Effects of Terpenoids on Nitrification in Soil

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Abstract
It has recently been hypothesized that vegetation in ponderosa pine (Pinus ponderosa Dougl.) ecosystems inhibits nitrification in these systems by releasing volatile terpenoids that retard oxidation of NH+4 by nitrifying microorganisms. This hypothesis is based largely on observations that exposure of a ponderosa pine ecosystem to fire decreased the amount of volatile organic compounds and stimulated production of NH+4 and NO−3 in the forest floor and that exposure of soil samples to vapors from a terpenoid mixture decreased production of NH+4 and NO−3 by mineralization of organic N in these samples. To test the validity of this hypothesis, we studied the effects of different amounts of six terpenoids (α‐terpinene, limonene, myrcene, α‐pinene, β‐pinene, and α‐phellandrene) on nitrification in soils incubated at 25 °C after treatment with (NH4)2SO4. The results showed that the terpenoids studied did not significantly affect nitrification in soil even when the amounts applied greatly exceeded the amounts that have been reported to occur in soil. They also indicated that the apparent inhibition of nitrification observed when soils were exposed to terpenoid vapors was due to immobilization of ammonium N by microbial activity stimulated by the organic C in these vapors.
Funding Information
  • Iowa State Water Resources Res. Inst.