Mongolian pine plantations enhance soil physico-chemical properties and carbon and nitrogen capacities in semi-arid degraded sandy land in China

Applied Soil Ecology 56 (2012) 1–9

Contents lists available at SciVerse ScienceDirect

Applied Soil Ecology journal homepage: www.elsevier.com/locate/apsoil

Mongolian pine plantations enhance soil physico-chemical properties and carbon and nitrogen capacities in semi-arid degraded sandy land in China Yuqiang Li a,∗ , Tala Awada b , Xinhua Zhou b , Wen Shang a , Yinping Chen c , Xiaoan Zuo a , Shaokun Wang a , Xinping Liu a , Jing Feng a a

Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, 320 Donggang West Road, Lanzhou 730000, China School of Natural Resources, University of Nebraska, Lincoln, NE 68583, USA c School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China b

a r t i c l e

i n f o

Article history: Received 19 May 2011 Received in revised form 17 January 2012 Accepted 21 January 2012 Keywords: Pinus sylvestris var. mongolica Litv. Soil light fraction Horqin Sandy Land Afforestation Active sand dunes

a b s t r a c t Horqin Sandy Land is a seriously desertified and an ecologically fragile region of China. Soil degradation and desertification in this region are the result of several decades of overgrazing, non-manure cropping with short fallow, and arbitrary land use and management. We investigated whether the afforestation of active sand dunes with Mongolian pine (Pinus sylvestris var. mongolica Litv.) enhances the carbon (C) and nitrogen (N) storages and the overall soil quality. We compared soil physico-chemical properties, and C and N storages in the total and light fraction soil organic matter of active sand dunes, and of 25- and 35year-old plantations. Soil water holding capacity, fine particle content and nutrients were significantly higher in plantations than in active sand dunes, with greater improvements occurring in the top 5 cm than in the 5–15 cm layer of the soil profile. Soil C and total N storages were 6.1 and 3.7 folds in 25year-old, and 10.2 and 5.3 folds in 35-year-old plantations compared to active sand dunes, respectively. Carbon and N storages in the light fraction were 20.9 and 15.8 folds in 25-year-old, and 36.1 and 25.0 folds in 35-year-old plantations, respectively, relative to active sand dunes. The light fraction played an important role in soil C sequestration and its amount is an indicator of the effects of afforestation on C storage in sandy soil. The upper 15 cm of the soil profile in the 35-year-old plantations of Mongolian pine has the capacity to sequester significant amount of C in the region, potentially offsetting part of the carbon that has been lost due to desertification over the past century in the Horqin Sandy Land. Our results conclude that afforestation with Mongolian pine has had positive impacts on soil quality and has increased the capacity for soil C sequestration in semi-arid degraded areas. © 2012 Elsevier B.V. All rights reserved.

1. Introduction At around four billion hectares, arid and semi-arid regions cover ∼30% of the terrestrial land area around the globe (Lal, 2001). These regions however, have been under continuous threat of land degradation due to natural and human disturbances, climate variability, and arbitrary land use and management. Re-vegetation has been shown to improve and restore some of the ecosystem services including the physical, biological and biogeochemical processes (Nosetto et al., 2006; Karam et al., 2011). Land degradation due to vegetation cover loss and the subsequent desertification has been attributed to a combination of climatic and anthropogenic factors, and has likely caused global soil C losses in the magnitude

∗ Corresponding author at: Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, 320 Donggang West Road, Lanzhou 730000, China. Tel.: +86 931 4967 219; fax: +86 931 4967 219. E-mail addresses: [email protected], [email protected] (Y. Li). 0929-1393/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.apsoil.2012.01.007

of 19–29 Pg (Lal, 2001). Re-vegetation aiming to restore ecosystem processes in these regions can potentially yield significant gains in C and N storages (Laclau, 2003; Lal, 2009), and improve soil quality especially in the upper soil profile (Davis and Condron, 2002; Grandy and Robertson, 2007). In semi-arid regions, re-vegetation through afforestation has been widely recognized as a measure for conserving soil and water, combating desertification, supplying timber, and increasing C and N storages (Grünzweig et al., 2003; Chen et al., 2010). Horqin Sandy Land, located in northern China (42◦ 41 to 45◦ 15 N, 118◦ 35 to 123◦ 30 E), is one of the most seriously desertified and ecologically fragile regions in China’s agro-pastoral ecotone. Land degradation and desertification are the result of several decades of overgrazing, non-manure cropping with a short fallow interval, and arbitrary land use and management in this region. As sites undergo degradation and reach a severe state of desertification, an estimated 90% of C and 86% of N are lost from the plant–soil system (Li et al., 2006). Afforestation has been widely adopted as an effective control for desertification in this region (Su et al., 2005; Hu et al., 2008).

2

Y. Li et al. / Applied Soil Ecology 56 (2012) 1–9

In the 1950s, Mongolian pine (Pinus sylvestris var. mongolica Litv.) was first planted in an area near Zhanggutai, Zhangwu County of Liaoning Province, which is located in the southeastern part of the Horqin Sandy Land (Zeng et al., 1996). This pine species has adapted well to the region and is one of the most popular species currently used for afforestation in the Horqin Sandy Land. Carbon sequestration is enhanced when the input of C into the system exceeds the amount of C that is lost due to plant harvest, physiological respiration, mineralization, erosion, and leaching (Lal, 2009). Quantifying changes in the pool size and fluxes of C and nutrients is fundamental in understanding the effects of land use change and management practices on ecosystem processes (Jaramillo et al., 2003). Afforestation can favor C sequestration through the accumulation of above- and below-ground biomass, and the reduction of C loss through the slowing of soil organic matter decomposition and soil erosion (Nosetto et al., 2006). In the Horqin Sandy Land, a number of studies have documented the effects of Mongolian pine or indigenous shrubs on vegetation restoration (Zhang et al., 2004), soil properties (Cao et al., 2008; Yu et al., 2008), and soil N mineralization rates and moisture regimes (Chen et al., 2006). However, none of these studies measured, in detail, the organic C and N in total soil and in its light fraction (soil components that can be isolated by flotation; Blackwood and Paul, 2003) following the establishment of Mongolian pine in degraded land. Light fraction is an important and dynamic component in soils because it reflects short-term shifts in soil organic matter turnover and storage (Murage et al., 2007). Studies have demonstrated that the light fraction is more sensitive than the total soil organic matter to changes in cropping and tillage practices (Larney et al., 1997; Tan et al., 2007), N application (Malhi et al., 2003), managementinduced changes in soil chemical and biological properties (He et al., 2008), and N immobilization (Compton and Boone, 2002). As an intermediate between plant residues and stable organic matter, this

fraction plays an important role in the cycling of C and N in soils (Curtin et al., 2007). The objectives of this research were to (1) investigate the soil physico-chemical properties, and C and N storages in total and light fraction soil organic matter in Mongolian pine plantations and in active sand dunes of the Horqin Sandy Land and (2) understand the mechanisms by which soil properties and C and N storages respond to plantations. Results from this study can provide the base data for the parameterization of regional models that can be used to determine soil C and N storages under Mongolian pine plantations at a landscape or regional scale. 2. Materials and methods 2.1. Study area The study was conducted at the Naiman Desertification Research Station, Chinese Academy of Sciences, China. The station is near Daqintala in Naiman County of Inner Mongolia (42◦ 58 N, 120◦ 43 E, 385 m a.s.l., Fig. 1) in the southern part of the Horqin Sandy Land. The study area is characterized by sand dunes, topographically alternating with gently undulating interdunal lowlands, with a sand deposit thickness of 20–120 m (Zhang et al., 2004). The soil is classified as Cambic Arenosols of sandy origin in the FAO soil classification system (FAO, 2006), and is characterized by coarse texture and loose structure. As a result, this type of soil is susceptible to damage by animal disturbance and wind erosion especially in areas with low vegetation cover. The region has a continental semi-arid monsoon temperate climate regime. The mean annual precipitation is 366 mm, of which 8.3% falls during the dormant season between November and April, and the mean annual potential evaporation is 1935 mm. The mean annual air temperature is 6.8 ◦ C, the mean minimum monthly temperature in January is −13.2 ◦ C, and the mean maximum monthly

Fig. 1. Location of study area (Horqin Sandy Land in Inner Mongolia, China).

