Evaluation of leaf-atmosphere water fluxes and physiological characterization of plants subjected to an in situ elevated CO2 experiment in Central Amazon

The Amazon Rainforest vegetation responses to climate change are still far from being fully understood, especially when the focus is not on the forest canopy stratum. Concerning the changes in water use related to rising atmospheric CO2 levels, the distinct responses between forest strata of the Amazon are still uncertain. The project presented here consists in exploring data from an experimental study coupled with a mathematical modeling approach, with the goal to elucidate, in relation to rising CO2 levels, the transpiration responses of Central Amazon understorey plants, which may influence the entire region due to forest-atmosphere water flux disturbances. More specifically, we artificially increase the CO2 atmospheric concentration inside open-top chambers installed in the understory, providing a way to evaluate the response of the plants inside the chamber to the increased CO2 levels. With the estimation of carbon assimilation and stomatal conductance processes parameters defined by mathematical models, it is possible to characterize physiologically the response of the individuals in the experiment and compare the differences between control and treatment groups. Then, the impact of these changes in the understory transpiration is estimated by measuring the leaf area index of the understory and combining the obtained stomatal conductance parameters with another mathematical model, which makes it possible to compare the impact of the experimental treatment in the amount of water that travels from the understorey plants to the atmosphere through stomata. The results and methodology from this study, in addition to the importance to accomplishing the main goal mentioned above, are also relevant for the use of Dynamic Global Vegetation Models (DGVM), as the mathematical equations employed are also frequently used in DGVM studies. Finally, the experimental site being studied is also where the first Free-Air CO2 Enrichment experiment in the Amazon, known as AmazonFACE, will be conducted, so the open-top chambers data can be considered a source of basal knowledge for the large scale project that is being implemented at the same location.