If we take some tea leaves and boil them then squeeze the solutes out we can see that salts and sugars are stored in the leaves. However, gravity will always make sure that denser solutes are kept on the move so there is a constant flushing out of these salts and sugars as they are moved to sink areas, like fruits and seeds and stored as timber as tubes become redundant and more are manufactured.
Deciduous trees during the fall when the leaves are shed move solutes to the roots and higher than normal concentrations are located in the roots in autumn.
I am convinced that when the leaves fall the pressure changes in the sap to positive and forces the salts and sugars down to the roots. I have also postulated that leeching from the roots during the fall may serve as a detox ready for the spring. And this positive pressure would surely apply to the increased root growth during the fall. Let’s not forget that minerals are shed with the leaves also. During the fall the salts would remain very sluggish as transport is arrested. During the spring the warmer climate begins to change the density of the sap enabling it to circulate before the leaves are formed.
Fruits and seeds being shed also serve to remove concentrated sugars and minerals and could be considered as providing a renal function.
There is also evidence of concentrations of heavy metals around the roots of plants growing in salt marsh. Could this be evidence for leeching from the roots in addition to leeching from the soils to the roots? Could the regular influx of brackish water in estuaries stimulate dialysis effect at the semi-permeable membrane in the roots?
Hope it's ok to copy your question to this thread as the answers are pertinent to my theory? If you object let me know and I will remove them.
Unfortunately trees are not selective enough as they are killed quite quickly with an introduction of heavy metals to their water supply, or for that matter an abundance of salt!
The questions still remain. After evaporation the trees are left with a heavy concentration of salts and minerals at their tops. Are all these minerals absorbed and considered as nutritious for a tree? or Does a tree have a kind of limbic/kidney/liver system that stores any unused solutes? or Does a tree send the unused solutes back down to the roots?
And another question. If a tree hates air getting into its plumbing, how do the leaves manage to let the relatively large H2O molecules out while keeping the smaller oxygen molecules from entering? Any help on these questions would be most appreciated!
Lmnol. Ocmno~r 43(2), 1998. 245-252
0 1998. by the American Society of Limnology and Oceanography. Inc.
Metal-rich concretions on the roots of salt marsh plants: Mechanism and rate of formation Bjorn Sundby INRS-Octanologie, University du Qubec, Rimouski, QC G5L 3Al
Carlos Vale IPIMAR, Avenida Brasilia, 1400 Lisboa, Portugal Zsabel CaCador and Fernando Catarino
Departemento de Biologia Vegetal, Universidade de Lisboa, Campo Grande C2, Lisboa, Portugal
Maria-JoLio Madureira and Miguel Caetano IPIMAR
The roots of the vascular plant Spartina maritima, growing in the saltmarshes of the Tagus Estuary, Portugal, are surrounded by tubular concretions whose diameter can reach >0.2 cm. Concretions are also found scattered within the sediment matrix in and below the root zone. The concretions comprise 4% (DW) of the sediment and contain 11.7 2 1.6% iron compared to 4.9 -C 0.3% iron in the sediment in which they are found. They are formed by the precipitation of iron oxides in the pores between the sediment grains; this has filled about one-sixth of the originally available pore space. To produce the concretions, the plants have extracted 0.25% Fe from the anoxic bulk sediment and concentrated it into the oxidized microenvironment surrounding each root. A mass-balance model using cylindrical geometry shows that the observed concretion density can be produced by a network of roots with l-cm spacing. The space between the roots limits the amount of Fe that is available to a given root and thus
determines the size of the individual concretion. Field observations and mathematical modeling show that plants can produce concretions on their roots in the space of a few weeks. The rhizoconcretions are 5-10 times enriched in Cd, Cu, Pb, and Zn with respect to the sediment surrounding them, and the smaller diameter concretions are more enriched than the larger ones. The preferential enrichment of the smaller diameter concretions, which was not observed for Fe and Mn, is independent of depth in the sediment for Cd and Cu; however, for Zn and Pb, the
preferential enrichment is most pronounced within the upper trace metal-contaminated sediment layer. The rhizoconcretions have acquired their load of metals via diffusion from the surrounding sediment. In the case of Fe and Mn, the concentration gradient that drives the diffusion is maintained by the precipitation of insoluble oxides. In the case of Cd, Cu, Zn, and Pb, the mechanism that maintains a concentration gradient toward the surface of the root is not know, but our data show that S. maritima is capable of mobilizing trace metals dispersed in reducing
anoxic estuarine sediment and concentrating them into the distinct oxidized microenvironments that surround the roots.