Abstract: We used high-sensitivity thermocouple was to monitor sap flow, especially for the sap flow and transpirational cooling in the leaves of Ferula krylovii, the measurement of which was difficult with the conventional sap flow meter. The thermal signals from sap flow, leaf temperature, and air temperature were recorded with highsensitivity thermocouples. The results showed that the thermal signal of sap flow could be expressed either with the value of the thermal peak or with the areas below the thermal peak which showed a higher sensitivity. The transpiration rate in the leaves of F. kryloviiincreased quickly and steadily with the increases of light intensity and air temperature, and decreased only when light intensity and air temperature began to decrease. The fact that no sign of transpiration regulation was seen indicates that the F. krylovii was a highly water consuming plant. The plant could maintain a temperature constantly below or equal to the air temperature through transpirational cooling, with a maximum decline of 6 ℃ in the leavesbelow the air temperature, thus effectively prevented the possible high temperature injury due to the absorption of high solar radiation at a price of large amount of water consumption. Our results indicated that the high-sensitivity thermocouples could be used not only in detecting sap flow, but also in cases that were difficult for the normal sap flow meters, with low cost.

Key words: Yellow River Delta, spatial variability, soil salinity, multi-scale