Biomass, morphology and nutrient contents of fine roots in four Norway spruce stands |
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Authors: | Werner Borken Guido Kossmann Egbert Matzner |
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Institution: | 1. Department of Soil Ecology, BayCEER, University of Bayreuth, Dr.-Hans-Frisch-Stra?e 1-3, 95448, Bayreuth, Germany
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Abstract: | Fine root systems may respond to soil chemical conditions, but contrasting results have been obtained from field studies in
non-manipulated forests with distinct soil chemical properties. We investigated biomass, necromass, live/dead ratios, morphology
and nutrient concentrations of fine roots (<2 mm) in four mature Norway spruce (Picea abies L.] Karst.) stands of south-east Germany, encompassing variations in soil chemical properties and climate. All stands
were established on acidic soils (pH (CaCl2) range 2.8–3.8 in the humus layer), two of the four stands had molar ratios in soil solution below 1 and one of the four
stands had received a liming treatment 22 years before the study. Soil cores down to 40 cm mineral soil depth were taken in
autumn and separated into four fractions: humus layer, 0–10 cm, 10–20 cm and 20–40 cm. We found no indications of negative
effects of N availability on fine root properties despite large variations in inorganic N seepage fluxes (4–34 kg N ha−1 yr−1), suggesting that the variation in N deposition between 17 and 26 kg N ha−1 yr−1 does not affect the fine root system of Norway spruce. Fine root biomass was largest in the humus layer and increased with
the amount of organic matter stored in the humus layer, indicating that the vertical pattern of fine roots is largely affected
by the thickness of this horizon. Only two stands showed significant differences in fine root biomass of the mineral soil
which can be explained by differences in soil chemical conditions. The stand with the lowest total biomass had the lowest
Ca/Al ratio of 0.1 in seepage, however, Al, Ca, Mg and K concentrations of fine roots were not different among the stands.
The Ca/Al ratio in seepage might be a less reliable stress parameter because another stand also had Ca/Al ratios in seepage
far below the critical value of 1.0 without any signs of fine root damages. Large differences in the live/dead ratio were
positively correlated with the Mn concentration of live fine roots from the mineral soil. This relationship was attributed
to faster decay of dead fine roots because Mn is known as an essential element of lignin degrading enzymes. It is questionable
if the live/dead ratio can be used as a vitality parameter of fine roots since both longevity of fine roots and decay of root
litter may affect this parameter. Morphological properties were different in the humus layer of one stand that was limed in
1983, indicating that a single lime dose of 3–4 Mg ha−1 has a long-lasting effect on fine root architecture of Norway spruce. Almost no differences were found in morphological properties
in the mineral soil among the stands, but vertical patterns were apparently different. Two stands with high base saturation
in the subsoil showed a vertical decrease in specific root length and specific root tip density whereas the other two stands
showed an opposite pattern or no effect. Our results suggest that proliferation of fine roots increased with decreasing base
saturation in the subsoil of Norway spruce stands. |
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Keywords: | Ca/Al ratio Fine roots Fine root biomass Fine root morphology Liming Mn concentration Nitrogen deposition Norway spruce |
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