Week 2: Trade agreements

The basic carbon-for-nutrient exchange, and the biological-market evidence that it behaves like a rate rather than a fixed act of generosity.

TB0815 · diorama S. Brandt, NHM Basel · CC BY 4.0

Dispatch 02

Date: 1 March 2027
Metaphor: Trade agreements — negotiated exchange with terms both sides can enforce
Phenomenon: Carbon-for-nutrient exchange in mycorrhizal mutualism, and biological market theory's account of how the exchange rate is set

Outline

the basic exchange: plant carbon (photosynthate) for fungal-scavenged phosphorus and nitrogen the root cannot reach on its own
why the fungus can get nutrients the root can’t: hyphae reach pore spaces roots cannot enter, and can access some bound nutrient pools directly
biological market theory: partners adjust how much they give based on what they are currently getting, not on fixed generosity
the labelling experiments: using radioactive and stable-isotope tracers for phosphorus and carbon, researchers showed plants preferentially route carbon toward fungal patches that deliver more phosphorus, and fungi reciprocate toward roots supplying more carbon
where “trade agreement” holds up — both sides’ contribution responds to the other’s — and where it doesn’t: neither partner is deciding anything: the adjustment is a biochemical response shaped by selection, not a negotiation anyone is having. Call it a market anyway, and feel the strain in the word.