Transpiration dynamics and water sources for selected indigenous trees under varying soil water content

Tfwala, C.M.; Rensburg, L. D. van; Bello, Zaid A.; Zietsman, P.C.

doi:10.1016/j.agrformet.2019.05.030

Cited by 13 publications

(17 citation statements)

References 53 publications

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“…This suggest that trees at the site are likely decoupled from recent precipitation and shallow soil moisture, and that information from other studies can be used to compare to annual tree transpiration at the site. For example, in a similar site at this region (P=241 mm) the ratio of annual/(dry season) transpiration of Vachellia erioloba (5 m height) was 3.9/0.6 mm d −1 (Tfwala et al, 2019). Multiplying this ratio with our 11 mm dry season tree transpiration results to 72 mm of annual tree transpiration.…”

Section: Discussionmentioning

confidence: 74%

The effect of rainfall amount and timing on annual transpiration in grazed savanna grassland

Räsänen

Aurela

Vakkari

et al. 2020

Preprint

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Abstract. The role of precipitation (P) variability on evapotranspiration (ET) and its two components transpiration (T) and evaporation (E) rates from savannas continues to draw significant research interest given its relevance to a number of eco-hydrological applications. The work here reports on six years of measured ET and energy flux components, and estimated T from a grazed savanna grassland collected at a research site situated in Welgegund, South Africa. During this period, annual P varied considerably in amount (421 mm to 614 mm), rainy season length and precipitation intensity. T was estimated using annual water use efficiency and gross primary production determined from eddy-covariance measurements of net ecosystem CO2 exchange rates. The computed annual T was highly constrained to 352 ± 8 mm (T/ET = 0.55) for four wet years when rainfall was near or above the long-term mean. This is explained by the near constant annual tree transpiration and moderate water stress of C4 grasses during these years. In a drought year with intermittent rainfall, the annual ecosystem T was reduced due to grass dieback-regrowth that alters the temporal dynamics of bare soil cover and infiltration, and complicates monthly T/ET relation to leaf-area index (LAI). However, annual ET remains approximately equal to annual precipitation (P) even during the drought year due to increased soil evaporation. Indeed, at annual scales, ET ≈ P and annual T is conservative despite variation in amount and timing in rainfall, due to constant water use of mature trees, and the ability of C4 grasses to maintain transpiration at moderate water stress and effectively use pulsed rainfall.

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Section: Discussionmentioning

confidence: 74%

The effect of rainfall amount and timing on annual transpiration in grazed savanna grassland

Räsänen

Aurela

Vakkari

et al. 2020

Preprint

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“…A recent study by Tfwala et al . (2019) on indigenous trees also reported trees depending almost entirely on groundwater during the dry season and also utilizing water from superficial soil layers during the rainy season. This dimorphic root structure of deep‐rooted crops helps them adapt easily to dynamic soil water availability conditions such as droughts.…”

Section: Resultsmentioning

confidence: 98%

“…Similar results to the findings presented above, though the investigation was conducted in the field and on trees, were reported by Dawson and Pate (1996) on their investigation using stable isotope analysis to determine the water source for Banksia prionotes, where they reported that the trees depended on groundwater during dry conditions and derived water from the topsoil layers using lateral roots after rainfall events. A recent study by Tfwala et al (2019) on indigenous trees also reported trees depending almost entirely on groundwater during the dry season and also utilizing water from superficial soil layers during the rainy season. This dimorphic root structure of deeprooted crops helps them adapt easily to dynamic soil water availability conditions such as droughts.…”

Section: Soil Water Conditions and Crop Water Usementioning

confidence: 94%

Influence of soils and different phases of reproductive growth stage on transpiration efficiency of irrigated canola

Tfwala

Haka

Rensburg

et al. 2020

Irrigation and Drainage

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Much has been reported on the agronomic aspects of canola (Brassica napus L.), but there is a lack of information on the crop's transpiration (T). The objective of this study was to evaluate the influence of soils and growth periods on the T, transpiration efficiency (TE) and transpiration efficiency coefficient (TEC) of canola under irrigation. Twenty-four lysimeters (2.5 m 2) were used for the study. The experimental treatments comprised two soil forms and four growth phases during the reproductive stage, all replicated three times. Irrigation was applied weekly through a surface drip system and a water table was maintained at 1200 mm from the surface through subirrigation. Soil water content was monitored using a neutron probe. The contribution of an accessible water table was up to 60% of the total T requirement of the crop during the investigation period. TE, calculated as above-ground biomass per unit transpiration, ranged between 2.81 and 3.32 g m −2 mm −1. TEC, obtained by normalizing TE to the vapour pressure deficit, resulted in values between 3.82 and 4.99 g kPa mm −1. Both TE and TEC were significantly different between growth periods and not amongst soils.

