Variable δD values among major biochemicals in plants: Implications for environmental studies

The stable hydrogen isotope composition (delta D) of major plant biochemicals is variable. We present delta D values for cellulose, hemicelluloses and lignin of six plant species. The delta D value for lignin is consistently lower than that of bulk tissue (by similar to 50 parts per thousand) and cellulose (by similar to 100 parts per thousand). We show that these differences can be used to assess the extent of degradation of organic matter from a single source. A decrease in the delta D-bulk of decomposing Spartina alterniflora roots and rhizomes from -72 parts per thousand to -87 parts per thousand was observed over 18 months, reflecting a relative enrichment of lignin content due to the preferential removal of polysaccharides from the detrital material. Similar changes in delta C-13 were observed previously during the degradation of these plant tissues. These findings indicate that the extent of organic matter degradation should be considered when using stable isotope approaches to assess possible sources of organic matter in soils and sediments. We show that the change in delta D-bulk of plant detritus is best described by an exponential equation, which is simpler than the multiple exponential decay (multi-G) model which best describes the change in delta C-13(bulk) of plant detritus. Therefore correcting for isotopic shifts caused by decomposition may be more easily accomplished using delta D. (C) 2012 Elsevier Ltd. All rights reserved.