Determination of microbial activity and
nitrogen and carbon forms in peat soils
in Estonia
M. Noormets1,2, T. Köster1, T. Tõnutare1, K. Kauer1, R. Kõlli1
& K. Karp2
1
Department of Soil Science and Agrochemistry,
Estonian Agricultural University, Estonia
2
Department of Horticulture, Estonian Agricultural University,
Estonia
Abstract
For plants in order to grow in different types of peat soils the microbial activity
and the release of nutrients is important. Therefore, it is important to perform the
monitoring of exhausted peat fields and peat lands in their natural state in order
to understand better their pedoecologial conditions. In the present study we
examined different nitrogen and carbon forms, and microbial activity, as well as
several agrochemical parameters in the different peat soils. Five study areas are
located in the county of Tartu (58° 22’ N, 26° 43’ E) in the southern part of
Estonia. One of the study areas is located in the county of Harjumaa (59° 6' N,
25° 22' E) in the north-western part of Estonia. The soil of the experimental
fields belongs to the soil subgroups of Fibri–Dystric Histosol according to the
WRB soil classification (1, 2, 3, 4 study area), with a soil acidity pHKCl 2.7-4.6.
The rest of the soils were Endorupti-Dystric Histosol (5) with pHKCl 2.5-2.7 and
Eutri-Fluvic Histosol (6) with pHKCl 6.5-7.2.
The preliminary results of this study suggest that the differences in the studied
parameters are representative. The study will also provide information about the
possibility to use some peat soils for recultivation. After comparison of the
different ecosystems, the lowest microbial biomass was found in the flood-plain
Eutri-Fluvic Histosol with the lowest content of organic carbon (27.4 %). The
content of available plant nutrients was medium to high while for phosphorus it
was very low or low for all the investigated peat soils starting from 6.8 mg kg-1 at
Fibri-Dystric Histosol in Sangla without plant cover and reaching 36.7 Pavb, mg
kg-1 in Sapi-Lulli covered by V. angustifolium.
Keywords: respiration rate, ash content, total biomass, mineralized N, biomass
C, biomass N, nutrients, peat soils.
Geo-Environment, J. F. Martin-Duque, C. A. Brebbia, A. E. Godfrey & J. R. Diaz de Teran (Editors)
© 2004 WIT Press, www.witpress.com, ISBN 1-85312-723-X
60 Geo-Environment
1
Introduction
The total territory of Estonia is 45 227 km², of which 23% is covered by mires
[22]. It is the largest area of mires in Northern Europe. The total area of mires is
1, 009, 101 ha while in the focus of processors there are 477, 000 ha because of
the peat deposition [28]. The total area of exhausted peat fields will be doubled
in the near future as a result of intensive peat production and there will be more
abandoned areas added to the already existing 22,000 – 24,000 ha. During the
recent decades, with the increasing threat of global climatic change, there has
been more discussion about the importance of peat soils in the global C turnover.
The issue of sinks and sources of CO2 and other gases, responsible for the
climatic changes has been in the centre of attention of many research interests [4,
9]. As the peat soils are sensitive to agricultural activities, especially soil tillage,
then the choice of the right species is important. After peat excavation the natural
plant succession is very slow to occur, unless the seed bank is presented in
topsoil [18, 21]. The agricultural use of peat soils includes draining that will
destroy the natural water system and disturb the normal water balance in that
area and in the neighbouring areas as well. In some cases unbalanced fertilization
is leading to eutrophication. The ombotrophic bogs are known by nutrient poor
environment. The capacity of these soils to ensure plants with nutrients depends
on atmospheric inputs. The opencast peat fields are very poor in essential
nutrients (N, P, and K) present in the accessible forms for plants where the
additional inputs of balanced fertilization is important for plants growth [20].
Moreover, in the opencast peat fields where the natural bog water system and the
plant cover is destroyed the mineralization and surface deflation is very fast if to
compare with peat formation. Rapid mineralization of organic matter in drained
and managed peatlands lowers the soil surface at an average rate of 3 cm per
year, as calculated for peatlands in the temperate zone [10].
The aim of the current study is to evaluate the content and the characteristics
of different soil organic matter from different soils on investigation areas and to
establish how they differed from each other by plant cover, exploitation and the
soil type.
