Drought and the Global Carbon Cycle

2013-15 New Investigator Award

Elliot Chang at the vacuum line, for cryogenic distillation of plant water samples. Photo credit: James O’Donnell

Drought is anticipated to have a major impact on the carbon cycle in the coming century. Forest mortality can lead to a large release of CO2, affects climate directly, as well as a shift in species dominance that could alter regional weather. Steve Pacala, Kelly Caylor, and Adam Wolf aim to develop a predictive model of plant water use and drought mortality that hinges on knowing the competition among plants for water below ground, and their drought avoidance strategies of leaves and wood.

Collecting plant stem samples for later extraction and isotopic analysis of water. The isotopic signature of this water will be used to determine the geography of a tree’s root water uptake, and thus how much trees steal water from other trees’ territory. Photo credit: Adam Wolf

To understand water theft among trees in a crowded stand, this research team has trucked in nearly 12,000 gallons of water and added an isotopic label to follow this water as it is applied to a single tree and eventually transpired. Custom electronics were developed to measure and divert rainfall and replace it with labeled water from cisterns.

To quantify this theft, students were trained in advanced tree climbing techniques, to allow access to the upper canopy for leaf and branch sampling, and even to conduct gas exchange measurements aloft.A lab component will aim to characterize the “hydraulics” of leaves, wood, roots, and soil, particularly the failure of the tree’s plumbing under drought. It is known that different trees are more or less adapted to drought, but it is not known how different species “pay” for this risk aversion. The team will aim to measure the costs, benefits, and risk avoidance along a drought resistance spectrum to better parameterize the Princeton/Geophysical Fluid Dynamics Laboratory climate model.

Educational Impacts

Students are being trained in a wide variety of research techniques, including the use and analysis of stable isotopes of water, plant hydraulics tools, leaf photosynthesis chambers, scanning electron microscopy, thermal imaging, as well as techniques in the field, such as use of micrometeorology sensors and sapflow probes.

2-days long tree climbing class that some members of the lab took in preparation for this summer’s field work.

A key theme in this research is innovation by experimentation: developing new tools and techniques to learn new science. During the 2013 fall semester Principal Investigators Wolf and Caylor taught a new course “Design and Implementation of Environmental Sensor Networks.” This class built upon competence in the digital world for early-career students in the environmental sciences who would not generally learn to write computer code or develop electronics. Students in the project are learning that science and engineering are creative outlets that reward patient troubleshooting. In subsequent seasons, students will be led to develop not only their own research ideas and experiments but to design and build their own equipment to conduct this work. The research team’s goal is to nurture students to tackle these difficult environmental challenges and to equip them with the necessary skills to make the change they wish to see.

Other Outcomes

Results from this work directly led to funding in four government sponsored grants to Princeton University, which draw from the modeling work and electronics work supported by this project:

  • National Science Foundation, Water Sustainability and Climate $1.9M 2014-2016 “WSC-Category 2 Collaborative: Impacts of Agricultural Decision Making and Adaptive Management on Food Security in Africa”
  • National Science Foundation, Macrosystems $600K 2014-2016 “Extreme events and ecological acclimation: Scaling from cells to ecosystems”
  • Jet Propulsion Laboratory: Strategic University Research Partnership $80K 2014-2015 “Adding Precision to Agricultural Practice Through Simultaneous Chlorophyll Fluorescence and Thermal Infrared Observations” (Participant)
  • NASA New Investigator Program, $300K 2014-2016 “Integrating crowdsourcing, in situ sensing, and spaceborne observation to understand the sustainability of smallholder agriculture in African wet savannas” (Participant)

Results from this work have been presented in national and international conferences:

  • Caylor, K.K. Wolf, A. (2014). Improving drought monitoring and forecasts with novel measurement techniques. Wisenet Conference, Duke University.
  • Wolf, A., Caylor, K.K. (2013) Drought prediction and ecological monitoring with the Internet of Things. O’Reilly Strata Conference: Making Data Work. New York.
  • Siegfried, B. Wolf, A., Caylor, K.K., Sheffield, J., Wood, E.F., Gosset, M., Cazanave, F. (2013). Development and field deployment of real-time precipitation sensors using cell- phone communications. 11th International Precipitation Conference, Wageningen University, Netherlands.
  • Wolf, A., Siegfried, B., O’Connor, M., Caylor, K.K. (2013). PULSE: The Princeton Low-cost Sensor Effort. Wireless Intelligent Sensor Networks (Wisenet), Duke University.
  • Herrera Estrada, J.E., Wolf, A., Chaney, N., Sheffield, J. (2013). Network design for the deployment of wireless low-cost sensors for drought monitoring. Wireless Intelligent Sensor Networks (Wisenet), Duke University.
  • Wolf, A., Weng, E., Shevliakova, E., Malyshev, S., Pacala, S. (2013). Implementation of diverse tree hydraulics in a land surface model. AGU Fall Meeting, San Francisco.
  • Gerlein, C., Wolf, A., Caylor, K.K. (2013) Stable isotopes in plant physiology: using water isotopes to study water fluxes in a temperate forest. AGU Fall meeting, San Francisco.

Results from this work are the basis of a provisional patent application in process at the Office of Technology Licensing. See the physical electronics and it the webapp for the data interface at:

Provisional patent by Adam Wolf, Ben Siegfried, and Kelly Caylor:

  • “Environmental Monitoring Platform, interface to self- describing sensors and flexible energy harvesting system”

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Kelly Caylor
Assistant Professor of Civil and Environmental Engineering
Frederick D. Petrie Professor in Ecology and Evolutionary Biology
Adam Wolf
Research Associate, Ecology and Evolutionary Biology

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