Advertisement

Journal of Soils and Sediments

, Volume 18, Issue 8, pp 2715–2726 | Cite as

Dissolved organic matter, nutrients, and bacteria in Antarctic soil core from Schirmacher Oasis

  • Viia LepaneEmail author
  • Kai Künnis-Beres
  • Enn Kaup
  • Bhupesh Sharma
Humic Substances in the Environment

Abstract

Purpose

This study focuses on the application of HPLC in dissolved organic matter (DOM) research in Antarctic environment together with nutrients and heterotrophic bacteria (HB) analyses. The specific aims were to investigate changes in DOM components characteristics and in nutrients in soil core from ground active layer and upper permafrost, to relate obtained data to active heterotrophic bacteria records after applying statistical data treatment methods, and to explore the potential impact of environment.

Materials and methods

A single Antarctic 1.9-m deep soil core drilled at a site without human impact from Schirmacher Oasis, located 70° 46′ 02″ S and 11° 45′ 11″ E, was explored. The chromophoric DOM (CDOM) was characterized by soil water analysis using multi-wavelength HPLC. Total organic carbon and total nitrogen were determined by elemental analysis, the total phosphorus by inductively coupled plasma spectrometry. The vertical changes in those nutrients and their ratios were investigated. The microbiological analysis was accomplished through the determination of psychrotrophic and psychrophilic aerobic HB numbers by colony-forming units counting method, and by epifluorescence microscopy examination. Cluster analysis using the Ward method and principal component analysis was performed on the chromatographic and microbiology data to reveal similar layers in studied soil core.

Results and discussion

In active soil layer, the CDOM was missing thus indicating rather active decomposition of organic material or organic debris by the local microbial community. In deep permafrost layers, the quantity of CDOM preserved in soil water increased. The content of total organic carbon in soil was low, between 0.05 and 0.2%, and decreased down the core. The vertical changes in nutrients (total N and P), the ratios C/N and C/P, followed total organic carbon profile suggesting similar sources. Microbiological analyses showed decreasing vertical concentrations of active HB. Statistical data treatment methods enabled clustering of soil core into three zones according to depth.

Conclusions

The obtained results contribute to better understanding of organic carbon-related processes in an almost un-polluted Antarctic environment. The CDOM, macronutrients, C/N, C/P, and HB profile characteristics of the Antarctic soil core clearly demonstrate the effect of environment (active or permafrost soil layers). The study demonstrated that combining HPLC with multi-wavelength detection and microbial analyses with statistical data treatment is potentially a promising tool of investigating changes in Antarctic soil DOM and in soil waters generally.

Keywords

Antarctic soil Dissolved organic matter Heterotrophic bacteria HPLC Nutrients 

1 Introduction

The composition of Antarctic soils has so far been insufficiently studied and little is known about the amounts, characteristics, and biocycling of dissolved organic matter (DOM) in the environment. Sources of soil organic matter include both endogenous inputs from photoautotrophs and exogenous inputs related to landscape history (for example, lake inundation and sediment deposition, in some cases inputs from bird colonies (Hofstee et al. 2006) and anthropogenic inputs in vicinities of research stations (Kaup and Burgess 2002). Since the terrestrial input of DOM in Antarctic regions is expected to be minimal, the origin of organic matter should be mostly autochthonous (Schwartzman 1999). The distribution and activity of soil organisms are closely linked to spatial patterns of soil biogeochemistry and the dissolved and particulate organic matter distribution.

There is also limited information about the microorganisms’ distribution structure and active heterotrophic bacteria (HB) number in Antarctic soils and upper permafrost layers. Typically, HB are the main producers, consumers, and transformers of DOM. Exoenzymatic activity of microorganisms plays an essential role in degradation of particulate organic matter in aquatic and terrestial environments. In both cases, the quality and quantity of DOM play a key role in the dynamics of carbon, nitrogen, and other elements in soils and sediments. In the Antarctic environment, DOM may be the most important energy and nutrient source for autochthonous and allochthonous heterotrophic microorganisms.

Analytical methods based on HPLC have often been used to characterize aquatic DOM on molecular level. The coupling of HPLC option–high-performance size exclusion chromatography (HPSEC), with diode-array detection (DAD), enables qualitative and semi-quantitative analysis of chromophoric DOM (CDOM). The non-destructive analysis, small sample volume, and minimal sample pretreatment are great advantages of the HPSEC-DAD approach, making the method suitable for environmental studies. HPSEC-DAD has been adapted and optimized for analysis of sediment water samples under various conditions (Akkanen et al. 2005; Lepane et al. 2004, 2010; O’Loughlin and Chin 2004). The advantage of the usage of this chromatographic system is a better understanding of the qualitative and quantitative DOM properties by detecting chromophoric compounds. This method has recently been applied for monitoring and detection of organic matter from surface waters (Liu et al. 2010).

In the present study, we have attempted to find out the relationships between the molecular and spectroscopic characteristics of CDOM and the concentration of active HB (capable of colony formation on low nutrient content agar media) in the ground active layer and upper permafrost core (1.9 m deep) taken from Schirmacher Oasis, situated in Dronning Maud Land about 80 km south of the Princess Astrid Coast of east Antarctica, in March 2009. The specific aims were (1) to investigate changes in CDOM components qualitative and quantitative characteristics and macronutrients by exploring Antarctic soil core records, (2) to find the similarities and differences in HPSEC-DAD chromatograms of CDOM and relate them to HB data after applying statistical data treatment methods, and (3) to explore the potential impact of environment on CDOM and HB records in investigated soil core.