2
Materials and methods
The five study areas (1, 3, 4, 5, and 6) are located in the county of Tartu (58° 22’
N, 26° 43’ E), in the southern part of Estonia. The study area 2 is located in the
Harju county (59° 6' N, 25° 22' E) in the north-western part of Estonia. The soil
of the experimental fields belongs according to the WRB soil classification, to
the soils subgroups of Fibri–Dystric Histosols (1, 2, 3, and 4 study area). The
rest of soils were Endorupti-Ombric Histosols (5) and Eutri-Fluvic Histosols (6).
The plant associations of the investigated areas are determined according to the
classification system developed by J. Paal [23]. Investigation area Sangla is used
currently for peat excavation, therefore no plant cover is presented.
Investigation area in Ardu is named by region where it is situated. There the
dominant plant species was Vaccinium angustifolium and accompanying species
Geo-Environment, J. F. Martin-Duque, C. A. Brebbia, A. E. Godfrey & J. R. Diaz de Teran (Editors)
© 2004 WIT Press, www.witpress.com, ISBN 1-85312-723-X
Geo-Environment
61
were Betula sp, Eriophorum vaginatum, Salix sp., Epilobium angustifolium,
Pinus sylvestris, and Calluna vulgaris. Current area is agriculturally exploited as
well. Sapi-Lulli peat bog had the dominant species as Vaccinium angustifolium
and in addition Pinus sp., Betula sp. and Eriophorum vaginatum. In bryophyte
canopy are represented Marchantia polymorpha, Ceratodon purpureus,
Polytrichum strictum, Funaria hygrometrica. Rahinge small size peat bogs,
named by region were it is situated is currently agronomically exploited. The
dominating plant species is Vaccinium angustifolium that is planted. Of
accompanying species were presented Pinus sylvestris, Betula sp. and
Eriophorum vaginatum. Tiksoja bog is classified as pine forest association
Sphagno-Pinetum. The main tree species was Pinus sylvestris and some Salix sp.
Accompanying species were Calluna vulgaris, Ledum palustre, Vaccinium
uliginosum and Vaccinium myrtillus. From bryophytes were represented
Polytrichum commune, P. strictum, Sphagnum sp. On investigation area at
Emajõe dominant plant association is Salicetum cinereo-myrsinifoliae, in the
bush canopy were accompanying species Salix sp., and Betula sp. In the grass
canopy is presented Carex cespitosa, C. acuta, C. elata, C. nigra, C. lasiocarpa,
Phragmites australis, Phalaris arundinacea, Filipendula ulmaria, Cirsium
oleraceum, Potentilla palustre. On the bryophyta canopy is presented
Plagiomnium ellipticum, Climacium dendroides, Calliergonella cuspidata, C.
cordifolium.
Table 1:
Investigation areas soils and plant associations’ types.
Number
of
investigation
area
1
Investigation
site
2
Ardu
3
Sapi-Lulli
4
Rahinge
5
Tiksoja
6
Emajõe
Sangla
Soil type
Soil
HSdy(fi)
Plant association or
dominating plant
species
Without plant
cover
V. angustifolium
Fibri–Dystric
Histosol
Fibri–Dystric
Histosol
Fibri–Dystric
Histosol
Fibri–Dystric
Histosol
EndoruptiOmbric
Histosol
Eutri-Fluvic
Histosol
HSdy(fi)
HSdy(fi)
V. angustifolium
HSdy(fi)
V. angustifolium
HSom
Sphagno-Pinetum
HSfv(eu)
Salicetum cinereomyrsinifoliae
For the current investigation the soil sampling was carried out in
September 2003, and the plant association description during the summers of
2000 – 2003 was made. Soils were described on the basis of test pits and the
samples for analysis were taken from the upper peat layer (0-20cm), the air-dried
and the dry matter content was determined by drying the sample at 105 oC to the
constant weight. Peat samples were analysed for organic C according to the
Tjurin method [34]. For the direct estimation of the organic matter content the
Geo-Environment, J. F. Martin-Duque, C. A. Brebbia, A. E. Godfrey & J. R. Diaz de Teran (Editors)
© 2004 WIT Press, www.witpress.com, ISBN 1-85312-723-X
62 Geo-Environment
loss-on-ignition (LOI) method [19] was used. For the determination of total N
the Kjeldahl method was used [26]. Available P, K, Ca and Mg were analysed
according to the Mehlich-3 method [11]. For the estimation of the microbial
biomass the fumigation-extraction method was used and for the characterization
of the microbial biomass activity a respiration rate was determined [29]. The
mineralization of nitrogen was determined by the method of Warning and
Bremner [31]. Electrical conductivity was determined in the filtered peat-water
extract (1:5, v/v). The pH was measured from the soil suspension with 1M KCl
(1:2,5 w/w) [26]. Water extractable organic carbon from soil-water extract
(1:100, w/v) was measured [27]. The chemical oxygen demand (COD) was
determined in a peat water suspension (1:100, w/v) similarly to Ranneklev &
GisselrØd [27], but instead of uncreated Cr(VI) in the final solution, we
determined spectrophotometrically (λ=590 nm) the amount of Cr(III), which is
formed as a result of oxidation reactions and the results were reported as L O2
100g-1. For the total phosphorus determination the soil was destroyed by wet
digestion and phosphorus was determined spectrophotometrically in the acid
extract by vanadomolybdophosphoric acid method [19].
