Microbes and climate change: On land & sea
Updated: Jun 8, 2020
This week, I've written a bonus Microbial Monday blog in honour of the global climate strikes. When we talk about climate change, often people only think in macro: plants, animals, humans, long-term climate patterns, the solar system... Lots of big things. However, the tiniest of beings on our planet are also affected by, and effect, global warming.
Today on Microbial Monday, we'll be discussing the roles of microbes in climate change. This will be a two-part series, with the second half coming out on the first Monday of October. In this first part, I'll give an overview of how microbes in the oceans and on land impact, and are impacted by, climate change. In two weeks, On October 7th (which is also another big climate change protesting date, in case you missed it), I'll focus on climate change and microbes in agriculture, infectious diseases, and climate change-addressing technologies.
Before we get into the microbes, though, let's briefly talk about what climate change is all about. Climate itself is a bigger idea than just weather: it refers to the long-term weather patterns in a specific place. That place might be a valley, a district, province or state, or even the whole planet. Climate change, it follows, is a change in the usual weather patterns in a specific place.
Normally, climate is pretty stable - for hundreds or millions of years on end. However in the last 100 to 200 years, the Earth's climate has started changing at a relatively rapid pace. I cannot stress enough that this is no longer a debate among scientists. Scientists agree that the Earth is warming, in the same way that scientists agree that vaccines work. To be specific, a paper published in 2016 found that at least 97% of scientists agree that the current observed global warming is definitely caused at least in part by humans, which is an even more specific stance than just, "the Earth is warming". Last I checked, Wikipedia knew of a grand total of 69 scientists worldwide who disagree with the scientific consensus on global warming. Just in the USA in 2018, there were 4.3 million people who held a science or engineering master or doctorate degree (and thereby are well deserving of the title of "scientist" in my opinion).
That checks out to a pretty darn low percentage of scientists who don't believe in (anthropogenic, i.e. human-caused) global warming. For reference, there are probably more people who do not believe that the Earth is a sphere, than scientists who do not believe that global warming is caused by humans.
Now that we've gotten that out of the way, what is global warming? It is mainly a problem of greenhouse gases doing just as their name implies: acting like a greenhouse, and warming the planet. Some greenhouse gases that I'll mention in this two-part series are carbon dioxide, methane, and nitrous oxide, but there are also others. I'm just simplifying things a bit.
So from here - let's jump in! How are microbes affected by, and how do they effect, climate change and global warming?
In the water
Marine microbes are tiny but mighty. Let's talk first about marine phytoplankton, which are tiny little microbes that are able to feed themselves just from sun, water, and carbon dioxide (CO2) in the air through the process of photosynthesis – the same as plants. Indeed, just like plants, marine phytoplankton pull out carbon from the air, and release oxygen as they 'breathe': a perfect reflection of the breathing of animals like us humans. In fact, marine phytoplankton are responsible for an impressive 50% of all photosynthetic 'carbon fixation' (i.e. pulling carbon from the air and turning it into solid, living things) and oxygen production every single year, even though they only weigh about one hundredth of the mass of the plants and microbes who do the other 50%.
Interestingly, some studies actually indicate that phytoplankton production will probably increase with rising CO2 levels levels. If you think about it, CO2 is kind of like food for them, so more food, more plankton. Unfortunately, it's not all good news. As the ocean warms, it also acidifies, and these two processes together are expected to drastically change the types and quantities of microbes, including phytoplankton, in the oceans. For example, we will probably see an increase in toxin-producing phytoplankton, kind of like the ones we see in red tide, simply because they fare better in warmer, more acidic waters. That's not such great news for us humans, or for other animals susceptible to their toxins.
Warmer and more acidic oceans also will likely be better living environments for the smaller and more hard-shelled (these plankton 'calcified' - with hard shells kind of like your nails) plankton, as opposed to big soft ones. These plankton are also less likely to sink, but rather to stay near the top of the ocean. Why is this important though? To understand, first you have to know that the deep ocean is a very important carbon sink. Every day, a lot of carbon in the form of sinking plankton is deposited on the ocean floor, where it usually stays for millennia - unless humans start drilling for oil, anyways. This stored carbon will then in theory not be released again as a greenhouse gas. It follows that more floaty plankton means less sinky plankton, and that the deep ocean will become less of a fossil sink simply because more carbon is staying at the surface.
