Plant leaf morphological characteristics related to hydrophobicity and foliar absorption

Foliar fertilization is a widely popular practice for the management of turfgrasses, as well as other ornamental and crop species; however the mechanisms of absorption into the plant leaf, and the characteristics that influence that uptake are still poorly understood. The plant leaf surface characteristics are variable depending on plant species, leaf side, and environmental conditions. Also, popular chemical solutions that are applied vary in chemistry and concentration, which can have an effect on the amount of absorption of the foliar applied solution. To this end, the primary objective of this dissertation was to determine the popular foliar solution and plant leaf surface characteristics that influence the hydrophobicity of the leaf surface and % 15N-labeled urea uptake of various warm- and cool-season plant species.;Due to the variation in chemistry and rates in foliar applied solutions that are popular in plant maintenance programs, a greenhouse studied was initiated to determine the effects of product, concentration and plant species on the hydrophobicity of the solution. It was determine plant species and product significantly affected the average contact angle of a solution placed on the leaf surface. All products with no regard to concentration or rate significantly reduced the average contact angle as compared to the control water. Interactions between plant species and product were found indicating the relationship among hydrophobicity of product differs depending upon plant species.;Based on the results that hydrophobicity of plant leaf surfaces are different a second investigation was initiated to determine plant leaf characteristics that could affect hydrophobicity. Plant leaf surface roughness, stomata size and density, cuticle wax and morphology and the hydrophobicity of the leaf were all found to have significant differences between species, cultivar, and leaf side. Warm-season plants on average had less leaf surface roughness, less cuticle wax, and increased stomata size as compared to cool-season plants. Plant cuticle morphology was influenced by the extractable primary alcohol content for both warm- and cool-season plants. Stomata density was found to be greater on the adaxial leaf side as compared to the abaxial side, and had a negative linear relationship with stomata size.;Absorption and uptake studies of a fluorescent tracer and 15N-labeled urea solution were conducted to investigate solution uptake of different grass species. Multiphoton imaging demonstrated uptake potentially occurs above vascular tissue and around stomata complexes. Absorption of 15N urea was different for species and cultivar, with higher uptake levels occurring in warm-season grasses as compared to cool-season grasses. It was determined that stomata density significantly affects percent 15N absorption when applied to the adaxial or abaxial leaf surface.;Based on the results from the previous studies, the relationships among plant leaf surface characteristics, hydrophobicity and 15N-labeled urea absorption were investigated to define parameters that influence foliar absorption. Increases in total cuticle wax, primary alcohol content and surface roughness consistently increased the hydrophobicity of the leaf surface, expect for the adaxial leaf side of cool-season plants. Multivariate analysis revealed that total cuticle wax and surface roughness are significant predictors of leaf surface hydrophobicity. The relationship of 15N-labled urea absorption and plant leaf characteristics was studied to confirm results from the hydrophobicity test. The multivariate analysis revealed that leaf surface roughness, total cuticle wax, and primary alcohol content all correlated negatively with % 15N recovery. This indicated a relationship between hydrophobicity and plant foliar N absorption. Multivariate regression analysis revealed that % 15N recovery can be accurately predicted by the parameters stomata size, leaf surface roughness, total cuticle wax and the interactions between these three variables. The model analysis revealed that increases in stomata size, leaf surface roughness and total cuticle wax decrease the % 15N recovery from a foliar applied solution. The analysis of the plant leaf surface characteristics and foliar applied 15N absorption demonstrates the influence the plant leaf surface has on foliar uptake of solutions and should continue to be investigated to improve management techniques.