ROLE OF THE BRYOPHYTE COVER IN ACCUMULATION OF THE BIOGENIC ELEMENTS IN TECHNOGENIC SUBSTRATE ON THE TERRITORY OF SULFUR EXTRACTION

Kyyak N.Ya., Baik O.L.

Institute of Ecology of the Carpathians, NAS of Ukraine

11, Stefanyk St., Lviv 79000, Ukraine

e-mail: kyyak_n@i.ua

Participating of bryophytes in restoration of the devastated territories of sulphur deposits

INTRODUCTION

The problem of termination of technogenic degradations of grounds and its phytomelioration has got global importance and requires the urgent decision. It concerns also the Western region of Ukraine, where during several decades the extraction of sulfur, sand and clay occurs by the open way. Process of formation and development of the plants cover and ecosystems in technogenic landscapes occurs as primary succession. In our primary investigation was shown, that overgrowing of tertiary marly clays, quaternary loams and sandy deposit occurs by the consecutive stages of development of bryophyte communities, which differ by specific structure, structural and functional organization.

Bryophytes possess wide ecological diapason allowing them to populate substrates of technogenic origins which are scarcely or not suitable for the population with vascular plants. The died off parts of gametophytes gradually form humus enriched substrate, what is the important link of primary soil forming process, where mosses play the essential role [1].

Till now the role of bryophytes in restoration of technogenic landscapes of sulphur deposits in the Subcarpathian region of Ukraine was not studied. Our primary investigations have shown that depending on the age of dump, bryophytes formed various, as to their power, communities consisted of 50 bryophytes species. So, the aim of this work was to investigate the influence of mosses cover on accumulation of organic carbon in the dump No1 substrate of Yazivsky sulphur deposit of the State mining-chemical enterprise “Sirka.

MATERIALS AND METHODS

The object of investigation was bryophytes from the dump No 1 of Yazivsky sulphur deposit (L’viv region, Yavoriv district), subordinated to Novoyavorivsk sulphur deposit of State mining-chemical enterprise „Sirka”. 3 moss species were collected for investigation: Barbula unguiculata Hedw., Bryum argenteum L. and Bryum caespiticium Hedw.

The substrate samples under moss cover have been chosen for the experiments and the surface substrate layer of 2-3 cm wide, where the bryophyte cover has the greatest influence, has been analysed [10]. The samples of the base substrate (without plant cover) have been used as control. The investigations have been carried out on 7 investigated dump transects (the dump crest and six transects in the base, on the slope and the top of the north and south slopes) in summer and autumn 2011-2013. The substrate has been chosen in 3 places within experimental plot, the average sample has been mixed and formed.

Determination of organic carbon content in the substrate was fulfilled by I.V. Turyn method in the modification of B.A. Nikityn [6], that is based on oxidation of organic substance by chromium mixture in strongly acidic medium. The optical density of solutions was measured spectrophotometrically on the spectrophotometer Specord 210 Plus having the wave length 590 nm and was expressed in percentage.

All experiments were carried out three times. The obtained results were processed by the methods of statistical analysis [7].

RESULTS

Contemporary subsoil cover of Precarpathian sulphur deposits is heterogeneous as to its mechanical composition and physical and chemical properties. The main rock of the dump No1, which was formed by dump maker of rotor complex during 1970-1989, is tertiary marl clays with admixtures of quaternary rocks. The plant development on such substrates is limited by unstable water regime, the lack of the main nutrition elements (especially nitrogen), high clay density, weak aeration, active erosive processes and other factors [5]. Although on the basis of the latest literary data it is possible to confirm, that general property of embryonic soils on the investigated territory is the formation of lacking power surface organogenic horizon, that shows essential natural potential of the surface ecosystems selfrestoration and renaturalization of the posttechnogenic landscapes of sulphur extraction enterprises [2; 4].

The ability of dump rocks to form fertile soil by 25-30 % depends on the presence of organic carbon in them. Taking into account this fact, the substrate which contains 0.5-1.0 % of organic carbon is considered to be the substrate of fertile ground layer [9]. The process of technogenic lands overgrowing takes place in such a substrate that provides the corresponding level of stable ground ecological functions creates natural preconditions for the development of ground cover on devastated territories. The content of organic carbon in the upper layer of the bare substrate (without plant cover) was 0,9–1,8 % in the territory of the dump No 1 (Table 1). Besides, the tendency to the content decrease of organic carbon from the dump base to the top by 1.5-2.0 times has been found out. First of all, this is caused by the conditions peculiarities on the dump top, which are the least favourable for the plants growth as the result of wind and water substrate erosions, as well as moisture deficit that leads to the slowing down renaturalization processes of rock substrates. Such difference in quantity of organic carbon on the dump top can be caused by washing out the surface substrate layer from the top to the dump base. Thus, the stripping dump No 1 rocks of Yazivsky deposit are potentially fertile and fit for plants overgrowing.

