Tuesday, 5 December 2017

Social Microbiology for Farmers & Economists

Most of us know that legumes can use root nodules to fix atmospheric nitrogen and make it available to the plant. That's the basis of the ryegrass & clover model that used to underpin pastoral agriculture in New Zealand & elsewhere, before we started buying nitrogen in bags.

Biological farmers know that this is just one of many potential symbiotic relationships between plants and living organisms in the soil. We try to feed our soil biology with complex foliar sprays & avoid damaging it with cultivation and harsh fertilisers. We dig holes, count worms, and measure brix levels in forage & outputs. But to be brutally honest, we really don't know much about the complex underground relationships between soil organisms and plants.

So it is a rare treat to listen to Toby Kiers, Professor of Evolutionary Biology at the Vrije Universiteit Amsterdam (currently visiting U of Canterbury) being interviewed on RNZ. She is using modern microbiological methods to examine the symbiosis between plants and soil organisms that lies at the heart of biological farming. 

It turns out that economic models are assisting her work, so now I'm even more interested. Economics students may know that some branches of game theory draw inspiration from evolutionary biology: apparently the inspiration was mutual. 

I can't hope to do justice to even this 1/2 hour interview here, let alone cover the details of Toby's work programme & how it might mesh with biological farming practices. So let's just cover a few basics.

Fungi expand plant root zones
Fungal networks in the soil can massively expand the (effective) surface area of plant roots to which they attach. They are embedded deeply into the plant roots: piercing the root cell walls and growing arbuscular (small tree) networks inside those root cells. These link the root cells with hyphae networks that the fungi spreads through the soil. So now we have a massively expanded network for collecting & exchanging soil nutrients.

Fungi trade P and N for C
The basic trade between fungal networks and plants is that the fungi collects P and N from the soil and trades them for C that the plant produces via photosynthesis. Farmers know that soil tests often show that there is lots of P down there, but if you're buying soluble forms of P your sales rep will probably tell you that the P showing up on the test is not "available". So you need to put more on. Active fungal networks would harvest that P for your plants.

The plant supplies C in the form of sugars that feed the fungi. This basic symbiotic trading relationship has existed for at least 400m years. Recently discovered: plants also supply lipids to the fungi. Maybe future work will find that other forms of C being supplied?

Underground nutrient trading works like a normal market
As in all trading environments, there is a balance between co-operation and competition. Consider things from the fungi's perspective in an established market. Fungi has incurred the fixed costs of penetrating the cell walls, building its arbuscular networks inside the root cells, and building out its hyphae networks into the soil. Conditions are perfectly set up for a long term nutrient trading relationship.

The existing underground nutrient market could be left to its own devices, stimulated using the methods of biological farming, or destroyed by switching to conventional methods: application of urea and soluble P.

The biological reason that last approach destroys the market is that fungi are "obligate biotrophes". They are great nutrient scavengers, but they can't survive on the nutrients they harvest: fungi needs feeding. If the farmer now supplies solid urea and soluble P, the plant doesn't need the fungi so it cuts off the flow of C. In response, the fungi effectively says: "now you're getting this stuff for free so you don't want to pay me in C? well that's me rooted. i'll just crawl away & die".

This is consistent with a theme Toby emphasised. The observed conduct of non-human parties to a beautiful (& potentially hugely productive) underground nutrient trading market can be explained as if the participants were rational humans interacting through markets.

This interview left me elated and depressed.

On the upside, it's great to know that the market model is broadly appropriate to these underground nutrient markets and that 90% of plants can access them (not brassicas though). This is consistent with my intuition but it's great to have scientific support.

Switching hats to economics, is it not incredibly average that this kind of science work doesn't get funded in NZ? We think we're so clever and classless and free, but look at the scoreboard: Toby is from Holland, which exports 4 times as much food as us by value. Yet we have far more good land and far fewer people.

Sadly, our farmers & ag policy makers remain in thrall to the people who sell us stuff. We could do much better by seriously investing in science like this, with broad applications/benefits but no commercial sponsor.

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