Invasive Earthworms Change the Diversity and Functioning of Soil Microbes in Boreal Forests

Earthworms are often considered as beneficial organisms that improve soil fertility and structure.

However, not all earthworms are native to Canada, and some of them can have negative impacts on the boreal forests that cover most of the country.

How Earthworms Invade the Boreal Forests

(Photo : JOEL SAGET/AFP via Getty Images)

Earthworms are not native to most of Canada's boreal forests, which were covered by glaciers during the last ice age.

The glaciers scraped away most of the soil and its inhabitants, leaving behind a thin layer of organic matter on top of the mineral soil.

This layer, known as the forest floor, is rich in carbon and nutrients, and supports a diverse community of plants, animals, and microbes.

However, human activities have introduced earthworms to these areas, either intentionally or accidentally.

Some of the sources of earthworm invasion include fishing bait, composting, gardening, agriculture, forestry, and road construction.

Once established, earthworms can spread rapidly through the forest, consuming the organic matter and mixing it with the mineral soil.

How Earthworms Affect the Soil Microbial Community

The soil microbial community is composed of bacteria and fungi that play important roles in decomposing organic matter, cycling nutrients, and storing carbon. These microbes are adapted to the conditions of the boreal forest soil, which is acidic, cold, and moist.

However, earthworm invasion can alter these conditions and affect the microbial community.

A recent study by researchers from the University of Alberta showed that earthworms affected fungal and bacterial communities in the first layer of mineral soil, just below the forest floor.

The study is one of the first to highlight how non-native earthworms are directly altering the soil microbial community in Canada's boreal forests.

The researchers analyzed soil samples from multiple forest sites in Alberta and Quebec, and found that earthworms induced shifts in the community composition of bacteria and fungi.

They also found that earthworms increased the diversity and abundance of some microbial groups, while decreasing others.

Some of these changes could have positive effects on the soil.

For example, earthworms increased the abundance of fungi that can live in symbiosis with trees, which could help them access nutrients and water.

Earthworms also increased the diversity of bacteria and fungi, which could make them more resilient to disturbance and better able to maintain soil functions.

However, some of these changes could also have negative effects on the soil. For example, earthworms favored bacteria that can grow quickly and use oxygen, which could speed up nutrient cycling and release carbon into the atmosphere.

Earthworms also reduced the amount of carbon stored in the forest floor by up to 94%, which could affect climate change mitigation.

Also Read: European Earthworm Invasion Responsible for the Decline of Species Diversity in North American Forests

What Are the Implications for the Boreal Forest Ecosystem

The changes in the soil microbial community caused by earthworm invasion could have wide-ranging effects on the boreal forest ecosystem.

The boreal forest is one of the largest terrestrial ecosystems on Earth, covering about 14% of its land surface.

It stores about 30% of the global terrestrial carbon and provides habitat for many species of plants and animals.

However, earthworm invasion could threaten these functions and services. By altering the soil microbial community, earthworms could affect the availability and cycling of nutrients such as nitrogen and phosphorus, which are essential for plant growth.

Earthworms could also affect the water balance and temperature of the soil, which could influence plant survival and distribution.

Moreover, earthworms could affect the interactions between plants and other organisms such as insects, birds, and mammals.

The effects of earthworm invasion on the boreal forest ecosystem are still poorly understood, and more research is needed to assess their magnitude and direction.

However, it is clear that earthworm invasion is a serious issue that needs to be addressed by policymakers and land managers.

Some possible strategies to prevent or reduce earthworm invasion include educating the public about their impacts, regulating their use as fishing bait or composting material, restoring native vegetation, and applying biocontrol agents.

Related article: New Research Reveals Earthworms Can Replace Expensive Synthetic Fertilizers