Study On Water Characteristic In Soil-plant-atomsphere Continuum(spac) Of Phyllostachys Pubescens

Dynamax Sap Flow Measuring System and CI-340 Portable Photosynthesis Pystem were used to monitor the sap flow velocity (SFV) and photosynthetic rate(Pn),transpiration rate (Tr) of the Phyllostachys pubescens stands in Miaoshanwu Nature Reserve, Zhejiang respectively. The soil water potential at 0-100 cm layer were measured with Equitensiometer-15 that is an instrument for measuring soil water potential.The total solar radiation, air temperature, air relative humidity, wind speed were also measured with an automatic weather station.By analysis water transportation patterns and scales in SPAC,it was aimed at to provide a theoretical foundation for instructing water Saving irrigation and controlling stand dencity.The main results indicated as follows:From march 1th in 2009 to february 28th in 2010,the total precipitation was 1816mm in main growth period of Phyllostachys pubescens ,consisted of throughfall,1436.6mm(79.11%); stemflow122.3mm(6.73%);and canopy interception,257.1mm(14.16%).The relationships between canopy interception,stemflow and total rainfall could be described significantly by a power function ,while the relationship between throughfall and total rainfall is linear.The amount of litter layer on forest floor was 6.660 t·hm-2. Maximum water retention ratio and water-holding capacity of litter were 269.4%. The surface run off from plot was low and only 31.61 mm, accounting for 0.22% of the total precipitation.The diurnal varitation of net photosynthetic rate(Pn) and transpiration rate(Tr) for Phyllostachys pubescens change with single peak curve in winter and spring.The mean of Pn in winter was 2.62μmol·m-2·s-1,which decresed to 1.24μmol·m-2·s-1 in spring.The mean of Tr in winter and spring were 0.3113mmol·m-2·s-1 and 0.2742mmol·m-2·s-1 respectively.The diurnal variations of SFV exhibited mono-peak curve with a distinct diurnal course in clear days and multi-peak pattern in cloudy or rainy days. Moreover, the average daily sap flow rate and diurnal sap flux in cloudy or rainy days were lower than that in sunny days. Magnitude of sap flow changed considerably between sunny and rainy days. The daily sap flux of Phyllostachys pubescens with different diameter followed similar pattern, the bigger ones had faster SFV and higher daily sap flux than the smaller. When the average soil water potential in 0-100 cm layer was between -13 to -10 kPa, no obvious correlation was found between SFV and the average soil water potential. But SFV was positively correlated with the soil water potential as the average soil water potential less than -200 kPa. So soil moisture became one of the main limiting factors for SFV. SFV had significant positive correlations with solar radiation, air temperature, vapor pressure deficit (VPD) and wind speed, but negative correlation with air relative humidity.