¹³C NMR and Isotopic (δ¹³C) Investigation of Modern Vegetation: a Tool to Understand the Input Material in Soil Organic Matter

Rakshit, Subhadeep (2015) ¹³C NMR and Isotopic (δ¹³C) Investigation of Modern Vegetation: a Tool to Understand the Input Material in Soil Organic Matter. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Subhadeep Rakshit (10MS31)) Subhadeep_Rakshit_10MS31_MS_thesis.pdf - Submitted Version Restricted to Registered users only Download (684kB)

Abstract

Soil organic carbon, one of the largest reservoirs of carbon, is a heterogeneous mixture of organic compounds with dominant contribution derived from decomposition of plants in various stages. Although general ideas about the processes and mechanisms of soil organic matter (SOM) degradation have been developed, a very few study has linked the SOM with its parent material. In this study an attempt has been made to generate a reference data set of carbon groups in bulk leaf sample of C₃ and C₄ plants to better understand the degradation dynamics and the source of organic matter (OM) in the soil. Bulk leaf tissue of ten C₃ and eight C₄ plants were examined by solid state ¹³C CPMAS NMR spectroscopy. Additionally, isotopic investigations (δ¹³C) has also been carried out on these samples to understand the relationship of bulk isotopic values with the relative contribution of carbon groups. NMR spectra indicate that alkyl, O-alkyl, aromatic and carboxylic carbon contribution is 15%, 65%, 5%, 15% and 7%, 85%, 3%, 5% on average respectively in C₃ and C₄ leaf samples. This reference data set can be used to estimate the contribution of different sources (dominantly from vegetation or mixed contribution from plant and heterotrophs) of OM in soil and to understand the preferential degradation of SOM. δ¹³C value of the studied samples were correlated with the carbon group contributions. It is found that contribution of different groups are correlated with δ¹³C value of C₄, but no correlation found in case of C₃ plants. Write few lines on why this is so…This sheds light on the controlling factors of δ¹³C value in plants. NMR spectra and the correlation with δ¹³C value provides implication in several fields such as alternative proxy for characterization of SOM degradation dynamics, paleoclimate reconstruction etc.

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