Description: Das Projekt "Carbon fluxes in a mature deciduous forest under elevated CO2'" wird vom Umweltbundesamt gefördert und von Universität Basel, Philosophisch-Naturwissenschaftliche Fakultät durchgeführt. This PhD thesis addressed several major aspects of the carbon (C) cycle in a c. 100-year-old, mixed deciduous forest under elevated CO2 with an emphasis on below-ground processes. The aim was to assess the responses of tree fine roots and soil respiration to canopy CO2 enrichment (ca.550 ppm) in this tallest forest studied to date. Furthermore, leaf gas-exchange of the five study species was examined to ascertain the long-term response of photosynthetic carbon uptake to elevated amospheric CO2. Investigations at the Swiss Canopy Crane (SCC) experimental site were guided by the following key questions: (1) Does below-ground C allocation to fine root production increase in response to CO2 enrichment in order to acquire more nutrients to match the enhanced C supply in the forest canopy? (2) Is below-ground metabolism enhanced and therefore forest soil respiration stimulated by canopy CO2 enrichment? (3) Is leaf-level photosynthesis persistently stimulated by elevated CO2 in this stand or had these mature broad-leaved trees reduced their carbon uptake by photosynthetic down-regulation under long-term CO2 enrichment? Findings from earlier studies at the SCC site, including 13C isotope tracing, all point towards an increased flux of C through CO2-enriched trees to the soil but neither fine root biomass nor soil respiration were stimulated by elevated CO2. Surprisingly, fine root biomass in bulk soil and ingrowth cores showed strong reductions by ca.30Prozent in year five and six but was unaffected in the following seventh year of CO2 enrichment. Given the absence of a positive biomass response of fine roots, we assumed that the extra C assimilated in the CO2-enriched forest canopy was largely respired back to the atmosphere via increases in fine root and rhizosphere respiration and the metabolization of increased root derived exudates by soil microbes. Indeed, 52Prozent higher soil air CO2 concentration during the growing season and 14Prozent greater soil microbial biomass both indicated enhanced below-ground metabolism in soil under CO2-enriched trees. However, this did not translate into a persistent stimulation of soil respiration. The lacking sink capacity for additional assimilates led us to assume downward adjustment of photosynthetic capacity in CO2-enriched trees thereby reducing carbon uptake in the forest canopy. Photosynthetic acclimation cannot completely eliminate the CO2-driven stimulation in carbon uptake, but a reduction could hamper the detection of a CO2 effect considering the low statistical power inevitably involved with such large-scale experiments. However, after eight years of CO2 enrichment we found sustained stimulation in leaf photosynthesis (42-49Prozent) indicating a lack of closure in the carbon budget for this stand under elevated atmospheric CO2.
Types:
SupportProgram
Origin: /Bund/UBA/UFORDAT
Tags: Kranich ? Laubbaum ? Lack ? Basel ? Kohlendioxidkonzentration ? Baum ? Baumwurzel ? Kohlenstoff ? Nährstoff ? Schweiz ? CO2-Budget ? Akklimatisation ? Bodenatmung ? Datierung ? Isotopentechnik ? Kohlendioxid ? Laubblatt ? Photosynthese ? Regulierung ? Rhizosphäre ? Waldboden ? Wirkung ? Pflanzenwurzel ? Gelöster organischer Kohlenstoff ? Isotop ? Wirkung ? Atmung ? Bodenluft ? Bohrkern ? Energie ? Gasaustausch ? Kohlenstoffkreislauf ? Laubwald ? Studie ? Vegetationsperiode ? Versorgung ? Boden ? Bodenprozess ? Mischwald ? Produktion ? Persistenz ? Fahrradfahren ? Stoffwechsel ? Biomasse ? Anreicherung ? Atmosphäre ? Wald ? Schadensregulierung ? NACHWEIS ? ASPEKT ? Erlass [Recht] ? BEWERTEN ? FRAGE ? BUDGET ? LEISTUNGSFAEHIGKEIT ? Vermehrung ? Betriebsvorschrift ? BAEUME ? DAUER ? DISSERTATION ? SIEBTE ? STARK ? STATISTISCH ? EXPERIMENT ? UNTER ? BESONDER ? BEREICH ? Art [Spezies] ? Atmungsaktivität ? UNTERSUCHUNG ? VERANTWORTUNG ? VERARBEITEN ? VERRINGERUNG ? VERTEILUNG ? Alterung ?
License: cc-by-nc-nd/4.0
Language: Deutsch
Time ranges: 2006-06-01 - 2009-12-31
Accessed 1 times.