Xylem sapflow and stomatal conductance of adult Norway Spruce in Open-Top Chambers: air pollution and drought effects

1997

7 Abb., 2 Tab., 22 Lit. Ang.

Unselbständiges Werk

12612

200104693

Whole-tree transpiration rates were measured continuously by monitoring xylem sap fluxed during a growing season on seven adult spruce trees: three trees were growing in filtered-air OTC's (Open-Top Chambers), two trees were growing in the open. During a drought from the end of July to mid-September, transpiration rates decreased in all of the trees. Daily total sap-flux densities (total sapflow / sapwood area) declined from 12-22 to 9-5 kg.dm-2.day-1, And the decline was correlated with decreases in predawn water potential (from -0.3 to -0.9 MPa) and in needle stmatal conductance (from 7-12.5 to 5 mmol.m-2.s-1). Over the growing season, trees in filtered-air OTC's transpired more than trees in ambient-air OTC's and in the open, even during a drought when the trees in the filtered air OTC's were subjected to a more severe water stress. Whole-tree hydraulic conductance, calculated from diurnal courses of xylem sap-flux and needle water potential, decreased with increasing soil water deficit. Moreover, the hydraulic conductance was about twice as large in trees in the filtered-air OTC's than in trees in ambient-air OTC's. It is concluded that seasonal variation in whole-tree transpiration and in stomatal conductance were mainly affected by soil drought, but long-term pollution effects via the soil-rhizospher zone seems also involved by alternating the soil-to-leaf hydraulic conductance.