Based on the data of the Estonian Meteorological and Hydrological
Institute. Vegetation period (181 days in 2003) was characterised by average
temperatures of 13 °C and the total precipitations of 421 mm. The average
temperature of many years for vegetation period was 12.2 °C.
ANOVA was used for statistical analysis and standard deviation (± SD) is
presented in tables.
3
Results and discussion
3.1 Soil organic matter on investigation areas
The annual peat loss by mineralization in agriculturally managed peat fields can
reach up to 10 – 15 t ha-2 [31]. Mineralization rate depends on cultivated species.
The experimental results in Estonia showed that in the uppermost 40 cm topsoil
there was peat mineralisation as much as 2.6 t ha-1 in peat soil during the
cultivation of different grass species [13]. The peat CO2-C respiration is
correlated positively with the increased temperature sum treatment and higher
peat N amounts [12]. However, poor substrate quality limits respiration more
than do low nutrient concentrations [3]. The respiration rate differed between
investigation sites. It was statistically higher in the Ardu and the Tiksoja sites,
4.2 and 5.0 µg CO2 g-1 per day, respectively. In the rest of the investigation areas
it ranged from 1.9 to 2.4 µg CO2 g-1 per day. The statistical analysis did not
confirm the significance on the respiration rate in the Rahinge and the Emajõe
flood-plain. The ash content was different between the Emajõe flood-plain (6)
31.6% and on the rest of investigation areas it ranged from 1.5 to 5.5%. The
content of mineralized N was the highest in the Emajõe flood-plain 0.51 mg g-1.
The next highest amount of mineralized N was found in the Tiksoja bog (0.45
mg g-1), it was confirmed with a statistical analysis. In the rest of the study sites
the mineralised N differed from 0.20 to 0.25 mg g-1. Hartman et al. [12]
Geo-Environment, J. F. Martin-Duque, C. A. Brebbia, A. E. Godfrey & J. R. Diaz de Teran (Editors)
© 2004 WIT Press, www.witpress.com, ISBN 1-85312-723-X
Geo-Environment
63
suggested that the availability of and the relationships between different N and C
forms depend on the temperature sum and the peat nitrogen content.
Table 2:
Peculiarities of peat on the different investigation areas.
Parameters of the
peat quality
Investigation area
1
2
3
4
5
6
Respiration,
µg CO2 g-1 per day
Ash content, %
2.4 ± 0.4
4.2 ± 0.4 1.9 ± 0.7
2.0 ± 1.0 5.0 ± 0.5
2.2 ± 0.2
3.6 ± 0.8
-
1.5 ± 0.1
5.5 ± 0.1
Mineralized N,
mg g-1
0.24
± 0.02
0.25
± 0.04
0.20
± 0.05
1.9
± 0.03
0.21
± 0.08
0.45
± 0.1
31.6
± 6.7
0.51
± 0.03
Total biomass,
mg g-1
8.6 ± 4.6
-
8.2 ± 5.7
13.5
± 2.4
17.3 ± 5.9
6.1 ± 1.8
Biomass C,
mg g-1
Biomass N,
µg g-1
4.3 ± 2.3
-
4.1 ± 2.8
6.8 ± 1.2 8.6 ± 3.0
3.0 ± 0.9
642
± 338
-
607
± 421
1004
± 181
1283
± 440
451
± 132
CWE, %
0.59
± 0.04
0.60
± 0.04
0.54
± 0.31
0.25
± 0.13
0.32
± 0.14
0.26
± 0.15
The C:N ratio in investigated peat soils differed significantly reaching from
10.5 in Eutri-Fluvic Histosol till 71.3 Fibri-Dystric Histosol in Ardu study site.