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“…3. The degree of saturation of the subsurface, as this influences (i) the hydraulic conductivity of the subsurface and thereby the magnitude of infiltration (Brunner et al, 2009a(Brunner et al, , 2009bTang et al, 2017), and (ii) root water uptake (Loheide II et al, 2005;Snyder & Williams, 2000;Stromberg et al, 2007;Tfwala et al, 2019;Yue et al, 2016). 4.…”

Section: Conceptual Modelmentioning

confidence: 99%

“…Vertical and horizontal water movement in the subsurface, as this enables infiltration and lateral flow of water away from the stream to the floodplain and increases water available for riverine vegetation (Boano et al., 2014; Brunner et al., 2017; Maina & Siirila‐Woodburn, 2020; Maxwell & Condon, 2016). The degree of saturation of the subsurface, as this influences (i) the hydraulic conductivity of the subsurface and thereby the magnitude of infiltration (Brunner et al., 2009a, 2009b; Tang et al., 2017), and (ii) root water uptake (Loheide II et al., 2005; Snyder & Williams, 2000; Stromberg et al., 2007; Tfwala et al., 2019; Yue et al., 2016). Evapotranspiration, as direct evaporation and transpiration, represent the largest sinks of water in arid regions (Maina & Siirila‐Woodburn, 2020; Tugwell‐Wootton et al., 2020; Villeneuve et al., 2015).…”

Section: Conceptual and Numerical Modelmentioning

confidence: 99%

Controls on Interactions Between Surface Water, Groundwater, and Riverine Vegetation Along Intermittent Rivers and Ephemeral Streams in Arid Regions

Schilling

Cook

Grierson

et al. 2021

Water Resources Research

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Intermittent rivers and ephemeral streams (IRES) make up the majority of waterways in arid and semi‐arid regions. While the physical underpinnings of surface water‐groundwater (SW‐GW) flow systems are well understood, how ephemerality, hydraulic properties and vegetation interact along IRES is not clear, posing severe challenges to their sustainable management. This study sought to identify the controls for SW‐GW‐vegetation interactions along IRES. To this end, numerical experiments on a quasi‐hypothetical IRES cross‐section with an integrated surface‐subsurface hydrological model were undertaken. The influence of different degrees of ephemerality on infiltration and riverine transpiration was tested by varying the duration of no‐flow periods. The influence of hydraulic conductivity (K), moisture retention capacity, root density, and local rainfall was also explored. Experiments showed that infiltration is controlled by ephemerality and K, with infiltration decreasing rapidly with increasing ephemerality and decreasing K. Transpiration is influenced by a complex interplay between ephemerality, hydraulic properties, and vegetation. While transpiration is strongly controlled by the degree of ephemerality, the capacity of the subsurface to maintain variably saturated conditions can strongly attenuate the effects of ephemerality. A large moisture retention capacity of the subsurface can partly compensate for the reduced infiltration under increasing ephemerality. Transpiration can be as large under ephemeral as under perennial conditions, especially where water table fluctuations exhibit large amplitudes within the zone of high root density. Overall, the results provide important insights into the complex dynamics of IRES and highlight how changes in flow dynamics can have significant impacts beyond instream processes.

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Transpiration dynamics and water sources for selected indigenous trees under varying soil water content

Cited by 13 publications

References 53 publications

The effect of rainfall amount and timing on annual transpiration in grazed savanna grassland

The effect of rainfall amount and timing on annual transpiration in grazed savanna grassland

Influence of soils and different phases of reproductive growth stage on transpiration efficiency of irrigated canola

Controls on Interactions Between Surface Water, Groundwater, and Riverine Vegetation Along Intermittent Rivers and Ephemeral Streams in Arid Regions

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