Influence of Floods and Pollutants on Development of Plant Abiotic Stress in the Amur River Floodlands

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The presented research has revealed that hydrological conditions (flooding depth, temperature regime of flood waters and flood duration) affect the survival of plant species. The resulting hydrological regime and high concentrations of pollutants in flood waters cause abiotic stress for floodplain vascular plants. The intensification of riverbed processes reduces the stability of the habitats of meadow complexes, disrupts the ratio of their species composition and affects changes in the structure of the vegetation cover. Consequences of such changes are still poorly understood. The concentration of soluble compounds of heavy metals in soils and their absorption by plant roots has a decisive influence on mechanisms of regulation of enzymes and metabolism of vascular plants. Emerging toxicity effect contributes to the development of abiotic stress on certain types of plant communities (phenomenon chlorosis). Plants affected by heavy metals have shorter root and stem lengths. It is emphasized that concentrations of Fe 3(2)+ , Zn 2(1)+ and Cu 2(1)+ in soil solutions identify the specificity of plant responses to abiotic stress. Mechanisms and interrelationships of these events are described. Despite significant progress in understanding of many aspects of floodings as an abiotic stressor no synthesis and analysis of the obtained data have been made so far. This study discusses the toxic effects caused by various heavy metals in plants. This is our first attempt to contribute to such research attempts. the Amur River floods riverbed processes heavy metals pollution plant communities the abiotic stress Figures Figure 1 Figure 2 Figure 3 Highlights • Most floodplain vegetation complexes if covered with sediment deposits over 0.6 m during floods die or undergo compositional and structural changes (Corydalis gorinensis, Lilium callosum). • Even after prolonged floodings (2019-2021) plant biodiversity in high floodplains retained 90% plant family composition, whereas low floodplain plant losses were registered to be 60% in initial family composition and 5% in species number. • Floodplain floodings over 40 days and water heating about 42 0 С caused Fe 2+ ion accumulation in plant roots. Such toxicity effect activated oxidative stress and some tree species (Betula platyphylla, Larix cajanderi) lost their leaves and died. • When floodplain floodings exceed 30 days pathogenic bacteria in soil affect plant roots. For instance, plant roofs death over 60% might cause abiotic stress on vascular plants of Asteraceae family ruderals and their extinction. 1. Introduction Catastrophic floods on the Amur Rever with high and prolonged water level rises are dangerous natural phenomena. The flood wave of 3–4 m/s activates riverbed processes and speeds up the erosion of river banks (Makhinov, 1014). Water from flooded swamps and wetlands enriched in organic acids increases solubility of pollutants brought from urban areas. Discharge of terrigenous and chemical substances during floods noticeably increases, thus causing significant pollution of floodplain soils. High contents of soluble pollutant compounds in soil solutions negatively affect nutrition of the root system of meadow vegetation. Heavy metals (HM) in high concentrations are known to have a decisive impact on plant metabolism and enzymes regulation mechanisms. Iron, copper, zinc and lead compounds are of the highest phytotoxicity (Kaznina, 2003 ). In particular, iron toxicity negatively affects the processes of amino acid binding and protein synthesis in plants (Asati A. et al, 2016). High concentrations of Zn 2(1)+ and Cu 2(1)+ in soil solutions disrupt the water balance in plants, thus causing a decreased chlorophyll synthesis, leave chlorosis and a premature aging of plants (Houda Bouazizi and al, 2010). It was reported by Verma and Dubey ( 2003 ) that soil contamination with lead results in a 40% decrease in plant root growth and up to 25% plant oppression. The resulting toxicity increases abiotic stress in the root system, which suppresses metabolic processes and disorganizes membrane structures, causes formation of reactive oxygen forms, inhibition of photosynthesis, and oppression of plants and decreases their bioproductivity (Dobrovolsky, 1998 ). Petroleum products in flood waters serve as a catalyst for abiotic stress, which intensifies irreversible changes in plants (Polevoy, 1989 ; Kvesitadze, 2005). When used by humans and animals such vegetation from contaminated areas may be the source of contamination with heavy metals and toxic components. Sedimentation and spatiotemporal heterogeneity of pollutants during floods intensify genetic disorders in the cytoplasm of biological molecules and suppress metabolic processes. Fluctuations of HM and OM concentrations in flood waters make it difficult to assess preconditions of plant abiotic stress. Change in species composition of plant complexes and the structure of their floodplain communities is the response to abiotic stress. However, concentration mechanisms of chemical compounds in the plant root system and their effect on metabolism have been poorly studied so far. The main problem in assessing soil contamination with heavy metals and organic compounds is the constant variability of their concentrations in flood waters. Many problems related to impacts of stress reactions on the synthesis of secondary metabolites have not been resolved. The present study aims at assessing abiotic stress dynamics under impacts of floods of different duration and heavy metal content in soils, the topic of significant interest for modern research. 2. Materials and methods The present study is based on the data of expeditionary studies undertaken after the Amur floods in 2013, 2019–2021 by the Institute of Water and Ecology Problems of the Far Eastern Branch of the Russian Academy of Sciences. To assess impacts of floods on soil pollution in the Amur floodplain, 3 key areas in the lower reaches of the Amur River were studied: a) the Bolshoy Ussuriysky Island, b) the Volchya-Bacha Island and c) the floodplain of the Gorin River mouth (Fig. 1 .). 210 geobotanical descriptions of key sites were made where the species biodiversity and dominant vegetation types were assessed. Plant community resistance to stress was compared to flood duration and different concentrations of heavy metals. Geographic interpolation methods were used to construct zones of solid sediment deposition and migration of elements in the key areas, and maps of flood zones and stability of plant communities in floodplain areas were compiled. To assess sediment distribution in the Amur floodplain we calculated the average mass of the deposited alluvium at various sites located at different distances from the river edge. The generally accepted method of dichromate oxidation was applied to calculate the total carbon in soils, as the main indicator of organic matter (OM) (Arinushkina, 1970 ). Measurements of concentrations of macro- and microelements (Fe, Mn, Cu, Pb, Zn, Ni) in floodplain soils (layer 0–30 cm) were carried out with inductively coupled plasma mass spectrophotometry (ICP MS) (Elan DRC II PerkinElmer device, USA) at the analytical center of the ITIG FEB RAS. Most data were collected in 2014, 2019–2022 under the project 12-I-O-ONZ-13 “Hazardous hydrological phenomena in the Amur basin: distribution, scale and dynamics” and supplemented with research materials under the RFBR BRICS project No. 19-55-80019/20. Biodiversity assessments in the Komsomolsky Nature Reserve were carried out after floods in 2014 and 2022. 3. Results and discussion 3.1. Specifics of the Amur River water regime and sediment accumulation in its floodplain. The unstable water regime of the Amur Rever results in varied channel processes, bank erosion and sediment discharge. The average long-term water discharge at the river mouth is 10.900 m 3 /s. The maximum measured Amur discharge near Khabarovsk was 46.200 m 3 /s (September 2013), the minimum was 153 m 3 /s (March 1922). Every year, about 369.1 km 3 of water, 24 mln tons of suspended sediment, 20.2 mln tons of dissolved substances and 5.3 mln tons of organic matter are carried into the sea. During floods, riverbed processes become more intensive and discharge of terrigenous and chemical matter increases. When flooding waters cover the floodplain, the largest fractions sediment along the channel, whereas most of fine fractions are carried with surface water flow onto the high floodplain areas covered with meadow vegetation. Characteristics of alluvium distribution throughout the Amur floodplain are shown in Table 1 . Dense herbaceous vegetation, typical to lowlands, much contributes to sedimentation processes in the floodplain. According to the alluvium distribution specifics in the floodplain three sedimentation zones were identified, each having distinctive relief forms, which peculiarities affect the diversity of plant complexes and their stability. 1. The bedside or low floodplain 70–100 m wide, where the bulk of sediments accumulates. Sandy ridges up to 400 m long and 0.5–1.2 m high can be formed after one flooding. 2. The high floodplain, which occupies the largest area in the island floodplain massifs and may be several kilometers wide in some places. Нigh ancient ridges there are of aeolian origin and are not flooded during floods. 3. The central floodplain is a flat surface with extensive gentle depressions and wide hollows. The flood wave rate is minimal here, making possible deposition of finest fractions of terrigenous materials. Table 1 Characteristics of Amur flood deposits in 2013, 2019–2021 Study area Floodplain characteristics Thickness of deposited alluvium and silts Depth and duration of floodplain flooding DTM* mass t/km 2 Sediment zone Landforms Alluvium, m Silts, m Depth, m Days Island Bolshoy Ussuriysky Low floodplain up to 200 Ridges, hollows 0.3–1.5 0.02–0.10 2–3 45–55 > 9000 Gorin River Mouth Low floodplain Trains 0.6–1.5 0.04–0.12 1.2–2.3 50–57 4500– –3600 High floodplain Hollows 0.15–1.2 0.05–0.32 2–3.5 36–45 Volchya-Bacha Island Central part of the floodplain Depressions 0.4–0.8 0.05–0.30 0.6–1.2 32–38 4500– –3500 Flat surface 0.3–1.6 0.01–0.05 0.3–1.0 30–50 Bars, ridges 1.0–1.6 < 0.01 1–2 4890 *DTM – deposited terrigenous material Intensity of channel processes affects the content of terrigenous material in the water flow and the rate of sedimentation of particles of different sizes on the floodplain. Studies were carried out during the floods of 2019–2021 in two Amur sections – 10 km upper the city of Khabarovsk, where the river is 2425 m wide and 7 km down Khabarovsk, where the river width is 1920 m. The obtained results showed that a significant amount of terrigenous discharge is affected by high water velocity and its turbulent regime. To estimate the transfer of solid mass through the stream cross section per time unit t and section length L , we used the equation of sediment discharge in turbulent streams (Karaushev, 2013 ; Makhinov and et al, 2022 ). G = kQV 1 L [С/ hg – (1– f )10 3 I ]/ dt where k is the coefficient for converting the mass of a solid substance in a water sample to its true mass; Q – water discharge, m 3 /s; V 1 – average flow velocity in the surface layer, m/s; L – distance between control sections, m; C – sedimentation rate in the water stream, kg/(m s 2 ); h – average flow depth, m; g – free fall acceleration, m/s 2 ; f – coefficient of friction in the bottom layer; I – bottom slope; 10 3 – water density, kg/m 3 ; t – time, sec. Calculations using the equation to determine the total mass of suspended sediment (SS, mg/dm 3 ) in the stream during the Amur floods were carried out under certain assumptions, when f – >1 (for the Amur - h ≥ 8 m, V 1 /V 2 ≥ 10, where V 2 –bottom current rate) (Table 2 ). Table 2 presents the obtained data on sedimentation of terrigenous material. The analysis of sediment discharge (fr. 0.001–0.05 µg ) shows that during the floods of 2013, 2019–2021 its mass increased to (2.4–2.6)10 7 t, the proportion of fine silt in it increased by 1.7 times, and OM increased by 3–4 times. The research results were further used to assess impacts of sedimentation of terrigenous materials on the structure of plant communities in the floodplain. Table 2 Average indicators of sedimentation characteristics of terrigenous material during the flood period on the Amur R. in 2013, 2019–2021 Straightened water stream ( km ) Structure of terrigenous matter discharge low water/Flood,% G, ton/sec Time flood days Mass of terrigenous discharge during floods, tons G f /∑G р Low water /floods V (m/s): min/max Low water/flood L 1 Gf – OM 0.001–0.2 µg G r . ∑Fraction 0.001–0.05 µg ∑Gр Gf 1.2/2.25 0.95 1.7/2.9 18.0/22.9 2.3/14.4 47–51 2.4•10 7 0.21•10 6 0.04/0.10 1.65/3.53 4.8/7.5 55.1/82.8 1.95/2.06 0.75 1.9/6.3 46.0/90.4 1.1/5.8 47–51 2.6•10 7 0.23•10 6 0.04/0.10 1.62/3.57 2.1/6.8 45.3/89.2 G – sediment discharge, ton/s; Gf – sediment discharge per flood ; OM – Organic matter (Due to the minimum limiting quantities of measurements the square deviation error in the calculations is 10–15%) When alluvium accumulation in floodplains exceeds 0.6 m (Table 1 ) plants become covered with sediments and many of them die, to name a few Corydalis gorinensis Van, Lilium callosum Siebold. Et Zucc. ). 