Effects of land use change on soil organic matter (SOM) characteristics: a comparison of crops, young forests and old forests

摘要

Changes in SOM characteristics were studied in a sequence of crop abandonment and substitution by secondary pine stands, and compared with old pine stands on never cropped sites, in Catalonia (NE Spain). Crop replacement by forests result in significant increases in soil C stock in the litter horizons and at the mineral soil surface (first 5 cm depth); below this treshhold crop abandonment may result in C losses, particularly in deep layers (>15 cm depth), which apparently can be recovered in the very long term. With crop replacement by secondary forest, SOM becomes less stable and more vulnerable to microbial attack, particularly at the soil surface. This increased vulnerability, which occurs in spite of the increased biochemical recalcitrance of forest- relative to crop soils, seems due to the decreased physical protection of SOM: the % of total SOM associated to the organomineral complex (< 20 μm) decreases with crop abandonment.