Physicochemical properties and elemental composition of soils in the natural habitats of Bryonia L. species from the southeastern Kyzylkum Desert, Kazakhstan

Propriedades físico-químicas e composição elementar de solos em habitats de espécies de Bryonia L. no sudoeste do Deserto de Kyzylkum, Cazaquistão

Abstract

The investigation of soil conditions in plant habitats is an important area of research that enables the assessment of environmental factors determining species distribution in arid ecosystems. The aim of the present study was to comprehensively evaluate the physicochemical properties of soils in the natural habitats of Bryonia melanocarpa Nabiev in the southern part of the Kyzylkum Desert, Kazakhstan. The study was conducted using three soil profiles comprising a total of 16 samples collected from different soil horizons. Soil analyses included particle-size distribution, soil reaction (pH), electrical conductivity (EC), calcium carbonate (CaCO₃) content, available phosphorus, exchangeable cations (Ca²⁺, Mg²⁺, K⁺, and Na⁺), and cation exchange capacity (CEC). The data were interpreted using heat maps, box plots, soil profile diagrams, and radar chart analysis. The investigated soils were characterized by slightly alkaline to alkaline conditions (pH 8.2-8.8), a predominance of exchangeable calcium, and relatively low cation exchange capacity (3.69-7.35 cmol(+)/kg). The highest CEC values, together with elevated concentrations of exchangeable magnesium and potassium, were recorded in the surface horizon of Profile 1. All soil profiles exhibited a decrease in available phosphorus with increasing depth, accompanied by a progressive increase in soil alkalinity. Profile 1 showed the highest carbonate content, whereas Profile 3 was distinguished by a heavier particle-size distribution and a relatively greater proportion of fine soil fractions. The obtained results demonstrate pronounced spatial heterogeneity in the soil conditions of Bryonia melanocarpa habitats and indicate that the combined effects of soil carbonate content, particle-size distribution, and cation exchange properties represent the principal edaphic factors shaping the ecological characteristics of this species in the southern Kyzylkum Desert.

Keywords:
Bryonia melanocarpa Nabiev; Kyzylkum Desert; soils; particle-size distribution; carbonates; cation exchange capacity (CEC); exchangeable cations; arid ecosystems

Resumo

A investigação das condições edáficas em habitats vegetais é uma importante área de pesquisa que permite avaliar os fatores ambientais determinantes da distribuição de espécies em ecossistemas áridos. O objetivo deste estudo foi avaliar de forma abrangente as propriedades físico-químicas dos solos nos habitats de Bryonia melanocarpa Nabiev, na porção sul do Deserto de Kyzylkum, Cazaquistão. O estudo foi conduzido utilizando três perfis de solo, totalizando 16 amostras coletadas em diferentes horizontes. As análises de solo incluíram a distribuição granulométrica, a reação do solo (pH), a condutividade elétrica (CE), o teor de carbonato de cálcio (CaCO₃), o fósforo disponível, os cátions trocáveis ​​(Ca²⁺, Mg²⁺, K⁺ e Na⁺) e a capacidade de troca catiônica (CTC). Os dados foram interpretados por meio de mapas de calor, gráficos de caixa, diagramas de perfis de solo e análise de gráficos de radar. Os solos investigados caracterizaram-se por condições de levemente alcalinas a alcalinas (pH 8,2-8,8), predominância de cálcio trocável e capacidade de troca catiônica relativamente baixa (3,69-7,35 cmol(+)/kg). Os valores mais elevados de CTC, juntamente com concentrações elevadas de magnésio e potássio trocáveis, foram registrados no horizonte superficial do Perfil 1. Todos os perfis de solo apresentaram redução do fósforo disponível com o aumento da profundidade, acompanhada por um incremento progressivo da alcalinidade do solo. O Perfil 1 apresentou o maior teor de carbonatos, enquanto o Perfil 3 distinguiu-se por uma distribuição granulométrica mais argilosa e uma proporção relativamente maior de frações finas do solo. Os resultados obtidos demonstram uma heterogeneidade espacial acentuada nas condições do solo dos habitats de Bryonia melanocarpa e indicam que os efeitos combinados do teor de carbonatos, da distribuição granulométrica e das propriedades de troca catiônica representam os principais fatores edáficos que moldam as características ecológicas dessa espécie no sul do Deserto de Kyzylkum.

