Spatial and temporal small-scale variability of nitrogen mobilization in a forest ecosystem with high N deposition in NW-Germany

For conifer stands in NW-Germany with high DIN load (23-35 kg N ha⁻¹ a⁻¹) and a long history of nitrogen export the risk of N mobilization were investigated. Ammonium is the most mobilized N species, pointing towards either conditions not favoring nitrification or, more likely - under the dominant aerobic conditions - a very high amount of ammonium in the forest floor. Independence of net nitrification and net ammonification from each other indicates the existence of two separate systems. The nitrifying system depends very much on biotic conditions - as a function of energy and moisture - and seems not to be directly related to N deposition. In contrast, for the ammonification system (Oe horizon) a correlation with the sum of ammonium deposition three months prior to sampling was found. However, the role of disturbance, i.e. nitrogen export, during the last centuries and the role of recovery of the N balance during the last 150 years is still not clear.     

Effect of long-term changes in soil chemistry induced by road salt applications on N-transformations in roadside soils

Of several impacts of road salting on roadside soils, the potential disruption of the nitrogen cycle has been largely ignored. Therefore the fates of low-level ammonium-N and nitrate-N inputs to roadside soils impacted by salting over an extended period (decades) in the field have been studied. The use of road salts disrupts the proportional contributions of nitrate-N and ammonium-N to the mineral inorganic fraction of roadside soils. It is highly probable that the degree of salt exposure of the soil, in the longer term, controls the rates of key microbial N transformation processes, primarily by increasing soil pH. Additional influxes of ammonium-N to salt-impacted soils are rapidly nitrified therefore and, thereafter, increased leaching of nitrate-N to the local waterways occurs, which has particular relevance to the Water Framework Directive. The results reported are important when assessing the fate of inputs of ammonia to soils from atmospheric pollution.     

Dose Dependent Interactions Between Ammonification Potential and Bacteria in Three Tropical Pond Ecosystems

Using six different doses of peptone (0.25, 0.50, 0.75, 1.0, 1.25 and 1.50 gl^-1) and nine different periods of inclubation (1, 2, 3, 4, 6, 8, 10, 12 and 14 days), the rates of ammonification potential (AP) were monitored in three tropical ponds of differetn ecological status, during winter and summer periods. During the winter, the AP (ammonifying bacteria) exhibited peaks on day 4 of incubation in all the test doses of peptone in all the three ponds, except in the lowest dose in eutrophic and chemically polluted pond where the peaks preceded by a day. the responses of AP to the lowest doses of substrate did not differ between summer and winter, while the AP-peaks at higher doses were delayed by 2 days in summer. the concentrations of nitrate in vitro were the inverse and direct functions of the AP and dissolved oxygen of water. at moderate dose (0.75 gl^-1) of peptone, both AP and dissolved oxygen at higher doses, and by AP at the lowest dose of peptone.