scholarly journals Effects of groundwater abstraction on two keystone tree species in an arid savanna national park

PeerJ ◽  
2017 ◽  
Vol 5 ◽  
pp. e2923 ◽  
Author(s):  
Eleanor Shadwell ◽  
Edmund February
Keyword(s):  
Soil Water ◽  
Water Use ◽  
Water Table ◽  
Tree Species ◽  
Dry Season ◽  
Leaf Water ◽  
Groundwater Abstraction ◽  
Stomatal Regulation ◽  
Water Potentials ◽  
Large Trees

BackgroundIn arid systems with no surface water, deep boreholes in ephemeral river beds provide for humans and animals. With continually increasing infrastructure development for tourism in arid wildlife parks such as the Kgalagadi Transfrontier Park in southern Africa, we ask what effects increased abstraction may have on large trees. Large trees in arid savannas perform essential ecosystem services by providing food, shade, nesting sites and increased nutrients for many other plant and animal species and for this are regarded as keystone species.MethodsWe determine seasonal fluctuations in the water table while also determining the water source for the dominant large tree species in the Auob and Nossob rivers in the Park. We also determine the extent to which these trees are physiologically stressed using leafδ13C, xylem pressure potentials, specific leaf area and an estimate of canopy death. We do this both upstream and downstream of a low water use borehole in the Auob River and a high water use borehole in the Nossob River.ResultsOur results show that the trees are indeed using deep groundwater in the wet season and that this is the same water used by people. In the dry season, trees in the Auob downstream of the active borehole become detached from the aquifer and use more isotopically enriched soil water. In the Nossob in the dry season, all trees use isotopically enriched soil water, and downstream of the active borehole use stomatal regulation to maintain leaf water potentials. These results suggest that trees in the more heavily utilised Nossob are under more water stress than those trees in the Auob but that trees in both rivers demonstrate physiological adaptation to the changes in available water with smaller heavier leaves, no significant canopy dieback and in the dry season in the Nossob stomatal regulation of leaf water potentials.DiscussionAn increase in abstraction of groundwater particularly at the Nossob borehole may cause an additional draw down of the water table adding to the physiological stress demonstrated in our study. The managers of the Kgalagadi Transfrontier Park have a mandate that includes biodiversity conservation. To fulfil this mandate, upper and lower thresholds for groundwater abstraction that allow for an adequate ecological reserve have to be determined.

scholarly journals Water use strategies of a young <i>Eucalyptus urophylla</i> forest in response to seasonal change of climatic factors in South China

2015 ◽  
Vol 12 (13) ◽  
pp. 10469-10510 ◽  
Author(s):  
Z. Z. Zhang ◽  
P. Zhao ◽  
R. Oren ◽  
H. R. McCarthy ◽  
J. F. Niu ◽  
...  
Keyword(s):  
Soil Water ◽  
Water Use ◽  
South China ◽  
Dry Season ◽  
Boundary Line ◽  
Eucalyptus Urophylla ◽  
Wet Season ◽  
Large Trees ◽  
Nocturnal Transpiration ◽  
The Difference