Palavras-chave:
Bryonia melanocarpa Nabiev; Deserto de Kyzylkum; solos; distribuição granulométrica; carbonatos; capacidade de troca catiônica (CTC); cátions trocáveis; ecossistemas áridos

1. Introduction

Desert and semi-desert ecosystems of Central Asia are among the most extreme terrestrial environments, characterized by high summer temperatures, extremely low precipitation, intense evapotranspiration, and soils with low organic matter content. Under such conditions, soil properties play a fundamental role in determining plant community composition, species distribution, productivity, and ecological stability. Therefore, investigating the physicochemical characteristics of soils associated with natural plant habitats is essential for understanding plant adaptation to harsh environmental conditions, nutrient cycling, and the functioning of desert ecosystems.

The Kyzylkum Desert, extending across Kazakhstan, Uzbekistan, and Turkmenistan, represents one of the most severe arid regions of Central Asia. The southern part of the Kazakh Kyzylkum is characterized by a sharply continental climate, prolonged drought periods, high evaporation rates, localized soil salinization, and low soil organic matter. Despite these unfavorable environmental conditions, the region supports a rich flora whose species have evolved a wide range of morphological, physiological, and biochemical adaptations that enable survival under persistent water deficit (Breckle and Wucherer, 2012).

Of particular interest is the occurrence of Bryonia melanocarpa Nabiev within this desert ecosystem. This perennial deciduous herb, possessing a robust root system, differs markedly in life form from the majority of typical desert species, which are predominantly shrubs, subshrubs, and ephemeral plants. The presence of a relatively large-leaved herbaceous species in one of the driest regions of Central Asia suggests the existence of specific ecological conditions that facilitate its successful establishment and persistence. This observation indicates that soil characteristics, including their physicochemical properties, nutrient availability, and the concentration of soluble salts, may play a key role in the formation of suitable habitats for this species.

Although numerous studies have focused on the taxonomy, phytochemical composition, and pharmacological properties of B. melanocarpa, its ecological characteristics, particularly the soil conditions supporting its natural populations, remain largely unexplored. This knowledge gap is especially evident for the southern Kyzylkum Desert of Kazakhstan, where information on soil chemical composition and its potential role in sustaining the growth and distribution of this species is virtually absent. Addressing this gap will improve our understanding of the ecological requirements of B. melanocarpa and identify the edaphic conditions that enable its persistence under extreme desert environments.

Therefore, the objective of the present study was to comprehensively evaluate the physicochemical properties and elemental composition of soils in the natural habitats of B. melanocarpa in the southern part of the Kyzylkum Desert, Kazakhstan. The findings provide new insights into the edaphic characteristics of the species' habitats, identify the soil factors that may contribute to its successful occurrence, and enhance our understanding of the relationships between soil properties and plant adaptation in arid ecosystems.

2. Materials and Methods

The research focused on the rare endemic species B. melanocarpa. The study was conducted within the natural habitats of this species located in the southeastern part of the Kyzylkum Desert, Kazakhstan (Figure 1). Field investigations were initiated in the spring of 2025 and included surveys of potential habitats. During the 2026 field season, three natural populations of B. melanocarpa were successfully located (Figure 2). Subsequently, detailed investigations of the soil characteristics of their habitats were carried out. Soil profiles were established within each population, and soil samples were collected for subsequent laboratory analyses of their physicochemical properties. During the field surveys, classical botanical methods, including route-reconnaissance surveys, were employed (Ussen et al., 2026). All laboratory analyses presented in this study were conducted at the laboratories of the University of Life Sciences in Poznań, Poland.

Figure 1
Study area in the southern Kyzylkum Desert, Kazakhstan.

