Schlüsselwörter
(Englisch)
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Carbon cycling; Climate change; dissolved organic matter; forest; mycorrhizae; radiocarbon; roots; soil; soil organic matter; temperature; tracer experiment; treeline; warming
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Forschungsprogramme
(Englisch)
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COST-Action FP0803 - Belowground carbon turnover in European forests
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Kurzbeschreibung
(Englisch)
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The feedback between belowground carbon (C) cycling and climatic changes is a key uncertainty in predicting global warming. So far, the temperature sensitivity of soil C dynamics has been studied by experimentally warming soils or air only, although in nature, air and soil temperatures differ on a daily and seasonal basis. This difference will affect the C flow in the plant and soil system because the above and belowground C cycles are closely coupled. In the proposed project, we will cool and warm soils as well as air of high altitude ecosystems to assess the effects of canopy and soil temperatures on pools and turnover of carbon in plants, roots, mycorrhiza, and soils. Our approach is to manipulate above- and belowground temperatures independently in a series of experiments that span a gradient ranging from highly controlled, but relatively simple model ecosystems to less controllable, but very realistic experiments in the field with treeline trees. We will trace 14CO2-pulses in plants and soil C fluxes such as soil respiration, DOC leaching, root and mycorrhizal growth and into soil organic matter pools. We will apply a novel and powerful 14C scanning technique, which allows us the quantitative mapping of recent assimilates in the plant and soil system at a spatial scale below 100 ìm. Our overall aim is to gain new insight into the coupling of the above- and belowground C cycles at different soil and air temperatures around the threshold for tree growth.
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Partner und Internationale Organisationen
(Englisch)
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AT, BE, CH, CZ, DE, DK, EE, ES, FI, FR, GR, HR, IE, IL, IS, IT, LT, LV, NL, NO, PL, PT, RO, SE, SI, SK, TR, UK
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Abstract
(Englisch)
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High altitude 'cold' ecosystems respond particularly sensitive to climatic warming. However, the impact on C cycling, in particular the coupling of above- and belowground C cycling are still highly uncertain. This project assessed the effects of air and soil temperature on pools and turnover of carbon in plants, roots, mycorrhiza, and soils in treeline ecosystems. Our experimental approach was to manipulate above- and belowground temperatures independently in model ecosystems with tree seedlings (Pinus mugo) and a common forb (Leucanthemopsis alpina) in the greenhouse and in the field at the alpine treeline. We have applied 14CO2-pulses and traced the 14C signal in above- and belowground biomass, soil organic matter and in soil C fluxes such as soil respiration, dissolved organic carbon (DOC) leaching, and mycorrhizal growth. The results of the 14C labeling showed that a substantial fraction of assimilated CO2 was allocated belowground demonstrating a close coupling of above- and belowground carbon cycles. The 14C uptake of trees in roots and shoots increased linearly with increasing temperatures. In comparison, 14C recovery in soils, mycorrhiza and soil-respired CO2 decreased strongly with soil cooling but did hardly change with soil warming, showing that rhizodeposition (the C transfer from roots into soils) has a temperature threshold. The consequences are that soil temperatures affect the pathways of C cycling in soils but that the magnitude strongly differs among cold and warmer temperatures. This makes prediction of climatic changes on belowground C cycle rather difficult. By studying different plant species, our experiment showed that low soil temperature is critical for tree growth at high altitudes while shallow rooting forbs might have a competitive advantage as they can also invest carbon into biomass production at cold temperatures. In an additional study, we studied the fate of 14C labeled litter-derived dissolved organic carbon (DOC) in differently developed soils. Leaching of DOC represent only a small C flux in soils, but the sorption of DOC in deeper soils might be key mechanism for the long-term stabilization of carbon in soils. However, so far, our knowledge on controlling factor of DOC sorption and turnover is uncertain. In this study, we produced 14C labeled litter in a greenhouse, extracted DOC and added it to soils of an alpine chronosequence . Finally, we traced its fate in soil-respired CO2, leached DOC and sorbed C. Our results show that although litter-derived DOC is highly bio-available, the largest fraction is retained in different soils. The immobilization occurred in the uppermost cm showing that it is extremely rapid and effective. Mineralization was quantitatively unimportant, indicating that the retention of DOC is predominantly an abiotic process - sorption to mineral surfaces. Hence, physico-chemical stabilization by sorption is the key mechanism to retain and stabilize DOC in alpine soils.
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Datenbankreferenzen
(Englisch)
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Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. +41 31 322 74 82 Swiss Project-Number: C09.0130
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