Abstract

Little is known about the chemical composition of soil organic matter in Espinal ecosystems of Acacia caven (Mol) with a gradient of vegetation cover in Chile. A. caven is widespread throughout regions with Mediterranean-type climates in the Southern Hemisphere, where the abundance of this species is associated with the degradation of the native forest. We chemically characterized humic acids (HAs) in bulk soil and physical soil particle size fraction samples taken from 0 to 5 cm soil depth of an Alfisol from two Espinal ecosystems with a gradient of A. caven vegetation of well-preserved Espinal (WPE; 51-80% soil cover) and a degraded Espinal (DE; less than 25% surface soil cover). In addition, we sampled a nearby native forest (NF) to compare the chemical quality of its soil organic matter with that of the Espinal ecosystems. The Alfisol was physically fractionated by wet sieving to obtain the following three particle size fractions: light (> 212 µm; LF), intermediate (53-212 µm; IF), and heavy (< 53 µm; HF). The HAs were extracted from the bulk soil and from each particle size fraction and then characterized by UV/VIS and 1H NMR spectroscopy. Our results indicate that regardless of the vegetation status, HAs of bulk soil and particle size fractions of an Alfisol were dominated by aliphatics. Only minor differences were observed in the chemical composition of HAs among the NF, WP and DE Espinal ecosystems, and among the three particle size fractions. © 2009 Elsevier B.V. All rights reserved.