Trees First Inhibit Then Promote Litter Decomposition in the Subarctic

Area of Science:

• Forest ecology
• Soil science
• Biogeochemistry

Background:

• Trees influence soil organic matter decomposition through belowground carbon allocation.
• The impact of trees on decomposition varies with substrate type and decomposition stage.
• The Gadgil effect describes competition between trees and soil microbes for nutrients.

Purpose of the Study:

• To investigate the effects of severed belowground carbon allocation on litter decomposition.
• To examine the role of tree competition in regulating decomposition dynamics over time.
• To understand the contrasting effects of tree presence on early- and late-stage litter decomposition.

Main Methods:

• Incubation of leaf and root litters in mountain birch forests for 4 years.
• Comparison of litter mass loss, chemical composition, and fungal colonization between girdled (carbon allocation severed) and control plots.
• Monitoring changes over early and late decomposition stages.

Main Results:

• Girdling initially stimulated leaf and root litter mass loss by 12% and 22%, respectively.
• This early stimulation suggests competitive release of saprotrophic decomposition.
• After 4 years, girdling hampered root litter mass loss by 30%, indicating late-stage priming by trees.

Conclusions:

• Tree-mediated competition affects litter decomposition differently across early and late stages.
• Early-stage decomposition is enhanced by removing tree competition (Gadgil effect).
• Late-stage decomposition may be promoted by the presence of trees, potentially through shrub and fungal interactions.