Effects of Phosphorus Deficiency on Leaf Surface Morphology: Absorption and Translocation of Foliar-Applied Phosphorus in Four Barley Cultivars.

Plant nutrient deficiencies can modify leaf surface properties and may affect the absorption of foliar fertilisers. This study examined how plant P-deficiency modified the adaxial leaf surface morphology of four barley cultivars and whether these modifications could be linked to quantitative differences in foliar-applied P absorption. Four Australian barley cultivars were grown hydroponically under P-sufficient and P-deficient conditions. A P radiolabelled foliar phosphate solution was applied to adaxial leaf surfaces for 2 or 7 days to investigate absorption and translocation. All cultivars showed different responses to P-deficiency (stomatal density, trichome density, thickness of the epidermal cell wall and cuticle). However, no clear trends were observed among the cultivars in their responses to P deficiency. Cultivars absorbed foliar-applied P regardless of plant P status. Remobilisation occurred from the treated leaf to untreated shoots in all but one cultivar. While P-deficient plants absorbed and accumulated significantly less foliar-applied P after 7 days, this was not linked to measured changes in stomatal or trichome density or the thickness of the epidermal cell wall and cuticle. Autoradiographs revealed that P accumulation was limited to newly emerging leaves in P-deficient plants, while P-sufficient plants also remobilized and accumulated P into older leaves and tillers. Relatively high P absorption (> 65% of foliar-applied P) in both P-sufficient and P-deficient plants suggests that foliar-applied P may be a useful fertiliser top-up strategy for barley. Due to the lower absorption in P-deficient barley, foliar applications should be made before severe P-deficiency symptoms are apparent to improve absorption.