Soil ecomorphs as a form of adaptation to the conditions of biogeocenosis

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Soil ecomorphs as a form of adaptation to the conditions of biogeocenosis

Galyna Zadorozhna

The spatial variability of the mechanical impedance of ordinary chernozem have been investigated within a regular grid (105 points). Ecomorphic analysis of the vegetation in each cell of the grid has been done. Cluster analysis, conducted on the basis of the statistical data allowed to distribute the existing changes in soil mechanical profiles in three clusters with characteristic for them, relative to the same type of dynamic properties. Environmental separation content of the soil plots on clusters studied using discriminant and variance analyzes. Statistical significance of variations of external properties associated with the spatial heterogeneity within soil plots belonging to different clusters allows them to be meaningfully interpreted and confirms the formation of ecological nature of the identified soil structures-ecomorphs.

Key words: soil penetration resistance, morphological features, environmental factors.

Задорожная Галина. Почвенные экоморфы как форма адаптации к условиям биогеоценоза. Исследуется пространственная вариабельность твердости чернозема обыкновенного по регулярной сетке (105 точек). Произведен экоморфический анализ растительности в каждой ячейке полигона. Кластерный анализ, проведенный на основе полученных статистических данных, позволил распределить имеющиеся профили изменения твердости почвы в три кластера с характерной для них относительно однотипной динамикой свойства. Экологическое содержание разделения участков почвы на кластеры изучено с помощью дискриминантного и дисперсионного анализов. Статистическая значимость изменений внешних признаков, сопряженных с пространственной неоднородностью почвенных участков, принадлежащих к разным кластерам, дает возможность их содержательного описания и подтверждает формирование экологического характера выявленных почвенных структур - экоморф.

Ключевые слова: твердость почвы, морфологические элементы, экологические факторы.

Задорожна Галина. Ґрунтові екоморфи як форма адаптації до умов біогеоценозу. Досліджено просторову варіабельність твердості чорнозему звичайного за регулярною сіткою (105 точок). Проведено екоморфічний аналіз рослинності. Кластерний аналіз, виконаний на основі отриманих статистичних даних, дав підставу розподілити наявні профілі зміни твердості ґрунту в три кластери з характерною для них відносно однотипною динамікою властивості. Екологічний зміст поділу ділянок ґрунту на кластери вивчено за допомогою дискри- мінантного й дисперсійного аналізу Статистична значимість змін зовнішніх ознак, пов'язаних із просторовою неоднорідністю ґрунтових ділянок, що належать до різних кластерів, уможливлює їх змістовий опис та підтверджує формування екологічного характеру виявлених ґрунтових структур - екоморф.

Ключові слова: твердість ґрунту, морфологічні елементи, екологічні фактори.

1. Formulation of Scientific Problem and its Significance

vegetation ecomorphic black soil

The core problem of biogeocenology is the study of the nature and depth of interaction between the living and bone components of the biogeocoenosis. Connections between the components of biogeocenosis determine its structural and functional organization. Among the regulatory mechanisms, the intraspecific and interspecies interconnections of plants, which are associated with trophic dependencies and transformation of environmental conditions, are of fundamental importance [2]. As a component of biogeocenosis, vegetation appears for a system of eco-morphs which are certain adaptations of individual species to the biocenosis taken as a whole and to each of its building blocks. The system of ecomorphs for the steppe of Ukraine, in which cenomorphs, adaptations of species to phytocenosis taken as a whole, appear for ecology-cenotic groups, was developed by A. L. Bel'gard in details [2; 18]. One of the branches of the development of this doctrine is the research workon the biotope phytoindication method, which is based on the fact that phytocenosis forms in a certain biotope as a result of adaptation to a complex of environmental effects, and the amplitude and frequency of certain species reflects adaptation to environmental factors that determine this cenosis. The referring of the species to a particular cenomorph is determined expertly on the ground of an analysis of their frequency in different types of phytocenosis. So, for example, plant species, which living conditions are optimal in the steppe, are called steppe species, those ones on the meadow are calledmeadow species, those ones in the forest are calledsilvants etc. Unified phytoindication scales [8; 18], one of which is the working system of cenomorphs, which was proposed in a report of the flora of the Dnepropetrovsk and Zaporozhye regions, are used as a matter of practice [22]. Phytoindication scales based on data for plant species preferences for climatic and edaphic characteristics of the growing area (temperature, light intensity, occurrence of nutrients, humidity, etc.) are a convenient tool for environmental evaluation, since they require far fewer labor contribution than a direct measurement of its climatic and edaphic parameters.

