Publikationen
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Brenzinger, K.; Kujala, K.; Horn, M.A.; Moser, G.; Guillet, C.; Kammann, C.; Müller, C. & Braker, G. (2017): Soil Conditions Rather Than Long-Term Exposure to Elevated CO2 Affect Soil Microbial Communities Associated with N-Cycling. Frontiers in Microbiology 8(1976), 1-14
DOI: http://dx.doi.org/10.3389/fmicb.2017.01976.
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DOI: 10.3389/fmicb.2017.01976
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Abstract:
Abstract:
Continuously rising atmospheric CO2 concentrations may lead to an increased transfer of organic C from plants to the soil through rhizodeposition and may affect the interaction between the C- and N-cycle. For instance, fumigation of soils with elevated CO2 (eCO2) concentrations (20% higher compared to current atmospheric concentrations) at the Giessen Free-Air Carbon Dioxide Enrichment (GiFACE) sites resulted in a more than two fold increase of long-term N2O emissions and an increase in dissimilatory reduction of nitrate compared to ambient CO2 (aCO2). We hypothesized that the observed differences in soil functioning were based on differences in the abundance and composition of microbial communities in general and especially of those which are responsible for N-transformations in soil. We also expected eCO2 effects on soil parameters, such as on nitrate as previously reported. To explore the impact of long-term eCO2 on soil microbial communities, we applied a molecular approach (qPCR, T-RFLP, and 454 pyrosequencing). Microbial groups were analyzed in soil of three sets of two FACE plots (three replicate samples from each plot), which were fumigated with eCO2 and aCO2, respectively. N-fixers, denitrifiers, archaeal and bacterial ammonia oxidizers, and dissimilatory nitrate reducers to ammonia were targeted by analysis of functional marker genes and the overall archaeal community by 16S rRNA genes. Remarkably, soil parameters as well as the abundance and composition of microbial communities in the top soil under eCO2 differed only slightly from soil under aCO2. Wherever differences in microbial community abundance and composition were detected, they were not linked to CO2 level but rather determined by differences in soil parameters (e.g. soil moisture content) due to the localization of the GiFACE sets in the experimental field. We concluded that +20% eCO2 had little to no effect on the overall microbial community involved in N-cycling in the soil but that spatial heterogeneity over extended periods had shaped microbial communities at particular sites in the field. Hence, microbial community composition and abundance alone cannot explain the functional differences leading to higher N2O emissions under eCO2 and future studies should aim at exploring the active members of the soil microbial community.
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Keywords: |
elevated CO2 |
N2O |
denitrifiers |
Ammonia Oxidizers |
N-fixers |
DNRA |
Free air carbon dioxide enrichment |
454 pyrosequencing |
Andresen, L.C.; Yuan, N.; Seibert, R.; Moser, G.; Kammann, C.; Luterbacher, J.; Erbs, M. & Müller, C. (2018): Biomass responses in a temperate European grassland through 17 years of elevated CO2. Global Change Biology 24, 3875-3885
DOI: http://dx.doi.org/10.1111/gcb.13705.
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DOI: 10.1111/gcb.13705
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Abstract:
Abstract:
Future increase in atmospheric CO2 concentrations will potentially enhance grassland
biomass production and shift the functional group composition with consequences
for ecosystem functioning. In the “GiFACE” experiment (Giessen Free Air Carbon
dioxide Enrichment), fertilized grassland plots were fumigated with elevated CO2
(eCO2) year-round during daylight hours since 1998, at a level of +20% relative to
ambient concentrations (in 1998, aCO2 was 364 ppm and eCO2 399 ppm; in 2014,
aCO2 was 397 ppm and eCO2 518 ppm). Harvests were conducted twice annually
through 23 years including 17 years with eCO2 (1998 to 2014). Biomass consisted of
C3 grasses and forbs, with a small proportion of legumes. The total aboveground biomass
(TAB) was significantly increased under eCO2 (p = .045 and .025, at first and
second harvest). The dominant plant functional group grasses responded positively at
the start, but for forbs, the effect of eCO2 started out as a negative response. The
increase in TAB in response to eCO2 was approximately 15% during the period from
2006 to 2014, suggesting that there was no attenuation of eCO2 effects over time,
tentatively a consequence of the fertilization management. Biomass and soil moisture
responses were closely linked. The soil moisture surplus (c. 3%) in eCO2 manifested
in the latter years was associated with a positive biomass response of both functional
groups. The direction of the biomass response of the functional group forbs changed
over the experimental duration, intensified by extreme weather conditions, pointing
to the need of long-term field studies for obtaining reliable responses of perennial
ecosystems to eCO2 and as a basis for model development.
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Keywords: |
climate change |
soil moisture |
forbs |
frost |
Giessen free air carbon dioxide enrichment |
grasses |
long-term response |
Free air carbon dioxide enrichment |