Evolution of soil properties on stabilized sands in the Tengger Desert, China

Geomorphology 59 (2004) 237 – 246 www.elsevier.com/locate/geomorph

Evolution of soil properties on stabilized sands in the Tengger Desert, China Duan Zhenghu a,b,*, Xiao Honglang b, Li Xinrong b, Dong Zhibao b, Wang Gang c a

Xinjiang Institute of Ecology and geography, Chinese Academy of Sciences; 40 Beijing South Road, Urumqi, 830011, P.R. of China b Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences; 260 Donggang West Road, Lanzhou, 730000, P.R. of China c State Key Laboratory of Arid Agroecology, Lanzhou University, 298 Tianshui Road, Lanzhou, 730000, P.R. of China Accepted 16 July 2003

Abstract The spatial and temporal patterns of pedogenesis on stabilized dunes at Shapotou, northwestern China, were studied on the time sequences of 0, 18, 35 and 43 years. The spatial pattern of soil formation was estimated by measuring the thickness of accumulated sand fractions on the stabilized dune surface and by analyzing the characteristics and properties of soil. The results showed that the environment of soil formation and circulation of soil material were influenced in the processes of shifting-sand fixation, and the mean soil particle size changed from >0.2 to < 0.08 mm in 0 – 20 cm soil depth with the succession from cultivated plants to natural vegetation. The capacity of available soil water increased fivefold. Deep infiltration of water in soil no longer occurred due to the increase in soil water capacity and the change of redistribution of soil water in profiles. Soil microorganisms evolved from simple to complex. Interaction of these processes obviously brought about accumulation of soil fertility, evolution of soil profiles and development of the profiles towards aripsamments. The difference of micro-topography is closely related to redistribution of material and energy in soil formation. D 2003 Elsevier B.V. All rights reserved. Keywords: Aeolian sandy soils; Fixation of shifting sand; Soil fertility; Tengger Desert

1. Introduction The deserts of China constitute one of the dustiest areas on earth (Littmann, 1991; Yang et al., 1994), but the stabilization of aeolian deposits is limited. The absence of vegetation results in the deflation and resuspension of fine particles from desert areas that eventually accumulate at vegetated desert margins

* Corresponding author. E-mail address: [email protected] (D. Zhenghu). 0169-555X/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2003.07.019

forming loess or loess-like deposits (Dan and Yaalon, 1971). Stabilized in the past by straw checkerboard barriers, the mobile dunes change into stabilized sand in the transition zone of arid grassland and soil nutrient depleted regions in north China (Ling et al., 1993). Aeolian deposition is determined by a number of factors, including distance from the sediment source (Tsoar and Pye, 1986), existing vegetation cover (Yaalon and Dan, 1974) and topography (Jorgenson, 1992). Some 60% of China’s deserts are sandy, much of it in the form of mobile dunes (Chao and Xing, 1982). Upon stabilization, the enrichment

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of dune surfaces through aeolian deposition of fine particles becomes an important geomorphological process (Danin, 1978). For example, in the Shapotou area, after decades of stabilization, the succession of cultivated plants on shifting sand gradually evolved naturally towards a natural vegetation. Vegetation cover varied between 20% and 40%, and yearly litter yield reached 43.6 g m 2 (Shi and Liu, 1995). Furthermore, soils evolved towards aripsamments and the surface morphology of aeolian-sand soil profile also changed (Zhen, 1987), sometimes even towards a macrobiotic crust (Duan et al., 2003). In the meantime, numerous microbes, mosses and herbs appeared in the surface soil layer (Shi et al., 1996; Li et al., 2002). As a result, the structure and function of desert ecosystem became better (Harper and Mar-

ble, 1998). With the development of a surface crust, substantial changes in soil properties such as erodibility, texture, structure, nutrient content and moisture content have occurred when compared with the original aeolian sand. The study on the evolution of soil properties in the processes of shifting-sand fixation is very significant for the desert rehabilitation and ecoenvironmental improvement.

