Forest Ecology and Management 330 (2014) 261–270 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco Properties of soil organic matter in Podzols under mountain dwarf pine (Pinus mugo Turra.) and Norway spruce (Picea abies (L.) Karst.) in various stages of dieback in the East Sudety Mountains, Poland E. Jamroz ⇑, A. Kocowicz, J. Bekier, J. Weber Wroclaw University of Environmental and Life Sciences, Institute of Soil Science and Environmental Protection, Grunwaldzka 53, 50-357 Wroclaw, Poland a r t i c l e i n f o Article history: Received 17 February 2014 Received in revised form 11 July 2014 Accepted 14 July 2014 Keywords: Soil organic matter Mountain pine Norway spruce Humic acids Subalpine ecosystems a b s t r a c t Dieback of forests because of industrial air pollution was observed in the East Sudety Mountain, Poland. The properties of soil organic matter in Podzols in the subalpine region under mountain dwarf pine and Norway spruce in various stages of dieback (without degradation, with about 50% brown needles and dead trees) were investigated. The content of carbon, nitrogen, humic substances and characteristics of humic acids (HA) from organic and mineral horizons were analyzed. Forest dieback influenced HA properties depending on the species. Under pine, it led to an increase in alkyl and carboxyl C, while an increase in aromatic C and O- alkyl C was found at spruce sites. Humic acids under Picea abies were characterized by more aliphatic structures, whereas HA under Pinus mugo were more aromatic in nature. HA created in soils under pine stands in the investigated area showed lower solubility, higher stability and a lower tendency to translocate to deeper parts of the soil profile, compared to those under Norway spruce. Organic matter under spruce monoculture can be more susceptible to oxidation and may have less impact on the stability of soil aggregates, than those under pine ecosystems. Conversion of spruce monocultures to mixed forest – more resistant to biotic and abiotic disturbances – or introduction of the pioneer tree species in Norway spruce stands may be an effective tool to prevent forest decline and ensuring the stability of forest ecosystems. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction The forest decline in Central Europe’s mountain regions observed since the 1970s is the response of the environment to industrial air pollution and climate change (Emmer et al., 2000; Lindner et al., 2010). Vulnerability to biotic and abiotic disturbances depends on the ability of forest ecosystems to cope with the impacts, and thus regional conditions may differently affect the severity of the changes in forest cover. Forest management is an important factor in ensuring the stability of forest ecosystems, especially in mountain areas, and should target nature-based restoration to ensure high biodiversity and sustainable development of the environment. Improving our knowledge about potential impacts in different European forest regions may help forest management to conserve forest ecosystems (Lindner et al., 2010). Polish forest resources are a substantial part of the natural environment of the country. They are also a significant part of the geographic space, occupying 30.4% of the country’s area, and are ⇑ Corresponding author. Tel.: +48 71 3205632. E-mail address: elzbieta.jamroz@up.wroc.pl (E. Jamroz). http://dx.doi.org/10.1016/j.foreco.2014.07.020 0378-1127/Ó 2014 Elsevier B.V. All rights reserved. mainly publicly owned (81.3%). Along with shelterbelts, forests are second only to agriculture as a form of land use in Poland. The main species in the lowlands is pine, with Norway spruce in the mountain regions, prevailing in 83% of forest stands (FinP, 2012; Galka et al., 2014; Gołos, 2013). In the mountainous Sudetes region, as in other part of the Central Europe, spruce monocultures are very common due to artificial introduction in the 19th century (Turcani and Hlasny, 2007; Hurt and Penaz, 2010; Kukla and Kuklova, 2011). This has resulted in many problems, such as susceptibility to fungi. Millions of cubic meters of trees are infested annually by spruce bark beetles, which increases mortality under extreme conditions like storms and snow (Spiecker, 2000; Tesar, 2000; Turcani and Hlasny, 2007). Forests in the Sudety Mountains have also suffered as a consequence of long-term air pollution, mainly from sulfur and nitrogen dioxides from the region of Black Triangle, an area on the borders of the Czech Republic, Germany and Poland. In the 20th century, about 50% of the forest area in the East Sudety Mts. was significantly destroyed by air pollution of industrial origin (Fabiszewski and Brej, 1996; Emmer et al., 2000). Forests ecosystems in the Sudety Mts. have also been affected locally by mining activities in recent centuries and the exploitation of uranium ore, which has been developed since 262 E. Jamroz et al. / Forest Ecology and Management 330 (2014) 261–270 1948 (Ciezkowski et al., 1996). All these factors of anthropogenic origin have induced long-term disturbances in the balance of the environment. Forest ecosystems contain 49–53% of total terrestrial organic carbon (Cerli et al., 2008); thus, they are considered to be particularly important to carbon sequestration. About 60–70% of the Earth’s soil organic carbon occurs as humic substances (Loffredo and Senesi, 2006). Monitoring of these stocks, however, is very complicated due to the transformation of soil organic matter, which plays a crucial role in carbon capture and storage. Spatial variability is an additional factor that hinders the monitoring of soil organic carbon stocks. Environmental factors – such as soil properties, plant species, temperature, moisture, as well as pollution – determine the content of soil organic matter (SOM) in the ecosystem and determine the rate of organic matter decomposition. These factors influence the chemical structure and properties of humic substances in organic and deeper horizons of the soil (Drewnik, 2006; Pollakova et al., 2011; Ussiri and Johnson, 2003). Properties of soil organic matter in forest ecosystems can differ depending on the parent rock, soil type, climate, altitude, type of management and especially on the