2 Materials and methods

2.1 Study site and sampling

Schirmacher Oasis (located between 70° 44′ and 70° 46′ S and 11° 20′ and 11° 55′ E) in Queen Maud Land (Fig. 1) is ca 20 km in length and 1–3 km wide, ca 35-km2 ice-free area, with a maximum elevation of 228 m (Bormann and Fritzsche 1995). The continental ice sheet in the south and the steep rock escarpment in the north, from where ca 80-km ice shelf extends to the Southern Ocean, border the oasis. Glacial erosion and frost weathering are major agents of Holocene landform modification. The Holocene ice-free period of the Schirmacher Oasis began more than 10,000 years ago (Hebert and Richter 1985; Phartiyal et al. 2011; Richter 1985). The rocks consist predominately of migmatitic garnet and biotite-amphibole gneisses (Paech et al. 1995). Many morphological depressions characterize the relief of the oasis and about two-thirds of them are filled with numerous lakes that range in from 2.2 km2 to small ponds of 0.002 km2 in area and cover about 20% of the surface area of the oasis (Richter and Bormann 1995a). There is continuous permafrost in the area and the seasonally thawing soil upper part, the active layer has been observed to reach, depending besides weather conditions on soil material and aspect of site 60–90 cm (Krüger 1995) or 20–60 cm (Gajananda 2007) thickness in the summer.
Fig. 1

Location of the sampling site

A single soil core to 2-m depth was taken as a basis of this study. Soil was drilled at site without human impact on 2 March 2009 ca 1 km east of Maitri Station (and 0.5 km east of Lake Zub) with coordinates 70° 46′ 02″ S and 11° 45′ 11″ E. The site was a flat moraine area, probably earlier occupied by a persistent snowfield. The surface moraine included mostly garnet gneisses boulders, pebbles, and gravel. The core material was more fine-grained by visual observations; the size of the rare gravel particles did not appear to exceed 15 mm. The active layer thickness during the summer before at the site was 70 cm. The core was sectioned into 15 samples for further chemical and microbiological analyses (Table 1). From the segmented core, 15 2-cm-long sections were selected for analysis. The segments were placed into sterile plastic bags, stored in field within a hole in the permafrost at a temperature of − 10 °C, and transported frozen to the laboratory. During transportation, the samples were held in insulated containers with gel packs of ice as refrigerant. In the laboratory, the samples were stored in a freezer at − 18 °C until analysis.
Table 1

Soil samples numbering, depths, and chromatographic data

No

Depth (cm)

Retention time (Rt), (min)

Molecular mass (MM) (Da)

1

3–4

22.40

278

2

11–13

n.d.

n.d.

3

17–19

n.d.

n.d.

4

26–27

n.d.

n.d.

5

62–63

22.78

230

6

71–74

n.d.

n.d.

7

76–77

n.d.

n.d.

8

83–85

22.80

227

9

93–97

22.91

216

10

102–104

22.43

273

12

133–136

22.52

262

13

153–157

22.42

276

14

172–175

22.44

272

15

190–193

22.32

290

Calibration equation log (MM) = − 0.2165 Rt + 7.2939 R2 = 0.9425

n.d. not detected

2.2 Weather and climate

The relatively small and elongated rocky oasis is largely ice-free also in winter. The climate is characterized by high wind speeds (average annual value 10 m s−1) and low atmospheric moisture (average annual value 52%). The average annual air temperature is equal to − 11.0 °C, close to several other antarctic coastal stations (AARI). The maximum and the highest minimum diurnal air temperatures during the year are typically observed in the summer months December and January. January is also the warmest month with average air temperature of − 0.4 °C when also rock surfaces have been observed to warm up to 25–30 °C during direct insolation (Richter and Bormann 1995b). Usually in summer, rapid snow and ice melting occurs, numerous relief depressions are filled with melt water and there is intense discharge from the ice sheet through lakes to the ice shelf. The mean air temperature of March (the time of sampling) recorded at Novolazarevskaya Station, Schirmacher Oasis during 1961–2009 has been − 7.7 °C (minimum − 11.4 °C; maximum − 6.1 °C) (AARI). Winds up to 45 m s−1 disperse the sediments and soils throughout the oasis, which affects the simple ecosystem of the area (Gajananda 2007). The annual average precipitation 309 mm is largely exceeded by annual evaporation of 580 mm (Haendel et al. 1995; AARI). The mean annual total solar radiation input 93.8 kcal cm−2, is rather high due to rare low cloudiness and dry air (Dolgin et al. 1976).

2.3 Chromatographic analyses

For analysis of aquatic phase (soil water), the core samples were slowly thawed at 4 °C and thereafter centrifuged at 2.328×g for 30 min. Obtained centrifugates were filtered through 0.45-μm Millipore filters before conducting the HPLC analysis. The molecular characteristics of DOM in soil core samples were determined using a HPLC system. The HPLC system comprised a Dionex P680 HPLC Pump, Agilent 1200 Series (Agilent Technologies, UK) diode array absorbance detector (DAD), a Rheodyne injector valve with a 20-μL sample loop. A BioSep-SEC-S 2000 PEEK size exclusion analytical column (length 300 mm, diameter 7.50 mm, Phenomenex, USA) preceded by a SecurityGuard cartridge (Phenomenex, USA) was used for separation. The applied flow rate was 0.5 mL min−1. The column packing material was silica bonded with hydrophilic diol coating, with particle size of 5 μ and a pore size of 145 Å. The mobile phase consisted of 0.10 M ammonium phosphate buffer at pH 6.8. V0 was determined with Blue Dextran (retention time Rt 22.221 min or 5.11 mL), Vt with sodium azide (Rt 24.86 min or 12.43 mL, MM65). Polystyrene sulphonate sodium salts (PSS) from Sigma-Aldrich PSS 17,000; PSS 13,000; PSS 6800; PSS4300; and PSS 210 have been used as calibration compounds. Calibration standards have been chromatographed; their retention times were plotted against the logarithm of their MM. The calibration equation is presented as note under Table 1.

