The Basis of Foliar Absorption of Fertilizers with Special Regard to the Mechanisms

Abstract

As the third organ of the higher plants after the shoot and the root, the leaf is essentially used for photosynthesis and transpiration. The leaf blade is flat in shape for this purpose. A bi-facial leaf has an adaxial assimilation parenchyma above an abaxial spongy mesophyll and the vascular bundles in the form of the ribs and has an epidermis on both sides. These have stomata either only on the underside or on both sides of the leaf, which enable gas to be exchanged for photosynthesis and respiration as well as releasing water vapour in stomatal transpiration. The fact that the leaf with its epidermis can also function as an organ that absorbs and excretes water and substances dissolved in it is only mentioned very incidentally in text books. Although the phenomenon has been known for some while, it was disregarded for a long time because of its relatively insignificant quantitative importance. But although this culticular transpiration accounts for only 5 – 10% of total transpiration, it proves that water at least is excreted via the epidermis and its cuticles. From the evidence of cuticular excretion of both inorganic (1, 5, 17) and organic materials such as sugar and amino acids (19) comes the ability of leaves to excrete and the possibility of dissolved substances passing from inside the cell wall and the cuticles to the outside. In theory, therefore, we can at least expect the reverse process to take place, i.e. that leaves can absorb water and substances dissolved in it.