Carbon and nitrogen dynamics along the decay continuum: plant litter to soil organic matter

• Published in: Plant and soil 1989-04, Vol.115 (2), p.189-198
• Main Authors: Melillo, J.M. (Ecosystems Center, Woods Hole, MA (USA). Marine Biological Lab.), Aber, J.D, Linkins, A.E, Ricca, A, Fry, B, Nadelhoffer, K.J
• Format: Article
• Language: English
• Subjects: Acid soils; Agronomy. Soil science and plant productions; AZOTE; Biological and medical sciences; CARBON; CARBONE; CARBONO; Chemical, physicochemical, biochemical and biological properties; DEGRADATION; DETERIORO; Forest litter; Forest soils; Fundamental and applied biological sciences. Psychology; HOJARASCA; ISOTOPE LABELLING; Lignin; LITIERE VEGETALE; MARCACION CON ISOTOPOS; MARQUAGE ISOTOPIQUE; Mineral soils; NITROGEN; NITROGENO; Organic matter; Organic soils; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Pine trees; PINUS RESINOSA; PLANT LITTER; Soil organic matter; Soil science
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/bf02202587

Decay processes in an ecosystem can be thought of as a continuum beginning with the input of plant litter and leading to the formation of soil organic matter. As an example of this continuum, we review a 77-month study of the decay of red pine (Pinus resinosa Ait.) needle litter. We tracked the changes in C chemistry and the N pool in red pine (Pinus resinosa Ait.) needle litter during the 77-month period using standard chemical techniques and stable isotope analyses of C and N. Mass loss is best described by a two-phase model: an initial phase of constant mass loss and a phase of very slow loss dominated by degradation of 'lignocellulose' (acid soluble sugars plus acid insoluble C compounds). As the decaying litter enters the second phase, the ratio of lignin to lignin and cellulose (the lignocellulose index, LCI) approaches 0.7. Thereafter, the LCI increases only slightly throughout the decay continuum indicating that acid insoluble materials ('lignin') dominate decay in the latter part of the continuum. Nitrogen dynamics are also best described by a two-phase model: a phase of N net immobilization followed by a phase of N net mineralization. Small changes in C and N isotopie composition were observed during litter decay. Larger changes were observed with depth in the soil profile. An understanding of factors that control 'lignin' degradation is key to predicting the patterns of mass loss and Í dynamics late in decay. The hypothesis that labile C is needed for iignin' degradation must be evaluated and the sources of this C must be identified. Also, the hypothesis that the availability of inorganic N slows 'lignin' decay must be evaluated in soil systems.