On the ecology of rare steppe species of the genus Iris in the Southern Urals

The research presents the experience of assessing the diversity of communities and ecology of 3 rare steppe species of the genus Iris L. in the Southern Urals: I. pumila L., I. scariosa Willd. ex Link and I. humilis Georgi which are distributed in the steppe and forest-steppe zones of the region and listed in the Red Data Book of Bashkortostan Republic (Krasnaya kniga…, 2011) and the Russian Federation (Krasnaya kniga…, 2008). We analyzed the ecology of communities with participation of rare species using indirect ordination, which makes it possible to identify important ecological patterns of species distribution and to give an ecological interpretation of syntaxonomic units. Totally, we collected 28 geobotanical releves within the studied coenopopulations in the Southern Urals (mainly, in the Urals and Transurals of the Republic of Bashkortostan, as well as adjacent areas of Chelyabinsk and Orenburg regions) to characterize the phytocenotic localization and ecology of rare steppe species of the genus Iris. Localities of the studied species are presented on the map (See Fig. 1). The size of the releves was 64-100 m2. Releves descriptions and classification were performed using the Braun-Blanquet approach (Westhoff and van der Maarel, 1978; Braun-Blanquet, 1964). The names of vascular plants species are given according to Cherepanov (1995). The impact assessment of complex environmental factor gradients was performed using DCA-ordination in the CANOCO 4.5 program (Ter Braak and Smilauer, 2002). DN Tsyganov’s scale which was adjusted for the Southern Urals region (Shirokikh and Zverev, 2012) was applied to estimate the environmental factors of habitats. The weighted average of environmental factors was calculated in the IBIS software (Zverev, 2007). We revealed that the phytocenosis with participation of rare steppe irises in the Southern Urals belongs to the class Festuco-Brometea Br.-Bl. et Tuxen ex Soo 1947, which unites the steppe vegetation of Southern Ukraine and Russia and includes 5 associations and 2 communities. I. pumila grows mainly on the steppe slopes of various expositions as part of the steppes of association Astragalo austriacae-Stipetum pulcherrimae Martynenko et al. 2018, which is a zonal type of the Pre-Ural steppe of the Republic of Bashkortostan. I. pumila also grows in the communities of the association Scorzonerо austriacaе-Stipetum lessingianae Yamalov 2011 prov., which is steppes with dominating Stipa lessingiana of the southern regions of Bashkortostan and in the basal community Stipa capillata [Festuco-Brometea] combining low-degraded steppe pastures, which are distributed mainly in the upland and slope habitats of the southern expositions. Among the rarest communities with participation of I. рumila, there are phytocoenoses of shrub steppes of association Spiraeo hypericifoliaе-Amygdaletum nanae Solomeshch et al. 1994, which are distributed mainly across the eastern and southeastern slopes of the ranges on stony substrates. I. scariosa was found in the phytocoenosis of the association Silene altaici-Elytrigietum pruiniferae Yamalov 2018 prov., characteristic of outcrops of igneous rocks on thermophilic slopes. Occasionally, I. scariosa is observed in the communities of Festuca pseudovina [ Helictotricho- Stipetalia], distributed to the flattened mountain slopes. Communities with I. humilis occur in the Southern Urals quite rarely and belong, according to their floristic composition, to the association Diantho acicularis-Orostachetum spinosae Schubert et al. 1981. The floristic composition of all noted communities is characterized by a high role of petrophytic species (Artemisia marshalliana, Astragalus helmii, Centaurea turgaica, Ephedra distachya, Hedysarum argyrophyllum, Koeleria sclerophylla, Orostachys spinosa, Tanacetum kittaryanum Thymus guberlinensis etc.). DCA-ordination of communities with participation of steppe species of the genus Iris showed that they are well separated in the space of the first two axes (See Fig. 2). The main axis is interpreted as a complex gradient of moisture-salinity variability. The second axis can be interpreted as the aridity-humidity gradient. The studied species of the genus Iris are plants of open habitats (steppes, meadows, river banks), therefore the lighting conditions (Lc) are critical for them (See Fig. 3-5). The critically important environmental factors also include the variability of moisture (fH) and the severity of the winter period (Cr). The low ecological amplitude of I. pumila and I. scariosa for a number of climatogenic environmental factors, such as aridity-humidity (Om) and associated soil moisture (Hd), and the amount of incoming heat (Tm) causes their confinement mainly to the steppe zone of the region. At the same time, the values of the continentality of climate factors (Kn) are in wider boundaries, especially for I. scariosa. Ordination analysis showed that, according to a complex of environmental factors, each species of the genus Iris occupies its own ecological niche. Therefore, in nature, the studied species are extremely rare in the same habitats and communities. According to the given values of ecological factors of the environment (See Table), I. pumila, I. scariosa and I. humilis in the Southern Urals have a rather narrow ecological amplitude, i.e. they are stenotopes, which largely determines their natural rarity in the region of the Southern Urals.