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See detailShort-term temperature impacts on soil respiration.
Buysse, Pauline ULg; Goffin, Stéphanie ULg; Carnol, Monique ULg et al

Poster (2009, June)

Despite considerable recent work on soil heterotrophic respiration, a mechanistic understanding of this process is still missing. Temperature is one of the most important driving factors. It can influence ... [more ▼]

Despite considerable recent work on soil heterotrophic respiration, a mechanistic understanding of this process is still missing. Temperature is one of the most important driving factors. It can influence the mechanism through multiple ways, whose importance may vary with time. An incubation experiment is set up to study short-term temperature influences on soil microbial respiration and its evolution through time. Soil samples are taken in spring from the surface layer (0-25cm) of a bare agricultural loamy soil situated in Lonzée in Belgium (Hesbaye region) and are homogenized before being placed into incubators at three different temperatures, namely 5, 15 and 25°C. Temperature is regulated by Peltier systems that warm up or cool down a sand bath containing jars with soil samples. Once a week, incubation temperatures are increased and decreased by 5°C-steps, starting from each incubator temperature, to achieve a one-day temperature cycle between 5 and 35°C. CO2 flux measurements are performed at each temperature step by a closed dynamic chamber system, after the temperature has stabilized in the samples. Microbial biomass (C and N) is determined four times during the temperature cycle by the fumigation-extraction technique and soil labile carbon is measured at the beginning of each cycle by the hot-water extraction method. Moisture levels in soil samples are regularly checked and adjusted to keep optimal soil moisture content. Between CO2 flux measurements, jars are left open to ensure that anaerobic conditions do not occur. Further investigations could include an assessment of the importance of substrate availability and depletion on microbial activity, and a model development related to the results provided by this experiment. [less ▲]

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See detailMicrobial biomass and C and N transformations in forest floors under European beech, sessile oak, Norway spruce and Douglas-fir at four temperate forest sites
Malchair, Sandrine ULg; Carnol, Monique ULg

in Soil Biology & Biochemistry (2009), 41

The purpose of this research was to compare soil chemistry, microbially mediated carbon (C) and nitrogen (N) transformations and microbial biomass in forest floors under European beech (Fagus sylvatica L ... [more ▼]

The purpose of this research was to compare soil chemistry, microbially mediated carbon (C) and nitrogen (N) transformations and microbial biomass in forest floors under European beech (Fagus sylvatica L), sessile oak (Quercus petraea (Mattuschka) Lieblein), Norway spruce (Picea abies (L) Karst) and Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) at four study sites. We measured soil chemical characteristics, net N mineralization, potential and relative nitrification, basal respiration, microbial and metabolic quotient and microbial biomass C and N under monoculture stands at all sites (one mixed stand). Tree species affected soil chemistry, microbial activities and biomass. but these effects 'varied between sites. Our results indicated that the effect of tree species on net N mineralization was likely to be mediated through their effect on soil microbial biomass, reflecting their influence on organic matter content and carbon availability. Differences in potential nitrification and relative nitrification might be related to the presence of ground vegetation through its influence on soil NH4 and labile C availability. Our findings highlight the need to study the effects of tree species on microbial activities at several sites to elucidate complex N cycle interactions between tree species, ground vegetation, soil characteristics and microbial processes. (C) 2009 Elsevier Ltd. All rights reserved. [less ▲]

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See detailBiomass production in experimental grasslands of different species richness during three years of climate warming
De Boeck, H. J.; Lemmens, CMHM; Zavalloni, C. et al

in Biogeosciences (2008), 5

Here we report on the single and combined impacts of climate warming and species richness on the biomass production in experimental grassland communities. Projections of a future warmer climate have ... [more ▼]

Here we report on the single and combined impacts of climate warming and species richness on the biomass production in experimental grassland communities. Projections of a future warmer climate have stimulated studies on the response of terrestrial ecosystems to this global change. Experiments have likewise addressed the importance of species numbers for ecosystem functioning. There is, however, little knowledge on the interplay between warming and species richness. During three years, we grew experimental plant communities containing one, three or nine grassland species in 12 sunlit, climate-controlled chambers in Wilrijk, Belgium. Half of these chambers were exposed to ambient air temperatures (unheated), while the other half were warmed by 3 degrees C (heated). Equal amounts of water were added to heated and unheated communities, so that warming would imply drier soils if evapotranspiration was higher. Biomass production was decreased due to warming, both aboveground (-29%) and belowground (-25%), as negative impacts of increased heat and drought stress in summer prevailed. Complementarity effects, likely mostly through both increased aboveground spatial complementarity and facilitative effects of legumes, led to higher shoot and root biomass in multi-species communities, regardless of the induced warming. Surprisingly, warming suppressed productivity the most in 9-species communities, which may be attributed to negative impacts of intense interspecific competition for resources under conditions of high abiotic stress. Our results suggest that warming and the associated soil drying could reduce primary production in many temperate grasslands, and that this will not necessarily be mitigated by efforts to maintain or increase species richness. [less ▲]