Y. Li et al. / Applied Soil Ecology 56 (2012) 1–9

3

Table 1 Site characteristics (the control plots were active sand dunes, referred as plantation age of 0). Plantation age (years)

Site

Altitude (m asl)

Stand density (trees/ha)

Trees

Understory vegetation

Surface litter (g m−2 )

DBH (cm)a

Height (m)

Coverage (%)

Aboveground biomass (g m−2 )

Number of species

35

1 2 3 Mean ± SE

367 366 373 369 ± 2

716 1214 1032 987 ± 145

11.1 11.7 10.9 11.3 ± 0.2

7.6 8.9 6.4 7.6 ± 0.7

24.6 23.7 25.0 24.4 ± 0.4

76.0 67.5 78.0 73.8 ± 3.2

12.0 14.0 11.0 12.3 ± 0.9

177.2 177.6 214.4 189.7 ± 12.3

25

1 2 3 Mean ±SE

363 365 366 365 ± 1

792 1233 889 971 ± 134

9. 6 8.1 8. 8 8.8 ± 0.6

4.8 5.9 6.0 5.5 ± 0.4

20.1 22.2 17.3 19.9 ± 1.4

67.1 49.3 42.9 53.1 ± 7.2

11.0 12.0 12.0 11.7 ± 0.3

86.4 108.9 69.7 88.3 ± 11.2

0

1 2 3 Mean ± SE

361 358 367 362 ± 3

n/a n/a n/a n/a

n/a n/a n/a n/a

n/a n/a n/a n/a

4.7 3.2 3.4 3.8 ± 0.5

11.4 5.9 6.2 7.8 ± 1.8

4.0 5.0 4.0 4.3 ± 0.3

a

0.0 0.0 0.0 0.0

DBH, diameter at breast height.

temperature in July is 23.5 ◦ C. The frost-free period ranges from 130 to 150 days. Mean wind speed is 4.3 m s−1 with occasional occurrences of gales ≥20 m s−1 in winter and spring when vegetation cover is lowest and soil is driest. The combination of these factors makes the soil in the region highly vulnerable to wind erosion. Historically, the native vegetation in the study area was dominated by grass species including Stipa grandis, Leymus chinensis, and Agropyron cristatum communities, along with sparsely scattered woody species like Ulmus pumila, Populus simonii, P. pseudo-simonii, and Quercus mongolica. The proper grazing intensity is 2–3 sheep equivalents per hectare in the sandy rangeland of this area (Zhao et al., 2005). Over the past decades, the grasses were overgrazed and the woody species were mostly harvested for fuel. This poor land management has led to both reduction in land vegetation cover and degradation in soil quality. As a result, the area has become dominated by active sand dunes covered mostly by annual forbs such as Agriophyllum squarrosum, Tribulus terretris, and Salsola collina. Horqin Sandy Land experienced the fastest rate of desertification from the late 1950s to the mid 1970s (9084 km2 ; Wu, 2005). To mitigate this, an extensive afforestation program using Mongolian pine and leguminous shrubs (e.g. Caragana microphylla) was initiated in the early 1970s in the region. We selected 25- and 35-year-old Mongolian pine plantations as study stands. These plantations were established on active sand dunes using nurseryraised seedlings in pits of 40× 40 × 40 cm3 in size, with spacing within and between rows of 1 × 3 m2 or 2 × 2 m2 . Three stands (replications) of each age class were established. Additionally, we selected three active sand dunes sites (low cover of native vegetation) as the control, each of which neighbors with a plantation site. In each of the nine established sites, one 50 × 50 m2 plot was established for sampling. All plots faced south with slopes <12◦ , and were located within 16 km from one another.

2.2. Measurements Vegetation measurements were completed in August 2009 (Table 1). In each of the plantation plots, tree diameter at breast height (DBH) was measured using a diameter tape, and canopy height was estimated using a clinometer for all trees. Nine 1 × 1 m2 subplots were randomly established within each plot and sampled for both accumulated litter and understory plant biomass. After removing the litter layer, soil samples were collected from the top 5 cm, and the 5–15 cm layer using a soil auger of 2.5 cm in diameter. Soil samples were collected from 8 to 12 core points

from each of the nine subplots that have been established in every plot. The soil samples collected from different core points within each subplot were mixed as a composite soil sample for each soil layer (i.e., top 5 cm, and 5–15 cm). Therefore, in every plot, a total of nine composite soil samples were obtained for each soil layer with a total of 162 composite samples across all plots. For the determination of soil bulk density and water capacity, three additional soil cores were taken from each subplot per soil layer using a soil auger equipped with a stainless-steel cylinder (5 cm in diameter and height).

2.3. Laboratory analyses Litter and understory plant biomass samples were dried at 60 ◦ C in an air-forced oven for 48 h and weighed to the nearest 0.1 g in a laboratory. Soil samples were air-dried and hand-sieved through a 2 mm mesh to remove roots and other debris. A portion of each airdried soil sample was ground to pass a 0.1 mm mesh for soil nutrient analyses. The remaining portion was stored at room temperature for the determination of the light fraction, particle size distribution, pH, and electrical conductivity. A subsample of the sampled soil was weighed and dried at 105 ◦ C for 24 h for the determination of gravimetric water content. The water holding capacities (saturation water capacity and field water capacity) were determined using the intact soil cores (ISSCAS, 1978). Briefly, the soil cores, covered at one end with a fine mesh, and left open at the other end, were saturated with water for 12 h. The resulting soil water content represented the saturation water capacity. The excess water was then drained by placing the samples on the surface of a sand bed for 6 h for the determination of the field water holding capacity (ISSCAS, 1978). Soil particle sizes were analyzed by the wet sieving method using sodium hexametaphosphate as the dispersing agent (ISO, 1998). A soil sample was separated by a nest of sieves with openings of 2, 0.1, and 0.05 mm into three fractions: coarse sand (2–0.1 mm), fine sand (0.1–0.05 mm), and silt + clay (<0.05 mm). Soil pH and electrical conductivity were determined in a 1:2.5 (w/w) and 1:5 (w/w) soil: water suspension at 25 ◦ C, respectively (Multiline F/SET-3; WTW, Weilheim, Germany). Soil organic C concentration was determined using the Walkley–Black dichromate oxidation procedure (Nelson and Sommers, 1982), soil inorganic C (carbonate) content was determined using the volumetric method (ISO, 1994), soil total N concentration was determined using the Kjeldahl procedure (McGill and Figueiredo, 1993), available N was determined using the alkaline diffusion method, and available P

