Abstract
BackgroundChanges in aboveground plant species diversity as well as variations of environmental conditions such as exposure of ecosystems to elevated concentrations of atmospheric carbon dioxide may lead to changes in metabolic activity, composition and diversity of belowground microbial communities, both bacterial and fungal.ResultsWe examined soil samples taken from a biodiversity × CO2 grassland experiment where replicate plots harboring 5, 12, or 31 different plant species had been exposed to ambient or elevated (600 ppm) levels of carbon dioxide for 5 years. Analysis of soil bacterial communities in these plots by temporal temperature gradient gel electrophoresis (TTGE) showed that dominant soil bacterial populations varied only very little between different experimental treatments. These populations seem to be ubiquitous. Likewise, screening of samples on a high-resolution level by terminal restriction fragment length polymorphism (T-RFLP) showed that increased levels of carbon dioxide had no significant influence on both soil bacterial community composition (appearance and frequency of operational taxonomic units, OTUs) and on bacterial richness (total number of different OTUs). In contrast, differences in plant diversity levels had a significant effect on bacterial composition but no influence on bacterial richness. Regarding species level, several bacterial species were found only in specific plots and were related to elevated carbon dioxide or varying plant diversity levels. For example, analysis of T-RFLP showed that the occurrence of Salmonella typhimurium was significantly increased in plots exposed to elevated CO2 (P < 0.05).ConclusionPlant diversity levels are affecting bacterial composition (bacterial types and their frequency of occurrence). Elevated carbon dioxide does not lead to quantitative alteration (bacterial richness), whereas plant diversity is responsible for qualitative changes (bacterial diversity).
Highlights
Changes in aboveground plant species diversity as well as variations of environmental conditions such as exposure of ecosystems to elevated concentrations of atmospheric carbon dioxide may lead to changes in metabolic activity, composition and diversity of belowground microbial communities, both bacterial and fungal
We found that soil bacterial community structure was only poorly resolved when analyzing bacterial populations by temperature gradient gel electrophoresis (TTGE)
The resolution of TTGE was too low for the monitoring of soil microbial diversity
Summary
Changes in aboveground plant species diversity as well as variations of environmental conditions such as exposure of ecosystems to elevated concentrations of atmospheric carbon dioxide may lead to changes in metabolic activity, composition and diversity of belowground microbial communities, both bacterial and fungal. Soil microorganisms are the driving force behind soil organic matter transformations such as mineralization of organic compounds These transformations are the basis of plant decomposition, soil aggregation, nutrient availability, soil fertility and, in general, soil ecosystem functioning. Anthropogenic activities resulting in e.g. increasing atmospheric carbon dioxide concentrations might induce specific responses (stimulation, inhibition) of soil microbes (bacteria, fungi) possibly mediated via altered growth of the plant communities [9,10,11,12] On both local and global scales, the wealth of soil microbial diversity is poorly appreciated and, the importance of soil organisms has been largely neglected [13]. Detailed knowledge on the control of ecosystem processes and functioning by this diversity is still lacking [15]
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