Zoologists, in their turn, developed a method of zoological diagnostics of soils. Taxonomic groups of large soil invertebrates are used in it as reliable indicators of the condition of natural communities [1; 11; 14; 27]. The ecomorphic approach, both in phytodiagnostics and in zoodiagnostics, is based on the frequency of species in biogeocenoses of various typesand uses information on the population requirements for environmental parameters.

In accordance withthe doctrine of biogeocenosis, the soil is a fullfledged component of it. Moreover, the soil has a special status of the bio-inert body. Many characteristics (for example, metabolism and exchange of energy), which are found in living beings, characterize the soil. G. M. Minkovskysuggests multi-level morphoelements of the soil to be considered as parts of the living organism, which are a functional whole: their functioning is consolidated ina single process. The scientist believes that the division of objects into «living» and «lifeless» does not matterin structural problems, the concept of «living» has a moral meaning. Authors [17; 19] suggest to search for new forms of soil material activity at the morphological level of the organization. We believe that the heterogeneity of soil properties is a phenomenon, while studying which it is possible to come to grips with the objective laws of the existence of soil as a component of biogeocenosis. The above-mentionedmakes it necessary to develop an eco-morphological approach in the study of soil as a component of biogeocenosis. In addition to the above, it is important to select the criteria against which the changesintervening in the soil caused by soil formation factors in the time dimension,which is typical for the variability of the bi-cenotic components, could be measured. Mechanical impedance of the soil is such a criterion. Spatial and temporal dynamics of impedance correlates with variations of the majority of soil characteristics which create conditions for plant growth and habitat for soil fauna [1; 16; 28; 32]. Therefore, impedance is anadequate diagnostic sign that can act as an integrated index of the state of the soil body [6; 20].

The objective of this paper is to evaluate the relationship between the spatial variation of the mechanical impedance of chernozem and environmental factors by means of the use of phytoindicator scales.

Materials and Methods. The collection of mechanicalimpedance data and the description of the vegetation was carried out on April 19, 2013 at a steppe site located on the upper part of the South-East slope of the ravine Kamyanistaya exposure (southern suburb of the Dniprocity, 48°38'67" south latitude, 35°09'05"westem longitude). The plot is located along the slope with an angle of 15°, from above it is bounded by a wood line and agricultural field adjacent to the range. The study was carried out on a regular gridwith 7x15 sample points, the distance between which is 3 m. Accordingly, the size of the range is 42 m x 18 m.

Studied soil was typical eroded high-carbonate mediumheavy-loamy on loess-like clayschernozem. This area is not used for economic operations.

Mechanical impedance of the soil was recorded using a cone-penetrometer Eijkelkamp. The average error of device measurement results was ± 8 %. Measurements of the mechanical impedance of the soil were made by a cone of cross-section 2 of cm2 in each cell of range to a depth of 50 cm at intervals of 5 cm (10 impedance indices in each of the 105 points of the plot).

To assess the environmental conditions, phytoindication scales were used [8]. They are based on a description of the abundanceof vegetation and provide an opportunity to assess the environmental conditions according to both climatic and edaphic characteristics. The phytoindication method uses the data of the species representation in the plant cover within the plot and the scope of species tolerance to particular environmental factors, in other words, the range of ecological minima and maxima scope. The group of edaphic factors were presented by such soil hydration indexesas Hd - soil humidity, fH - variability of moisture, which takes is sensitive to the amplitude of change in the soil moisture index, Ae - aeration of soil, Rc - acidity, Sl - total salt regime, Ca - carbonate content in soil and Nt - nitrogen content. The group of climatic factors were presented by such parameters of thermal characteristics of the soil as Tm - thermal climate, Om - humidity, Cr - cryoclimate and Kn - climate continentality, which is considered asthe value of the function of annual amplitude of air temperature. Besides these specified factors, Lc - light in plant community was considered as a microclimatic scale.

A large number of researchers have proved that plant communities are more accurate and better indicators than selected specieswhich are characterized by a wider ecological amplitude and, as a rule, belong to different types of communities. Therefore, for a more complete indication, the scales of the coenomorphs by A. L. Bel'gard [2] and V. V. Tarasov [22] were given in the paper. They provide an opportunity to estimate the biotopes as a whole [18, 23] and in regardto some of the environmental factors [13]. Cenomorphs are represented by steppe species, meadow species, psammophytes, plants which live in sand, silvants, which are forest species, ruderants, which are ruderal species. Steppe speciesand meadow species form the majority of the vegetation cover, therefore just these ecomorphs were used as predictors of the soil mechanical impedance (variables St and Pr represent the ecomorphs' projective cover, %).

