Carbon and nitrogen metabolism of an eutrophication tolerative macrophyte, Potamogeton crispus, under NH 4+ stress and low light availability

Abstract

Submersed macrophytes in eutrophic lakes often experience high NH 4 + concentration and low light availability in the water column. This study found that an NH 4 +–N concentration of 1 mg L −1 in the water column apparently caused physiological stress on the macrophyte Potamogeton crispus L. The plants accumulated free amino acids (FAA) and lost soluble carbohydrates (SC) under NH 4 + stress. These stressful effects of NH 4 + were exacerbated under low light availability. Shading significantly increased NH 4 + and FAA contents and dramatically decreased SC and starch contents in the plant shoots. At an NH 4 +–N concentration of 1 mg L −1 in the water column, neither growth inhibition nor NH 4 + accumulation was observed in the plant tissues of P. crispus under normal light availability. The results showed that 1 mg L −1 NH 4 +–N in the water column was not toxic to P. crispus in a short term. To avoid NH 4 + toxicity, active NH 4 + transportation out of the cell may cost energy and thus result in a decline of carbohydrate. When NH 4 + inescapably accumulates in the plant cell, i.e. under NH 4 + stress and shading, NH 4 + is scavenged by FAA synthesis.