, Volume 105, Issue 1, pp 87-103

Root turnover in a beech and a spruce stand of the Belgian Ardennes

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Abstract

The theoretical basis of fine root turnover estimation in forest soils is discussed, in relation to appropriate experimental techniques of measurement. After sequential coring, the correct expression is the sum of significant positive increments of live and dead roots of the various diameter categories, to which the transfer of dead roots to organic matter derived from roots, OMDR, has to be added. This should not be confounded with dead root mineralization. The transfer rates should first be estimated in root dimensions and not in weight of dry matter.

The measurements were carried out in a 120 year old beech (Fagus sylvatica L.) stand and a 35 year old Norway spruce (Picea abies Karst) stand, in the Eastern Ardennes, Belgium.

The turnover rate of fine roots (diam. <5 mm) was 4393 kg ha−1 year−1 (root dry weight), including 711.2 kg ha−1 year−1 for dead root transfer to OMDR, for beech.

For spruce, turnover rate was 7011 kg ha−1 year−1 (root dry weight), including 1498 kg ha−1 year−1 for dead root transfer to OMDR.

Under beech, there was a slight root density increase in spring. No seasonal fluctuations were observed under spruce, but a strong irreversible drop in live root growth was found in the later season 1980–1981, corresponding to a decrease of tree height growth and trunk radius increment.

Turnover rates were further expressed in dry weight and in amounts of elements (kg ha−1 year−1) (Ca, Mg, K, Na, Al, N, P, S).

Correlative relations between root dimensions and dry weight and element concentrations show that the derived values, and in particular root specific density (dry weight volume−1) vary according to species, root category, and seasonal sampling.

Various schemes of seasonal variations of root growth, described in Europe, show that the major dependance on general climate is obscured by environmental factors (soil, exposure, species). It is suggested that root density fluctuation approach the steady state on an annual basis under mild Atlantic conditions.