(1. College of Soil and Water Conservation, Beijing Forestry University,100083, Beijing;2. Key Lab. of Soil & Water Conservation and Desertification Combating of Ministry of Education, Beijing Forestry University, 100083,Beijing; 3. International Center for Bamboo and Rattan, 100102,Beijing:China)
Abstract：Stem sap flow of Robinia pseudoacia and Pinus tabulaepormis trees on the Loess Plateau,western Shanxi Province, was measured with the thermal dissipation probe (TDP) method during the growing season from April to October, 2010. Combined with some concurrent meteorological factors, the diurnal and seasonal variations of stem sap flow of both species were comparatively studied. The model of sap flow and meteorological factors was established. The results showed that: 1) the sap velocity of R.pseudoacia was lower than that of P. tabulaepormis and no significant diurnal variation in early May. In late May, the average diurnal flow velocity of R. pseudoacia was higher than that of P. tabulaepormis.Their diurnal variations were similar, and their flow velocity began to increase quickly from 9:00am and peaked at about 12:00am. 2) In August, the average diurnal flow velocity of R. pseudoacia was also higher than that of P. tabulaepormis. Their diurnal fluctuations were approximately same, and the time when flow velocity began to increase quickly and peaked was basically identical with that in May, but the diurnal peak values were 1.79 and 1.49 times as much as that in May. The average value of flow velocity in August was 3.01 and 1.48 times as much as that in May, respectively. 3)Stem sap flow and monthly water consumption present seasonality law. Water consumption was high from June to September. Sap flow velocity reached a minimum at April and a maximum at July. From April to October during the whole growing season, the water consumption of R. pseudoacia was 1.63 times as much as that of P.tabulaepormis. The regression analysis revealed that the main affecting factors of sap flow velocity were solar total radiation and vapor pressure deficit for R. pseudoacia and solar total radiation and atmospheric temperature for P. tabulaepormis, respectively.
2012, Vol. 10 
