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

  1. How does strength of resource gradient affect dynamics?
    • Physics?
  2. Extent of fungal diversity improving N access of the plant
    • Plant benefits from fungal competition
  3. At what level of resource do fungi stop helping?
    • Tragedy of the commons?
  4. Plant sensitivity to shift from helpful to unhelpful fungus
    • Makes only sense if there are more fungi or fungus-independent nutrient uptake pathway.
  5. Spatial scale on which plant can discriminate between fungal partners. How?
    • Plays a role for C allocation to different fungi.
  6. 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?
  7. 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.