3.2. Floodplain biodiversity specifics. Natural and climatic conditions and great species diversity make vegetation of the Amur and Gorin floodplains very unique. The floodplain area with small wetlands is about 20% of river valleys. Reed meadows prevail among representatives of plant complexes. The dominant are Calamagrostis langsdorffii (Link) Trin, Sanguisorba parviflora (Maxim.) Takeda, Carex schmidtii Meinsh and Rosa davurica Pall. Most flora representatives have a relatively low frequency of occurrence, whereas the projective cover of species can be high (Kryukova, 2013 ). Before the 2013 flood, the floodplain flora was well studied. It was estimated to contain 490 species of vascular plants, one species being unique to the region ( Corydalis gorinensis Van) and protected only in the Komsomolsky Nature Reserve (Van and Sheenko, 2016 ). Sevent species of plants are listed in the Red Book of the Russian Federation, and 28 are listed in the Red Book of the Khabarovsky Krai. Most significant of them are Caldesia reniformis (D. Don) Makino, Aldrovanda vesiculosa L., Lilium callosum Siebold. et Zucc., Corydalis gorinensis , Coleanthus subtilis (Tratt.) Seidel and several others (Sheenko, 2020 ). However, despite significant research progress many aspects of floodings as a factor of abiotic stress on floodplain vegetation are still unclear, no synthesis and analysis of collected data has been done so far. Plant adaptation and description of mechanisms of stress resistance in plant communities are of great scientific and practical interest. 3.3. Abiotic stress on plant communities. In is already known (Kryukova, 2013 ) that hydrological conditions (flooding depth and duration, temperature regime and pollution of flood waters) affect abiotic stress on vascular plants of the Amur floodplain. Plant stress is manifested in certain physiological changes, disruption of metabolic processes and changes in membrane qualities. Being under stress, plants activate their protective mechanisms, which result in inhibition of plant growth and photosynthesis (Prasad and et al, 2001; Duque and et al, 2013 ). Penetration of HMs into the root system and toxic ions into plant sells activates detoxication (HM ion binding by ligands in the cytoplasm). Mineral nutrition, leave growth and composition of photosynthetic pigments in them are disturbed and plants fall into anabiosis. Temporary inhibition of plant growth and development is the result of their adaptation to abiotic stress during prolonged floodings. 3.4. Effects of pollutants on abiotic stress on plants. Floods and their duration affect HMs concentrations in soils and increase HM geochemical activity. The obtained data proves soil enrichment with such trace elements as Fe, Ba, Pb, Zn, Fe, Mn. (Table 3 ). Table 3 Average content of silts during the Amur floodplain floods in 2013, 2019–2021 Area of studies pH water C org % Levels of migration activity Gross content of trace elements in soils /silts % mg/kg Fe Mn Zn Pb Cu Co Sr / Ni Bolshoi Ussuriysky Island 5.9/ 6.3 8, 6 2,3 a {Fe, Cu, Pb, Zn f {Mn, Sr d { Ni, Co 4.80 0.82 59.90 50.90 29,02 28.30 21.7 19.3 329/16 4.41 4.01 0.64 0.51 32.50 19,11 17.2 sl. 16.4 sl. 275/cl sl. Gorin R. Estuary 6.0/ 6.2 4.1 2.1 a { Fe, Zn, Pb f { Mn, Ni, Sr, Co d { Mn, Cu, Ni 4.66 0.27 66.80 28.20 5.80 21.6 339/12 3.85 0.16 54.50 27.20 1.50 15.5 298/9 Volchya Bacha Island 6.1/ 6.4 3.1 1.8 a { Fe, Mn, Cu, Pb f { Pb, Mn, Zn, Sr d { Sr, Ni, Co 3.75 0.08 72.30 32.30 23. 0 30.0 299/10 3.30 0.06 35.40 31.10 sl. 19.0 192/sl Average content of elements in the lithosphere determine the territory background (Vinogradov,1962) 4.65 0.85 50 10 20 80 340/58 C org – analyst S.I. Levshina; trace elements – analyst K.V. Utkina; a – levels of accumulation of elements; f – levels of correspondence of element concentrations to their region background; d – levels below the region background High contents of { Fe – Mn in soils are caused by the geochemical territory background, affected by numerous deposits of ferromanganese ores (Vinogradov, 1962 ; Makhinova et al, 2014 ). Iron and manganese compounds impact solution buffering and intensify dissolution processes of compounds containing copper, lead and zinc. Floodings over 10 days increase the buffering capacity of soil solutions and ion exchange processes, which is consistent with their migration activity (Table 3 ). High concentrations of copper, lead, nickel and zinc compounds in soil solutions are the result of pollution of industrial and waste waters from Khabarovsk, Komsomolsk-on-Amur and Amursk. Floodings of swamps and organic matter flux with floodwaters onto the floodplain activate mechanisms of dissolution of chemical compounds. Deposition of fine OM fractions on the soil surface undergoes acidification. Unfavorable conditions for plant metabolism arise. Disruption and restructuring of metabolism cause a shift in the pro-antioxidant balance in the direction of LPO activation (lipid peroxidation), which is a signal for triggering the stress response (Duque and et al, 2013 ; Kreslavsky and et al, 2012 ). Organic colloids (chelates) and soluble aggressive fractions of fulvic acids (FA) with a molecular weight of < 2.0 kDa penetrate through the pores to the root system. In the “pockets” of the root system, FAs dissolve pollutants coming from urban areas (potassium salts, urea, phosphates) and promote their ion exchange forming hydro complexes [Fe(H 2 O) 5 (OH)] 2+ , [Fe(H 2 O) 4 (OH) 2 ] + , [Cu(H 2 O) 6 ] 2+ or ammonia [Cu(NH 3 ) 4 (OH) 2 (Linnik and et al, 2004 ). The most toxic for plants are iron hydroxo complexes [Fe(H 2 O) 5 (OH] 2+ in which the unpaired electron in the outer electron orbital of free hydroxyl radicals (OH − ) has high chemical activity (Goldovskaya, 2005 ; Sayet and et al, 1990 ]. Other metals with variable valence (Cu, Zn) can also take part in formation of free radicals. In plant cells free radicals (OH − ) suppress enzyme systems and cause oxidative abiotic stress (dismutation reaction) (Cramer and et al, 2011 ; Merzlyak, 1999 ; Bityutsky, 1999 ). An excess of iron ions in plants is indicated by root growth inhibition, legging of shoots, blackening of leaves tips and stems at the base (the phenomenon of chlorosis). This is most often evident in the floodplain of the Gorin River mouth. Рlants affected with heavy metals have shorter roots and stems. Analysis of ecological conditions of plant communities before and after floodings revealed the following regulators of abiotic stress: 1. Effect of flood duration 2019–2021 maintained conditions of toxicity of soil solutions, reducing the role of antioxidant defense in the self-healing of plant communities. 2. The high geochemical activity of Zn and Pb in the presence of FA with a molecular weight of < 2.0 kDa forms soluble organomineral compounds in the root area, which are available for absorption and can serve as blockers of SH groups in the cytoplasm of biological molecules (Nanda and Agrawal, 2016 ) Besides the direct effect of heavy metals on plants, they can also cause cell toxicity through overproduction of reactive oxygen species (ROS) that disrupt antioxidant defense systems and cause oxidative stress ( Rui and et al, 2016 ; Chori and et al, 2016). 3. Floodings over 30 days enhance anaerobic bacteria development in soils and conversion of two valent forms of iron into trivalent ones Fe 2+ → Fe 3+ , thus decreasing activation of metabolic processes. Iron oxide (FeO), absorbing dissolved oxygen, is reduced to Fe 2 O 3 and becomes inaccessible to plant roots. Lack of oxygen and iron in the root system leads to rapid development of abiotic stress and depletion of plants. When thin roots die, plants are legging, turn yellow and often die (Kondratiev and et al, 2018 ). Thus, impacts on the root system of polluted flood waters enriched with heavy metals are manifested in the following two patterns of stress reaction: a) mechanisms of HM absorption cause the effect of cellular toxicity due to the overproduction of reactive oxygen species (ROS), which disrupt antioxidant defense systems and cause oxidative stress, resulting in depletion and death of fine roots in certain plant species, b) decrease in the activity of enzymes, carbohydrate and lipid metabolism, as a stress response to disruption of the mechanisms of photosynthesis and processes of inhibition of protein synthesis (Rout and Sahoo, 2015 ). And changes in metabolism and structure of protein molecules are accompanied by concentration of secondary metabolic products in plant organs, which causes genetic disorders and leads to the death of plants. Studies of the ecological state of the floodplain vegetation cover in the Lower Amur reaches after the floods of 2013, 2019–2021 made it possible to identify, according to the stability degree, 5 plant community structures (PCS) associated with various elements of the floodplain relief (Fig. 2). 1. Stable PCS are typical to bars, riverbanks and the surface of superimposed floodplains. Tree and shrub communities maintain a constant structure in the vegetation cover. Broad-leaved oak, willow-poplar, poplar, ash-elm forests are widespread here. Also Juglans mandshurica Maxim., Phellodendron amurense Rupr., Maackia amurensis Rupr. et Maxim., Malus baccata (L.) Borkh., Ligustrina amurensis Rupr., Crataegus dahurica Koehne ex CK Schneid, etc. may be found there. These floodplain areas are flooded only during periods of high water content in the Amur with no evident effect on the state of the vegetation cover. However, during the catastrophic flood in 2013, the floodplain in these areas was covered with water for less than 20 days, but resulted in the death of certain tree species - Betula platyphylla Sukacz., Larix cajanderi May (Fig. 3 ). Structures of plant communities: 1. stable, 2. weakly stable, 3. dynamic, 4. unstable, 5. disturbed; 6. flow direction 2. Weakly stable PCS are developed in large depressions of the central floodplain with a predominance of upland shrubs and perennial species of meadow herbaceous plants – Crataegus dahurica, Hemarthria sibirica (Gand.) Ohwi, Spodiopogon sibiricus Trin., Aster tataricus L. fil., Boltonia lautureana Debeaux, Geranium erianthum DC., Pycnostelma paniculatum (Bunge) K. Schum, etc. High floodplains are flooded over 40 days only in time of high water content in the Amur. Affected plant species recover quickly. However, the 2013 flood produced a significant impact on certain herbaceous plant species. There was habitat reduction of ruderal, meadow and edge-forest species, but all of them regained their positions in the composition of plant communities in subsequent years (Kryukova, 2013 ; Sheenko 2020 ). The pattern of PCS habitats (Fig. 3 ) changes depending on conditions of species recovery. 