All solutions for HPLC measurements were prepared using ultra-pure water passed through a MilliQ water system, filtered with 0.45-μm pore size filters (Millipore), and degassed. The chromatograms were recorded and processed by Agilent ChemStation software. Full details of the used method are described previously (Lepane et al. 2004, 2010).

The qualitative analysis of DOM was carried out by multi-wavelength absorbance spectra, registered at wavelengths range of 205 to 400 nm. The identification of the peaks in the chromatograms was carried out by extracting the absorbance spectra of the peak from the DAD data and comparing those with the spectra of reference compounds. As reference compounds, the protein standards and tryptophan (Aqueous SEC1, Phenomenex, USA) and the International Humic Substances Society (IHSS) natural organic matter (IHSS Nordic Reservoir NOM IR108 N) were used. Since only the parts of DOM that contain aromatic structures and/or double bonds contribute to the absorbance signal, the detected compounds were operationally named as chromophoric DOM (CDOM).

As semi-quantitative CDOM characteristic, the total chromatogram peak areas, representing the total UV-absorbing fraction of DOM in each sample were used in the data analysis. The detector response (the height of the chromatogram at the ith elution volume) refers to the amount of DOM in a specific molecular size fraction. The sum of all peak heights represents the total amount of DOM capable of UV adsorption in the sample (Peuravuori and Pihlaja 1997; Vartiainen et al. 1987; Matilainen et al. 2006). We calculated the total chromatogram peak areas at wavelength 210 nm. Also the absorbance values at retention time 22 min were used for the differentiation of samples. Three to four replicate runs were performed for each sample. In general, relative standard deviations on replicated measurements did not exceed 5% (obtained by comparison of total peak areas).

2.4 Chemical analyses

The chemical analyses of macronutrients in thawed soil core samples were carried out according to standard procedures. Total organic carbon (TOC) and total nitrogen (N-tot) were determined by elemental analysis (ISO 10694 1995; ISO 13878 1998). The total phosphorus (P-tot) content by inductively coupled plasma (ICP) (ISO 11047 1998). The C/N and C/P ratios were calculated and presented as atomic ratios in present study.

2.5 Bacterial analyses

To estimate the number of actually or potentially active HB 10 g of the soil/permafrost probe was suspended in 30 mL of sterilized distilled water and mixed for 2 h on a rotary shaker. For the next dilutions, the suspensions were diluted with distilled sterile water by 10 times. The suspensions and dilutions were simultaneously spread on the plates of two nutrient-poor agar media: M-R2 Agar (the modified R2 Agar medium by Fries et al. 1994) and oligo agar (Allen and Brock 1968). Both of the media contained 1 g yeast extract, 15 g Difco agar and main macro and trace elements. The oligo agar contained 1 g tryptone and 0.05 g DL-β glycerophosphate and the M-R2 Agar 1 g peptone and 1 g sodium pyruvate as the additional carbon source per liter of distilled water. Triplicate spread plates were prepared for the each dilution for incubation at two temperatures: psychrophiles at 4 °C and psychrotrophs at 20 °C. Colonies (CFUs) were counted after 2 weeks incubation at 20 °C or after 4 weeks incubation at 4 °C.

2.6 Epifluorescence microscopic examination

The epifluorescence microscopy technique (Hobbie et al. 1977; Zimmermann 1977) with acridine orange (AO) staining was used for organisms-based organic matter (pro- and eukaryotic cells, plants fragments, etc.) vertical distribution examination. For microscopic examination 10 mL of the ten times diluted with distilled water thawed (slowly at 4 °C) core samples were fixed with 0.2 μm filtrated 37% formaldehyde (final concentration 2%) and filtered onto 0.2-μm pore size black polycarbonate membrane filter (diameter 25 mm). The biological material (pro- and eukaryotic cells, plants fragments, etc.) retained on the filter surface were stained with AO solution in distilled water (1:104). AO is a fluorescent dye that binds to nucleic acids, but also other cellular components. AO fluorescence in visible light can be red, orange, or green at illumination with wavelengths 450–490 nm. Cells produce green fluorescence if double-stranded nucleic acids (DNA) are prevailing in the cell (inactive cell) and orange fluorescence if single-stranded nucleic acids (RNA) are prevailing (active cells). The examination was performed using Zeiss Axioplan 40 epifluorescent microscope fitted with real time digital camera.

2.7 Statistical analyses

Obtained data were statistically treated by cluster and principal component analyses. Cluster analysis using the Ward method was applied to reveal similar layers in studied soil core (Brereton 2003). The analysis was performed on the chromatographic- and microbiology data. As descriptors for CDOM, total chromatogram areas, the chromatogram heights, i.e., absorbance at 210 nm at retention time 22 min, the HB numbers for all samples were included into the analysis. The Euclidean distance was used as a measure of the similarity–dissimilarity of the samples. Factor analysis was conducted on data as well using principal components method (Lepane and Kudrjašova 2001). The statistical analyses were carried out using WinSTAT for Excel software (R. Fitch Software, Germany).