2. Materials and methods The study area lies at the southern edge of the Tengger Desert at Shapotou, northwestern China (105j00VE, 37j40VN) (Fig. 1). Site elevation is 1300 – 1350 m. Mean annual precipitation is around

Fig. 1. Geographical situations of the major deserts (sandy lands) and location of the Shapotou in China. (1) Kurban Tunggut Desert; (2) Taklimakan Desert; (3) Kumtag Desert; (4) Qaidam Basin Desert; (5) Badain Jaran Desert; (6) Tengger Desert; (7) Ulan Buh Desert; (8) Qubqi Desert; (9) Mu Us Desert; (10) Otindag Desert; (11) Horqin Sandy Land; (12) Nenjiang Sandy Land; (13) Huang-Huai-Hai Plain Sandy Land.

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180 mm, falling predominantly during the months between May and September (Zhao, 1988). Precipitation is highly variable, dependent on the strength and extent of the summer monsoonal system. Temperatures average 24.3 jC in July and 6.9 jC in January. Mean annual pan potential evaporation is 2508 mm. The highest wind speed occurs in the late spring (April – May), with an average wind velocity of 3.5 m s 1, and the wind direction is predominantly northwesterly (Li, 1988). The Shapotou Desert Research Station was established in 1956 to investigate methods of stabilizing shifting dunes, which threatened the Baotou –Lanzhou railway line as it crossed the Tengger Desert. The stabilization method was a combination of windbreaks, straw checkerboard barriers and planted xerophytic shrubs (Fig. 2). A willow branch fence was first constructed at the edge of the stabilized area, greatly reducing the entry of blowing sand (Lin et al., 1984). The straw checkerboard barriers were made of wheat and rice straw embedded in the sand roughly in a 1  1 m grid, with the straw protruding 10 –15 cm above the surface. Xerophytic shrub seedlings, such as Artemisia ordosica, Krasch., Hedysarum scoparium, Fisch. and C.A. Mey, Caragana korshinskii, Kom.

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and Calligonum mongolicum, Turc’z were planted within the checkerboards (Fearnehough et al., 1998). The stabilized area was further expanded in 1965 and 1981. As a consequence of shifting-sand fixation, both vegetation and geomorphology displayed apparent change (Fig. 3). Soil samples were collected from different sites representing different topographic and time sequences. The pedons were described according to Guthrie and Witty (1982) before being sampled. The sand layer and thickness of surface ‘‘grey sand’’ were composed of deposited aeolian particles, desert sand and organic matter and constituted a developing dune soil (Fearnehough et al., 1998). In order to examine the effects of time on sand soil development, dunes stabilized since 1956, 1965 and 1981 and a shiftingsand site outside the stabilized area were chosen. In 1999, these gave a time sequence covering 43 years. Based on the genetic horizon of 1.2-m soil layer (including soil crust), soil samples of the stabilized dunes of different ages and types were collected for particle size and physical and chemical analysis (Fig. 4). Soil particle size was determined using the pipette method (Wang, 1983). The soil chemical properties— N, P and K content—were determined using routine

Fig. 2. Plan of different-year stabilized site in Shapotou. The characters in brackets indicate the measure of stabilization dunes in every area.

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Fig. 3. Changes in landscape ecosystem in the processes of shifting-sand fixation. (A) Shifting dunes; (B) stabilized sand with straw checkerboards; (C) landscape of initial intruded vegetable; (D) landscape of stabilizing 43 years; (E) lichen and moss of 1956 stabilized sand area after rain; (F) herbage vegetable of 1956 stabilized sand area in September.

Fig. 4. Changes in soil profile morphology on stabilized sand dunes. (A) Leeward slope dunes stabilized in 1981; (B) leeward slope dunes stabilized in 1965; (C) leeward slope dunes stabilized in 1956; (D) windward slope dunes stabilized in 1956; (E) hollow dunes stabilized in 1956.