4

Y. Li et al. / Applied Soil Ecology 56 (2012) 1–9

Table 2 Two-way ANOVA for soil properties in two soil layers (0–5 and 5–15 cm), in active sand dunes and under 25- and 35-year-old Mongolian pine plantations. Plantation age

Plantation age × soil layer

Soil layer

F

P

F

P

F

P

Soil physical properties Bulk density Saturation water capacity Field water capacity Coarse sand (2.0–0.1 mm) Fine sand (0.10–0.05 mm) Silt + clay (<0.05 mm)

47.10 72.82 20.23 276.77 227.49 227.26

<0.001 <0.001 <0.001 <0.001 <0.001 <0.001

33.41 9.59 9.40 164.40 118.80 169.99

<0.001 0.004 0.004 <0.001 <0.001 <0.001

7.82 2.46 0.54 33.81 21.78 41.75

0.001 0.100 0.586 <0.001 <0.001 <0.001

Soil chemical properties Soil organic C Soil inorganic C Total N Available N Available P Available K pH EC

168.97 19.11 168.55 261.95 171.61 180.39 84.53 142.55

<0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001

135.11 3.48 114.42 229.31 254.59 131.37 6.18 1.75

<0.001 0.064 <0.001 <0.001 <0.001 <0.001 0.014 0.189

36.27 2.87 29.56 48.64 56.79 18.94 0.25 2.46

<0.001 0.060 <0.001 <0.001 <0.001 <0.001 0.780 0.089

was determined using the Olsen method (Olsen et al., 1954). Available K was extracted with 1 M ammonium acetate and determined by a flame photometer (ISSCAS, 1978). The light fraction was extracted from soils using the procedure in Murage et al. (2007). An air-dried bulk soil sample around 20 g was weighed into a 100 mL centrifuge tube, followed by the addition of 80 mL NaI at a density of 1.8 g cm−3 . The liquid in the tube was then swirled by hand for 30 s, and the content was dispersed using a probe-type sonic disrupter for 1 min. After sedimentation for 30 min, the solution was centrifuged at 8000 × g for 30 min. The samples were kept still overnight. Suspended light fraction material was suctioned to a Whatman No. 1 filter paper, and washed thoroughly with five aliquots of 0.01 M CaCl2 and ten aliquots of distilled deionized water. The light fraction was dried at 55 ◦ C for 16 h, then weighed to the nearest 0.0001 g and ground using an agate mortar and pestle. The light fraction dry matter content was expressed as a percentage of total soil mass. The organic C and N concentrations of light fraction were determined with the same procedure that was used for bulk soil. 2.4. Data analyses The C and N storages in total soil and light fraction were calculated using the following equations (Duan et al., 2001), C or N storage in total soil = (soil C or N concentration) × (soil bulk density) × (soil layer thickness) C or N storage in light fraction = (C or N concentration in light fraction) × (light fraction dry matter content) ×(soil bulk density) × (soil layer thickness) Measured variables were analyzed by plantation age, soil layer, and their interaction using two-way ANOVA (see Table 2). Further, these variables and their resultant C and N storages were analyzed by plantation age using one-way ANOVA (see Tables 3–5). Mean comparisons were performed using the least-significant-difference (LSD) test. Correlation coefficients among soil properties were calculated using Pearson’s correlation coefficient (Table 6). The statistical analysis was performed using version 13.5 of the SPSS software (SPSS, Chicago, IL, USA).

3. Results 3.1. Soil physical properties Measured soil physical properties significantly differed not only between the active sand dunes (control, referred to as plantation age of zero in Tables 1–6) and pine plantations but also between the two plantations (25- and 35-year-old) and the two soil layers (0–5 cm, and 5–15 cm of the soil profile). Significant interaction of plantation by soil layer was also found for these properties except for the soil saturation water and field water capacities (Table 2). Analysis of the soil particle size distribution (Table 3) indicated that the coarse sand content was significantly higher in the active sand dunes relative to plantations, and decreased significantly with increasing plantation age in both investigated soil layers. In the combined soil layer of 0–15 cm, the coarse sand content was 8 and 14% lower in the 25- and 35-year-old Mongolian pine plantations, respectively, relative to the active sand dunes. This decline was mirrored by significant increases in the fine sand, and silt + clay contents in the soil with increased plantation age; the former increased by 2.7 and 4.7 folds, and the latter by 15.0 and 24.2 folds, in the 25and 35-year-old plantations, respectively, in the top 15 cm of the soil profile compared to active sand dunes. Soil bulk density did not differ between the 25- and the 35-year-old Mongolian plantations, but was significantly lower than that of the active sand dunes in the two investigated soil layers (Table 3). The soil saturation and field water holding capacities were significantly greater in plantations than in active sand dunes for the two investigated soil layers, but did not differ between the two plantations (25- vs. 35-year-old), except for the saturation water holding capacity in top 5 cm layer of the soil profile (Table 3). 3.2. Soil chemical properties Soil chemical properties showed significant responses to plantation age in the two investigated soil layers, except for the soil inorganic C and electrical conductivity. There were also insignificant interaction of plantation by soil layer for soil inorganic C, pH, and electrical conductivity (Table 2). Soil organic C concentration, total and available N, and electrical conductivity (Table 4) were improved significantly in the Mongolian pine plantations relative to the active sand dunes. This improvement continued with increasing plantation age (25- to 35year-old). Soil inorganic C (Table 4) showed a similar trend, but content, although higher in the 25-year-old plantation compared to the active sand dunes, it was not significant. A significant increase,

Y. Li et al. / Applied Soil Ecology 56 (2012) 1–9

5

Table 3 Changes in soil physical properties and light fraction dry matter in two soil layers (0–5 and 5–15 cm) and the combined layer (0–15 cm) in active sand dunes (referred as plantation age of 0) and under 25- and 35-year-old Mongolian pine plantations (mean ± SE). Soil properties

Layer (cm)

Plantation age (years) 0

25

35

Coarse sand (2.0–0.1 mm, %)

0–5 5–15 0–15

97.00 ± 0.18 a 98.01 ± 0.08 a 97.50 ± 0.12 a

86.46 ± 0.35 b 93.03 ± 0.38 b 89.75 ± 0.29 b

79.09 ± 1.28 c 89.45 ± 0.61 c 84.27 ± 0.84 c

Fine sand (0.10–0.05 mm, %)

0–5 5–15 0–15

2.24 ± 0.13 c 1.46 ± 0.07 c 1.85 ± 0.09 c

8.77 ± 0.26 b 4.80 ± 0.24 b 6.78 ± 0.21 b

13.55 ± 0.79 a 7.46 ± 0.42 a 10.50 ± 0.52 a

Silt + clay (<0.05 mm, %)

0–5 5–15 0–15

0.28 ± 0.04 c 0.08 ± 0.01 c 0.18 ± 0.02 c

4.10 ± 0.17 b 1.67 ± 0.15 b 2.88 ± 0.11 b

6.49 ± 0.53 a 2.56 ± 0.23 a 4.53 ± 0.34 a

Bulk density (g cm−3 )

0–5 5–15 0–15

1.62 ± 0.01 a 1.63 ± 0.01 a 1.63 ± 0.01 a

1.49 ± 0.01 b 1.57 ± 0.01 b 1.53 ± 0.01 b

1.46 ± 0.02 b 1.55 ± 0.02 b 1.51 ± 0.02 b

Saturation water capacity (%)