tree species, particularly in the forest floor horizons (Banach-Szott and Debska, 2008; Lal, 2005; Ussiri and Johnson, 2007). The effect of tree species on carbon stocks and nitrogen content has been described by several researchers (Cools et al., 2013; Hedde et al., 2008; Lal, 2005; Schulp et al., 2008; Smolander and Kitunen, 2002; Vesterdal et al., 2008; Zhang et al., 2008), but only a few papers have reported the characteristics of humic fractions and the rates of decomposition and humification, under various tree species in subalpine areas affected by anthropogenic activity. The composition of litter differs widely among plant species and consists mainly of a mixture of polysaccharides and lignin, aliphatic biopolymers and tannins (Kögel-Knabner, 2002). The results of Ussiri and Johnson (2007) confirmed that changes in forest cover can induce the transformation of humic substances, thereby accelerating the rate of mineralization. The rate of litter decomposition and the direction of humic substance transformation depend on many factors, including the properties of the litter (the chemical composition associated with different types of residue), the ratios of available C to N, the presence of phosphorus, the amount of lignin limiting microbial activity in the soil and moisture and oxygen content (Traversa et al., 2008). Organic matter decomposition, contributing to nutrient release and site fertility, is typically described by a gradual decrease in carbohydrates, an increase in carboxyl and alkyl carbon, as well as the breakdown of lignin (Ussiri and Johnson, 2007; Traversa et al., 2008). Decomposition processes also control the flux of CO2 from the soil and dissolved organic matter release, which precedes carbon turnover (Prescott, 2005). Recent studies on lignin, a major component of plant litter, have shown that its degradation is controlled by the availability of easily degradable carbon sources (Klotzbücher et al., 2011). Low molecular-weight humic substances, like fulvic acids (FA) (which are the labile fraction of humus, particularly in harsh climatic conditions with a large amount of precipitation) are leached to the deeper part of the soil. This is a typical occurrence, particularly in podzolic soils (Falsone et al., 2012). Low pH in the litter can decrease microbial decomposition of the low molecular-weight organic fraction, which is transported to the mineral soil horizons, enhancing nutrient translocation to the deeper part of soil (Buurman and Jongmans, 2005). Humic acids (HA) play a crucial role in many soil processes, mineral weathering, formation of soil aggregates, metal binding and organic matter stabilisation, but they are particularly important in mountain soils as they stabilise soil aggregates to diminish erosion processes (Bronick and Lal, 2005; Smeck and Novak, 1994). The aim of this work was to determine the properties of soil organic matter in Podzols of the subalpine region of the East Sudety Mountains, Poland, under mountain dwarf pine (Pinus mugo Turra.) and Norway spruce (Picea abies (L.) Karst.) in various stages of dieback (without degradation, with about 50% brown needles and dead trees). (i) We hypothesize that organic matter under Norway spruce (NS) will be more sensitive to die-back of the trees than that under Pinus mugo (PM). Organic matter under spruce monoculture will be more susceptible to oxidation and may have less impact on the stability of soil aggregates, than those under pine ecosystems. (ii) We further hypothesize that decomposition of soil organic matter under NS produces more low molecular humic substances, which are more easily leached to the deeper part of the soil profile. 2. Material and methods 2.1. Study site The study area (50°120 N 16°500 E) was located in the subalpine _ zone of the Śnieznik massif, which is the highest mountain (1425 m a.s.l.) of the East Sudety Mountains (Fig. 1). Its climatic conditions are characterized by annual precipitation of 1179 mm and mean annual temperature of 2.4 °C (Piasecki, 1996). Forests in the investigated area are classified as high mountain coniferous forest and consist of Norway spruce monocultures (P. abies (L.) Karst.), accompanied by mountain dwarf pine (P. mugo Turra.) at higher elevation. The type of vegetation is described as Pinetum mughi sudeticum and Plagiothecio-Piceetum (Goczol-Gontarek, 1996). Trees show different stages of degradation that appears as the deformation of needles and a gradual process of dying. In the most degraded ecosystems, natural plant communities have been replaced by subalpine meadow with the expansion of common grasses (Athyrium alpestre, Descchampsia flexuosa) and other species (Campanula barbata, Avenastrum planiculme, Athyrium alpestre, Hieracium alpinum, Hypochoeris uniflora, Mulgedium alpinum, Crepis conyzifolia) and particularly, under Norway spruce, Calluna vulgaris and Vaccinium myrtillus (Fabiszewski and Brej, 1996). The age of the forests in the study area is 90 years. To protect high mountain coniferous forests and subalpine meadows, the forest stands receive no management and they are left as a ‘‘dead forest’’. The investigation sites were located at an altitude of 1280– 1290 m a.s.l. under spruce forest (NS) and 1380–1400 m a.s.l. under mountain dwarf pine (MDP), representing different stages of degradation: without degradation signs (MDP A, NS A), with about 50% brown needles (MDP B, NS B), and without needles (MDP C, NS C). 2.2. Soils To reduce the effect of parent rock on the character of humus, all stands were located on the same soil type, Haplic Podzol (FAO, 2006) derived from gneiss. Soil profiles were located on relatively flat areas about 100 m away from each other, to avoid the influence of slope processes. There were three replicated soil profiles for each stand (A,B,C). Soil samples (about 200 g) were taken from each stand and from each genetic soil horizon. Two samples were prepared from each horizon for chemical analysis. Detailed structural analyses of humic acids were performed on samples from the Oa and Bhs horizons. Mineral horizons had the texture of loamy sand, with the presence of about 40–60% of particle size >2 mm, and very low pH throughout the whole profile. Selected soil properties are presented in Table 1. Humic substances were extracted from the 263 E. Jamroz et al. / Forest Ecology and Management 330 (2014) 261–270 Fig. 1. Study area, east Sudety Mountains. Oi, Oe, Oa and Bhs horizons. A detailed analysis was performed on humic acids from the Oa and Bhs horizons. 