title: Spacing of silver birch seedlings grown in containers of equal size affects their morphology and its variability.
abstract: Silver birch (Betula pendula Roth) seedlings were grown individually in containers arranged in rows radiating from a central point (Nelder plot) at densities spanning the range from 207 to 891 plants m(-2). Height of one set of seedlings was measured at weekly intervals and additional seedlings were harvested each week for dry mass and leaf area measurements. Height and shoot:root dry mass ratio increased with plant density. Seedling-to-seedling variability in dry mass, but not height, increased with increasing plant density. The red to far-red (R:FR) photon ratio in horizontally propagated radiation decreased with increasing density, even when plant densities and leaf area index values were low. In a separate experiment, elongating internodes of seedlings were irradiated locally by red and far-red light emitting diodes and stem elongation measured. Far-red light markedly increased stem elongation, suggesting that changes in light quality sensed by growing internodes are involved in the observed responses to growth density.
authors.affiliation: Faculty of Forestry, University of Joensuu, PO Box 111, 00101 Joensuu, Finland. pedro.aphalo@helsinki.fi
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: Aphalo
authors.forename: Risto
authors.initials: R
authors.lastname: Rikala
mesh_terms: D029662:Betula / Q000033:anatomy & histology* / Q000254:growth & development*; D003116:Color; D008027:Light; D018515:Plant Leaves / Q000254:growth & development / Q000528:radiation effects; D036226:Seedlings / Q000033:anatomy & histology* / Q000254:growth & development*