Effect of wheat phosphorus status on leaf surface properties and permeability to foliar-applied phosphorus

This study aimed to analyse the effect of phosphorus (P) nutritional status on wheat leaf surface properties, in relation to foliar P absorption and translocation. Plants of Triticum aestivum cv. Axe were grown with three rates of root P supply (equivalent to 24, 8 and 0 kg P ha(-1)) under controlled conditions. Foliar P treatments were applied and the rate of drop retention, P absorption and translocation was measured. Adaxial and abaxial leaf surfaces were analysed by scanning and transmission electron microscopy. The contact angles, surface free energy and work-of-adhesion for water were determined. Wheat leaves are markedly non-wettable, the abaxial leaf side having some degree of water drop adhesion versus the strong repulsion of water drops by the adaxial side. The total leaf area, stomatal and trichome densities, cuticle thickness and contact angles decreased with P deficiency, while the work-of-adhesion for water increased. Phosphorous deficient plants failed to absorb the foliar-applied P. Phosphorous deficiency altered the surface structure and functioning of wheat leaves, which became more wettable and had a higher degree of water drop adhesion, but turned less permeable to foliar-applied P. The results obtained are discussed within an agronomic and eco-physiological context.