Abstract. To depict the wet (April with a soil water content, SWC, of 37 %) and dry (October with a SWC of 24.8 %) seasonal changes in the water use and physiological response of a Eucalyptus urophylla plantation in subtropical South China characterized by monsoon climate, the whole-year (June 2012 to May 2013) transpiration of E. urophylla was monitored using the TDP method. Daily transpiration (ET) in October averaged 5.7 ± 2.9 kg d−1 and was 58.0 % higher than that in April (3.6 ± 2.3 kg d−1). The difference is consistent with that of the radiation and evaporative demand of the two months, while the nocturnal transpiration (ET-NOC) in the wet season (0.18 ± 0.021 kg d−1) was almost twice that in the dry season (0.11 ± 0.01 kg d−1). Trees displayed a higher stomatal conductance (GS) (53.4–144.5 mmol m−2 s−1) in the wet season and a lower GS (45.7–89.5 mmol m−2 s−1) in the dry season. The leaf-soil water potentials (ΨL) of the two months (April and October) were −0.62 ± 0.66 and −1.22 ± 0.10 MPa, respectively. A boundary line analysis demonstrated that the slight improvement in the GS by SWC in wet season was offset by a significant decrease in D, and the slope of GS sensitivity to D (dGS/dlnD) in response to GSref (references GS at D = 1 kPa) was affected by the variance of radiation instead of SWC. Specific hydraulic conductivity (ks) of trees of different sizes decreased by 45.3–65.6 % from the wet to the dry season. Combining the decreased maximum reference GS at D = 1 kPa (GSref-max) by 22.4 % with the constant max GS (GSmax) when ΨL < −1.2 MPa, we shed some light on the mechanism underlying the high water-use efficiency (WUE) of this Eucalyptus specie. With a slight change in GSref-max and high sensitivity of ks to decreasing ΨL, large trees used water more efficiently than small ones did. In addition, the −m in the dry season (0.53 ± 0.007) was lower than that in the wet season (0.58 ± 0.01) due to the difference in the ratio of GS to the boundary layer conductance (gb) in the two months. The negative relationship between −m (except when light is limited) and Q proved to be a plastic response to environmental changes for E. urophylla but did not change with decreased ks as expected.

Water stress affects the productivity, growth components, competitiveness and water relations of phalaris and white clover growing in a mixed pasture

1992 ◽  
Vol 43 (3) ◽  
pp. 659 ◽  
Author(s):  
L Guobin ◽  
DR Kemp ◽  
GB Liu
Keyword(s):  
Water Stress ◽  
Soil Water ◽  
White Clover ◽  
Leaf Growth ◽  
Leaf Water ◽  
Water Potentials ◽  
Relative Water ◽  
Dry Conditions ◽  
Leaf Appearance ◽  
Water Contents

The effect of water stress during summer and recovery after rain on herbage accumulation, leaf growth components, stomatal conductance and leaf water relations of white clover (Trifolium repens cv. Haifa) and phalaris (Phalaris aquatica cv. Australian Commercial) was studied in an established mixed pasture under dryland (dry) or irrigated (wet) conditions. Soil water deficits under dry conditions reached 150 mm and soil water potentials in the top 20 cm declined to nearly -2 MPa after 50 days of dry weather. Water stress severely restricted growth of both species but then after rain fell, white clover growth rates exceeded those of phalaris. Under irrigation, white clover produced twice the herbage mass of phalaris but under dry conditions herbage production was similar from both species. Leaf appearance rates per tiller or stolon were slightly higher for white clover than phalaris but were reduced by 20% under water stress in both species. Leaf or petiole extension rates were more sensitive to water stress than leaf appearance rates and declined by 75% in phalaris and 90% in white clover. The ratio of leaf or petiole extension rates on dry/wet treatments was similar for both species in relation to leaf relative water contents, but in relation to leaf water potentials phalaris maintained higher leaf growth rates. Phalaris maintained a higher leaf relative water content in relation to leaf water potentials than did white clover and also maintained higher leaf water potentials in relation to the soil water potential in the top 20 cm. Stomata1 conductances for both species declined by 80-90% with increasing water stress, and both species showed similar stomatal responses to bulk leaf water potentials and leaf relative water contents. It is suggested that the poorer performance of white clover under water stress may be due principally to a shallower root system than phalaris and not due to any underlying major physiological differences. The white clover cultivar used in this study came from the mediterranean region and showed some different responses to water stress than previously published evidence on white clover. This suggests genetic variation in responses to water stress may exist within white clover. To maintain white clover in a pasture under dry conditions it is suggested that grazing practices aim to retain a high proportion of growing points.

