Soil nematode community succession in stabilised sand dunes in the Tengger Desert, China.
Abstract: In order to examine how nematodes respond to sand dune succession after stabilisation and reclamation techniques, nematode communities were investigated in sand dunes stabilised for 0, 16, 26, 43, and 51 years in the Tengger Desert, China. Our results revealed that the abundance of nematodes; the proportion of fungivores, omnivores, and predators; maturity index (MI); Shannon index; evenness; and structure index (SI) were affected significantly by the age of stabilised sand dunes, and were correlated with soil physical and chemical properties to different degrees. There were differences in nematode abundance, the proportion of fungivores, Shannon index, and evenness between the shifting dunes and the stabilised dunes, but not within the different succession stages of the stabilised dunes. MI showed a tendency to increase with dune age and SI increased significantly with dune age. MI, and especially SI, could act as robust indicators of stabilised sand dune succession. Redundancy analysis using data on nematode community composition showed that shifting sand dunes were clearly separated from stabilised sand dunes, and younger sand dunes stabilised for 16 and 26 years were also separated from older dunes stabilised for 43 and 51 years to a lesser degree. The results indicated that changes in nematode communities could predict initial sand dune stabilisation due to the planting of artificial vegetation, and clearly differentiate sand dune succession accompanied by vegetation succession and variation of soil properties.

Additional keywords: diversity, soil characteristic, trophic groups.
Article Type: Report
Subject: Sand dunes (Research)
Nematoda (Environmental aspects)
Soil biology (Research)
Authors: Dejuan, Zhi
Wenbin, Nan
Xiaoxia, Ding
Qinjian, Xie
Hongyu, Li
Pub Date: 08/01/2009
Publication: Name: Australian Journal of Soil Research Publisher: CSIRO Publishing Audience: Academic Format: Magazine/Journal Subject: Agricultural industry; Earth sciences Copyright: COPYRIGHT 2009 CSIRO Publishing ISSN: 0004-9573
Issue: Date: August, 2009 Source Volume: 47 Source Issue: 5
Topic: Event Code: 310 Science & research
Geographic: Geographic Scope: China Geographic Code: 9CHIN China
Accession Number: 208746642
Full Text: Introduction

Land desertification is a serious environmental and socioeconomic problem drawing global attention. In China, it is also a severe eco-environmental issue. Deserts and sandy lands cover 1.52 x [10.sup.6] [km.sup.2], and they are spreading at an alarming rate, on average 2100 [km.sup.2] annually (Mitchell et al. 1998). China began work to combat desertification in the early 1950s. Some of the pioneering works including the installing of wind breaks, straw checkerboards, and the planting of xerophytic shrubs were carried out at Shapotou in Ningxia Autonomous Region. Now Shapotou is a successful model for control of desertification. Using stabilisation and reclamation techniques in the Shapotou region, soil particle size decreased, total nitrogen increased, and the sand surface was immobilised. Those changes facilitated the formation of microbiotic crusts, which have led to the colonisation by annual plants (Li et al. 2003; Wang et al. 2006). As a result, restoration efforts created favourable conditions for various soil fauna, insects, arachnids, birds, and some desert animals (Liu et al. 1999, 2002; Yu et al. 2002; Kuai and Liu 2004; Li et al. 2004; Liu and Yang 2005).

Previous research indicated that the success of sand dune stabilisation led to the replacement of the barren shifting sand dune by a complex functioning desert ecosystem. Nematodes, as one of the best indicators within the soil biota, are closely related to soil environment and sensitive to soil environmental changes, and they could provide insights into ecological succession (Wasilewska 2006). However, little is known of how nematode communities respond to stabilised sand dune succession after using stabilisation and reclamation techniques in the Tengger Desert of China.

