Sap Flow Of Pinus Sylvestris Var. Mongolica In Yulin Shaanxi

In the arid, semi-arid areas of northern China, water is considered to be the main limiting factor in the vegetation construction, as one of the most important afforestation tree species growing in this region, Pinus sylvestris var. mongolica has many merits for drought resisting, sand preventing, etc. so it is necessary to carry out a study on water consumption traits of Pinus sylvestris var.mongolica. In this paper, the thermal dissipation method were applied for three different stems (26.4cm,19.4cm and 11.7cm) of Pinus sylvestris var. mongolica in Yulin botanical garden of Shaanxi province (for the convenience of discussion, we use big, medium and small to represent sample trees), then analyzed and the relationship between different trunk sap flow velocities and made a comparsion. moreover, the the diurnal and seasonal variations of liquid sap flow and its relationship with meteorological variables(such as total solar radiation intensity, air temperature, air relative humidity, wind speed, soil moisture, etc) were investgated,, the main conclusions are as follows:(1) There was a significant linear correlation between the sap flow velocity of large, medium and small trees under the north and south sides, and the average sap flow velocity were 114%,96% and 8% respectively on the north side, with the diameter decreases, the difference of mean sap flow velocity was reduced; We analyzed such a difference by using the least significant difference method (LSD). results showed that, there was a significant difference of sap flow velocity between north and south, such a difference was not obvious in smaller tree.(2) Take small tree for example. Compared to the sap flow velocity under rainy, cloudy and sunny days, sap flow starting time is becoming late, and stopping at an earlier time; the reason is in the rain and cloudy weather, meteorological factors changed drastically, which caused more variation rate of flow generation each month. In May a day with an average sap flow was 3.99cm/h, in July September, 2.90cm/h 4.57cm/h, respectively, in July September the minimum sap flow; sap flow start time in May July in the morning 7:00,8:00 in September. Divided into single peak type, sap flow velocity, curve of two peaks type and multi peaks type, two peaks type, strong solar radiation in high temperature period, multi peak appeared in the change of meteorological factors of cloudy and overcast days.(3) The big tree during the whole study period the average sap flow velocity was 22.2L/d, the total sap flow was 3781.1L, Pinus sylvestris var. mongolica in daily sap flow velocity was 11.8L/d, the total sap flow is 2004.8L, a small pine daily sap flow velocity was 5.4L/d, the total sap flow was 914.5L. Three trees of Pinus sylvestris var. mongolica daily sap flow dynamics showed a similar trend, from early May to late June is gradually reduced, the minimum value appeared in late June, were 8.9 L/d,5.3 L/d,1.7 L/d, the average daily sap flow increased rapidly in early July, after early July average daily sap flow change trend is gentle, in early July to late August day the sap flow was maintained at a high level, the peak appeared in early August, the peak were 29.9 L/d,15.7 L/d,7.6 L/d, after the end of August the average daily sap flow gradually decreased, until early October the average daily sap flow is slightly lower than the average value.(4) This paper uses multiple linear regression method, the sap flow velocity and total solar radiation intensity, air temperature, air relative humidity, wind speed, soil volumetric water content by stepwise regression analysis, results showed that the total solar radiation and atmospheric relative humidity are the main factors affecting the sap flow velocity, which was negatively correlated with air relative humidity and the sap flow velocity, total solar radiation and sap flow was positively correlated.(5) This paper uses multiple linear regression method, the daily total solar radiation and daily average air temperature, average air relative humidity, average wind speed, average daily soil moisture and sap flow was analyzed. The correlation of each environmental factor on May and fluid flow is weak, the fitting effect of regression model, in July the various environmental factors and on the sap flow strong correlation, regression model fitting effect is better, the main factors affecting on the sap flow velocity on the total solar radiation and daily average relative humidity.