CORRELATIONS BETWEEN THE C-13 CONTENT OF PRIMARY AND SECONDARY PLANT-PRODUCTS IN DIFFERENT CELL COMPARTMENTS AND THAT IN DECOMPOSING BASIDIOMYCETES

Relative carbon isotope ratio (deltaC-13 values) of primary and secondary products from different compartments of annual plants, pine needles, wood, and decomposing Basidiomycetes have been determined. An enrichment in C-13 was found for storage tissues of annual plants, because of the high level of the primary storage products sucrose and starch; however, the enrichment was even greater in leaf starch. All of these compounds had the same relative C-13 enrichment in positions 3 and 4 of glucose. Secondary products in conifer needles (lignin, lipids) were depleted in C-13 by 1 to 2 parts per thousand relative to carbohydrates from the same origin. Air pollution caused a small decrease in deltaC-13 values; however, the relative content of plant products, especially of the soluble polar compounds, was also affected. Decomposing fungi showed a global accumulation of C-13 by 4 parts per thousand relative to their substrates in wood. Their chitin was enriched by 2 parts per thousand relative to the cellulose of the wood. Hence, Basidiomycetes preferentially metabolize ''light'' molecules, whereas ''heavy'' molecules are preferentially polymerized. Our results are discussed on the basis of a kinetic isotope effect on the fructose-1,6-bisphosphate aldolase reaction and of metabolic branching on the level of the triose phosphates with varying substrate fluxes.