2.3. Extraction, fractionation and purification of humic acids (HA) and fulvic acids (FA) Humic substances were extracted from the soil using the procedure recommended by the International Humic Substances Society (Swift, 1996). Extracts were purified with a 0.1 M HCl/0.3 M HF solution in polypropylene tubes, left overnight and centrifuged. The precipitate was transferred to a Visking dialysis tube (Spectra/PorÒ 7 MWCO 10,000, Spectrum Europe B.V., Breda, The Netherlands) and was dialyzed against distilled water until a Cl test with AgNO3 was negative. After this procedure, the humic acids were freeze dried. Humic acids from the Oa horizon were extracted without HCl/HF treatment. FA extracts were passed through a column of XAD – 8 according to the procedure and finally through H+ – saturated cation exchange resin. The eluat was freeze dried. Elemental analysis of HA and FA was performed for C, H, and N using a Perkin–Elmer 2000 instrument. Oxygen was calculated from the mass balance. The ash content was determined by combustion overnight in a muffle furnace at 550 °C. On the basis of the elemental composition of HA, the degree of internal oxidation (x) was calculated according to the Zdanov formula (1965): x ¼ ð2O þ 3N  HÞ=C ð1Þ where O, N, H, C represent concentrations of elements in HA molecules expressed as atomic percent. Fourier transform infrared (FTIR) as well as 13C NMR techniques were used to analyze the structure and composition of humic acid molecules. The application of these methods in organic matter studies has become a valuable tool to provide information about the nature and functional groups, as well as the proportions of aromatic and aliphatic moiteties to better understand processes that occur in the environment (Kögel-Knabner, 1997; Malcolm, 1990; Cocozza et al., 2003; Drosos et al., 2009). FTIR has been developed Table 1 Selected properties of bulk soil samples in the study area. Object Horizon Depth cm pH (KCl) SOC (g kg1) Ntot (g kg1) C:N ratio MDP A Oi Oe Oa E Bhs 19–15 15–7 7–0 0–13 13–51 3.6 2.9 2.9 3.1 3.7 443.3 396.9 257.4 88.4 111.8 20.4 18.5 11.9 4.4 5.8 22.0 22.0 22.0 20.0 19.0 MDP B Oie Oa E Bhs 10–5 5–0 0–17 17–29 3.3 3.0 2.8 3.5 430.0 215.1 24.1 64.2 22.7 13.2 1.7 3.1 19.0 16.0 14.0 21.0 MDP C Oie Oa E Bhs 14–10 10–0 0–11 11–33 3.5 2.7 2.7 3.6 426.0 229.7 19.1 49.0 21.0 11.7 1.1 2.2 20.0 20.0 17.0 22.0 NS A Oi Oe Oa E Bhs 13–9 9–4 4–0 0–20 20–41 2.8 2.9 2.9 3.2 4.0 357.2 352.8 229.0 19.7 54.6 15.4 12.9 11.4 ND 3.0 23.0 23.0 20.0 ND 18.0 NS B Oie Oa E Bhs 12–4 4–0 0–13 13–45 2.9 2.7 3.0 3.6 332.1 210.5 25.1 77.1 14.8 9.1 1.6 3.8 22.0 23.0 15.0 20.0 NS C Oie Oa E Bhs 12–8 8–0 0–9 9–23 2.9 2.8 2.7 3.2 301.2 201.3 13.1 43.5 14.1 10.1 1.2 2.2 22.0 20.0 11.0 20.0 ND – no data. Legend: MDP – Pinus mugo stand, NS – Picea abies stand A – without deformation of needles; B – with 50% brown needles; C – dead trees, without needles. and successfully applied to the study of humic substances of different origin and importance of this method is to provide the principal classes of chemical groups which are present in the soil organic matter (Shnitzer, 1971; Inbar et al., 1992; Senesi et al., 1991; Haberhauer et al., 1998; Cocozza et al., 2003; Traversa et al., 2008). 264 E. Jamroz et al. / Forest Ecology and Management 330 (2014) 261–270 Fourier transform infrared spectra were recorded with a FTIR Bruker 66/s spectrometer using potassium bromide pellets (300 mg KBr) containing 0.3–0.6 mg of freeze dried humic acid. Solid-state 13C NMR spectra of humic acids were obtained using a 300 MHz AMX Bruker NMR spectrometer at a resonance frequency of 226.35 MHz, using standard procedures (Bonanomi et al., 2011; Conte et al., 2004) applying a ramped-cross polarization magic angle spinning technique RAMP-CP (Given et al., 1984) with a spinning speed of 8 kHz. A contact time of 5 ms and a pulse delay of 500 ms were used. Dry humic acids were packed in a 4 mm diameter cylindrical zirconia rotors with Kel-F caps. The spectra were recorded at LB (Lorentzian line broadening) 50 and the spectral width was 473 ppm. The number of scans for the samples was 10,000. 13C – CPMAS NMR spectra were integrated using Bruker Topspin version 2.1 program. A relative concentration of functional groups were determined as the ratio of studied resonance lines integral area to integral area of all resonances up to 220 ppm. The NMR spectra were divided into the following chemical shift regions: Alkyl C: 0–45 ppm; O-alkyl C: 45–110 ppm; Aromatic C: 110–160 ppm; Carboxyl C: 160–210 ppm. Cross-polarization, magic angle spinning nuclear magnetic resonance (solid state CPMAS–NMR) is the most common type of NMR and is generally used in the study of humic substances to compare differences in the concentration of functional groups (Barancikova and Makovnikova, 2003; Wilson et al., 1983; Wilson, 1987; Swift, 1996; Kögel-Knabner, 1997). Content of total organic carbon was analyzed with a CS-mat 5500 instrument (Strohlein GmbH & Co., Kaarst, Germany, currently Bruker AXS Inc., Madison, WI, USA). Total nitrogen was analyzed by the Kjeldahl method using a Buchi Labortechnik GmbH N analyzer. Results were verify using Statistics for Windows 9.0. Means were compared by the t-test, at a confidence level of p < 0.05. 3. Results and discussion 3.1. Content of humic substances In oligotrophic conifer forests, most of the organic carbon is stored in the O horizons. The litter composition in the investigated area depended on the vegetation type but was generally poor in nitrogen; together with the low pH, this led to slow decomposition of organic matter as evidenced by a relatively high C:N ratio (Table 1). The contribution of humic substances in soil organic matter (SOM) depended on the stand type and site degradation, particularly in B horizons (Fig. 2). In illuvial horizons, the share of fulvic acids in soil organic matter extracted under mountain pine was significantly lower than under spruce. In spruce stands, the share of FA in SOM, was greater than HA in Bhs horizons and significantly increased with soil depth, which is typical for the podsolization process where soluble humic substances are exported from the forest floor to the deeper part of the soil profile (Rumpel et al., 2002; Ussiri and Johnson, 2007; Falsone et al., 2012). 