The influence of environmental factors on the composition and structure of associations of plant communities of floodplain meadows

The article discusses the patterns of formation of plant associations in the composition of meadow, floodplain phytocenoses, depending on environmental factors. The aim of this research is to determine the stability of the ecosystem as a whole, since the most important indicator of the state of the ecosystem is the structure of the vegetation cover of the soil. Monitoring of plant communities was carried out and the influence of a number of environmental factors on the composition and structure of meadow associations of floodplain meadows was studied.


Introduction
An important component of environmental protection is the assessment of the state and prediction of possible changes in plant communities under the influence of various factors.[1,2,3] At the same time, environmental conditions can be characterized as a limiting factor that has a significant impact on the formation of vegetation cover.
Changing environmental factors and climate fluctuations inevitably affect plant cenoses; meadow floodplain ecosystems are especially susceptible to this effect, since they are highly dynamic and vulnerable.Vegetation cover is a very good indicator of ecological conditions [3,4].
The spatio-temporal structure of plant phytocenoses is a consequence of the direct impact of environmental factors, in connection with which the long-term dynamics of productivity and the composition of plant associations is a reflection of the ratio of ecological regimes [5].
There are many environmental factors that caused changes in the structure of associations and composition, but the main ones are: flooding, local soils, relief [6,7].