3. Dynamic PCS are found in the zone of transitional heights between low and high floodplains, where mesophilic perennial meadow-herbaceous plants and shrubs predominate. Plant communities are formed by Calamagrostis langsdorffii (Link) Trin., Thalictrum amurense Maxim., Sanguisorba parviflora (Maxim.) Takeda., Artemisia integrifolia L., Vicia amurensis Oett., Lathyrus pratensis L., Lysimachia davurica Ledeb., Spiraea salicifolia L., S. humilis Pojark, which are adapted to prolonged floodings. Silt deposit accumulation due to flood waters leads to plant biomass increase on reed grass meadows. After floods the general direction of succession changes in PCS is characterized by a decrease in the proportion of such aspect-forming mesophytic species of cereal-sedge-herb meadows as: Iris setosa Pall. ex Link, Thalictrum amurense , Vicia amurensis , Geranium wlassowianum Fisch. ex Link, Veronicastrum sibiricum (L.) Pennell, Saussurea amurensis Turcz. ex D.C., Veratrum oxysepalum Turcz, etc. These species give way to hygrophilous species Persicaria lapathifolia (L.) S. F. Gray, Lycopus lucidus Turcz. ex Benth., Carex vesicata Meinsh., Phragmites australis (Cav.) Trin. ex Steud. PCS dynamism is manifested in changes in the spectra of ecological-coenotic groups and density of plant communities. It is associated with suppression of certain species and their restoration (for example, Amur corydalis, and some species of ruderals from Asteraceae). 4. Unstable PCS of low floodplain are dominated by hygrophilic, meso-hygrophilic perennial herbaceous plants: Calamagrostis langsdorffii , Carex appendiculata (Trutv. et C.A. Mey.) Kük., Carex schmidtii Meinsh., Cyperus orthostachyus Franch. et Savat., Bidens radiata Thuill., Anemonidium dichotomum (L.) Holub, Caltha palustris L. These plants are adapted to survival on moist and waterlogged soils, and in annually flooded areas. They tolerate significant flooding for long periods. However, restoration of species composition here is slow. There has been a loss of a number of species within the ruderals from the family Asteraceae (Kryukova, 2013 ). 5. Disturbed PCS are associated with riverbed towpaths and depressions in the low floodplain. Many specimens of riverbed plants were completely buried by alluvial sediments, and that caused reduction in species diversity in habitats of meadow and shallow meadow communities. Dominant plants here are one- or two-year-old species, namely such ephemerals of low-water areas of rivers and lakes as Polygonum arenastrum Boreau, Eleocharis wichurae Boeck., Fimbristylis aestivalis (Retz.) Vahl, F. verrucifera (Maxim.) Makino., Carex bohemica Schreb., Scirpus komarovii Roshev., Cyperus michelianus (L.) Delile, Centipeda minima (L.) A. Br et Aschers. Here, PCS are often represented by unformed plant groups, composition and diversity of which depend on the water level during low-water periods. In years of low water content, these habitats are occupied by perennial representatives of the families Poaceae, Asteraceaea, Polygonaceae, Cyperaceae , etc., including ruderal species that actively invade free habitats in the absence of competition from other plant species of indigenous flora. The analysis of PCS heterogeneity after floodings revealed the following specifics. - About 30% of species from the family Asteraceae belonging to ruderals have been lost. Some species of Asteraceae were not found in the floodplain; perhaps their ability to recover in places where water stood for a long time was lost. - Differences in structure were registered in the cereal families; the proportion of bluegrass, celery, legumes and rosaceae species decreased. According to R.V. Kaygorodov ( 2010 ) the extinction of certain plant species was caused with disturbances in the structure of biomolecules and loss of their functional activity due to high concentrations of active hydroxyl radicals (HO − ), which, interacting with organic matter, form hydroperoxides (ROOH) of DNA, proteins and lipids. As a result, cellular and molecular mechanisms that maintain homeostasis and plant cell integrity, under conditions of toxic stress in certain plant species, lead to decrease in their biochemical adaptation and death (Chirkova, 2002 ; Chudinova and Orlova, 2006 ). After floods in 2019–2021, biodiversity conservation in high floodplain areas was more than 90%; differences in family composition were insignificant. In areas of low floodplain, preservation of families of higher plants was less than 60% of their previous number, and the number of species decreased. The largest number of lost species was noted among ruderals and Asteraceae. It has been established that flooding of high floodplains for up to 20 days does not disrupt the development of the growing season of meadow vegetation, and even coupled with good moisture, rapid growth of many cereal species is observed. Flood duration of 30–40 days delays vegetation processes, and floods over 40 days cause inhibition of plant growth and sometimes their death due to disruption of the oxygen regime in polluted waters. Species composition in low floodplains restores rather slowly. With prolonged moistening by groundwaters, meadow grasses are replaced by sedges and other moisture-loving species of herbaceous vegetation. 4. Conclusions 1. It has been established that conditional processes and high concentrations of pollutants in flood waters are regulators of abiotic stress on vascular plants of floodplains. The most significant impact factors are duration of floods, thickness and composition of alluvial deposits, OM flux and predominance of iron group compounds among pollutants. Floodings over 30 days enhance anaerobic bacteria activities in soils and dissolved oxygen involvement in oxidation reactions (for example, during the reduction of iron Fe 2+ → Fe 3+ ). Disturbed oxygen regime causes abiotic stress on plants and leads to their growth inhibition. High contents of toxic substances and flood duration drastically reduce the level of stability of physiological activity of some vascular plants and, primarily, ruderals. Floodplain floodings for over 30 days do not disrupt the PCS development, and rapid growth of meadow vegetation is registered due to good soil moisture conditions in the post-flood period. 2. Significant factors of biotic stress are mobile compounds of Fe, Zn and Pb in high concentrations in soil solutions, which are blockers of HS groups of biological molecules, and as such reduce the activity of enzymes, carbohydrate and lipid metabolisms. Plants exposed to heavy metal toxicity display such symptoms as chlorosis, stunted growth, root browning and death. Distortion of photosynthesis and processes of protein synthesis inhibition causes concentrations of products secondary metabolism in plant organs, which in its turn resulted in genetic disorders and plant death. Annual floods for three years (2019–2021) maintained the toxic effect in soil solutions for the root system, reducing the efficiency of their self-healing processes. 3. The catastrophic flood of 2013 resulted in the loss of many species in the floodplain vegetation cover. Studies, undertaken in these areas in 2015, revealed the loss of 30% of species, 34% of genera and 12% of families of higher plants from their previous number. In the three years of consecutive floods (2019–2021), ongoing channel processes caused changes in plant community structure in the low floodplain. The species composition here has been changed insignificantly, although new developments of the riverbed affected species habitat area. The quality of stagnant water in depressions affected plant complexes of the central floodplain. Many plant species were damaged, but their recovery in 2022 was more effective than in 2015. 4. Our studies of vegetation biodiversity suffering abiotic stress due to drastic Amur floods in 20013, 2019–2021 made possible to identify 5 plant community structures (PCS). Heterogeneity of plant habitat distribution within plant communities is distorted by flood waters heavily polluted with heavy metals, which significantly affect plant root systems. Mechanisms of heavy metal absorption decrease enzyme activities and disrupt mechanisms of photosynthesis and protein synthesis inhibition, causing cell toxicity effects. Changes in metabolism and protein molecular structures result in concentrations of secondary metabolism products in plants, causing generic transfers and plant death. Declarations Acknowledgments. The study was carried out with the financial support of the Russian Foundation for Basic Research (RFBR) within the framework of the scientific project No. 19–55–80022/20. We thank I.V. Perminova, Doctor of Sciences (Chemistry) and Professor of Moscow State University, Faculty of Chemistry, for valuable advices in preparing this article. References Arinushkina, E.V., 1970. Guide to chemical analysis of soils. 2nd ed. M: Publishing House MU, 488. Asati, A., Pichode, M., Nikhil, K., 1999. Effect of heavy metals on plants: an overview. International Journal of Application or Innovation in Engineering and Management. 2016; 5:23 19–4847, 56–66/ [Electronic resource]. https://paper.researchbib.com/view/paper/74028. Bityutsky, N.P., 1999. Microelements and plants. St. Petersburg, SPbU Publishing House, 232. Chirkova, T.V., 2002. Physiological basis of plant resistance. St. Petersburg: SPbU Publishing House, 244. Chudinova, L.A., Orlova, N.V., 2006. Physiology of plant resistance: textbook. Manual for the special course / Perm. State Univ, 124. Cramer, GR., Urano, K., Delrot S., Pezzotti, M., Shinozaki K., 2011. Effects of Abiotic Stress on Plants: a Systems Biology Perspective // BMC Plant Biol. 11. [Electronic resource]. URL: https:// bmcplantbiol.biomedcentral. com / articles /10.1186/1471-2229-11-163. . Dobrovolsky, V.V., 1998. Fundamentals of biogeochemistry: textbook. M.: Higher School, 413. Duque, A.S., Almeida, A.M., Silva, A.B., Silva, J.M., Farinha, A.P., Santos, D., Fevereiro, P., Araujo, S.S. 2013. Abiotic Stress Responses in Plants: Unraveling the Complexity of Genes and Networks to Survive. Biology, Environmental Science. [Electronic resource]. URL: http://dx.doi.org /10.5772/52779. . Sayet, Yu.E., Revich, B.A., Yanin, E. P., 1990. Environmental Geochemistry M: Nedra, Moscow, 335. Ghori, N.H., Ghori, T., Hayat, M.Q., Imadi, S.R., Gul, A., Altay, V., Ozturk, M., 2019. Heavy metal stress and responses in plants. International Journal of Environmental Science and Technology. 16:1807-1828. DOI: 10/1007/s13762-019-02215-8 [Electronic resource] https://link.springer.com/article/10.1007/s13762-019-02215-8. Goldovskaya, L.F., 2005. Environmental chemistry. M.: Mir, 296. Houda Bouazizi, Hager Jouili, Anja Geitmann, Ezzeddine El Ferjani, 2010. Copper toxicity in expanding leaves of Phaseolus vulgaris L.: antioxidant enzyme response and nutrient element uptake. Ecotoxicol Environ Saf. 73(6):1304-1308. https://doi.org/10.1016/j.ecoenv.2010.05.014. Karaushev, A.V., 2013. Theory and methods for calculating sediment load and water quality in rivers and reservoirs. Selected works, St. Petersburg, 249. Kaygorodov, R.V., 2010. Plant resistance to chemical pollution textbook. / comp. R.V. Kaygorodov; Perm. State Univ., Perm, 151. Kaznina, N.M., 2003. Lead and cadmium effect on growth, development and some other physiological processes in annual cereals (early stages of ontogenesis): abstract. dis. cand. Biol. Sci. Petrozavodsk, 23. Clemens, S., 2006. Toxic metal accumulation, response to exposure and mechanism of tolerance in plants. Biochimie. 