AUTHOR=Spanner Gustavo C. , Gimenez Bruno O. , Wright Cynthia L. , Menezes Valdiek Silva , Newman Brent D. , Collins Adam D. , Jardine Kolby J. , Negrón-Juárez Robinson I. , Lima Adriano José Nogueira , Rodrigues Jardel Ramos , Chambers Jeffrey Q. , Higuchi Niro , Warren Jeffrey M. 

TITLE=Dry Season Transpiration and Soil Water Dynamics in the Central Amazon

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 13 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.825097

DOI=10.3389/fpls.2022.825097

ISSN=1664-462X

ABSTRACT=With future projections of more intense and frequent droughts in the tropics, there is increasing importance in understanding the impacts of extensive dry periods on tree and ecosystem-level transpiration, and concurrent carbon uptake. Here we investigate soil and tree water extraction dynamics in an old-growth upland forest in central Amazonia during the 2018 dry season. Tree water use was assessed via radial patterns of sap flow in eight dominant canopy trees, each a different species, with a range in diameter, height and wood density. Paired multi-sensor soil moisture probes were installed adjacent to six of those trees and quantified volumetric water content dynamics and soil water extraction within the upper 100 cm. To link depth-specific water extraction patterns to root distribution, fine root biomass was assessed through the soil profile to 235 cm. To scale tree water use to the plot level, (stand transpiration), basal area was measured for all trees within a 5 m radius around each soil moisture probe. The sensitivity of tree transpiration to reduced precipitation varied by tree, with some increasing and some decreasing water use during the dry period. Tree-level water use scaled with sapwood area, from 11-190 liters per day. Stand level water use based on multiple plots encompassing sap flow and adjacent trees varied from ~1.7 to 3.3 mm per day, increasing linearly with plot basal area. Soil water extraction was dependent on root biomass, which was dense at the surface (i.e., 45% in the upper 5 cm) and declined dramatically with depth. As the dry season progressed and the upper soil dried, soil water extraction shifted to deeper levels and model projections suggest that much of the water used during the month-long dry-down could be extracted from the upper 2-3 m. Results indicate wide variation in rates of soil water extraction across the research area and temporally through the soil profile. The results provide key information on whole-tree contributions to transpiration by canopy trees as water availability changes, and simultaneous stand level dynamics of soil water extraction that can be used to inform mechanistic models that project tropical forest response to drought.