Figure 2
(A) Profile 1; (B) Profile 2; (C) Profile 3; (D) Bryonia melanocarpa habitats; (E) Bryonia melanocarpa.

2.1. Determination of soil physicochemical properties and chemical composition

The physicochemical properties of soils from the natural habitats ofBryonia melanocarpaNabiev were evaluated through a comprehensive analysis of soil chemical parameters, including soil reaction (pH), electrical conductivity (EC), water-soluble salts, water-extractable ions, available nutrients, and exchangeable cations. The analytical procedures followed internationally accepted methods of soil chemical analysis and were adapted according to approaches previously applied for the characterization of soils supporting desert vegetation in Kazakhstan (Mamurova et al., 2025).

2.2. Water extract analysis and assessment of soil salinity

Water extracts were prepared to determine the concentration of water-soluble constituents and to evaluate soil salinity. Soil samples were air-dried at room temperature, carefully cleared of plant residues, and passed through a 2-mm sieve. Water-soluble compounds were extracted using distilled water at a soil-to-water ratio of 1:5 (w/v). The suspensions were thoroughly mixed, allowed to reach equilibrium, and subsequently filtered through qualitative filter paper following the procedure described by Mamurova et al. (2025).

The water extracts were analyzed for the major soluble cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺) and anions (HCO₃⁻, CO₃²⁻, Cl⁻, and SO₄²⁻). Soil pH was measured potentiometrically using a glass electrode, whereas electrical conductivity (EC) was determined by conductivity meter and expressed in mS cm⁻¹ (FAO, 2006; USDA, 1998).

Water-soluble calcium and magnesium concentrations were determined by complexometric titration with ethylenediaminetetraacetic acid (EDTA). Sodium and potassium were measured by flame photometry. Chloride ions were determined by the Mohr argentometric titration method, while bicarbonate and carbonate ions were quantified by acid-base titration using hydrochloric acid with phenolphthalein and methyl orange as indicators. Sulfate concentrations were determined turbidimetrically following precipitation with barium chloride (Mamurova et al., 2025).

The total soluble salt content was calculated as the sum of the major soluble cations and anions. To comprehensively evaluate soil salinity and sodicity, the salinity coefficient (Z), sodium adsorption ratio (SAR), and exchangeable sodium percentage (ESP) were also calculated. Soil salinity and sodicity were interpreted according to internationally accepted classification criteria based on pH, EC, SAR, and ESP values (USDA, 1998; Stavi et al., 2021).

2.3. Determination of available nutrients by the Mehlich 3 extraction method

The availability of mineral nutrients was assessed using the Mehlich 3 extraction procedure, a widely accepted multinutrient soil test that enables the simultaneous determination of plant-available macro- and micronutrients (Mehlich, 1984). This method is commonly applied for the assessment of available phosphorus, potassium, calcium, magnesium, iron, manganese, zinc, copper, and other essential elements.

Prior to extraction, soil samples were air-dried at room temperature and sieved through a 2-mm mesh. Available elements were extracted using the Mehlich 3 solution at a soil-to-extractant ratio of 1:10 (w/v), followed by continuous shaking and filtration of the resulting extracts.

The concentrations of extracted elements (P, K, Ca, Mg, Fe, Mn, Zn, Cu, and others) were determined using either atomic absorption spectrometry (AAS) or inductively coupled plasma optical emission spectrometry (ICP-OES), depending on the analytical protocol. The obtained data were used to evaluate soil nutrient availability and to characterize the edaphic conditions associated with the natural habitats of B. melanocarpa (Mehlich, 1984; Roy et al., 2006).

2.4. Determination of exchangeable cations and cation exchange capacity (CEC)

The composition of the soil exchange complex was evaluated by determining the concentrations of exchangeable Ca²⁺, Mg²⁺, Na⁺, and K⁺, together with the cation exchange capacity (CEC). Exchangeable cations were extracted from the soil matrix using a neutral salt extracting solution and subsequently quantified by standard analytical procedures.

