it is well known that mineral nutrients move entirely in xylem and such movement depends entirely on the  transpiration stream, along the way most of the nutrients are taken up by the living cells, the xylem parenchyma, so in fact , the concentration of nutrients is very small indeed, some time, the water potential of the xylem sap is-0.05  MPA. There is also some movement from the xylem to the phloem. I am really unaware of published work on the effect of PH on mobility of nutrients in the xylem. probably the PH had an effect on the mobility of ions in living cells, such those of the leaf, as well as root epidermis and cortex. but, of course the PH had a profound effect on ion mobility and availability in soil solution. As for the  phloem, as you know most of the trans located substance are photosynthetic products , but there is Little transfer of nutrients to the phloem, and here again there is little evidence to suggest that the mobility is influenced by the PH.

This is a very interesting question. Unfortunately I don't have literature on this either. I would just like to note that the pH of the xylem should depend on the pH of the roots and the rizosphere and be regarded in this context as well.

Some studies shown that nitrate and total ionic concentrations (cations+anions), and the proportion of cations influenced xylem pH such that xylem pH increases as nitrate and total ionic concentrations decrease, and the proportion of cations increases (DOI:10.1093/jxb/err370). Also osmotic stress conditions can influence the pH of the xylem. The pH value of xylem sap increased under osmotic stress.

Mangrove trees grow with their roots immersed in sea water.Now the  sap in the xylem of this plant is almost pure water. so ,it seems to me  that most nutreints are taken by living cell of the xylem--parenchyma cells. what is the importance of change in PH of the xylem under such conditions.

Hi

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