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methods (Nanjing Institute of Soil Sciences, Chinese Academy of Sciences, 1978). The soil bulk density was determined using the cutting ring method. The number of bacteria, fungi and actinomyces was determined using the flat panel smear methods (Xu and Zheng, 1986). At the same time, the field survey and the analyses of crust and dust particle sizes were conducted. The amount of aeolian deposition was studied using a transect of dust traps that consisted of metal cylinders 350 mm high and 250 mm in diameter, sediment being collected through a funnel at the base of the cylinder. Measurements of aeolian deposition have been made at Shapotou since August 1990 (Zhang et al., 1993). Traps were placed away from shrubby vegetation at different topographic positions and remained in the field for 3 years from 1994 to 1996. Trapped sediment was dried and weighed monthly. In order to examine changes in surface morphology after sand dunes stabilized, the topography of the region of the artificial stabilized sand dunes was measured using a Theodolite and compared to 1964 measured results. Because the existing topography reduced from northwest to southeast in the stabilized area, we calculated relative height and undulation degree at all points using the regional inclination as a base level. Statistical analysis (ANOVA with LSD and regression analysis) was carried out by using SPSS 10.0 for Windows at a p V 0.05 significance level.

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3. Results and discussion 3.1. Changes in soil texture Soil succession was significantly accelerated due to the improvement of soil-forming environment and the quickening of mobile aeolian-sand soil towards aripsamments in the processes of shifting-sand fixation. Shifting sand (parent material) in Shapotou region has a mean particle size of >0.2 mm, of which >0.2 mm particles occupy 30– 40% and >0.02 mm particles f 95%, while silt-sized particles do not occur, and, therefore, it has a better water permeability and poor water retentiveness. During the processes of shiftingsand fixation, large amounts of silt-sized particles (0.01 – 0.05 mm) were deposited on the sand surface and thereby altered the original soil mechanical composition. Generally, >0.2 mm particles in surface layer reduced by 5% or less, 0.02 – 0.2 mm fine sand content decreased by 60 –80%, 0.02– 0.002 mm silt content reached 14– 20% and < 0.01 mm physical clay content increased from 1.5% to 2%. Soil hygroscopicity and plasticity significantly improved. Mean particle-size value decreased to 0.08 –0.14 mm and tended to become finer with time. This shows that shifting sand is no longer the only soil substrate and that other transported materials, including dustfall, also play an important role in altering soil texture (Table 1).

Table 1 Influences of different sand-fixing ages and landform positions on soil mechanical composition (%) Soil-forming factors Sand-fixing age (years)

Landform position

Dust 0 18 35 43 43 43 43 43

Height 5.2 m Leeward slope Leeward slope Leeward slope Leeward slope Leeward slope Leeward slope Interdune depression Interdune depression

Particle size (mm) Soil depth (cm) 0 – 20 0 – 17 0 – 20 0 – 20 15 – 20 40 – 50 0–7 0–4

n

< 0.01 (% F S.E.)

< 0.02

< 0.05

< 0.10

< 0.20

< 0.50

10 5 5 5 5 3 3 5 5

24.2 F 4.1 0.2a F 0.1 3.2b F 0.3 5.0c F 0.7 8.0dC F 1.6 3.5B F 0.3 1.2A F 0.2 9.0C F 1.8 7.2C F 1.6

38.5 0.3 4.8 6.0 12.5 4.1 1.5 12.0 10.0

60.4 0.4 8.5 11.0 24.0 5.0 1.8 25.2 20.0

80.6 0.76 22.1 29.9 53.8 12.5 6.5 53.6 41.8

97.4 99.3 95.1 92.3 98.2 91.8 59.8 95.0 95.7

100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Mean content of particle size < 0.01 mm marked (a) are significantly different (Student’s t test, p V 0.005) from those marked (b), (c) and (d). Mean content of particle size < 0.01 mm in the 43-year stabilized sand area marked (A) are significantly different (Student’s t test, p V 0.05) from those marked (B) and (C).

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Table 2 Physical parameters of surface soil layer Land type

Maximum hygroscopic moisture (% F S.E.)

Wilting coefficient (% F S.E.)

Moving aeolian-sand soil Fixed aeolian-sand soil (1956)

0.45a F 0.02

0.61a F 0.09

1.62b F 0.05

3.03b F 0.54

Capillary water (% F S.E.)