The lower value is characteristic for a relatively stabilized soil organic matter
that was characteristic to the flood plain well decomposed peat, area that is not
flooded for a long time but influenced by high level of ground water [24]. Higher
value of C:N relationship is characteristic for well preserved peat [35]. Water
soluble peat organic carbon (CWE, %) is considered to be the most labile and
mobile form of peat organic carbon. The content of water dissolved C (CWE, %)
was statistically lower in the peat soils of the Rahinge and the Emajõe floodplain (0.25 and 0.26 %, respectively). In the rest of the investigation areas it was
from 0.32 to 0.60 %. The chemical oxygen demand that is used for oxidation of
water soluble organic material in peat soil, was in the first three study sites from
1.01 to 1.12 L O2 100g-1, in Rahinge and Tiksoja it was 0.47 and 0.6 L O2 100g-1,
respectively. On the Emajõe flood-plain it was 0.48 L O2 100g-1.
The agricultural use of peat soils employs drainage, leading to the aeration of
the surface horizons, and fertilisation, leading to eutrophication, both of which
cause a large increase in microbial decay rates [2]. If to compare the different
ecosystems, then the lowest microbial biomass was found in the flood-plain
Eutri-Fluvic Histosol with the lowest content of organic carbon (27.4 %). The
content of total biomass reached at investigated areas up to 17.3 mg g-1 on
Endorupti Ombric Histosol at undisturbed ecosystem that is covered by forest.
The biomass C comprised of it 50%. There is a linear correlation between the
soil microbial biomass and microbial C and N, also the respiration rates
displayed similar results to the microbial biomass. The microbial biomass and
the activity of microorganisms is dependent on several factors including
Geo-Environment, J. F. Martin-Duque, C. A. Brebbia, A. E. Godfrey & J. R. Diaz de Teran (Editors)
© 2004 WIT Press, www.witpress.com, ISBN 1-85312-723-X
64 Geo-Environment
available carbon which that is the fraction of soil organic carbon that
heterotrophic microorganisms can easily use as carbon and energy sources [7].
The presence of Sphagnum and its litter under decomposition, in natural
peatlands, brings C available to microorganisms. Then results of the study of
Croft et al [6] demonstrated that peat mining decreased bacterial population as
well as the populations of hemicellulolytic and cellulolytic microorganisms of
peatlands for microbial decomposition. It is known that heterotrophic microbes
in soils play important roles in N dynamics, and that their metabolism is often
restrained by the availability of C in the soil [7, 14]. It is mentioned in the
literature that the composition and the activity of the microorganisms in natural
mires depends on pH, oxygen, groundwater level, soil temperature and available
nutrients. The peat soils of excavated mires may initially be regarded as
biologically dead and with only slowly regaining biological activity. It has been
emphasised that only by liming, fertilising and planting the dormant microflora
can be reactivated [16]. The experiments made in Estonia confirm that in the
case of liming the plant invasion is activated in the ombotrophic peat bog. Here
the use of plant species which tolerates the high level of soil acidity and have
native myhcorrhizae could be encouraged. Both, V. oxycoccus and V.
angustifolium growth are dependent on native myhcorrhizae which supplies plant
nutrient levels and growth rates in acid peat soils [5]. Here it is important that the
organic matter returns to the soil. V. angustifolium will shed the foliage and in
this way the return and the production of organic matter is guaranteed.
3.2 Nutrient pool of investigated peat soils
Ombotrophic peatlands are acid wetlands (pH < 4.8) with extremely low
concentrations of mineral elements [33]. The soil pH was statistically lower from
our investigation area at Sangla (4.2 pHKCl) and higher in the Emajõe flood-plain
(6.9 pHKCl) where the dominating soil was Eutri-Fluvic Histosol. In the rest of
the investigation areas the soil acidity ranged from 2.4 to 2.9 pHKCl.
The electrical conductivity was quite similar in all the investigation areas
varying from 0.51 to 0.65 mS. Statistically higher electrical conductivity was
found in the investigation area in the Emajõe (0.65 mS) flood-plain.
