In addition to endogenous and climatic factors, wood formation is strongly influenced by the mineral element supply of the soil. Forest decline research during the last decade showed that the tree growth in many forest stands in Germany is mainly limited by K, Ca and Mg supply, respectively. The subsequent investigations were therefore primarily directed to the seasonal variation of the K, Ca and Mg content and distribution in the cambial region of spruce in relation to the mineral element supply of the soil.
For a 110 year-old spruce stand the element content and element distribution in the cambial region of four fertilized trees (fertilization in 1986, K, Ca, Mg) and four unfertilized controls were investigated in monthly intervals from September 1991 to September 1992 by means of bulk analysis (Optical Emission Spectroscopy with Inductively Coupled Argon Plasm, ICP-PES) and subcellular element analysis (Energy Dipersive X-Ray Analysis, TEM-EDX). Bulk analyses were carried out for the sequential tissues obtained by micro preparation technique: Outer phloem, inner phloem, cambium, differentiating zone of the xylem, differentiated xylem. After a rapid freeze fixation procedure the samples were embedded and cross sections of 0.5mm thickness were prepared. The element distribution in these sections was studied by TEM-EDX. The data were calibrated with standard substances of the same matrix as the investigated samples. During the vegetation period, the K content of the cambium of the unfertilized trees decreased from May to September, whereas the K content of the fertilized trees increased during earlywood formation from April to July and decreased in August and September during latewood formation. The Ca and Mg content in the cambium decreased from April through September in the unfertilized trees and from April to August in the fertilized trees. In total, the cambium of the fertilized trees showed higher K, Ca and Mg contents compared to the unfertilized controls.
In addition, subcellular element analyses revealed that Ca and Mg are mainly located in the cell wall, whereas K is located in the cell wall as well as in the protoplast. The higher K, Ca and Mg content in the cambium of the fertilized trees was mainly caused by higher element concentrations in the cell wall. The element concentration in the soil solution strongly correlates with the element content in the needles and fine roots, but there is only a moderate relationship with the K, Ca and Mg content in the cambial region. From these experiments it is concluded that the determination of the mineral element supply of the cambial zone requires additional flux measurements.
Keywords: element content, bulk- and subcellular element analysis, cambium, Picea abies (L.) Karst.
Correspondence: O. Dunisch, Institute of Wood Biology, Hamburg University, and Hamburg-Harburg Institute of Wood Biology and Wood Preservation, Federal Research Center of Forestry and Forest Products, Leuschnerstr. 91, D-21031 Hamburg, Germany
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