3 Results

3.1 Nutrients

The concentrations of TOC, N-tot, and P-tot and their vertical changes are provided in Fig. 2. The concentration of TOC reached to 0.1% in the near surface layer of active soil (depth 1 to 4 cm). In the deeper active soil layers, from 11 to 27 cm, the organic carbon concentration fluctuated and increased up to 0.2% at the depth of 26–27 cm. The concentrations of organic carbon decreased to 0.05% at the depth of 62 cm and stabilized at that level down to 193 cm. The values for N-tot varied between 0.005 and 0.024% and showed large variation at depths 11 to 63 cm, similarly to organic carbon. N-tot concentrations at deeper soil samples were more or less constant (~ 0.01%). P-tot concentrations changed from 500 to 750 mg kg−1. The upper part of the studied core (depth 1 to 27 cm) had relatively high P-tot concentrations (average 702 mg kg−1) in comparison with the lower part (depth 62 cm and deeper) with average 547 mg kg−1. Both nutrients were correlated with TOC as seen from Fig. 3 but correlations were different for surface (0 to 63 cm) and deep (> 71 cm) samples. N-tot concentrations increase with the increase of TOC (R 0.99, Fig. 3a) for surface (active layer) samples and do not correlate with TOC at higher depths. P-tot has similar trend as N-tot as observed from Fig. 3b but correlation is weaker (R 0.529). Contrary to N behavior, the P-tot and TOC are strongly correlated in deeper (permafrost) samples (R 0.843) but P content decreases when TOC increases.
Fig. 2

The vertical changes in TOC, nutrients (N-tot and P-tot), and the ratios C/N and C/P in the Antarctic soil core

Fig. 3

Correlations between TOC and nutrients. a N-tot; b P-tot

3.2 CDOM characteristics

The soil samples CDOM was characterized by aquatic phase (soil water) analysis using HPLC (HPSEC) with DAD. Separation of soil water from particulate matter was done according to method optimized for pore-water (Lepane et al. 2010). In the present study, multi-wavelength HPLC analysis has been carried out to detect changes in CDOM composition and molecular mass profile down the core. The absorbance spectra were examined from 205 to 400 nm. The multi-wavelength plots allowed the most suitable detection wavelength for Antarctic CDOM components to be selected. Figure 4 displays the HPLC chromatograms detected at wavelength of 210 nm of aquatic phase from the different layers of studied soil core.
Fig. 4

Selected chromatograms of Antarctic soil core CDOM detection at wavelength 210 nm with absorbance spectra at peak maxima. a Sample 1, depth 3–4 cm; b sample 3, depth 17–19 cm; c sample 5, depth 62–63 cm; d sample 10, depth 102–104 cm; e sample 12, depth 133–136 cm. For chromatographic data see Table 1

The UV absorbance at 250–280 nm has been widely used to provide an estimation of aromatic compounds and humic substances (Filella 2010). However, those wavelengths were not suitable for detection in case of Antarctic samples. The organic compounds absorbed UV light only at monitored wavelengths 205 to 230 nm; thus, the wavelength 210 nm was selected for detection and characteristic comparison. The HPSEC-DAD analysis confirmed the absence of absorption maxima at wavelength region 250–350 nm, reflecting the lack of aromatic and humic compounds in studied Antarctic soil CDOM. The chromatograms of Antarctic soil water were different; the intensities and positions of the peaks changed in different soil layers (Fig. 4), reflecting changes in the concentrations and possible transformation of organic constituents. The chromatographic data have been provided in Table 1. The retention times for detected peaks were around 22–23 min. For comparison, the IHSS NOM standard sample eluted from our HPLC system at Rt 19.6 min, and tryptophan (MM 204) at 22.24 min. Corresponding to PSS calibration, the relative molecular masses were estimated to be from 216 to 290. In permafrost layers, the molecular masses for CDOM were nearly constant, slightly increasing down the core. In soil layers numbered as 2, 3, 4, 6, and 7, no CDOM absorbance was detected at all, absorbance was mainly scatter (Fig. 4b). Thus, it was not possible to find a chromatographic peak and to register peak absorbance spectra. Analysis of HPSEC peak areas (as rough estimation of CDOM quantity) showed increasing down-core concentrations starting from depth 133 to 193 cm (Fig. 5a). Thus, the CDOM quantity changes in soil water down the core were not in accordance with TOC data (Fig. 2), suggesting the majority of organic matter in studied soil core was non-chromophoric (aliphatic).
Fig. 5

Changes in quantitative chromatographic (peak areas at 210 nm) and microbiology data (heterotrophic bacteria numbers) in Antarctic soil core; a data arranged into three regions I, II, and III; b cluster separation

3.3 Bacteria

The microbiological analyses of soil core samples were accomplished through the HB numbers determination and epifluorescence microscopic examination. Some of the results are presented in Fig. 5a together with the CDOM data. The colony-forming aerobic HB number was high in near surface layers (3–19 cm), with maximum at the depth of 17–19 cm: in average, 245·103 CFU per gram wet probe (incubated at 20 °C) and 438·103 CFU per gram wet probe (incubated at 4 °C) (Fig. 6). HB number decreased roughly 100 times from the depth of 26 cm and decreased slightly down to 115 cm. The near surface active soil HB numbers were roughly 1.7 times higher at 4 °C than incubated at 20 °C, but from 26 cm and deeper the numbers of aerobic HB did not depend on the cultivation temperature and the colony counts of two incubation temperature were very similar. This type of aerobic HB vertical distribution indicated that the psychrophilic bacteria prevailed of the Antarctic active soil aerobic HB communities (counts at 4 °C were significantly higher than at 20 °C.) The growth of aerobic HB was totally lacking in the permanently frozen deeper soil from 130 cm and deeper, but also in the active soil at the depth of 62–63 cm. Figure 6 shows the vertical distribution of mean HB numbers (CFU) per gram of core sample incubated at 4 and 20 °C for both media used. It is evident by inspection that at 20 °C, the differences in plate count results between M-R2 agar and oligo agar were small throughout the 14-day incubation period. Studies of the effects of incubation temperature and plating medium indicated that, for M-R2 agar and oligo agar the differences in counts for two media were not significantly different at any incubation temperature. Incubation temperature strongly affected the maximal colony count attainable. The data presented on Fig. 6 clearly showed that incubation at 20 °C resulted in a significant reduction in the maximal colony count of cold environment samples compared with incubation at 4 °C. No single medium and set of incubation conditions can be expected to recover all viable bacteria present in a natural substrate samples.
Fig. 6

