Sampling of plant material for chemical analysis

Sampling procedure and plant parts which are sampled strongly depend on the scope of the investigation. In contrast to sampling of abiotic components trace element concentrations of plant materials are strongly dependent on plant age, organ and tissue function, genotypic character of uptake, translocation and allocation, and are modified by the impact of other organisms. The consequences of these dynamic processes are considerable differences in element matrices. After the identification of the individual in the field the aim of the investigation will decide on the plant part(s) to be sampled, either at random or selectively. The most frequently taken plant parts in space and time are the leaves, either deciduous or evergreen. Leaf age, their position and insertion on the plant, their longevity, infestations by pathogens, injury by herbivores, and exposure to atmospheric components determine the element concentration; therefore a rigid sampling protocol is necessary. Due to their different chemical compositions, twigs and stems have to be separated into bark inclusive of phloem and wood. Exposure to precipitation and colonisation by epiphytes and bark decomposers have to be noted. In the case of roots, many chemical elements are only adsorbed to the root cell walls and are not, or only to very low degree, translocated to the other root cell components and from roots to shoots. In addition to high fragility of fine roots and root hairs and their strong association with soil particles and soil organic matter, roots of most plant species have an intimate symbiotic association with mycorrhizal fungi. The change in the degree of infestation with endomycorrhizal fungi during one growing season and the change of ectomycorrhizal partners during life history are important aspects of sampling for monitoring purposes. The great variation of rooting depth during ontogeny, dependent on soil conditions, requires control of this parameter in the field. A protocol for random and selected sampling will be presented.