188 search hits
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Soil organic matter dynamics in a temperate forest influenced by extreme weather events
(2011)
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Andrea Schmitt
- Climate models predict an increase in surface temperature and a change in intensity and kind of precipitation in the future for Europe depending on the region with effects on C cycling and soil organic matter (SOM). We investigated the influence of extreme weather events (frost/drought) on the quality and quantity of SOM in a Haplic Podzol under a 140 years old Norway spruce forest in the Fichtelgebirge mountains (Bavaria, German) within two laboratory and two field studies. In one laboratory study, we investigated the effect of frost intensity and repeated freeze/thaw cycles. Undisturbed soil columns comprising organic layer and top mineral soil were treated as followed: Control (+5 °C), frost at –3 °C, –8 °C and –13 °C. After a two-week freezing period, frozen soils were thawed at +5 °C and irrigated with 80 mm water at a rate of 4 mm per day. After the third cycle, SOM pools of the treatments were compared with those of non-dried control columns. Under field conditions from late December 2005 until middle of February 2006 we removed the natural snow cover during winter on three replicate plots. Hence we induced soil frost to 15 cm depth (in a depth of 5 cm below surface up to -5°C) from January to April 2006, while the snow-covered control plots never reached temperatures below 0 °C. In the second laboratory experiment after air-drying for five weeks, undisturbed soil columns were re-wetted at different intensities (8, 20 and 50 mm per day) and time intervals, so that all treatments received the same amount of water per cycle (100 mm). After the third cycle, SOM pools of the treatments were compared with those of non-dried control columns. Under field conditions, a throughfall exclusion (TE) experiment was conducted in the summers 2006 and 2007 using a roof installation followed by re-wetting compared to non-manipulated control plots. On 18th January 2007, the heavy low pressure system Kyrill caused large damages at our control plots whereas the TE sites were less influenced. Therefore, for this study, only data were used from the control plots before Kyrill and from the soil structure undisturbed TE plots. SOM quantity and quality was followed by biomarker analysis: lignin, neutral sugars and phospholipid fatty acids (PLFA) as measure for microbial biomass. Amounts of lignin contents were not significantly affected by repeated freeze/thaw cycles. However, intensive frost slightly enhanced lignin mobilization in the O layer and the translocation into the B horizon. While soil frost did not influence lignin concentrations, the decomposition rate of vanillyl monomers (Ac/Ad)v decreased at the end of the frost period, these results confirm reduced mineralisation under frost. In contrast, lignin phenols were not systematically affected by the drying/rewetting-experiment and the moisture regime. The sum of PLFA (soil microbial biomass) was not affected by the frost respectively drying event, suggesting that most soil microorganisms were well adapted or recovered more quickly than the accumulation of microbial residues such as microbial sugars directly after the experiment. However, PLFA patterns indicate that fungi are more susceptible to soil frost than bacteria. The ratio of fungi to bacteria were generally not altered through drying, however, at least in the L horizon, warmer and drier weather led to a dominance of fungi while a cooler and moister regime favoured bacteria. Increasing water stress was indicated by a higher PLFA (cy17:0+cy19:0)/ (16:1w7c+18:1w7c) ratio suggesting that the microbes suffered from water stress in the organic layer and uppermost mineral soil. While soil microbial biomass was not affected by the moisture regime, the structure of soil microbial community changed. Gram-positive bacteria and actinomycetes were reduced whereas gram-negative bacteria, fungi and protozoa were stimulated by the reduced moisture regime. In the subsequent summer after the freezing experience, soil microbial biomass was significantly higher at the snow-removal plots (SM) compared to the control despite lower CO2 respiration and increasing water stress indicator. These results suggest that soil microbial respiration and therefore the activity was not closely related to soil microbial biomass but more strongly controlled by substrate availability and quality. Both freezing/thawing and drying/re-wetting reduced the amount of microbial sugars due to reduced mineralisation. However, also the hydrolysable plant sugars decreased in all soil horizons. We postulated that the only possible explanation for the disappearance of plant and microbial sugars upon soil freezing or drying are chemical alterations of sugar molecules leading to SOM stabilization, also known as SOM aging. Further studies are required to quantify the effect of temperature or moisture regime to the observed changes in soil sugar concentrations.
