Importance of hydraulic lift in maintaining carbon assimilation during drought

North Carolina State University

SUMMARY: Eastern Threat Center scientists and cooperating researchers are examining carbon-water interactions and their influence on ecosystem processes. Hydraulic lift, the process by which deep roots make water available to shallow fine roots, helps maintain ecosystem productivity during dry conditions. This process, along with vapour pressure threshold limits, can determine whether an ecosystem is a carbon source or sink and has major implications for forecasting ecosystem processes in a changing climate.

EFETAC'S ROLE: This project is supported by Eastern Threat Center funding and collaborative research.

STATUS: Ongoing

PROGRESS: While the phenomenon of hydraulic lift is known to contribute to plant water status in dry environments, these research findings were the first to (1) demonstrate that it can also play a major role in wet environments under high evaporative demand situations and (2) make a quantitative connection between the additional water obtained due to hydraulic lift and the amount of assimilated carbon that can be maintained due to the available water. Based on our knowledge, this is the first time that such a link has been defined in quantitative terms, and it has major implications for forecasting ecosystem processes under changing climate conditions. Noormets and others (2010) demonstrated that the decline in assimilation efficiency at the canopy level under drought conditions was attributable primarily to declines in hydraulic conductance, and only secondarily to decreased stomatal conductance. In addition, the study found that contrary to expectations, the respiratory costs of primary production decreased during drought conditions.

Findings from two publications (Domec and others 2010; Noormets and others 2010) were recognized as two of the top ten major developments of the year at the 2011 Annual Ameriflux meeting. Domec and others (2010) quantified the effects of hydraulic lift in forest ecosystems, which was recognized as a major scientific advancement in the Forum section of New Phytologist (Katul and Siqueira 2010). Recent modeling efforts across sites in North Carolina, the western US and Brazil indicate that hydraulic lift may be adversely affected under higher temperatures atmospheric carbon dioxide.

Domec, J.C., King, J.S., Noormets, A., Treasure, E.A., Gavazzi, M.J., Sun, G., McNulty, S.G.  2010.  Hydraulic redistribution of soil water affects whole stand evapotranspiration and net ecosystem carbon exchange. New Phytologist 187: 171-183 (PDF)

Domec, J.C., J. Ogée, A. Noormets, J. Jouangy, M. Gavazzi, E. Treasure, G. Sun, S. McNulty, and J.S. King. 2012. Interactive effects of nocturnal transpiration and climate change on the root hydraulic redistribution and carbon and water budgets of Southern US pine plantations. Tree Physiology 32(6):707-723. (PDF)

North Carolina State University

CONTACT: Michael Gavazzi, Eastern Threat Center Biological Scientist, or (919) 549-4064

Updated: April 2015

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