Nitrification in soils of secondary vegetational successions from Eucalyptus forest and grassland to cool temperate rainforest in Tasmania

• Published in: Plant and soil 1989-03, Vol.115 (1), p.59-73
• Main Authors: Ellis, R.C. (Division of Forest Research CSIRO, Hobart, Tasmania (Australia). Tasmanian Regional Lab.), Pennington, P.I
• Format: Article
• Language: English
• Subjects: Acid soils; Agronomy. Soil science and plant productions; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; EUCALYPTUS; FOREST SOILS; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Grassland soils; GRASSLANDS; HERBAGE; METABOLISME DE L'AZOTE; METABOLISMO DEL NITROGENO; Nitrification; NITROGEN METABOLISM; Organic matter; Perfusion; Physics, chemistry, biochemistry and biology of agricultural and forest soils; PRADERAS; Quaternary ammonium compounds; Rain forests; Soil inoculation; Soil microorganisms; Soil science; Soil treatment; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; SOL DE FORET; SUELO FORESTAL; TASMANIA; TASMANIE
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/BF02220695

Rates of nitrification in well drained granitic soils from forest stands and grassland of differing successional status and from beneath isolated individuals of several tree species were compared in a series of laboratory experiments. Fresh samples were perfused with distilled water or nutrient solution for 10 to 14 weeks at 20°C. The following treatments were applied to the soils singly and in combination: 200 and 400 µg N g⁻¹ as (NH₄)₂ SO₄; 100 µg P g⁻¹ as KH₂PO₄; 4000 µg CaCO₃ g⁻¹; inoculation of non-nitrifying soil with nitrifying soil; perfusion of nitrifying soil with leachate from non-nitrifying soil. Nitrification was absent or occurred at only a low rate in many soils; it generally increased as succession proceeded from mature grassland or eucalypt forest towards climax temperate rainforest, but decreased in mature climax forests. However, the influence of individual tree species was often paramount. Nitrification was stimulated by disturbance of a stand by disease. A possible inhibitor of nitrification in a rainforest soil could not be removed by leaching with water, nor transferrred via the leachate to a nitrifying soil. Addition of P was without effect on either total amount of nitrate produced or on net mineralisation of soil N, but sometimes increased the rate of nitrification of added ammonium. Non-nitrifying rainforest soil of pH 4.3 was induced to nitrify only after addition of (NH₄)₂ SO₄, inoculation with a nitrifying soil, and addition of CaCO₃ to raise pH by 3 units. However, once nitrification had commenced it could continue with little change in rate while pH decreased to a value of 3.4. It was concluded that rate of nitrification is dependent upon the presence of particular tree species in a stand, upon its history of disturbance, and hence in part upon the stand's successional status. It is not limited by pH per se within the range found in these soils, although an increase in pH may be necessary to initiate nitrification. In some soils the rate of nitrification may be limited by the level of ammonium substrate, and nitrifiers are virtually absent from others. Overall microbial activity is limited by lack of utilisable carbon substrate.