3.2. Elemental analysis of humic and fulvic acids The elemental composition of humic and fulvic acids is presented in Table 2. In the HA, from both the Oa and Bhs horizons, the concentration of carbon was significantly lower under spruce than mountain pine. Under degraded P. mugo, molecules of humic acids were characterized by a significantly lower content of carbon in comparison with non-degraded stands. FA from Oa horizons under P. mugo and Norway spruce were characterized by a higher content of carbon in comparison with Bhs horizons. The degree of forest dieback was correlated with an increase in carbon content in fulvic acids from Oa horizons. The concentrations of hydrogen were significantly lower in humic and fulvic acids extracted from the Bhs horizon in both stands in comparison to the Oa horizon, which confirms the statement that the humification process, which is more advanced in mineral horizons, leads to a decrease in H in HA molecules (Falsone et al., 2012; Martin et al. 1998). Atomic ratios are often used to establish the source of organic matter, the degree of condensation or the environmental conditions under which humic substances are formed (Banach-Szott et al., 2014; Giovanela et al., 2004; Martin et al., 1998; Ussiri and Johnson, 2007). The H/C atomic ratio, as an indicator of aliphacity (Rice and MacCarthy, 1991), shows that humic acids from the NS stands in both the Oa and B horizons were more aliphatic (higher H/C) and less humified (Ferreira et al., 2013) than at MDP sites, Fig. 2. The content of humic and fulvic fraction in soil profile under mountain pine and Norway spruce. Legend: MDP – Pinus mugo stand, NS – Picea abies stand A – without deformation of needles; B – with 50% brown needles; C – dead trees, without needles. Oi, Oe, Oa, Bhs – soil horizons. 265 E. Jamroz et al. / Forest Ecology and Management 330 (2014) 261–270 Table 2 Elemental composition of humic acids (HA) and fulvic acids (FA) from Podzols under mountain pine and Norway spruce – in atomic percentage of moisture and ash free sample. Sample %C HA %C FA %H HA %H FA %N HA %N FA %O HA %O FA Oa MDPA MDP B MDP C NS A NS B NS C 35.9a 35.3ab 35.1b 32.7d 34.3c 34.8bc 33.1d 33.4c 34.7b 32.7e 34.6b 35.5a 41.1c 41.1c 42.5a 42.4b 40.4d 42.4ab 39.1a 37.8b 36.5d 37.3c 36.2e 35.7f 2.1a 1.7b 1.9ab 1.8c 1.8bc 1.6c 1.8a 1.7b 1.3d 1.5c 1.7b 1.9a 20.9e 21.9c 20.5f 23.1b 23.4a 21.2d 26.0e 27.2c 27.6b 28.5a 27.6b 26.9d Bhs MDPA MDP B MDP C NS A NS B NS C 36.6a 36.0b 33.9d 34.3c 30.6f 32.8e 28.4a 26.2b 29.0a 29.0a 26.3b 24.3c 38.1d 36.2e 36.5e 39.1b 38.3c 40.6a 26.0a 24.3c 23.5d 25.9a 25.2b 23.7d 2.2b 1.8c 1.8c 2.4ab 1.9cd 2.5a 0.7a 0.6a 0.6a 0.5a 0.7a 0.6a 23.1f 26.0c 27.8b 24.2d 29.2a 24.1e 45.0e 48.9b 46.8d 44.6f 47.8c 51.4a Means followed by the same letter are not significantly different at p < 0.05 (acc. t-test). Legend: see Table 1. Table 3 Atomic ratios and degree of internal oxidation of humic acids (HA) and fulvic acids (FA) from Podzols under mountain pine and Norway spruce. Sample H/C HA H/C FA O/C HA O/C FA C/N HA C/N FA x HA Oa MDPA MDP B MDP C NS A NS B NS C 1.15c 1.16c 1.21b 1.30a 1.18bc 1.22b 1.18a 1.13a 1.05b 1.14a 1.05b 1.01b 0.58a 0.62a 0.58a 0.71a 0.68a 0.61a 0.79a 0.81a 0.80a 0.87a 0.80a 0.76a 17.09c 20.76a 18.47bc 18.17bc 19.06b 21.75a 18.39f 19.65d 26.69a 21.80b 20.35c 18.68e 0.19 0.22 0.12 0.28 0.34 0.14 Bhs MDPA MDP B MDP C NS A NS B NS C 1.04d 1.00e 1.08c 1.14b 1.25a 1.24a 0.92b 0.93b 0.81d 0.89c 0.96a 0.98a 0.63e 0.72d 0.82b 0.71d 0.95a 0.74c 1.58c 1.87b 1.61c 1.54c 1.82b 2.12a 16.64c 20.00a 18.83ab 14.29de 16.11cd 13.12e 40.57d 43.67c 48.33b 58.00a 37.57e 40.50d 0.40 0.59 0.72 0.48 0.84 0.46 Means followed by the same letter are not significantly different at p < 0.05 (acc. t-test). Legend: see Table 1. Fig. 3. FTIR spectra of humic acids from the Oa horizons under mountain pine and Norway spruce forest. Legend: see Fig. 2. regardless of tree degeneration (Table 2). In relatively undisturbed forests under P. mugo, HA from the Oa horizon had a more aliphatic character than those from illuvial horizons, while HA from the B horizons under the Norway spruce forest in stands B and C were more aliphatic than HA from the Oa. Fulvic acids from the Oa horizons also had a more aliphatic character than those from Bhs horizons, regardless of the tree species (Table 2). In the Oa horizons there were no significant differences in degree of aliphaticity between P. mugo and Norway spruce stands. Many aliphatic structures are known to be recalcitrant during the decomposition process (Ussiri and Johnson, 2003); therefore, they may be more present in Oa horizons than in mineral soil horizons. Natural stands of both species confirmed this statement. The chemical nature of the decomposed material plays an important role in the building of humic substances; therefore, a lower content of nitrogen in spruce needles than in pine (Birmann and Körner, 2009) affected lower N concentration in HA from the spruce stands and may be one of the factors influencing lower humification of litter under Norway spruce in comparison with pine, particularly in harsh mountain conditions. In humic acids from the Bhs horizons on both stands, except NS A object, higher values of the O/C ratio and the degree of internal oxidation (x) were found in comparison to the litter. HA of the spruce stands had higher oxidation indices than those of P. mugo. The forest litter consists of not only litterfall from the trees but also undergrowth vegetation. Among the trees in the PlagiothecioPiceetum community in the area of investigation, perennial shrubs such as Calluna vulgaris or Vaccinium myrtillus were more often found, while in the Pinetum mughi sudeticum community, common mountain grasses were found, particularly in the sites with dead or dying trees. The decomposition of such different materials leads to the formation of humic substances of different humification degree and structure. 