Habitat engineering and carbon storage: the importance of Sphagnum moss in peatlands
You know what really bogs me? How infrequently mainstream conversations surrounding climate change discuss the importance of peatlands and Sphagnum in carbon storage. I know what you are thinking... am I really going to stand by using that terrible pun in the first line of my first article? And the answer is yes. Start with the bar low and things can only improve, now onto the article.
Peatlands are a fascinating environment found across the world. Not only do they support a wide range of organisms and play crucial ecological roles, but they also act as one of the most efficient carbon sinks, storing twice as much carbon as the world’s forests. This ability to store carbon is a result of an interesting bit of biochemistry and the efforts of Sphagnum moss to engineer themselves the perfect environment. However, the carbon stored within peatlands is at risk of being released as a direct result of climate change. The rising temperatures and prevalence of droughts threatens the delicate biochemical processes that keep the carbon locked within peat bogs.
As mentioned, one of the defining characteristics of peatlands is the slow rate of decomposition. This is caused by the low levels of oxygen, high acidity, and overall lack of nutrients present in their waterlogged conditions. Peat formation varies substantially and is heavily dependent on the climate, with it taking millennium to form in some areas whilst others have produced 20m of peat within the last 10,000 years . High acidity and a lack of both oxygen and nutrients does not make them look like a particularly appealing place to inhabit. However, as an ecosystem they support a myriad of flora and fauna. But dominating this habitat are the Sphagnum mosses. Undoubtedly the most prominent organisms in peatlands and actually regarded as the most ecologically dominant group of mosses . You may think that Sphagnum thrives in peat bogs due to the conditions being perfect for their needs, interestingly this is not the case. In fact, Sphagnum actually engineers these conditions within peatlands to make them perfect for themselves. In doing so, they create an environment that most other plants struggle in, enabling their dominance. Sphagnum growth stimulates the build-up of peat. The acidity, low nutrient, and slowly permeable nature of peat reduces the growth of other plants, which increases the light available for Sphagnum. Therefore, peat production as a direct response to Sphagnum growth acts as a positive feedback loop to further increase the growth of Sphagnum. Not only are Sphagnum mosses responsible for many of the defining characteristics of peatlands but they are also essential for their notorious carbon storing abilities.
A bit of chemistry
We have established that slow decomposition is key to the formation of peatlands and is why the carbon storage is so high. It was originally believed that simply the lack of oxygen and nutrients, along with the high acidity were the driving factors behind this slow rate of decomposition. However, the driving force behind these conditions is the inhibition of a group of enzymes known as phenol oxidases and the resulting build-up of the phenolic compounds that they breakdown. Phenolic compounds are incredibly widespread within the plant kingdom and are involved in a variety of important processes, including plant defence responses, increasing the attractiveness of the plant to pollinators, as well as being responsible for antibacterial and anti-fungal properties .
Sphagnum contains its own specific phenolic compound known as Sphagnum acid (p-hydroxy-beta-(carboxymethyl)-cinnamic acid - in case you were wondering) . Sphagnum acid is a very stable compound and is, unsurprisingly, the most prevalent phenolic compound in peatlands. By suppressing the activities of phenolic compound degrading bacteria and fungi, Sphagnum acid plays a key role in the build-up of phenolic compounds . Combined with the low oxygen levels in peatlands also reducing the activity of phenolic oxidases (that breakdown phenolic compounds) it is easy to see how they accumulate .
This build-up results in the inhibition of certain enzymes produced by bacteria and fungi which act as crucial agents of the carbon and nutrient cycles [7,8,9], thereby keeping the carbon stored within the peatlands rather than being cycled back into the atmosphere. The inhibition of the phenol oxidase enzymes and bacterial activity has become known as the "enzymic latch" on the global carbon stores.
Side note, this inhibitory effect on bacterial and fungal enzymes is what gives Sphagnum its antimicrobial properties, leading to it being used in medicine, specifically as an antiseptic in wound dressings during the first world war.
To summarise, the limitation of phenol oxidases, causes a build-up of phenolic compounds, which subsequently prevents the decomposition of organic compounds and inhibits the carbon cycle, resulting in the substantial accumulation of carbon in peatlands.
The climate change concern
Right, we've seen that, for their size peatlands store a huge quantity of carbon and I've discussed the role of Sphagnum in this carbon accumulation but why is it at risk of being released as climate change progresses?
A well-known consequence of climate change is an increase in the frequency, distribution and intensity of droughts and this is detrimental for the carbon stored in peatlands. It has been shown that drought conditions, and the eventual re-wetting of peat that has been subjected to drought, impacts the concentration of phenolic compounds in peatlands . This is because, under drought conditions, the activity of phenolic compound degrading enzymes (phenolic oxidases) increases, as does the presence of bacteria, ultimately reducing the concentration of the crucial phenolic compounds. Additionally, this initiates a feedback loop, as the reduced presence of phenolic compounds enables further microbial growth and therefore further breakdown of those compounds, resulting in a biochemical cascade. What is more concerning, is that this cascade goes beyond the initial drought phase and continues to be affected during the post-drought recovery phase. This makes sense, because when the rain finally comes to the drought-exposed peat, the nutrient levels will suddenly spike, altering the pH and ultimately increasing the rate of decomposition that is so vital to the storage of carbon. To put some numbers to this situation, it was found that under simulated drought conditions the diversity and abundance of phenolic compound degrading bacteria increased by 129.4% and the activity of phenolic-degrading enzymes went up by 83% . Therefore, it is easy to see how an increase in droughts leads to the loss of the carbon stored within peatlands.
Despite acting as large carbon stores and their fragility, you don't tend to hear so much about peatlands in mainstream discussions surrounding climate change. Often the conversations focus on forests and oceans, both of which are important, and the carbon stored within them is also under threat from human activities. However, I hope that we start seeing peatlands become more of a focus and projects that aim to preserve and regenerate them being emphasised (something I may write another article on).
To summarise, the rising temperatures and the resulting increase in droughts associated with climate change pose a substantial risk to carbon stored within peatlands by affecting the concentration of phenolic compounds which are responsible for their carbon storing abilities.
To finish off
Thank you for reading my first article on this website, I greatly appreciate it and I hope that you found it interesting. I actually spent some time researching this topic and studying a gene family involved in the production of phenolic compounds in Sphagnum as part of my molecular biology masters. I aim to cover a wide range of topics and keep a balance between slightly heavier science and overall relevance within each article. However, it has been a long time since I have written articles for a blog rather than university assignments, so I welcome any feedback. I often have a tendency to write too much or go too deep and part of the point of this blog is to improve on those things. So please do send me feedback and again, thanks for reading.
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