Vertical distribution, depth from 3 to 193 cm, of psychrotrophic (a) (cultivated at temperature 20 °C) and psychrophilic (b) (cultivated at temperature 4 °C) aerobic heterotrophic bacteria detected by colony-forming units (CFU) counting method using spread-plating technique and two nutrients poor agar cultivation media

In order to have better understanding about bacteria in soil core, the samples have been subjected to microscopic analysis and selected photos are presented in Fig. 7. In epifluorescence microscopy photos, green color represents inactive cells and yellow/orange color–the physiologically active, living cells, and red color—plants fragments (detritus). Epifluorescence microscopy showed high microbial diversity and potentially high biological activity of the soil active layer (samples 1, 3, 5, and 8). The core analyses resulted in the high bacterial total numbers (6–26·106 cells per gram wet probe) in soil active layer at depth 3–30 cm (Fig. 7). It occurred that at least during the Antarctic summer, primary production and bacterial degradation of the plant matter occur in the upper active soil layers simultaneously. The microscopic examination also demonstrated rather sterile conditions in permafrost deeper than 115 cm (Fig. 7, samples 11 to 15). Surprisingly, the highest eukaryote organisms (e.g., diatoms) number and diversity and also the highest concentration of plants fragments were detected just on the surface of the permafrost (Fig. 7, sample 10, 102–104 cm). The biota of the mentioned core sample was very similar to the near bottom lake communities.
Fig. 7

Pro- and eukaryotic microorganisms and plant fragments in soil core samples visualized by epifluorescence microscopy (green— inactive or dead cells, yellow to orange—physiologically active cells), scale 5 μm for all

3.4 Comparison of HPLC and microbial analyses results

The statistical cluster and principal components analyses of data were performed to reveal similar or different zones in Antarctic soil core. Based on CDOM and microbiology data, the core was divided into three depth zones: I 3–19 cm with characteristic high HB number (152000–487,000 CFU/1 g wet probe) and absence of CDOM; II 0.26–1.15 m with low HB number (1000–2000) and relatively low CDOM concentration; and III 1.3–1.9 m with relatively high CDOM content and absence of colony-forming HB (Fig. 5).

The principal component analysis (PCA) was carried out to reveal which of the studied dataset, chromatographic or/and microbiology, was best to discriminate between the soil layers. The results based on chromatographic, microbiology and combination of both data are shown in Fig. 8. The HPLC data enabled to differentiate between the deepest soil zones CDOM variables (marked with circle on Fig. 8a) and the II zone with the top layer (sample 1). Considering first principal component (PC) all those samples were quite close. Soil layers CDOM variables from depths 11–27 cm to 71–77 cm were similar in respect to second PC. The validated variance was 86.4% for the first two principal components (53.4% for PC1 and 33.0% for PC2). The PCA analysis conducted on microbiology data resulted in not separable groups as indicated by circles (Fig. 8b). Top zone (I) samples were separated by both principal components. The rest of the soil core samples were mainly scattered on the PCA plot. The first PC explained 29.3% and the second 18.4% of the variation in the data.
Fig. 8

Principal component analysis of Antarctic soil core chromatographic (a), microbiology (b), and their combination (c) data

The combination of chromatographic and microbiology variables resulted in clear grouping of soil layers on PCA plot shown in Fig. 8c. The variance was 91.1% for the two PCs (81.1% for PC1 and 10.0% for PC2). Sample 10 that is identified as lake water above the permafrost layer (see Fig. 7) is clearly separated from both groups.

4 Discussion

4.1 Chemistry of CDOM and biological macronutrients in soil

The DOM in soils can be a substrate for microbial growth but its production is also partly mediated by microbes (Smolander and Kitunen 2002). Because of that, it is very important to know the quantity of this fraction in soils. The Antarctic soil DOM is composed of relatively small molecules. DOM is reported to contain dissolved carbohydrates (simple sugars and amino sugars), amino acids/peptides, and other low molecular mass carboxylic acids, like lactic and formic acids (Vestin et al. 2008). Among those chemical compound classes listed, sugars are not considered chromophoric and they remained undetected in the present study. Indeed, the results of our study indicate the absence of aromatic and humic substances in soil aquatic phase (soil water). The detection wavelength 210 nm enabled detection of amino acids and simple carboxylic acids. Identification attempts of separated chromatographic peak resulted in most cases with respective spectra of protein standards (Fig. 4d, e), with 78–98% probability. Since the Rt values were close to the lower separation range, the compounds are identified most-likely as peptides/ amino acids. Indeed, the UV spectrum (Fig. 4d) is characteristic for polypeptides and also amino acids. Those constituents are considered as biologically labile. Thus our results support the assumption that Antarctic soil CDOM likely originates from microbial activity. The content of organic carbon in the studied Antarctic soil core was very low. The horizontal distribution of total organic carbon (TOC) for Schirmacher Oasis surface soil layer (depth 2.5–5.1 cm) has been detected and reported by Gajananda (2007). He reported TOC values for the studied site 1.63–1.77%. Our results, which characterized the active soil layer (from 3 to 60 cm) and upper permafrost, are more in accordance with the organic carbon contents reported in the soils of the McMurdo Dry Valley (range 0.01 to 0.2%) (Moorhead et al. 1999). The macronutrients N and P were quite well following the profile of TOC. The mineralization of organic compounds can be estimated by calculating the C/N ratio. The higher ratio should indicate the more refractory organic matter and thus the lower availability to microbial degradation. The calculated C/N atomic ratios were between 10 and 12 (characteristic to soil layers 3 to 27 cm) and below 6 in deeper layers. Correspondingly, the C/P ratios varied in upper layers from 3.5 to 7.9, and from 1.8 to 3.4 at deeper zones. To explain our results, also the temperature on site must be taken into consideration. During Antarctic summer, the soil layers (Table 1, nos. 1–5) melt down to 63 cm (active layer), during winter, all soil is frozen. Soil layers deeper than no. 6 are frozen all the year (permafrost layers). The large vertical variation observed for TOC can thus be explained considering temperature effect. N-tot reached maximum value in the 26–27 cm layer, where also the HB number was the highest and decreased more than twice in the depth of 62 cm. N-tot and P-tot data indicate that macronutrients can move with water in soil profile until permafrost layer is reached and their utilization depend in great deal on the length of microbiologically active temperature period (liquid water availability). Weak sorption by soil materials is reported characteristic to nitrates (Szajdak and Karabanov 2010). The C/N ratio in organic soils has been reported to be between 6 and 10; in lake deposits 13–15 (Kalisz et al. 2010). Very low (1–2), intermediate (8–13), and high (> 40) C/N values have been reported in Antarctic soils (Arenz and Blanchette 2011). The reason for such high C/N ratio was anthropogenic (woody debris left by humans).

