[hinkley]

One of the things Susan Simard proved was that deep rooted trees that had found subterranean water continue pulling that water at full speed at night when transpiration is low, and that water finds its way into the fungal networks in the soil and into nearby plants.

Simard attributes intention to this, but osmosis is “fair”. It seeks to move water to where sugars are and sugars to where water is. So a plant giving up sugars will receive water, and one low on water will give up sugars in the process of equalization.

Do fungi contain pumps to maintain disequilibrium in this work? I could not say. But even when they first learned the trick of tapping roots the basic premise would have worked in a rudimentary fashion woth no further optimization.

[fc417fc802]

I don't understand how osmosis enters into this? Capillary action is sufficient to explain water traveling up the roots to a point where it was removed. Evaporation from leaves is sufficient to explain removal during the day. You'd need some other explanation for extraction by fungi or etc at night.

As a largely unrelated aside, there will still be a chemical potential across a membrane that doesn't permit a solute to cross. So water can diffuse into a concentrated solution without the solute flowing backwards into the reservoir. Alternatively, small solutes can leave while larger solutes are retained. This is the basis of dialysis.

[hinkley]

In retrospect what I wrote became a bit more of a non sequitur than I meant.

Trees aren't even accessing water at ground level most times but pulling it up from 5-30 feet down. Fungal distribution is also a capillary action network (with asterisks) and ends up making some of that pumping more horizontal, but at the expense that if a tree's root sap is high in sugar due to dehydration, then the fungal network both introduces water to those roots but also exports sugar at the same time. Simard tries to anthropomorphize this process. It's my only real complaint with her work.

The asterisks are that fungal networks can react to information faster than the documented transport mechanisms work so we don't really know how the heck they do their thing yet. So it's possible that they're also maintaining nutrient gradients to feed themselves beyond the straight arbitrage that osmosis represents.