Porosity (% F S.E.)

Bulk density (g/cm3 F S.E.)

Specific gravity (g/cm3 F S.E.)

4.01a F 0.42

40.07a F 3.32

1.62a F 0.02

2.70a F 0.03

19.18b F 1.63

45.10b F 3.84

1.36 F 0.02

2.47b F 0.03

Mean physical parameters of surface soil layer marked (a) are significantly different (Student’s t test, p V 0.05) from those marked (b). n = 5.

3.2. Improvement of soil water-holding capacity Owing to the changes in material composition and mechanical composition, the bulk density and specific gravity of fixed aeolian-sand soil significantly decreased, but its porosity and water-holding capacity are largely enhanced (Table 2). For example, the change in soil water-holding capacity significantly affected the redistribution dynamical changes of soil moisture after 30.5 mm rainfall on 18 August 1998 (Fig. 5), and in the subsequent 3 days, Fig. 2 shows that owing to the lower water-holding capacity of shifting sand, the following rainfall water continuously seeped through the soil and exhibited a roughly uniform distribution with depth. In contrast, much of the rainwater was concentrated within 10 cm surface layer of the 35-year cultivated vegetation area and no water recharged the soil below 40 cm depth. For the former, water was present at depth, whereas for the latter, rainwater only favored the shallow-rooted

plants, but surface evaporation loss greatly increased. From the comparison of four water distribution diagrams, it can be seen that for the different years of fixed aeolian soils, the dividing line of rainwater deeplayer recharge lies between 10 and 20 years. In normal years, soil evaporation on bare shiftingsand surface is 60 –70% of annual precipitation, but in dry years it may account for z 90% (Chen, 1991; Feng et al., 1995). Annual precipitation could seep down to z 5 m below the surface of shifting sand to recharge deep layer of soil moisture, on the average, accounting for 10% of annual precipitation (Chen, 1991). However, in the cultivated vegetation area, much of the precipitation is consumed by plant transpiration in addition to soil surface evaporation. Root systems of perennial sand-binding shrubs are mostly distributed in the 1 –3-m soil layer (Liu et al., 1991), while those of annual herbs with the 10-cm soil layer. Although the evaporation of vegetated soil is less than that of shifting sand, the transpiration of

Fig. 5. Redistribution processes of soil moisture after rainfall in different ages of fixed sandy land.

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plants is large, accounting for 20 – 40% of annual precipitation (Chen, 1991; Feng et al., 1995), and thus affecting deep infiltration of soil moisture. 3.3. Variations of soil micro-flora Microorganism numbers in fixed aeolian-sand soil in the Shapotou Region are a few tens of times higher than that in unvegetated shifting sand (Table 3), due to high organic matter content and high soil fertility in the surface layer of fixed aeolian-sand soil. Fungi and bacteria in fixed aeolian-sand soil are mostly concentrated in the surface layers and decrease rapidly with depth. The total number of bacteria in shifting sand often exceeds that in fixed aeolian-sand soil, but their distribution increases with depth. This is because surface layer of shifting sand is very dry and therefore unfavorable to microorganism survival. The number of microorganisms as an indicator of soil fertility can reflect the increase in soil fertility from shifting sand to aeolian-sand soil fixed by cultivated vegetation. 3.4. Nutrient accumulation The increase in water-holding capacity and plant biomass in surface layers of fixed aeolian-sand soil greatly speeds up the accumulation and mineralization of organic matter. Furthermore, the fixed surface is favorable as a trap for airborne nutrients (for example, dustfall and rainfall) and to avoid soil nutrient loss. The changes in soil-forming condition thereby enable the shifting-sand ecosystem of lower biological activity to develop towards a soil ecosystem of higher biological activity. From shifting sand to fixed aeolian-sand soil, higher plants developed as soil organic matter signif-

