Hydraulic redistribution in Amazonian trees Rafael S. Oliveira 1, Todd E. Dawson 1, Stephen S. Burgess 1,2 Daniel C. Nepstad 3 1 University of California, Berkeley 2 University of Western Australia 3 Woods Hole Research Center

Rainfall – Flona Tapajós 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

Seca plot Control plot

V = thermal diffusivity x Ln T 1 probe distance T 2 T2T2 T1T1 Heater Heat Ratio Method Flow velocity (V) is logarithmically related to the ratio of temperature increases up- and downstream from a heater

Results Upward hydraulic redistribution (hydraulic lift) during the dry season

Results Downward HR during dry-wet season transition Heavy rain

Downward HR during dry-wet season transition

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