The CDOM and TOC profiles down the soil core were showing difference (Figs. 2 and 5a). In active soil layer, the CDOM was missing, thus indicating rather active decomposition of organic molecules by the local microbial community. In permafrost layers, there was a very small quantity of CDOM preserved in soil water. However, we observed increasing down-core CDOM concentrations starting from depth 133 to 193 cm (Fig. 5a). Those layers might represent very old carbon archives deposited thousands of years ago under different temperature regimes (Barrett et al. 2006). Our TOC and CDOM results indicate that a large part of carbon might exist as carbohydrates especially in active layer samples.

4.2 Factors influencing the vertical distribution of HB in soil

Seasonal temperature variations and related fluctuations of soil and temperature around the freezing point of water play a major role in the shaping of structure and composition of the soil microbial communities. Bacteria might be the main organisms responsible for the turnover of organic matter in Antarctic soils. The amount of HB reflects directly to the local soil temperature and the available substrate—the amount and composition of particular organic matter and DOM. Thus, the high concentration of organic matter should theoretically cause the high numbers of HB. The near surface active soil layer, in our case down to 27 cm, contained rather huge number of metabolically active HB at the end of local summer in March. On northern slopes in the Schirmacher Oasis, there can be up to 120 days per year with thaw-freeze episodes in soil layers (Richter and Bormann 1995b). In the near surface active soil layer, the aerobic psychrophilic HB dominated. In this layer, HB numbers were roughly 1.7 times higher at 4 °C if compared to the theoretically optimal growth temperature of HB (20 °C). In deeper soil, from 26 to 115 cm, the numbers of aerobic HB did not depend on the cultivation temperature: the colony counts at 4 and at 20 °C were very similar or even the same. Thus in the ice-free Antarctic soils, it is possible to define at least two HB communities. The HB community in the active soil layer has been acclimated with rapid and extreme temperature fluctuations and contain as well as the mesophilic, psychrotrophic, and psychrophilic HB. The bacterial community of mostly frozen deeper soil contains primarily the psychrotrophic HB. Between the two communities, there was rather thin soil layer (62–63 cm depth), where the growth of HB was absent. Richter and Bormann (1995b) reported that in Schirmacher Oasis, the temperature variations around the freezing point were usually observed immediately above the frost table. Our microbiological analyses indicated a HB-free zone between the regularly thaw-freeze active soil and permanently frozen permafrost layer. The unsuitable growth conditions for HB in this thin soil layer can be a result of historical factors, but it can be also caused by the actual organic substrate limitation, which is demonstrated on the core vertical profiles of TOC, N-tot and P-tot (see Fig. 2). Balke et al. (1991) measured the local conditions of chemical weathering processes and expressed quite clearly that throughout the Schirmacher Oasis possibilities exist for chemical alteration and migration of substances. They pointed out that the time span is certainly very restricted and under current local climate conditions lasts for only a little more than 10 weeks. The 10-week period can be sufficient to support the HB growth and organic matter degradation activity in the near surface active soil layer. At greater depths, frost weathering will not occur, for temperatures will remain below zero throughout the year. The fact that following intense radiation (UV can kill bacteria) the frost weathering was decreased, however, at very shallow depths in the case of a soil profile with detritus (Richter and Bormann 1995b) supports our assumption that bacteria have an essential role of mineral and organic material transformation and recycling in ice-free Antarctic soils. We can speculate that not only the estimated global warming but also the intensifying human activity both substantially alter the microbial communities of the Antarctic soils by putting added pressure on the nutrient cycle to further speed up the melting process.

5 Conclusions

The obtained results contribute to better understanding of organic carbon-related processes in a relatively un-polluted Antarctic environment. The CDOM, macronutrients, C/N, C/P, and HB profile characteristics of the Antarctic soil core clearly demonstrate the effect of environment (active or permafrost soil layers). The content of TOC in soil was low, between 0.05 and 0.2%, indicating the absence of higher plants, and composed mainly of non-chromophoric carbohydrates. In soil water CDOM, the low molecular mass components, possibly of microbial origin, that were attributed to amino acids/peptides or aliphatic carboxylic acids, dominated. Their record changes suggest that carbon turnover is regulated by biological processes driven by HB. This is supported by the high HB numbers in the near active soil layer (down to 27 cm) and very rich community of not colony-forming prokaryotes and eukaryotes just above the permafrost (102–104 cm deep). Although our study was limited on Schirmacher Oasis, the results obtained can be useful for further research. The study demonstrated that combining HPLC with multi-wavelength detection and microbial analyses is potentially a promising tool of investigating changes in Antarctic soil CDOM and in soil waters generally.

