Hydraulic redistribution in Hydraulic redistribution in Amazonian treesAmazonian trees

Rafael S. OliveiraRafael S. Oliveira11, Todd E. , Todd E. DawsonDawson11, Stephen S. Burgess, Stephen S. Burgess1,21,2

Daniel C. Nepstad Daniel C. Nepstad 33

11University of California, BerkeleyUniversity of California, Berkeley22University of Western AustraliaUniversity of Western Australia

33Woods Hole Research CenterWoods Hole Research Center

Rainfall – Flona Tapajós

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Rainfall total ~ 2100 mm

Intro• About half of the Amazon rainforest is subject to

seasonal droughts of three months or more

• El Niño years – severe droughts

• Despite this drought, several studies have shown that these forests, under a strongly seasonal climate, do not exhibit significant water stress during the dry season

Intro• Deep water uptake - mechanism to explain the absence of seasonal water

stress

• However, majority of fine roots are near the soil surface - deep soil water uptake can be limited by very low densities of fine roots at depth

• Alternative mechanisms?

Protium sp. – dimorphic roots

laterals

taproot

Objectives

• Determine patterns (direction, timing and magnitude) of soil water redistribution by roots of three common tree species and assess the role of such phenomenon in the broader scheme of plant water uptake patterns in natural and droughted conditions in an Amazonian forest

Methods

Methods

Seca plot Control plot

V = thermal diffusivity x Ln T1

probe distance T2

T2

T1

Heater

Heat Ratio MethodHeat Ratio Method

Flow velocity (V) is logarithmically related to the ratio of temperature increases up- and downstream from a heater

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Days

Vh

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Lateral rootTap root

ResultsUpward hydraulic redistribution (hydraulic lift)

during the dry season

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Days

Vh

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h-1 )

Lateral rootTap root

Results Downward HR during dry-wet season transition

Heavy rain

Downward HR during dry-wet season transition

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Lateral root

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Conclusions

• During dry periods, upward HR was observed in 3 species in both plots . During rewetting periods, downward HR was observed.

• Direction of water movement in a plant is determined by competing sinks and water sources in the soil, plant and the atmosphere.

Implications

• About half of the rain that falls in the Amazon has its origin from evapotranspiration of the forest

• We believe that HR may increase dry-season rates of ET by effectively reducing hydraulic resistance to soil moisture uptake from depth.

• As a consequence, HR may influence regional climate in Amazonian as the results for a recent climatic modeling study suggest

• HR should be incorporated into the models used to predict ecosystem responses to water deficits that may result from land-use or global change.

Acknowledgments

• IPAM staff at Santarém, especially Levinaldo Seixas

• CNPq (Brazilian research council)

• Staff and colleagues at the Department of Integrative

Biology at UC Berkeley