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QUANTITIES OF INDOLE-3-ACETIC ACID IN SECONDARY TRANSFORMD PEAT-MOORSH SOILS
* Research Center for Agricultural and Forest Environment, Polish Academy of Sciences * Institute for Problems of Natural resources Use and Ecology, National Academy of Sciences of Belarus
INTRODUCTION
Long-term cultivation and agricultural use of peat-lands and their exploitation has revealed to a number of effects including lowering of the water table, increased aeration, and changes in plant communities, and the release of carbon. These processes show the disturbance of the thermodynamic balance in peat. The decline in peat soil moisture content resulting from drainage leads to shrinkage of the peat. Volume change due to shrinkage is the result of several forces acting at micro-scale, and its mechanism and magnitude differ from those in mineral (clay) soils. Drainage in particular results in a sharp change of biotic and abiotic conversions and consequent degradation of peat organic matter. In general, this leads to the progressive differentiation of the hydrophobic peptides and total amino acid contents.
Plant growth-regulating compounds call phytohormones, represent wide group of substances produced by plants and microorganisms in the rhizosphere that enhance seed germination and plant growth [1, 2]. These substances are synthetized in one part of the plant and translocated to another part to influence a whole range of physiological and developmental processes at low concentrations. These compounds stimulate plant growth, biofertilization (fixation of atmospheric N2 or solubilization of nutrients) and can protect against plant pathogens. Numerous plant processes are know to be controlled by plant growth regulators, but
the mechanisms of control have remained elusive [36].
Indole-3-acetic acid (IAA) belongs to phytohormones-auxin (Fig. 1). IAA is formed in soils mineral and organic soils (peat, moorsh and sapropels) from tryptophane by enzymatic conversion (Fig. 2) [7-10].
Fig. 1. Indole-3-acetic acid (IAA)
This substance is also created during natural conditions in compost and in inorganic and organic soils under different cultivated plants [11-14]. Some kinds of peat and sapropels are commonly used for the preparation of organic fertilizers for agriculture, horticulture, floriculture, and pomology as well as for substrate and growing media. Therefore, the investigation of IAA is very important.
This compound seems to play an important function in nature as result to its influence on regulation of plant growth and development [6, 7]. A principal feature of IAA is its ability to affect growth, development and health of plants [14]. This compound activates root morphology and metabolic changes in the host plant. The physiological impact of this substance is in-
(B) Decarboxylase
CO2 CH2CH2NH2
-CH2CHCOOH (A) Oxydase
NH2
Tryptophane (C) Peroxydase
3-(2-aminoethyl)-indole
H2O
NH3
ox,U
CH2COCOOH
N
indole-3-pyruvate acid
CO2
CH2CHO
3-indoleacetanal
Indole-3-acetic acid
Fig. 2. The formation of indole-3-acetic acids from tryptophane in soil
volved in cell elongation, apical dominance, root initiation, parthenocarpy, abscission, callus formation and the respiration [15, 16].
The aim of this work was to estimate the content of indole-3-acetic acid in different Polish peat- moorshes utilized as meadows
MATERIALS AND METHODS
Samples of peat-moorsh soils were taken from Czarna Wies, Otoczne and Kwatera 17 sites located in the Middle Biebrza Basin (Poland). The sites can be characterized as follows:
- Czarna Wies - peat-moorsh soil profile with low degree of decomposition (sedge-moss peat) with a minor influence of a drainage system, and with significant surface level changes, used as an extensive meadow;
- Otoczne - peat-moorsh soil profile with medium degree of decomposition (sedge-reed peat) with only the influence of a drainage system, used as an extensive meadow;
- Kwatera 17-peat-moorsh soil profile with medium degree of decomposition (alder peat) located in a drainage sub-irrigation system with managed groundwater level, used as an intensive meadow.
Samples were collected at two different depths: the first 5-10 cm and the second in the layer 45-80 cm (Table 1).
