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Published online on November 21, 2005, 10.1073/pnas.0508785102
PNAS | December 6, 2005 | vol. 102 | no. 49 | 17576-17581


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ENVIRONMENTAL SCIENCES_PS / PLANT BIOLOGY
Root functioning modifies seasonal climate

Jung-Eun Lee *, {dagger}, Rafael S. Oliveira {ddagger} §, Todd E. Dawson {ddagger}, and Inez Fung *, {dagger}, ¶

Departments of *Earth and Planetary Science and {ddagger}Integrative Biology, and Berkeley Atmospheric Science Center, University of California, Berkeley, CA 94720

Contributed by Inez Fung, October 6, 2005

Hydraulic redistribution (HR), the nocturnal vertical transfer of soil water from moister to drier regions in the soil profile by roots, has now been observed in Amazonian trees. We have incorporated HR into an atmospheric general circulation model (the National Center for Atmospheric Research Community Atmospheric Model Version 2) to estimate its impact on climate over the Amazon and other parts of the globe where plants displaying HR occur. Model results show that photosynthesis and evapotranspiration increase significantly in the Amazon during the dry season when plants are allowed to redistribute soil water. Plants draw water up and deposit it into the surface layers, and this water subsidy sustains transpiration at rates that deep roots alone cannot accomplish. The water used for dry season transpiration is from the deep storage layers in the soil, recharged during the previous wet season. We estimate that HR increases dry season (July to November) transpiration by {approx}40% over the Amazon. Our model also indicates that such an increase in transpiration over the Amazon and other drought-stressed regions affects the seasonal cycles of temperature through changes in latent heat, thereby establishing a direct link between plant root functioning and climate.

Amazon | evapotranspiration | hydraulic redistribution

Author contributions: J.-E.L., R.S.O., T.E.D., and I.F. designed research; J.-E.L. and R.S.O. performed research; and J.-E.L., R.S.O., T.E.D., and I.F. analyzed data and wrote the paper.

Conflict of interest statement: No conflicts declared.

Abbreviations: AGCM, atmospheric general circulation model; ET, evapotranspiration; HL, hydraulic lift; HR, hydraulic redistribution.

§ Present address: Lab. Ecologia Isotópica, Centro Energia Nuclear para Agricultura, Universidade de São Paulo, Av. Centenário, 303, 13.416-000, Piracicaba, São Paulo, Brazil.

{dagger} To whom correspondence may be addressed. E-mail: jelee{at}atmos.berkeley.edu or ifung{at}berkeley.edu.

© 2005 by The National Academy of Sciences of the USA


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