Rainfall exclusion in an eastern Amazonian forest alters soil water movement and depth of water uptake

Abstract

Deuterium-labeled water was used to study the effect of the Tapajós Throughfall Exclusion Experiment (TTEE) on soil moisture movement and on depth of water uptake by trees of Coussarea racemosa, Sclerolobium chrysophyllum, and Eschweilera pedicellata. The TTEE simulates an extended dry season in an eastern Amazonian rainforest, a plausible scenario if the El Niño phenomenon changes with climate change. The TTEE excludes 60% of the wet season throughfall from a 1-ha plot (treatment), while the control 1-ha plot receives precipitation year-round. Mean percolation rate of the label peak in the control plot was greater than in the treatment plot during the wet season (0.75 vs. 0.07 m/mo). The rate was similar for both plots during the dry season (ca. 0.15 m/mo), indicative that both plots have similar topsoil structure. Interestingly, the label peak in the control plot during the dry season migrated upward an average distance of 64 cm. We show that water probably moved upward through soil pores-i.e., it did not involve roots (hydraulic lift)-most likely because of a favorable gradient of total (matric + gravitational) potential coupled with sufficient unsaturated hydraulic conductivity. Water probably also moved upward in the treatment plot, but was not detectable; the label in this plot did not percolate below 1 m or beyond the depth of plant water uptake. During the dry season, trees in the rainfall exclusion plot, regardless of species, consistently absorbed water significantly deeper, but never below 1.5-2 m, than trees in the control plot, and therefore may represent expected root function of this understory/subcanopy tree community during extended dry periods.

Seasonal water use patterns of semi-arid plants in China

“…This suggests that the main water source for P. orientalis was at lower soil depths after long periods without rain. This is similar to the findings of Romero-Saltos et al (2005). Roots utilized water in the upper soil layers that was recharged by the earlier rainfall (Fig.…”

Implementing and Evaluating Variable Soil Thickness in the Community Land Model, Version 4.5 (CLM4.5)

“…Lee et al (2005) showed that the inclusion of this process improved the simulation of climate over the Amazon in CLM coupled to the Community Atmosphere Model. However, Romero-Saltos et al (2005) observed that water moved upward during dry periods in the Amazon through the soil rather than through the roots. The impacts of land-atmosphere feedbacks and deep root distributions should be explored further using variable soil depth in LSMs.…”

Seasonal water use patterns of woody species growing on the continuous dolostone outcrops and nearby thin soils in subtropical China

“…In water-limited environments, where evaporative demand exceeds precipitation and water tends to be unavailable in upper soil horizons, plants are likely to have deep roots and extract water from deep soil layers (or groundwater) (Lilley and Fukai 1994;Sekiya and Yano 2002;Romero-Saltos et al 2005;West et al 2008). Actually, many perennial plants in arid and semiarid zones, as well as in seasonally dry regions, have a dimorphic root system: a network of branched surface roots potentially takes up water from upper soil layers, while deeper roots extract water stored deep in the soil that has been recharged from antecedent precipitation (Williams and Ehleringer 2000;Kulmatiski et al 2006).…”