Table 1
The depth of sampling and basic characteristic of peat-moorsh soils
Place of sampling Sampling depth [cm] Soil type Degree of decomposition in von Post scale
Czarna Wies 5-10 Moorsh -
50-70 sedge-moos peat H1
Otoczne 5-10 Moorsh -
45-50 sedge-reed peat H5
Kwatera 17 5-10 Moorsh
70-80 alder peat H6
Soils were sampled in 10 replications for each layer at each site. Samples were air dried and crushed to pass a 1 mm-mesh sieve. These 10 replications collected for each layer were mixed in order to prepare “mean sample”, which then was used for the potentio-metric determination of pH (in H2O and in 1M KCl) and for the measurements of dissolved organic carbon (DOC) as well as total organic carbon (TOC). Twice distilled water from silica glass equipment was used for the laboratory analysis. For the investigation of DOC, soil samples were heated in redistilled water in
the temperature of 100 °C by two hours under reflux condenser. Extracts were separated by using the mean filter paper and analysed on TOC 5050A equipment produced by Shimadzu, Japan [17, 18].
IAA was extracted from air-dry soil samples with methanol, and its concentration was determined by spectrofluorimetric method with ^excitation= 290 nm and Xemission= 368 nm (Szajdak, unpublished data).
All the experiments were run in triplicate, and the results were averaged. All the chemicals used in this study were of analytical grade. The precision based on replicate analyses, were ±0.01 for pH measurements, ±3 % for TOC, ±3 % for DOC, ±4 % for IAA, ±3 %.
RESULTS AND DISCUSSION
Chemical and biochemical as well as and physical processes in peat are of catalytic character. Thus, these processes and their mechanisms occurring in peat forming plants are significantly dependent on the properties of the environment. The considered peat-moorsh soils with pH (in H2O) ranging from 5.05 to 6.02 belong to middle acidic. However, the samples taken from upper layer (5-10 cm) of Kwatera 17 soil profile
It can be seen from the data presented in Table 2, that no significant concentrations of TOC were detected in the investigated moorsh soil samples collected from the layer 5-10 cm. These concentrations ranged from 37.19 % to 38.20 %. The highest amount of TOC equal to 38.20 % was measured for the sample from Kwatera 17. The lowest content of TOC equal to 37.17 % was measured for Czarna Wies soil.
It was observed that all samples collected from the peat layers located at the depth from 45 to 80 cm were characterized by higher contents of TOC in comparison with moorsh samples collected from 5 to 10 cm. The concentration of TOC for the depth 45-60 cm ranged from 40.2 % to 45.5 %. The highest amount of TOC equal to 45.5 % was determined for the sample collected from Otoczne and the lowest value equal to 40.2 % was determined for the sample collected from Kwatera
17. Generally, the sample collected from Kwatera 17 from the moorsh layer (5-10 cm) characterized the highest content and the peat sample collected from 7080 cm for the same profile characterized the lowest concentration of TOC from all of investigated samples.
represent very acidic properties, the most acidic among investigated soil layers (Table 2).
Soil organic matter is a critical component of the soil-plant ecosystem. It constitutes the major part of organic carbon. There are different class of biogenic, heterogeneous, dynamics and refractory organic compounds, characterizing various contents of C and N having molecular structure. A principal feature of organic matter is its ability to absorb and retain water molecules. Depletion of organic matter causes a loss of water holding capacity, poor aggregation, acceleration of soil erosion, poor retention of applied nutrients as well as reduced soil biological and enzymatic activities. Changes of land use changes or agricultural management lead to changes in soils organic matter content [17]. Drying of peat as a result of agricultural use leads to considerable shrinkage, activation of erosion, decrease of the nutrients content as well as decrease of the biological and enzymatic activities. Shrinkage of peat increases with the increase of the peat decomposition and humification degree. Thus, shrinkage of peat is related to its humic components [19].
