Abstract: A Dynamax sap flow measuring system was applied to monitor the diurnal variation of sap flow velocity of Phyllostachys pubescens stands in Miaoshanwu Nature Reserve in Zhejiang. In the meantime, Equitensiometer (EQ-15) was applied to measure the soil water potential at 0-100 cm, and an automatic weather station was utilized to record the total solar radiation, air temperature, air relative humidity, and wind speed. The diurnal variation of the sap flow velocity exhibited mono-peak curve, with a distinct diurnal course on clear days, and a multi-peak pattern on cloudy or rainy days. The average daily sap flow rate and the diurnal sap flux were lower on cloudy or rainy days than on sunny days. The magnitude of the sap flow changed considerably between sunny and rainy days. The daily sap flux of P. pubescens with different stem diameter followed similar pattern, but the stands with bigger stem diameter had the faster sap flow velocity and the higher daily sap flux. When the soil water potential in 0-100 cm layer was between -13 to -10 kPa, no obvious correlation was found between the sap flow velocity and the soil water potential. However, when the soil water potential was less than -200 kPa, the sap flow velocity was positively correlated with the soil water potential, and soil moisture content became one of the main limiting factors. The sap flow velocity had significant positive correlations with solar radiation, air temperature, vapor pressure deficit, and wind speed, but negative correlation with air relative humidity. Taking the solar radiation, air temperature, vapor pressure deficit, air relative humidity, and wind speed as independent variables and the sap flow velocity as dependent variable, the multiple linear equations of the sap flow velocity and environmental factors were established by stepwise regressing.

Key words: Rice, Water deficit stress, Leaf water potential, Photosynthesis, Dry matter partitioning