Effects of phosphorus deficiency on root hydraulic conductivity in Fraxinus pennsylvanica

A study was designed to examine the influence of phosphorus deficiency on root hydraulic characteristics in green ash (Fraxinus pennsylvanica Marsh.). Seedlings were grown in nutrient solution complete with phosphorus for 7 days before omitting phosphorus from one half of the seedlings. The effects of phosphorus deficiency, plant size, and biomass distribution on root hydraulic conductivity were determined on excised root systems after 17 to 48 d of growth with or without phosphorus. Phosphorus deficiency reduced root conductivity and decreased leaf weight ratios (leaf dry weight/total plant dry weight) in green ash seedlings. In both the high (with phosphorus) and low phosphorus (without phosphorus) treatments, root conductivity increased linearly with increased root phosphorus concentration. However, the relationship between root phosphorus and root conductivity differed in magnitude in the high and low phosphorus treatments, suggesting that factors besides phosphorus nutrition were influencing root conductivity. Root conductivity increased with leaf weight ratio similarly in high and low phosphorus plants regardless of seedling size, tissue phosphorus, or age. Root conductivity decreased with seedling age, possibly because of increased root suberization. Root conductivity to water appears to change in response to a change in biomass distribution in green ash.