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icantly increased. The organic matter content in the surface soil layer on the leeward slope of the sandy land fixed for 39 years was 10 times that of shifting sand (Table 4). Owing to the influence of microtopographical conditions, the accumulated amount of organic matter in interdune depressions is highest: The same trend has been observed for N, P and K, and especially obvious is the available K accumulation. The nutrient content in the aeolian sand fixed by natural vegetation in the control plot is roughly the same as that in the sandy land fixed by cultivated vegetation for several decades. However, the soillayer thickness in the cultivated vegetation plot is shallow, and its nutrient content at depth is less than that of the sand land fixed by natural vegetation. 3.5. Evolution of soil profile morphology Although the mobile aeolian-sand soil at the study area exhibits some fertility features, it is essentially devoid of higher plants and the biological processes in areas of wind activity are quite weak. Except for the difference in dark and light color caused by soil moisture content and the weak stratified structure formed in the wind deposition processes, the whole soil profile is composed of loose yellow-brownish fine sand, suggesting that it is still in initial pedogenesis. The profile of aeolian-sand soil in the cultivated vegetation area can be divided into a crust, a transitional layer and the original shifting-sand layer. The crust is light gray in color (10YR 6/3 –6/4) and mainly composed of silt and fine sand (Duan et al., 2003). It has weak stratified structure formed by blowing sand, dustfall and litter after the sandy land was fixed by vegetation. In addition, it also exhibits an obvious monsoon rhythm in features. Under the influences of

Table 3 Microorganism numbers under different soil conditions (100 individuals/kg soil F S.E.) Soil type (g/kg)

Soil depth (cm)

Bacteria

Fungi

Actinomyces

Total number

Soil organic carbon

Fixed aeolian-sand soil (1965) (1)

0–1 1–6 6 – 16 0–1 1–6 6 – 16

6196a F 282 2537b F 96 63c F 21 23a F 2 95b F 7 261c F 16

10.2a F 0.7 5.4b F 0.3 1.5c F 0.1 0.4a F 0.06 0.6b F 0.05 0.5ab F 0.05

20.1a F 1.3 22.8a F 1.5 6.7b F 0.5 50.4a F 4.6 214.8b F 15.4 40.2c F 3.8

6226a F 288 2565b F 99 71c F 22 74a F 7 311b F 22 302b F 20

11.73a F 0.96 4.77b F 0.34 1.13c F 0.08 0.70a F 0.05 0.72a F 0.06 0.66b F 0.05

Moving aeolian-sand soil (2)

Mean microorganism numbers and soil organic matter under different depth marked (a) are significantly different (Student’s t test, p V 0.05) from those marked (b) and (c). n = 3. All mean microorganism numbers and soil organic matter under fixed aeolian-sand soil marked (1) are significantly different (Student’s t test, p V 0.05) from those marked (2). n = 3.

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Table 4 Variations of soil nutrients in the process of shifting-sand fixation Sand-fixing age (a) Dune position

0 (Shifting sand)

Composite sample

Sampling Organic Total nutrient content (g/kg) depth (cm) carbon (g/kg) N P K

0–5 40 – 50 14 Leeward slope 0 – 17 30 Leeward slope 0 – 20 39 Leeward slope 0–2 15 – 20 40 – 50 Interdune depression 0 – 7 Windward slope 0–5 26 Windward slope 0–5 Sand land fixed by Windward slope 0–5 natural vegetation 20 – 54 54 – 76 76 – 100

0.86 0.82 2.48 4.33 8.14 5.59 0.45 11.07 9.20 5.36 5.57 1.97 1.39 0.87

landform and sand flow, annual deposited thickness in the area varies between 1 and 10 mm. The crusts around shrubs and herbs are covered by 2– 8 mm of litter with lichen and mosses. Beneath it is an organicmatter-stained layer, 5 – 10 cm in thickness. It has a compact and lumpy structure and contains large amounts of plant roots and undecomposed litter. The transitional layer below the soil crust is virtually the sand layer formed before being fixed, yellowish-brown in color (10YR 5/4 – 5/6), 15 –20 cm thick and contains some roots. Owing to the prolonged migration of humus, fine soil particles and mineral elements during pedogenesis, this layer has a higher fertility than shifting sand (Table 4). It also has a certain consistence and weak block structure. Soils on the leeward slope have a thicker crust, but roots are few due to deficient moisture. Soil crusts in the interdune depressions are thin, although the depressions have been fixed by vegetation for 20– 30 years. Because heavy-rain-induced runoff often flows to the interdune depression, the dense root layer is much thicker than the soil crust. The shifting sand at the bottom still retains its original deposition condition, belonging to loose and structureless aeolian sand. With the increase in crust thickness, soil water condition becomes worse, hence, only a few fine root system and coarse shrub root exist in this layer. During the sand fixation processes by cultivated vegetation, the differentiation of soil body is significantly reinforced, although its evolution processes are

