Growth and biomass allocation of sweet flag (Acorus calamus L.) under different nutrient conditions

The antropogenically-induced process of eutrophication is accompanied by changes in the structure and function of the whole wetland ecosystem. Since the shift in a species ability to survive in original habitats is a commonly observed feature, the performance of individual wetland plants under high nutrient load is of a particular interest. Acorus calamus is a common littoral plant species of the European wetlands, which are characteristic by high trophic status. The effect of nutrients (N, P) per se, as a key part of the complex eutrophication process on the growth, biomass allocation, and biometric characteristics of Acorus calamus, is the main aim of the study. The study follows the effects of different levels of phosphorus (0.5 and 1.5 mM) and nitrogen (1.87; 7.5 and 18.5 mM), likewise the effect of NH4+ and NO3− form, on the growth of Acorus. Special attention is dedicated to the growth of underground organs, particularly roots, because of their direct contact with the flooded substrate.While P enrichment (1.5 mM) had no substantial effect on the growth of Acorus, high N treatment (18.5 mM) negatively affected its growth. 50, 30 and 50% reduction in shoot, rhizome, and root biomass accumulation, respectively, was found under high N supply. On the whole, lower number of roots with high proportion of short (30–60 mm long) roots, together with higher proportion of young roots with no developed lateral roots and high proportion of injured roots, particularly those more differentiated with developed lateral roots, characterised root system of Acorus plants growing under high N supply in comparison to the conditions of lower nutrient supply. Some similar features found under high N supply were founded also under pure NH4+ nutrition. Since NH4+-N was the only N-form elevated under high N treatment, we tried to separate the effect of NH4+ only nutrition and the effect of high N load. Possible consequences of intensive NH4+-N nutrition are discussed in connection with differences between the growth reactions of plants under experimental conditions and under eutrophic natural sites where other factors than high N influence growth of the plants.