A Depth-Controlled Tracer Technique Quantifies the Location, Extent, and Timing of Water Uptake in a Sub-Tropical Savanna
Document Type
Article
Journal/Book Title/Conference
New Phytologist
Volume
1
Issue
188
Publication Date
2010
First Page
199
Last Page
209
Abstract
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As described in the two-layer hypothesis, woody plants are often assumed to use deep soils to avoid competition with grasses. Yet the direct measurements of root activity needed to test this hypothesis are rare.
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Here, we injected deuterated water into four soil depths, at four times of year, to measure the vertical and horizontal location of water uptake by trees and grasses in a mesic savanna in Kruger National Park, South Africa.
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Trees absorbed 24, 59, 14 and 4% of tracer from the 5, 20, 50, and 120 cm depths, respectively, while grasses absorbed 61, 29, 9 and 0.3% of tracer from the same depths. Only 44% of root mass was in the top 20 cm. Trees absorbed tracer under and beyond their crowns, while 98% of tracer absorbed by grasses came from directly under the stem.
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Trees and grasses partitioned soil resources (20 vs 5 cm), but this partitioning did not reflect, as suggested by the two-layer hypothesis, the ability of trees to access deep soil water that was unavailable to grasses. Because root mass was a poor indicator of root activity, our results highlight the importance of precise root activity measurements.
Recommended Citation
Kulmatiski, A., K.H. Beard, R.J.T. Verweij, and E.C. February. 2010. A depth-controlled tracer technique quantifies the location, extent, and timing of water uptake in a sub-tropical savanna. New Phytologist.188(1):199-209.