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Documentation and Instruction Manual of the Eddy-Covariance Software Package TK3
(2011)
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Matthias Mauder
Thomas Foken
- no abstract
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Der Markenwert touristischer Destinationen und seine Implikationen für das Destinationsmanagement aus tourismusgeographischer Perspektive. Herleitung und Überprüfung eines empirischen Messinstruments am Beispiel des UNESCO Weltkulturerbe Bamberg.
(2010)
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Sebastian Raum
- Vor dem Hintergrund aktueller Diskurse bezüglich subjektiv aufgeladener, imaginativer Geographien legt der Tourismus dem städtischen Raum ein Bezugssystem auf, welches nach Bildern, Geschichten und Gebäuden auf die Destination abgestimmt ist und es ermöglicht, die Destination zielgruppengerecht zu vermarkten. Als besonders zugkräftiges Argument dieser Kommodifikation beziehungsweise Touristifikation von Räumen hat sich inzwischen die Eintragung einer Destination in die Liste der UNESCO-Welterbestätten herausgestellt. Ziel der UNESCO-Welterbekonvention ist in erster Linie der Schutz des gemeinsamen Erbes aller Menschen. In den Augen vieler Kommunalpolitiker und City Manager dient das UNESCO-Prädikat jedoch vorwiegend einem möglichst effektiven Destinationsmarketing (Place Branding) und damit der Steuerung einer positiven Entwicklung des Markenwertes ihrer Destination. Ziel der vorliegenden Arbeit war es, ein modulares Messinstrument zur Bestimmung des Markenwertes eines touristischen Zielgebietes zu entwickeln. Nachdem bislang lediglich ein rein akademischer Diskurs zum Thema Markenwert für touristische Destinationen geführt wurde, kann ein solches Messinstrument durch einen interdisziplinären Ansatz unter Verwendung von Aspekten aus Ökonomie, Dienstleistungsmanagement und der Stadt- und Tourismusgeographie konkrete Handlungsempfehlungen zur touristischen Inwertsetzung und möglichst konfliktfreien Nutzung von Destinationen liefern. Nach einer Analyse und Darstellung des Standes der Wissenschaft zu den Themen Destination, Destinationsmarke und Markenwert wurde ein Modell entwickelt, welches es erlaubt, den Markenwert einer Destination zu ermitteln. Das Modell wurde dann am Beispiel der UNESCO-Welterbestadt Bamberg getestet und der Markenwert für die Destination exemplarisch ermittelt. Auf Basis der dort ermittelten Ergebnisse gelang es, strategische wie auch konkrete Handlungsempfehlungen für die betrachtete Destination abzuleiten sowie allgemeine Empfehlungen zur Vermarktung von UNESCO-Welterbestätten auszusprechen. Für Bamberg werden konkret eine strategische Destinationsentwicklung unter Beteiligung aller relevanten Gremien sowie eine stringente Zielgruppenorientierung und eine darauf ausgerichtete Umsetzung aller Maßnahmen empfohlen. Allgemein wird für UNESCO-Welterbestätten eine bessere Kooperation untereinander angemahnt. Ferner bedürfen alle Maßnahmen stets der Berücksichtigung der jeweiligen Position im Lebenszyklus der betreffenden Destination.
