Great efforts are made to describe carbon cycling in view of climate change and CO2 emission. Thanks to plants and fungi working together belowground - a combination known as mycorrhiza - large quantities of carbon are stored in soils. But until now, this process has been neglected in these calculations. By constructing global maps of the distribution of the most common mycorrhizal types, Nadia Soudzilovskaia opened up possibilities to quantify the role of mycorrhizas in carbon fluxes.
Improving our understanding of the global carbon cycle
In carbon cycling, plants play a major role. They take up carbon dioxide from the atmosphere and convert it into carbohydrates with the help of sunlight. Part of the assimilated carbon is then used as an energy source by the plants themselves, part is stored in plant tissue, and part is transported to soil fungi that live in close intimacy with plant roots. In these so-called mycorrhiza, fungi help plants to take up nutrients from the soil in exchange for carbohydrates (sugars). Part of the carbon that is delivered to these fungi ends up stably stored in soil.
Obviously, mycorrhizal symbioses have a large impact on carbon fluxes. Still, in describing carbon cycling, they have been largely ignored until now. ‘The problem was a lack of information on the distribution of these symbioses,’ Nadia Soudzilovskaia points out. ‘I realised that we needed a detailed global map.’ With a team, she started to collect field data on vegetation, plant species, mycorrhizal plant-fungus associations, and soil carbon content. ‘It quickly became clear that we could not limit our search to English literature; we had to cover studies in all main languages. It took four years to collect, consolidate and standardise the data.’
Almost each species of land plants is involved in a mycorrhizal symbiosis. There are several types of these symbioses, two of which are widespread over earth. In arbuscular mycorrhizal symbioses, fungi invade plant root cells; in ectomycorrhizal symbioses, they form dense hyphal networks around root tips. Plants associated with ectomycorrhizal symbiosis are almost exclusively woody plants; their fungal partners include well-known forest mushrooms like truffle and death cap. Among arbuscular mycorrhizal plants, trees and shrubs as well as herbs occur.
‘To slow down climate change, we must stop removing this vegetation type. In abandoned agricultural lands, it is helpful to restore native vegetation.’
Soudzilovskaia constructed global maps of the distribution of mycorrhizal types, which were published in Nature Communications in November 2019. As these maps show, plants associated with arbuscular mycorrhiza abundantly occur in the southern part of North America, South America, and southern parts of Europe and Asia. Ectomycorrhizal plants dominate temperate and cold regions of the northern hemisphere and are abundant in tropical Africa and Asia.
Importantly, the two main mycorrhizal types differ in how much carbon is stored in the soil, Soudzilovskaia concludes from analysing the relation between relative abundance of both types and soil carbon content. Ectomycorrhizal plants (fungi around the roots) transfer relatively more carbon to soil compared to arbuscular mycorrhizal plants (fungi invading roots). ‘This is because they pay their fungal partners more; some plants deliver as much as 50 per cent of their carbon to their fungal associate,’ she tells.
She also showed that on all continents, the relative abundance of ectomycorrhizal plants has decreased as a consequence of forest logging, urbanisation and replacement of native vegetation by crop fields and pastures. ‘Crop plants are mainly arbuscular mycorrhizal plant species or plants that do not form mycorrhizas at all. Compared to ectomycorrhizal vegetation, crop plants retain more carbon to store in leaves, fruits and roots and so give higher yields.’ Also, mycorrhizal fungi disappear from agricultural land because they don’t tolerate ploughing, fertilisation and fungicide use. While ectomycorrhizal plants cannot grow without their fungal partner, arbuscular mycorrhizal plants can, provided that the soil is enriched with nutrients.
It is known that agricultural practices have caused major soil carbon loss; Soudzilovskaia linked this to large scale loss of ectomycorrhizal vegetation. ‘To slow down climate change, we must stop removing this vegetation type. In abandoned agricultural lands, it is helpful to restore native vegetation.’
Nadia Soudzilovskaia (Moscow, 1974) studied Computer Science at Moscow Technical University and found an appropriate job, but didn’t really like it. After two years of working as a software developer, she switched to her true love, biology, and started a PhD research in Ecology at Moscow State University. During this period, she collaborated with biologists of Vrije Universiteit Amsterdam. After graduating and thanks to an NWO Rubicon grant, she started to work as a postdoctoral researcher in Amsterdam in 2006. In 2015, she settled in Leiden with an NWO Vidi grant on a tenure track position, and currently she is an assistant professor. In her research she combines her expertise in Informatics and Ecology.