266 E. Jamroz et al. / Forest Ecology and Management 330 (2014) 261–270 Fig. 4. FTIR spectra of humic acids from the Bhs horizons under mountain pine and Norway spruce forest. Legend: see Fig. 2. 3.3. FTIR analysis of humic acids The FTIR spectra of humic acids from the Oa and Bhs horizons under spruce and mountain pine were similar (Fig. 3). However, there were some differences in their intensity at 2922 cm1 and 2852 cm1. These bands were more intense in the mineral horizon of the spruce stands, especially in degraded areas (NS B and NS C). These bands represent aliphatic CAH vibrations of aliphatic methyl and methylene groups (Senesi et al., 1990). This indicates that content of aliphatic groups was greater in mineral horizons, together with the degree of degeneration of the trees. These differences were more intense on the spruce stands than on the pine stands. This is also consistent with the results obtained from elemental analysis of humic acids (Table 3) and a study by Bonifacio et al. (2006) reporting a higher degree of aliphaticity in mineral horizons of humic acids in the Karkonosze Mts. The peak at 1725 cm1 is assigned to C@O stretching of COOH and ketones. An absorption band in the region of 1640–1620 cm1 was more intense in the Oa horizon in mountain pine ecosystems than in spruce stands (Fig. 3). In degraded forest stands (MDP C, NS C), this band was less intense. The band may be associated with aromatic C@C, C@O groups of quinones, and ketones (Traversa et al., 2008). The absorption band at about 1554 cm1, the most intense band in the Bhs horizon of the degraded spruce stand, indicates NAH and CAN bending of amide II and aromatic C@C (Traversa et al., 2008). Haberhauer et al. (1998) suggested that the intensity of this peak may reflect the decomposition of organic matter. Changes in vegetation towards grasses in a mountain pine region have resulted in the formation of organic matter with a higher degree of humification than in spruce stands. The reason for this effect may be the high content of polyphenols in spruce needles and bilberry litter, which reduce the decomposition processes in spruce stands (Albers et al., 2004; Gallet and Lebreton, 1995). In all horizons, humic acids featured a sharp band at about 1060 cm1, which was less intense in degraded forest sites (B,C), indicating the presence of polysaccharides or polysaccharide-like substances (Gonzalez-Perez et al., 2008; Inbar et al., 1989). Absorption bands in this region, called the ‘‘fingerprint region’’ are affected by the molecular structure (Swift, 1996). Bands at 560 cm1 and 475 cm1, which were only found in the Bhs horizon, are associated with inorganic material, such as quartz minerals (Haberhauer et al., 1998). These studies are consistent with the results of Traversa et al. (2008) and Couteaux et al. (1995) indicating the aromatic nature of litter organic matter. On the basis of our study, humic acids from O horizons under mountain pine are more aromatic than those Fig. 5. Distribution of C in humic acids from the Oa horizons based on 13 C NMR analysis. Legend: see Fig. 2. E. Jamroz et al. / Forest Ecology and Management 330 (2014) 261–270 Fig. 6. Solid-state Fig. 7. Solid-state 13 13 C NMR spectra for humic acids isolated from the Oa horizons under mountain pine and Norway spruce forest. C NMR spectra for humic acids isolated from the Bhs horizons under mountain pine and Norway spruce forest. 267 268 E. Jamroz et al. / Forest Ecology and Management 330 (2014) 261–270 from Norway spruce. The findings from the FTIR spectra also confirm the results of the HA elemental composition (Tables 2 and 3). 3.4. 13 C NMR analysis of humic acids Example spectra of humic acids extracted from Podzols under P. abies and P. mugo are presented in Figs. 6 and 7 and distribution of C in humic acids based on 13C NMR analysis is presented in Fig. 5. All spectra have large peaks of alkyl intensity (0–45 ppm) in both the Oa and Bhs horizons, which mainly come from surface waxes and cutin (Kögel-Knabner, 1997; Lorenz et al., 2000). The alkyl C resonances were more intense in spruce stands without degradation than in areas with P. mugo. However, the degradation process also caused an increase in alkyl-C in humic acids from pine stands in comparison to those from spruce. High alkyl C may be connected with high concentration of resins which are present in pine species and are more resistant to decomposition than lignins (KögelKnabner, 2002; Strukelj et al., 2013). The signal at 30 ppm, reflects methyl C in long-chain aliphatic compounds of variable origin such as cutin acids, fatty acids, lipids, and others (Kögel-Knabner, 1997). Sharp peaks from carbohydrates were found in the O-alkyl C region (50–110 ppm), which were more intense in the Oa horizon than in Bhs horizons (Kögel-Knabner, 1997). The peak at 55– 57 ppm, a methoxyl signal, was particularly sharp in non-degraded pine stands in the Oa and Bhs horizons; this was assigned to lignin. The peak at 72 ppm comes from carbohydrates and was particularly sharp in the Oa horizon, although it dominated the O-alkyl C region in the Bhs horizon as well. In the aromatic and unsaturated C region (110–160 ppm), there was a peak at 130 ppm contributed by aromatic carbon in lignin (Baldock and Preston, 1995); again, this was sharpest in the Oa horizon under P. mugo. With increasing forest dieback, we observed an increase in signals in the aromatic and phenolic regions, which probably are connected with slower degradation of lignins compared with carbohydrates. Alternatively, this may come from lignin-like aromatic by-products which can form during decomposition processes (Strukelj et al., 2013). In the region of carbonyl groups (160–220 ppm), we observed a sharp peak at 173 ppm, particularly in the humic acids from dying P. mugo stands. Zech et al. (1987), while comparing the decomposition of pine and spruce needles, observed that the process was accompanied by an increase in aliphatic substances as well as carboxyl content. An increase in carboxyl groups with an increase in tree degeneration in the humic acids of organic horizons under mountain pine was reported by Jamroz (2012) on the basis of the E4/E6 ratio and by Bonifacio et al. (2006) in humic acids from Podzols in the Karkonosze Mountains on the basis of the E4/E6 ratio and FTIR analysis. In our study, we have shown that stable aliphatic compounds like cutin and lipids, which are probably of microbial origin, accumulate during SOM transformation processes (decomposition and humification) despite tree degeneration under mountain dwarf pine, while the spruce ecosystem favored a decrease in aliphaticity in the Oa horizon under conditions of a disturbed ecosystem. In the mineral horizons, aliphatic compounds were more pronounced under Norway spruce, confirming the results from the FTIR analysis (Fig. 4). Dieback of the trees was accompanied by changes in vegetation towards grasses, which are richer in the cellulosic component (Ververis et al., 2004). Enrichment of aliphatic groups in humic acids may be, according Bonifacio et al. (2006), connected with these shifts. 