Abstract
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.
Highlights
Wetland vegetation constitutes an integral functional component of aquatic ecosystems and a important role is assigned to submerged macrophytes, i.e. macroscopic algae and higher plants
The stands studied in Lake Niesłysz were characterised by a low frequency of angiosperms in favour of charophytes, mainly C. aspera and C. filiformis, which is emphasized by the central position of the stands studied in this lake in the Principal Component Analysis (PCA) ordination space (Fig. 2B) and by the fact that in none of the study sites in this lake a common angiosperm, namely Ceratophyllum demersum L., was found (Table 1; Fig. 2)
N. obtusa tended to develop mass occurrence and create stands of simple structure in lakes with less mineralized and less fertile, but clearer water. This result is in line with the common opinion on the requirements of N. obtusa (Urbaniak, 2003; Kabus, 2016) and charophytes in general (Krause, 1981; Schubert et al, 2018), which is reflected in the definition of the formed by charophytes European Natura 2000 habitat 3140 ‘‘Hard oligo-mesotrophic waters with benthic vegetation of Chara spp.’’ The share of non-charophyte species decreased from the most mineralised and fertile water of Lake Lednica, through a minor share in less productive water of Lake Złoty Potok, to be negligible in Lake Niesłysz, which is characterised by the lowest solute and total nitrogen concentrations in water amongst the lakes surveyed
Summary
Wetland vegetation constitutes an integral functional component of aquatic ecosystems and a important role is assigned to submerged macrophytes, i.e. macroscopic algae and higher plants. Through multiple feedback mechanisms, including interactions between species within a macrophyte community, abundant SAV generates and maintains the clear-water state in a given body of water (Jeppesen et al, 1997; Scheffer & Jeppesen, 2007; Schubert et al, 2018). The role of SAV in the network of feedback mechanisms varies and significant differences were found between angiosperms and macroscopic algae from a group of charophytes (Blindow et al, 2014). The dominance of single taxa at the expense of the overall SAV species diversity can occur along with water eutrophication, followed by the complete disappearance of submerged vegetation (Zhang et al, 2017)
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