As well as encouraging the growth of floaty plankton, warmer and more acidic waters will change the functioning of the marine microbial community. For example, microbes in the ocean are very important contributors from getting nitrogen out of the sky, and into a usable form of nitrogen for themselves and other plants and animals in the seven seas. Microbes perform a similar job on land, too, as you might remember from this blog post about the happy relationship between Frankia and butterfly bushes.
Nitrogen fixation doesn't happen in a bubble, though. In fact, nitrogen fixation is inhibited in more acidic oceans. To make matters worse, the more-or-less opposite of nitrogen fixation, release of that nitrogen back into the atmosphere as a gas, happens more in acidic oceans. You might already know that the heavy-duty fertilizer humans use on farms is basically just nitrogen. Limited nitrogen fixation in warmer waters means less microbe-produced fertilizer for other plants, animals, and microbes in the ocean.
These community and functional changes in the microbes within the oceans can have pretty far-reaching effects on all of the other water-dwellers around them. Ocean food chains are built on our microbial buddies. All these tiny microbes provide the base of the food pyramid for everything else to be able to live there. When the smallest members of the marine ecosystems are affected, we can expect that the slightly bigger predators who feed on them, and the slightly bigger predators that feed on those, will also be affected. We don't yet know exactly how this will go down, but for example, data from smaller plankton blooms have already shown us that coastal ecosystems can be hard-hit by major upheavals in their microbial communities.
On the land
Pick up some soil. Take a look at it. It's full of CARBON! On the earth, soil organic carbon stores about 2000 billion tonnes of organic carbon! That's a lot! And, all of this carbon in the soil is under the direct control of soil microbes: they live in it, they produce it, they eat it, and they change it into other forms.
Just as they do in the water, soil microorganisms help regulate the amount of organic carbon stored in soil and released back to the atmosphere. On one hand, soil microbes help the growth of plants by funneling nitrogen and other nutrients to them, which impacts the storage of carbon in vegetation. On the other hand, microbes in the soil also break down plant matter, like dropped leaves and old logs, which releases greenhouse gases. It's all about the balance between these two processes.
The big problem now, is that we're rather out of balance. Small-scale studies have shown that when soil warms up, we lose more carbon to the atmosphere. This ends up cycling into a positive feedback loop: soil warms, greenhouse gases are released, and soil warms some more.
Two ecosystem types that scientists are particularly concerned will enter such a positive feedback loop are permafrost, and peat lands. Let's start with permafrost.
Permafrost describes exactly what you think it does: permanently frozen land. This frosty soil contains a lot of accumulated carbon in plant and animal and microbe matter that isn't degraded by microbes, simply because it's too cold! All of this frozen carbon makes permafrost one of the greatest terrestrial carbon sinks. However, as it warms, microbes start eating up all of that tasty carbon, and some of these microbes release greenhouse gasses, which kickstart the warming into a new cycle.
Something similar happens in peat lands, another important carbon sink, as they warm. Unlike permafrost, peat lands are not frozen, but they are still resistant to microbial decomposition and therefore net carbon sinks. In peat bogs, plant litter isn't decomposed because it is saturated with water, slightly acidic, and the plants that grow there produce natural anti-microbial compounds. Normally, peat moss, or Sphagnum moss, is one of the main components of the peat landscape. However, with increased temperature and reduced soil water content, as we see with global warming, more shrubs will start growing in these peaty areas, and totally overturn the soil and the normal microbial processes. Simply put, less water, less acid, and less peat moss acid = more oxygen and tasty plants for microbes to eat up. This in turn means more microbes eating up all the new plant litter, and releasing CO2 and methane… turning peat bogs from carbon sinks into carbon sources.
So, this concludes our survey of climate change and microbes in the water and on the land. On October 7th, check back for the post on microbes and climate change in agriculture, infectious disease, and microbiotechnology!
Until then, always think critically, and check your sources. Today, my main sources were: 1. Hutchins DA, Jansson JK, Remais J V, Rich VI, Singh BK, Trivedi P. Climate change microbiology — problems and perspectives. Nat Rev Microbiol. 2019;17(6):391-396. doi:10.1038/s41579-019-0178-5
2. Cavicchioli R, Ripple WJ, Timmis KN, et al. Scientists’ warning to humanity: microorganisms and climate change. Nat Rev Microbiol. 2019;17(9):569-586. doi:10.1038/s41579-019-0222-5