[GpsFrontier]

I had asked what/how do the roots get thier share of the starches and sugars (the plants "food") which are produced by the leaves ? I am making an assumption here that there MUST be some flow from leaves to the roots via the phloem of the starches and sugers.

From what I have read so far this would be correct. However I don't see the process of exudation being related to the distribution of food, other than without proper food all parts of the plant wont be able to function properly. Also, as best as I can tell at this point, it would only occur during transpiration. Because transpiration would be needed for the hydraulic proses that would be responsible for the distribution of food.

transpiration occurs when water and nutrients are being converted to starches and sugars. Without light, the clorophyl bearing parts of the plant cannot convert the nutrients

I would also agree with that. However there are always exceptions to the rule. That's why I try not to lump all plants and species of plants together, instead I'd rather say "in general." One such exception I can think of is white asparagus. Witch is the same as regular asparagus, but lacks the chlorophyll and grows in complete darkness. It's a true plant, and not a fungus like mushrooms, witch also grow in darkness. I have no doubt that other plants and species of plants have adapted similar ability's, weather in whole, or in part. So I would only feel comfortable with this statement as a general statement. Again, I'm not a botanist.

water and nutrients stop flowing from the roots to the leaves up through the xylem.

As best I know, transpiration would be needed for the hydraulic process that would be responsible for the distribution of all fluid thought the entire plant. Of coarse, as mentioned before there is always exceptions to the rule (I'm sure). Therefor, I would also agree that water and nutrients stop flowing from the roots to the leaves when transpiration has stopped (in general).

I'm wondering if this time when transpiration has ceased (in darkness) is when the roots get fed and perhaps do most of their exudation regardless of species. The link did mention that root exudation is cyclic.

As for the roots being feed, I'm sure this generally happens during transpiration. Again because transpiration would be needed for the hydraulic proses that would be responsible for the distribution (flow) of food thought the plant. And again I don't see the distribution of food, and exudation being related. I look at exudation as similar to human glands. Where while the plant is using the chlorophyll and feeding, it's continuing to store the converted chemicals and compounds in these glands. Then when/if needed, the plant can secrete these compounds in the needed locations (day or night).

For instance, a plant that uses a chemical or compound to attract bees to its flowers, would want to secrete these during the day when bees would be looking for food. Or in the case of peas where they secrete these chemicals and compounds in order to help facilitate the conversion of nitrogen in soil, I'd assume it was best to do this at night when the plant is not up-taking it right a way. Allowing the compounds time to actually convert the elements in the soil into the desired nitrogen. Also I would not think the plant would want to secrete these compounds when the nitrogen levels in the soil are sufficient, but would store them until needed.