Several products of hydrolysis of peat humic substances were studied for their relevance to molecular structure and to changes occurring during humification. Primary polysaccharides, representing undecomposed plant carbohydrates, can be converted to lev-ulinic acid on prolonged hydrolysis. However, humic substances yield higher levels of levulinic acid than those obtainable by conventional methods of carbohydrate hydrolysis. This excess is attributed to altered carbohydrates, presumably attached to the humic acid molecular structure. The primary polysaccharides in pyrolysis studies are associated with dianhydromon-osacharide fragments, whereas secondary polysaccharides yield furan fragments. The fen peat showed a steady increase of nonpolypeptide nitrogen with increasing depth. The loss of some of phenolic compounds and fulvic acids components by natural drainage of the bog waters may account for the apparent changes in organic matter content with advanced humification [19].
Dissolved organic matter can contribute significantly to cycling of soil nutrients. It can be a substrate
Table 2
IAA and chemical characteristics of peat moorsh soils
Place of sampling, pH TOC DOC IAA
depth of sampling in cm, H2O 1 N KCl [%] [%] ^g kg-1 dry mass
Czarna Wies 5-10 cm, 5.54 5.19 37.19 12.81 110.1
Czarna Wies 50-70 cm, 5.66 5.16 44.02 5.80 86.1
Otoczna 5-10 cm 6.02 5.46 38.10 10.80 122.7
Otoczna 45-50 cm, 6.10 5.63 45.58 7.55 87.1
Kwatera 17; 5-10 cm 5.05 4.70 38.20 19.39 128.7
Kwatera 17; 70-80 cm, 5.88 5.39 40.23 5.34 69.3
TOC - total organic carbon, DOC - dissolved organic carbon, IAA - indole-3-acetic acid
for microbial growth, but its production is also partly mediated by microbes. This fraction is responsible for the microbiological activity [17, 18]. It was shown relationship between the content of dissolved organic carbon and the amount of CO2 evolution from soils to the atmosphere. This fraction of organic carbon is also connected with the movement of xenobiotics in soils. Because of that it seems to be very important to know the actual quantity of this fraction in soils.
It was shown for all investigated peat-moorsh soil samples that the concentrations of DOC, on the contrary to TOC concentrations, decreased with the increase of the depth of the soil profiles (Table 2). The amounts of DOC measured for 0-10 cm depths ranged from 10.80 % to 19.39 %. The highest content of DOC equal to 19.39 % was determined for moorsh sample collected from Kwatera 17, and the lowest equal to 10.8% for the sample collected from Otoczne. The samples collected from peat layers located at depth from 45 to 80 cm revealed lower contents of DOC lower than in moorsh layers, which ranged from 5.34 % to 7.55 %. Contrary to TOC measurements the moorsh sample from Kwatera 17 representing depth 0-10 cm was characterized by the highest concentration of DOC, but the peat sample collected from depth 70-80 cm showed the lowest content.
The concentrations of IAA in high layers of all investigated peat-moorsh soils utilized as meadows were higher than in deeper layer and ranged from 110.1 to 128.7 ^g kg-1 dry mass (Table 2). The highest content of IAA was determined in peat-moorsh soil
from Kwatera 17 and was equal to 128.7 kg-1 dry mass. The quantities of IAA in deeper layers ranged from 69.3 to 87.1 ^g kg-1 dry mass. It was observed decrease of IAA concentrations with increase of the depth of sampling in all investigated place of sampling. The change of IAA concentration with increase of the depth was also observed in our previous studies [9]. The range between these two layers decreased from 21.8 to 46.2 %. The highest decrease was observed for the place Kwatera 17 and was equal to 46 %. This sample was also characterized the highest value H6 of decomposition degree in von Post scale (Table 1). It was also interesting that the lowest decrease of the concentrations of IAA was shown for the sample taken from Czarna Wies. However, this sample revealed the lowest H1 decomposition degree in von Post scale.
CONCLUSIONS
The study revealed the impact of secondary transformed peat-moorsh soils on the content of IAA. The highest amounts of IAA were observed in the highest secondary transformed peat-moorsh soil, but the smallest in the lowest secondary transformed peat-moorsh soil. The decrease of the concentrations of IAA with increase of the depth of sampling was shown. It was observed the relationship between the concentrations of dissolved organic carbon and IAA in samples of secondary transformed peat-moorsh soils.
Поступила в редакцию 20.02.2008
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