Notes

Acknowledgements

The authors are thankful to the members of Indian Antarctic Expedition for logistic support and assistance during sampling.

References

  1. AARI- Arctic and Antarctic Research Institute, Russian Federation NADC, Project Antarctica. http://www.aari.aq. Accessed 26 March 2017
  2. Akkanen J, Lyytikäinen M, Tuikka A, Kukkonen JVK (2005) Dissolved organic matter in pore water of freshwater sediments: effects of separation procedure on quantity, quality and functionality. Chemosphere 60(11):1608–1615.  https://doi.org/10.1016/j.chemosphere.2005.02.045 CrossRefGoogle Scholar
  3. Allen SD, Brock TD (1968) The adaptation of heterotrophic microorganisms to different temperatures. Ecology 49(2):343–346.  https://doi.org/10.2307/1934466 CrossRefGoogle Scholar
  4. Arenz BE, Blanchette RA (2011) Distribution and abundance of soil fungi in Antarctica at sites on the Peninsula, Ross Sea Region and McMurdo Dry Valleys. Soil Biol Biochem 43(2):308–315.  https://doi.org/10.1016/j.soilbio.2010.10.016 CrossRefGoogle Scholar
  5. Balke J, Haendel D, Krüger W (1991) Contribution to the weathering-controlled removal of chemical elements from the active debris layer of Schirmacher Oasis, East Antarctica. Z Geol Wiss 19:153–156Google Scholar
  6. Barrett JE, Virginia RA, Parsons AN, Wall DH (2006) Soil carbon turnover model for the McMurdo Dry Valleys, Antarctica. Soil Biol Biochem 38(10):3065–3082.  https://doi.org/10.1016/j.soilbio.2006.03.025 CrossRefGoogle Scholar
  7. Bormann P, Fritzsche D (eds) (1995) The Schirmacher Oasis, Queen Maud Land, East Antarctica. Justus Perthes Verlag, GothaGoogle Scholar
  8. Brereton RG (2003) Chemometrics: data analysis for the laboratory and chemical plant. Wiley, ChichesterCrossRefGoogle Scholar
  9. Dolgin IM, Marshunova MS, Petrov LS (eds) (1976) Spravochnik po klimatu Antarktidy, Tom I (Handbook of Antarctic Climate), vol Vol. (I). Gidrometeoizdat, Leningrad (in Russian)Google Scholar
  10. Filella M (2010) Quantifying humics in freshwaters:purpose and methods. Chem Ecol 26(sup2):177–186.  https://doi.org/10.1080/02757540.2010.494159 CrossRefGoogle Scholar
  11. Fries MR, Zhou J, Chee-Sanford J, Tiedje JM (1994) Isolation, characterization, and distribution of denitrifying toluene degraders from a variety of habitates. Appl Environ Microbiol 60(8):2802–2810Google Scholar
  12. Gajananda K (2007) Soil organic carbon and microbial activity: east Antarctica. Eur J Soil Sci 58(3):704–713.  https://doi.org/10.1111/j.1365-2389.2006.00857.x CrossRefGoogle Scholar
  13. Haendel D, Kaup E, Loopmann A, Wand U (1995) Physical and hydrochemical properties of water bodies. In: Bormann P, Fritzsche D (eds) The Schirmacher Oasis, Queen Maud Land, East Antarctica. Justus Perthes Verlag, Gotha, pp 279–295Google Scholar
  14. Hebert D, Richter W (1985) Moränen des Schelfeises als Höhenmarken in der Schirmacher Oase, Dronning Maud Land, Ostantarktika. Geod Geophys Veröff Berlin, R I 12:88–94Google Scholar
  15. Hobbie JE, Daley RJ, Jasper S (1977) Use of Nuclepore filters for counting bacteria by fluorescence microscopy. Appl Environ Microbiol 33(5):1225–1228Google Scholar
  16. Hofstee EH, Balks MR, Petchey F, Campbell DI (2006) Soils of Seabee Hook, Cape Hallett, northern Victoria Land, Antarctica. Antarct Sci 18(04):473–486.  https://doi.org/10.1017/S0954102006000526 CrossRefGoogle Scholar
  17. ISO 10694 (1995) Soil quality - determination of organic and total carbon after dry combustion(elementary analysis). http://infostore.saiglobal.com/en-gb/Standards/ISO-10694-1995-209525/. Accessed 9 May 2017
  18. ISO 11047 (1998) Soil quality - determination of cadmium, chromium, cobalt, copper, lead, manganese, nickel and zinc - Flame and electrothermal atomic absorption spectrometric methods. http://www.iso.org/standard/23117.html. Accessed 9 May 2017
  19. ISO 13878 (1998) Soil quality - determination of total nitrogen content by dry combustion (elemental analysis). http://www.iso.org/standard/23117.html. Accessed 9 May 2017
  20. Kalisz B, Lachacz A, Nitkiewicz M (2010) Transformation of organic matter in reclaimed post-lacustrine soils. In: Szajdak LW, Karabanov AK (eds) Physical, chemical and biological processes in soils. Prodruk, Poznan, pp 283–296Google Scholar
  21. Kaup E, Burgess JS (2002) Surface and subsurface flows of nutrients in natural and human impacted lake catchments on Broknes, Larsemann Hills, Antarctica. Antarct Sci 14(4):343–352.  https://doi.org/10.1017/S0954102002000123 CrossRefGoogle Scholar
  22. Krüger W (1995) Frost and insolation weathering. In: Bormann P, Fritzsche D (eds) The Schirmacher Oasis, Queen Maud Land, East Antarctica. Justus Perthes Verlag, Gotha, pp 190–199Google Scholar
