Mineralization of Soil Organic Matter and Added Carbon Substrates in Two Acidic Soils with High non-exchangeable Aluminum

Mineralization of soil organic matter and of added ¹⁴C labelled substrates were studied on samples from two acidic forest soils, “Cademario”-sample from the Bh-horizon of a cryptopodzolic soil rich in humus and nonexchangeable Al and “Sagno”-sample from the A-horizon of a Haplumbrept with moderate humus- and Al-content. The respiration rates for the two soils were not different when related to the content of organic matter. When treated with Na₂CO₃, the CO₂ production rate in the Sagno soil increased about three fold whereas no significant difference was observed for Cademario samples. This is attributed to the more pronounced dissolution of organic matter due to the pH increase in the Sagno soil. N-mineralization was different in the two soils. During a 28 day incubation period, 0.11% and 0.34% of the total organic N was released in the Cademario and Sagno samples, respectively. Na₂CO₃ treatment stimulated N-mineralization in both soils but the mineral N-form was primarily nitrate in the Sagno sample and ammonium in the aluminum-rich sample from Cademario. Glucose, succinate and salicylate added to the soils were mineralized in this order. However, CO₂ evolution was much slower in the case of salicylate, especially in the untreated soils, a fact which is attributed to the Al-complexing power of this substrate.