Stuckenietum subretusae — new association of aquatic vegetation from the southern part of the Lena River delta (Republic of Sakha (Yakutia))

Abstract

A nearly circumpolar hypoarctic species Stuckenia subretusa (Hagstr.) Holub is a rare species that grows in Yakuyia in lakes and reservoirs of deltaic systems of the large rivers (Lena, Kolyma, Yana, Indigirka, Anabar) mainly north of 68° N(Bobrov, Mochalova, 2014, 2017; Egorova, 2016; Opredelitel’…, 2020). The species is listed for Taymyr Peninsula as the most common in the plain part of the southern tundra and in the forest tundra (Pospelova, Pospelov, 2007) and as rarer in the typical tundra (Polozova, Tikhomirov, 1971). In general, this is a rather rare species. Besides the Taymyr Peninsula and Yakutia it occurs in the Bolshezemelskaya tundra, in the mouth of the Yenisey River, in Chukotka Peninsula and Alaska (Yurtsev et al., 2010; Bobrov et al., 2021). Stuckenia subretusa is a critical taxon associated by some authors (Kaplan, 2008; Konspekt…, 2012) with S. vaginata (Turcz.) Holub. However, both morphological and molecular genetic differences between these taxa were shown later (Volkova et al., 2017). It was also shown that S. subretusa is found in the lower reaches and estuarine areas of the large rivers in Asia, mainly north of 68° N, in Europe — of 67°, while the northern limit of the distribution of S. vaginata in Yakutia — 64°, in Europe — 66° (Bobrov, Mochalova, 2014), therefore these species are geographically separated. In July 2021, during a geobotanical survey of the islands of the southern part of the Lena River delta, thickets of S. subretusa were found on Sasyl-Ary Isl. (Fig. 1) in a shallow flow (channel) of 2 km total length, 130–150 m width and from 4–5 cm to 1.5 m depth with a very sluggish current. The bottom substrate is silty sands. Permafrost is 2–3 m depth. Thickets of S. subretusa were found only at 4–30 cm water depths. The thickets are monospecies with projective cover from 35 to 80 % (Fig. 2). Single specimens of Tephroseris palustris (L.) Rchb. were met rarely, at 4–5 cm water depths. Part of the thickets was located on wet sand along the shallows of the channel. S. subretusa was not found on neighboring islands. Five geobotanical relevés were made within the flow according to the generally accepted methodology with georeferencing using 12-channel GPS in the WGS-84 coordinate system on sample plots of 10×10 m. The classification was carried out on the principles of the ecological-floristic approach (Westhoff, van der Maarel, 1973). Estimation of the species projective cover in Table is given according to the Brown-Blanquet scale (Becking, 1957): r — single; + — less than 1 %; 1 — 1–5 %; 2 — 6–25 %; 3 — 26–50 %; 4 — 51–75 %; 5 — 76–100 %. The syntaxon name is given in accordance with the International Code of Phytosociological Nomenclature (Theurillat et al., 2021). The described communities belong to the class Potamogetonetea Klika in Klika et Novák 1941, the order Potamogetonetalia Koch 1926, and the alliance Potamogetonion Libbert 1931. We consider these as a part of a new association. The ass. Stuckenietum subretusae ass. nov. (Table). Nomenclature type (holotypus) — relevé No. L21-108а (Table, relevé 3). Republic of Sakha (Yakutia), Bulunsky district, Sasyl-Ary Isl., shallow channel in the Lena River delta, in water (N 72.35989°, E 126.41968°), 07/20/2021. N. N. Lashchinskiy is an author. Diagnostic species of the association is Stuckenia subretusa (= Potamogeton subretusus). The association includes monospecies communities of Stuckenia subretusa, sometimes with a single presence of other species. It is possible that communities of this species are floristically richer in southerner regions. These are reliably found in other parts of the Lena River delta (Nikolin et al., 2017), on Taimyr Peninsula (Krasnoyarsk Territory) in the Kha­tanga River (Pospelova, Pospelov, 2007), as well as in the Komi Republic (Chemeris, Bobrov, 2020), where their productivity is from 142 to 409 g/m2 of air-dry matter. In general, the association distribution area apparently coincides with the species range (northern regions of the Komi Republic, Krasnoyarsk Territory, Yakutia, Chukotka Autonomous District (Russia) and Alaska (USA).