.2. Measurements and data analysis2.2.1. Biomass, soluble carbohydrates and xylem sapThe roots of the seedlings were separated from the soil in thepots by washing. Fresh root, stem and leaf samples were dried ina forced air oven at 65◦C for 60 h to determine biomass. Anthronecolourimetry was used to measure the content of water-solublecarbohydrates in the roots (Zou, 1995). Root activity was measuredby the triphenyltetrazolium chloride (TTC) method (Li et al., 2000).Xylem sap extraction was measured by weighing. The abovegroundparts of the seedlings were clipped at the stem base. The stemwounds were then covered immediately with approximately 0.2 gof absorbent cotton, which was tightly wrapped around the stemwith plastic sheeting to prevent evaporation. After 12 h, the cottonwas weighed again. The weight increase of absorbent cotton corre-sponded to the amount of xylem sap from the roots. The increase inweight was divided by 1 g/cm3to obtain the sap volume. The rateof xylem sap delivery from the roots to the leaves was expressedas the volume of xylem sap per hour. The cotton was then placedand compacted at the bottom of a 10 mL syringe with a piston, andthe sap from each sample was pooled in a 5 mL centrifuge tube. Theextracts were used to measure plant hormone and NO3−contentsin the xylem sap. The root-to-leaf delivery rate of NO3−by xylemsap was expressed as the product of their NO3−concentrations andthe delivery rates of xylem sap from the roots to the leaves.