ABOUT THE BIOCHEMICAL STRUCTURE OF THE ME DITERRANEAN SECONDARY VEGETAL UNITS

Chemical analysis (about 20 parameters) of the leaves of 37 plants rep resentative of the Mediterranean mattoral reveals a clear biochemical and ecological structuration. This phytochemical organization could be dependent on the synecological relationships between plants and herbi vores (''T'' and ''a'' tactics). Even if the tannin plant frequency is here relatively low (about half of the species), these defensive mole cules are particularly effective owing to the development of the pheny l-trihydroxylation. Tanniferous plants are significantly richer in tot al phenols and cellulose, but reversely poorer in proteins, soluble su gars, potassium and magnesium. On an other defensive level, the most s clerophyllous plants are significantly poorer in proteins, potassium a nd phosphore and somewhat richer in lignin. Multivariate analysis firs tly opposes the plants rich in phenolic substances (Ericaceae) to thos e rich in nitrogen and potassium (Papilionaceae). Both sclerophylly an d - with opposite signs - alimentary value are found on the same struc turing axis, which confirms the synecological determinism of the recor ded organization. Moreover, the classic C/N ratio appears as a common feature of this phytochemical gradient and links this part of the ecos ystem to its pedological substrate. A short comparison is made with ot her phytocenosis, located in severe or not severe environments, initia ting a more general approach of the structuration of the phytocenosis in the frame of the bioenergetic allocations.