Modified source-sink dynamics govern resource exchange in ectomycorrhizal symbiosis
Summary
Symbiosis between tree roots and fungi as a trade explains mutualism development on evolutionary timescale but not experimental results. Instead think of it as source-sink dynamics.
I. Introduction
- sometimes C invest and N return are uncorrelated or even negatively correlated
- reward schemes depend on the scale
II. Source-sink dynamics remain a useful model for resource movement
- source-sink dynamics: flow from high concentration to low concentration
- gradient and conductivity govern speed
- fungal biomass drives C sink strength which can lead to positive feedback
- fungi can monompolize N if it’s available at high level, induce artificial N scarcity
- nutrients and water also move according to source-sink dynamics
- plant, fungi, and environment change rates making thinkgs more complex
III. Beyond source-sink: modifications to resource movement
- plant and fungi have different interests, modify simple source-sink dynamics
- plant defense might change resource transfer
- C transfer sometimes mostly explained by expression of genes involved in defense and stress response
- high variation of fungi and immune responses lead to a variety of altered source-sink dynamics
- other functional diversities have also influence
- molecular tools not yet completely understood
- fungal competition also a factor in favor of the plant
IV. Conclusions
- source-sink dynamics a good first approximation
- altered by a lot of factors
Box 1 - Future research directions
- How does strength of resource gradient affect dynamics?
- Physics?
- Extent of fungal diversity improving N access of the plant
- Plant benefits from fungal competition
- At what level of resource do fungi stop helping?
- Tragedy of the commons?
- Plant sensitivity to shift from helpful to unhelpful fungus
- Makes only sense if there are more fungi or fungus-independent nutrient uptake pathway.
- Spatial scale on which plant can discriminate between fungal partners. How?
- Plays a role for C allocation to different fungi.
- Can we predict plant-fungal compatibility from genomic data?
- How fast are those genomic gata changing? Does it make sense to identify genes if they change too fast?
- Differences in resource transfers with adult trees and seedlings.
- Also adult fungi and youg ones? Have different levels of need?
My remarks
- no citation of “The mycorrhizal tragedy of the commons”
- So what do we learn? That it’s complex, lots of interests, strategies, external factors. Thanks.
- We probably learn about the future research directions. This thought is supported by the relatively new references.