88:1707-1719. PMID: 16914250 https://doi.org: 10.1016/j.biochi.2006.07.003 Kondratiev, M.N., Ronzhina, E.S., Larikova, Yu.S., 2018. Abiotic stress effect on the metabolism of secondary compounds in plants // Scientific journal Izvestia KSTU, 349, 203–219. Kreslavsky, V.D., Los, А.F., Allahverdiev, S.E. et al. The signal role of active oxygen forms in plant stress. Plant Physiology. 2012. 59 (2). 163–178. Kryukova, M.V., 2013. Vascular plants of the Lower Amur region. Vladivostok: Dalnauka, 354. Kvesitadze, G.I., Khatisashvili, G.A., Sadunishvili, T.A. et al., 2005. Metabolism of anthropogenic toxicants in higher plants / ed. I.N. Popova. M: Nauka, 199. Linnik, P.N., Vasilchuk, T.A., Linnik, R.P., 2004. Humic substances of natural waters and their importance for aquatic ecosystems (review). Ibid. 40, 1. 81–107. Makhinov, A.N., 2014. Main factors in the formation of catastrophic floods in the Amur River basin in 2013. Readings in memory of V.Ya. Levanidova. 4. 435–443. Makhinov, A.N., Makhinova, A.F., Kim, V.I., 2022. Dynamics of channel processes of the Amur River and migration of heavy metals during floods. Ecology and industry of Russia, 26(2). 58–63. DOI: 10.18412/1816-0395-2022-2-58-63. Makhinova, A.F., Makhinov, A.N., Kuptsova, V.A., Liu, Shuguang, Yermoshin, V.V. 2014. Landscape-Geochemical Zoning of the Amur Basin (Russian Territory). Journal of Pacific Geology. 33(2). 76–89. DOI: 10.1134/s1819714014020043/ Merzlyak, M.N., 1999. Activated oxygen and plant life. Sorosovsky education magazine. 9. 20–26. https://www.pereplet.ru/nauka/Soros/pdf/9909_020.pdf-Rus. Nanda, R., Agrawal, V. 2016. Elucidation of zinc and copper induced oxidative stress, DNA damage and activation of defense system during seed germination in Cassia angustifolia Vahl. Environmental and Experimental Botany. 125:31. 41. Polevoy, V.V. 1989. Physiology of plants: textbook for biol. specialist. Universities. M.: Higher school, 464. Rout, G., Sahoo, S. 2015. Role of iron in plant drowth and metabolism. Reviews in Agricultural Science. 3. 1–24. DOI: 10.7832/ras.3.1. Rui, H., Chen, C., Zhang, X, Shen Z., Zhang, F. 2016. Cd-induced oxidative stress and lignification in the roots of two Viciasatia L. Varieties with different Cd tolerances. Journal of Hazardous Materials. 301:304–313. Sheenko, P.S. 2020. Impacts of the catastrophic flood in 2013 on the Amur floodplain flora in the vicinity of Komsomolsk-on-Amur. Bulletin of the Far Eastern Branch of the Russian Academy of Sciences. 5. 116–124. DOI: 10.37102/08697628.2020.213.5.010. Suraj Varma, Ekta and Manish Jangra. 2021. Heavy metals stress and defense strategies in plants: An overview. Journal of Pharmacognosy and Phytochemistry 10(1): 608-614. Van, V.M., Sheenko, P.S. 2016. Illustrated guide to the Komsomolsky Nature Reserve. Ed. 2nd, rev. and additional Khabarovsk: Khabar. Reg. typogr., 304. Verma, S., Dubey, R.S. 2003. Lead toxicity induces lipid peroxidation and alters the activities of antioxidant enzymes in growing rice plants. Plant Science. 164:645–655. Vinogradov, A.P. 1962. Average content of chemical elements in main types of magmatic rocks in the earth crust. Geochemistry. 7. 555–571. 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Makhinov","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwElEQVRIiWNgGAWjYHACZmYGAyDF3sDAkFBAkhaeA0AtBkRrAQGJBCBBjBb+aYcfGxcU3JEzuPk68cMDA4Z8gwMEtEjcTjNOnmHwzNjgdu5mCaDDLDcQ0sJwO8H4MI/B4cSZs3M3gLQYELRF/nb6Z4iWmWc3/yBKi8HtHONkkJZ+Cd5txNlieDun2BioxZifJ3ebRYKBhIEkIS1yt9M3S/P8OSzHxn52880fFTYGfIS0oAMJEtWPglEwCkbBKMAKAF09PfZGe2xTAAAAAElFTkSuQmCC","orcid":"","institution":"Institute of Water and Ecological Problems FEB RAS: Institut vodnyh i ekologiceskih problem DVO RAN","correspondingAuthor":true,"prefix":"","firstName":"Aleksei","middleName":"","lastName":"Makhinov","suffix":""},{"id":309930393,"identity":"c8a17563-0a5c-4794-9530-2b8411522fb6","order_by":1,"name":"Maria Kryukova","email":"","orcid":"","institution":"Institute of Water and Ecological Problems FEB RAS: Institut vodnyh i ekologiceskih problem DVO RAN","correspondingAuthor":false,"prefix":"","firstName":"Maria","middleName":"","lastName":"Kryukova","suffix":""},{"id":309930394,"identity":"329f1ba8-904a-402d-9670-90819aad9a93","order_by":2,"name":"Aleksandra Makhinova","email":"","orcid":"","institution":"Institute of Water and Ecological Problems FEB RAS: Institut vodnyh i ekologiceskih problem DVO RAN","correspondingAuthor":false,"prefix":"","firstName":"Aleksandra","middleName":"","lastName":"Makhinova","suffix":""}],"badges":[],"createdAt":"2024-06-03 08:36:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4520397/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4520397/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":58384549,"identity":"f1bbd97d-7df1-4c53-a773-49e9fc369277","added_by":"auto","created_at":"2024-06-14 18:35:00","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":761540,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4520397/v1/ed930057f3d34a0beb40e23b.png"},{"id":58384546,"identity":"abd71b9f-4372-41a0-b02d-5f63e2ce1fc8","added_by":"auto","created_at":"2024-06-14 18:35:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":833666,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4520397/v1/385a5cc94b9d23ad0aea219e.png"},{"id":58386083,"identity":"c66352fd-8d95-44de-b306-8f2b404acd46","added_by":"auto","created_at":"2024-06-14 18:43:00","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1717992,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4520397/v1/a3c0868efce42ea1a41cf61c.png"},{"id":58555069,"identity":"987f84b5-ebe9-4a8d-b2c2-774bed0042eb","added_by":"auto","created_at":"2024-06-18 07:48:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4919092,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4520397/v1/073b8143-32ed-4ba2-9654-afc9ae59f97c.pdf"}],"financialInterests":"","formattedTitle":"\u003cp\u003eInfluence of Floods and Pollutants on Development of Plant Abiotic Stress in the Amur River Floodlands\u003c/p\u003e","fulltext":[{"header":"Highlights","content":"\u003cp\u003e\u003cstrong\u003e\u0026bull;\u0026nbsp;\u003c/strong\u003eMost\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003efloodplain vegetation complexes if covered with sediment deposits over\u0026nbsp;0.6 m during floods die or undergo compositional and structural changes (Corydalis gorinensis, Lilium callosum).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026bull;\u0026nbsp;\u003c/strong\u003eEven after prolonged floodings\u0026nbsp;(2019-2021)\u0026nbsp;plant biodiversity in high floodplains\u0026nbsp;retained 90% plant family composition, whereas low floodplain plant losses were registered to be 60% in initial family composition and 5% in species number.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026bull;\u0026nbsp;\u003c/strong\u003eFloodplain floodings over\u0026nbsp;40 days and water heating about 42\u003csup\u003e0\u003c/sup\u003eС\u0026nbsp;caused\u0026nbsp;Fe\u003csup\u003e2+\u0026nbsp;\u003c/sup\u003eion accumulation in plant roots. Such toxicity effect activated oxidative stress and some tree species\u0026nbsp;(Betula platyphylla, Larix cajanderi) lost their leaves and died.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026bull;\u0026nbsp;\u003c/strong\u003eWhen\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003efloodplain floodings exceed 30 days pathogenic bacteria in soil affect plant roots. For instance, plant roofs death over 60% might cause abiotic stress on vascular plants of Asteraceae family ruderals and their extinction.\u0026nbsp;\u003c/p\u003e"},{"header":"1. Introduction","content":"\u003cp\u003eCatastrophic floods on the Amur Rever with high and prolonged water level rises are dangerous natural phenomena. The flood wave of 3\u0026ndash;4 m/s activates riverbed processes and speeds up the erosion of river banks (Makhinov, 1014). Water from flooded swamps and wetlands enriched in organic acids increases solubility of pollutants brought from urban areas. Discharge of terrigenous and chemical substances during floods noticeably increases, thus causing significant pollution of floodplain soils. High contents of soluble pollutant compounds in soil solutions negatively affect nutrition of the root system of meadow vegetation.\u003c/p\u003e \u003cp\u003eHeavy metals (HM) in high concentrations are known to have a decisive impact on plant metabolism and enzymes regulation mechanisms. Iron, copper, zinc and lead compounds are of the highest phytotoxicity (Kaznina, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). In particular, iron toxicity negatively affects the processes of amino acid binding and protein synthesis in plants (Asati A. et al, 2016). High concentrations of Zn\u003csup\u003e2(1)+\u003c/sup\u003e and Cu\u003csup\u003e2(1)+\u003c/sup\u003e in soil solutions disrupt the water balance in plants, thus causing a decreased chlorophyll synthesis, leave chlorosis and a premature aging of plants (Houda Bouazizi and al, 2010). It was reported by Verma and Dubey (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2003\u003c/span\u003e) that soil contamination with lead results in a 40% decrease in plant root growth and up to 25% plant oppression. The resulting toxicity increases abiotic stress in the root system, which suppresses metabolic processes and disorganizes membrane structures, causes formation of reactive oxygen forms, inhibition of photosynthesis, and oppression of plants and decreases their bioproductivity (Dobrovolsky, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Petroleum products in flood waters serve as a catalyst for abiotic stress, which intensifies irreversible changes in plants (Polevoy, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1989\u003c/span\u003e; Kvesitadze, 2005). When used by humans and animals such vegetation from contaminated areas may be the source of contamination with heavy metals and toxic components.\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eSedimentation and spatiotemporal heterogeneity of pollutants during floods intensify genetic disorders in the cytoplasm of biological molecules and suppress metabolic processes. Fluctuations of HM and OM concentrations in flood waters make it difficult to assess preconditions of plant abiotic stress. Change in species composition of plant complexes and the structure of their floodplain communities is the response to abiotic stress. However, concentration mechanisms of chemical compounds in the plant root system and their effect on metabolism have been poorly studied so far. The main problem in assessing soil contamination with heavy metals and organic compounds is the constant variability of their concentrations in flood waters. Many problems related to impacts of stress reactions on the synthesis of secondary metabolites have not been resolved.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe present study aims at assessing abiotic stress dynamics under impacts of floods of different duration and heavy metal content in soils, the topic of significant interest for modern research.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cp\u003eThe present study is based on the data of expeditionary studies undertaken after the Amur floods in 2013, 2019\u0026ndash;2021 by the Institute of Water and Ecology Problems of the Far Eastern Branch of the Russian Academy of Sciences. To assess impacts of floods on soil pollution in the Amur floodplain, 3 key areas in the lower reaches of the Amur River were studied: a) the Bolshoy Ussuriysky Island, b) the Volchya-Bacha Island and c) the floodplain of the Gorin River mouth (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.). 210 geobotanical descriptions of key sites were made where the species biodiversity and dominant vegetation types were assessed. Plant community resistance to stress was compared to flood duration and different concentrations of heavy metals.\u003c/p\u003e \u003cp\u003eGeographic interpolation methods were used to construct zones of solid sediment deposition and migration of elements in the key areas, and maps of flood zones and stability of plant communities in floodplain areas were compiled.