Growth Suppression and Raised Tissue Cl- Contents in NH4+-fed Marigold, Petunia, and Salvia

Abstract

Ageratum houstanianum Mill. (tolerant), Tagetes patula L. (French marigold, very sensitive), Petunia hybrida Vilm. (sensitive), and Salvia splendens F. Sellow et. Roem & Schult. (very sensitive) were grown with NO 3 - , NH 4 + NO 3 - , or NH 4 + as the N source to examine whether NH 4 + -related growth suppression (NH 4 + -RGS) in the NH, -sensitive species was associated with excessive Cl- absorption from the nutrient solution. Amounts of Cl- applied were 4 or 11 meq·liter -1 (Expt. 1) and 0 or 4 meq·liter -1 (Expt. 2). When fertilized with NH 4 + as a sole N source, marigold, petunia, and salvia showed NH 4 + -RGS symptoms with yield reduction regardless of altered Cl- levels in the nutrient solution, while ageratum showed no such symptoms. When grown with NH 4 + solution, these sensitive plants had shoot fresh and dry weight reductions of ≈ 50% compared to those grown with the NH 4 + + NO 3 - solution. Plants fertilized with NH 4 + showed more severe NH 4 + -RGS symptoms when grown in rockwool (RW) than in peat-lite mix (PL). The NH 4 + -grown plants contained more NH 4 + and much more Cl - in the tissue than plants fertilized with NO 3 - or NH 4 + + NO 3 - , irrespective of the Cl - level in the nutrient solution. However; NH 4 + -RGS symptoms in marigold, petunia, and salvia appear to be caused by the uptake of NH 4 + , but not in association with Cl- from the nutrient solution.