Thorburn Peter J, Walker Glen R
CSIRO Division of Water Resources, Centre for Groundwater Studies, Private Mail Bag #2, 5064, Glen Osmond, SA, Australia.
Oecologia. 1994 Dec;100(3):293-301. doi: 10.1007/BF00316957.
The stable isotopes H and O were used to determine the water sources of Eucalyptus camaldulensis at three sites with varying exposure to stream water, all underlain by moderately saline groundwater. Water uptake patterns were a function of the long-term availability of surface water. Trees with permanent access to a stream used some stream water at all times. However, water from soils or the water table commonly made up 50% of these trees' water. Trees beside an ephemeral stream had access to the stream 40-50% of the time (depending on the level of the stream). No more than 30% of the water they used was stream water when it was available. However, stream water use did not vary greatly whether the trees had access to the stream for 2 weeks or 10 months prior to sampling. Trees at the third site only had access to surface water during a flood. These trees did not change their uptake patterns during 2 months inundation compared with dry times, so were not utilising the low-salinity flood water. Pre-dawn leaf water potentials and leaf C measurements showed that the trees with permanent access to the stream experienced lower water stress and had lower water use efficiencies than trees at the least frequently flooded site. The trees beside the ephemeral stream appeared to change their water use efficiency in response to the availability of surface water; it was similar to the perennial-stream trees when stream water was available and higher at other times. Despite causing water stress, uptake of soil water and groundwater would be advantageous to E. camaldulensis in this semi-arid area, as it would provide the trees with a supply of nutrients and a reliable source of water. E. camaldulensis at the study site may not be as vulnerable to changes in stream flow and water quality as previously thought.
稳定同位素氢和氧被用于确定在三个不同程度接触溪水的地点的赤桉的水源，所有地点的地下均为中度盐碱化地下水。水分吸收模式是地表水长期可利用性的函数。常年有溪水的树木在任何时候都使用一些溪水。然而，来自土壤或地下水位的水通常占这些树木用水的50%。季节性溪流旁的树木有40%-50%的时间可以接触到溪流（取决于溪流的水位）。当有溪水时，它们使用的溪水不超过30%。然而，无论在采样前树木接触溪流2周还是10个月，溪水的使用量变化不大。第三个地点的树木仅在洪水期间能接触到地表水。与干旱时期相比，这些树木在2个月的淹没期内没有改变其吸收模式，因此没有利用低盐度的洪水。黎明前叶水势和叶片碳含量测量表明，常年有溪水的树木比最少被洪水淹没地点的树木经历的水分胁迫更低，水分利用效率也更低。季节性溪流旁的树木似乎会根据地表水的可利用性改变其水分利用效率；当有溪水时，其水分利用效率与常年溪流旁的树木相似，在其他时候则更高。尽管会造成水分胁迫，但在这个半干旱地区，吸收土壤水和地下水对赤桉是有利的，因为这会为树木提供养分供应和可靠的水源。研究地点的赤桉可能不像之前认为的那样容易受到溪流流量和水质变化的影响。
