The tree phyllosphere microbiome - an overlooked and important sink for carbon monoxide?
Lead Research Organisation:
University of Warwick
Department Name: School of Life Sciences
Abstract
In this project, we will investigate whether microorganisms associated with the above ground parts of trees are important as degraders of the gas carbon monoxide.
Carbon monoxide, CO, is a product of incomplete combustion processes and is known to most people as a potentially lethal gas and component of air pollution. However, it is also a naturally occurring trace gas that is produced by natural environmental processes which contribute to its background atmospheric concentration of just 50-150 parts per billion.
Even at these trace levels in the atmosphere, at which CO is not toxic, this gas plays an important role because it affects the lifetime of other atmospheric gases. It is referred to as a short-lived climate forcer and an indirect greenhouse gas. This is due to it reacting with hydroxyl (OH) radicals which are important for reactions of a wide range of atmospheric trace gases, some of which contribute to the greenhouse effect such as methane and tropospheric ozone. Elevated levels of CO in the atmosphere therefore have an indirect impact on climate, by removing OH radicals which could otherwise react with methane and ozone, thereby increasing the lifetime and effect that these important greenhouse gases have. In addition, CO affects air quality and human health at higher concentrations.
The ability of specific microorganisms to degrade CO has long been known, and previous studies have established that CO degrading microorganisms are present in soils and in the oceans. By degrading CO, these microorganisms contribute to the natural cycling of CO and either remove it from the atmosphere or prevent it from being emitted to the atmosphere from soils and seawater, thus contributing to regulating its natural low concentrations.
We have recently shown that the above ground parts of trees are colonised by CO degrading microorganisms. At the global scale, the phyllosphere of trees is a vast habitat for microorganisms, microbial activities in the phyllosphere are therefore also of global importance. Microorganisms inhabiting the phyllosphere (primarily the leaves and stems) are in direct contact with the atmosphere and are therefore able to take up CO produced by photochemical reactions in live plant tissue or take it up from the surrounding air. Their CO degradation activity has not been shown previously. Only in our previous work on CO-degrading microorganisms associated with tree leaves has the potential of CO degradation been shown; these findings warrant further investigation because it means that a potentially major global removal mechanism for CO has not been recognised previously.
Understanding this process is fundamentally important because it will allow to disentangle how CO-degrading microorganisms in the phyllosphere affect CO fluxes from vegetation. Identifying the diversity of phyllosphere CO-degrading microorganisms, understanding which of them are active, and how their activity is affected by environmental factors is vital to provide a better comprehension of how the CO-fluxes from vegetation are regulated and how they vary across temporal and spatial scales.
In incubation experiments, we will be able to determine degradation of CO at environmental concentrations, and then identify and characterise these CO-degrading microorganisms using modern metagenomic and metatranscriptomics approaches which are based on the sequencing of the DNA and RNA of the phyllosphere microorganisms, respectively.
The insights from our work will thus provide fundamental new insights into the global cycle of CO and contribute to a better understanding of how the composition of the atmosphere is affected by microbial activities. It will also allow us to examine how CO degrading microorganisms fundamentally affect atmospheric chemistry and CO emission from vegetation, a process that affects global climate.
Carbon monoxide, CO, is a product of incomplete combustion processes and is known to most people as a potentially lethal gas and component of air pollution. However, it is also a naturally occurring trace gas that is produced by natural environmental processes which contribute to its background atmospheric concentration of just 50-150 parts per billion.
Even at these trace levels in the atmosphere, at which CO is not toxic, this gas plays an important role because it affects the lifetime of other atmospheric gases. It is referred to as a short-lived climate forcer and an indirect greenhouse gas. This is due to it reacting with hydroxyl (OH) radicals which are important for reactions of a wide range of atmospheric trace gases, some of which contribute to the greenhouse effect such as methane and tropospheric ozone. Elevated levels of CO in the atmosphere therefore have an indirect impact on climate, by removing OH radicals which could otherwise react with methane and ozone, thereby increasing the lifetime and effect that these important greenhouse gases have. In addition, CO affects air quality and human health at higher concentrations.
The ability of specific microorganisms to degrade CO has long been known, and previous studies have established that CO degrading microorganisms are present in soils and in the oceans. By degrading CO, these microorganisms contribute to the natural cycling of CO and either remove it from the atmosphere or prevent it from being emitted to the atmosphere from soils and seawater, thus contributing to regulating its natural low concentrations.
We have recently shown that the above ground parts of trees are colonised by CO degrading microorganisms. At the global scale, the phyllosphere of trees is a vast habitat for microorganisms, microbial activities in the phyllosphere are therefore also of global importance. Microorganisms inhabiting the phyllosphere (primarily the leaves and stems) are in direct contact with the atmosphere and are therefore able to take up CO produced by photochemical reactions in live plant tissue or take it up from the surrounding air. Their CO degradation activity has not been shown previously. Only in our previous work on CO-degrading microorganisms associated with tree leaves has the potential of CO degradation been shown; these findings warrant further investigation because it means that a potentially major global removal mechanism for CO has not been recognised previously.
Understanding this process is fundamentally important because it will allow to disentangle how CO-degrading microorganisms in the phyllosphere affect CO fluxes from vegetation. Identifying the diversity of phyllosphere CO-degrading microorganisms, understanding which of them are active, and how their activity is affected by environmental factors is vital to provide a better comprehension of how the CO-fluxes from vegetation are regulated and how they vary across temporal and spatial scales.
In incubation experiments, we will be able to determine degradation of CO at environmental concentrations, and then identify and characterise these CO-degrading microorganisms using modern metagenomic and metatranscriptomics approaches which are based on the sequencing of the DNA and RNA of the phyllosphere microorganisms, respectively.
The insights from our work will thus provide fundamental new insights into the global cycle of CO and contribute to a better understanding of how the composition of the atmosphere is affected by microbial activities. It will also allow us to examine how CO degrading microorganisms fundamentally affect atmospheric chemistry and CO emission from vegetation, a process that affects global climate.
