Nitrogen mineralization and nitrate reduction in forests

The mineralization of soil nitrogen was studied in four forests growing on krasnozem soils. Soils from Silver Wattle (Acacia dealbata Link.) and Mountain Ash (Eucalyptus regnans F. Muell.) forests showed considerable nitrification in laboratory incubations. Messmate (Eucalyptus obliqua L'Herit) and Monterey Pine (Pinus radiata D. Don) forest soils were predominantly ammonifiers. Forests having significant soil nitrification were found to have considerable nitrate reductase activity (NRA) in root or leaf tissue or both. NRA may therefore be useful as an indication of soil nitrification in natural ecosystems. The occurrence of nitrification in Australian forests appears to be predominantly related to the amount of N present and its rate of turnover rather than to inhibitory effects.