0–5 5–15 0–15

17.96 ± 1.06 c 17.01 ± 0.77 b 17.48 ± 0.72 c

24.76 ± 0.33 b 23.83 ± 0.31 a 24.30 ± 0.20 b

28.35 ± 1.29 a 24.42 ± 0.54 a 26.39 ± 0.70 a

Field water capacity (%)

0–5 5–15 0–15

15.84 ± 0.94 b 14.37 ± 0.87 b 15.11 ± 0.70 b

20.66 ± 0.24 a 18.42 ± 1.17 a 19.54 ± 0.61 a

22.61 ± 1.09 a 19.17 ± 1.04 a 20.89 ± 0.89 a

Light fraction dry matter (g kg−1 soil mass)

0–5 5–15 0–15

0.53 ± 0.05 c 0.50 ± 0.05 c 0.51 ± 0.04 c

12.81 ± 0.94 b 4.55 ± 0.64 b 8.68 ± 0.59 b

21.09 ± 0.89 a 9.35 ± 0.75 a 15.22 ± 0.66 a

Letters of a, b, and c indicate significant differences at P < 0.05 in a property between sites (within the same row).

Table 4 Changes in soil chemical properties and light fraction (LF) C and N concentrations in two soil layers (0–5 and 5–15 cm) and the combined layer (0–15 cm) in active sand dunes (referred as plantation age of 0) and under 25- and 35-year-old Mongolian pine plantations (mean ± SE). Soil properties

Layer (cm)

Plantation age (years)

Soil organic C (g kg−1 )

0–5 5–15 0–15

0.349 ± 0.015 c 0.289 ± 0.011 c 0.319 ± 0.012 c

3.539 ± 0.157 b 1.261 ± 0.053 b 2.400 ± 0.088 b

5.686 ± 0.271 a 2.288 ± 0.150 a 3.987 ± 0.177 a

Total N (g kg−1 )

0–5 5–15 0–15

0.079 ± 0.003 c 0.071 ± 0.002 c 0.075 ± 0.002 c

0.455 ± 0.019 b 0.206 ± 0.011 b 0.331 ± 0.011 b

0.626 ± 0.026 a 0.311 ± 0.018 a 0.468 ± 0.018 a

Soil inorganic C (g kg−1 )

0–5 5–15 0–15

0.046 ± 0.005 b 0.055 ± 0.005 b 0.050 ± 0.004 b

0.122 ± 0.008 b 0.098 ± 0.011 b 0.110 ± 0.007 b

0.430 ± 0.064 a 0.228 ± 0.048 a 0.329 ± 0.052 a

Available N (mg kg−1 )

0–5 5–15 0–15

9.01 ± 0.19 c 7.59 ± 0.20 b 8.30 ± 0.15 c

34.44 ± 0.92 b 18.29 ± 0.86 a 26.36 ± 0.68 b

41.81 ± 1.27 a 20.39 ± 0.70 a 31.10 ± 0.76 a

Available P (mg kg−1 )

0–5 5–15 0–15

4.67 ± 0.17 b 4.32 ± 0.17 b 4.49 ± 0.13 b

16.55 ± 0.43a 7.20 ± 0.28 a 11.88 ± 0.26 a

16.82 ± 0.59 a 7.91 ± 0.31 a 12.37 ± 0.37 a

Available K (mg kg−1 )

0–5 5–15 0–15

82.59 ± 6.48 b 69.63 ± 4.83 b 76.11 ± 5.53 b

199.63 ± 7.43 a 122.96 ± 5.39 a 161.30 ± 5.85 a

205.19 ± 4.98 a 139.26 ± 2.77 a 172.22 ± 3.34 a

pH

0–5 5–15 0–15

7.17 ± 0.04 b 7.23 ± 0.03 b 7.20 ± 0.03 b

7.11 ± 0.02 b 7.22 ± 0.03 b 7.16 ± 0.02 b

7.70 ± 0.05 a 7.84 ± 0.05 a 7.77 ± 0.05 a

EC (␮S cm−1 )

0–5 5–15 0–15

15.04 ± 0.36 c 14.70 ± 0.32 b 14.87 ± 0.27 c

46.56 ± 1.82 b 45.26 ± 2.58 a 45.91 ± 1.85 b

60.63 ± 2.75 a 51.44 ± 2.92 a 56.04 ± 2.74 a

Light fraction C (g kg−1 LF)

0–5 5–15 0–15

86.6 ± 2.7 b 80.9 ± 1.4 c 83.8 ± 1.7 b

121.5 ± 4.4 a 138.5 ± 10.5 a 130.0 ± 7.0 a

133.5 ± 2.9 a 114.5 ± 5.0 b 124.0 ± 3.8 a

Light fraction N (g kg−1 LF)

0–5 5–15 0–15

7.3 ± 0.9 a 6.2 ± 0.5 a 6.7 ± 0.7 a

0

25

Letters of a, b, and c indicate significant differences at P < 0.05 in a property between sites (within the same row).

35

7.9 ± 0.7 a 7.6 ± 1.1 a 7.7 ± 0.9 a

7.8 ± 0.6 a 5.9 ± 0.5 a 6.8 ± 0.5 a

6

Y. Li et al. / Applied Soil Ecology 56 (2012) 1–9

Table 5 Changes in storage of the soil organic carbon (SOC), soil inorganic carbon (SIC), total nitrogen (TN), and light fraction carbon (LFC) and light fraction nitrogen (LFN) in two soil layers (0–5 and 5–15 cm) and the combined layer (0–15 cm) in active sand dunes (referred as plantation age of 0) and under 25- and 35-year-old Mongolian pine plantations (mean ± SE). Soil properties

Layer (cm)

Plantation age (years) 0

25

35

0–5 5–15 0–15

28.31 ± 1.23 c 46.90 ± 1.78 c 75.21 ± 2.46 c

263.96 ± 11.70 b 198.26 ± 8.29 b 462.22 ± 15.85 b

414.37 ± 19.76 a 355.64 ± 23.34 a 770.01 ± 35.65 a

SIC (g m−2 )

0–5 5–15 0–15

3.72 ± 0.42 b 8.89 ± 0.83 b 12.61 ± 1.00 b

9.07 ± 0.62 b 15.38 ± 1.68 b 24.45 ± 1.77 b

31.32 ± 4.64 a 35.41 ± 7.41 a 66.73 ± 11.32 a

TN (g m−2 )

0–5 5–15 0–15

6.37 ± 0.28 c 11.50 ± 0.24 c 17.87 ± 0.44 c

33.95 ± 1.44 b 32.43 ± 1.74 b 66.38 ± 2.28 b

45.61 ± 1.89 a 48.30 ± 2.76 a 93.91 ± 3.89 a

LFC (g m−2 )

0–5 5–15 0–15

3.71 ± 0.37 c 6.58 ± 0.64 c 10.29 ± 0.81 c

116.04 ± 8.50 b 98.98 ± 13.86 b 215.02 ± 16.76 b

205.17 ± 8.67 a 166.32 ± 13.40 a 371.49 ± 17.80 a

LFN (g m−2 )

0–5 5–15 0–15

0.31 ± 0.03 c 0.51 ± 0.05 c 0.82 ± 0.06 c

7.52 ± 0.55 b 5.41 ± 0.76 b 12.93 ± 0.97 b

11.97 ± 0.51 a 8.50 ± 0.68 a 20.47 ± 0.95 a

SIC/SOC (%)

