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Soil-age driven inverse coupling of biogenic weathering and nutrient recycling on ecosystem level.

Leitung:Prof. Dr. Roberto Godoy, Dr. Jens Boy
Bearbeitung:Cesar Andres Marin Daza
Förderung durch:Fondo Nacional de Desarollo Cientifico y Tecnologico (FONDECYT)

Ecosystems are believed to be in steady transition from a relatively nutrient saturated early state, where weatherable bedrock can deliver most nutrients demanded, towards a late state, where forest selfsustainability depends on external nutrient inputs via atmospheric depositions. Thus, a clear gradient can be expected regarding the ecophysiological functioning of the successional species living in such a transformative ecosystem from biogenic-weathering oriented species towards recycling specialists. To test this hypothesis of an inverse coupling between biogenic weathering- and nutrient recycling ability, our project aims at comparing biogenic weathering ability to recycling efficiency on ecosystem level along a soil chronosequence (1 to >100 kyrs) under five pristine old-growth forest stands in Southern Chile, where atmospheric depositions are still low enough to investigate into ecosystem retrogression without nutrient limitations being biased by anthropogenic influence. Biogenic weathering will be detected by confocal laser scanning microscopy (CLSM) and raster electron microscopy (REM-EDX) at the surfaces of a set of five freshly broken minerals containing different amounts of K, Mg, Ca, and P, exposed to the soils along the chronosequence. Nutrient recycling ability will be determined by nutrient budget calculations based on biogeochemical flux monitoring data, taking all input (wet and dry deposition, mineral weathering) into account. Our detailed hypotheses are that i) along the soil chronosequence, biogenic weathering potential decreases over time as the recycling potential of the successional state of the vegetation increases, ii) the reaction of the pristine forest ecosystems to nutrient source transformation during its development is centered to the reaction of the microbial community, especial fungi and mycorrhizal symbioses, and iii) under the low deposition scenario in Chile, only decline of nutrients with bedrock origin will correlate to ecosystem age, while especially N stocks will be restored by nitrogen-fixing symbionts when required.