Impact of Nitellopsis obtusa (Desv.) J. Groves, a regionally alien and invasive charophyte, on macrophyte diversity in the species native range

This study aimed to determine the relationships between the abundance of Nitellopsis obtusa, a controversial charophyte, locally red-listed in its native Eurasian range but invasive in North America, and the species diversity of macrophyte stands dominated by N. obtusa. Three lakes of different morphology, productivity and catchment were surveyed in the species native range. In each lake, the species composition and cover of three N. obtusa-dominated stands were determined monthly from spring to autumn and illustrated by the Shannon-Wiener diversity index. Water chemistry supplemented vegetation study. The species diversity turned out to be lake-specific and declined with the increasing share of N. obtusa, which developed mass occurrence in less mineralised and less fertile waters, leaving no space and limiting light and nutrient availability for large and branchy macrophytes. We postulate that this mechanism makes N. obtusa a superior competitor in less fertile waters and seems common to both native and invaded territories, as is the pool of macrophyte species most frequently co-occurring with N. obtusa.

Automated summary

This study aimed to investigate the relationship between the abundance of the controversial charophyte Nitellopsis obtusa and the species diversity of macrophyte stands dominated by N. obtusa. It was found that N. obtusa tends to dominate in less mineralized and less fertile waters, limiting the space and nutrient availability for larger macrophytes, resulting in a decline in overall species diversity in these areas. This mechanism makes N. obtusa a superior competitor in less fertile waters both in its native and invaded territories.