The Characteristics Of Water Use Of Main Tree Species In Liupan Mountains Of Ningxia

In this paper, several main tree species including Quercus liaotungensis, Pinus armandii, Tilia paucicostata, Betula Platyphylla, Betula albo-sinensis, Betula utilis, Larix principis-rupprechtii, Populus davidiana, Prunus davidiana and Hippophae rhamnoides were selected to study the water use characteristics of trees in the South (Xiangshuihe catchment, semi-humidity area) and North (Diediegou catchment, semi-arid area) of Liupan mountain, Ningxia. During the gowing seasons from 2005 to 2007, the transpiration and its'response to the micrometeorological factors of the trees were studied by the method of sap flow measurements, and the drought-resistant of tree species were also analyzied with the comparison of the water parameters of these tree species measuring by PV technique, and the main results were shown as follows:1) The sap flow measurements of different stem directions and stem positions of Larix principis-rupprechtii showed that, there had a significantly difference in sap flow density between the upper stem and lower stem. And sap flow density in the upper stems were highter than lower stems during daytime; but it were lower than lower stems in the night time, and the values were relative stable. Also, there had a significantly difference in sap flow density between southern and northern of stem, and the sap flow density in southern stems were highter than northern stems. The sap flow of different size trees in diameter of Larix principis-rupprechtii were also measured, and the results indicated that sap flow density of different size trees had a significantly difference, but there had not significantly linely relationship between different size classes in diameter and sap flow density.2) In the condition of three typical climatic days, the fluncuation of sap flow density of Larix principis-rupprechtii were quitely different. In sunny days, sap flow density showed a regularly daily variation, it presented a single-curve or multiple-curve in the the daytime, but it was relative low and the values was below 0.1g·cm^-2·min^-1 during night times. In cloudy days, sap flow density showed significantly fluctuation with variation of solar radiation in the daytime, and it was also stable and lower than 0.050 g·cm^-2·min^-1 during night times. In rainy days, the sap flow density of the tree species maintained lower values in the whole day, and it had no significantly variation.3)In the condition of three typical climatic days (suuny day, cloudy day and rainy day), daily average sap flow density of Betula albo-sinensis, Betula Platyphylla,Pinus armandii, Betula utilis and Larix principis-rupprechtii were significantly different. Daily average of sap flow density of Larix principis-rupprechtii was relatively highest with the value of 0.137 g·cm^-2·min^-1, the values of Betula albo-sinensis and Betula Platyphylla was 0.063 g·cm^-2·min^-1and 0.071g·cm^-2·min^-1 respectively, the values of Pinus armandii and Betula utilis was closely and relatively lowest, and the values were 0.057 g·cm^-2·min^-1 and 0.056 g·cm^-2·min^-1 respectively. The results indicated that transpiration of Larix principis-rupprechtii was stronger than other four tree species in the same climate conditions.4)Solar radiation had a very significant effect on sap flow density of all of five measured tree species (Betula albo-sinensis, Betula Platyphylla,Pinus armandii, Betula utilis and Larix principis-rupprechtii), and the relationship between solar radiation and sap flow density could be well fitted with logarithmic function, but the correlation coefficient were different due to different sense of stomatal conductance to light among these tree species. The effects of vapor pressure deficit (VPD) on the sap flow density of these tree species presented a two-phase curve: when the values of VPD was ranged 0⁰.5Kpa, the sap flow density increased qickly with increasing VPD, it meant that VPD was a signicant factor to affect the sap flow of these tree species; but sap flow density became flatten with the add of VPD when VPD>0.5 Kpa, it indicated that VPD was not a determine factor to influence the sap flow of tree species.5)The order of drought-resistant characteristics of the ten woody species were different, which was evaluated by single water parameter measured by the PV curve technique. Generally, the osmotic potential at the primary plasmolysis state (Ψo) was considered as a better index for the evaluation of plant drought-resistant. The results indicated that the ability of drought resistance of 7 woody species in the Xiangshuihe watershed was followed as: Betula utilis>Betula Platyphylla>Betula albo-sinensis> Quercus liaotungensis>Larix principis-rupprechtii>Pinus armandii>Tilia paucicostata; the ability of drought resistance of 4 tree species in the Diediegou watershed was followed as: Prunus davidianas>Populus davidiana> Larix principis-rupprechtii>Hippophae rhamnoide.6)A comprehensive evaluation of the drought-resistant characteristics of the ten species was conducted by using fuzzy function method, and the result indicated that the ability of drought resistance of 7 woody species in the Xiangshuihe watershed was followed as: Tilia paucicostata>Pinus armandii>Quercus liaotungensis>Larix principis-rupprechtii>Betula Platyphylla>Betula albo-sinensis>Betula utilis; the ability of drought resistance of 4 woody species in the Diediegou watershed was followed as: Larix principis-rupprechtii>Prunus davidiana>Hippophae rhamnoides>Populus davidiana. And the result was similar to that of the method by using the ratio of bound water to free water as an evaluate index, it meant that the ability of water storage in plant body played a very important role in evaluating the characteristics of drought-resistance of tree species. There had a significant difference in drought-resistant characteristics of Larix principis-rupprechtii between two different regions, the ability of drought-resistant of this tree species was stronger in Diediegou watershed than Xiangshuihe watershed, it suggested that the ability of drought-resistant of the same tree species could be enhanced as a result of long-term acclimation to drought.