Reaction of root systems of grand fir ( Abies grandis Lindl.) and Norway spruce ( Picea abies Karst.) to seasonal waterlogging

Abstract

Effects of seasonal waterlogging on rooting depth and rooting intensity (root counts per unit profile wall area) were analysed on profile walls in 14 stands of pure grand fir ( Abies grandis Lindl.) and pure Norway spruce ( Picea abies Karst.), varying from 20 to 31 years old, in a mountainous region in western Germany. The sites vary from non-waterlogged to strongly seasonally waterlogged. We found that seasonal waterlogging in compacted soils is a main stress factor that strongly influences the root distribution of both species. However, roots of grand fir were more tolerant, expanded to greater depths (in general more than 20 cm), and attained higher densities (more than 30%) than roots of Norway spruce. The roots of grand fir even penetrated into the compact Sd-horizon of pseudogleys, whereas the Sw-horizon (seasonally waterlogged horizon) prevented deeper rooting of spruce and contributed to its plate-shaped root system. In addition, a study on the dynamics of fine root biomass and chemistry from waterlogged and non-waterlogged periods was carried out by core sampling in a 25-year-old grand fir stand. During the waterlogged period, the fine roots had considerably greater dead (5558 kg ha −1) than live biomass (3594 kg ha −1). At the beginning of the non-waterlogged period, the total biomass of live fine roots increased by 50%, and the dead fine roots decreased by 27%. The influence of waterlogging on the vitality of the fine roots is recognizable in their chemical composition: under waterlogged condition, live fine roots contained distinctly less K, Mg and Zn, but more Mn, than during the non-waterlogged period.