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo assess sediment distribution in the Amur floodplain we calculated the average mass of the deposited alluvium at various sites located at different distances from the river edge. The generally accepted method of dichromate oxidation was applied to calculate the total carbon in soils, as the main indicator of organic matter (OM) (Arinushkina, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1970\u003c/span\u003e). Measurements of concentrations of macro- and microelements (Fe, Mn, Cu, Pb, Zn, Ni) in floodplain soils (layer 0\u0026ndash;30 cm) were carried out with inductively coupled plasma mass spectrophotometry (ICP MS) (Elan DRC II PerkinElmer device, USA) at the analytical center of the ITIG FEB RAS.\u003c/p\u003e \u003cp\u003eMost data were collected in 2014, 2019\u0026ndash;2022 under the project 12-I-O-ONZ-13 \u0026ldquo;Hazardous hydrological phenomena in the Amur basin: distribution, scale and dynamics\u0026rdquo; and supplemented with research materials under the RFBR BRICS project No. 19-55-80019/20. Biodiversity assessments in the Komsomolsky Nature Reserve were carried out after floods in 2014 and 2022.\u003c/p\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec4\"\u003e\n \u003ch2\u003e3.1. Specifics of the Amur River water regime and sediment accumulation in its floodplain.\u003c/h2\u003e\n \u003cp\u003eThe unstable water regime of the Amur Rever results in varied channel processes, bank erosion and sediment discharge. The average long-term water discharge at the river mouth is 10.900 m\u003csup\u003e3\u003c/sup\u003e/s. The maximum measured Amur discharge near Khabarovsk was 46.200 m\u003csup\u003e3\u003c/sup\u003e/s (September 2013), the minimum was 153 m\u003csup\u003e3\u003c/sup\u003e/s (March 1922). Every year, about 369.1 km\u003csup\u003e3\u003c/sup\u003e of water, 24 mln tons of suspended sediment, 20.2 mln tons of dissolved substances and 5.3 mln tons of organic matter are carried into the sea.\u003c/p\u003e\n \u003cp\u003eDuring floods, riverbed processes become more intensive and discharge of terrigenous and chemical matter increases. When flooding waters cover the floodplain, the largest fractions sediment along the channel, whereas most of fine fractions are carried with surface water flow onto the high floodplain areas covered with meadow vegetation. Characteristics of alluvium distribution throughout the Amur floodplain are shown in Table \u003cspan\u003e1\u003c/span\u003e. Dense herbaceous vegetation, typical to lowlands, much contributes to sedimentation processes in the floodplain.\u003c/p\u003e\n \u003cp\u003eAccording to the alluvium distribution specifics in the floodplain three sedimentation zones were identified, each having distinctive relief forms, which peculiarities affect the diversity of plant complexes and their stability.\u003c/p\u003e\n \u003cp\u003e1. The bedside or low floodplain 70\u0026ndash;100 m wide, where the bulk of sediments accumulates. Sandy ridges up to 400 m long and 0.5\u0026ndash;1.2 m high can be formed after one flooding.\u003c/p\u003e\n \u003cp\u003e2. The high floodplain, which occupies the largest area in the island floodplain massifs and may be several kilometers wide in some places. Нigh ancient ridges there are of aeolian origin and are not flooded during floods.\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u003cspan\u003e3. The central floodplain is a flat surface with extensive gentle depressions and wide hollows. The flood wave rate is minimal here, making possible deposition of finest fractions of terrigenous materials.\u003c/span\u003e\u0026nbsp;\u003c/p\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eCharacteristics of Amur flood deposits in 2013, 2019\u0026ndash;2021\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eStudy area\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eFloodplain characteristics\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eThickness of deposited alluvium and silts\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eDepth and duration of floodplain flooding\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eDTM* mass\u003c/p\u003e\n \u003cp\u003et/km\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSediment zone\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLandforms\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAlluvium, m\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSilts, m\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDepth, m\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDays\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eIsland Bolshoy\u003c/p\u003e\n \u003cp\u003eUssuriysky\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLow floodplain up to 200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRidges,\u003c/p\u003e\n \u003cp\u003ehollows\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u0026ndash;1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.02\u0026ndash;0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u0026ndash;3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e45\u0026ndash;55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;9000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eGorin River Mouth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLow floodplain\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTrains\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.6\u0026ndash;1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.04\u0026ndash;0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.2\u0026ndash;2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50\u0026ndash;57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e4500\u0026ndash;\u003c/p\u003e\n \u003cp\u003e\u0026ndash;3600\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHigh floodplain\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHollows\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.15\u0026ndash;1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.05\u0026ndash;0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u0026ndash;3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e36\u0026ndash;45\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eVolchya-Bacha Island\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eCentral part of the floodplain\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDepressions\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4\u0026ndash;0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.05\u0026ndash;0.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.6\u0026ndash;1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32\u0026ndash;38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e4500\u0026ndash;\u003c/p\u003e\n \u003cp\u003e\u0026ndash;3500\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFlat surface\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u0026ndash;1.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.01\u0026ndash;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u0026ndash;1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30\u0026ndash;50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBars, ridges\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.0\u0026ndash;1.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u0026ndash;2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026gt;\u0026thinsp;4890\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"8\"\u003e\n \u003cp\u003e*DTM \u0026ndash; deposited terrigenous material\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eIntensity of channel processes affects the content of terrigenous material in the water flow and the rate of sedimentation of particles of different sizes on the floodplain. Studies were carried out during the floods of 2019\u0026ndash;2021 in two Amur sections \u0026ndash; 10 km upper the city of Khabarovsk, where the river is 2425 m wide and 7 km down Khabarovsk, where the river width is 1920 m. The obtained results showed that a significant amount of terrigenous discharge is affected by high water velocity and its turbulent regime.\u003c/p\u003e\n \u003cp\u003eTo estimate the transfer of solid mass through the stream cross section per time unit t and section length \u003cem\u003eL\u003c/em\u003e, we used the equation of sediment discharge in turbulent streams (Karaushev, \u003cspan\u003e2013\u003c/span\u003e; Makhinov and et al, \u003cspan\u003e2022\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eG\u0026thinsp;=\u0026thinsp;kQV \u003csub\u003e1\u003c/sub\u003e L [С/ hg \u0026ndash; (1\u0026ndash; \u003cem\u003ef\u003c/em\u003e )10\u003csup\u003e3\u003c/sup\u003e I ]/ dt\u003c/p\u003e\n \u003cp\u003ewhere k is the coefficient for converting the mass of a solid substance in a water sample to its true mass; Q \u0026ndash; water discharge, m\u003csup\u003e3\u003c/sup\u003e/s; V\u003csub\u003e1\u003c/sub\u003e \u0026ndash; average flow velocity in the surface layer, m/s; L \u0026ndash; distance between control sections, m; C \u0026ndash; sedimentation rate in the water stream, kg/(m s\u003csup\u003e2\u003c/sup\u003e); h \u0026ndash; average flow depth, m; g \u0026ndash; free fall acceleration, m/s\u003csup\u003e2\u003c/sup\u003e ; \u003cem\u003ef\u003c/em\u003e \u0026ndash; coefficient of friction in the bottom layer; I \u0026ndash; bottom slope; 10\u003csup\u003e3\u003c/sup\u003e \u0026ndash; water density, kg/m\u003csup\u003e3\u003c/sup\u003e ; t \u0026ndash; time, sec.\u003c/p\u003e\n \u003cp\u003eCalculations using the equation to determine the total mass of suspended sediment (SS, mg/dm\u003csup\u003e3\u003c/sup\u003e) in the stream during the Amur floods were carried out under certain assumptions, when \u003cem\u003ef\u003c/em\u003e \u0026ndash; \u0026gt;1 (for the Amur - h\u0026thinsp;\u0026ge;\u0026thinsp;8 m, \u003cstrong\u003eV\u003c/strong\u003e\u003csub\u003e1\u003c/sub\u003e \u003cstrong\u003e/V\u003c/strong\u003e\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026ge;\u0026thinsp;10, where \u003cstrong\u003eV\u003c/strong\u003e\u003csub\u003e2\u003c/sub\u003e \u0026ndash;bottom current rate) (Table \u003cspan\u003e2\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eTable \u003cspan\u003e2\u003c/span\u003e presents the obtained data on sedimentation of terrigenous material. The analysis of sediment discharge (fr. 0.001\u0026ndash;0.05 \u0026micro;g ) shows that during the floods of 2013, 2019\u0026ndash;2021 its mass increased to (2.4\u0026ndash;2.6)10\u003csup\u003e7\u003c/sup\u003et, the proportion of fine silt in it increased by 1.7 times, and OM increased by 3\u0026ndash;4 times. The research results were further used to assess impacts of sedimentation of terrigenous materials on the structure of plant communities in the floodplain.\u003c/p\u003e \u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 2\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eAverage indicators of sedimentation characteristics of terrigenous material during the flood period on the Amur R. in 2013, 2019\u0026ndash;2021\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eStraightened water stream ( km )\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eStructure of terrigenous matter discharge low water/Flood,%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eG, ton/sec\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eTime\u003c/p\u003e\n \u003cp\u003eflood\u003c/p\u003e\n \u003cp\u003edays\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eMass of terrigenous discharge during floods, tons\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eG \u003csub\u003ef\u003c/sub\u003e /\u0026sum;G \u003csub\u003eр\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003eLow water /floods\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cstrong\u003eV\u003c/strong\u003e(m/s): min/max Low water/flood\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eL\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGf\u003csub\u003e\u0026ndash;\u003c/sub\u003eOM\u003c/p\u003e\n \u003cp\u003e0.001\u0026ndash;0.2 \u0026micro;g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eG\u003csub\u003er\u003c/sub\u003e. \u0026sum;Fraction\u003c/p\u003e\n \u003cp\u003e0.001\u0026ndash;0.05 \u0026micro;g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026sum;Gр\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGf\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.2/2.