title: Effects of prolonged drought on the anatomy of sun and shade needles in young Norway spruce trees.
abstract: Predicted increases in the frequency and duration of drought are expected to negatively affect tree vitality, but we know little about how water shortage will influence needle anatomy and thereby the trees' photosynthetic and hydraulic capacity. In this study, we evaluated anatomical changes in sun and shade needles of 20-year-old Norway spruce trees exposed to artificial drought stress. Canopy position was found to be important for needle structure, as sun needles had significantly higher values than shade needles for all anatomical traits (i.e., cross-sectional needle area, number of tracheids in needle, needle hydraulic conductivity, and tracheid lumen area), except proportion of xylem area per cross-sectional needle area. In sun needles, drought reduced all trait values by 10-40%, whereas in shade needles, only tracheid maximum diameter was reduced by drought. Due to the relatively weaker response of shade needles than sun needles in drought-stressed trees, the difference between the two needle types was reduced by 25% in the drought-stressed trees compared to the control trees. The observed changes in needle anatomy provide new understanding of how Norway spruce adapts to drought stress and may improve predictions of how forests will respond to global climate change.
authors.affiliation: Departement of Forest Botany, Dendrology and Geobiocoenology Mendel University in Brno Zemědělská 3 61300 Brno Czech Republic.
authors.forename: Roman
authors.initials: R
authors.lastname: Gebauer
authors.affiliation: Departement of Forest Botany, Dendrology and Geobiocoenology Mendel University in Brno Zemědělská 3 61300 Brno Czech Republic.
authors.forename: Daniel
authors.initials: D
authors.lastname: Volařík
authors.affiliation: Departement of Forest Botany, Dendrology and Geobiocoenology Mendel University in Brno Zemědělská 3 61300 Brno Czech Republic.
authors.forename: Josef
authors.initials: J
authors.lastname: Urban
authors.affiliation: Norwegian Institute of Bioeconomy Research PO Box 115 N-1431 Ås Norway.
authors.forename: Isabella
authors.initials: I
authors.lastname: Børja
authors.affiliation: Norwegian Institute of Bioeconomy Research PO Box 115 N-1431 Ås Norway.
authors.forename: Nina Elisabeth
authors.initials: NE
authors.lastname: Nagy
authors.affiliation: Norwegian Institute of Bioeconomy Research PO Box 115 N-1431 Ås Norway.
authors.forename: Toril Drabløs
authors.initials: TD
authors.lastname: Eldhuset
authors.affiliation: Norwegian Institute of Bioeconomy Research PO Box 115 N-1431 Ås Norway.
authors.forename: Paal
authors.initials: P
authors.lastname: Krokene
keywords: Climatic change; Picea abies; drought; hydraulic conductivity; light quality; needle growth; tracheid; xylem transport