Results and discussion
In the floodplain conditions of the Bolshoi Kinel River, flooding is one of the most effective factors affecting the composition and structure of associations.The influence of the river activity as a factor of flooding weakens downstream.This is especially noted in the middle zone of the floodplain, where the banks of the river are high and water outflow occurs only in years of strong floods, when the duration of flooding was about 60 days.In this regard, there is both the distribution of associations, and the composition and structure in them [8].
Thus, in the central and terraced zones of the floodplain, rather wide massifs are occupied by associations with dominants from legumes or xerophytic forbs.The composition of the associations refers to the steppe meadows.In such associations, there are: grooved fescue, thin-legged graceful, steppe timothy, and small, but formed by separate groups.Along with these species, there are: steppe meadowsweet, tuberous gooseberry, thyme-colored snakehead, silver cinquefoil, meadow sage, mountain clover, white sweet clover and many others.The occurrence of these species is due to the short period of flooding (5-10 days, or areas are not flooded at all).Humidification in this case is caused only by precipitation, snow melting, proximity to groundwater, and this is not enough for the steppe and forest-steppe zones, the influence of which extends beyond the floodplain of the Bolshoy Kinel River.
Another example of changes in the composition of associations depending on the period of flooding is the bonfire-couch grass association in the near-channel zone of the lower belt of the floodplain of the Bolshoy Kinel River.This association has an almost monodominant composition with an abundance of bromeless awnless and sparsely occurring creeping couch grass, species of mesophytic forbs are rarely found in it.The areas where the bonfire-couch grass association is widespread are subjected to relatively long (30-60 days) and frequent flooding.
Depending on the factor of flooding, there is also the structure of associations, one of the expressions of which is the height of the herbage (above-ground layering).In associations common in areas with a shorter (5 -10 day) period of flooding, the herbage of meadows on average does not exceed 60 cm.creeping, etc.) and herbs (veronica long-leaved, loosestrife vine, water omezhnik, etc.).
In associations common in areas with a long period of flooding, a herbage up to 120 cm and higher is formed (brome-couch grass association of the near-channel zone of the lower floodplain belt).
The period of flooding also affects the fodder value of the herbage, the content of the most nutritious substance in it -protein.Thus, the association with the dominant meadow fescue, spreading in areas of the near-river zone of the floodplain that are not flooded enough (5-10 days), contains a small amount of protein (9.23%) in the herbage that forms the association.Associations with the dominant couch grass, common in areas of both the near-river and central zones with a long period of flooding (up to 30 days), contain from 11.5 to 13.8% protein in the herbage.This is due to the development of vegetative organs, in particular, leaves.
The composition of the soil also influences the formation of herbage.Depending on the composition of the soil, its fertility, enrichment with alluvial deposits, aeration, the composition of the components and the structure of associations change significantly.
In the floodplain of the Bolshoi Kinel River, an example of the dependence of the distribution of an association, its composition and structure on various soil characteristics can be the couch grasscornflower association of the central zone of the lower belt of the floodplain.This association has an almost monodominant structure and the height of couch grass shoots is up to 120 cm and above.The soils in the areas occupied by the noted association are characterized by the presence of a thick layer of alluvium.
The soils of the central and terraced zones of the middle belt of the floodplain of the Bolshoy Kinel River in some massifs are characterized by a significant content of humus (5-8%), on which a herbage is formed with the dominance of legumes.In particular, mountain clover, mouse peas, multi-colored elm, white sweet clover, etc., which determines the formation of legume-forb-grass associations.
The herbage of these associations is up to 45 cm high and contains from 12 to 16% protein.
The relief structure of the floodplain is determined by the physical and geographical conditions of the environment (parent rocks, hydrological regime, climate, soil).The influence of all these factors was reflected in the structure of the relief of the ecological zones of the floodplain of the Bolshoy Kinel River.
The relief elements of the floodplain include: ridges, elevated platforms, interridges, depressions (depressions and depressions).These factors determined the specificity of the relief structure in the middle zone of the floodplain of the Bolshoy Kinel River, the expression of which is as follows: the floodplain is elevated high above the level of the river bed, the banks break vertically, water overflows the banks only in years of heavy floods and with a duration of more than 60 days.The near-river zone of the floodplain of the middle belt has high ridges almost throughout its entire length, on which associations with dominants such as ground reed grass, red fescue, etc., form almost monodominant groups.
The central zone of the floodplain has wide, more leveled massifs with the presence of depressions and depressions in the relief, where prolonged stagnation of water occurs both as a result of snow melting and the proximity of standing groundwater.On such a relief, grass stands are formed in all floodplain zones with the presence of hydromesophytes from forbs, sedges and grasses, which are included in the marshy type of meadows.
On the relief elements of the intergries, which are found in the central and near-terrace zones of all belts of the floodplain of the Bolshoy Kinel River, communities with a predominance of mesophytic forbs and rhizomatous-loose-shrub and loose-shrub grasses (meadow foxtail, meadow fescue, marsh bluegrass, etc.) are widespread.The highest occurrence of these species was noted in the conditions of the upper and lower belts of the floodplain of the Bolshoi Kinel River.
Considering various ecological conditions in all floodplain zones, we are convinced of the patterns of distribution of communities, groups of associations associated with changes in habitat conditions.Ecological factors associated with an increase in the level of the meadow have a great influence on the growth of a wide variety of species, which, in turn, causes the complication of the structure of associations.
Based on the study of the influence of environmental factors on the composition and structure of meadow associations, we present in Table 1 the distribution of groups of meadow associations by floodplain zones.Of all the variety of environmental factors encountered in the meadows, we indicate in this table only three, the most dominant: topography, flooding, soil.Of course, all the listed groups of associations (in Table 1) cannot spread in such a sequence in any section of the transverse profile of the floodplain.In nature, we encounter a complex set of factors that provide diversity in the distribution of associations.

Conclusion
On arrays subjected to prolonged flooding with good (in terms of botanical composition) herbage and high biological productivity, carry out surface improvement (fertilization, overseeding of grasses); Arrays with insufficient flooding and low fertile soils, where it develops with poor (in terms of botanical composition) herbage, with low biological productivity, subject to radical improvement (destroy natural vegetation of low nutritional value and sow cultivated fodder plants -cereals (awnless bonfire, meadow foxtail) in mixtures with legumes -alfalfa.A set of measures taken on the farms, taking into account the peculiarities of the development of vegetation and the nature of the use of the floodplain, will improve the meadow herbage and increase their productivity by 2-2.5 times.

Table 1 .
Ecology of meadow vegetation of the floodplain of the Bolshoy Kinel River.