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e0.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.7/2.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e18.0/22.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e2.3/14.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e47\u0026ndash;51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e2.4\u0026bull;10\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e0.21\u0026bull;10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e0.04/0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.65/3.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.8/7.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e55.1/82.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.95/2.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.9/6.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e46.0/90.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e1.1/5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e47\u0026ndash;51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e2.6\u0026bull;10\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e0.23\u0026bull;10\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e0.04/0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.62/3.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.1/6.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e45.3/89.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"9\"\u003eG \u0026ndash; sediment discharge, ton/s; Gf \u0026ndash; sediment discharge per flood ; OM \u0026ndash; Organic matter (Due to the minimum limiting quantities of measurements the square deviation error in the calculations is 10\u0026ndash;15%)\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003cp\u003eWhen alluvium accumulation in floodplains exceeds 0.6 m (Table\u0026nbsp;\u003cspan\u003e1\u003c/span\u003e) plants become covered with sediments and many of them die, to name a few \u003cem\u003eCorydalis gorinensis\u003c/em\u003e Van, \u003cem\u003eLilium callosum\u003c/em\u003e Siebold. Et Zucc.\u003cem\u003e).\u003c/em\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\"\u003e\n \u003ch2\u003e3.2. Floodplain biodiversity specifics.\u003c/h2\u003e\n \u003cp\u003eNatural and climatic conditions and great species diversity make vegetation of the Amur and Gorin floodplains very unique. The floodplain area with small wetlands is about 20% of river valleys. Reed meadows prevail among representatives of plant complexes. The dominant are \u003cem\u003eCalamagrostis langsdorffii\u003c/em\u003e (Link) Trin, \u003cem\u003eSanguisorba parviflora\u003c/em\u003e (Maxim.) Takeda, \u003cem\u003eCarex schmidtii\u003c/em\u003e Meinsh and \u003cem\u003eRosa davurica\u003c/em\u003e Pall. Most flora representatives have a relatively low frequency of occurrence, whereas the projective cover of species can be high (Kryukova, \u003cspan\u003e2013\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eBefore the 2013 flood, the floodplain flora was well studied. It was estimated to contain 490 species of vascular plants, one species being unique to the region (\u003cem\u003eCorydalis gorinensis\u003c/em\u003e Van) and protected only in the Komsomolsky Nature Reserve (Van and Sheenko, \u003cspan\u003e2016\u003c/span\u003e). Sevent species of plants are listed in the Red Book of the Russian Federation, and 28 are listed in the Red Book of the Khabarovsky Krai. Most significant of them are \u003cem\u003eCaldesia reniformis\u003c/em\u003e (D. Don) Makino, \u003cem\u003eAldrovanda vesiculosa\u003c/em\u003e L., \u003cem\u003eLilium callosum\u003c/em\u003e Siebold. et Zucc., \u003cem\u003eCorydalis gorinensis\u003c/em\u003e, \u003cem\u003eColeanthus subtilis\u003c/em\u003e (Tratt.) Seidel and several others (Sheenko, \u003cspan\u003e2020\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eHowever, despite significant research progress many aspects of floodings as a factor of abiotic stress on floodplain vegetation are still unclear, no synthesis and analysis of collected data has been done so far. Plant adaptation and description of mechanisms of stress resistance in plant communities are of great scientific and practical interest.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\"\u003e\n \u003ch2\u003e3.3. Abiotic stress on plant communities.\u003c/h2\u003e\n \u003cp\u003eIn is already known (Kryukova, \u003cspan\u003e2013\u003c/span\u003e) that hydrological conditions (flooding depth and duration, temperature regime and pollution of flood waters) affect abiotic stress on vascular plants of the Amur floodplain. Plant stress is manifested in certain physiological changes, disruption of metabolic processes and changes in membrane qualities. Being under stress, plants activate their protective mechanisms, which result in inhibition of plant growth and photosynthesis (Prasad and et al, 2001; Duque and et al, \u003cspan\u003e2013\u003c/span\u003e). Penetration of HMs into the root system and toxic ions into plant sells activates detoxication (HM ion binding by ligands in the cytoplasm). Mineral nutrition, leave growth and composition of photosynthetic pigments in them are disturbed and plants fall into anabiosis. Temporary inhibition of plant growth and development is the result of their adaptation to abiotic stress during prolonged floodings.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\"\u003e\n \u003ch2\u003e3.4. Effects of pollutants on abiotic stress on plants.\u003c/h2\u003e\n \u003cp\u003eFloods and their duration affect HMs concentrations in soils and increase HM geochemical activity. The obtained data proves soil enrichment with such trace elements as Fe, Ba, Pb, Zn, Fe, Mn. (Table\u0026nbsp;\u003cspan\u003e3\u003c/span\u003e).\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eAverage content of silts during the Amur floodplain floods in 2013, 2019\u0026ndash;2021\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"13\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eArea of studies\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003cp\u003e\u003csub\u003ewater\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eC\u003csub\u003eorg\u003c/sub\u003e %\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"3\"\u003e\n \u003cp\u003eLevels of\u003c/p\u003e\n \u003cp\u003emigration\u003c/p\u003e\n \u003cp\u003eactivity\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"9\"\u003e\n \u003cp\u003eGross content of trace elements in soils /silts\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e%\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"7\"\u003e\n \u003cp\u003emg/kg\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMn\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eZn\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003ePb\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCu\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCo\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSr / Ni\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eBolshoi\u003c/p\u003e\n \u003cp\u003eUssuriysky\u003c/p\u003e\n \u003cp\u003eIsland\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e5.9/\u003c/p\u003e\n \u003cp\u003e6.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e8, 6\u003c/p\u003e\n \u003cp\u003e2,3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e {Fe, Cu, Pb, Zn\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003ef\u003c/strong\u003e {Mn, Sr\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003ed\u003c/strong\u003e { Ni, Co\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\" rowspan=\"2\"\u003e\n \u003cp\u003e59.90\u003c/p\u003e\n \u003cp\u003e50.90\u003c/p\u003e\n \u003cp\u003e29,02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e28.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e329/16\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.41\u003c/p\u003e\n \u003cp\u003e4.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.64\u003c/p\u003e\n \u003cp\u003e0.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e32.50\u003c/p\u003e\n \u003cp\u003e19,11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17.2\u003c/p\u003e\n \u003cp\u003esl.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16.4\u003c/p\u003e\n \u003cp\u003esl.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e275/cl\u003c/p\u003e\n \u003cp\u003esl.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eGorin R.\u003c/p\u003e\n \u003cp\u003eEstuary\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e6.0/\u003c/p\u003e\n \u003cp\u003e6.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e4.1\u003c/p\u003e\n \u003cp\u003e2.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e { Fe, Zn, Pb\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003ef\u003c/strong\u003e { Mn, Ni, Sr, Co\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003ed\u003c/strong\u003e { Mn, Cu, Ni\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e66.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e28.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e339/12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e54.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e27.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e298/9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eVolchya Bacha Island\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e6.1/\u003c/p\u003e\n \u003cp\u003e6.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e3.1\u003c/p\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e { Fe, Mn, Cu, Pb\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003ef\u003c/strong\u003e { Pb, Mn, Zn, Sr\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003ed\u003c/strong\u003e { Sr, Ni, Co\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e72.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e32.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e23. 0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e299/10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e35.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003e31.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003esl.