Carbohydrate transport mechanism... Potassium
In the leaves are veins, in the dirt are roots, on the tips if the leaves are the areas of rapid growth, on the tips of the roots is the highest area of absorption.
So?!? is what most people think. Duh! I know this already.
Each vein corresponds to a root. Each leaf tip receives it's nutritional supply from a localized group of root hairs. They feed each other. All night the roots are exuding what the plants cells in the leaves produced. Excess is most of the time non localized, because it is typically in the entire root zone.
A localized excess isn't talked about because it's not understood. Potassium causes leaf tips to burn the very tips and almost all of them. That's not a localized excess, that's a general excess.
Your leaves are indicators of excess potassium in a very specific way and it has happened to almost all of us at some point. It is precipitates in the soil reacting with new solution creating changes in pH to a very localized group of root hairs whose only reaction is to process the excess and feed it to "its" section of the plant. Thus the burn starting from A tip, just one serration on a leaf, that very little growing edge. It goes backwards from there down the vein in a circular fashion as the excess is coming from the roots. The roots are pumping it up at a rapid rate and it's toxic to the leaf. It is going in between the cells of the leaf and burning.
Why is it so localized? Because as the soil dries in certain areas the chemical reactions take place. You then re wet this area and another reaction take place. Back and forth constantly. It's normal it typically stays in balance. Sometimes it doesn't. Don't ask why unless you're a scientist and then don't ask me.
Stick a straw in the soil, wait a few days for the root zone to surround it recover
and encase it well.
Then feed that straw with a pipette of whatever you wish to see react. Remember not to flood the entire root zone. Just feed those root hairs in that tiny section. Look for the damage on your girl in a few days.