0–5 5–15 0–15

13.72 ± 1.65 a 20.35 ± 2.22 a 17.19 ± 1.35 a

3.54 ± 0.24 b 7.25 ± 0.71 b 5.16 ± 0.32 b

6.92 ± 0.88 b 8.40 ± 1.17 b 7.65 ± 0.96 b

LFC/SOC (%)

0–5 5–15 0–15

13.70 ± 1.40 c 15.56 ± 1.84 b 14.50 ± 1.23 b

43.66 ± 2.32 b 45.87 ± 4.79 a 46.46 ± 3.62 a

52.35 ± 2.19 a 47.84 ± 3.29 a 50.38 ± 2.30 a

LFN/TN (%)

0–5 5–15 0–15

5.55 ± 0.67 c 4.57 ± 0.49 b 4.80 ± 0.41 c

22.07 ± 1.20 b 14.99 ± 1.18 a 18.91 ± 1.03 b

27.19 ± 1.05 a 18.37 ± 1.39 a 22.56 ± 0.99 a

−2

SOC (g m

)

Letters of a, b, and c indicate significant differences at P < 0.05 in a property between sites (within the same row).

however, was observed between 25- and 35-year-old plantations. A similar trend was reported for the soil pH (Table 4). Available P and K rates (Table 4), while significantly higher in plantations relative to active sand dunes, leveled off at age of 25, without any further significant increase from age 25–35 years. Overall, in the combined soil layer of 0–15 cm, compared to the active sand dunes, the 25and 35-year-old Mongolian pine plantations had 7.5 and 12.5 folds soil organic C concentration; 4.4 and 6.2 folds total N; 2.2 and 6.6 folds soil inorganic C; 3.2 and 3.7 folds available N; 2.6 and 2.8 folds available P; 2.1 and 2.3 folds available K; and 3.1 and 3.8 folds the electrical conductivity, respectively. 3.3. Light fraction organic matter The light fraction dry matter accounted for a small portion of the total soil mass (Table 3), but was strongly (P < 0.01) correlated with soil C and N concentrations, available nutrients, fine particles, and water holding capacity (Table 6). The light fraction C concentration (Table 4) was 263 times the value of total soil C in active sand dunes, but was only 54 and 31 times the value in the 25 and 35-year-old plantations, respectively. Similarly, the light fraction N concentration (Table 4) was 89, 23 and 15 times the value of total soil N, in active sand dunes, and the 25- and 35-year-old plantations, respectively. In terms of content expressed as percentage of total soil mass, the organic C and N in the light fraction were significantly higher in the plantations compared to active sand dunes and continued to increase significantly with plantation age (Table 4). 3.4. Carbon and nitrogen storages The organic C and N storages in both light fraction and total soil increased significantly with plantation age in the two investigated soil layers (Table 5). In the combined layer of 0–15 cm, the organic C storage in the total soil was 6.1 and 10.2 folds in the 25- and

35-year-old plantations, respectively, compared to active sand dunes, whereas the total N storage increased only by 3.7 and 5.3 folds, respectively. Soil inorganic C storage (Table 5), which showed no significant difference between the active sand dunes and the 25year-old plantation, accounted for a small proportion of total soil C storage. The organic C storage in the light fraction increased to 20.9 and 36.1 folds, whereas the N storage increased to 15.8 and 25.0 folds, in the 25- and 35-year-old plantations, respectively, compared to active sand dunes. The proportions of total soil organic C and N storages accounted for by the light fraction C and N were also significantly higher in plantations compared to active sand dunes (Table 5). The average soil organic C accumulation rate in plantations was 15.5, 19.9 and 30.8 g C m−2 y−1 from 0 to 25, 0 to 35 and 25 to 35, respectively. Compared to soil organic C, the soil inorganic C showed a slower accumulation rate, and was 0.5, 1.5 and 4.2 g C m−2 y−1 for the corresponding periods, respectively. The total N accumulation rate during the three periods was 1.9, 2.2 and 2.8 g N m−2 y−1 , respectively.

4. Discussion 4.1. Effects of afforestation on soil properties Improving soil fertility after re-vegetation is a complex ecological process that is simultaneously impacted by a number of biotic and abiotic factors (Cao et al., 2008). Afforestation, considered as an effective option to sequester C in semi-arid regions, can increase C influx through higher and more efficient plant use of resources for primary production (Nosetto et al., 2006). Soil organic C gain can improve soil quality by increasing water holding and nutrientretention capacities (Evrendilek et al., 2004), therefore, enhancing ecosystem biodiversity and resilience (Hernandez-Ramirez et al.,

−0.83** −0.91** 0.81** 0.96** −0.89** 0.89** 0.77* 0.63 −0.45 0.77* 0.97** 0.86** 0.74* −0.59 0.86** −1.00** −0.99** −0.84** −0.71* 0.55 −0.84** −0.65 0.69* 0.59 0.89** 0.96** −0.86** 0.79* 0.57 −0.57 0.61 0.47 0.65 0.64 −0.66 0.74* 0.53 0.60 −0.80** 0.80** 0.76* 0.88** 0.74* −0.76* 0.80** 0.83** 0.43 0.85** −0.85** 0.85** 0.82** 0.92** 0.86** −0.79* 0.86** 0.97** 0.80** 0.57 0.93** −0.85** 0.86** 0.80** 0.96** 0.93** −0.85** 0.92** 0.72* 0.60 0.56 0.92** 0.72* −0.58 0.64 0.47 0.73* 0.74* −0.82** 0.86** 0.82** 0.97** 0.93** 0.85** 0.69* 0.85** −0.88** 0.90** 0.82** 0.95** 0.88** −0.86** 0.98** *

**

P < 0.05. P < 0.01.

– 0.99** 0.85** 0.96** 0.91** 0.82** 0.75* 0.86** −0.88** 0.90** 0.82** 0.95** 0.89** −0.85** 0.97** Soil organic C Total N Soil inorganic C Available N Available P Available K pH EC Coarse sand Fine sand Silt + clay Saturation water capacity Field water capacity Bulk density Light fraction dry matter

Coarse sand EC pH Available K Available P Available N Soil inorganic C Total N Soil organic C

Table 6 Pearson’s correlation coefficients (n = 9) among soil properties in active sand dunes and under 25 and 35-year-old Mongolian pine plantations.

