Kurzbeschreibung
(Englisch)
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The proposed project aims to quantify the allocation patterns of recently-fixed carbon from the canopy to the soil in response to environmental stress, to identify whether canopy-soil interactions are sink- or source-driven, and to assess the sensitivity of belowground carbon allocation and soil respiration to environmental change. Results of this research, based on stable carbon isotope applications to trace the fate of recently-fixed carbon and CO2 fluxes, will not only increase our understanding of biosphere-atmosphere CO2 fluxes and ecosystem functioning, but also help us to identify critical ecosystem responses to future environmental change, such as drought or combined climatic stressors. Such information is highly relevant for developing adaptation strategies for production systems in agriculture and forestry in Switzerland, Europe and elsewhere. The project contributes to WP 1 and WP 2 of COST Action ES806 (Stable Isotopes in Biosphere-Atmosphere-Earth System Research).
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Partner und Internationale Organisationen
(Englisch)
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AT, BE, CH, DE, DK, ES, FI, FR, GR , HR, IL, IT, LU, NL, NO, PL, PT, RS, SE, SI, SK, UK
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Abstract
(Englisch)
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The project CARE contributed to Work Packages 1 and 2 of COST Action ES806 (Stable Isotopes in Biosphere-Atmosphere-Earth System Research), which ended in Nov. 2013. We aimed to quantify the allocation patterns of recently fixed carbon from the canopy to the soil in response to environmental stress (obj. 1), to identify whether canopy-soil interactions are sink- or source-driven (obj. 2), and to assess the sensitivity of belowground carbon allocation and soil respiration to environmental change (obj. 3). We used stable isotope techniques (natural abundance and 13CO2 labelling) to investigate short-term coupling between photosynthesis and soil respiration, and carbon allocation to different components in response to different environmental conditions. The results are based on climate chamber experiments with young beech saplings (Fagus sylvatica) and bean plants (Phaseolus vulgaris). One pulse-labelling experiment with beech was performed to adress the sensitivity of carbon allocation in response to increased temperatures, drought and the combination of both. Destructive harvests allowed to track the label 13C in different plant tissues and compounds during a nine day chase period. Soil CO2 efflux, isotopic composition of soil CO2 efflux, and phloem sap samples complemented the extensive sampling. Generally, a fast transport of recently fixed carbon from the leaves to the roots (within one day) and into soil respiration (within two days) was observed. Drought strongly affected relative stem and root biomass distribution, although short-term carbon allocation was not impacted. Increased temperatures, however, slowed down carbon allocation to the roots. Recently fixed carbon was mainly incorporated in root starch, while leaf starch only served as an intermediate storage, clearly pointing to different functionalities of the same compound in different plant tissues. In another experiment with beech, gas exchange and its isotopic composition of shoot and root systems were monitored separately using laser spectroscopy during drought and subsequent recovery. Stomatal conductance (gs) decreased by 65%, simultaneously, photosynthetic discrimination decreased by 8‰, which caused a significant increase in 13C of recent metabolites (1.5-2.5‰) that could then be traced to an increase in 13C of soil respiration (1-1.5‰). However, all plant physiological variables recoverd within four days after re-watering, soil respiration within seven days. The drought signal persisted longer in 13C of photoassimilates compared to 13C of soil respiration (seven vs. three days, respectively). Overall, we found strong coupling under both environmental conditions, with gs playing a pivotal role driving this coupling. Thus, this project contributed to the understanding of carbon transport processes within the plant and to the soil under changing environmental conditions, and increased our knowledge about the drivers of above- to belowground coupling during stress and stress release periods. The rather resilient behavior of is likely to help beech, particularly at young age and thus with not yet fully developed root systems, coping with more frequent drought events in the future in Central Europe, the area of dominance for beech in the natural vegetation. Within the last year, Friederike Gnaedinger complemented the study with her Master thesis about 'Diurnal transport and storage of recently fixed carbohydrates in beans (Phaseolus vulgaris)'. It focused on carbon and nitrogen allocation during the first 24 h after labelling for the treatments: control, low light, 50% cutting of beans and no nitrogen supply. Furthermore, Fiona Cimei examined the contribution of carbon fixed in pods to the overall carbon pool of beans during her Master thesis with the title 'Are pods of beans (Phaseolus vulgaris) permanent carbon sinks during growth?' The PhD student, Carola Blessing, actively participated at the Annual Conference of the GfÖ 2013 (talk and poster), and submitted her thesis end of June 2014. The defense is scheduled for 11 July 2014.
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