THE PHYSIOTYPE CONCEPT - AN APPROACH INTEGRATING PLANT ECOPHYSIOLOGY AND SYSTEMATICS

Several attempts have been made to arrange plants in certain groups ac cording to their physiological properties. Whereas chemotaxonomy place d emphasis on so-called ''secondary metabolites'' to improve our knowl edge on natural systematic relationships on different hierarchy levels , ''the physiotype concept'' of KINZEL 1972, 1982 and ALBERT & KINZEL 1973 strongly incorporates ecological aspects. According to this conce pt, the term ''physiotype'' refers to a certain taxonomic unit (specie s, genus, family etc.) with common physiological features, which enabl e it to cope successfully with specific ecological situations. Origina lly the ''physiotype-concept'' focused mainly on mineral ion and organ ic acid metabolism and soluble carbohydrate patterns. However, towards an overall understanding of the ecological behaviour of a taxon, as m any physiological attributes as possible must be taken into account. A ccording to new findings in the fields of plant ecophysiology, stress physiology and biochemical ecology, the physiotype concept must also c onsider the occurrence of low molecular weight compounds acting as cyt oplasmic osmolytes (compatible solutes), and bioactive natural compoun ds. This holds true also with regard to attributes of the nitrogen met abolism, particularly the preferential form of inorganic nitrogen upta ke. Furthermore, to characterize a certain plant taxon in a holistic a pproach, the combination of physiological and biochemical with morphol ogical and anatomical features has to be considered.