Phosphorus speciation of dormant grapevine (Vitis vinifera L.) canes in the Barossa Valley, South Australia

Background and Aims: The phosphorus ( P) contained in annual prunings can represent a substantial proportion of annual vineyard P addition. Availability of P to the growing vines is controlled by the forms of P present. Solution P-31 nuclear magnetic resonance spectroscopy was used to investigate the chemical composition of P in dormant canes taken from two cultivars of Vitis vinifera L., Shiraz and Viognier, collected from nine vineyards. Methods and Results: The main forms of P detected were similar, although the proportion of these varied; orthophosphate comprised 37-57% of total P, phospholipids 8-15%, myo-inositol hexakisphosphate ( phytate) 20-34% and a specific isomer of myoinositol pentakisphosphate ( rarely identified previously in plant material) 9-25%; DNA and pyrophosphate contributed < 1% of total P. Variation in P composition appeared unrelated to grape cultivar, but varied with vine P status. Higher total P concentration correlated with proportionately more orthophosphate and phytate. Conclusions: Grapevine prunings represent a nearly equal combination of immediately available and potentially recalcitrant forms of P. Significance of the Study: This study is one of the first to examine the P composition of dormant grapevine canes, which is a prerequisite to predicting the contribution they make to P nutrition.