Soil water extraction by a mixed eucalypt forest during a drought period

Soil Research ◽  
1986 ◽  
Vol 24 (1) ◽  
pp. 25 ◽  
Author(s):  
T Talsma ◽  
EA Gardner
Keyword(s):  
Soil Water ◽  
Water Use ◽  
Water Table ◽  
Unsaturated Flow ◽  
Growth Ring ◽  
Soil Water Potential ◽  
Water Extraction ◽  
Depth Interval ◽  
Summer Drought ◽  
Drought Period

Eucalypt trees growing on deep soils, with a water table at about 8 m depth, showed no apparent drought effects during the 1982-83 dry period in south-east Australia when gross precipitation was only 388 mm. At the end of the drought, soil water to 4 m depth was depleted to a soil water potential of -0.5 MPa and under these conditions unsaturated flow from the water table to the lower root zone was calculated to be 0.17 mm day-1. Water extraction over the depth interval from 0 to 6 m in the drought year was 533 mm, some 200 mm in excess of that used during a year of average rainfall. The contribution to tree water use from unsaturated flow from the water table was calculated to be small (15 mm) even in a drought year, and in most years water movement would be towards the water table to yield a deep drainage term estimated between 40 and 100 mm. Growth ring studies indicated that the lower water use, estimated at 2.6 mm day-1 during the spring-summer drought, did not affect the slowly growing E. radiata species, but reduced stem diameter growth of the faster growing E. dalrympleana and E. pauciflora species.

Groundwater use by dominant tree species in tropical remnant vegetation communities

2006 ◽  
Vol 54 (2) ◽  
pp. 155 ◽  
Author(s):  
A. P. O'Grady ◽  
P. G. Cook ◽  
P. Howe ◽  
G. Werren
Keyword(s):  
Soil Water ◽  
Water Use ◽  
Tree Species ◽  
Temporal Patterns ◽  
Terrestrial Vegetation ◽  
Spatial And Temporal Patterns ◽  
Groundwater Use ◽  
Vegetation Communities ◽  
Remnant Vegetation ◽  
Water Potential Measurements

Defining groundwater dependence and water-use requirements of terrestrial vegetation represents a significant challenge to water-resources managers. Terrestrial vegetation may exhibit complex spatial and temporal patterns of groundwater dependence. In this study we have assessed the sources of water used by dominant tree species in remnant vegetation of Pioneer Valley, Mackay, in northern Queensland. Water use by tree species was determined by sapflow techniques and the sources of water were investigated by using a combination of isotopic and water-potential measurements. Within the remnant vegetation communities of the Pioneer Valley there were complex patterns of water use and water-resource partitioning. However, all communities within the study showed some degree of groundwater use. Riparian communities that were reliant on groundwater discharge for maintenance of river baseflow exhibited high species diversity and complex forest structure and different species within these communities accessed a range of water sources including shallow soil water, river water and groundwater. In contrast, the woodlands and open forest were principally reliant on soil water. Although, species such as Corymbia clarksoniana appeared to be reliant on groundwater for their dry-season water-use requirements. This study demonstrated use of groundwater by remnant vegetation communities in the Pioneer Valley but determination of groundwater dependence requires a better understanding of the temporal patterns of water use and sources of water used by each species.

Impact of soil water potential pattern on root water uptake distribution and leaf water potential

2021 ◽  
Author(s):  
Ali Mehmandoost Kotlar ◽  
Mathieu Javaux
Keyword(s):  
Water Potential ◽  
Root System ◽  
Soil Water ◽  
Water Flow ◽  
Water Uptake ◽  
Leaf Water Potential ◽  
Root Water Uptake ◽  
Leaf Water ◽  
Hydraulic Lift ◽  
Water Potentials