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See detailCombined effects of climate warming and plant diversity loss on above- and below-ground grassland productivity
De Boeck, H. J.; Lemmens, CMHM; Gielen, B. et al

in Environmental and Experimental Botany (2007), 60(1), 95-104

Projections of global change predict both increases of the surface temperature and decreases of biodiversity, but studies on the combined impact of both on terrestrial ecosystems are lacking. We assessed ... [more ▼]

Projections of global change predict both increases of the surface temperature and decreases of biodiversity, but studies on the combined impact of both on terrestrial ecosystems are lacking. We assessed the impact of these two global changes on above- and below-ground productivity of grassland communities. Experimental ecosystems containing one, three or nine grassland species were grown in 12 sunlit, climate-controlled chambers in Wilrijk, Belgium. Half of these chambers were exposed to ambient air temperatures, while the other half were warmed by 3 degrees C. Equal amounts of water were added to heated and unheated communities, so that any increases in evapotranspiration due to warmer conditions would result in a drier soil. Warming led to a decreased productivity of both above-ground plant parts (-18%) and roots (-23%), which coincided with a significantly lower soil water content. Complementarity in resource use and/or facilitation slightly enhanced above-ground productivity in multi-species communities, regardless of the induced warming. Interactive effects between temperature treatment and species richness level were found below-ground, however, where warming nullified the positive effect of richness on root productivity. Future warmer conditions could further increase losses of productivity associated with declining species numbers. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailBiomass production in experimental grasslands of different species richness during three years of climate warming
de Boeck, H. J.; Lemmens, CMHM; Gielen, B. et al

in Biogeosciences Discussions (2007), 4

Here we report on the single and combined impacts of climate warming and species richness on the biomass production in experimental grassland communities. Projections of a future warmer climate have ... [more ▼]

Here we report on the single and combined impacts of climate warming and species richness on the biomass production in experimental grassland communities. Projections of a future warmer climate have stimulated studies on the response of terrestrial ecosystems to this global change. Experiments have likewise addressed the importance of species numbers for ecosystem functioning. There is, however, little knowledge on the interplay between warming and species richness. During three years, we grew experimental plant communities containing one, three or nine grassland species in 12 sunlit, climate-controlled chambers in Wilrijk, Belgium. Half of these chambers were exposed to ambient air temperatures (unheated), while the other half were warmed by 3 degrees C (heated). Equal amounts of water were added to heated and unheated communities, so that warming would imply drier soils if evapotranspiration was higher. Biomass production was decreased due to warming, both aboveground (-29%) and belowground (-25%), as negative impacts of increased heat and drought stress in summer prevailed. Complementarity effects, likely mostly through both increased aboveground spatial complementarity and facilitative effects of legumes, led to higher shoot and root biomass in multi-species communities, regardless of the induced warming. Surprisingly, warming suppressed productivity the most in 9-species communities, which may be attributed to negative impacts of intense interspecific competition for resources under conditions of high abiotic stress. Our results suggest that warming and the associated soil drying could reduce primary production in many temperate grasslands, and that this will not necessarily be mitigated by efforts to maintain or increase species richness. [less ▲]

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See detailDo plant species and climate warming influence nitrification and ammonia oxidiser community structure
Malchair, Sandrine ULg; Carnol, Monique ULg

in Belgian Biodiversity Platform, 2007 Conference: Biodiversity and Climate Change, 21-22 May 2007, Brussels (2007)

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See detailHow do climate warming and plant species richness affect water use in experimental grasslands?
De Boeck, H. J.; Lemmens, CMHM; Bossuyt, H. et al

in Plant and Soil (2006), 288

Climate warming and plant species richness loss have been the subject of numerous experiments, but studies on their combined impact are lacking. Here we studied how both warming and species richness loss ... [more ▼]

