| Water is alimiting factor for revegegation in gneiss rocky mountainous area of Pingshan county, Hebei. Therefore, it is very meaningful to study and master the water consumption by transpiration of the main planting tree species in the area. In this research, from three angles: the variation of sap flow, its correlation to environmental factors and to soil water content, to sdudy water-consumption Characteristics of the main planting tree species Pistacia chinensis, Robinia pseudoacacia, Prunus sibirica, Pyrus bretschneideri Rehd., Prunus davidiana., Zizyphus jujuba, Vitex negundo var. heterophylla, stem sap flow and the related environmental factors of them was continuously detected with the thermal dissipation probe (TDP) and automatic weather station in the rocky mountainous area of Pingshan county, Hebei. All of these conclusions will provide the scientific basic for the main planting tree species'selection and arrangement. The results showed that:(1)In four continuous typical sunny days,concerning Pistacia chinensis, the diurnal variation of sap flow veloeity showed as a broad-peaked curve; the stem sap flow started from 6:10 to 6:40, ascended to the peak from 8:40 to 12:00 and fell into the trough from 21:20 to 1:10 the next day. Concerning Robinia pseudoacacia, the diurnal variation of sap flow veloeity showed as a double-peaked curve; the stem sap flow started from 6:10 to 6:50, ascended to the peak from 15:40 to 16:00 and fell into the trough from 21:20 to 23:50. Concerning Prunus sibirica and Pyrus bretschneideri Rehd., the diurnal variations of sap flow veloeity showed as a single-peaked curve; the stem sap flow of Prunus sibirica started from 5:50 to 6:10, ascended to the peak from 9:50 to 10:40 or from 17:00 to 17:10 and fell into the trough from 1:40 the next day to 2:20 the next da; the stem sap flow of Pyrus bretschneideri Rehd. started from 6:10 to 6:50, ascended to the peak from 14:20 to 15:40 and fell into the trough from 3:30 the next day to 4:40 the next day. Concerning Prunus davidiana., the diurnal variation of sap flow veloeity showed as a double-peaked curve; the stem sap flow started from 6:40 to 7:10, ascended to the peak from 9:50 to 13:00 and fell into the trough from 22:40 to 23:20. Concerning Prunus sibirica and Pyrus bretschneideri Rehd., the diurnal variations of sap flow veloeity showed as a single-peaked curve with fluctuations.the stem sap flow of Zizyphus jujuba started from 6:20 to 7:20, ascended to the peak from 15:00 to 16:20 and fell into the trough from 19:50 to 21:10; the stem sap flow of Vitex negundo var. heterophylla started from 6:00 to 6:40, ascended to the peak from 11:00 to 13:50 and fell into the trough from 20:40 to 23:10. Comparing all of them, the order of the peak of sap flow velocity was: Pyrus bretschneideri Rehd.>Prunus davidiana.>Prunus sibirica>Pistacia chinensis>Robinia pseudoacacia>Zizyphus jujuba>Vitex negundo var. heterophylla; the order of the average of sap flow velocity was: Pyrus bretschneideri Rehd.>Prunus davidiana.>Prunus sibirica> >Vitex negundo var. heterophylla>Zizyphus jujuba. Pistacia chinensis>Robinia pseudoacaciaThe diurnal variations of water consumption of all tree species were similar to that of sap flow veloeity. The peak time of water consumption and percentage was respectively: Pistacia chinensis:8:0017:00,75.11%;Robinia pseudoacacia:8:0019:00,84.43%;Prunus davidiana.:9:0017:00,77.69%;Pyrus bretschneideri Rehd.:10:0017:00,63.20%;Prunus sibirica:8:0018:00,77.87%。Zizyphus jujuba:8:0018:00,89.98%;Vitex negundo var. heterophylla:8:0017:00,91.80%. the average of daily water consumption was respectively: Pistacia chinensis:13.33L,Robinia pseudoacacia:2.06L,Prunus sibirica:12.20L,Pyrus bretschneideri Rehd.: 22.60L,Prunus davidiana.: 11.88L,Zizyphus jujuba: 0.54L,Vitex negundo var. heterophylla: 0.61L. The order was: Pyrus bretschneideri Rehd.>Pistacia chinensis>Prunus sibirica>Prunus davidiana.>Robinia pseudoacacia>Vitex negundo var. heterophylla>Zizyphus jujuba.(2) In different weather types, the diurnal variations of sap flow veloeity of all tree species were different. In sunny days and cloudy days, they showed significantly as"n".Howerer, In cloudy days they showed as narrower peak than that in sunny days. In rainy days, the sap flow veloeity of Pistacia chinensis was always low in the whole day, and showed as a line. The diurnal variations of the sap flow veloeity of Robinia pseudoacacia showed as a double-peaked curve. The diurnal variations of the sap flow veloeity of Zizyphus jujuba,Vitex negundo var. heterophylla showed significantly as a double-peaked curve. The diurnal variations of the sap flow veloeity of Prunus sibirica, Pyrus bretschneideri Rehd., Prunus davidiana.showed significantly as a single-peaked curve. As far as the time of diurnal variations of the sap flow veloeity was concerned, the sap flow of all all tree species started erlier and fell into the trough later in sunny days than in cloudy days. But in rainny days the variations were not regular. The orders of the peak of sap flow velocity were all: sunny days>cloudy days > rainy days. The orders of the average of sap flow velocity ang the average of daily water consumption of arbors were significantly: sunny days>cloudy days > rainy days. That of Zizyphus jujuba and Vitex negundo var. heterophyllawas was sunny days> rainy days >cloudy days; but the average of sap flow velocity and the average of daily water consumption in cloudy days were similar to that in rainy days.