A Study On The Sap Flow Rate Of Pinus Tabulaeformis Trees During Summer In Taiyue Mountain, Shanxi Province, China

The sap flow rate of 32-year-old Pinus tabulaeformis were investigated as well as the influence of environmental factors on the rate in Taiyue Mountain, China's Shanxi Province from June to August in 2005. The techniques of thermal dissipation sap velocity probe (TDP) and ICT-2000 were used in the study. in addition to comparing the water conduction efficiency of sapwood and heartwood of trees in summer under various weather conditions, the sapflow rates in sapwood and heartwood of Pinus tabulaeformis trees were measured. A TDP80 probe and a method of heat balance were adopted in the measurement. According to the measured data of sapwood area, heartwood diameter and diameter under bark of 36 Pinus tabulaeformis trees, the linear regressive equations were established. Results indicate the curve of sap flow rate presented a two-peaked pattern in sunny days: diurnal sap flow increased from 7:30 and reached the first peak at 11:00 (0.00297cm s^-1) and second peak at 13:00 (0.00294 cm s^-1) . Between the two peaks, the rate dropped down slightly to 0.00273 cm s^-1 at 12:00. Generally, sunny days had larger sap flow rates than cloudy days, and in the last place rainy days. The sap flow rate under the same weather condition had a trend to rise with the increase in the diameter at breast height. The sap flow rates in different days were affected mainly by such environmental factors as solar radiation, relative humidity and air temperature. The average daily sap flow amount was positively correlated with the cross area at breast height of trees. The average daily sap flow per tree amount in mid-summer was 10.3733 dm³d^-1, of which the diurnal amount was 8.6663 dm³ d^-1. For the 32-year-old P. tabulaeformis plantation, the average daily transpiration rate in summer was 12843dm3 hm^-1d^-1, and the diurnal transpiration amounted to 10730dm³ hm^-1d^-1, accounting for 83.55% of the whole day . sapflow rate at night is less than 5% (for 60-year-old P. tabulaeformis)and accounts for about 15%(for the 30-year-old one ) of that in the daytime, and for the 30-year-old P. tabulaeformis theaverage diurnal sapflow (11.7 dm³ d^-1) makes up 84% of daily total sapflow (13.9 dm³ d^-1); for 60-year-old ones, the daytime (67.5 dm³ d^-1) accounts for roughly 96% of daily total sapflow (69.9 dm³ ·d^-1). Water consumption by transpiration of 30- and 60-year-old P. tabulaeformis amounts to 85% and 95% of the daily total water consumption. In the daily total sapflow for 30- and 60-year-old pines, the sapflow in sapwood contributes 72% and 61%, and that in heartwood makes up 28% and 39%, respectively. These results also imply that the heartwood of P. tabulaeformis, which has not completely lost its water conducting functions, should not be ignored in the measurement.