Fine sand

Silt + clay

Saturation water capacity

Field water capacity

Bulk density

Y. Li et al. / Applied Soil Ecology 56 (2012) 1–9

7

2011). Soil organic matter and nutrients are also often associated with higher soil fine particles (Saggar et al., 2001). Our results showed that soil C and N concentrations, water holding capacities, fine particle contents, and available nutrients positively responded to Mongolian pine plantations improving the overall soil productivity. This improvement can be mainly ascribed to plantation-induced vegetation recovery and the resulting litter accumulation (Table 1), and to the increase in fine soil particles (Table 3). The content of soil coarse sand proportionally decreased with the increase in plantation age in this study, due in part to the increase in fine particles such as silt and clay resulting from the (1) biological interaction between plants and soil (Saggar et al., 2001; Pei et al., 2008) and (2) wind deposition of fine particles from neighboring active sand dunes due to the reduction in wind speed and the breakage of large turbulent eddies by canopy in plantations compared to active sand dunes. It should be noted that as the soil particle size distribution and texture are intrinsic characteristics of the soil, and therefore are not expected to be modified by plantations, the change in the absolute amount of coarse particles in these sites should be insignificant. Afforestation and subsequent amelioration to ecosystem C stocks due to biomass and litter accumulations have been examined in semi-arid regions (Grünzweig et al., 2003; Laclau, 2003). However, findings depend on ecosystem type (Jackson et al., 2002), plantation age (Nosetto et al., 2006), soil fertility (Chen et al., 2010), and tree species (Hu et al., 2008). Our results are consistent with the findings of Su and Zhao (2003) and Cao et al. (2008) who reported higher soil organic C in stands of C. microphylla shrub than in active sand dunes, and faster C accumulation rates in the initial 13 years of stand development than in older stands (i.e., 13–28 years). On the other hand, Nosetto et al. (2006) reported that the soil C was unaffected by tree planting in the semi-arid ecosystems of Argentina, and Hu et al. (2008) documented that soil organic C initially decreased following sandy grasslands afforestation with P. simonii in the Horqin Sandy Land, but recovered to the grasslands C levels after 15 years. Similarly, Chen et al. (2010) found that the conversion of sandy grasslands to forest did not result in an increase in soil C until the forest matured. These results, as well as our findings, show that site improvement associated with woody plant establishment varies by ecosystem and vegetation type prior to plantation. Grasslands and non-active stabilized sand dunes [e.g., Sandhills of NE, USA which are dominated by C4 grasses, Eggemeyer et al. (2009)] harbor more organic matter and store more carbon and nutrients than active sand dunes. These grasslands have shown to experience an overall increase in biomass and C storages with woody plant establishment due mostly to aboveground accumulation. However, soil C storage in many cases have been found to decrease with the increase in woody species due to shifts in C storage allocation patterns from mainly below- in grasslands, to above-ground in wooded areas (D. Wedin, personal communication). This is not the case in active sand dunes, which are characterized by very little structural integrity and significantly lower soil organic matter than native grasslands (Chen et al., 2010). Significant changes in soil properties often occur in the upper soil profile during the restoration process of degraded lands (Grandy and Robertson, 2007; Shrestha and Stahl, 2008). Su et al. (2005) reported that soil fine fraction, water holding capacity, organic C, and total N increased more noticeably in the 0–5 cm than in the 5–20 cm soil layer after planting shrubs on active sand dunes. This is consistent with our observations that afforestation effects on soil physico-chemical properties were more pronounced in the upper soil (0–5 cm) than in the deeper soil layer (5–15 cm) (Tables 3 and 4). In fact, most of the examined soil physico-chemical properties in this study differed significantly between the two investigated soil layers.

8

Y. Li et al. / Applied Soil Ecology 56 (2012) 1–9

The coefficients of vertical variation (CVs) for soil C, N, and available nutrients were higher (P < 0.05) in the plantations than in active sand dunes. The vertical variations in soil properties have been attributed to differences in root distributions, and in the above- and below-ground biomass allocation patterns (Shrestha and Stahl, 2008). 4.2. Light fraction as an indicator of soil quality improvement and C sequestration A number of studies have examined the role of light fraction as an early indicator of soil quality improvement and C sequestration in response to land-use and management practices (Six et al., 2002; Bending and Turner, 2009). Haynes (2000) reported that soils under rotation between pasture and crops over a period of 2–5 years exhibited no change in total soil organic C, but the light fraction C increased significantly when switching from crops to pasture, and decreased significantly when switching from pasture to crops. Soon et al. (2007) found that the light fraction dry matter and C contents showed an apparent response to tillage after four years, whereas the effect of tillage on total soil C was not apparent until the 12th year. The light fraction is characterized by a much higher C content than the bulk soil (Leifeld and Kögel-Knabner, 2005; Tan et al., 2007); therefore, the light fraction C represents a relatively large proportion of total soil C, accounting for up to 63% in a range of ecosystems, compared to the light fraction dry matter which usually accounts for 0.08–16.4% of the bulk soil mass (Boone, 1994; Parker et al., 2002; Laik et al., 2009). Our results show that the light fraction is an indicator of soil quality improvement and C sequestration during the restoration process of active sand dunes. The light fraction dry matter content was strongly correlated with soil organic C, total N, and other soil physico-chemical properties (Table 6). The concentration ratio of the light fraction C to the total soil organic C reached up to 263 in active sand dunes and 43 in plantations. The soil organic C gain following afforestation was primarily attributed to an increase in C content in the light fraction that accounted for more than 50% of the increase in soil organic C. These results demonstrate that the change in the light fraction C is more responsive than the total soil organic C to afforestation in desertified lands. Accordingly, soil properties and C and N storages are improved through increased generation of the light fraction in soils due to the plantation-enhanced biological interaction with the soil matrix. 4.3. Potential of C sequestration with afforestation in Horqin Sand Land Historically, the Horqin Sand Land was dominated by native grasslands, however, the area has experienced intensive desertification in the last decades. In 2000, the desertification reached 50,198 km2 , or 47.6% of the total area of the Horqin Sand Land (Wu, 2005). The total amount of C lost from the plant–soil system due to desertification has been estimated to be 107.53 Mt in this region during the last century (Zhou et al., 2008). Our results supported by Su and Zhao (2003), Cao et al. (2008), and Hu et al. (2008) evidenced the significant potential for soil C sequestration with afforestation in this area. The potential on average is 19.9 g C m−2 y−1 by age 35. This potential is smaller in young plantations (15.5 g C m−2 y−1 , from age 0 to 25 years), and greater in older plantations (30.8 g C m−2 y−1 , from age 25 to 35 years) (Table 5). Of the total desertified land area, about 9687 km2 has been heavily and severely degraded (Wu, 2005). The upper 15 cm soil layer in this area could potentially sequester 7 Mt C provided that these active sand dunes are all afforested and grew to an average age of 35 years. This amount could offset 6.3% of the carbon lost due to desertification during last century (107.53 Mt). This estimate

does not include the potential C gain from biomass and litter accumulations, which, when added, would significantly increase this estimate. Overall, Mongolian pine plantations in Horqin Sandy Land have a great potential to sequester C, and therefore, it is important to continue to comprehensively evaluate the effects of these plantations on ecosystem C sequestration and other ecosystem services in this region. Although the depths used for soil C studies vary in the literature (Fornara and Tilman, 2008; Maia et al., 2009), numerous studies have focused on the upper soil profile to investigate the impacts of land cover/use change on soil properties and C stocks, since most of these changes have been found to occur in this segment of the soil profile [e.g., soil samples were collected in the upper 5 cm (Grandy and Robertson, 2007; Allington and Valone, 2010), 10 cm (Lal, 1996), 15 cm (Chen et al., 2010; Su et al., 2010), or 20 cm (Evrendilek et al., 2004) of the soil profile]. In the Horqin Sand Land, Huang et al. (2008) concluded that soil properties in the 20–100 cm profile did not significantly change in a 21-year-old pine plantation, compared to active sand dunes. Similarly, in our previous study that investigated soil properties in enclosures established for vegetation recovery in these sandy grasslands (Li et al., 2011), soil samples were collected to a 100 cm depth. Results showed that significant responses occurred mostly in the upper 10 cm of the soil profile, hence the focus of this study on soil properties and C storage in the 0–15 cm of the soil profile.

