Labile and recalcitrant pools of carbon and nitrogen in organic matter decomposing at different depths in soil: an acid hydrolysis approach

摘要

The quality of soil organic matter (OM) depends on its distribution among labile and recalcitrant pools and the quality of each pool considered. OM quality is assumed to decrease as decomposition proceeds, but to verify (his assumption it is necessary to define quality in operative terms. Here we study the change in OM quality during decomposition of mixtures of four plant materials (Medicago sativa whole ground plants, and ground litter of Eucalyptus globulus, Quercus ilex and Pinus halepensis) with a mineral red earth, incubated at different depths (5, 20, and 40 cm) for 2 years. OM quality was evaluated from acid hydrolysis, considering three pools: (a) Labile Pool 1, obtained by hydrolysis with 5 N H2SO4 at 105 degreesC for 30 min; (b) Labile Pool II, obtained by hydrolysis with 26 N H2SO4 at room temperature overnight, then with 2 N H2SO4 at 105 degreesC for 3 h; and (c) Recalcitrant Pool, the unhydrolyzed residue. In agreement with previously published results, the recalcitrant C/total OC (RIC), and recalcitrant N/total N (RIN) ratios are regarded as indicators of global OC and N quality. In addition, in Labile Pools I and 11, the ratio carbohydrate C/polyphenol C is used as indicator of OC quality.