&lt;p&gt;Root water uptake is a major process controlling water balance and accounts for about 60% of global terrestrial evapotranspiration. The root system employs different strategies to better exploit available soil water, however, the regulation of water uptake under the spatiotemporal heterogeneous and uneven distribution of soil water is still a major question. To tackle this question, we need to understand how plants cope with this heterogeneity by adjustment of above ground responses to partial rhizosphere drying. Therefore, we use R-SWMS simulating soil water flow, flow towards the roots, and radial and the axial flow inside the root system to perform numerical experiments on a 9-cell gridded rhizotrone (50 cm&amp;#215;50 cm). The water potentials in each cell can be varied and fixed for the period of simulation and no water flow is allowed between cells while roots can pass over the boundaries. Then a static mature maize root architecture to different extents invaded in all cells is subjected to the various arrangements of cells' soil water potentials. R-SWMS allows determining possible hydraulic lift in drier areas. With these simulations, the variation of root water and leaf water potential will be determined and the role of root length density in each cell and corresponding average soil-root water potential will be statistically discussed.&lt;/p&gt;

Tropical rainforests under severe drought stress: distinct water use strategies among and within species

2021 ◽  
Author(s):  
Angelika Kübert ◽  
Kathrin Kühnhammer ◽  
Ines Bamberger ◽  
Erik Daber ◽  
Jason De Leeuw ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Soil Water ◽  
Water Use ◽  
Leaf Gas Exchange ◽  
Physiological Responses ◽  
Leaf Water ◽  
Severe Drought ◽  
Subsequent Recovery ◽  
Species Specific

&lt;p&gt;Increasing drought in the tropics is a major threat to rainforests and can strongly harm plant communities. Understanding species-specific water use strategies to drought and the subsequent recovery is therefore important for estimating the risk to tropical rainforest ecosystems of drought. Conducting a large-scale long-term drought experiment in a model rainforest ecosystem (Biosphere 2 WALD project), we evaluated the role of plant physiological responses, above and below ground, in response to drought and subsequent recovery in five species (3 canopy species, 2 understory species). The model rainforest was exposed to a 9.5-week lasting drought. Severe drought was ended with a deep water pulse strongly enriched in &lt;sup&gt;2&lt;/sup&gt;H, which allowed us to distinguish between deep and shallow rooting plants, and subsequent rain (natural abundance range of &lt;sup&gt;2&lt;/sup&gt;H). We assessed plant physiological responses by leaf water potential, sap flow and high resolution monitoring of leaf gas exchange (concentrations and stable isotopes of H&lt;sub&gt;2&lt;/sub&gt;O and CO&lt;sub&gt;2&lt;/sub&gt;). Thereby, we could derive plant water uptake and leaf water use efficiency (WUE&lt;sub&gt;leaf&lt;/sub&gt;) in high temporal resolution, revealing short-term and long-term responses of plant individuals to drought and rewetting. The observed water use strategies of species and plants differed widely. No uniform response in assimilation (A) and transpiration (T) to drought was found for species, resulting in decreasing, relatively constant, or increasing WUE&lt;sub&gt;leaf&lt;/sub&gt; across plant individuals. While WUE&lt;sub&gt;leaf&lt;/sub&gt; of some plant individuals strongly decreased due to a breakdown in A, others maintained relatively high T and A and thus constant WUE&lt;sub&gt;leaf, &lt;/sub&gt;or increased WUE&lt;sub&gt;leaf&lt;/sub&gt; by decreasing T while keeping A relatively high. We expect that the observed plant-specific responses in A, T and WUE&lt;sub&gt;leaf&lt;/sub&gt; were strongly related to the plant individuals' access to soil water. We assume that plant individuals with constant WUE&lt;sub&gt;leaf&lt;/sub&gt; could maintain their leaf gas exchange due to access to water of deeper soil layers, while plants with increasing/decreasing WUE&lt;sub&gt;leaf&lt;/sub&gt; mainly depended on shallow soil water and only had limited or no access to deep soil water. We conclude that the observed physiological responses to drought were not only determined by species-specific water use strategies but also by the diverse strategies within species, mainly depending on the plant individuals' size and place of location. Our results highlight the plasticity of water use strategies beyond species-specific strategies and emphasize its importance for species&amp;#8217; survival in face of climate change and increasing drought.&lt;/p&gt;

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