Exchangeable calcium and magnesium were determined by complexometric titration with ethylenediaminetetraacetic acid (EDTA), whereas exchangeable sodium and potassium were measured by flame photometry. Cation exchange capacity (CEC) was calculated as the sum of exchangeable base cations and expressed as cmol(+)/kg of soil. These parameters were used to evaluate the nutrient-retention capacity of the soils and to characterize the chemical environment of the natural habitats of Bryonia melanocarpa (Mamurova et al., 2025; Sparks, 1996).

2.5. Determination of soil particle-size distribution

Soil particle-size distribution was determined by separating the mineral fractions into sand, silt, and clay according to internationally accepted soil texture classification procedures (USDA, 1993; FAO, 2006).

The obtained data were used to characterize the physical properties of the soils, including water infiltration, water-holding capacity, and the potential influence of soil texture on plant growth under arid environmental conditions.

3. Results

The heat map of standardized (z-score) values of exchangeable cations (Ca, K, Mg, and Na) and cation exchange capacity (CEC) revealed pronounced differences among the studied soil profiles and their respective horizons (Figure 3). The most contrasting values were observed in the upper horizon of Profile 1 (2 cm depth), where the maximum CEC value of 7.35 cmol(+)/kg was recorded, substantially exceeding those of all other samples. This horizon also exhibited the highest concentration of exchangeable magnesium (4.36 cmol(+)/kg) and an elevated level of exchangeable potassium (1.21 cmol(+)/kg), indicating a greater capacity of the surface soil layer to retain exchangeable cations.

Figure 3
Heat map of standardized (z-score) values of exchangeable cations (Ca²⁺, Mg²⁺, K⁺, Na⁺) and cation exchange capacity (CEC) across soil profiles and horizons of Bryonia melanocarpa habitats.

In the remaining samples, CEC values varied within a narrower range of 3.69-5.49 cmol(+)/kg, suggesting relatively uniform cation exchange properties in the deeper soil horizons and among the other studied soil profiles. Calcium was the dominant exchangeable cation in all analyzed samples, with concentrations ranging from 1.50 to 2.12 cmol(+)/kg. The contents of exchangeable magnesium and potassium generally decreased with increasing soil depth, whereas exchangeable sodium remained low and showed only minor variation (0.16-0.33 cmol(+)/kg).

Overall, the standardized analysis demonstrates that the surface horizon of Profile 1 is characterized by the highest cation exchange capacity and increased concentrations of exchangeable Mg and K, whereas deeper horizons and other soil profiles exhibit relatively homogeneous distributions of exchangeable cations and comparable CEC values.

3.1. Vertical distribution of soil chemical properties

The vertical distribution of cation exchange capacity (CEC), soil reaction (pH), and available phosphorus (P) revealed distinct differences among the investigated soil profiles (Figure 4).

Figure 4
Vertical distribution of soil pH, cation exchange capacity (CEC), and available phosphorus (P) across soil profiles

Across all three profiles, soil pH showed a gradual increase with depth. In the upper horizons, soil reaction was slightly alkaline, with pH values ranging from 8.2 to 8.5, whereas in the deeper horizons, pH increased to 8.7-8.8, indicating an intensification of soil alkalinity with increasing depth. The most pronounced increase in pH was observed in Profile 1, where the difference between the upper and lower horizons reached approximately 0.5 pH units.

The values of cation exchange capacity (CEC) exhibited less consistent depth-related patterns. The highest CEC value (7.35 cmol(+)/kg) was recorded in the surface horizon of Profile 1, followed by a sharp decrease to 4.5-5.0 cmol(+)/kg, after which the values remained relatively stable throughout the profile. In Profile 2, an opposite trend was observed: after relatively low values in the upper horizon, CEC increased to a maximum of approximately 5.5 cmol(+)/kg at a depth of about 35 cm and subsequently gradually decreased toward the lower horizons. Profile 3 demonstrated the most uniform vertical distribution of CEC, with values ranging from 4.1 to 4.7 cmol(+)/kg and no pronounced local maxima.

