Magnesium (Mg) and rubidium (Rb) absorption by tall fescue

Abstract

Abstract Kinetic experiments were conducted to examine Mg+2 [28Mg] and K+ [86Rb] absorption by 2‐week‐old tall fescue (Lolium multiflorum Lam. X Festuca arundinacea Schreb.) seedlings. Magnesium absorption was linear for 180 min and was approximately 3.5 ueq Mg+2 g dry weight‐1.h‐1 from a 0.0625 mM Mg+2 solution. Shoot accumulation of Mg was reduced by increased solution K+. A curvilinear concentration absorption isotherm for roots was obtained for Mg+2. The resultant hyperbolic Hofstee plot could be separated into two linear components with Km values of 0.833 and 0.0117 mM, suggesting that two systems are operable in Mg+2 absorption. Increased solution pH increased Mg+2 absorption both in the presence and absence of NH+ 4. At pH 6.5 NH+ 4 increased Mg+2 absorption 75%; at pH 3.5 the increase was more than 6‐fold. Potassium absorption was linear through 60 min and was decreased by increased Mg2+ levels. Shoot accumulation of [86Rb] was decreased by the first increment of Mg+2, whereas further increases in...