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Microbial utilization of litter carbon under the effect of extreme weather events

Steffen Heinrich1, Michaela Dippold2, Christiane Werner1, Yakov Kuzyakov2, Bruno Glaser3
1 Agro-Ecosystem Research, University of Bayreuth
2 Department of Soil Science of Temperate and Boreal Ecosystems, University of Göttingen
3 Soil Biogeochemistry, Martin-Luther University Halle-Wittenberg

O 2.6 in Environmental controls on fluxes and processes in ecosystems

17.07.2014, 11:00-11:20, H18

As a consequence of climate change an increase of average annual temperature and in the frequency of extreme meteorological events is expected. For example, extreme summer-droughts followed by heavy rainfall events are likely to increase. This may change SOM quality, composition, microbial community functioning and thus C-turnover in temperate forest ecosystems. Therefore, we performed a tracer experiment in a Norway spruce forest in the “Fichtelgebirge” to verify the influence of strong drying as well as wetting on the microbial community and SOM turnover. In 2010, plots with artificially desiccated, continuously irrigated and not modified experimental sites were established at a Norway spruce forest on podzol. At each plot we added 13C enriched spruce litter to simulate annual litter fall. Thereafter, we assessed the effect of extreme weather events on microbial community structure by PLFA analysis. In addition, we analyzed the 13C incorporation into bulk soil, microbial biomass and PLFA of the organic horizon and the mineral soil up to 10 cm. Additionally, respired CO2 was quantified by closed chambers. Drought reduced the microbial biomass only in the organic horizon, while in the mineral soil no decrease could be detected compared to the control and irrigated plots. The depletion of the microbial biomass in the organic horizon of the drought plots resulted also in a strong reduced incorporation of litter-derived C: Incorporation of litter derived 13C was factor three lower in the drought plots compared to the control and irrigation plots. Furthermore, after the drought period of 90 days the proportion of 13C in CO2 from soil respiration was reduced by about 95% on the drought plots compared to the control and irrigated plots confirming the reduced degradation of litter-derived C and thus a reduced C-turnover under dry conditions. PLFA-analysis showed high amounts of gram positive bacterial, gram negative bacterial and fungal fatty acids, whereas actinomycets and protozoa represented minor groups. An increased ratio of the cy-PLFA to (16:1w7c+18:1w7c) on the drought plots of the organic layer suggest that bacteria suffered from water stress. In comparison to other microbial groups only the fungi were not depleted by drought showing the advantage of hyphae compared to the single cells of prokaryotic groups. Both, in the organic horizon and the mineral soil, most 13C was incorporated in the gram negative bacteria and fungi, whereas actinomycetes and protozoa showed the lowest incorporation. This tendency was even enhanced for the drought plots. Gram positive bacteria showed a low incorporation of litter derived C despite their high abundance, which reflects their general preference for old SOM-derived C sources. The combination of 13C-labeling and 13C partitioning in microbial and SOM pools provides a sensitive tool to understand the mechanisms of SOM turnover under changing environmental conditions like extreme whether events.



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last modified 2014-04-06