Nematodes are ubiquitous inhabitants of the soil system (Pen-Mouratov et al. 2003). They occupy a central position in the detritus food web by regulating the rates of soil organic matter decomposition, and nutrient mineralisation and cycling, thus contributing to the biotic and functional status of soils (Neher 2001; Yeates 2003). As a numerically important component of soil fauna in desert ecosystems (Steinberger et al. 1989), nematodes have been the focus of several studies under natural plant cover with respect to their response to temperature, moisture, organic matter, electric conductivity, [K.sup.+], [Na.sup.+], [Ca.sup.2+] and rain episodes (Steinberger and Loboda 1991; Steinberger and Sarig 1993; Liang and Steinberger 2001; Steinberger et al. 2001; Liang et al. 2002; Pen-Mouratov et al. 2003, 2004a, 2004b). Jiang et al. (2007) reported vertical distribution of soil nematodes in sandy lands after planting of Caragana microphylla in Horqin, China. Responses of soil nematodes to sand dune restoration after vegetation have not been well documented; although there have been studies on nematode community development from sand dunes via dune shrubs to dune forests (Goralczyk 1998; Verhoeven 2002; Wall et al. 2002), they are limited to coastal dunes. Only a few studies have described nematode community changes during the primary succession of soils at reclaimed mining sites (Hanel 2002; Hohberg 2003; Frouz et al. 2008). So far, relatively little is known of soil nematode community development under extreme environmental conditions in nutrient-deficient environments, such as sand dunes.

In the present work, nematode community composition and the characteristics of nematode community structure were investigated in a chronological sequence of sand dune stabilisation in the Tengger Desert, China. Relationships between the composition and the structure of nematode communities and environmental conditions were also examined. The objectives of this study were to examine the relationship between changes in soil environment and nematode communities during sand dune stabilisation, and to determine whether stabilised sand dune succession was reflected by succession changes in nematode community composition. In contrast to the coastal system, sand dunes in our system progress from shifting sand dunes to dunes with deep-rooted shrubs, and subsequently to dunes with shallow-rooted shrubs and herbs, in which nutrients and water availability are limited. Previous studies revealed that habitat conditions have gradually improved since sand dunes were stabilised (Liu et al. 2002; Yu et al. 2002; Kuai and Liu 2004; Li et al. 2004; Liu and Yang 2005). Therefore, we hypothesised that the nematode community development should parallel the stabilised sand dune succession. We expected that in response to stabilised sand dunes in the Shapotou region, nematode abundance, diversity and maturity index would increase, and the structure of the nematode communities would change distinctively along an age sequence.

Materials and methods

Sampling sites

The samples were collected in the Shapotou region on the south-east of the Tengger Desert (37[degrees]32'N, 105[degrees]02'E), at an altitude of 1300 m a.s.l., with an average annual temperature of 9.6[degrees]C and average precipitation of 186 mm/year. The natural predominant plants are Hedysarum scoparium and Agriohyllum squarrosum with coverage of ~1% of the land area. Because the shifting sand dunes threaten the Baotou Lanzhou railway line crossing the Tengger Desert, several stabilisation and reclamation techniques were used. First, a sand barrier made of woven willow branches or bamboo serves as windbreak. Behind the sand barrier, straw checkerboards of 1 by 1 [m.sup.2] were established. The straw was inserted to a depth of 150-200 mm, and it protruded ~100-150mm above the dune surface. These measures have contributed to the stabilisation of sand dunes, and significantly reduced wind velocity by 20-40% at a height 0.5 m above the surface (Zou et al. 1981; Fullen and Mitchell 1994). This remained intact for 4-5 years. Finally, xerophytic shrubs such as Caragana korshinslai, Hedysarum scoparium, and Artemisia otdosica were planted in straw checkerboard plots (Li et al. 2000; Wang et al. 2006). These measures led to the cessation of shifting sand dunes. As a result, a 16-km-long artificial vegetation system was established with 500-m width on the north of the railway and 200-m width on the south of the railway at Shapotou. The artificial vegetation system at Shapotou was launched by the same approaches of sand dune stabilisation as above in 1956, 1964, 1981, and 1991, respectively (Table 1). The sites were arranged in a chronological pattern, sand dunes stabilised in 1956 were in the vicinity of the north of the railway, and sand dunes stabilised in 1991 were the most distant from the railway and near to shifting sand dunes.

