Both high and low water nitrogen and phosphorus concentrations differentially affect turion formation in Potamogeton crispus

Abstract

Plants of Potamogeton crispus, a submersed macrophyte, were cultivated in the water free of algae and containing different concentrations of inorganic nitrogen (0.2 and 20 mg N L−1) and phosphorus (0.02 and 2.0 mg P L−1). The changes in plant growth and turion formation and the carbohydrate contents in plants and turions were investigated, and the endogenous abscisic acid (ABA) levels and the expressions of ABA biosynthetic genes in the stem apices analysed. The purpose of this study was to clarify the effects of water N and P levels on the plant growth and propagation capacity of P. crispus and to reveal whether ABA metabolism is involved in the turion formation of the plant under different ambient nutritional conditions. Finding the biomass of plants was not affected by the water N and P concentrations, except for those grown in water with low N and high P that had higher biomass accumulation and carbohydrate contents. Higher P promoted plant N uptake from the water, but higher N inhibited plant P uptake from the water with high P. High water N significantly delayed the turion initiation of P. crispus. Plants formed more apical turions with a greater size and more carbohydrate reserves when grown in water containing low N and low P, which leads to higher propagation of the plant population. The combination of high N and high P in water inhibited the formation and growth of turions, resulting in significant attenuation of the propagation capacity. High N combinated with low P or high P combinated with low N promoted the formation of more axillary turions and total turions but inhibited the turion growth. ABA levels and the expressions of ABA biosynthetic genes in stem apices at the turion initiation were changed by water N and P levels. The elevated ABA levels were consistent with the increased total turion number per plant when grown in the water with low N and/ or low P. The up-regulation of ZEP (zeaxanthin epoxidase) or NCED6 (9-cis-epoxycarotenoid dioxygenase6) may account for the ABA accumulation in the stem apices. The involvement of ABA metabolism in the turion formation relies on varying gene expression patterns when the plant grows in water containing different N and P concentrations.