The content of total N (Ntot, %) was in the first two study area soils 0.6 – 0.9
%. In the Sapi-Lulli, Rahinge and Tiksoja bogs it was from 1.0 to 1.2 %. The
statistically higher content of Ntot, % was found in the soils in the Emajõe floodplain (2.6 Ntot, %). The turnover of the microbial biomass has a great importance
for the availability of plant nutrients, especially for P [1]. Phosphorous is the
nutrient that is transferred in negligible amounts by rain to the ecosystem in
contrast to N [8]. Based on the data from Statistical Office of Estonia in the
region of Ida-Virumaa the emission of nitrogen oxides from stationary sources
during the last three years was in average 10, 732 t [30]. Where the emission is
the highest if compared to other Estonian regions. The content of available
phosphorus was very low or low for all the investigated peat soils starting from
6.8 mg kg-1 at Fibri-Dystric Histosol in Sangla without plant cover reaching to
36.7 Pavb, mg kg-1 in Sapi-Lulli covered by V. angustifolium. Jakobsen [15] found
that the uptake in forms of phosphate is important for the absorption and the
Geo-Environment, J. F. Martin-Duque, C. A. Brebbia, A. E. Godfrey & J. R. Diaz de Teran (Editors)
© 2004 WIT Press, www.witpress.com, ISBN 1-85312-723-X
Geo-Environment
65
translocation of calcium. If the normal function of a root has ceased, the active
absorption of nutrients will cease too, as found in the different experiments for
the adsorption and the utilization of potassium, magnesium, calcium and
phosphorus. The basis of Estonian energetic and some branches of industry is the
local oil shale. During the processing there is emission by the combustion
devices of sulfur dioxide and the fly ash. While the calcium oxide is the
dominant alkaline component constituting 30.5 % of oil shale fly ash and it is
resulting in 21.8 % Ca [17]. Calcium oxide has emitted in a two different form as
CaSO4 and CaCO3 [17, 25]. The content of plant available Ca and Mg had a high
content. The content of plant available potassium in studied Histosols varied
from medium to high. The studied level of available K showed statistically
lowest content in topsoil in the Emajõe flood-plain (147.3 Kavb, mg kg-1). The
research results from current study are on accordance with other results done in a
past in Estonia at the well composed peat soils by Heinsalu et al [13] by them
was found that the content of Kavb was 232.4 mg kg-1.
Table 3:
The quality of peat soils from different types of the investigation
area (M±SD).
Parameters of the
peat soil quality
Ntot, %
Ptot, %
Ctot, %
Pavb, mg kg-1
Kavb, mg kg-1
Caavb, mg kg-1
Mgavb, mg kg-1
Investigation area
1
0.9 ± 0.1
0.03
± 0.01
38.5
± 4.4
6.8
± 0.1
390
± 2.9
11096
± 220
1492
± 19.3
2
0.6 ± 0.4
0.04
± 0.01
42.8
± 1.0
13.8
± 0.5
726
± 16.5
2179
± 24
394
± 2.4
3
1.2 ± 0.4
0.04
± 0.01
40.5
± 2.5
36.7
± 6.0
444
± 11.1
2945
± 89
568
± 19.1
4
1.0 ± 0.1
0.03
± 0.01
45.1
± 2.3
11.9
± 0.6
387
± 8.3
5014
± 45
857
± 21.9
5
6
1.0 ± 0.1 2.6 ± 0.2
0.06 ± 0 0.19
± 0.05
41.3
27.4
± 2.1
± 3.5
28.4
8.5
± 1.2
± 0.3
547
147
± 4.5
± 3.3
3384
19722
± 33
± 623
410
793
± 6.1
± 12.0
*tot – total nutrients,
*avb – available nutrients.
4
Conclusions
The results of this study suggest that the difference of studied parameters is
represented between the investigations areas. Those were caused by the diverse
on investigation area soil types and exploitation. The analyses done by us
showed that there was relatively high content of potassium, magnesium and
calcium on the investigated Histosols. The content of Pavb was low and there was
observed variability on the content of available nutrients at investigation areas.
The highest level in microbial biomass was observed in the investigation area
that had natural plant cover as Sphagno-Pinetum and soil type as EndoryptiOmbric Histosol. The characterisation of water and nutrient pathways in all the
Geo-Environment, J. F. Martin-Duque, C. A. Brebbia, A. E. Godfrey & J. R. Diaz de Teran (Editors)
© 2004 WIT Press, www.witpress.com, ISBN 1-85312-723-X
66 Geo-Environment
types of wetlands is needed to improve our understanding of the process
operating at all the scales in natural systems and also damaged peat lands.
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