopes
are correlated negatively with ring width. We also found that 18O is
high negative correlated with precipitation indicators, rather than 13C.
Our results suggest that isotopes variation are surrogates of tree
growth in humid and non-seasonal forests. Besides, the 18O accumulation,
which is strongly related to rainfall during the less rainy month
(February: 370 mm on average), could be a better indicator of the effect
of precipitation on the woody tissue rate change. However, 13C is more
related to tissue formation processes. In conclusion, we found evidence
of intra-annual variation in isotopes and tree growth in one hyper-humid
forest challenging the effect of the dry season of tree growth and
potentially suggesting the water excess as an additional limiting factor
controlling growth rhythms in tropical trees.