Transformation of plant biochemicals to geological macromolecules during early diagenesis

Chemical and isotopic changes in plant biochemicals that were transformed i nto organic geochemicals have been measured in anaerobic, freshwater marsh environments. In two litter bag studies, plant biochemicals decayed extensi vely in the first year, as recorded by dry weight, C:N ratios, delta(15)N o f bulk tissue and amino acids, and delta(13)C of individual amino acids. Mo lecular analyses of Rubisco revealed that the high-molecular-weight enzyme subunit could be recognized antigenically for at least 12 months, but conce ntrations and amounts declined. Geochemical compounds, advanced glycation e ndproducts, were not found in fresh plants, but formed gradually with first indications documented at 3 months. The organic remains of plants were rew orked or replaced by microbial products from decomposition, as indicated by a shift in the isotopic composition of individual amino acids in total pla nt protein. In experiments with Rubisco, isotopic changes over time in the individual amino acids in the 50-60 kDa molecular weight range were substan tial. These high-molecular-weight substances were no longer pristine molecu les. Biochemical and isotopic tools for studying living processes have been demonstrated to be effective and novel approaches to identify and quantify altered geochemical remnants.