Abstract
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 (32)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 (32)P accumulation was limited to newly emerging leaves in P-deficient plants, while P-sufficient plants also remobilized and accumulated (32)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.