(3) The variation of sap flow veloeity of Pistacia chinensis as a single-peaked curve in May; as a broad-peaked curve in June, July and August, as a double-peaked curve in September and October. The variation of sap flow veloeity of Robinia pseudoacacia as a double-peaked curve in all months. The variation of sap flow veloeity of Prunus sibirica as a single-peaked curve in all months except June for a double-peaked curve. The variation of sap flow veloeity of Zizyphus jujuba as a double-peaked curve in May and October with low fluctuation, and as a single-peaked curve from June to September with high fluctuation. The variation of sap flow veloeity of Vitex negundo var. heterophylla as a double-peaked curve in May, September, October with low fluctuation, and as a single-peaked curve from June to August with high fluctuation. As far as the time of diurnal variations of the sap flow veloeity was concerned, the sap flow-Starting time of all tree species were"late-early-late"in all months, and that was earliest in June.The water consumptions of all tree species in each month were different. Those of all tree species showed as a"low-high-low"trend, except for Pistacia chinensis for a"hingh-low-high-low"trend. The water consumption of Pistacia chinensis was mainly in May, and from July to September, accounting for 73.09% of total water consumption in the year. The water consumption of Robinia pseudoacacia was mainly in from July to September, accounting for 55.24%. The water consumption of Prunus sibirica was mainly in from April to July, accounting for 77.41%. The water consumption of Pyrus bretschneideri Rehd. was mainly in from April to June, accounting for 51.48%. The water consumption of Prunus davidiana. was mainly in from April to June, accounting for 60.52%. The water consumption of Zizyphus jujuba was mainly in in May, July and August, accounting for 59.59%. The water consumption of Vitex negundo var. heterophylla was mainly in from July to September, accounting for 60.56%(4) Correlation analysis showed that,in sunny days and cloudy days, the main factors of affeeting the stem sap flow of trunks of all tree species were sun radiation, air temperature and air relative humidity. But in rainny days, the main factors of affeeting the stem sap flow of each tree species were different. For Pistacia chinensis, Robinia pseudoacacia, Zizyphus jujuba, Vitex negundo var. heterophylla,the main factors of affeeting the stem sap flow were air temperature, air relative humidity, soil moisture and soil temperature. ForPrunus sibirica, Pyrus bretschneideri Rehd., Prunus davidiana., those were sun radiation, air temperature, air relative humidity and soil temperature. During the growing season, the main factors of affeeting the stem sap flow of trunks of all tree species were sun radiation, air temperature and air relative humidity. The influence of left environmental factors on the sap flow is generally small, but there are exceptions.(5) Pyrus bretschneideri Rehd. were treated by supporting1.5, 1.0, 0.5,0 times of precipitation and being made drought , formed soill water steps, to study the the influence of soil moisture on the stem sap flow. The result was that:, the diurnal variation of sap flow veloeity of all treatments showed as a single-peaked curve, except for 0 times of precipitation and drought treatmen with a double-peaked curve in the late. The order of the average of sap flow velocity was: W1>W2>W3>W4>W5. Correlation analysis showed that: the correlation coefficient between sap flow velocity and soil moisture under each treanment was respectively: W1:0.183;W2:0.041;W3:0.008; W4:0.032;W5:0.0324, and all were significant except W1. The order was: W3>W2>W4>W5>W1.(6)Combined with the sap flow velocity of Robinia pseudoacacia, Zizyphus jujuba, Vitex negundo var. heterophylla, the observation of's anatomical structure, indicated that the order of the efficacy, safety and drought resistance of their water system was: Robinia pseudoacacia > Vitex negundo var. heterophylla > Zizyphus jujuba. The order relative conductivity and vulnerability index was: Vitex negundo var. heterophylla > Zizyphus jujuba > Robinia pseudoacacia. While the order of the average of sap flow velocity was: Vitex negundo var. heterophylla > Zizyphus jujuba > Robinia pseudoacacia. Trends of them are similar. That indicated that water consumption rates of trees were determined by the ratio of relative conductivity and vulnerability index, namely their comprehensive presentation.(7)Taking environmental factors as independent variables and the sap flow velocity as dependent variable, forty eight amultiple linears equationwas were established by stepwise regression, and the regressions were all significant, the adjusted R2 were all greater than 0.8. By inspection, the error rate of all amultiple linears was less than 10%, and had applieation value, except May, October of Zizyphus jujuba and May, September of Vitex negundo var. heterophylla. As far as selected independent variables were concerned, in forty eight amultiple linears equationwas, air temperature had been selected forty eight times, soil moisture forty three times, air relative humidity forty two times, sun radiation forty times, soil temperature thirty nine times, wind speed only ten times. The order of the universality for the influence of environmental factors on the sap flow was: air temperature> soil moisture> air relative humidity> sun radiation> soil temperature> wind speed.
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