Soil moisture depletion under simulated drought in the Amazon: impacts on deep root uptake

Authors


Author for correspondence:
Daniel Markewitz
Tel: +1 706 542 0133
Email: dmarke@warnell.uga.edu

Summary

  • Deep root water uptake in tropical Amazonian forests has been a major discovery during the last 15 yr. However, the effects of extended droughts, which may increase with climate change, on deep soil moisture utilization remain uncertain.
  • The current study utilized a 1999–2005 record of volumetric water content (VWC) under a throughfall exclusion experiment to calibrate a one-dimensional model of the hydrologic system to estimate VWC, and to quantify the rate of root uptake through 11.5 m of soil.
  • Simulations with root uptake compensation had a relative root mean square error (RRMSE) of 11% at 0–40 cm and < 5% at 350–1150 cm. The simulated contribution of deep root uptake under the control was c. 20% of water demand from 250 to 550 cm and c. 10% from 550 to 1150 cm. Furthermore, in years 2 (2001) and 3 (2002) of throughfall exclusion, deep root uptake increased as soil moisture was available but then declined to near zero in deep layers in 2003 and 2004.
  • Deep root uptake was limited despite high VWC (i.e. > 0.30 cm3 cm−3). This limitation may partly be attributable to high residual water contents (θr) in these high-clay (70–90%) soils or due to high soil-to-root resistance. The ability of deep roots and soils to contribute increasing amounts of water with extended drought will be limited.

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