The most substantial depth-related changes were observed in the distribution of available phosphorus. In all soil profiles, the highest concentrations were detected in the surface horizons (approximately 15-33 mg/kg), followed by a pronounced decline with increasing depth. The highest surface concentration of available phosphorus was recorded in Profile 3 (approximately 33 mg/kg), followed by Profile 2 (approximately 18 mg/kg) and Profile 1 (approximately 15 mg/kg). Below 30-40 cm depth, available phosphorus concentrations decreased by approximately 2-3 times, reaching predominantly 8-12 mg/kg in the lower horizons. This pattern reflects phosphorus accumulation in the upper soil layers, likely associated with organic matter inputs and enhanced biological activity.

Overall, the studied soil profiles exhibited distinct patterns of vertical variation in chemical properties. A common feature among all profiles was an increase in soil alkalinity with depth and a decrease in available phosphorus concentrations, whereas the distribution of CEC was determined by the specific characteristics of each soil profile. Profile 1 showed the greatest contrast due to its high surface CEC value, while Profile 3 was characterized by the most homogeneous distribution of this parameter throughout the soil depth.

3.2. Distribution patterns of exchangeable cations in soil profiles

The analysis of exchangeable cation distribution in the studied soil profiles provided insights into the spatial heterogeneity of the soil exchange complex and revealed differences in the accumulation patterns of major exchangeable bases. Comparative assessment of Ca²⁺, Mg²⁺, K⁺, and Na⁺ concentrations was performed using 16 soil samples and statistical analysis of value distributions (box plots), allowing the characterization of both the average accumulation levels of elements and their variability within individual soil profiles (Figure 5).

Figure 5
Distribution of exchangeable cations (Ca²⁺, Mg²⁺, K⁺, and Na⁺) across soil profiles from natural habitats ofBryonia melanocarpabased on box-plot analysis.

In all investigated soils, divalent calcium and magnesium dominated the exchange complex, which is a typical feature of arid soils developing under conditions of limited leaching of base cations and high evaporation intensity. Exchangeable calcium exhibited the most stable distribution among the studied profiles, with median values remaining within a narrow range of approximately 1.8 cmol(+)/kg. The greatest variability in Ca²⁺ concentrations was observed in Profile 1, reflected by a wider interquartile range, indicating heterogeneous calcium distribution within this soil profile. In contrast, Profile 2 demonstrated the most compact distribution of Ca²⁺ values, suggesting a more uniform calcium content across the analyzed horizons.

Unlike calcium, magnesium distribution showed more pronounced differentiation among the soil profiles. The highest levels of exchangeable Mg²⁺ were recorded in Profile 2, where median concentrations approached 1.9 cmol(+)/kg and were accompanied by increased variability. Profile 1 generally exhibited lower median magnesium values (approximately 1.3 cmol(+)/kg); however, this profile contained the highest individual value, exceeding 4.3 cmol(+)/kg, indicating localized magnesium accumulation within a specific soil horizon. In Profile 3, exchangeable magnesium concentrations remained relatively stable at approximately 1.7 cmol(+)/kg, reflecting a more uniform distribution of this element throughout the soil profile.

The distribution of monovalent cations showed less pronounced differences among the studied sites; however, distinct patterns were observed for potassium. The highest exchangeable K⁺ concentrations were recorded in Profile 2, where median values reached approximately 1.0 cmol(+)/kg and the upper quartile exceeded 1.3 cmol(+)/kg. This profile demonstrated the strongest potassium accumulation among all studied soils, which may be associated with differences in the mineralogical composition of parent materials and a higher capacity of the soil matrix to retain exchangeable nutrient forms. In Profiles 1 and 3, exchangeable potassium concentrations were lower and stabilized at approximately 0.75 cmol(+)/kg.

