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Abstract "Heft 29"

Freiburger Bodenkundliche Abhandlungen

Schriftenreihe des

Institut für Bodenkunde und Waldernährungslehre
der Albert-Ludwigs-Universität Freiburg i.Br.
Schriftleitung: F. Hädrich

Heft 29

Stephan Raspe

Biomasse und Minieralstoffgehalte der Wurzeln von
Fichtenbeständen (Picea abies Karst.) des Schwarzwaldes und Veränderungen nach Düngung

Freiburg im Breisgau 1992

ISSN 0344-2691


Rootage of two typical spruce ecosystems of the Black forest (SW Germany) is characterized and effects of sulfatic fertilizer additions on the distribution and nutritional status of fine roots are presented. Research is conducted at the ARINUS-sites Schluchsee and Villingen, which are representative for Central European forest sites by their parent material - granite and Mesozoic quartz sandstone respectively - and their associated soils. The 40 to 60 year-old pure spruce stand at Schluchsee grows on a highly permeable podzol. At Villingen, the 80 - 100 year-old studied spruce plantation stocks on acid brown forest soils with tendency to periodical waterlogging respsctively stagnogleys. Site dependency of root growth especially with respect to nutrient supply is discussed.

Following excavation root biomass was determined in different diameter classes. At both sites spruce builds up a typical sinker root system. The main part of root mass is located in the forest floor and the upper 30 cm of the mineral soil. Limit of rooting occurs in 1.20 m depth at the site Villingen, whereas at Schluchsee a minor number of roots grow up to 2 m depth in old root tubes from the former mixed beech fire stand. However, at both sites intensive fine root growth is restricted to the upper 10 cm of the soil. At Villingen, this depends on the periodical change of water logging and drought as well as on the fact that N supply is only in the forest floor sufficient. At Schluchsee in contrast, poor Mg supply is a limiting factor for fine root growth.
The content of nutrients in root tissue clearly reflects the supply in the soil. At the Schluchsee site with a deep incorporation of organic matter in the mineral soil N, S and P nutrition of roots is optimal in the whole profile. In contrast to these elements, variation with depth in Mg content reflect to the extremely closed Mg cycle. Nutrient content of roots from Villingen confirm the insufficient N, P and K nutrition as shown by foliar analysis. It is to be excluded that Al-toxicty is the reason for the shallow fine root growth.

Effects of fertilization (MgSO4, (K2/Mg)SO4, (NH4)2SO4) on the distribution, vitality and nutritional status of fine roots were investigated by periodically repeated core sampling. Two and respectively three vegetation periods after MgSO4 fertilization at Schluchsee the concentration of fine roots has significantly increased by 75 % and 120 %. Furthermore, a shift of fine root mass from the O horizon into the mineral soil occured. However, there is no evidence for an increase in fine root turnover. The (K2/Mg)SO4 treatment at Villingen did not affect distribution of fine roots. Although (NH^SC), addition had a distinct effect on fine root distribution no damage on fine roots could be observed. In contrast, concentration of fine roots in the upper soil increased at the N deficient site Villingen. Based on the site-specific conditions N nutrition of fine roots in relation to water supply and mineralization is discussed.

Changes in the nutrient contents of fine roots indicate a considerable uptake of ions originating from the fertilizers. The extremely low Mg content of fine roots at the Schluchsee site reach those of well Mg-supplied stands after MgSO4 fertilization. The (K2/Mg)SO4, and respectively (NH4)2SO4 fertilization, resulted in a more uniform nutrition of K and N, respectively. Changes of nonfertilized element contents are described and related to the experiments. Although soil solution showed a marked initial drop in pH and increase of Al3+ concentrations after fertilizer application root damage has not been observed at any plot. Nevertheless, Al content of roots increased. These findings emphasize that threshold values reported for 'Al-toxictiy' are highly questionable.

Distribution and nutrition of the fine roots are discussed based on nutrient supply in the soil. The close relationship between exchangeable Mg in the soil and the depth distribution of fine roots as well as their Mg concentrations emphasize the role of this element for fine root growth at the Schluchsee site. Thus, a clearly positive and effective reaction to the MgSO4 treatment is to be observed.

Application of readily soluble fertilizers stimulates fine root growth in mineral soil horizons, if a shalllow fine root distribution is due to an insufficient nutrient supply. In the case of Mg deficiency, distribution of exchangeable Mg2+ in the solid soil affects depth variations in fine root growth. Therefore the reaction of roots to Mg addition depends on the amount of adsorbed fertilizer Mg in the mineral soil. However, the positive effect of Mg fertilization on root distribution is limited when superficial rootage besides a general insufficient nutrient supply is also due to soil physical conditions. Therefore, silviculture should favor site-adapted deeper rooting tree species especially on sites affected by stagnant water.

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