5. Conclusion The establishment of Mongolian pine (Pinus sylvestris var. mongolica Litv.) on active sand dunes in the semi-arid Horqin Sandy Land had positive impacts on the soil physico-chemical properties, C sequestration, and N storage. The soil water holding capacity, fine particle content, soil organic and inorganic C, total N, available N, P and K, and light fraction organic matter increased with plantation age. Greater responses were observed in the upper 0–5 cm than in the 5–15 cm layer of the soil profile. The soil light fraction played an important role in soil C sequestration, and its amount is an indicator of C storage in sandy soils. Our results confirm that the Horqin Sandy Land afforestation with Mongolian pine is a positive way to restore and to increase soil C and improve soil quality in these semi-arid desertified lands.

Acknowledgments This research was supported by the National Natural Science Foundation of China (40901049; 31170413), Major State Basic Research Development Program of China (973 Program, 2009CB421303), and Knowledge Innovation Program of CAS (KZCX2-EW-QN313). Our appreciation goes to the anonymous reviewers for their constructive comments.

References Allington, G.R.H., Valone, T.J., 2010. Reversal of desertification: the role of physical and chemical soil properties. J. Arid Environ. 74, 973–977. Bending, G.D., Turner, M.K., 2009. Incorporation of nitrogen from crop residues into light-fraction organic matter in soils with contrasting management histories. Biol. Fert. Soils 45, 281–287. Blackwood, C.B., Paul, E.A., 2003. Eubacterial community structure and population size within the soil light fraction, rhizosphere, and heavy fraction of several agricultural systems. Soil Biol. Biochem. 35, 1245–1255. Boone, R.D., 1994. Light fraction soil organic matter: origin and contribution to net nitrogen mineralization. Soil Biol. Biochem. 26, 1459–1468. Cao, C.Y., Jiang, D.M., Teng, X.H., Jiang, Y., Liang, W.J., Cui, Z.B., 2008. Soil chemical and microbiological properties along a chronosequence of Caragana microphylla Lam. plantations in the Horqin sandy land of Northeast China. Appl. Soil Ecol. 40, 78–85.

Y. Li et al. / Applied Soil Ecology 56 (2012) 1–9 Chen, F.S., Zeng, D.H., Fahey, T.J., Liao, P.F., 2010. Organic carbon in soil physical fractions under different-aged plantations of Mongolian pine in semi-arid region of Northeast China. Appl. Soil Ecol. 44, 42–48. Chen, F.S., Zeng, D.H., Zhou, B., Singh, A.N., Fan, Z.P., 2006. Seasonal variation in soil nitrogen availability under Mongolian pine plantations at the Keerqin Sand Lands. China J. Arid Environ. 67, 226–239. Compton, J.E., Boone, R.D., 2002. Soil nitrogen transformations and the role of light fraction organic matter in forest soils. Soil Biol. Biochem. 34, 933–943. Curtin, D., Beare, M.H., McCallum, F.M., 2007. Sulphur in soil and light fraction organic matter as influenced by long-term application of superphosphate. Soil Biol. Biochem. 39, 2547–2554. Davis, M.R., Condron, L.M., 2002. Impact of grassland afforestation on soil carbon in New Zealand: a review of paired-site studies. Aust. J. Soil Res. 40, 675–690. Duan, Z.H., Xiao, H.L., Dong, Z.B., He, X.D., Wang, G., 2001. Estimate of total CO2 output from desertified sandy land in China. Atmos. Environ. 35, 5915–5921. Eggemeyer, K.D., Awada, T., Harvey, F.E., Wedin, D.A., Zhou, X.H., Zanner, C.W., 2009. Seasonal changes in depth of water uptake for encroaching trees Juniperus virginiana and Pinus ponderosa and two dominant C4 grasses in a semiarid grassland. Tree Physiol. 29, 157–169. Evrendilek, F., Celik, I., Kilic, S., 2004. Changes in soil organic carbon and other physical soil properties along adjacent Mediterranean forest, grassland, and cropland ecosystems in Turkey. J. Arid Environ. 59, 743–752. FAO, 2006. FAO/IUSS Working Group WRB, World reference base for soil resources 2006. World Soil Resources Reports 103. FAO, Rome. Fornara, D.A., Tilman, D., 2008. Plant functional composition influences rates of soil carbon and nitrogen accumulation. J. Ecol. 96, 314–322. Grandy, A.S., Robertson, G.P., 2007. Land use intensity effects on soil C accumulation rates and mechanisms. Ecosystems 10, 59–74. Grünzweig, J.M., Lin, T., Rotenberg, E., Schwartz, A., Yakir, D., 2003. Carbon sequestration in arid-land forest. Glob. Change Biol. 9, 791–799. Haynes, R.J., 2000. Labile organic matter as an indicator of organic matter quality in arable and pastoral soils in New Zealand. Soil Biol. Biochem. 32, 211–219. He, Y., Xu, Z.H., Chen, C.R., Burton, J., Ma, Q., Ge, Y., Xu, J.M., 2008. Using light fraction and macroaggregate associated organic matters as early indicators for management-induced changes in soil chemical and biological properties in adjacent native and plantation forests of subtropical Australia. Geoderma 147, 116–125. Hernandez-Ramirez, G., Sauer, T.J., Cambardella, C.A., Brandle, J.R., James, D.E., 2011. Carbon sources and dynamics in afforested and cultivated corn belt soils. Soil Sci. Soc. Am. J. 75, 216–225. Hu, Y.L., Zeng, D.H., Fan, Z.P., Chen, G.S., Zhao, Q., Pepper, D., 2008. Changes in ecosystem carbon stocks following grassland afforestation of semiarid sandy soil in the southeastern Keerqin Sandy Lands. China J. Arid Environ. 72, 2193–2200. Huang, G., Zhao, X.Y., Su, Y.G., Yue, G.Y., 2008. Assessment on the effects of Pinus sylvestris var. mongolica plantation on microenvironment improvement in the Horqin Sandy Land. China J. Arid Zone Res. 2, 212–218 (in Chinese). ISO, 1994. Soil Quality – Determination of Carbonate Content – Volumetric Method. International Organization for Standardization, Geneva, Switzerland. ISO, 1998. Soil Quality – Determination of Particle Size Distribution in Mineral Soil Material – Method by Sieving and Sedimentation. International Organization for Standardization, Geneva, Switzerland. ISSCAS (Institute of Soil Sciences, Chinese Academy of Sciences), 1978. Physical and Chemical Analysis Methods of Soils. Shanghai Science Technology Press, Shanghai (in Chinese). Jackson, R.B., Banner, J.L., Jobbagy, E.G., Pockman, W.T., Wall, D.H., 2002. Ecosystem carbon loss with woody plant invasion of grasslands. Nature 418, 623–626. Jaramillo, V.J., Kauffman, J.B., Lyliana, R.R., Cummings, D.L., Ellingson, L.J., 2003. Biomass, carbon, and nitrogen pools in Mexican tropical dry forest landscapes. Ecosystems 6, 609–629. Karam, F., Doulis, A., Ozturk, M., Dogan, Y., Sakcali, S., 2011. Eco-physiological behaviour of two woody oak species to combat desertification in the east Mediterranean – a case study from Lebanon. Procedia. Soc. Behav. Sci. 19, 787–796. Laclau, P., 2003. Biomass and carbon sequestration of ponderosa pine plantations and native cypress forests in northwest Patagonia. Forest Ecol. Manage. 180, 317–333. Laik, R., Kumar, K., Das, D.K., Chaturvedi, O.P., 2009. Labile soil organic matter pools in a calciorthent after 18 years of afforestation by different plantations. Appl. Soil Ecol. 42, 71–78. Lal, R., 1996. Deforestation and land-use effects on soil degradation and rehabilitation in western Nigeria. II. Soil chemical properties. Land Degrad. Develop. 7, 87–98. Lal, R., 2001. Potential of desertification control to sequester carbon and mitigate the greenhouse effect. Climatic Change 51, 35–72. Lal, R., 2009. Sequestering carbon in soils of arid ecosystems. Land Degrad. Develop. 20, 441–454. Larney, F.J., Bremer, E., Janzen, H.H., Johnston, A.M., Lindwall, C.W., 1997. Changes in total, mineralizable and light fraction soil organic matter with cropping

