Juncus Bulbosus Tissue Nutrient Concentrations and Stoichiometry in Oligotrophic Ecosystems: Variability with Seasons, Growth Forms, Organs and Habitats

Aquatic plant nutrient concentrations provide important information to characterise their role in nutrient retention and turnover in aquatic ecosystems. While large standing biomass of aquatic plants is typically found in nutrient-rich localities, it may also occur in oligotrophic ecosystems. Juncus bulbosus is able to form massive stands even in very nutrient-dilute waters. Here we show that this may be achieved by tissues with very high carbon-to-nutrient ratios combined with perennial (slow) growth and a poor food source for grazers inferred from plant stoichiometry and tissue nutrient thresholds. We also show that the C, N, P and C:N:P stoichiometric ratios of Juncus bulbosus vary with the time of year, habitats (lakes versus rivers) and organs (roots versus shoots). We found no differences between growth forms (notably in P, inferred as the most limiting nutrient) corresponding to small and large plant stands. The mass development of J. bulbosus requires C, N and P, whatever the ecosystem (lake or river), and not just CO2 and NH4, as suggested in previous studies. Since macrophytes inhabiting oligotrophic aquatic ecosystems are dominated by isoetids (perennial plants with a high root/shoot ratio), attention should be paid to quantifying the role of roots in aquatic plant stoichiometry, nutrient turnover and nutrient retention.

Effects of nuisance submerged vegetation on the fauna in Norwegian rivers

The abundance of aquatic vegetation is increasing in rivers and lakes worldwide. The aim of this study was to find how the macrophyte Juncus bulbosus Linnaeus affects salmonids and benthic macroinvertebrates in Norwegian rivers. The proliferation of J. bulbosus in the study rivers commenced after the development of hydropower in the 1960s and 1970s. J. bulbosus is now considered a nuisance for humans in many areas of the rivers. We found a higher density of juvenile fish and higher density, weight and species richness of invertebrates in areas with J. bulbosus than in areas with gravel, suggesting that the vegetation is not limiting fish and invertebrates. This may be because macrophytes increase the surface area and provide shelter, food and a variety of ecological niches. Adult salmonid fish can be negatively affected when their spawning grounds are covered by vegetation. However, overgrowth is not common and may take years since fish clear the river bed of macrophytes during redd digging, indicating competition between macrophytes and fish for riverbed habitat. Our results suggest that one should not assume that outgrowths of macrophytes have negative impacts on the ecosystem. It is important to map all impacts and distinguish nuisance to humans from effects on the ecosystem.

Biomass allocation to anchoring structures in the aquatic macrophytes from the subcontinental and Atlantic climates in Europe

Biomass allocation to anchoring structures in 10 species of aquatic macrophytes in two types of the cool and humid temperate climate in Europe, subcontionental (NW Poland) and Atlantic (W France), was examined. The study focused on the weight of anchoring organs in <em>Chara delicatula</em> Ag., <em>Ch. fragilis</em> Desv., <em>Juncus bulbosus</em> L., <em>Littorella uniflora</em> (L.) Asch., <em>Luronium natans</em> (L.) Raf., <em>Potamogeton pectinatus</em> L., <em>P. perfoliatus </em>L., <em>P. natans</em> L. and <em>Ranunculus fluitans</em> (Lam.) Wimm., as well as submerged structures in <em>Hydrocharis morsus-ranae</em> L. The plants were collected from 10 geographically distant lakes and 2 rivers with a current velocity of 0.3-0.5 m s^-1. It was assumed that biomass allocation to anchoring structures in rooting macrophytes depends on the time that mechanical forces, which can remove the plants from the occupied area, exert their effect. It was found that, in the Atlantic and subcontinental climates, the ratio between the biomass of underground (or submerged) and above-ground structures (U/A index), calculated for the ramets of <em>Chara fragilis</em>, <em>Hydrocharis morsus-ranae</em> and <em>Ranunculus fluitans</em>, has similar values (p&gt;0.05). Nevertheless, among seven species of <em>Cormophyta</em>, which were anchored in the lake or pond littoral, six (<em>Juncus bulbosus</em>, <em>Littorella uniflora</em>, <em>Luronium natans</em>, <em>Potamogeton pectinatus</em>, <em>P. perfoliatus</em> and <em>P. natans</em>) had higher values of the U/A index in the Atlantic climate than in the subcontinental type (p &lt; 0.05). This can be explained by the lack of ice cover and, consequently, a longer time of wave action than in the subcontinental climate.

Juncus bulbosus (Juncaceae), a species new to South America (Chile)

The first localities of <em>Juncus bulbosus</em> (<em>Juncaceae</em>) for South America (Chile) and for the whole south-western part of the world (S latitude and E longitude) are described, including precise geographical location and climatic conditions. General remarks on the invasiveness of the species and on the possibility of finding it in other parts of the world are given. The distribution of the species world-wide requires further studies, since the bulbous rush has become an invasive plant in areas where it did not occur before.

How really extensive is the original material of Juncus kochii (Juncaceae)? - A taxonomic and nomenclatural revision

The identity of the original material of <em>Juncus kochii</em> F. W. Schultz (<em>Juncaceae</em>) is discussed. The taxon at present is best regarded as <em>Juncus bulbosus</em> L. subsp. <em>kochii</em> (F. W. Schultz) Reichg. The relevant literature (protologue and references therein) was searched and details of all original elements were compiled. Nomenclatural and taxonomic remarks are given. <em>Juncus welwitschii</em> Hochst. ex Steud. is here excluded as a synonym of <em>Juncus bulbosus</em> subsp. <em>kochii</em>.

Rejection of some original materiał of Juncus kochii (Juncaceae) as useless for typification

The identity of the potential original material of <em>Juncus kochii</em> is discussed. The taxon at present is best regarded as <em>Juncus bulbosus</em> L. subsp. <em>kochii</em> (F.W. Schultz) Reichg. The relevant literature (protologue and references therein) was searched and details of all residual original elements were compiled. Taxonomic remarks are given. The herbarium material from the environs of Bitche (Moselle, Lorraine) and Gérardmer (Vosges, Lorraine) – both in France, has been rejected as useless for typification of <em>J. kochii</em> (because of taxonomic reasons), though it was listed both in the protologue and also as indirect references therein Schultz’s earlier publications.