4. Conclusions In the subalpine region of the East Sudety Mountains, degradation processes together with podsolization and the type of vegetation influence the properties of soil organic matter. The background of forest dieback connected with acid deposition via atmospheric precipitation and fog and cloud deposition is in line with atmospheric circulation. Most of deposition is concentrated along SW–W–NW–N–NE (Błaś et al., 2010). Properties of the crown layer are also important for the modification of air pollution flow (Tesar, 2000). These are the distinct reasons for differences in forest health and the various impacts of degradation processes on soil properties, particularly on soil organic matter. Low molecular fulvic fractions under P. abies are more easily transported to the deeper part of the soil profile than under mountain pine, which may favor the leaching of nutrients from upper soil horizons in forest ecosystems composed of spruce monocultures. The humic acids of the Norway spruce stands both in the Oa and B horizons were more aliphatic and less humified than those under mountain pine. Therefore organic matter under spruce monoculture can be more susceptible to oxidation and may have less impact on the stability of soil aggregates, than those under pine ecosystems. The results obtained from the FTIR analysis confirm those from the elemental analysis and 13C NMR spectroscopy and showed an increase in the aliphaticity of HA in the most degraded stands, particularly in P. mugo stands. Humic acids under P. abies were characterized with more aliphatic structures, whereas HA under P. mugo had a more aromatic nature, which may be connected with changes in the plant community toward subalpine grasses. This suggests that humic acids of pine stands in the investigated area are characterized by less solubility, higher stability and a lower tendency to migrate to deeper parts of the soil profile. Forest dieback led to an increase in the alkyl C and carboxyl content in the pine stands and an increase in aromatic C and O- alkyl C at the spruce sites, reflecting the lower degree of decomposition of the spruce litter. Sustainable forest management in a changing environment should take into account that narrowing biodiversity of the monocultures and negative changes in soil organic matter and soil properties do not ensure stability of the ecosystems (Lindner et al., 2010; Spiecker, 2000). Conversion of spruce monocultures to mixed forest – more resistant to biotic and abiotic disturbances – or introduction of the pioneer tree species in Norway spruce stands (rowan or/and birch) may be an effective tool to prevent forest decline and improve the properties of soil organic matter to diminish erosion processes in mountain regions. Acknowledgements Authors thank Dr. Maria Jerzykiewicz from the Faculty of Chemistry at Wroclaw University for help with the FTIR and 13C NMR analysis. We wish to express our thanks to the two anonymous Reviewers and Editor of the Journal for their helpful and constructive suggestions. The project was supported by the Polish Ministry of Science and Higher Education (Grant No. 2P06S05929). References Albers, D., Migge, S., Schaefer, M., Scheu, S., 2004. Decomposition of beech leaves (Fagus sylvatica) and spruce needles (Picea abies) in pure and mixed stands of beech and spruce. Soil Biol. Biochem. 36, 155–164. Baldock, J.A., Preston, C.M., 1995. Chemistry of carbon decomposition processes in forests as revealed by solid-state carbon-13 nuclear magnetic resonance. carbon forms and functions in frest soils. In: McFee, W.W., Kelly, J.M. (Eds.). Soil Science Society of America, Madison, WI, pp. 89–117. Banach-Szott, M., De˛bska, B., 2008. Content of phenolic compounds in fulvic and humic acid fractions of forest soils. Polish J. Environ. Stud. 17 (4), 463–472. Banach-Szott, M., Debska, B., Rosa, E., 2014. Effect of soil pollution with polycyclic aromatic hydrocarbons on the properties of humic acids. J. Soils Sediments 14, 1169–1178. Barančíková, G., Makovníková, J., 2003. The influence of humic acid quality on the sorption and mobility of heavy metals. Plant Soil Environ. 49 (12), 565–571. E. Jamroz et al. / Forest Ecology and Management 330 (2014) 261–270 Birmann, K., Körner, C., 2009. Nitrogen status of conifer needles at the alpine treeline. Plant Ecol. Divers. 2 (3), 233–241. http://dx.doi.org/10.1080/ 17550870903473894. _ Sobik, M., Klimaszewska, K., Nowiński, K., Namieśnik, J., Błaś, M., Polkowska, Z., 2010. Fog water chemical composition in different geographic regions of Poland. Atmos. Res. 95, 455–469. Bonanomi, G., Incerti, G., Barile, E., Capodilupo, M., Antignani, V., Mingo, A., Lanzotti, V., Scala, F., Mazzoleni, S., 2011. Phytotoxicity, not nitrogen immobilization, explains plant litter inhibitory effects: evidence from solid-state 13C NMR spectroscopy. New Phytol. 191, 1018–1030. Bonifacio, E., Santoni, S., Celi, L., Zanini, E., 2006. Spodosol-Histosol evolution in the Krkonose National Park (CZ). Geoderma 131, 237–250. Bronick, C.J., Lal, R., 2005. Soil structure and management: a review. Geoderma 124, 3–22. Buurman, P., Jongmans, A.G., 2005. Podzolisation and soil organic matter dynamics. Geoderma 125, 71–83. Cerli, C., Celi, L., Kaiser, K., Guggenberger, G., Johansson, M.