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Characterization of recently 14 C pulse‐labelled carbon from roots by fractionation of soil organic matter
Author(s) -
Hedley M. J.,
Saggar S.
Publication year - 2005
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1111/j.1365-2389.2004.00669.x
Subject(s) - chemistry , fractionation , organic matter , soil organic matter , alkali metal , soil water , environmental chemistry , agronomy , soil science , chromatography , organic chemistry , environmental science , biology
Summary The inability of physical and chemical techniques to separate soil organic matter into fractions that have distinct turnover rates has hampered our understanding of carbon (C) and nutrient dynamics in soil. A series of soil organic matter fractionation techniques (chemical and physical) were evaluated for their ability to distinguish a potentially labile C pool, that is ‘recent’ root and root‐derived soil C. ‘Recent’ root and root‐derived C was operationally defined as root and soil C labelled by 14 CO 2 pulse labelling of rye grass–clover pasture growing on undisturbed cores of soil. Most (50–94%) of total soil + root 14 C activity was recovered in roots. Sequential extraction of the soil + roots with resin, 0.1 m NaOH and 1 m NaOH allocated ‘recent’ soil + root 14 C to all fractions including the alkali‐insoluble residual fraction. Approximately 50% was measured in the alkali‐insoluble residue but specific activity was greater in the resin and 1 m NaOH fractions. Hot 0.5 m H 2 SO 4 hydrolysed 80% of the 14 C in the alkali‐insoluble residue of soil + roots but this diminished specific activity by recovering much non‐ 14 C organic matter. Pre‐alkali extraction treatment with 30% H 2 O 2 and post‐alkali treatment extractions with hot 1 m HNO 3 removed organic matter with a large 14 C specific activity from the alkali‐insoluble residue. Density separation failed to isolate a significant pool of ‘recent’ root‐derived 14 C. The density separation of 14 C‐labelled roots, and roots remixed with non‐radioactive soil, showed that the adhesion of soil particles to young 14 C‐labelled roots was the likely cause of the greater proportion of 14 C in the heavy fraction. Simple chemical or density fractionations of C appear unsuitable for characterizing ‘recent’ root‐derived C into fractions that can be designated labile C (short turnover time).