Paalme, T.; Torn, K., and Martin, G., 2024. Variation of essential macroelement contents in two common charophyte species, Chara aspera and Chara tomentosa, inhabiting shallow brackish waters of the Baltic Sea. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 946-950. Charlotte (North Carolina), ISSN 0749-0208.

Nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), and sulfur (S) are considered essential mineral plant nutrients that contribute to growth, photosynthesis, and various metabolic and physiological processes. In this study, quantification and comparison of macronutrients in two common charophyte species, Chara aspera and C. tomentosa, collected monthly (March 2014 to March 2015) in semi-enclosed shallow Rame Bay in the NE Baltic Sea were carried out. Combustion analysis (Dumas method) and microwave plasma-atomic emission spectrometry (MP-AES) were used to determine the concentrations of mineral elements in charophytes. The main goal of this investigation was to complement the knowledge of the mineral composition of brackish water charophytes. Thus, the effects of species and season/month on mineral element content both in charophyte shoots and rhizoids were examined. Our analysis showed significant species-specific variations in macroelement content. Mg, K, P, Na, and S content was significantly higher in C. tomentosa; no statistically significant differences between species were found in N content, while Ca content was remarkably higher in C. aspera. As a rule, the elemental content in rhizoids and shoots of the same charophyte species varied considerably. The magnitude and direction of differences in macroelement content between species and shoots and rhizoids of the same species depended on the time the charophytes were collected. Seasonal variation in macroelement content could be explained by changing demands for metabolic and physiological processes at different growth phases of charophytes, as well as by the concentration and availability of these elements in the surrounding environment.