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Partnerships for enhanced engagement in research (PEER)
Cycle 4 (2015 Deadline)

Functional diversity of interrelated photosynthesis and water use of Central Amazonian trees

PI: Tomas Domingues (, University of São Paulo
U.S. Partner: Pierre Gentine, Columbia University
Project Dates: November 2015 - October 2018

Project Overview

4-445 Tree Canopy Measurements
Team member Maquelle Garcia takes measurements at the top of the tree canopy (photo courtesy of Dr. Domingues).

This project will generate novel understanding on the diversity of plant traits related to water use and photosynthesis. The functional diversity present in a given community is a key dimension of biodiversity that effectively modulates how forests respond to disturbances, such as logging, precipitation, and temperature extremes or the increase in carbon dioxide concentration. It also determines the extent of the feedback between forest and climate, therefore informing us on possible consequences of forest mortality or land use change. To better predict the resilience of the forest and its capacity to provide ecosystem services, it is essential to evaluate the current spectrum of functional diversity, still a major unknown component in biodiversity research. Dr. Domingues and his colleagues will use a new approach looking at the carbon and water cycles as fundamentally coupled at both the leaf and tree level. In order to achieve a qualitative and quantitative assessment of water and carbon strategies by Amazonian trees, they will continuously monitor both the transport of water in tree trunks and the continuous expansion and contraction of the tree’s bole diameter, which relates to water storage, mobilization of photosynthetic products, and growth. This will be complemented by leaf-level measurements of photosynthetic apparatus and hydraulics to comprehend the individual link of photosynthesis with water usage. This novel dataset will demonstrate the coupling between transport of water and carbon within trees and how it relates to forest productivity. The new data will be applied to broader scales by using land-surface and ecosystem models to simulate the interaction between forest and atmosphere at different scenarios of functional diversity. This step will be achieved by collaboration with U.S. Government-supported partner Pierre Gentine, who is implementing a soil-plant-atmosphere-continuum model able to reproduce the carbon and water relationship in the Community Land Model. Brazilian students will also receive much-needed training in computational modeling.

The proposed research will shed light on the role of biodiversity not only in maintaining and improving quality of life for inhabitants of the Amazon region but also for improving water security in other areas. By characterizing current variability in water and carbon use strategies expressed by Amazonian trees, it is possible to assess how much biodiversity loss within this group is tolerable, without seriously compromising ecosystem functioning. The information to be generated by this project will help in evaluating ecosystem integrity in areas where disturbance has already occurred. For example, it will be possible to assess disparities between pristine forest and secondary vegetation, in terms of ecosystem response to water stress whether from bottom up (soil to leaves induced by dry soil conditions) or top down (from leaves to soil induced by dry or hot weather conditions), according to species composition of the community. As a result, plant communities can be evaluated in terms of resilience to further climatic extremes. The products of this research will also aid in guiding species selection for vegetation restoration efforts. For example, such information will be of great value to local community initiatives focusing on production of tree saplings for reforestation programs or ecosystem improvement actions.

Summary of Recent Activities

During the last quarter of 2017, Dr. Domingues and his large and enthusiastic team continued acquiring field data at their study sites in the Amazon (sap flow through tree trunks, tree trunk diameter, photosynthesis measurements on leaves, leaf samples for chemistry, plant vouchers for herbaria, micrometeorological monitoring, etc.). Thanks to PEER funds, they have purchased a pressure bomb, which is a device for measuring the water potential of plant materials. With this equipment, they can assess different strategies employed by plants for dealing with water use. If they allow high transpiration rates, the water potential within the xylem drops significantly, increasing the risk of embolism in the transporting tissue, but assuring high carbon uptake. On the other hand, some plant species controls transpiration by closing the stomates, sacrificing carbon uptake, but improving survivorship. The pressure bomb is a key piece of equipment to help the researchers understand the diversity of strategies used by Amazonian tree species, when used together with the other equipment acquired with PEER support, including a portable photosynthesis system, automatic dendrometers, and sap flow sensors.

On October 16-21, 2017, the team’s research site hosted the 3rd Amazonia and Climate Change Field Course, where 24 students (mostly from Brazil, but also from a few other countries) spent a week immersing themselves in the forest for classes, discussions, research, and interaction with top researchers. Also in October, Dr. Domingues made a presentation at the biannual Brazilian Ecological Society meeting, held in Lavras, Minas Gerais. He spoke on the topic “Effect of climate and soil factors on leaf attributes in rainforest savannas and forests.” At the same meeting, Maquelle Garcia presented her ongoing PhD work as a poster entitled “Strong stomatal control of canopy trees in the Central Amazon during the 2015 El Niño drought.”

As it moves into Year 3, the project is entering the data analysis and manuscript preparation phase. The PI visited Manaus in late November 2017 and will be there again February 17-24, 2018. The goals for this February gathering will include manuscript preparation, participation in the PhD qualifying exam of his student Maquelle Garcia, collection of data at the field station, equipment performance monitoring, organization of datasets, and discussion of further project ideas with the team members. Undergraduate student Andréia Don Pedro will also be participating in the February field visit, gaining a unique opportunity to get firsthand experience with fieldwork in the Amazon. Later in the year (tentatively scheduled for July 2018), the PI is also planning to visit his U.S. partner Pierre Gentine, in New York. The main objective of this working visit will be to advance the analysis of the sap flow and automatic dendrometer data, which by then will comprise very large files requiring collective effort on the development of computer scripts for data analysis.

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