Climate, Plants and SoilsThe PRIME-TIME project aims to understand whether increasing trees and shrubs in the Arctic will change the amount of carbon (C) stored in the soil.
Soils in northern ecosystems (the Tundra and Boreal) make up half of the total soil of the global soil C pool. They therefore have great potential to control the climate, depending on whether they sequester or release C in the future. Due to climate change, areas of the Arctic have already warmed four times faster than the global average. If anthropogenic C emissions are not reduced, the Arctic could warm by up to 11 °C by the end of this century. Warming of the Arctic tundra is allowing the expansion (increased growth and ground cover) of shrubs and increases in the extent of the northern tree-line onto what is typically a low-productivity ecosystem. Whilst larger plants in the arctic store more C in their biomass than typical tundra species, recent evidence suggests they may have the opposite effect on the C storage of the whole ecosystem. Studies on the ground have found that where there are more shrubs and or trees in tree-line areas, there is up to two times less soil carbon than in tundra. This may suggest that where shrub and tree expansion occurs in the Arctic, there will be a loss of C from the soil to the atmosphere that would far out-weigh the increase in biomass. Tundra soils (left) contain more soil carbon than forest soils (right) at our field sites in Sweden.
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Arctic shrubs (foreground) and mountain birch tree which forms the tree-line in sub-arctic Sweden
Priming, Roots and FungiPrevious evidence has suggested that trees may stimulate decomposition of soil C via ‘rhizosphere priming’. Rhizosphere priming is the transfer of sugars from the roots to the soil which increases the activity of the microbial community. This, in turn, releases nutrients that are bound in the soil. The plant uses this strategy to ‘unlock’ nutrients from the soil.
The majority of trees and woody shrubs form a symbiontic association with a mycorrhizal fungus. Mycorrhiza comes from the ancient Greek ‘myco’ for fungus and ‘rhiza’ for root (therefore 'fungus-root'). The fungus lives on the root of the plant where it is allocated sugars by the plant and allowed to grow through the soil. In exchange, the fungus scavenges for nutrients and then passes them to the plant host. Due to the production of enzymes by the mycorrhizae, there may be an increase in soil decomposition as they extract nutrients for their tree hosts. |
Our Aims
The PRIME-TIME project aims to answer the following questions:
- Are arctic trees and shrubs involved in ‘Priming’ soil C.
- Will increasing shrubs and trees in the arctic result in a loss of C from the soil to the atmosphere?
- Are mycorrhizal fungi involved in the priming of arctic soils?