Water availability is a critical limiting element in semi-arid ecosystem productivity and
presents particular challenges in Sahelian countries such as Senegal. The landscapes are
characterized by the presence of two common semi-arid shrubs (Piliostigma reticulatum
and Guiera senegalensis), both of which may be important hydraulic regulators in these
water-limited ecosystems. Dry season observations revealed higher moisture levels in soil
surrounding the shrub shallower roots relative to bare soil. This observation led us to
hypothesize that these shrubs may participate in a natural irrigation phenomenon termed
as "hydraulic redistribution" (HR). This dissertation reports on three studies performed to
ascertain the existence of and investigate the characteristics of this hypothesized
phenomenon. The first study investigated seasonal variability in soil water and shrub root
patterns. Soil moisture content declined steadily in the 0.9-1.2 m depth range and
increased in the 0.2-0.4 m depth range, which supports the HR hypothesis. The second
study quantified plot scale water balance fluxes. Notably, shrub water uptake from the
water table served as a crucial contribution to the system water balance. The third study
investigated the magnitude and dynamics of HR during the dry season. Crop-shrub
associations were evaluated from measurements of soil moisture and potential, root sap
flow and plant physiological measurements. This study proved the existence of HR and
quantified the HR magnitude (~0.1 mm d⁻¹). For shrubs and annual crops in close
association with shrubs, HR clearly provides a mechanism for drought-stress avoidance
and maintenance of plant physiological functions. At the landscape scale, the interplay
between shrub root morphology and HR may play a vital role in ecosystem function with
practical implications for nutrient cycling and water balance in arid ecosystems. / Graduation date: 2006
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37141 |
| Date | 02 December 2005 |
| Creators | Kizito, Fred |
| Contributors | Dragila, Maria Ines |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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