AMMONIUM DECREASES MUSKMELON ROOT-SYSTEM HYDRAULIC CONDUCTIVITY

The flow of water through plant roots is controlled by two driving for ces, the transpiration rate (Delta P) and osmotic potential difference between the soil solution and inside the root (Delta pi), and the roo t system hydraulic conductivity [L(root), (L . m(-2))]. Plant water st atus 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 determ ined 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) decrea sed leaf water potential [psi(leaf) (MPa)] which, in turn, may alter t he behavior of the leaves as observed in other studies.