Exchangeable sodium concentrations remained low in all analyzed samples, generally below 0.3 cmol(+)/kg. The limited variability of Na⁺ among profiles indicates the absence of significant sodium accumulation within the soil exchange complex and suggests no evident signs of sodicity or secondary salinization in the studied sites. Such sodium distribution is typical for desert soils where, in the absence of intensive salt input, calcium- and magnesium-dominated exchange complexes are maintained.

Overall, the observed differences reflect the spatial heterogeneity of soil chemical conditions within the study area. Profile 1 was characterized by moderate concentrations of major exchangeable cations, increased calcium variability, and a localized magnesium maximum, indicating heterogeneous distribution of exchangeable bases. Profile 2 represented the most chemically contrasting soil profile, characterized by the highest accumulation of exchangeable potassium and the highest average magnesium content while maintaining relatively stable calcium levels. Profile 3 demonstrated the most balanced distribution of exchangeable cations with the lowest variability among measured parameters, indicating more stable conditions of soil exchange complex formation.

The obtained results suggest that differences in exchangeable base composition among soil profiles may be related to variations in soil texture, carbonate content, and elemental migration processes under the arid soil-forming conditions of the southeastern Kyzylkum Desert.

3.3. Spatial variability of soil chemical profiles

Radar analysis of integrated soil chemical properties revealed pronounced differentiation among the investigated soil profiles, reflecting the heterogeneity of soil-forming processes and the distribution of major components of the soil environment within the natural habitats ofBryonia melanocarpa. The results indicate that each profile possesses a specific combination of chemical characteristics, forming an individual soil chemical “signature” (Figure 6).

Figure 6
Comparative assessment of soil chemical profiles based on normalized physicochemical parameters (CaCO₃, EC, pH, CEC, available P, and exchangeable cations) in Bryonia melanocarpa habitats.

The most distinctive features were observed in Profile 1, which exhibited the highest relative content of carbonate compounds (CaCO₃). After normalization of values within the range from 0 to 1, the carbonate index in this profile reached approximately 0.75, substantially exceeding the values recorded for Profile 2 (~0.35) and Profile 3 (~0.45). The high carbonate content represents one of the major characteristics of Profile 1 soils and indicates intensive accumulation of carbonate compounds under arid climatic conditions. Such a distribution pattern is typical of desert ecosystems, where limited precipitation, high evaporation rates, and weak downward water movement contribute to the preservation and accumulation of carbonates within the soil profile.

Elevated CaCO₃ concentrations significantly influence a range of soil chemical properties, including buffering capacity, soil reaction, and nutrient availability. In calcareous soils, a considerable proportion of phosphorus may become transformed into less plant-available forms due to interactions with calcium compounds, potentially limiting phosphorus bioavailability. This pattern is consistent with the obtained results, showing that Profile 1, despite its high carbonate content, exhibited moderate available phosphorus concentrations and relatively moderate cation exchange capacity (CEC) values.

In contrast, Profile 2 was characterized by the strongest influence of soluble salts, as indicated by elevated electrical conductivity (EC) values and the highest pH values among the studied profiles. This combination suggests the development of a more alkaline soil environment with increased concentrations of soluble components. At the same time, CaCO₃ content in this profile was intermediate, indicating that carbonate accumulation was not the primary factor controlling the chemical composition of these soils. Profile 2 also demonstrated the highest concentrations of exchangeable potassium and magnesium, suggesting an enhanced capacity of the soil exchange complex to retain exchangeable nutrient elements.

Profile 3 occupied an intermediate position for most chemical parameters and demonstrated the most balanced distribution of the analyzed characteristics. A distinctive feature of this profile was the relatively high content of available phosphorus and an increased proportion of fine-textured fractions, which may contribute to greater sorption capacity and improved retention of nutrient elements. At the same time, CaCO₃ content remained lower than in Profile 1, indicating a less pronounced carbonate accumulation regime.

