Segetal, or weed, communities are the stands of the weed plant species which are formed under the influence of edafo-climatic conditions and the mode of soil disturbance within the processing of crop rotation (agrotechnical factor) (Mirkin, Naumova, 2012). This paper is the second part of weed community study in the South Ural, assigned to the class Papaveretea rhoeadis S. Brullo et al. 2001, syntaxon unites the weed communities of winter cereals with two orders: Aperetalia spica-venti J. Tx. et Tx. in Malato-Beliz et al. 1960 and Papaveretalia rhoeadis Hüppe et Hofmeister ex Theurillat et al. 1995; and three alliances (Khasanova et al., 2018). Data on diversity, floristic, ecological and spatial differentiation of mesoxeric and xeric weed communities of the alliances Caucalidion Tx. ex von Rochow 1951 and Lactucion tataricae Rudakov in Mirkin et al. 1985 in steppe and southern part of the forest-steppe zones are given (Table 1; Fig. 1).
The dataset contains 756 relevés: 647 made by authors during the field seasons of 2002–2018, while 109 taken from published monography (Mirkin et al., 1985).
The alliance Caucalidion combines weed communities on rich carbonate chernozem soils in the forest-steppe zone. Diagnostic species are Galeopsis bifida, G. ladanum, Galium aparine, Erodium cicutarium, Persicaria lapathifolia, Silene noctiflora, Thlaspi arvense. This alliance occupies the central position within class between communities of forest zone of the alliance Scleranthion annui and these of the steppe zone of the alliance Lactucion tataricae. The last alliance combines weed communities of the steppe zone and southern part of the forest-steppe one on south and typical chernozem soils. Two species are diagnostic: Lactuca tatarica and Panicum miliaceum. Alliances are differentiated in sample plot species richness and coenoflora: 145 species in alliance Caucalidion coenoflora (mean species number per plot is 16), and 207 species in that of Lactucion tataricae (consequently 13 species). There are 8 associations, 4 subassociations, 6 variants, 1 unrank community within these two alliances, among which 5 associations and all subassociations are new.
The alliance Caucalidion includes 4 associations with spatiall and crop differentiation, which are mainly character for the forest-steppe part of the Trans-Urals within the bounds of forest-steppe region of the eastern slope of the Southern Urals. Two associations are new: Cannabio ruderalis–Galeopsietum ladani ass. nov. hoc loco (Table 2; holotypus hoc loco — relevé 7) unites weed communities of winter, less often — spring crops; Lycopsio arvensis–Camelinetum microcarpae ass. nov. hoc loco (Table 4; holotypus hoc loco — relevé 3) unites weed communities of row crops, mainly sunflower, less often — cereals. In the same area the communities of the ass. Cannabio ruderalis–Sinapietum arvensis Rudakov in Mirkin et al. 1985 (Table 3) unite the weed communities of mainly winter cereals — wheat and rye. These communities, described in 1980s, previously were widespread in the Trans-Urals (Mirkin et al., 1985), while now occur locally in the northern part of this area. The communities of ass. Centaureo cyani–Stachyetum annuae Abramova in Mirkin et al. 1985, also described in the 1980s, were not found in the 2010s.
The diversity of the most xerophytic alliance Lactucion tataricae is represented by 4 associations which occur both in the Trans-Urals and the Cis-Urals. The most common in the last area are weed row crops (beet, nute, flax, sunflower, corn, peas, buckwheat) communities of the ass. Echinochloo crusgalli–Panicetum miliacei ass. nov. hoc loco (Table 5; holotypus hoc loco — relevé 5. They are common in five natural districts: Predbelskiy forest-steppe one, forest and forest-steppe of Belebey Upland, Cis-Urals steppe one, forest and forest-steppe one on Zilair Plateu, and Zabelskiy district of the broad-leaved forests. The weed communities of spring and winter cereals of the ass. Lathyro tuberosi–Convolvuletum arvensis ass. nov. hoc loco (Table 6; holotypus hoc loco — relevé 5) are common only within the Cis-Urals steppe district.
The communities of ass. Lactuco serriolae–Tripleurospermetum inodori ass. nov. hoc loco (Table 7; holotypus hoc loco — relevé 2) which unites the weed communities of winter cereals, are common in the steppe zone and the southern part of the forest steppe one of the Trans-Urals and the Cis-Urals within the Cis-Urals steppe, Trans-Urals steppe, and Predbelskiy forest-steppe districts. The communities of the ass. Lactucetum tataricae Rudakov in Mirkin et al. 1985 are associated exclusively with the steppe zone of the Trans-Urals. The Lactuca tatarica community (Table 8), distributed in the steppe and southern part of the forest steppe zones of the Trans-Urals, probably is derived from the ass. Lactucetum tataricae under the intensive chemical weeding of cereal crops.
Floristic differentiation of associations is confirmed by the results of the ordination analysis (Fig. 2), the diagram of which shows the distribution of communities along the moisture (first axis) and the complex soil richness–salinity gradient and agrocoenotic factor (second axis).
Ecological and agrochemical assessment of the state of technogenically disturbed soil cover of the steppe zone of the Volga region