J. Denouden et D. Vogels, MECHANICAL RESISTANCE BY AN ECTORGANIC SOIL LAGER ON ROOT DEVELOPMENTOF SEEDLING PINUS-SYLVESTRIS, Plant and soil, 197(2), 1997, pp. 209-217
We investigated early root development of Pinus sylvestris seedlings i
n relation to bulk density and natural particle layering in an ectorga
nic soil layer from a bracken (Pteridium aquilinum) stand. Responses i
n root development to two levels of bulk density (0.07 and 0.15 g/cm(3
)) in mixed bracken substrate were compared with effects in peat of si
milar bulk densities, and in sand of three different bulk densities (0
.37, 0.52, and 0.67 g/cm(3)). The effect on root growth of the natural
horizontal layering of the organic particles was examined by comparin
g intact with mixed ectorganic bracken soil profiles of similar bulk d
ensities (resp. 0.09 and 0.07 g/cm(3)). Root length growth was signifi
cantly reduced in the organic and sandy substrates of high bulk densit
y. Root diameter was not affected by bulk density in the organic subst
rate, but increased with higher bulk density in sand. Preservation of
horizontal layering in the intact ectorganic profile significantly red
uced root length compared with mixed substrate of similar bulk density
. Roots growing in high bulk density, and intact, organic substrate sh
owed increased twisting, which resulted in a smaller depth reached by
the root relative to total root length produced. In sand, root twistin
g did not change with increased bulk density. It is suggested that roo
ts growing through organic substrate follow a path of least resistance
. This implies that organic particle size and orientation are more imp
ortant in determining root development than bulk density. This study p
oints out that the natural layering of organic particles presents anot
her constraint on the establishment of plant species in sites with a w
ell-developed ectorganic soil layer. Disturbance of this layer may the
refore enhance establishment of seedlings by reducing the mechanical r
esistance of the ectorganic soil profile to developing seedling roots.