J Soils Sediments (2013) 13:34–42 DOI 10.1007/s11368-012-0604-z
SOILS, SEC 1 & SOIL ORGANIC MATTER DYNAMICS AND NUTRIENT CYCLING & RESEARCH ARTICLE
Similar quality and quantity of dissolved organic carbon under different land use systems in two Canadian and Chinese soils Shanghua Sun & Jianjun Liu & Yongfu Li & Peikun Jiang & Scott X. Chang
Received: 12 June 2012 / Accepted: 11 September 2012 / Published online: 25 September 2012 # Springer-Verlag 2012
Abstract Purpose The quality and quantity of dissolved organic carbon (DOC) in the soil can be used as indicators of the effects of perturbations on soil C. We studied the effects of land use systems (native forest, grassland, and arable land) in both Alberta, in western Canada, and Heilongjiang, in northeast China, on the quality and quantity of soil DOC. Materials and methods We studied the UV absorption, humification index (HIX), and biodegradability of waterextractable organic C, which is operationally defined as DOC. The relationship between biodegradability and the structural chemistry of soil organic matter studied with 13 C-nuclear magnetic resonance (NMR) spectroscopy was also investigated. Results and discussion The UV absorption and HIX, biodegradability of DOC, and the proportion of organic matter functional groups were not different among the land use types in both Canada and China. When the samples from
both countries were considered together, the extractability of DOC was negatively correlated with soil organic carbon content and carbonyl C, and positively correlated with Oalkyl C; the biodegradability of DOC was positively correlated with soil C/N ratio, and negatively correlated with the specific UV absorbance and HIX. Conclusions The main effect of land use type on soil organic matter was on its content but not the labile C characteristics or organic matter functional group composition, indicating the dominant control of the climate on the quality of DOC of the organic matter under different land use types we studied in the two cold temperate regions.
Responsible editor: Nicole J. Mathers
Dissolved organic matter (DOM), often measured as dissolved organic carbon (DOC), accounts for less than 0.25 % of the total soil organic carbon (SOC) (Zsolnay 1996; Chantigny 2003). Despite its low concentration, DOM is an important fraction of soil organic matter (SOM) in the soil and plays an important role in multiple soil ecological properties and functions, including as a source of energy and nutrients for microorganisms (Zsolnay 1996), for the translocation of nutrients and contaminants within the soil (Kalbitz and Popp 1999; Zsolnay 2003), and in C sequestration (Guggenberger and Kaiser 2003; Kaiser and Kalbitz 2012; Tipping et al. 2012). Although the annual input of DOC into ecosystems is high, the concentration of DOC in mineral soil horizons is low as low amounts of DOC enter into mineral soils in the form of leachates (Guggenberger and Zech 1993; Michalzik and Matzner 1999; Solinger et al.
S. Sun : J. Liu (*) College of Forestry, Northwest A & F University, Yangling, Shaanxi, People’s Republic of China e-mail:
[email protected] S. Sun : S. X. Chang (*) Department of Renewable Resources, University of Alberta, 442 Earth Sciences Building, Edmonton, AB, Canada T6G 2E3 e-mail:
[email protected] Y. Li : P. Jiang Zhejiang Provincial Key Laboratory of Carbon Cycling in Forest Ecosystems and Carbon Sequestration, and Joint Laboratory of Forestry Soil and the Environment between the Institute of Soil Science, Chinese Academy of Sciences, and School of Environmental and Resource Sciences, Zhejiang A & F University, Lin’an 311300( Zhejiang, People’s Republic of China
Keywords 13C-NMR . Biodegradability . Dissolved organic matter . Land use type
1 Introduction
J Soils Sediments (2013) 13:34–42