9

and tillage intensities in semiarid southern Alberta, Canada. Soil Till. Res. 42, 229–240. Leifeld, J., Kögel-Knabner, I., 2005. Soil organic matter fractions as early indicators for carbon stock changes under different land-use? Geoderma 124, 143–155. Li, Y.Q., Zhao, H.L., Zhao, X.Y., Zhang, T.H., Chen, Y.P., 2006. Biomass energy, carbon and nitrogen stores in different habitats along a desertification gradient in the Semiarid Horqin Sandy Land. Arid Land Res. Manage. 20, 43–60. Li, Y.Q., Zhao, H.L., Zhao, X.Y., Zhang, T.H., Li, Y.L., Cui, J.Y., 2011. Effects of grazing and livestock exclusion on soil physical and chemical properties in desertified sandy grassland, Inner Mongolia, northern China. Environ. Earth Sci. 63, 771–783. Maia, S.M.F., Ogle, S.M., Cerri, C.E.P., Cerri, C.C., 2009. Effect of grassland management on soil carbon sequestration in Rondônia and Mato Grosso states. Brazil Geoderma 149, 84–91. Malhi, S.S., Harapiak, J.T., Nyborg, M., Gill, K.S., Monreal, C.M., Gregorich, E.G., 2003. Total and light fraction organic C in a thin Black Chernozemic grassland soil as affected by 27 annual applications of six rates of fertilizer N. Nutr. Cycl. Agroecosyst. 66, 33–41. McGill, W.B., Figueiredo, C.T., 1993. Total nitrogen. In: Carter, M.R. (Ed.), Soil Sampling and Methods of Analysis. Canadian Society of Soil Science/Lewis Publishers, Boca Raton, pp. 201–211. Murage, E.W., Voroney, P., Beyaert, R.P., 2007. Turnover of carbon in the free light fraction with and without charcoal as determined using the 13 C natural abundance method. Geoderma 138, 133–143. Nelson, D.W., Sommers, L.E., 1982. Total carbon, organic carbon and organic matter. In: Page, A.L., Miller, R.H., Keeney, D.R. (Eds.), Methods of Soil Analysis, Part 2. , second ed. Agronomy, Madison, pp. 539–577. Nosetto, M.D., Jobbágy, E.G., Paruelo, J.M., 2006. Carbon sequestration in semi-arid rangelands: Comparison of Pinus ponderosa plantations and grazing exclusion in NW Patagonia. J. Arid Environ. 67, 142–156. Olsen, S.R., Cole, C.W., Watanabe, F.S., Dean, L.A., 1954. Estimation of Available Phosphorus in Soils by Extraction with Sodium Bicarbonate. U. S. Dept Agric, Washington, Circular 939. Parker, J.L., Fernandez, I.J., Rustad, L.E., Norton, S.A., 2002. Soil organic matter fractions in experimental forested water sheds. Water Air Soil Pollut. 138, 101–121. Pei, S.F., Fu, H., Wan, C.G., 2008. Changes in soil properties and vegetation following exclosure and grazing in degraded Alxa desert steppe of Inner Mongolia, China. Agr. Ecosyst. Environ. 124, 33–39. Saggar, S., Yeates, G.W., Sheperd, T.G., 2001. Cultivation effects on soil biological properties, microfauna and organic matter dynamics in Eutric Gleysol and Gleyic Luvisol soils in New Zealand. Soil Till. Res. 58, 55–68. Shrestha, G., Stahl, P.D., 2008. Carbon accumulation and storage in semi-arid sagebrush steppe: effects of long-term grazing exclusion. Agric. Ecosyst. Environ. 125, 173–181. Six, J., Callewaert, P., Lenders, S., De Gryze, S., Morris, S.J., Gregorich, E.G., Paul, E.A., Paustian, K., 2002. Measuring and understanding carbon storage in afforested soils by physical fractionation. Soil Sci. Soc. Am. J. 66, 1981–1987. Soon, Y.K., Arshad, M.A., Haq, A., Lupwayi, N., 2007. The influence of 12 years of tillage and crop rotation on total and labile organic carbon in a sandy loam soil. Soil Till. Res. 95, 38–46. Su, Y.Z., Wang, X.F., Yang, R., Lee, J., 2010. Effects of sandy desertified land rehabilitation on soil carbon sequestration and aggregation in an arid region in China. J. Environ. Manage. 91, 2109–2116. Su, Y.Z., Zhang, T.H., Li, Y.L., Wang, F., 2005. Changes in soil properties after establishment of Artemisia halodendron and Caragana microphylla on shifting sand dunes in Semiarid Horqin Sandy Land, Northern China. J. Environ. Manage. 36, 272–281. Su, Y.Z., Zhao, H.L., 2003. Soil properties and plant species in an age sequence of Caragana microphylla plantations in the Horqin Sandy Land, north China. Ecol. Eng. 20, 223–235. Tan, Z., Lal, R., Owens, L., Izaurralde, R.C., 2007. Distribution of light and heavy fractions of soil organic carbon as related to land use and tillage practice. Soil Till. Res. 92, 53–59. Wu, W., 2005. Study on dynamic evolvement of modern sandy desertification land in Horqin Sandy Land. Ocean Press, Beijing, pp. 189–226. Yu, Z.Y., Chen, F.S., Zeng, D.H., Zhao, Q., Chen, G.S., 2008. Soil inorganic nitrogen and microbial biomass carbon and nitrogen under pine plantations in Zhanggutai sandy soil. Pedosphere 18, 775–784. Zeng, D.H., Jiang, F.Q., Fan, Z.P., Zhu, J.J., 1996. Stability of Mongolian pine plantations on sandy soil. China J. Appl. Ecol. 7, 337–343 (in Chinese). Zhang, T.H., Zhao, H.L., Li, S.G., Li, F.R., Shirato, Y., Ohkuro, T., Taniyama, I., 2004. A comparison of different measures for stabilizing moving sand dunes in the Horqin Sandy Land of Inner Mongolia, China. J. Arid Environ. 58, 203–214. Zhao, H.L., Zhao, X.Y., Zhou, R.L., Zhang, T.H., Drake, S., 2005. Desertification processes due to heavy grazing in sandy rangeland, Inner Mongolia. J. Arid Environ. 62, 309–319. Zhou, R.L., Li, Y.Q., Zhao, H.L., Drake, S., 2008. Desertification effects on C and N content of sandy soils under grassland in Horqin, northern China. Geoderma 145, 370–375.