Climate warming and plant species richness loss have been the subject of numerous experiments, but studies on their combined impact are lacking. Here we studied how both warming and species richness loss affect water use in grasslands, while identifying interactions between these global changes. Experimental ecosystems containing one, three or nine grassland species from three functional groups were grown in 12 sunlit, climate-controlled chambers (2.25 m(2) ground area) in Wilrijk, Belgium. Half of these chambers were exposed to ambient air temperatures (unheated), while the other half were warmed by 3 degrees C (heated). Equal amounts of water were added to heated and unheated communities, so that warming would imply drier soils if evapotranspiration (ET) was higher. After an initial ET increase in response to warming, stomatal regulation and lower above-ground productivity resulted in ET values comparable with those recorded in the unheated communities. As a result of the decreased biomass production, water use efficiency (WUE) was reduced by warming. Higher complementarity and the improved competitive success of water-efficient species in mixtures led to an increased WUE in multi-species communities as compared to monocultures, regardless of the induced warming. However, since the WUE of individual species was affected in different ways by higher temperatures, compositional changes in mixtures seem likely under climatic change due to shifts in competitiveness. In conclusion, while increased complementarity and selection of water-efficient species ensured more efficient water use in mixtures than monocultures, global warming will likely decrease this WUE, and this may be most pronounced in species-rich communities. [less ▲]

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See detail'Do plant species and climate warming influence nitrification and ammonia oxidiser community structure
Malchair, Sandrine ULg; Carnol, Monique ULg

in 11th International symposium on microbial ecology (ISME-11) 'The Hidden Powers – Microbial Communities in Action', Vienna, Austria, August 20-25, 2006, Book of Abstracts (2006)

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See detailEnd-of-season effects of elevated temperature on ecophysiological processes of grassland species at different species richness levels
Lemmens, CMHM; De Boeck, H. J.; Gielen, B. et al

in Environmental and Experimental Botany (2006), 56

The combined effect of declining diversity and elevated temperature is a less-studied aspect of global change. We investigated the influence of those two factors and their possible interactions oil leaf ... [more ▼]

The combined effect of declining diversity and elevated temperature is a less-studied aspect of global change. We investigated the influence of those two factors and their possible interactions oil leaf ecophysiological processes in artificial grassland communities. Changes at the leaf level are at the basis of changes at the community level (and vice versa) but have remained largely unexplored in biodiversity experiments. We focused on end-of-season responses to assess whether species richness and air temperature affect the duration of the growing season. Grassland model ecosystems were used in 12 sunlit, climate-controlled chambers. Half of these chambers were exposed to ambient air temperatures, while the other half were Nvarnied 3 degrees C. Each chamber contained 24 plant communities, created with nine grassland species: three grass species. three nitrogen (N) fixers and three non-N-fixing dicots. Each plant community consisted of either one, three or nine species in order to create different species richness levels. Various ecophysiological variables (processes and characteristics) and above ground biomass were influenced by temperature. In several variables, the effects of temperature and species richness varied with species. No single-factor species richness effect was found due to opposite responses of the species canceling out the effect. We expect that these interactions may increase with time. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

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See detailImpacts of elevated CO2 on net nitrification and on the community structure of ammonia oxidising bacteria
Malchair, Sandrine ULg; Carnol, Monique ULg

in Biodiversity: state, stakes and future; 7,8 & 9 April 2004, Louvain-la-Neuve, Belgium, Symposium, Programme, Abstracts, Participants (2004)

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See detailElevated atmospheric CO2 influences ammonia oxidiser community structure and net nitrification
Carnol, Monique ULg; Malchair, Sandrine ULg

Conference (2003, September)

The control of soil nitrogen (N) availability under elevated atmospheric CO2 is central to predicting changes in ecosystem carbon storage and primary productivity. The effects of elevated CO2 on ... [more ▼]

The control of soil nitrogen (N) availability under elevated atmospheric CO2 is central to predicting changes in ecosystem carbon storage and primary productivity. The effects of elevated CO2 on belowground processes have so far attracted limited research and they are assumed to be controlled by indirect effects through changes in plant physiology and chemistry. In this study, we investigated the effects of a 4-year exposure to elevated CO2 (ambient + 400 μmol mol-1) in open top chambers under Scots pine (Pinus sylvestris L.) on net nitrification and the community of ammonia-oxidising bacteria. Net nitrate production was significantly increased for soil from the elevated CO2 treatment in the field when incubated in the laboratory under elevated CO2, but there was no effect when incubated under ambient CO2. Net nitrate production of the soil originating from the ambient CO2 treatment in the field was not influenced by laboratory incubation conditions. These results indicate that a direct effect of elevated atmospheric CO2 on soil microbial processes might take place. Molecular analysis of the ammonia-oxidising bacteria from the same soils before laboratory incubation was investigated using a PCR-based approach targeting the 16S rRNA gene of beta-subgroup ammonia oxidisers. After specific PCR, DGGE (Denaturing Gradient Gel Electrophoresis) and sequence analysis were used to determine ammonia-oxidiser community structure. First results indicate the disappearance of Nitrosospira clusters I, II and III under elevated CO2 but also call for systematic analysis of replicates to take into account methodological and sample variability. [less ▲]

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