Humus Components and Soil Biogenic Structures in Norway Spruce Ecosystems

Whether the structure of Oa and A horizons varies according to animal activity is still a matter of conjecture, especially in amphi, a humus form with mixed features of mull and moder, which has been described in environments with strong seasonal contrasts. The Oa and A horizons of spruce [Picea abies (L.) Karst.] coniferous forests of the Province of Trento (Italy) were sampled in six sites with a total of 134 humus profiles along transect lines, embracing the variety of parent rocks, climate, and vegetation conditions that prevail at the upper montane level in this region. The distribution of humus components (plant debris, roots, animal feces, minerals) was assessed by an optical method and analyzed with correspondence analysis (CA). Moder humus forms were characterized by enchytraeid activity, with concomitant deposition of organic and mineral-organic feces in Oa and A horizons, respectively. Conversely, amphis were characterized. by the concomitant deposition of organic and mineral-organic earthworm feces in Oa and A horizons, respectively. We conclude that Oa and A horizons of moders and amphis differed only quantitatively in the content of mineral matter in animal feces. The fine-grained mineral-organic structure that is mostly found in the A horizon of amphis results from. the alimentary activity of small epigeic earthworms that mix organic matter with mineral matter, like anecic earthworms do in mulls.