The Physiotype Concept - An Approach Integrating Plant Ecophysiology and Systematics

Several attempts have been made to arrange plants in certain groups according to their physiological properties. Whereas chemotaxonomy placed emphasis on so-called "secondary metabolites" to improve our knowledge 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 concept, the term "physiotype" refers to a certain taxonomic unit (species, genus, family etc.) with common physiological features, which enable it to cope successfully with specific ecological situations. Originally, the "physiotype-concept" focused mainly on mineral ion and organic acid metabolism and soluble carbohydrate patterns. However, towards an overall understanding of the ecological behaviour of a taxon, as many physiological attributes as possible must be taken into account. According to new findings in the fields of plant ecophysiology, stress physiology and biochemical ecology, the physiotype concept must also consider the occurrence of low molecular weight compounds acting as cytoplasmic osmolytes (compatible solutes), and bioactive natural compounds. This holds true also with regard to attributes of the nitrogen metabolism, particularly the preferential form of inorganic nitrogen uptake. Furthermore, to characterize a certain plant taxon in a holistic approach, the combination of physiological and biochemical with morphological and anatomical features has to be considered.