Bayreuther Institut für Terrestrische Ökosystemforschung
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Stadler, B; Michalzik, B; Müller, T: Linking aphid ecology with nutrient fluxes in a coniferous forest, Ecology, 79(5), 1514-1525 (1998)
Flows of dissolved organic carbon (DOC) in throughfall and soil solutions in forest ecosystems vary spatially and temporally. The sources of this variability, however, are unknown. Phytophagous insects, such as aphids, have not been considered as potential source of organic carbon although aphids feeding on trees excrete copious amounts of honeydew. The key processes determining the origin, flow and path of honeydew from the phyllosphere of a Norway spruce stand to the soil were followed. The chemical composition of the needle leachates, throughfall and soil solution were used to calculate fluxes of dissolved organic carbon (DOC) and Hexose-C in an aphid infested and uninfested Norway spruce stand. At the individual aphid level, the amount of honeydew produced is dependent on temperature, the developmental stage and nutritional status of spruce. At the population level, colony growth and natural enemies influenced the amount of honeydew available in the phyllosphere. The growth rates of microorganisms on spruce needles were significantly increased when honeydew was available. The study of the fate of honeydew and associated metabolites within a forest stand showed that the concentrations of DOC and Hexose-C in throughfall were reduced on the way to the soil and there were no differences in the soil solutions from infested and uninfested stands. However, the distribution and abundance of honeydew producing Homoptera had a marked effect on the spatial and temporal variability in the DOC concentrations in throughfall. High DOC concentrations in throughfall during summer are not exclusively due to the leaching of nutrients from leaves but may be attributed to the excreta of aphids. These results stress the importance of studying physiological and life-history processes in addition to the traditional biomass approach when ecosystems are investigated. The results are discussed with respect to the type of information that is preserved, transformed or lost when borders of different scales of observation are crossed. We stress the importance to identify key processes at different spatiotemporal scales by linking the biology of individuals and populations with flows of energy and matter within an ecosystem and to be able to identify ecosystem changes at a multitude of scales. Neue Seite 1


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