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Role of Dissolved Organic Nitrogen in the Soil Nitrogen Cycle of Forest Ecosystems
(2010)
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Bettina Schmidt
- In the last years, dissolved organic N (DON) has been shown to be a crucial part of the soil N cycle in forest ecosystems. Despite this, information on its dynamics, sources and fate is still lacking. Especially data from (sub)tropical forest ecosystems are scarce. Therefore, this study investigated (i) the magnitude and drivers of DON fluxes in a subtropical montane forest, (ii) the biodegradability of DON from forest floors, (iii) the abiotic formation mechanism for DON in forest floors as postulated by the Ferrous Wheel Hypothesis and (iv) the link between DON and dissolved organic C (DOC) dynamics. In a field study (2005-2008), average DON fluxes in forest floor percolates and seepage (60 cm) of a subtropical montainous cypress forest (16 and 8 kg N ha-1 yr-1, respectively) were similar to fluxes in other (sub)tropical ecosystems, and dominated total N fluxes. Dissolved organic N concentrations in the soil were independent of the water flux (meaning that no dilution effect was visible). This implies that first, the pool size of potentially soluble DON is variable and second, that this pool is hard to deplete. In contrast, the linear relationship between soil organic solute and water fluxes was positive, showing that precipitation is an important driver for DON losses in this ecosystem. Although this has also been reported from temperate ecosystems, this relationship did not hold when analyzing the combined data from various (sub)tropical and temperate forest ecosystems. The biodegradability of DON was highest in inoculated spruce-Oi water extracts in a 21-day incubation experiment, while in extracts from beech-Oi and Oa horizons, DON concentrations only slightly decreased. Dissolved organic N was recalcitrant in spruce-Oa and cypress-Oa extracts, indicating that this DON could add to the formation of stable soil N pools. As various additions of NO3- never influenced DON biodegradation, it is concluded that microbes do not necessarily prefer mineral N over DON as substrate. Mineralization was always more important than microbial uptake in samples without NO3- additions, and denitrification only played a minor role in spruce-Oi samples (as indicated by a negative balance of all N species after 21 days). Fluorescence excitation-emission spectroscopy and subsequent parallel factor analysis identified four groups of fluorophores in the extracts. The initial concentration of two of these so-called factors was correlated with DON biodegradation, but protein-like fluorescence (which has been suggested as a proxy for dissolved organic matter biodegradation) was shown to be independent of DON biodegradation due to similar excitation-emission-maxima of recalcitrant compounds. Therefore, these factors might not always be suitable to predict DON biodegradation. The abiotic reaction of NO2- with DOC (as postulated by the last step of the Ferrous Wheel Hypothesis) was tested in a second incubation experiment in extracts with varying DOC concentrations and qualities and NO2- additions under oxic conditions. Concentrations of added NO2- never decreased within 60 min, indicating, that no DON formation from added NO2- took place. The results show, that the last step of the Ferrous Wheel Hypothesis (which has been suggested to be fast) is unlikely to occur in forest floors. Dissolved organic N and C fluxes were both highly dependent on precipitation at the cypress site, suggesting a strong link between these two classes of compounds. This assumption was supported by the first incubation experiment, where both DON and DOC biodegradation were not influenced by NO3- additions. Moreover, DOC dynamics closely resembled DON dynamics, which suggests that DON biodegradation could be driven by microbial C demand. Therefore, the often used separation of DON and DOC into functionally different compound classes is not always warranted. In conclusion, this study emphasized the need to include DON in biogeochemical N studies of both temperate and (sub)tropical ecosystems, and provided new and important insights regarding DON biodegradation, possible DON sources in forest floors and the link between DON and DOC dynamics in forest ecosystems.
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Comparison ot the sonic anemometer Young Model 81000 during VOITEX-99
(1999)
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Thomas Foken
- no abstract
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Proceedings of the International Conference of "Atmospheric Transport and chemistry in Forest Ecosystems" Castle of Thurnau, Germany Oct 5 to Oct 8, 2009
(2009)
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Johannes Lüers
Thomas Foken
- no abstract
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Dokumentation des Experiments STINHO-1 ; 24.09.2001 bis 10.10.2001
(2002)
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Matthias Göckede
Thomas Foken
Jörg Gerchau
Claudia Liebethal
Matthias Mauder
- no abstract
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ATEM Software for Athmospheric Turbulence Exchange Measurements using Eddy Covariance and Relaxed Eddy Accumulation Systems and Bayreuth whole-air REA system setup
(2005)
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Johannes Ruppert
- no abstract
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Klimatologische und mikrometeorologische Forschungen im Rahmen des Bayreuther Institutes für Terrestrische Ökosystemforschung (BITÖK); 1989 - 2004
(2005)
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Thomas Foken
- keine Zusamennfassung
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Dokumentation des Experiments am Standort Weidenbrunnen, Juli/August 1998
(1999)
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Alexander Mangold
- keine Zusammenfassung
