| The two tree water consumption characteristics, Populus simonii and Robinia pseudoacacie, and the interactions mechanism with environment factors were both studied at the level of leaf and singletree in terms of the modern technology of heat pulse sap flow and thermal dissipation sap flow probe (TDP). The two main purposes of study are to provide the science evidence in estimating the ecologic water consumption rules and to arrange better densities of the two tree species stand. The main suggestions are showed as below.1) It shows that the leaf transpiration rates of the two tree species increased with the radiation and they, for example, were 77.66g/m2 . h for Populus simonii and 20.98g/m2 . h for Robinia pseudoacacie at 8:00, but were 229.73g/m2 . h for Populus simonii and 143.94g/m2 . h for Robinia pseudoacacie at 12:00 ~ 15:00, which were the peak points of the two tree species respectively. Then, the transpiration rates decreased smoothly. The transpiration rates of reaction to environment factors of the two tree species were different in the condition, which the radiation, air temperature had significantly effect on Populus simonii, but the soil temperature in 10cm, relative humidity and wind speed had little effect on it. For Robinia pseudoacacie, on the other hand, the leaf transpiration velocity was well relative with solar radiation, but there were not significant different between the leaf transpiration velocity and the air temperature, relative humidity, soil temperature and wind speed.2) The normal rules of sap flow of the two tree species from day to night were that it began from 7:00-8:00, and increased smoothly with the strength adding of solar radiation, air temperature and soil temperature. When it reached peak at 12:00-15:00, the value became to decrease gradually. At 19:00, it decreased more slowly, but till daybreak, it get the minimum point. The interest phenomena found was that there was sap flow in nighttime, although it was faintly, which would be stem water restoration and storage for day transpiration.3) It is demonstrated the sap flow values probed in the stem were varieties in different directions. The value sequence was westward > northward > southward > eastward. At different directions of the stem, the change rules of sap flow rates, from daytime to nighttime, were the similarity, but the only different point was the value of peak. From transect of stem, the sap flow rates decreased gradually from sapwood to duramen. Also, there was not distinct regulation between the sap flow velocity and the diameter, but thesap flux density and the water consumption were increasing with tree diameter.4) According to the measurement on sap flow of the two tree species, the sapwood of Robiniapseudoacacie was smaller than Populus simonii, which were 14.8% and 81.8%.5) Based on the analysis, the multi-linearity models of the two tree species were built between sap flow rate and micrometeorological factors, which showed a significant correlation (Populus simonii: Vs = 9.467 - 0.109RH+0.322Ta + 4.108 X 10 ~ 3ESR -0.268Ts, R2=0.963; Robinia pseudoacacie: Vs=6.033 X 10-3ESR+0.749Ta- 9.502, R2= 0.956)6) With the Populus simonii as example, the significant correlation between the sapwood width and tree diameter (Ysy=2.87+0.23 XXsy, R2=0.97), the stand water consumption models were successfully established from singletree water consumption monitored by thermal dissipation technology.
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