Soil stores the largest volume of carbon on land. The release of these huge amounts is mainly governed by the most diverse community on Earth — microbes. However, many microbial soil species have overlapping metabolic functions and the effect of microbial diversity on carbon decomposition rates has been overlooked until recently. The article “Microbial biodiversity contributes to soil carbon release: a case study on fire disturbed boreal forests” in FEMS Microbiology Ecology reveals that microbial diversity, especially bacterial diversity, plays a fundamental role in soil carbon emissions. Xuan Zhou explains for the #FEMSmicroBlog why we should not neglect microbial diversity in soil research.
Why microbial diversity has been overlooked in soil respiration?
Although soil microorganisms account for a large part of biodiversity on Earth, many different species often share similar functions in an ecosystem. This leads to the widely accepted concept that many microbial species are redundant and the change of species diversity has fewer effects on ecosystem functions. Thus, to predict soil carbon dioxide emission, most terrestrial ecosystem models merely consider environmental factors.
Yet, recent research also suggests that soil content needs to be studied. Soil contains a mixture of highly diverse organic compounds, such as starch, cellulose, lignin and more. Some organic compounds are easily decomposed and are thus considered labile carbon. Similarly, others are more difficult to decompose and are thus referred to as recalcitrant carbon.
Many microbes tend to decompose labile carbon since it is easier to gain energy from it. Hence, the decomposition of labile carbon will not be affected if a few species are missing within a community.
Only a few species are able to decompose recalcitrant carbon. So, the question arises whether the decomposition of recalcitrant carbon is affected if an ecosystem lacks those species.
The assumption was that the more diverse a microbial community is, the larger the spectrum of carbon compounds that can be decomposed. This would further result in larger amounts of released carbon. Although the climate determines the activity of soil microbes, the composition of soil communities ultimately determines their decomposition rates.
The study “Microbial biodiversity contributes to soil carbon release: a case study on fire disturbed boreal forests” in FEMS Microbiology Ecology aimed at linking the increasing microbial diversity to soil carbon dioxide emissions. The work investigated boreal forests that experienced natural fires along a gradient of time periods (3 years, 25 years, 46 years and >100 years after a fire).
In these ecosystems, microbial communities form natural gradients of microbial diversities. By modelling both environmental factors and microbial traits, the study tried to explain the changes in soil carbon dioxide emission with increased microbial diversities.
Since bacteria and fungi are the main decomposers in soil, this study compared the contributions of bacterial and fungal diversities on soil respiration. Bacteria are the most diverse group of organisms and different bacterial clades are more specific to decompose certain types of carbon compounds.
Unlike bacteria, fungal clades are more multifunctional. Previous studies have shown that an increased fungal richness does not necessarily increase the decomposition of carbon. Thus, the study hypothesised that a change in fungal diversity would contribute less to carbon decomposition than a change in bacterial diversity.
High bacterial diversity increases carbon emission
The study “Microbial biodiversity contributes to soil carbon release: a case study on fire disturbed boreal forests” demonstrates that higher microbial diversity increases soil respiration. The model including microbial diversity better explains the variation in soil respiration than the alternative model excluding it. This shows how important it is to consider microbial diversity when modelling carbon release from soil.
Although both fungal and bacterial diversities contribute to soil respiration, bacterial diversity impacts soil respiration to greater extents than fungal diversity. Interestingly, while the amount of fungi within soil plays a dominant role in soil decomposition, fungal diversity has fewer effects. This is likely because many metabolic activities of different fungal species are overlapping.
Furthermore, a higher microbial diversity mainly drives the decomposition of recalcitrant carbon. Since most species are able to decompose labile carbon, microbial diversity does not necessarily correlate with the decomposition of labile carbon.
This study shows that soil respiration is increased when microbial diversity is high. These results provide clear evidence that microbial diversity should not be neglected when predicting carbon release from soil.
- Read the article “Microbial biodiversity contributes to soil carbon release: a case study on fire disturbed boreal forests” by Zhou et al. (2022).
Xuan Zhou’s research background sits at the interface of ecology and soil microbiology. She completed her PhD in 2020 on a topic of how forest fire affects microbial community and functionalities in permafrost soils with Dr. Frank Berninger at University of Helsinki. Her interests are microbial ecology and biogeochemistry. Currently, she continues to investigate microbial functions (e.g. carbon decomposition) in forest soils after priming effects at the Department of Environmental and Biological Sciences, University of Eastern Finland.
About this blog section
The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.
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