Moss mites may tell us about carbon cycling on peatlands

Hi all!

I’m Jemina, a Forest and Atmospheric Sciences student at Helsinki University. This summer I joined Minna Väliranta’s research group at the Environmental Change Research Unit (ECRU) as a HiLIFE Research Trainee. In this blog post, I will briefly introduce you to the hidden life of moss mites. I had the opportunity to investigate a topic new to the whole group and to begin working on my Master’s thesis on the subject.

Moss mite communities may tell us about carbon cycling on peatlands

Organic matter on peatlands is generated and decomposed continuously. Sphagnum moss stems reach up towards the sun while old growth beneath them begins to disintegrate. A mire is formed when growth is faster than decomposition and partially broken-down material compacts into peat. In anoxic conditions under water, peat releases carbon and nutrients very slowly. Peatlands are some of the most efficient carbon banks that nature has to offer. Sometimes, however, decomposition accelerates and exceeds the carbon sequestration of vegetation. This may happen on peatlands modified by human activities or because of changes in climate, but also as a result of the natural development of mires. Whether our peatlands will be carbon sinks or sources in the near future, and how long it will take for possible changes to occur, is a timely topic to research. These different kinds of trajectories are being studied at the University of Helsinki by my supervisor senior research fellow Minna Väliranta and her group.

But how does peat eventually break down? The most effective primary decomposers are microbes, changing the chemical composition of plant matter. Small soil organisms affect decomposition both directly and indirectly: by consuming plant material and other organisms, transporting microbes, and regulating the spread of fungi. Part of the decomposition process depends on the activity of moss mites, a group of tiny insects.


Hard workers underground

Moss mites (Oribatida) are arachnids less than a millimeter in size. Like their better-known relatives, mites have eight legs. Unlike ticks, they are not harmful to humans. On the contrary – without them forestry or food production would be significantly harder. Moss mites play an important role in maintaining the well-being of the earth, as they release nutrients back into the soil. Despite their name, moss mites thrive in a wide variety of environments and are abundant in deserts, anthills, tree foliage, fields, and mires. Hundreds of thousands of moss mites can be found in one square meter of forest soil!

About 12,000 moss mite species are known to the world, and the number is growing constantly as research is carried out. Moss mites can adapt to almost any kind of environment. Some of the species have adjusted to especially harsh conditions, and so mites can also be found in nutrient-poor, acidic and wet peatlands. These environments are demanding for other soil modifiers: for example earthworms cannot be found in peat. This is why moss mites are especially important in peatland environments.

The wide range of species also reflects on the moss mites’ menu. Some species are vegetarians, some enjoy fungal mycelium for food, and others are opportunists eating whatever comes their way. In addition to nutrition, other environmental conditions also affect which moss mite species thrive in each place. Moisture has been found to be an important distinguishing factor, along with soil acidity and phosphorus content.

Knowing moss mite species and their preferences is useful. When any certain species is found, we can deduce that the environmental conditions it requires are also met. Due to their small size, moss mites move very little during their lifetime. It has been noticed that horizontal movement can be just within tens of centimeters. They are also long-lived among insects and can live up to five years in cool habitats. Changes in the species composition in a certain place therefore also reflect a change in the environment. Monitoring of moss mites can show, for example, improving moisture conditions at a restored bog site.

While moss mite communities can tell us about the current state of mires and peatlands, they may also be useful when looking for information of the past.  As peat accumulates, not only plant material but also fossils of small organisms are buried in it. The layered peat deposits of a mire can be dated. By studying the moss mite species at chosen intervals, we can gain information about the environmental conditions that prevailed at the mire tens, hundreds or even thousands of years ago. Moss mites have a hard chitinous shell that survives decomposition quite well. However, small sensory hairs on the mites’ shells may break easily, which often makes it difficult to identify mites to the species level from fossil samples.


Oribatid mites have a hard, chitinous shell and eight legs.


Research is challenging due to the large variety of species

The microscopic size of the organisms and the large variety of species is a challenge in studying moss mites. Determining the species level of mites is hard, and differences between species are sometimes only detectable with the help of DNA research. When I started learning about moss mites, I also noticed that identification guides are poorly available and none of them are in Finnish.

The presence and activity of moss mites has, however, been studied in quite a wide variety of environments in Finland. Riikka Elo noticed in her dissertation that anthills support the life of rich moss mite communities. Inkeri Markkula showed in her work that certain moss mite species in the peat archives can tell us if permafrost has previously been present at northern mires. Ritva Penttinen, now retired, has had a long career in tick and mite research at the Turku University Zoological Museum, and has extensively mapped Finnish moss mite species.

In planning my own research, I have been most interested in the question of whether the moss mite community could tell us something about the rate of soil carbon decomposition. Since mites stay put in a very small area, the species composition can significantly change within the scale of just a few meters. By collecting moss samples from different kinds of mire surfaces and separating the mites from them, my intention is to compare the found species and their abundances with carbon flux measurements from each location. Doing research is always an adventure, and I still can’t be sure what I’ll find along the way! I will keep you posted as the research continues.