I'm trying to make yogurt and watch funny kitten videos, and I walked around for a half hour this morning looking for my eye glasses and I was wearing them the whole time (to be fair, I was distracted by having to wear a mask in my own house while a realtor and a herd of strangers poked around). Thinking about science that wasn't even my field is a lot of effort right now, so I googled ion transport in roots.
Problem solved (maybe-I didn't go too deep into it).
"Experimenters have also assumed that the water flow into roots is small enough that bulk streaming of the solution contributes negligibly to the ionic fluxes. Henriksen et al. (1992) have carried out an analysis that confirms the general validity of the assumption. Calculations have also been carried out for imbibing seeds (Shabala et al. 2000a) which took up water to increase their volume by 10% per hour.
Their conclusion was that the contribution to fluxes by bulk solution flow was negligible."
Link:
https://onlinelibrary.wiley.com/doi/...0.2001.00661.x
External ion concentration (fertilizer salts) is stopped at the endoderm layer cell membranes surrounding the core of the root cylinder (the stringy part). The cell membrane ion channels (and probably some other stuff) control what gets into the cell (or the cell would die from imbalance). Once ions move past the endoderm layer (or cell storage vacuole membranes) and into the apoplastic (free space) water system in the cell walls and xylem tubes they move based on a diffusion and electro-something gradient set up by a sink at the point where the ions are being used (or put into storage). Temperature plays a role.
I don't even know if the elongating cell walls that need calcium are anywhere near stomates where bulk transport of water would be carrying ions, if it were carrying ions. Certainly a bud at the end of a flower spike would be a long way away from a lot of stomates. I don't know the relationship of differentiating and functioning stomates vs where nutrients are needed most in growing leaves (chicken or egg?). At night when the photo sugar is used up the ions are going into storage vacuoles throughout the plant so the calcium or nitrate or whatever ions needed for growth when the sugar returns may come from nearby vacuoles more than the roots/external pot water.
That brings up another topic. Movement of photosynthate (sugar = building blocks for everything) is moving from the mature leaves to growth zones against the water movement. Active transport shoves it into the phloem vessels in the leaves and it moves via a diffusion gradient (iirc) from there. BTW, another wobbly factoid in my brain from way back = more magnesium is needed for this sugar shoving machinery in cold weather or the plant leaf poisons itself (osmotic stress?) with sugar build up and has to turn red to shade itself.
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