Bayreuther Institut für Terrestrische Ökosystemforschung
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Role of Dissolved Organic Nitrogen Compounds (DON) in the Nitrogen Cycle of Forest Ecosystems


From 01/1995 to 12/1997

Principal Investigator: Egbert Matzner
Staff: Beate Michalzik
Grant: 0339476 B Vorhersage und Erklärung des Verhaltens und der Belastbarkeit von Ökosystemen unter veränderten Umweltbedingungen

While many investigations have focussed on mineral nitrogen the role of dissolved organic nitrogen within the N-cycle has been often neglected. From October`95 to`97 fluxes of total N, ammonium, nitrate, DON and DOC (dissolved organic carbon) were recorded in a Norway Spruce forest ecosystem. Fluxes were determined in bulk and throughfall precipitation, in soil solution of two depths (20, 90 cm) and in the runoff. Field monitoring was supplemented by laboratory incubation experiments in which the production of DON depending on temperature (5, 10,15°C) and soil material (Oh, Ah) was investigated. The origin and stability of DON in throughfall collectors was analysed by microbial studies of the phyllosphere flora and by field incubation experiments with precipitation samples. DON fluxes in the forest floor were 5-7 kg N*ha-1*yr-1 and about equal to the NH4-N fluxes. In relation to the DON input with throughfall (3 kg N*ha-1*yr-1), the forest floor can be considered as a netto source for DON. DON as well NH4-N concentrations decreased rapidly with increasing soil depth. N fluxes were dominated by NO3-N. Seasonal variability of DON fluxes decreased with increasing depth.DON is mostly represented by aminoacid-N (50 - 80 % of DON) . Aminosugar-N was less important reaching 5 - 15 % of DON. The microbial production of DON in throughfall samplers could be excluded. The origin of DON in throughfall samplers is likely due to microbial transformations of atmospherically deposited Ninorg into Norg compounds. Thus DON should be considered as a N input. Aphid infestation on spruce caused an increase of DOC fluxes in the throughfall by excretion of honeydew. The excretion of honeydew into the phyllosphere promoted the growth of bacteria, yeast and moulds. Concerning the N fluxes in throughfall under aphid infestation compared with control trees, Ninorg fluxes were diminished while fluxes of particle amino-N raised. Our results support the hypothesis that DON in throughfall represents an input to the ecosystem and emphazise the role of DON for the overall N turnover. (final report 1998)

List of publications of this Project

Stadler, B; Michalzik, B: Effects of phytophagous insects on micro-organisms and throughfall chemistry in forested ecosystems: herbivores as switches for the nutrient dynamics in the canopy., Basic and Applied Ecology, 1, 109-116 (2000) -- Details
Michalzik, B; Stadler, B: Effects of phytophagous insects on soil solution chemistry: herbivores as switches for the nutrient dynamics in the soil., Basic and Applied Ecology, 1, 117-123 (2000) -- Details
Michalzik, B; Müller, T; Stadler, B: Aphids on Norway spruce and their effects on forest floor solution chemistry, Forest Ecology and Management, 118, 1-10 (1999) -- Details
Stadler, B; Michalzik, B: The impact of spruce aphids on nutrient flows in the canopy of Norway spruce, Agricultural and Forest Entomology, 1, 3-9 (1999) -- Details
Stadler, B; Michalzik, B: Aphid infested Norway spruce are "hot spots" in throughfall carbon chemistry in coniferous forests, Canadian Journal of Forest Research, 28, 1717-1722 (1998) -- Details
Michalzik, B; Dorsch, T; Matzner, E: Stability of dissolved organic nitrogen (DON) and mineral nitrogen in bulk precipitation and throughfall, Z. Pflanzenernährung Bodenkunde, 160, 433-434 (1997) -- Details
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