2001). Some of the DOC is adsorbed by soil minerals, contributing to the low DOC concentrations in the mineral soil. The biodegradation of DOC is another reason for the low DOC concentrations in mineral soils. The degradation of DOC in the soil has been extensively studied; however, the mechanisms and controls of the biodegradation of DOC in soils are still poorly understood (Kalbitz et al. 2000; Marschner and Kalbitz 2003). Kalbitz et al. (2003) reported that the biodegradation of DOC depends on its chemical composition. Various factors affect the quality and quantity of DOC, among those land use change is one of the most important factors in terrestrial ecosystems. Change of land use type can substantially alter SOC dynamics and other soil properties (Merino et al. 2004). Converting forests to arable lands is known to decrease both the total SOC and DOC concentrations (Haynes 2000; Akagi and Zsolnay 2008). However, information on the impact of land use change on the amount and composition of DOC is fragmented and sometimes contradictory (Chantigny 2003). It has been found that DOC in the forest floor contained more large organic matter molecules, whereas arable soils contained a greater proportion of small molecules, such as carbohydrates and amino acids (Strobel et al. 1999; Leinweber et al. 2001). Soil management such as cultivation was found to increase the humification of DOC (Kalbitz 2001), but Akagi and Zsolnay (2008) found that long-term removal of vegetation did not have a major influence on the quality of DOC. We studied three different land use systems (native forest, grassland, and arable land) both in northern Canada and northern China, two regions with similar climatic conditions characterized by long and cold winters and mild summers. The objective of this study was to assess the quality, quantity, and biodegradability of DOC under different land uses. Because DOC is an important and labile fraction of SOM, we also examined the structural composition of SOM under different land uses using 13C-nuclear magnetic resonance spectroscopy (NMR) to investigate the linkage between SOC and DOC.
2 Materials and methods 2.1 Field sites and soil sampling The soil samples used in this study were collected from native forest and adjacent grassland and arable lands in the cold temperate region in both Canada and China. The sampling site in Canada is located near Linaria (54°12′N and 114°8′W), in central Alberta. The annual mean temperature is 3 °C and annual mean precipitation is 463 mm (Environment Canada 2007). The Canadian forest site consisted mostly of native aspen (Populus tremuloides Michx.) and the Canadian
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grassland site was seeded with a mixture of tall fescue (Festuca arundinacea Schreb.), orchardgrass (Dactylis glomerata L.), and red clover (Trifolium pratense). The sampling site in China is located in Beian (48°33′N and 126°16′E), in Heilongjiang province. This site has a mean annual temperature of 2 °C and a mean annual precipitation of 440 mm (Lang et al. 2010, 2011). Tree composition in the Chinese forest site mainly consisted of aspen (Populus bonatii Levl.), silver birch (Betula pendula), and linden (Tilia miqueliana Maxim.), and the grassland site was seeded with orchardgrass (Dactylis glomerata L.) and mat bulrush (Scirpus trigueter L.). For both countries, the current land use has been practiced for at least 50 years based on the local history but the exact land use conversion dates are not available. For the Canadian site, three 20×20 m replicated plots were randomly established for each land use type for soil sampling in September 2008. All land use types were adjacent to each other within an area of about 4 km2 that had similar soil conditions. In each sampling plot, after the removal of surface litter, 20 soil cores (4.7 cm diameter) were randomly collected from the 0 to 20 cm layer and mixed to form a composite sample. For the Chinese site, three randomly selected sampling plots (15×15 m) about 100 m apart from each other were established in each land use type for soil sampling in August 2008. After the removal of the litter, one composite sample of the top 20 cm of the soil was collected from each plot based on about 10 samples randomly collected within each plot. Soils in the Canadian and Chinese study sites were Albic Luvisol and Kastanozem (Haplic), respectively, based on the FAO system (WRB 2007) of soil classification (Table 1). Since the soil types were different, land use effects on soil properties and processes were only assessed within each country. 