SAMPLING OF PLANT-MATERIAL FOR CHEMICAL-ANALYSIS

Sampling procedure and plant parts which are sampled strongly depend o n the scope of the investigation. In contrast to sampling of abiotic c omponents trace element concentrations of plant materials are strongly dependent on plant age, organ and tissue function, genotypic characte r of uptake, translocation and allocation, and are modified by the imp act of other organisms. The consequences of these dynamic processes ar e considerable differences in element matrices. After the identificati on of the individual in the field the aim of the investigation will de cide on the plant part(s) to be sampled, either at random or selective ly. The most frequently taken plant parts in space and time are the le aves, either deciduous or evergreen. Leaf age, their position and inse rtion on the plant, their longevity, infestations by pathogens, injury by herbivores, and exposure to atmospheric components determine the e lement concentration; therefore a rigid sampling protocol is necessary . Due to their different chemical compositions, twigs and stems have t o be separated into bark inclusive of phloem and wood. Exposure to pre cipitation and colonisation by epiphytes and bark decomposers have to be noted. In the case of roots, many chemical elements are only adsorb ed to the root cell walls and are not, or only to very low degree, tra nslocated to the other root cell components and from roots to shoots. In addition to high fragility of fine roots and root hairs and their s trong association with soil particles and soil organic matter, roots o f most plant species have an intimate symbiotic association with mycor rhizal fungi. The change in the degree of infestation with endomycorrh izal fungi during one growing season and the change of ectomycorrhizal partners during life history are important aspects of sampling for mo nitoring purposes. The great variation of rooting depth during ontogen y, dependent on soil conditions, requires control of this parameter in the field. A protocol for random and selected sampling will be presen ted.