Tropical trees’ adaptation to climate changes

A team of researchers, involved in CEBA, confirmed that Amazonian trees display a clear physiological response to increasing atmospheric CO₂ concentrations over the past century (publication Bonal et al., 2011).

Damien Bonal, who used to work for INRA in Kourou (French Guiana) and now works for INRA within the UMR EEF (Ecology and Ecophysiology of Forests) in Nancy, along with other INRA scientists and botanists of IRD Montpellier and Cayenne, studied the morphological and physiological response of leaves of tropical rainforest species to the increase in air CO₂ concentrations over the last two centuries. Namely, they wanted to test whether this increase would affect their ratio of photosynthesis to transpiration, i.e. their water use efficiency, which can be estimated using the stable isotope signature of carbon and oxygen in leaves (δ¹³C, δ¹⁸O).
Leaf samples were gathered from international herbariums (French Guiana and Europe) for 2 tropical rainforest tree species, basralocus (Dicorynia guianensis) and humiria (Humiria balsamifera). The samples covered a 200-year time period and the whole Guiana shield.
They observed a sharp decrease in δ¹³C (carbon isotope composition) with increasing air CO₂ concentrations since 1950, without significant changes in leaf morphological traits. Based on different scenarios of change concerning the response of leaf physiological parameters to changing environmental conditions, their work reveals that an increase in photosynthesis explained the observed trends for these two species, allowing them to maintain a constant ratio between intercellular CO₂ concentrations inside the leaf and air CO₂ concentrations.
In other words, in the last century, these two tree species adapted to CO₂ atmospheric fertilization by assimilating more carbon from the atmosphere and no further down regulation of other physiological mechanisms. This result is consistent with previous studies showing increased tree growth patterns in the Amazonian region over the last 50 years.

• For more information on the publication: https://www.labex-ceba.fr/publication/leaf-functional-response
  
• To access the publication: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-3040.2011.02333.x/abstract