-B., Cignetti, A., Zanini, E., 2008. Changes in humic substances along an age sequence of spruce stands planted on former agricultural land. Org. Geochem. 39, 1269–1280. Ciezkowski, W., Kryza, H., Kryza, J., Pulina, M., Rehak, J., Stasko, S., Tarka, R., 1996. The impact of anthropogenic factors upon quantity and quality of underground water. In: Jahn, A., Kozlowski, S., Pulina, M. (Eds.), The Massif of Snieznik, Changes in the natural environment, Polish Ecological Agency, pp. 147–168 (in Polish with English Abstract). Cocozza, C., D’Orazio, V., Miano, T.M., Shotyk, W., 2003. Characterization of solid and aqueous phases of a peat bog profile using molecular fluorescence spectroscopy, ESR and FT-IR, and comparison with physical properties. Org. Geochem. 34, 49– 60. Conte, P., Spaccini, R., Piccolo, A., 2004. State of the art of CPMAS 13C-NMR spectroscopy applied to natural organic matter. Prog. Nucl. Mag. Res. Sp. 44, 215–223. Cools, N., Vesterdal, L., De Vos, B., Vanguelova, E., Hansen, K., 2013. Tree species is the major factor explaining C:N ratios in European forest. Forest Ecol. Manag. 311, 3–16. Couteaux, M.M., Bottner, P., Berg, B., 1995. Litter decomposition, climate and litter quality. Trends Ecol. Evol. 10, 63–66. Drewnik, M., 2006. The effect of environmental conditions on the decomposition rate of cellulose in mountain soils. Geoderma 132, 116–130. Drosos, M., Jerzykiewicz, M., Deligiannakis, Y., 2009. H-binding groups in lignite vs. soil humic acids: NICA-Donnan and spectroscopic parameters. J. Colloid Interface Sci. 332 (1), 78–84. Emmer, I.M., Wessel, W.W., Koojiman, A., Sevink, J., Fanta, J., 2000. Restoration of degraded central – European mountain forest soils under changing environmental circumstances. In: Klimo et al. (Eds.), Spruce Monocultures in Central Europe – Problems and Prospects. European Forest Institute, pp. 81–92. Fabiszewski, J., Brej, T., 1996. Dynamic floral and vegetative changes. In: Jahn, A., Kozlowski, S., Pulina, M. (Eds.), The Massif of Snieznik, Changes in the natural environment, Polish Ecological Agency, pp. 219–228 (in Polish with English Abstract). Falsone, G., Celi, L., Capimi, A., Simonov, G., Bonifacio, E., 2012. The effect of clear cutting on podzolisation and soil karbon dynamice in Boral forests (Middle Taiga zone, Russia). Geoderma 177–178, 27–38. FAO 2006. World Reference Base for Soil Resources. World Soil Resources Report No. 103, FAO, Rome. Ferreira, F.P., Vidal-Torrado, P., Otero, X.L., Buurman, P., Martin-Neto, L., Boluda, R., Macias, F., 2013. Chemical and spectroscopic characteristics of humic acids in marshes from the Iberian Peninsula. J. Soils Sediments 13 (2), 253–264. FinP, 2012. Forests in Poland. In: Milewski, W. (Ed.). The State Forests Information Centre, Warsaw. Galka, B., Labaz, B., Bogacz, A., Bojko, O., Kabala, C., 2014. Conversion of Norway spruce forests will reduce organic carbon pools in the mountain soils of SW Poland. Geoderma, <http://dx.doi.org/10.1016/j.geoderma.2013.08.029>. Gallet, C., Lebreton, P., 1995. Evolution of phenolic patterns in plants and associated litters and humus of a mountain forest ecosystem. Soil Biol. Biochem. 27 (2), 157–165. Giovanela, M., Parlanti, E., Soriano-Sierra, E.J., Soldi, M.S., Sierra, M.M.D., 2004. Elemental compositions, FT-IR spectra and thermal behavior of sedimentary fulvic and humic acids from aquatic and terrestrial environments. Geochem. J. 38, 255–264. Given, P.H., Spackman, W., Painter, P.C., Road, C.A., Ryan, N.J., Alemany, L., Pugmire, L.J., 1984. The fate of cellulose and lignin in peats: an exploratory study of the input to coalification. Org. Geochem. 6 (C), 399–407. Goczol-Gontarek, M., 1996. Karkonosze National Park and Karkonosze. In: National Research Council. Biodiversity Conservation in Transboundary Protected Areas. The National Academies Press, Washington, DC, pp. 147–150. Gołos, P., 2013. Value of forest resources in Poland (in Polish with English Summary). Sylwan 157 (1), 3–16. Gonzalez-Perez, M., Torrado, P.V., Colnago, L.A., Mertin-Neto, L., Otero, X.L., Milori, D.M.B.P., Gomes, F.H., 2008. 13C NMR and FTIR spectroscopy characterization of humic acids in spodosols under tropical rain forest in southeastern Brazil. Geoderma 146, 425–433. Haberhauer, G., Rafferty, B., Strebl, F., Gerzabek, M.H., 1998. Comparison of the composition of forest soil litter derived from three different sites at various decompositional stages using FTIR spectroscopy. Geoderma 83, 331–342. Hedde, M., Aubert, M., Decaens, T., Bureau, F., 2008. Dynamics of soil carbon in a beechwood chronosequence forest. For. Ecol. Manage. 255 (1), 193–202. 269 Hurt, V., Penaz, J., 2010. Possibilities of assessing the condition of cultivated spruce stands intended for transformation to close-to-nature forests as exemplified by a supraregional biocentre – the first stage. Beskydy 3 (2), 139–150. Inbar, Y., Chen, Y., Hadar, Y., 1989. Solid-state carbon-13 nuclear magnetic resonance and infrared spectroscopy of composted organic matter. Soil Sci. Soc. Am. J. 53, 1695–1701. Inbar, Y., Hadar, Y., Chen, Y., 1992. Characterization of humic substances formed during the composting of solid wastes from wineries. Sci. Total Environ. 113, 35–48. Jamroz, E., 2012. Properties of soil organic matter in the forest soils under mountain _ dwarf pine in the Śnieznik Kłodzki Reserve. Sylwan 156 (11), 825–832. Klotzbücher, T., Kaiser, K., Guggenberger, G., Gatzek, C., Kalbitz, K., 2011. A new conceptual model for the fate of lignin in decomposing plant litter. Ecology 92 (5), 1052–1062. Kögel-Knabner, I., 1997. 13C and 15N NMR spectroscopy as a tool in soil organic matter studies. Geoderma 80, 243–270. Kögel-Knabner, I., 2002. The macronolecular organic composition of plant and microbial residues as inputs to soil organic matter. Soil Biol. Biochem. 34, 139– 162. Kukla, J., Kuklova, M., 2011. Impact of long-term cultivation of spruce monocultures on development of forest soils. Beskydy 4 (2), 161–172. Lal, R., 2005. Forest soils and carbon sequestration. For. Ecol. Manag. 220, 242– 258. Lindner, M., Maroschek, M., Netherer, S., Kremer, A., Barbati, A., Garcia-Gonzalo, J., Seidl, R., Delzon, S., Corona, P., Kolstrom, M., Lexer, M.J., Marchetti, M., 2010. Climate change impacts, adaptive capacity, and vulnerability of European forest ecosystems. For. Ecol. Manag. 