Ammonium decreases muskmelon root system hydraulic conductivity

The flow of water through plant roots is controlled by two driving forces, the transpiration rate (Delta P) and osmotic potential difference between the soil solution and inside the root (Delta pi), and the root system hydraulic conductivity [L(root), (L . m(-2))]. Plant water status is affected by the source of nitrogen (N) supplied to the plant. This study was undertaken to isolate the effect of ammonium (NH4)-N on L(root), from other factors affecting water transport through plants. The effect of NH4-N on muskmelon (Cucumis melo L.) L(root) was determined by estimating conductance at high water flux rates where osmotic effects are negligible. Ammonium decreased L(root) by about 50%. At a given transpiration rate, the NH4-N-induced decrease in L(root) decreased leaf water potential [psi(leaf) (MPa)] which, in turn, may alter the behavior of the leaves as observed in other studies.