ISOTOPE AND MOLECULAR EVIDENCE FOR DIRECT INPUT OF MAIZE LEAF WAX N-ALKANES INTO CROP SOILS

The contribution of plant carbon to crop soils can be followed by isotope labelling at natural abundance, such as growing a C-4 plant on a soil which was previously under C-3 vegetation. For this purpose, carbon isotope compositions and relative abundances of n-alkanes of maize leaf waxes and maize crop soils were compared. Isotope values of soil n-alkanes increased with time of maize cultivation as the result of maize carbon integration into soil organic matter. With increasing time of cultivation, the increase in isotopic difference between n-heptacosane (C-27) and n-nonacosane (C-29) is explained, at least partly, by a direct input of maize leaf n-alkanes. The amount of maize-derived carbon within each n-alkane has been calculated by isotopic means.