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e192/sl\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eAverage content of elements in the lithosphere determine the territory background (Vinogradov,1962)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e340/58\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"13\"\u003eC\u003csub\u003eorg\u003c/sub\u003e \u0026ndash; analyst S.I. Levshina; trace elements \u0026ndash; analyst K.V. Utkina; \u003cstrong\u003ea \u0026ndash;\u003c/strong\u003e levels of accumulation of elements; \u003cstrong\u003ef \u0026ndash;\u003c/strong\u003e levels of correspondence of element concentrations to their region background; \u003cstrong\u003ed \u0026ndash;\u003c/strong\u003e levels below the region background\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eHigh contents of \u003cstrong\u003e{\u003c/strong\u003eFe \u0026ndash; Mn in soils are caused by the geochemical territory background, affected by numerous deposits of ferromanganese ores (Vinogradov, \u003cspan\u003e1962\u003c/span\u003e; Makhinova et al, \u003cspan\u003e2014\u003c/span\u003e). Iron and manganese compounds impact solution buffering and intensify dissolution processes of compounds containing copper, lead and zinc. Floodings over 10 days increase the buffering capacity of soil solutions and ion exchange processes, which is consistent with their migration activity (Table\u0026nbsp;\u003cspan\u003e3\u003c/span\u003e). High concentrations of copper, lead, nickel and zinc compounds in soil solutions are the result of pollution of industrial and waste waters from Khabarovsk, Komsomolsk-on-Amur and Amursk. Floodings of swamps and organic matter flux with floodwaters onto the floodplain activate mechanisms of dissolution of chemical compounds. Deposition of fine OM fractions on the soil surface undergoes acidification. Unfavorable conditions for plant metabolism arise. Disruption and restructuring of metabolism cause a shift in the pro-antioxidant balance in the direction of LPO activation (lipid peroxidation), which is a signal for triggering the stress response (Duque and et al, \u003cspan\u003e2013\u003c/span\u003e; Kreslavsky and et al, \u003cspan\u003e2012\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eOrganic colloids (chelates) and soluble aggressive fractions of fulvic acids (FA) with a molecular weight of \u0026lt;\u0026thinsp;2.0 kDa penetrate through the pores to the root system. In the \u0026ldquo;pockets\u0026rdquo; of the root system, FAs dissolve pollutants coming from urban areas (potassium salts, urea, phosphates) and promote their ion exchange forming hydro complexes [Fe(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e5\u003c/sub\u003e(OH)]\u003csup\u003e2+\u003c/sup\u003e, [Fe(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e+\u003c/sup\u003e, [Cu(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e6\u003c/sub\u003e]\u003csup\u003e2+\u003c/sup\u003e or ammonia [Cu(NH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e4\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e (Linnik and et al, \u003cspan\u003e2004\u003c/span\u003e). The most toxic for plants are iron hydroxo complexes [Fe(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e5\u003c/sub\u003e(OH]\u003csup\u003e2+\u003c/sup\u003e in which the unpaired electron in the outer electron orbital of free hydroxyl radicals (OH\u003csup\u003e\u0026minus;\u003c/sup\u003e) has high chemical activity (Goldovskaya, \u003cspan\u003e2005\u003c/span\u003e; Sayet and et al, \u003cspan\u003e1990\u003c/span\u003e]. Other metals with variable valence (Cu, Zn) can also take part in formation of free radicals. In plant cells free radicals (OH\u003csup\u003e\u0026minus;\u003c/sup\u003e) suppress enzyme systems and cause oxidative abiotic stress (dismutation reaction) (Cramer and et al, \u003cspan\u003e2011\u003c/span\u003e; Merzlyak, \u003cspan\u003e1999\u003c/span\u003e; Bityutsky, \u003cspan\u003e1999\u003c/span\u003e). An excess of iron ions in plants is indicated by root growth inhibition, legging of shoots, blackening of leaves tips and stems at the base (the phenomenon of chlorosis). This is most often evident in the floodplain of the Gorin River mouth. Рlants affected with heavy metals have shorter roots and stems.\u003c/p\u003e\n \u003cp\u003eAnalysis of ecological conditions of plant communities before and after floodings revealed the following regulators of abiotic stress:\u003c/p\u003e\n \u003cp\u003e\u003cspan\u003e1. Effect of flood duration 2019\u0026ndash;2021 maintained conditions of toxicity of soil solutions, reducing the role of antioxidant defense in the self-healing of plant communities.\u003cbr\u003e\u003c/span\u003e\u003cspan\u003e2. The high geochemical activity of Zn and Pb in the presence of FA with a molecular weight of\u003cbr\u003e\u003c/span\u003e \u003cspan\u003e\u0026lt;\u0026thinsp;2.0 kDa forms soluble organomineral compounds in the root area, which are available for absorption and can serve as blockers of SH groups in the cytoplasm of biological molecules (Nanda and Agrawal, \u003cspan\u003e2016\u003c/span\u003e) Besides the direct effect of heavy metals on plants, they can also cause cell toxicity through overproduction of reactive oxygen species (ROS) that disrupt antioxidant defense systems and cause oxidative stress ( Rui and et al, \u003cspan\u003e2016\u003c/span\u003e; Chori and et al, 2016).\u003cbr\u003e\u003c/span\u003e\u003c/p\u003e\n \u003cp\u003e3. Floodings over 30 days enhance anaerobic bacteria development in soils and conversion of two valent forms of iron into trivalent ones Fe\u003csup\u003e2+\u003c/sup\u003e \u0026rarr; Fe\u003csup\u003e3+\u003c/sup\u003e, thus decreasing activation of metabolic processes. Iron oxide (FeO), absorbing dissolved oxygen, is reduced to Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and becomes inaccessible to plant roots. Lack of oxygen and iron in the root system leads to rapid development of abiotic stress and depletion of plants. When thin roots die, plants are legging, turn yellow and often die (Kondratiev and et al, \u003cspan\u003e2018\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThus, impacts on the root system of polluted flood waters enriched with heavy metals are manifested in the following two patterns of stress reaction: a) mechanisms of HM absorption cause the effect of cellular toxicity due to the overproduction of reactive oxygen species (ROS), which disrupt antioxidant defense systems and cause oxidative stress, resulting in depletion and death of fine roots in certain plant species, b) decrease in the activity of enzymes, carbohydrate and lipid metabolism, as a stress response to disruption of the mechanisms of photosynthesis and processes of inhibition of protein synthesis (Rout and Sahoo, \u003cspan\u003e2015\u003c/span\u003e). And changes in metabolism and structure of protein molecules are accompanied by concentration of secondary metabolic products in plant organs, which causes genetic disorders and leads to the death of plants.\u003c/p\u003e\n \u003cp\u003eStudies of the ecological state of the floodplain vegetation cover in the Lower Amur reaches after the floods of 2013, 2019\u0026ndash;2021 made it possible to identify, according to the stability degree, 5 plant community structures (PCS) associated with various elements of the floodplain relief (Fig.\u0026nbsp;2).\u003c/p\u003e\n \u003cdiv\u003e\n \u003c/div\u003e\n \u003cp\u003e1. Stable PCS are typical to bars, riverbanks and the surface of superimposed floodplains. Tree and shrub communities maintain a constant structure in the vegetation cover. Broad-leaved oak, willow-poplar, poplar, ash-elm forests are widespread here. Also \u003cem\u003eJuglans mandshurica\u003c/em\u003e Maxim., \u003cem\u003ePhellodendron amurense\u003c/em\u003e Rupr., \u003cem\u003eMaackia amurensis\u003c/em\u003e Rupr. et Maxim., \u003cem\u003eMalus baccata\u003c/em\u003e (L.) Borkh., \u003cem\u003eLigustrina amurensis\u003c/em\u003e Rupr., \u003cem\u003eCrataegus dahurica\u003c/em\u003e Koehne ex CK Schneid, etc. may be found there. These floodplain areas are flooded only during periods of high water content in the Amur with no evident effect on the state of the vegetation cover. However, during the catastrophic flood in 2013, the floodplain in these areas was covered with water for less than 20 days, but resulted in the death of certain tree species - \u003cem\u003eBetula platyphylla\u003c/em\u003e Sukacz., \u003cem\u003eLarix cajanderi\u003c/em\u003e May (Fig.\u0026nbsp;\u003cspan\u003e3\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eStructures of plant communities: 1. stable, 2. weakly stable, 3. dynamic, 4. unstable, 5. disturbed; 6. flow direction\u003c/p\u003e\n \u003cp\u003e\u003cspan\u003e2. Weakly stable PCS are developed in large depressions of the central floodplain with a predominance of upland shrubs and perennial species of meadow herbaceous plants \u0026ndash; \u003cem\u003eCrataegus dahurica, Hemarthria sibirica\u003c/em\u003e (Gand.) Ohwi, \u003cem\u003eSpodiopogon sibiricus\u003c/em\u003e Trin., \u003cem\u003eAster tataricus\u003c/em\u003e L. fil., \u003cem\u003eBoltonia lautureana\u003c/em\u003e Debeaux, \u003cem\u003eGeranium erianthum\u003c/em\u003e DC., \u003cem\u003ePycnostelma paniculatum\u003c/em\u003e (Bunge) K. Schum, etc. High floodplains are flooded over 40 days only in time of high water content in the Amur. Affected plant species recover quickly. However, the 2013 flood produced a significant impact on certain herbaceous plant species. There was habitat reduction of ruderal, meadow and edge-forest species, but all of them regained their positions in the composition of plant communities in subsequent years (Kryukova, \u003cspan\u003e2013\u003c/span\u003e; Sheenko \u003cspan\u003e2020\u003c/span\u003e). The pattern of PCS habitats (Fig.\u0026nbsp;\u003cspan\u003e3\u003c/span\u003e) changes depending on conditions of species recovery.\u003cbr\u003e\u003c/span\u003e \u003cspan\u003e3. Dynamic PCS are found in the zone of transitional heights between low and high floodplains, where mesophilic perennial meadow-herbaceous plants and shrubs predominate. Plant communities are formed by \u003cem\u003eCalamagrostis langsdorffii\u003c/em\u003e (Link) Trin., \u003cem\u003eThalictrum amurense\u003c/em\u003e Maxim., \u003cem\u003eSanguisorba parviflora\u003c/em\u003e (Maxim.) Takeda., \u003cem\u003eArtemisia integrifolia\u003c/em\u003e L., \u003cem\u003eVicia amurensis\u003c/em\u003e Oett., \u003cem\u003eLathyrus pratensis\u003c/em\u003e L., \u003cem\u003eLysimachia davurica\u003c/em\u003e Ledeb., \u003cem\u003eSpiraea salicifolia\u003c/em\u003e L., \u003cem\u003eS. humilis\u003c/em\u003e Pojark, which are adapted to prolonged floodings. Silt deposit accumulation due to flood waters leads to plant biomass increase on reed grass meadows. After floods the general direction of succession changes in PCS is characterized by a decrease in the proportion of such aspect-forming mesophytic species of cereal-sedge-herb meadows as: \u003cem\u003eIris setosa\u003c/em\u003e Pall. ex Link, \u003cem\u003eThalictrum amurense\u003c/em\u003e, \u003cem\u003eVicia amurensis\u003c/em\u003e, \u003cem\u003eGeranium wlassowianum\u003c/em\u003e Fisch. ex Link, \u003cem\u003eVeronicastrum sibiricum\u003c/em\u003e (L.) Pennell, \u003cem\u003eSaussurea amurensis\u003c/em\u003e Turcz. ex D.C., \u003cem\u003eVeratrum oxysepalum\u003c/em\u003e Turcz, etc. These species give way to hygrophilous species \u003cem\u003ePersicaria lapathifolia\u003c/em\u003e (L.) S. F. Gray, \u003cem\u003eLycopus lucidus\u003c/em\u003e Turcz. ex Benth., \u003cem\u003eCarex vesicata\u003c/em\u003e Meinsh., \u003cem\u003ePhragmites australis\u003c/em\u003e (Cav.) Trin. ex Steud. PCS dynamism is manifested in changes in the spectra of ecological-coenotic groups and density of plant communities. It is associated with suppression of certain species and their restoration (for example, Amur corydalis, and some species of ruderals from Asteraceae).\u003cbr\u003e\u003c/span\u003e \u003cspan\u003e4. Unstable PCS of low floodplain are dominated by hygrophilic, meso-hygrophilic perennial herbaceous plants: \u003cem\u003eCalamagrostis langsdorffii\u003c/em\u003e, \u003cem\u003eCarex appendiculata\u003c/em\u003e (Trutv. et C.A. Mey.) K\u0026uuml;k., \u003cem\u003eCarex schmidtii\u003c/em\u003e Meinsh., \u003cem\u003eCyperus orthostachyus\u003c/em\u003e Franch. et Savat., \u003cem\u003eBidens radiata\u003c/em\u003e Thuill., \u003cem\u003eAnemonidium dichotomum\u003c/em\u003e (L.) Holub, \u003cem\u003eCaltha palustris\u003c/em\u003e L. These plants are adapted to survival on moist and waterlogged soils, and in annually flooded areas. They tolerate significant flooding for long periods. However, restoration of species composition here is slow. There has been a loss of a number of species within the ruderals from the family Asteraceae (Kryukova, \u003cspan\u003e2013\u003c/span\u003e).