HEAT OF COMBUSTION, DEGREE OF REDUCTION AND CARBON CONTENT .3. INTERRELATED METHODS OF ESTIMATING THE CONSTRUCTION COST OF PLANT-TISSUES

During the last decade, degree of reduction (calculated from elemental composition), heat of combustion and carbon content have been propose d as 3 ways of estimating the construction cost of plant tissues. Ther e is a fairly good agreement among these 3 methods, as they are all ba sed on the link between the energy content of biomass and its reductio n level. This relationship is not absolute and the regression coeffici ent between heat of combustion and degree of reduction may vary accord ing to the chemical composition of biomass. The relation between degre e of reduction and carbon content is implicitly based on the consequen ces in terms of molecular weight of the replacement of 1 oxygen atom b y 2 hydrogen atoms in the process of reduction of photoassimilates (ca rbohydrates) into the various biomass compounds. Different trends can be observed on woody and non-woody tissues, which get richer in energy by increasing their content in lignin and lipids, respectively. Final ly, the biosynthetic efficiency is also affected by the chemical compo sition of biomass. Therefore, while these 3 methods provide efficient and fairly simple tools for the estimation of the construction cost of biomass, they should not be used without considering what the dominan t compounds of the plant tissues under study are and without choosing proper parameters in consequence.