0.06 0.06 0.20 0.16 0.31 0.08 0.05 0.32 0.26 0.23 0.33 0.08 0.05 0.02

0.06 0.04 0.10 0.14 0.17 0.08 0.05 0.17 0.15 0.13 0.17 0.12 0.14 0.11

7.75 6.34 10.46 10.46 10.46 10.46 9.46 10.46 10.46 8.47 8.34 9.17 8.80 9.17

Available nutrient content (mg/kg) N

P

K

7.05 – 34.11 14.58 25.40 18.50 3.45 34.97 29.48 3.29 23.50 8.10 11.60 9.30

1.34 0.22 1.70 1.99 4.53 0.84 1.20 5.40 3.34 2.44 5.29 2.18 1.93 1.33

48 54 104 75 100 104 42 79 112 70 95 – – –

similar to those under natural vegetation condition, because of greater plant density, the differentiation rate of the former is much faster than the latter. Fine soil layers deposited at different landform positions can be classified into three configurations: First, a fine soil layer developed on the leeward slope of sand dunes has the greatest depth and it thickens at an annual rate of 5 –8 mm. During the initial sand fixation stage, comparatively large amounts of aeolian sand join the formation of soil profile. Some 20 years later, the shifting sand has been largely fixed except at its margin, and annual deposition is reduced to 2– 5 mm. Fine sand transported by winds in windy season and silt transported by weak wind formed interbeds or crossbeds, with a total thickness >20 cm. Due to limited precipitation in the region, there is white crystal or powdery gypsum layer and calcareous deposits formed at 10 – 15 cm depth. Second, the windward slope of sand dune is eroded, so has the least accumulated sand and dustfall. Although there is Table 5 Mean value contrast of topographical changes of 385 measuring points in the sandy land fixed by cultivated vegetation (unit: m) Observed year

Relative height

Undulation degree

Vertical range

1964 1984 Annual mean decrease

5.97 4.93 0.05

1.50 1.36 0.01

10.31 5.99 0.22

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Table 6 Mean dust deposition rate of different topographic positions (kg/ha2) Position

January February March April May

Dune crest 55 Interdune 106 depression

208 417

272 635

314 773

June July August September October November December Annual mean

884 423 2004 961

525 626

433 588

107 235

56 132

136 268

88 172

3500 6938

Height between dune crest and interdune depression is 8.2 m. Level distance between dust traps is 25 m.

bedding formed by blown sand and dust, it is dominated by silt with an indistinct sequences. Annual deposition thickness varies between 0.5 and 0.8 mm. The thickness of fine soil layer in the sandy land fixed during the 1950s to the 1960s is 2 –5 cm. Third, the interdune depression is covered by silt deposits without bedding. The annual deposition varies between 1.0 and 1.5 mm, and, locally, the thickness of fine soil layer reaches 5– 8 cm and contains a certain amount of organic matter. 3.6. Microtopographical influences Differences in surface morphology often govern the redistribution of materials, and thereby affect soil development. During the fixation processes of shifting sand, the area’s relief evolved towards uniformed direction (Table 5). Mass balance obviously appears as a negative value for the positive landforms, such as the dune crest, and a positive value for the negative landforms, including interdune depression, with leeward slope having the largest mass accumulation. Owing to the changes in climate, landform and biological condition, each year, f 40 mg/m2 of dustfall in the vegetated area joins the soil-forming processes as a parent material. Furthermore, landform plays a very important role in the redistribution of materials, hence, the windward slope differs from leeward slope by two times or more in deposition rate (Table 6). In the initial stage of shifting-sand fixation, dust plays an important role in binding soil particles and stabilizing the sand surface, dust improves the conservation capacity of soil nutrients and moisture, thus providing an important condition for vegetation succession. In the latter stage, the infiltration rate of water in the sandy land fixed by cultivated vegetation for less than 30 years greatly decreases and heavy rain may cause surface runoff, which carries fine soil particles from slopes to interdune depressions. It is this difference in mass balance

