Growth, morphology, ammonium uptake and nutrient allocation of Myriophyllum brasiliense Cambess. under high NH₄ ⁺ concentrations

Abstract

The effects of high NH₄ ⁺ concentration on growth, morphology, NH₄ ⁺ uptake and nutrient allocation of Myriophyllum brasiliense were investigated in hydroponic culture. The plants were grown under greenhouse conditions for 4 weeks using four levels of NH₄ ⁺ concentration: 1, 5, 10 and 15 mM. M. brasiliense grew well with a relative growth rate of c.0.03 day⁻¹ at NH₄ ⁺ concentration up to 5 mM. At the higher NH₄ ⁺ concentrations the growth of the plants was stunted and the plants had short roots and few new buds, especially when grown in 15 mM NH₄ ⁺ where the submerged leaves were lost and there were rotten roots and submerged stems. To avoid NH₄ ⁺ toxicity, the plants may have a mechanism to prevent cytoplasmic NH₄ ⁺ accumulation in plant cells. The net uptake of NH₄ ⁺ significantly decreased and the total N significantly increased in the plants treated with 10 and 15 mM NH₄ ⁺, respectively. The plant may employ NH₄ ⁺ assimilation and extrusion as a mechanism to compensate for the high NH₄ ⁺ concentrations. However, the plants may show nutrient deficiency symptoms, especially K deficiency symptoms, after they were exposed to NH₄ ⁺ concentration higher than 10 mM. The present study provides a basic ecophysiology of M. brasiliense that it can grow in NH₄ ⁺ enriched water up to concentrations as high as 5 mM.