  23. Lepane V, Kudrjašova M (2001) High-performance size exclusion chromatographic characterization of humic substances and dissolved organic matter from Baltic aquatic environment. Oil Shale 18:350–372Google Scholar
  24. Lepane V, Leeben A, Malashenko O (2004) Characterization of sediment pore-water dissolved organic matter of lakes by high-performance size exclusion chromatography. Aquat Sci 66(2):185–194.  https://doi.org/10.1007/s00027-004-0703-z CrossRefGoogle Scholar
  25. Lepane V, Tõnno I, Alliksaar T (2010) HPLC approach for revealing age-related changes of aquatic dissolved organic matter in sediment core. Procedia Chem 2(1):101–108.  https://doi.org/10.1016/j.proche.2009.12.016 CrossRefGoogle Scholar
  26. Liu S, Lim M, Fabris R, Chow CWK, Drikas M, Korshin G, Amal R (2010) Multi-wavelength spectroscopic and chromatography study on the photocatalytic oxidation of natural organic matter. Water Res 44(8):2525–2532.  https://doi.org/10.1016/j.watres.2010.01.036 CrossRefGoogle Scholar
  27. Matilainen A, Vieno N, Tuhkanen T (2006) Efficiency of the activated carbon filtration in the natural organic matter removal. Environ Int 32(3):324–331.  https://doi.org/10.1016/j.envint.2005.06.003 CrossRefGoogle Scholar
  28. Moorhead DL, Doran PT, Fountain AG, Lyons WB, McKnight DM, Priscu JC (1999) Ecological legacies: impacts on ecosystem of the McMurdo Valleys. Bioscience 49(12):1009–1019.  https://doi.org/10.1525/bisi.1999.49.12.1009 CrossRefGoogle Scholar
  29. O’Loughlin EJ, Chin Y-P (2004) Quantification and characterization of dissolved organic carbon and iron in sedimentary porewater from Green Bay, WI, USA. Biogeochemistry 71(3):371–386.  https://doi.org/10.1007/s10533-004-0373-x CrossRefGoogle Scholar
  30. Paech H-J, Stackebrandt W, Wetzel H-U (1995) Generalization of the geological history of the Schirmacher Oasis and Nunatak Metamorphic Complexes. In: Bormann P, Fritzsche D (eds) The Schirmacher Oasis, Queen Maud Land, East Antarctica. Justus Perthes Verlag, Gotha, pp 126–133Google Scholar
  31. Peuravuori J, Pihlaja K (1997) Molecular size distribution and spectroscopic properties of aquatic humic substances. Anal Chim Acta 337(2):133–149.  https://doi.org/10.1016/S0003-2670(96)00412-6 CrossRefGoogle Scholar
  32. Phartiyal B, Sharma A, Bera SK (2011) Glacial lakes and geomorphological evolution of Schirmacher Oasis, East Antarctica, during Late Quaternary. Quat Int 235(1-2):128–136.  https://doi.org/10.1016/j.quaint.2010.11.025 CrossRefGoogle Scholar
  33. Richter W (1985) Remarkable morphological forms in the Schirmacher Oasis, Dronning Maud Land, East Antarctica. Z Geol Wiss 13:381–398Google Scholar
  34. Richter W, Bormann P (1995a) Hydrology. In: Bormann P, Fritzsche D (eds) The Schirmacher Oasis, Queen Maud Land, East Antarctica. Justus Perthes Verlag, Gotha, pp 259–278Google Scholar
  35. Richter W, Bormann P (1995b) Geomorphology. In: Bormann P, Fritzsche D (eds) The Schirmacher Oasis, Queen Maud Land, East Antarctica. Justus Perthes Verlag, Gotha, pp 171–206Google Scholar
  36. Schwartzman DW (1999) Life, temperature, and the earth: the self-organizing biosphere. Columbia University Press, New YorkGoogle Scholar
  37. Smolander A, Kitunen V (2002) Soil microbial activities and characteristics of dissolved organic C and N in the relation to tree species. Soil Biol Biochem 34(5):651–660.  https://doi.org/10.1016/S0038-0717(01)00227-9 CrossRefGoogle Scholar
  38. Szajdak LW, Karabanov AK (2010) Physical, chemical and biological processes in soils. Prodruk, PoznanGoogle Scholar
  39. Vartiainen T, Liimatainen A, Kauranen P (1987) The use of TSK size exclusion columns in determination of the quality and quantity of humus in raw waters and drinking waters. Sci Total Environ 62:75–84.  https://doi.org/10.1016/0048-9697(87)90484-0 CrossRefGoogle Scholar
  40. Vestin JLK, Norström SH, Bylund D, Lundström US (2008) Soil solution and stream water chemistry in a forested catchment II: influence of organic matter. Geoderma 144(1-2):271–278.  https://doi.org/10.1016/j.geoderma.2007.11.027 CrossRefGoogle Scholar
  41. Zimmermann R (1977) Estimation of bacterial number and biomass by epifluorescence microscopy and scanning electron microscopy. In: Rheinheimer G (ed) Microbial ecology of the brackish water environment. Ecol stud 25, Berlin, pp 103–120.  https://doi.org/10.1007/978-3-642-66791-6_10

Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Institute of Chemistry and BiotechnologyTallinn University of TechnologyTallinnEstonia
  2. 2.Institute of Marine SystemsTallinn University of TechnologyTallinnEstonia
  3. 3.Institute of GeologyTallinn University of TechnologyTallinnEstonia
  4. 4.Shriram Institute for Industrial ResearchDelhiIndia

Personalised recommendations