Earthworms don’t stop shaping soil processes when they die. A new study shows they can still help store carbon in the soil, even after death. “This is quite surprising”, says lead author Tullia Calogiuri. “Most of our knowledge about earthworms comes from their activity while alive, such as burrowing, feeding, and producing feces. Finding that they also play a role after death is exciting”.
Calogiuri, a PhD candidate at the Soil Biology and Soil Chemistry groups of Wageningen University & Research, investigated the role that both live and dead earthworms can have on the capture of carbon through enhanced mineral weathering. Together with co-authors Alix Vidal, Mathilde Hagens and Jan Willem van Groenigen she published the findings in
Communications Earth and Environment.
Enhanced mineral weathering is a relatively new nature-based carbon removal technology, gaining traction in the fight against climate change. It involves stimulating a naturally occurring process, where rocks break down while at the same time capturing carbon from the atmosphere. This carbon can be stored either in the soil by binding to minerals (carbon stabilisation) or be dissolved in water (carbon capture). The enhancement of mineral weathering can be done by spreading very fine rocks on soils, where the rocks themselves break down more rapidly due to their small size. While physical and chemical factors (e.g. erosion and rock size) drive these processes, biological factors such as earthworms can also play an important role. These have remained underexplored until now.
In a laboratory experiment, the authors traced the different fates of carbon over four months under the influence of either live or dead earthworms. The overall outcome of the study was clear: “On average, dead earthworms increased carbon capture by 16% in the form of dissolved carbon”, says Alix Vidal, assistant professor in the Soil Biology group of Wageningen University & Research. “We also found that dead earthworms led to the same increase in stabilisation of organic carbon as live earthworms. These findings highlight the importance of considering the full life cycle of earthworms in carbon dynamics”.
Fuel for tiny soil workers
The research team, which included collaborators from the Universities of Antwerp, Hamburg, Kleve and Uppsala, further explored the mechanisms behind this effect. They found that dead earthworms increased both the presence and the activity of microbes over time compared to live earthworms by releasing important nutrients for microbial growth when their bodies decompose. “This suggests that dead earthworms influence carbon dynamics indirectly, via stimulating microbial processes”, says Sara Vicca, professor at the University of Antwerp. “Microbes can speed up the breakdown of minerals, which stimulates the formation of new mineral surfaces that can bind carbon. They can also stimulate the release of mineral products to form dissolved carbon”.
Earthworms needed - in any condition
Does this mean that dead earthworms are more important than live ones in the capture and stabilisation of carbon? “Not at all”, says Jan Willem van Groenigen, professor in the Soil Biology group of Wageningen University & Research. “They are equally important, but in different ways. Live earthworms enhance carbon stabilisation directly through strengthening bonds between minerals and carbon. Their mineral digestion helps to make that happen. In contrast, dead earthworms increase both carbon stabilisation and capture indirectly through strengthening microbial activity. Besides, they are two sides of the same coin – you can’t have dead earthworms without also having live earthworms, and vice versa. Our study paves the way on further understanding the role of dead earthworms in a wider range of soil processes side by side to living ones”.
Further research
There are still many unknowns around the effect of live earthworms on enhanced weathering, let alone the role of dead earthworms. The authors conclude that earthworms can influence carbon capture and stabilisation beyond their lifespan. More research is needed to explore how dead earthworms affect a wider range of soil processes, and to fully understand their contribution to the cycling of carbon and nutrients in the soil.