Olykan, Sonya Theresa2024-01-092024-01-091987https://hdl.handle.net/10182/16723A substrate amendment technique was used to identify the mechanism of N0₃⁻-N production in two Pinus radiata samples. Site 1 had an initial pH of 4.68 and a predominant N-form of NH4⁺. The initial pH of site 2 was 5.95 and N0₃⁻ was the predominant form of N. Nitrogen was added at 150μg/g of oven dry humus (in peptone and ammonium sulphate) and C was added at 550μg/g as starch. The samples amended with peplone (organic N) increased N03- production compared to the control after a 42 day incubation. The addition of ammonium sulphate inhibited the production of N0₃⁻-N for site 1 but significantly increased it in the site 2 sample. The starch amendment (a source of readily-mineralisable C) produced N0₃⁻-N levels equivalent to those of the control for site 1 but significantly suppressed N0₃⁻-N production in the site 2 sample. These results suggested that site 1 produced N0₃⁻ heterotrophically whereas in site 2 N0₃⁻ production occurred via the autotrophic pathway. A further incubation used acetylene to block the autotrophic oxidation (by Nitrosomonas) of NH4⁺ to N0₂⁻ and chlorate to block the oxidation of N0₂⁻ to N0₃⁻ by the autotroph Nitrobacter. These inhibitors were not expected to affect N0₃⁻ production by the heterotrophs. The results showed that both acetylene and chlorate interfered with the heterotrophic production of N0₃⁻ occurring in the site 1 sample. Acetylene effectively blocked the production of N0₃⁻ in the site 2 sample which also showed a significant increase in the levels of NH4⁺ -N compared to the control. Chlorate reduced N0₃⁻ production in the site 2 sample but did not inhibit it. The effect of rates of N at 150 and 300μg/g. added in ammonium sulphate and peptone. and rates of readily-mineralisable C at 550, 1100, 2200, 11000μg/g, added as starch, were used to investigate the mechanism of heterotrophic nitrification in the site 1 sample during a 35 day incubation. The addition of ammonium sulphate inhibited N0₃⁻-N production while peptone promoted it. The starch amendment at 550μg/g increased the production of N0₃⁻-N above the control level. Starch additions above 1100μ gig resulted in the immobilization of inorganic N. These results suggested that the limitation to heterotrophic nitrification in the site sample was a lack of readily -mineralisable C.https://researcharchive.lincoln.ac.nz/pages/rightsacid forest humusincubationnitrification potentialautotrophsheterotrophsammonium sulphatepeptonestarchinhibitorsacetylenechloratereadily-mineralisable carbonDissertationDigital thesis can be viewed by current staff and students of Lincoln University only. If you are the author of this item, please contact us if you wish to discuss making the full text publicly available.ANZSRC::410604 Soil chemistry and soil carbon sequestration (excl. carbon sequestration science)ANZSRC::300704 Forest health and pathologyANZSRC::300701 Agroforestry