Drier climate shifts leaf morphology in Amazonian trees
The humid forests of Amazonia are experiencing longer and more intense dry seasons, which are predicted to intensify by the end of the 21st century. Although tree species often have long generation times, they may still have the capacity to rapidly respond to changing climatic conditions through adaptive phenotypic plasticity. We, therefore, predicted that Amazonian trees have shifted their leaf morphology in response to the recent drier climate. We tested this prediction by analysing historical herbarium specimens of six Amazonian tree species collected over a 60-year period and comparing changes in leaf morphology with historical precipitation data. Moreover, we explored spatial and temporal biases in herbarium specimens and accounted for their potentially confounding effect in our analysis. We found pronounced biases in herbarium specimens, with nearly 20% of specimens collected in close geographic proximity and around the 1975s. When accounting for such biases, our results indicate a trend of decreasing leaf size after the 1970s, which may have been spurred by an observed reduction in rainfall. Our findings support the hypothesis that (some) Amazonian trees have the capacity to adaptively change their leaf phenotypes in response to the recent drier climate. Nevertheless, the unavoidable spatial and temporal biases in herbarium specimens call for caution when generalizing our findings to all Amazonian trees.
KeywordsAmazonian trees Climate change Leaf morphology Historical herbarium specimens
We thank three anonymous referees and Ülo Niinemets for thoughtful comments on the present manuscript. This work was funded by the Brazilian National Council for Scientific and Technological Development CNPq: JS is supported by CNPq #152816/2016-0, RJL by CNPq #310953/2014-6, ACMM by CNPq #310349/2015-0, and RAC by CNPq #163055/2014-9.
Author contribution statement
ACMM, RJL, IMS, JS, and RAC conceived and designed the research. IMS, JGS, TLPS, and JWS collected data. JS and RAC analysed data. RJL, ACMM, RAC, and JS wrote the manuscript; other authors provided editorial advice.
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