The pioneers of bryophyte species which were used in investigations settling on the dump slopes cause both mechanical and chemical influence on the substrate. First of all, they fix the movable slopes substrate mechanically and prevent it from scattering light fractions. The species that form the life form of dense and loose turf – Bryum caespiticium and Bryum argenteum play a special part in these processes. Besides, the species Bryum caespiticium forms dense rhizoid tomentum, which penetrates into substrate densely, providing plants with additional fixation on the slopes. It has been found out during investigations that rhizoid tomentum reached 2 cm in some turfs Bryum caespiticium. Penetrating into the substrate moss rhizoids form dense net, increasing porosity and promoting enrichment of substrate with oxygen and moisture.

Table 1

Content of organic carbon in the substrate under moss cover on the territory of the dump No 1 (August 2011)

Locality of substrate samples collection under moss turfs	Content of organic carbon, %
	North slope	South slope
Uncovered substrate (control)
crest of the dump	1,72±0,12
base	1,64±0,13	1,82±0,23
slope	1,66±0,21	1,62±0,14
top	1,23±0,10	0,92±0,15
Bryum caespiticium
crest of the dump	4,53±0,21*
base	2,56±0,12*	2,32±0,22*
slope	2,84±0,23*	2,65±0,25*
top	2,36±0,22*	2,04±0,21*
Bryum argenteum
crest of the dump	3,92±0,22*
base	2,56±0,20*	1,94±0,11*
slope	2,73±0,27*	2,43±0,27*
top	2,21±0,24*	2,11±0,23*
Barbula unguiculata
crest of the dump	3,26±0,21*
base	2,15±0,13*	2,04±0,21
slope	2,23±0,21	2,02±0,11*
top	1,95±0,23*	1,56±0,22*

Footnote: – * the difference compared to control (base substrate) is statistically reliable at p<0.05.

According to literature data mosses localize the largest number of carbon in aging brown shoot parts [8], localization of C_org. specificity in moss turfs Bryum caespiticium, Bryum argenteum and Barbula unguiculata has been estimated (Fig. 1). It has been found out that the largest quantity of carbon in accumulated in dead part of moss turfs. C_org. content amounted to 16.3±1.5 % in the dead shoot parts in Bryum caespiticium, in Bryum argenteum it was 14.5±1.3% and 12.5±1.2 % in Barbula unguiculata. The quantity of organic carbon was 3-4 times smaller in green shoot parts of these moss species.

We established direct dependence between bedding thickness and the content of organic carbon in the substrate under vegetable cover in natural moss samples. The maximum content of organic carbon in the substrate under moss cover was determined on the dump crest (3.9-4.5 %).

Fig. 1. The content of organic carbon in green and dead shoot parts of mosses.

The highest content of organic carbon was in the substrate under mosses Bryum caespiticium and Bryum argenteum (2.8±0.2 % and 2.7±0.2 %) on the north slope, that is almost 1,7 times higher compared to the carbon quantity in bare substrate from this dump plot (Table 1).

The carbon quantity was 1.4 times higher under turfs Barbula unguiculata compared to its content in the substrate without turfs. Similar tendency of organic carbon content change in the substrate under investigated moss species has been observed in the slope base as well. The smallest quantity of organic carbon under moss turfs has been found on the top, although comparing to its quantity in bare substrate on this dump plot, its content increased almost 2.4 times, that shows essential bryophyte contribution in accumulation of organic substances even under unfavourable ecological conditions.

The results of determining content of organic carbon in the substrate under moss cover on the south dump No 1 slope show the similar conformity: the highest content is in the substrate under mosses on the slope and in the dump base, and the lowest content is on the top.

The highest quantity of organic carbon is in the substrate under Bryum caespiticium and Bryum argenteum. In general, the quantity of organic carbon has increased 1.5-2.6 times in bedding substrate layer under moss turfs on all dump levels compared to its content in the bare dump substrate.

On the basis of the obtained results it is possible to confirm, that the process of primary ground formation which is on the stage organic substance accumulation in the surface ground layer, occurs with bryophyte participation on the dump territory. Organogenic horizon having thickness of 0-3 cm, characterized by wide range of organic carbon content (1.5-1.7 %) is formed under moss cover.

It is known, that the growth of organic carbon content in technogenic grounds taken place until its losses, as the result of mineralization and washing out processes do not become equal with the entrance of organic substance to the ground block of ecosystems as dead organic remnants. This process can last from 20 to 50 years according to the data of many investigators. Then it continues mainly at the expense of qualitative transformations of organic substance. That is, the total regularity of the processes of organic substance accumulation is the following: relatively rapid accumulation of organic carbon, at the initial period of younds ontogenesis and the following slowing down of humus accumulation rates with the change of components correlation of organic substance [3].