\u003cbr\u003e\u003c/span\u003e \u003cspan\u003e5. Disturbed PCS are associated with riverbed towpaths and depressions in the low floodplain. Many specimens of riverbed plants were completely buried by alluvial sediments, and that caused reduction in species diversity in habitats of meadow and shallow meadow communities. Dominant plants here are one- or two-year-old species, namely such ephemerals of low-water areas of rivers and lakes as \u003cem\u003ePolygonum arenastrum\u003c/em\u003e Boreau, \u003cem\u003eEleocharis wichurae\u003c/em\u003e Boeck., \u003cem\u003eFimbristylis aestivalis\u003c/em\u003e (Retz.) Vahl, \u003cem\u003eF. verrucifera\u003c/em\u003e (Maxim.) Makino., \u003cem\u003eCarex bohemica\u003c/em\u003e Schreb., \u003cem\u003eScirpus komarovii\u003c/em\u003e Roshev., \u003cem\u003eCyperus michelianus\u003c/em\u003e (L.) Delile, \u003cem\u003eCentipeda minima\u003c/em\u003e (L.) A. Br et Aschers. Here, PCS are often represented by unformed plant groups, composition and diversity of which depend on the water level during low-water periods. In years of low water content, these habitats are occupied by perennial representatives of the families \u003cem\u003ePoaceae, Asteraceaea, Polygonaceae, Cyperaceae\u003c/em\u003e, etc., including ruderal species that actively invade free habitats in the absence of competition from other plant species of indigenous flora.\u003cbr\u003e\u003c/span\u003e\u003c/p\u003e\n \u003cp\u003eThe analysis of PCS heterogeneity after floodings revealed the following specifics.\u003c/p\u003e\n \u003cp\u003e- About 30% of species from the family Asteraceae belonging to ruderals have been lost. Some species of Asteraceae were not found in the floodplain; perhaps their ability to recover in places where water stood for a long time was lost.\u003c/p\u003e\n \u003cp\u003e- Differences in structure were registered in the cereal families; the proportion of bluegrass, celery, legumes and rosaceae species decreased. According to R.V. Kaygorodov (\u003cspan\u003e2010\u003c/span\u003e) the extinction of certain plant species was caused with disturbances in the structure of biomolecules and loss of their functional activity due to high concentrations of active hydroxyl radicals (HO\u003csup\u003e\u0026minus;\u003c/sup\u003e), which, interacting with organic matter, form hydroperoxides (ROOH) of DNA, proteins and lipids. As a result, cellular and molecular mechanisms that maintain homeostasis and plant cell integrity, under conditions of toxic stress in certain plant species, lead to decrease in their biochemical adaptation and death (Chirkova, \u003cspan\u003e2002\u003c/span\u003e; Chudinova and Orlova, \u003cspan\u003e2006\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eAfter floods in 2019\u0026ndash;2021, biodiversity conservation in high floodplain areas was more than 90%; differences in family composition were insignificant. In areas of low floodplain, preservation of families of higher plants was less than 60% of their previous number, and the number of species decreased. The largest number of lost species was noted among ruderals and Asteraceae.\u003c/p\u003e\n \u003cp\u003eIt has been established that flooding of high floodplains for up to 20 days does not disrupt the development of the growing season of meadow vegetation, and even coupled with good moisture, rapid growth of many cereal species is observed. Flood duration of 30\u0026ndash;40 days delays vegetation processes, and floods over 40 days cause inhibition of plant growth and sometimes their death due to disruption of the oxygen regime in polluted waters.\u003c/p\u003e\n \u003cp\u003eSpecies composition in low floodplains restores rather slowly. With prolonged moistening by groundwaters, meadow grasses are replaced by sedges and other moisture-loving species of herbaceous vegetation.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003e1. It has been established that conditional processes and high concentrations of pollutants in flood waters are regulators of abiotic stress on vascular plants of floodplains. The most significant impact factors are duration of floods, thickness and composition of alluvial deposits, OM flux and predominance of iron group compounds among pollutants. Floodings over 30 days enhance anaerobic bacteria activities in soils and dissolved oxygen involvement in oxidation reactions (for example, during the reduction of iron Fe\u003csup\u003e2+\u003c/sup\u003e \u0026rarr; Fe\u003csup\u003e3+\u003c/sup\u003e). Disturbed oxygen regime causes abiotic stress on plants and leads to their growth inhibition. High contents of toxic substances and flood duration drastically reduce the level of stability of physiological activity of some vascular plants and, primarily, ruderals.\u003c/p\u003e\n\u003cp\u003eFloodplain floodings for over 30 days do not disrupt the PCS development, and rapid growth of meadow vegetation is registered due to good soil moisture conditions in the post-flood period.\u003c/p\u003e\n\u003cp\u003e2. Significant factors of biotic stress are mobile compounds of Fe, Zn and Pb in high concentrations in soil solutions, which are blockers of HS groups of biological molecules, and as such reduce the activity of enzymes, carbohydrate and lipid metabolisms. Plants exposed to heavy metal toxicity display such symptoms as chlorosis, stunted growth, root browning and death. Distortion of photosynthesis and processes of protein synthesis inhibition causes concentrations of products secondary metabolism in plant organs, which in its turn resulted in genetic disorders and plant death. Annual floods for three years (2019\u0026ndash;2021) maintained the toxic effect in soil solutions for the root system, reducing the efficiency of their self-healing processes.\u003c/p\u003e\n\u003cp\u003e\u003cspan\u003e\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003e3. The catastrophic flood of 2013 resulted in the loss of many species in the floodplain vegetation cover. Studies, undertaken in these areas in 2015, revealed the loss of 30% of species, 34% of genera and 12% of families of higher plants from their previous number. In the three years of consecutive floods (2019\u0026ndash;2021), ongoing channel processes caused changes in plant community structure in the low floodplain. The species composition here has been changed insignificantly, although new developments of the riverbed affected species habitat area. The quality of stagnant water in depressions affected plant complexes of the central floodplain. Many plant species were damaged, but their recovery in 2022 was more effective than in 2015.\u003c/p\u003e\u003cspan\u003e\n \u003cp\u003e4. Our studies of vegetation biodiversity suffering abiotic stress due to drastic Amur floods in 20013, 2019\u0026ndash;2021 made possible to identify 5 plant community structures (PCS). Heterogeneity of plant habitat distribution within plant communities is distorted by flood waters heavily polluted with heavy metals, which significantly affect plant root systems. Mechanisms of heavy metal absorption decrease enzyme activities and disrupt mechanisms of photosynthesis and protein synthesis inhibition, causing cell toxicity effects. Changes in metabolism and protein molecular structures result in concentrations of secondary metabolism products in plants, causing generic transfers and plant death.\u003c/p\u003e\n\u003c/span\u003e\n\u003cp\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eAcknowledgments.\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eThe study was carried out with the financial support of the Russian Foundation for Basic Research (RFBR) within the framework of the scientific project No. 19\u0026ndash;55\u0026ndash;80022/20.\u003c/p\u003e\n\u003cp\u003eWe thank I.V. Perminova, Doctor of Sciences (Chemistry) and Professor of Moscow State University, Faculty of Chemistry, for valuable advices in preparing this article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eArinushkina, E.V., 1970. Guide to chemical analysis of soils. 2nd ed. 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Role of iron in plant drowth and metabolism. Reviews in Agricultural Science. 3. 1\u0026ndash;24. DOI: 10.7832/ras.3.1.\u003c/li\u003e\n\u003cli\u003eRui, H., Chen, C., Zhang, X, Shen Z., Zhang, F. 2016. Cd-induced oxidative stress and lignification in the roots of two Viciasatia L. Varieties with different Cd tolerances. Journal of Hazardous Materials. 301:304\u0026ndash;313.\u003c/li\u003e\n\u003cli\u003eSheenko, P.S. 2020. Impacts of the catastrophic flood in 2013 on the Amur floodplain flora in the vicinity of Komsomolsk-on-Amur. Bulletin of the Far Eastern Branch of the Russian Academy of Sciences. 5. 116\u0026ndash;124. DOI: 10.37102/08697628.2020.213.5.010.\u003c/li\u003e\n\u003cli\u003eSuraj Varma, Ekta and Manish Jangra. 2021. Heavy metals stress and defense strategies in plants: An overview. Journal of Pharmacognosy and Phytochemistry 10(1): 608-614. \u003c/li\u003e\n\u003cli\u003eVan, V.M., Sheenko, P.S. 2016. Illustrated guide to the Komsomolsky Nature Reserve. Ed. 2nd, rev. and additional Khabarovsk: Khabar. Reg. typogr., 304.\u003c/li\u003e\n\u003cli\u003eVerma, S., Dubey, R.S. 2003. Lead toxicity induces lipid peroxidation and alters the activities of antioxidant enzymes in growing rice plants. Plant Science. 164:645\u0026ndash;655. \u003c/li\u003e\n\u003cli\u003eVinogradov, A.P. 1962. Average content of chemical elements in main types of magmatic rocks in the earth crust. Geochemistry. 7. 555\u0026ndash;571.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"the Amur River, floods, riverbed processes, heavy metals, pollution, plant communities, the abiotic stress","lastPublishedDoi":"10.21203/rs.3.rs-4520397/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4520397/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEffects of floods on chemical pollution of floodplain soils and abiotic stress on plants were assessed. The presented research has revealed that hydrological conditions (flooding depth, temperature regime of flood waters and flood duration) affect the survival of plant species. The resulting hydrological regime and high concentrations of pollutants in flood waters cause abiotic stress for floodplain vascular plants. The intensification of riverbed processes reduces the stability of the habitats of meadow complexes, disrupts the ratio of their species composition and affects changes in the structure of the vegetation cover. Consequences of such changes are still poorly understood. The concentration of soluble compounds of heavy metals in soils and their absorption by plant roots has a decisive influence on mechanisms of regulation of enzymes and metabolism of vascular plants. Emerging toxicity effect contributes to the development of abiotic stress on certain types of plant communities (phenomenon chlorosis). Plants affected by heavy metals have shorter root and stem lengths. It is emphasized that concentrations of Fe\u003csup\u003e3(2)+\u003c/sup\u003e, Zn \u003csup\u003e2(1)+\u003c/sup\u003e\u003cem\u003e \u003c/em\u003eand Cu\u003csup\u003e2(1)+\u003c/sup\u003e\u003cem\u003e \u003c/em\u003ein soil solutions identify the specificity of plant responses to abiotic stress. Mechanisms and interrelationships of these events are described. Despite significant progress in understanding of many aspects of floodings as an abiotic stressor no synthesis and analysis of the obtained data have been made so far. This study discusses the toxic effects caused by various heavy metals in plants. This is our first attempt to contribute to such research attempts.\u003c/p\u003e","manuscriptTitle":"Influence of Floods and Pollutants on Development of Plant Abiotic Stress in the Amur River Floodlands","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-14 18:34:55","doi":"10.21203/rs.3.rs-4520397/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"9d044aa0-e713-4804-b137-01ca8bacaccd","owner":[],"postedDate":"June 14th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-06-18T07:40:11+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-14 18:34:55","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4520397","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4520397","identity":"rs-4520397","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}