2.2 Soil organic carbon and total nitrogen and DOC extraction After the soil samples were air-dried and sieved through a 2mm sieve, total soil C and N concentrations were determined using a Carlo Erba NA 1500 elemental analyzer (Carlo Erba Instruments, Milan, Italy). The DOC was extracted with a low-ionic-strength aqueous solution. We used 10 mL of 10 mmolL−1 CaCl2 to extract (at 2:1 v/w of extractant/soil ratio) the soluble organic C because it is regarded as an acceptable surrogate to soil solution DOC collected in situ (Zsolnay 2003). While extraction of DOC from fresh soil samples are preferred (Jones and Willett 2006), extraction using air-dried soil samples have also been commonly done (Sparling et al. 1998; McDowell et al. 2006). In our case, we had to ship airdried soil samples from China to the laboratory in Alberta and thus the only feasible method to obtain DOC was to extract air-dried soil samples. The DOC was obtained by extracting the soil in a shaker for 10 min
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J Soils Sediments (2013) 13:34–42
Table 1 Soil total nitrogen (TN), organic carbon (SOC), and carbon-to-nitrogen ratio of the study sites in Alberta, Canada, and Hailongjiang, China Country, soil type
Land use
TN (g kg−1) SOC (g kg−1) C/N ratio
Vegetation
China, Kastanozem (Haplic) Forest
Canada, Albic Luvisol
Aspen (Populus bonatii Levl.), silver birch (Betula pendula), linden (Tilia miqueliana Maxim.) Grassland Orchardgrass (Dactylis glomerata L.) and mat bulrush (Scirpus trigueter L.) Arable land 4-year soybean (Glycine max) and 1-year wheat (Triticum aestivum L.) rotation Forest Trembling aspen (Populus tremuloides Michx.) Grassland Tall fescue (Festuca arundinacea Schreb.), orchardgrass (Dactylis glomerata L.), red clover (Trifolium pratense) Arable land 4-year rotation of barley (Hordeum vulgare)–barley–wheat (Triticum aestivum L.)–canola (Brassica napus)
4.7±0.52a
67.1±5.30a
14.3±0.54a
2.3±0.03b
30.3±0.99b 12.8±0.28a
3.1±0.10b
41.2±1.58b 13.2±0.07a
1.7±0.14a 2.0±0.12a
22.6±3.25a 24.8±1.37a
13.3±0.74a 12.4±0.20a
2.1±0.21a
24.5±1.69a
11.9±0.47a
Values are mean±SD. Different letters indicate significant differences among the three land uses within each country
and filtrating through a glass fiber filter (Fisherbrand Glass Fiber Circles, Grade 6) and the extracts were further filtered through 0.2-μm cellulose acetate Corning syringe filters (Fisher Scientific). The DOC concentration was measured by a Shimadzu TOC-V CSH/CSN analyzer (Shimadzu Corporation, Kyoto, Japan). 2.3 Determination of aromaticity and humification index (HIX) Subsamples of the DOC were used for analyses of UV–vis absorption to determine the degree of aromaticity (Kalbitz et al. 2003) and of fluorescence absorbance to determine HIX of the DOC. Samples were analyzed for UV–vis absorbance in 1-cm-path-length quartz cuvettes using a Thermo Spectronic Genesys 10S UV–Visible spectrometer, for absorbance at 280 nm against a blank (deionized water). Specific UV absorbance was calculated by dividing the measured absorbance (per centimeter) by the concentration of DOC (in milligrams per liter) of the sample. The unit of specific UV absorbance is thus given as liters per milligram of C per centimeter. The fluorescence spectra were obtained with a Photon Technologies International MP-1 spectrofluorimeter (Birmingham, NJ, USA) using quartz cuvettes. Fluorescence emission spectra were collected at an excitation wavelength of 254 nm and an emission wavelength range of 280–500 nm. The humification index (HIX) was then calculated as the area in the upper quarter (∑435–480) of the usable emission spectra divided by the area in the lower usable quarter (∑300– 345 nm) (Zsolnay et al. 1999). The HIX provides information about aromatic structures (Kalbitz et al. 2003) and the complexity of the molecules. 2.4 Biodegradability of DOC To determine the biodegradability of DOC (BDOC), an aliquot of 5 mL of the extractant and 50 μL of a soil
microbial inoculum were mixed together. The soil microbial inoculum was prepared by taking 5 g of soil from each sample and mixed, then 1 g of the composite soil was taken and shaken with 10 mL of distilled water, and passed through a 5-μm filter (Fisherbrand filter paper Q2). The DOC concentration in the microbial inoculums was below detection limit (