that leads to the difference in soil-profile development and morphology and even causes obvious differentiation of soil physiochemical properties, particle size and nutrient accumulation.

4. Conclusions In the succession from cultivated vegetation to natural vegetation in the experiment plot of shiftingsand fixation in the past few decades in the Shapotou Region, significant changes took place in soil fertility due to changes in soil-forming environments and material cycles. Firstly, shifting sand is no longer the only source of soil substrate. Fine particles such as dustfall exert significant effects on soil texture, modal particle size reduced from >0.2 to < 0.08 mm and tended to become finer with time. Secondly, soil water-holding capacity improved and nearly increased fivefold. In the process of water redistribution in soil body, deep infiltration usually no longer occurred. Thirdly, the number of microorganisms in relation to the content and distribution of organic matter shows that the evolution of soil fertility and microbes is an interactive process. Fourthly, after 39 years of fixation, the organic matter content in the sandy land increased tenfold compared to shifting sand and other nutrients also significantly increased, this is because the process of nutrient loss, as occurs under shiftingsand condition, virtually stopped. Fifthly, soil profiles display obvious differentiation, organic layer and illuvial horizons have preliminarily formed and its configuration tends to evolve towards aripsamments.

Acknowledgements This study was supported by the National Natural Science Foundation of China (90202015), the Gongguan Project of National (2002BA517A11) and the

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Innovation Project of Chinese Academy of Sciences (KZCX3-SW-324). The authors thank Dr. Ian Livingstone, Dr. Mike Fullen and Dr. Richard Harper for their critical review of the manuscript. References Chao, S., Xing, J., 1982. Origin and development of the Shamo (sandy deserts) and the Gobi (stony deserts) of China. In: Smiley, T.S. (Ed.), The Geological Story of the World’s Deserts. Striae, vol. 17. Uppsala University Press, Uppsala, pp. 79 – 91. Chen, W., 1991. Water balance in 29-year cultivated vegetation plots on both sides of Baolan railway in Shapotou region. Study Shifting Sand Control. (2), 66 – 75 (in Chinese). Dan, J., Yaalon, D.H., 1971. On the origin and nature of paleopedological formations in the coastal fringe areas of Israel. In: Yaalon, D.H. (Ed.), Paleopedology—Origin, Nature and Dating of Paleosols. Israel Univ. Press, Jerusalem, pp. 245 – 260. Danin, A., 1978. Plant species diversity and plant succession in a sandy area in the Northern Negev. Flora 167, 409 – 422. Duan, Z., Wang, G., Xiao, H., Dong, Z., 2003. Abiotic soil crust formation on dunes in an extremely arid environment: a 43-year sequential study. Arid Land Res. Manag. 17, 43 – 54. Fearnehough, W., Fullen, M.A., Mitchell, D.J., Trueman, I.C., Zhang, J., 1998. Aeolian deposition and its effect on soil and vegetation changes on stabilized desert dunes in northern China. Geomorphology 23, 171 – 182. Feng, J., Chen, H., Liu, Y., 1995. Water consuming features and water balance of cultivated vegetation on sandy land. Study Desert Ecosyst. (1), 143 – 148 (in Chinese). Guthrie, R.L., Witty, J.E., 1982. New designations for soil horizons and layers and the new soil survey manual. Soil Sci. Soc. Am. J. 46, 443 – 444. Harper, K.T., Marble, J.R., 1998. A role for non-vascular plants in management of arid and semi-arid rangelands. In: Tueller, P.T. (Ed.), Application of Plant Sciences to Rangeland Management. Martinus Nijhoft Publishers/Junk, Amsterdam, pp. 135 – 169. Jorgenson, D.W., 1992. Use of soils to differentiate dune age and to document spatial variation in aeolian activity, northeast Colorado, USA. J. Arid Environ. 23, 19 – 34. Li, J., 1988. Wind regime and shifting sand movement in Shapotou area. J. Desert Res. 8 (3), 41 – 52 (in Chinese with English abstract). Li, X., Wang, X., Li, T., Zhang, J., 2002. Microbiotic soil crust and its effect on vegetation and habitat on artificially stabilized desert dunes in Tengger Desert, North China. Biol. Fertil. Soils 35, 147 – 154. Lin, Y., Jin, J., Zou, B., Cong, Z., Wen, X., Tu, X., Ye, J., Zhang, B., Wang, H., 1984. Effect of fence techniques in leveling sand accumulation around sandbreaks—case study in Shapotou Dis-

