Calcium carbonate content for two morphotypes of an indicator charophyte species across a depth and light gradient in a mesotrophic lake

This study investigates the role of light availability and depth for calcium carbonate (CaCO₃) content in two distinct morphotypes of Lychnothamnus barbatus in Lake Kuźnickie, a mesotrophic lake in Western Poland. Lychnothamnus barbatus is a rare charophyte with high ecological and paleoecological significance, exhibiting phenotypic plasticity to adapt to environmental conditions. Fieldwork conducted in August 2019 encompassed sampling across a depth gradient (0.5–6.5 m), with measurements of photosynthetically active radiation (PAR), water chemistry, and L. barbatus biomass. Laboratory analyses included loss-on-ignition (LOI) to quantify organic matter and CaCO₃ content in dry plant material. Results revealed significant differences in CaCO₃ encrustation efficiency between morphotypes, with the elongated, deep-water morphotype displaying lower encrustation rates than shallow water morphotype. These findings underscore the utility of L. barbatus as a bioindicator for both contemporary and historical aquatic ecosystems, offering insights into carbonate precipitation in a model temperate mesotrophic lake hosting one of the biggest population of the globally rare charophyte. • Calcium carbonate content in L. barbatus varies along depth and light gradient. • Two morphotypes of L. barbatus exhibit distinct encrustation efficiencies. • Phenotypic plasticity enhances adaptability of L. barbatus to varied habitats. • Results improve understanding of carbonate dynamics in mesotrophic lakes. • Findings support the bioindicative value of L. barbatus in aquatic ecosystems.