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Abstract "Heft 36"

Freiburger Bodenkundliche Abhandlungen

Schriftenreihe des

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

Heft 36

Martin Gülpen

Xylemfluß, Elementtransport und Bindung von Calcium und Magnesium in
Fichten (Picea abies [L.] Karst.) von den ARINUS-Versuchsflächen im Schwarzwald

Freiburg im Breisgau 1996

ISSN 0344-2691


Xylem sap flow, nutrient translocation and bondage of calcium and magnesium in Norway spruce (Picea abies [L] Karst.) was studied on two Sites in the "Schwarzwald" (South-West Germany) with naturally acid soils. The studies were undertaken on experimental Sites of the ARINUS research project. In this project the impact of restabilisation fertilisations and experimental nitrogen and sulfur applications on nutrient dynamics in the eco- and hydrosphere is examined using an experimental watershed approach. According to the site conditions the experimental Sites "Schluchsee" and "Villingen" were classified as representative for montane forest sites in Germany. At Schluchsee soils are corse-textured, well drained Podzols derived from granite bedrock of the "Bärhalde". At Villingen Dystric Cambisols with a periodical influence of stagnant water have developped on sand stone. On both experimental sites monocultural Stands of Norway spruce at the age of 45 to 65 (Schluchsee) and 80 to 120 (Villingen) years construct the forest Stands. During the eighties the trees exhibited yellowing Symptoms of the needles. For both spruce Stands Iow magnesium supply (in Villingen also Iow potassium supply) was detemined by needle analysis. From 1988 onwards on five watersheds experimental fertilizer applications were established (MgSO4, K2/MgSO4, (NH4)2SO4, Ca/MgCO3). The calcium and magnesium nutrition of the trees was examined by using different methodological approaches. Xylem sap concentrations, xylem sap flow and different fractions of calcium and magnesium bonding in needles and sapwood were examined.

During the analyses of xylem sap, in addition to the determination of magnesium and calcium concentrations, potassium was included into the analysis. Very similar mechanisms of xylem translocation were observed for magnesium and calcium. Calcium and magnesium concentrations in the xylem sap were well correlated according to the different treatments on the watersheds. This was also true for the concentrations  of watersoluble   magnesium   and   calcium   in   the   sapwood. This watersoluble fraction represents only a minor part of the total element content in wood. The main portion (about 95%) is bound exchangeably to pectin in the cell walls. This fraction can be remobilized completely by exchange processes. Calcium and magnesium mobility in the xylem is discussed to be mainly dependent from these exchange processes. By calculating element translocation rates in the xylem using data from sap concentrations and sap flow it could be shown, that these translocation rates can explain a major part of magnesium and calcium uptake rates estimated by ecosystem nutrient flux balances. In addition to the translocation by ion exchange processes the translocation with the mass flow of the xylem sap has a high significance for the mobility of these elements in the xylem. For potassium, whose mobility in the xylem is fairly independent from exchange processes, very high translocation rates were calculated compared to the estimated uptake rates from ecosystem balances. This can be explained with the high mobility of this element in the plant, where this element must circulate intemally in the plant.

The element concentrations in the xylem sap were compared to concentrations in the soil solution from lysimeters in 30 cm soil depth. It was be shown, that soil solution from lysimeters can not represent the whole amount of plant available nutrients. Moreover, element concentrations in the xylem sap are also influenced by internal processes in the plant.

By chemical fractionation of different bonding forms of calcium and magnesium in spruce needles, differences in the behaviour of both elements were determined. For calcium it was pointed out, that Contents of more than 2 mg/g dry matter calcium is bound as calcium oxalate, a substance of Iow solubility. Independent from the total calcium content of the needles the fractions of water soluble and pectate bound calcium, which are possibly active in the cell metabolism, remain constant. By the attained data it is concluded, that the precipitation of calcium oxalate in the needles is an immobilisation of surplus-calcium. This leads to the conclusion that Iow calcium contents of more than 2 mg/g dry matter are not a sign of a deficient nutritional Status. Total calcium contents of 2 mg/g dry matter are always attained under field conditions. An application of calcium on sites with Iow calcium supply will thus not impove the nutritional Status of Norway spruce.

With the applied method of fractionated analysis it was shown that the major part of magnesium in needles was water soluble. This refers to the important functions of magnesium in energy metabolism, protein synthesis and the processes of photosynthesis. In relation to the content of water soluble magnesium the fraction of chorophyll bound magnesium is very Iow (about 10-15%). A distinct dependence of this fraction from the total magnesium content can only be expected when yellowing Symptoms occur (total magnesium contents less than about 300 ppm). Considering the discussed functions of magnesium in the metabolism of the needles a latent deficiency can also be expected during Iow contents when yellowing Symptoms are lacking.

Data from xylem sap flow measurements in spruces on four measurement plots of the ARINUS experimental Sites were correlated to meteorological parameters. The diurnal course of sap flow from Single spruce trees from one measurement plot react parallel to the influence of different day length, the occurence of clouds and rain. The sap flux densities of the measured trees from one plot were well correlated. Also between the mean xylem sap flow of trees from different plots or different experimental Sites good correlations with regression coefficients of 0,9 or 0,8, respectively, were found. Therefore variations between Single trees were mainly caused by different level of sap flow. Differences between the measurement plots of the experimental Site in Villingen could be explained by differences in stand structure. Differences between the sites at Schluchsee and Villingen could also be correlated to the different tree ring structure of the spruce trees.

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