Quantitative characteristics of the representation of ecological forms of plants with different preferences for humidity of environment are characterized by a hygromorph scale. Hygromorphs were represented by xerophytes (humidity level 1), mesoxerophytes (humidity level 2), xeromesophytes (humidity level 3), mesophytes (humidity level 4) and hygromesophytes (humidity level 5). The humidity index (Hygr) was estimated as:

where i - humidity level; Pi - hygromorphs projective cover of corresponding humidity level. Trophomorphs are ecomorphs, adapted to certain trophotopes. In the plant community within the plot, they were represented by oligotrophs (trophicity level 1), mesotrophs (trophicity level 2) and megatrophs (trophicity level 1). The trophicity index (Troph_B) was estimated as:

where j - trophicity level; Pj - trophomorphs projective cover of corresponding trophicity level.

Plants may be classified ecologically, according to their requirement of light. Such ecological groups are named as heliomorphswhich were represented within the plot by heliosciophytes (solar radiation level 2), sciophytes (solar radiation level 3), and heliophytes (solar radiation level 4). The solar radiation index (Hel) was estimated as:

where z - solar radiation level; Pz - heliomorphs projective cover of corresponding solar radiation level.

In statistical calculations, descriptive statistics, geostatistical, cluster, dispersion and discriminant analyzes were used.

Results and its Discussion. Mean values of the mechanical impedance of studied soil increased with depth, from 1,34 ± 0,04 MPa to 1,60 ± 0,03 (table 1). The layer of 10-15 cm from the surface exhibits the lowest level of the mechanical impedance, the deepest studied layer of 45-50 cm exhibits the highest level of the mechanical impedance. When moving downwards on a profile, the mechanical impedance as a whole tends to increase. The coefficient variation of the indicators differs significantly in the layers of 5-10 and 10-15 cm downwards on a profile, where it is the highest (31,40 and 30,42 %). The parameters of the layers located above and below are less variable, the coefficient variation ranges from 17,89 to 22,77 %.

Table 1 Mechanical Impedance of Soil: Descriptive Statistics

Explanation of Symbols. x - mean (MPa), SE - standard error, CV - coefficient variation (%), SDL - spatial dependence level (%), R - radius of influence (m).

The descriptive stage of the study gives an idea of average profile, the characteristics of which are too approximate, as evidenced by the difference in the coefficients variation related to the data of different soil layers. For deeper analysis of the regimentation of soil mechanical impedance indicators, geostatistics tools were used. With their help, the degree of spatial dependence of the mechanical impedance data was determined layer-by-layer, that is, spatial relation of SDL. When interpreting it, it should be taken into account that if its level is within the range from 0 to 25 %, then it is a case of strong spatial dependence; if it is within the range from 25 to 75 %, the dependence of the variable is moderate; if it is greater than 75 %, the variable is considered to be weakly spatially dependent [22; 25]. According to the results of our studies, the mechanical impedance of chernozem comes with a high degree of spatial dependence in the surface layer, a weak one in the layer of 40-45 cm from the surface and the middle one in all other layers of the studied soil depth.

Cluster analysis based on the obtained geostatistical data provided an opportunity to sort conditionally provided profiles of the soil mechanical impedance (105 points) into four clusters with relatively single-type dynamics of characteristics which is specific to them (fig. 1). The proximity of sites was measured in the Euclidean distance. As a merge rule, the Ward's Method was used.

Fig. 1 Clusteranalysison Mechanical Impedance, Ward's Method, the Euclidean Distance Note. The Rectangles Indicate the Amount of Clusters For a Solution of 4 Clusters

Division into clusters provided an opportunity to organize the observed data into demonstrative structures, for a meaningful description of the differences between them. Sites belonging to the same cluster are characterized by the same change in the mechanical impedance with a penetration. Figure 2 shows the dynamics of the soil mechanical impedance along the profile for each of the selected clusters.

Fig. 2 Changeinthe Mechanical Impedance with a Penetration Along the Profile Typical for the Different Clusters: by the Abscissa Axis, Clusters Numbers are Indicated, by the Ordinate Axis, Soil Mechanical Impedance, MPA is Indicated