Incubation conditions of forest soil yielding maximum dissolved organic nitrogen concentrations and minimal residual nitrate

摘要

Soil is a dominant long-term sink for N in forest ecosystems . With increasing atmospheric N deposition in forests caused by combustion of fossil fuels, concern over effects of N loading on ecosystem sustainability is substantial. Net primary productivity Is thought to be limited by N in most temperate forests, but much of the N from deposition appears to be immobilized in the organic matter of the soil rather than being taken up by plants. However, the mechanisms of N immobilization as well as the bioavailability and ultimate fate of organic N remain poorly understood. One hypothesized pathway of immobilization is abiotic reduction of nitrate to nitrite and reaction of nitrite with dissolved organic matter to produce dissolved organic nitrogen (DON). Studying the fate of DON would be facilitated by the development of a ~(15)N label in a realistic soil DON product. In the present study, we tested incubation conditions that would permit nitrate immobilization to DON during 24 h, followed by conditions that would minimize the remaining nitrate. Water content and N concentrations were varied in 1-8-day incubations of organic horizon to study the dynamic of nitrate reduction and DON formation.