© 1994 Heron Publishing—Victoria, Canada
Element concentrations in the xylem sap of Picea abies (L.) Karst. seedlings extracted by various methods under different environmental conditions
Anke Berger (1), Ram Oren (2) and Ernst-Detlef Schulze (1)
1. Universität Bayreuth, Lehrstuhl Pflanzenökologie, Universitätsstrasse 30, 95440 Bayreuth, FRG / 2. School of the Environment, Duke University, Durham, NC 27706, USA / Received June 28, 1993
Summary
We used a Scholander pressure chamber to assess the effects of various extraction methods under different environmental conditions
on element concentrations in xylem sap of 3-year-old Picea abies (L.) Karst. seedlings. Sap from excised shoots contained higher element concentrations when extracted at low than at high
over-pressures. When comparing plants differing in water status, we found that a high extraction over-pressure introduced
a systematic error into the data. For example, in well-watered non-transpiring plants relative to unwatered transpiring plants,
potassium concentrations were 70% higher in sap extracted at 0.1 MPa over-pressure, but only 10% higher in sap extracted at
1.0 MPa over-pressure. Moreover, treatment effects depended on the time of day when the sap was extracted. Increased water
flux in transpiring plants relative to non-transpiring plants resulted in reduced xylem sap element concentrations when samples
were collected after 9 h of transpiration, but not after 4 to 6 h of transpiration. Drought had little effect on xylem sap
element concentrations, indicating that rates of element release into xylem conduits, element depletion by growing tissues,
and water flow maintained a balance that may prevent nutrient stress during short-term drought.
Keywords:
drought, plant water potential, Scholander pressure chamber, xylem sap element concentrations, water stress, xylem sap extraction.