259, 698–709. Loffredo, E., Senesi, N., 2006. The role of humic substances in the fate of anthropogenic organic pollutants in soil with emphasis on endocrine disruptor compounds. In: Twardowska, I. et al. (Eds.), Soil and Water Pollution Monitoring, Protection and Remediation. Springer, pp. 3–23. Lorenz, K., Preston, C.M., Raspe, S., Morrison, I.K., Feger, K.H., 2000. Litter decomposition and humus characteristics in Canadian and German spruce ecosystems: information from tannin analysis and 13C CPMAS NMR. Soil Biol. Biochem. 32, 779–792. Malcolm, R.L., 1990. Variations between humic substances isolated from soils, stream waters, and groundwaters as revealed by 13C-NMR spectroscopy. In: MacCarthy, P., Clapp, C.E., Malcolm, R.L., Bloom, P.R. (Eds.), Humic Substances in Soil and Crop Sciences: Selected Readings. American Society of Agronomy, Soil Science Society of America, Madison, pp. 13–36. Martin, D., Srivastava, P.C., Ghosh, D., Zech, W., 1998. Characteristics of humic substances in cultivated and natural forest soils of Sikkim. Geoderma 84, 345– 362. Piasecki, J., 1996. Selected features of climate in the Massif of Snieznik. In: Jahn ,A., Kozlowski, S., Pulina, M. (Eds.), The Massif of Snieznik, Changes in the natural environment, Polish Ecological Agency, pp. 189–206 (in Polish with English Abstract). Polláková, N., Gonet, S.S., Dêbska, B., Heczko, J., 2011. Soil organic matter under introduced and indigenous woody plants in arboretum mlyňany. Polish J. Soil Sci. 44 (2), 133–141. Prescott, C.E., 2005. Do rates of litter decomposition tell us anything we really need to know? For. Ecol. Manag. 220, 66–74. Rice, J.A., MacCarthy, P., 1991. Statistical evaluation of the elemental composition of humic substances. Org. Geochem. 17 (5), 635–648. Rumpel, C., Kogel-Knabner, I., Bruhn, F., 2002. Vertical distribution, age and chemical composition of organic carbon in two forest soils of different pedogenesis. Org. Geochem. 33, 1131–1142. Schulp, C.J.E., Nabuurs, G.J., Verburg, P.H., de Waal, R.W., 2008. Effect of tree species on carbon stocks in forest floor and mineral soil and implications for soil carbon inventories. For. Ecol. Manag. 256, 482–490. Senesi, N., Miano, T.M., Sposito, G., 1990. Molecular and metal chemistry of leonardite humic acid in comparison to typical soil humic acids. In: Proceedings of the International Conference on Peat Production and Use-Peat 90, Jyväskylä, 11–15 June 1990. The Association of Finnish Peat Industries, pp. 412–421. Senesi, N., Miano, T.M., Provenzano, M.R., Brunetti, G., 1991. Characterization, differentiation and classification of humic substances by fluorescence spectroscopy. Soil Sci. 152, 259–271. Shnitzer, M., 1971. Characterization of humic constituents by spectroscopy. Soil biochemistry, vol. 2. In: McLaren, A.D., Skujins, J. (Eds.). Marcel Dekker, New York, pp. 60–95. Smeck, N.E., Novak, J.M., 1994. Weathering of soil clays with dilute sulfuric acid as influenced by sorbed humic substances. Geoderma 63, 63–76. Smolander, A., Kitunen, V., 2002. Soil microbial activities and characteristics of dissolved organic C and N in relation to tree species. Soil Biol. Biochem. 34, 651– 660. Spiecker, H., 2000. Growth of Norway spruce (Picea abies [L.] Karst.) under changing environmental conditions in Europe. In: Klimo et al. (Eds.), Spruce Monocultures in Central Europe – Problems and Prospects. European Forest Institute, pp. 11–26. Strukelj, M., Brais, S., Quideau, S.A., Angers, V.A., Kebli, H., Drapeau, P., Oh, S.-W., 2013. Chemical transformations in downed logs and snags of mixed boreal species during decomposition. Can. J. For. Res. 43, 785–798. Swift, R.S., 1996. Organic matter characterization. In: Methods of soil analysis. Part 3. Chemical methods – SSSA Book Series no.5 Soil Science Society of America and American Society of Agronomy, pp. 1011–1068. 270 E. Jamroz et al. / Forest Ecology and Management 330 (2014) 261–270 Tesar, V., 2000. The impact of air pollution and strategies for spruce monoculture conversion in central Europe. In: Klimo et al. (Eds.), Spruce Monocultures in Central Europe – Problems and Prospects. European Forest Institute, pp. 27–34. Traversa, A., D’Orazio, V., Senesi, N., 2008. Properties of dissolved organic matter in forest soils: influence of different plant covering. For. Ecol. Manag. 256, 2018– 2028. Turcani, M., Hlasny, T., 2007. Spatial distribution of four spruce bark beetles in north-western Slovakia. J. For. Sci. 53, 45–52. Ussiri, D.A.N., Johnson, C.E., 2003. Characterization of organic matter in a northern hardwood forest soil by 13C NMR spectroscopy and chemical methods. Geoderma 111, 123–149. Ussiri, D.A.N., Johnson, C.E., 2007. Organic matter composition and dynamics in a northern hardwood forest ecosystem 15 years after clear-cutting. For. Ecol. Manag. 240, 131–142. Ververis, C., Georghiou, K., Christodoulakis, N., Santas, P., Santas, R., 2004. Fiber dimensions, lignin and cellulose content of various plant materials and their suitability for paper production. Ind. Crop Prod. 19, 245–254. Vesterdal, L., Schmidt, I.K., Callesen, I., Nilsson, L.O., Gundersen, P., 2008. Carbon and nitrogen in forest floor and mineral soil under six common European tree species. For. Ecol. Manag. 255, 35–48. Wilson, M.A., 1987. NMR Techniques and Applications in Geochemistry and Soil Chemistry. Pergamon Press, Oxford. Wilson, M.A., Heng, S., Goh, K.H., Pugmire, R.J., Grant, D.M., 1983. Studies of litter and acid insoluble soil organic matter fractions using 13C-cross polarization nuclear magnetic resonance spectroscopy with magic angle spinning. J. Soil Sci. 34, 83–97. Zdanov, J.A., 1965. Mean oxidation degree of carbon and amino acids. Biochimija 30, 1257–1259 (in Russian). Zech, W., Johansson, M.B., Haumaier, L., Malcolm, R.L., 1987. CPMAS 13C NMR and IR spectra of spruce and pine litter and of the Klason lignin fraction at different stages of decomposition. Z. Pflanz. Bodenkunde 150 (4), 262–265. Zhang, Y., ZhaoY, C., Shi, X.Z., Lu, X.X., Yu, D.S., Wang, H.J., Sun, W.X., Darilek, J.L., 2008. Variation of soil organic carbon estimates in mountain regions: a case study from Southwest China. Geoderma 146, 449–456.