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I am interested in identifying the maximum potential dissolved sucrose (%w/w) that plant sap could have, and which (biological, physical, chemical) factors constrain the observed sucrose concentrations.

For example, sugar maple has one of the highest sucrose contents at 6%, and the solution also contains fructose, glucose, organic acids, minerals (K, Ca, Mn, Zn, Na, Cl), amino acids, volatile organic compounds, phenols, enzymes (according to Wikipedia), and most sap flow occurs when temperatures cross the freezing point each day.

Is there a way that I can calculate this theoretical maximum from "first principles" of organic- or bio-chemistry, or is this a question better suited for empirical study?

this is a biological application of my question at physics.SE

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As the concentration of sugars in the sap increases, so does viscosity. At high viscosity, the sap will not flow at a sufficient rate to provide nourishment to the different plant tissues.

In addition, there are limitations to concentrating the solutes in the sap. As the sap becomes more concentrated, the plant would be working against a osmotic gradient to further increase that concentration. That energy cost may be too great.

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