Overall, the spatial variability of soil chemical properties is determined by the complex interaction of carbonate accumulation, soluble salt composition, soil texture, and the capacity of the soil exchange complex to retain nutrients. Among the investigated parameters, CaCO₃ content represents one of the most diagnostically significant factors for distinguishing soil profiles in the southeastern part of the Kyzylkum Desert. The pronounced carbonate accumulation in Profile 1 reflects specific soil-forming processes under extreme aridity, whereas differences between Profiles 2 and 3 are primarily associated with variations in salinity regime, nutrient availability, and textural characteristics.

The obtained results demonstrate that chemical heterogeneity of the soil environment represents an important ecological factor influencing the habitat conditions and distribution ofBryonia melanocarpawithin desert ecosystems of Central Asia.

3.4. Soil particle-size distribution and textural characteristics

The analysis of particle-size distribution revealed pronounced differences in the proportions of soil mechanical fractions among the three investigated profiles, reflecting the heterogeneity of soil physical properties and water-physical regimes. Sand fractions constituted the dominant component of the solid phase in all studied soils; however, their relative proportions differed considerably among profiles (Figure 7).

Figure 7
Comparative analysis of soil texture based on the distribution of sand, silt, and clay fractions among soil profiles ofBryonia melanocarpahabitats.

Profile 1 was characterized by the dominance of the fine sand fraction (0.25-0.10 mm), which accounted for up to 67% of the total soil mass. The proportion of medium sand (0.50-0.25 mm) was comparatively lower, reaching approximately 30%. This distribution pattern indicates a light-textured soil with high infiltration capacity and limited ability to retain moisture and dissolved nutrients. The content of fine particles (<0.05 mm) was minimal in this profile, suggesting weak development of the clay component and low sorption capacity.

In Profile 2, a redistribution of sand fractions was observed compared with Profile 1. The proportion of fine sand decreased to 44%, whereas the contribution of medium sand increased to 52%. At the same time, a slight increase in silt and fine-textured fractions was recorded, indicating a more complex particle-size composition and potentially greater capacity for moisture and nutrient retention.

The most pronounced textural changes were observed in Profile 3, which exhibited the heaviest and most fine-textured composition among the studied soils. Medium sand (0.50-0.25 mm) represented the dominant fraction, accounting for approximately 59%, while the proportion of fine sand decreased to 36%. In addition, this profile demonstrated the highest accumulation of particles smaller than 0.05 mm and the 0.10-0.05 mm fraction, indicating an increased contribution of silt and clay components. Such a texture promotes higher sorption capacity, improved water retention, and greater ability of the soil to preserve available nutrient forms.

Coarse fractions (2-1 mm and 1-0.5 mm) occurred only in minor amounts across all investigated profiles and did not significantly influence the overall physical properties of the soils.

Overall, the particle-size composition of the studied soils demonstrated a gradual increase in textural fineness from Profile 1 to Profile 3. Profile 1 represents the lightest sandy soil with high filtration capacity, Profile 2 occupies an intermediate position, whereas Profile 3 is characterized by a heavier texture with enhanced water-holding capacity and sorption properties. The observed textural differences may substantially influence moisture distribution, nutrient accumulation, and the formation of suitable ecological conditions forBryonia melanocarpain the arid ecosystems of the southeastern Kyzylkum Desert.

4. Discussion

The obtained results are consistent with current concepts regarding the role of edaphic factors in shaping desert ecosystems. Glazovskaya (2012) and Moustafa et al. (2026) demonstrated that spatial heterogeneity of soil conditions represents one of the key factors determining plant community structure and species distribution in hyper-arid deserts. Recent studies further indicate that soil habitat properties play a fundamental role in regulating plant-environment interactions. Munns and Tester (2008) and Peng et al. (2026) showed that variations in soil conditions significantly influence elemental cycling processes and functional characteristics of rhizosphere microbial communities associated with ephemeral plants.

Similarly, the present study demonstrated that the habitats ofBryonia melanocarpaare characterized by pronounced heterogeneity in soil physicochemical properties, expressed through differences in carbonate content, cation exchange capacity, particle-size composition, and the distribution of exchangeable cations among the studied profiles. The most contrasting characteristics were observed in Profile 1, which exhibited high carbonate accumulation and the maximum cation exchange capacity, confirming the important role of edaphic factors in shaping the ecological niche of this species in the southern part of the Kyzylkum Desert.