The results of two year analysis of organic carbon content in not populated substrate and the substrate under turfs of investigated mosses show positive dynamics of its increase in all investigated transects, but the rate of accumulation of organic carbon in upper horizons of posttechnogenic ground is different, it depends on the dump territory relief, microclimatic conditions and plants projective covering (Table 2).

Table 2

Content of organic carbon in the substrate under moss cover on the territory of the dump No 1 (August 2013)

Locality of substrate samples collection under moss turfs	Content of organic carbon, %
	North slope	South slope
Uncovered substrate (control)
crest of the dump	1,75±0,12
base	1,71±0,17	1,84±0,25
slope	1,59±0,25	1,65±0,14
top	1,19±0,12	0,92±0,24
Bryum caespiticium
crest of the dump	4,75±0,41*
base	2,70±0,25*	2,45±0,21*
slope	2,95±0,13*	2,48±0,16*
top	2,41±0,2*	2,11±0,10*
Bryum argenteum
crest of the dump	4,06±0,32*
base	2,68±0,15*	2,05±0,18*
slope	2,91±0,32*	2,52±0,23*
top	2,23±0,21*	2,16±0,14*
Barbula unguiculata
crest of the dump	3,36±0,31*
base	2,22±0,11*	2,13±0,21*
slope	2,31±0,22	2,10±0,15*
top	2,01±0,20*	1,56±0,09*

Footnote: – * the difference compared to control (base substrate) is statistically reliable at p<0.05.

The changes of organic carbon content in the uncovered substrate were not essential during this period. The highest indices of organic carbon content in the bedding layer under moss cover have been determined on the crest and in the dump base, especially under the species B. caespiticium with dense turfs, which accumulate organic substances. The tendency of decreasing organic carbon content has been observed in the substrate under moss turfs from the base to the dump top of the north and south exposition as before.

Conclusion

Bryophyte cover provides the formation of humus horizons on the surface of technogenic substrates that is connected with the character of the dump substrate population by moss turfs which form the whole dense cover on the dump substrate surface. Colonizing technogenic exfoliation bryophytes perform complex action on the dump substrate:

– They initiate the processes of upper horizons structuring (under moss cover technogenic soil is loosened, acquires coarse lumplike structure, its porosity increases, that promotes substrate enrichment with oxygen and moisture.

– On the slopes mosses fix movable substrate mechanically and prevent scattering of its light particles.

– Mosses accumulate organic substance.

Taking into account the fact, that moss turfs overgrow and are concentrated in the upper layer 0-3 cm of the ground substrate, it is natural that almost all organic substances which are the potential source of humus at the initial stage of ground formation are concentrated on the surface or in the ground having the thickness of 0-3 cm, where the process of their mineralization and humus formation take place.

The high variability of organic substance content is determined by both specific moss peculiarities and the microconditions on the dump territory. The highest content of organic carbon in the upper dump horizons has been established under moss species which have the life form of short dense (or friable) turf B. caespiticium and B. argenteum. The lowest indices of organic carbon content have been determined on the dump top that may be caused by both tension of ecological factors on this plot (high insolation level, moisture deficit), and the periodic transference of upper horizons of ground formation substrate down the slope as the result of morphodynamic processes characteristic of technogenic landscapes.

The rate of humus formation in upper horizons of posttechnogenic ground on the dump territory is different, it depends on the microrelief, microclimatic conditions, projective bryophytes covering and their species composition. On the basis of organic carbon content monitoring during 2011–2013, the accumulation rates of carbon within the investigated plots amounted to 0.02–0.10% C_org.per year on the average. The changes of organic carbon content in the uncovered substrate were not essential during this period. The highest indices of organic carbon content in the bedding layer under moss cover have been determined on the crest and in the dump base, especially under the species B. caespiticium with dense turfs, which accumulate organic substances. The tendency of decreasing organic carbon content has been observed in the substrate under moss turfs from the base to the dump top of the north and south exposition as before.

It is obvious, that essential changeability of organic carbon accumulation rate can be caused by the fact that essential part of organic substance on the dump territory is represented by humus compounds and not decomposed organic remnants (mainly by the dying off products of moss turfs and by the introduced falling of vascular plants). This can point to the slow mineralization of plant remnants as the result of specific hydrological conditions and unripeness of microorganism groups, which are the main destructors of organic remnants.

Thus, the common property of young soil on the dump No 1 of Yazivske deposit sulphur extraction is the appearance and development of not intense surface organogenic horizon. At the early stages of ground formation bryophytes as pioneer plants play the key role in this process promoting accumulation of organic substance and in this way creating the conditions for the development of other higher plants and soil biota.

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