trict. J. Desert Res. 4 (3), 16 – 26 (in Chinese with English abstract). Ling, Y., Qu, J., Hu, M., 1993. Formation of sand surface crust and micro-environmental changes. J. Appl. Ecol. 4 (4), 393 – 398 (in Chinese with English abstract). Littmann, T., 1991. Dust storm frequency in Asia: climatic control and variability. Int. J. Climatol. 11, 393 – 412. Liu, Y., Li, Y., Yang, X., 1991. Root systems of psammophytes. Study Shifting Sand Control (2), 185 – 209 (in Chinese). Nanjing Institute of Soil Sciences, Chinese Academy of Sciences, 1978. Analysis of Soil Physical and Chemical Properties. Shanghai Science and Technology Press, Shanghai, pp. 66 – 208. In Chinese. Shi, Q., Liu, J., 1995. Dynamics of natural vegetation in cultivated vegetation plots on both sides of Baolan rainway in Shapotou Region. Study Desert Ecosyst. (1), 105 – 115 (in Chinese with English abstract). Shi, Q., Liu, J., Li, Y., 1996. Transmutation and renovation measures of artificial vegetation on both sides of Shapotou railway section. J. Desert Res. 16 (Suppl. 1), 25 – 29 (in Chinese with English abstract). Tsoar, H., Pye, K., 1986. Dust transport and the question of desert loess formation. Sedimentology 34, 139 – 153. Wang, R., 1983. Soil particle analysis. In: Li, Y.K. (Ed.), Soil and Agricultural Chemistry Routine Analysis. Chinese Science Press, Beijing, pp. 23 – 54. In Chinese. Xu, G., Zheng, H., 1986. Soil Microorganism Analysis Methods Manual. Chinese Agriculture Press, Beijing, pp. 102 – 136. In Chinese. Yaalon, D.H., Dan, J., 1974. Accumulation and distribution of loess-derived deposits in the semi-desert and desert fringe areas of Israel. Z. Geomorphol. Suppl.bd 20, 91 – 105. Yang G., Huang, Z., Zhao, X., Hu, M., Ling, Y., 1994. A study on several problems concerning dust storms in Northwest China. Lanzhou Institute of Desert Research, Academia Sinica, Desertification and Its Control in China. IUGG/CAS Summer Training School for Combating Desertification. August 15 – 25. Lanzhou, pp. 163 – 183. Zhang, J., Di, X., Wang, S., 1993. Character of regional ecological changes during the establishment of preventive system, Shapotou. Institute of Desert Research. Academia Sinica, Lanzhou. Gansu Scientific Technology Publishing House, Lanzhou. In Chinese. Zhao, X., 1988. Problems of revegetation on sand dunes in Shapotou area. Shapotou Scientific Experimental Station, Lanzhou Institute of Desert Research. Academia Sinica. Studies of Dune Control in Shapotou Area, Tengger Desert (2), Ningxia People’s Publishing House, pp. 27 – 58. Zhen, J., 1987. Changes in surface morphology of shifting sand land after being fixed in Shapotou area at southeastern fringe of Tengger Desert. J. Desert Res. 7 (1), 9 – 17 (in Chinese with English abstract).