The results demonstrate that soils associated with natural populations ofB. melanocarpain the southern Kyzylkum Desert exhibit pronounced spatial and vertical heterogeneity, which is a typical feature of arid ecosystems in Central Asia. In desert environments, vegetation distribution is controlled not only by climatic factors but also by local soil characteristics, including particle-size composition, carbonate accumulation, soil reaction, exchangeable base content, and nutrient availability. Previous studies have shown that changes in hydrological regimes, climate variability, and degradation processes substantially affect ecosystem structure in Central Asia, particularly in arid regions where soil characteristics represent one of the major factors determining vegetation stability (Budnikov, 2001; Lioubimtseva and Henebry, 2009; Chen et al., 2013; Yu et al., 2019).

The soils ofB. melanocarpahabitats exhibited slightly alkaline to alkaline conditions, with pH values ranging from 8.2 to 8.8, which corresponds to general patterns of soil formation in desert regions of Kazakhstan. Similar pH values were reported by Mamurova et al. (2025) for soils associated with populations ofZygophyllum fabagoin the Ili-Balkhash region, where soil pH ranged from 8.4 to 8.9. The authors attributed the alkaline character of these soils to intensive carbonate accumulation, low precipitation levels, and limited removal of soluble compounds. These processes are also characteristic of the southern Kyzylkum Desert, where high evaporation rates and water deficiency promote carbonate accumulation within soil profiles.

The present study confirms this pattern, as the highest carbonate content was detected in Profile 1, where the normalized CaCO₃ index reached approximately 0.75, substantially exceeding the values recorded for Profile 2 (~0.35) and Profile 3 (~0.45). High carbonate content represents one of the most important characteristics of the studied soils. Under arid conditions, carbonates act as a major component of the soil system, influencing buffering capacity, soil reaction, and nutrient availability.

5. Conclusions

The soils of natural habitats of Bryonia melanocarpa in the southern part of the Kyzylkum Desert are characterized by slightly alkaline to alkaline conditions (pH 8.2-8.8), relatively low cation exchange capacity, and a predominance of exchangeable calcium within the soil exchange complex, which corresponds to the characteristics of arid calcareous soils.

The most pronounced physicochemical differences were observed in Profile 1, where the surface horizon exhibited the highest cation exchange capacity (7.35 cmol(+)/kg), increased concentrations of exchangeable magnesium and potassium, and the highest carbonate content, reflecting intensive carbonate accumulation under dry climatic conditions.

All investigated soil profiles demonstrated a consistent increase in soil alkalinity with depth accompanied by a simultaneous decrease in available phosphorus content, indicating the accumulation of available phosphorus forms primarily in the upper soil horizons as a result of biological processes.

Soil particle-size composition differed substantially among the profiles: Profile 1 was dominated by fine sand fractions associated with high water permeability, whereas Profile 3 exhibited increased proportions of medium sand and fine-textured fractions, contributing to greater potential water-holding capacity and soil sorption ability.

The obtained results demonstrate pronounced spatial heterogeneity of soil conditions within the habitats of B. melanocarpa. The most important edaphic factors determining the ecological conditions for species occurrence include soil carbonate content, particle-size composition, and patterns of exchangeable cation distribution, which collectively regulate soil water regime, nutrient availability, and the functioning of the soil exchange complex.

These findings expand current knowledge of the ecological requirements of B. melanocarpa in desert ecosystems of Central Asia and provide a scientific basis for further investigations into plant adaptation to arid environments, as well as for the development of conservation strategies for natural populations of this species.

Data Availability Statement

The data supporting the findings of this study are available within the article.

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*

e-mail: [e-mail]

Editor:

Takako Matsumura Tundisi

Publication Dates

• Publication in this collection
  21 Sept 2026
• Date of issue
  2026

History

• Received
  23 July 2026
• Accepted
  21 Aug 2026