With the stabilisation of sand dunes, vegetation succession had been distinguished by the colonisation of biological crusts. Thereafter, crusts gradually increased in thickness, then caused reduction in water infiltration, thus leading to a reduction in moisture content in deeper soil layers. Consequently, the deep-rooted planted shrubs became degraded and were gradually replaced by natural vegetation of shallow-rooted shrubs and annual herbs (Li et al. 2002).

Soil sampling

Four soil samples were collected with a corer (50 mm diameter) from sand dunes stabilised for 0, 16, 26, 43, and 51 years, respectively, on 10-13 May 2007. Each sample was a composite sample of 5 bulked soil cores from a plot of 25 by 25 [m.sup.2]. Each soil core was excavated to a depth of 0-100 and 100-200 mm from each sampling site. The plots were located at distances apart of not less than 50 m, and a total of 40 plots were identified in this work. Because the active dispersal of nematodes is limited (Griffiths et al. 1998; Young et al. 1998), we assumed independence between samples and we treated our pseudo replicates as real replicates. All samples were transported to the laboratory and stored at 4[degrees]C until analysed.

Soil physical and chemical properties

Soil particle size was determined by nested sieves. Particles <50 [micro]m in diameter were defined as 'fine', and >75 [micro]m and <250 gm 'coarse'. Soil pH and electric conductivity values were measured in a soil water suspension (1:2.5 and 1:5, respectively). Soil water content (% on a dry-weight basis) was determined gravimetrically by drying samples at 105[degrees]C for 48 h. Soil total organic matter was determined by oxidisation with dichromate in the presence of [H.sub.2]S[O.sub.4]. The resultant suspension was titrated with FeS[O.sub.4] using o-phenanthroline hydrate as indicator. Soil total nitrogen was determined by the Kjeldahl digestion, then distilled by NaOH and measured by titration with [H.sub.2]S[O.sub.4] using boric acid as indicator (Agricultural Chemistry Speciality Council, Soil Science Society of China 1983).

Nematode communities

Nematodes in each sample were extracted from 100 g fresh soil by the Whitehead and Hemming tray method (Whitehead and Hemming 1965). After extraction for 48 h, the nematodes were preserved in a 4% formaldehyde solution for further analysis. Total number of nematodes (N) was counted, and all nematodes in each sample were identified to genus level using a compound microscope. Trophic groups were classified as bacterivores (Ba), fungivores (Fu), plant feeders (PI), predators (Pr), and omnivores (Ore) according to Yeates et al. (1993), also based on the distinct gut contents. Algal-feeding nematodes were grouped into omnivores because they often feed on a variety of food sources such as algae and fungi (Neher et al. 2005).

The characteristics of nematode communities were described by the following indices:

* Abundance and trophic groups: (1) N, total nematode individuals per 100g dry soil; (2) trophic group composition, which were represented as the proportion of Ba, Fu, Pl, Pr, and Om in total individuals, respectively (Wu et al. 2005).

Diversity and maturity indices: Ht, Shannon index of generic diversity,

H' = [s.summation over (i=l)] [P.sub.i] ln [P.sub.i],

where P is the proportion of individuals in the ith taxon (Shannon 1949); J', evenness,

J' = H'/[H'.sub.max] and [H'.sub.max] = ln S,

where S is the number of nematode taxa identified in a sample (McSorley and Frederick 1996). These indices were based on genera because species identifications are not only too time-consuming to be practical (Ritz and Trudgill 1999) but the data are far more complex to interpret. It is more common to apply these indices to generic level and allow comparison between studies; MI, maturity index,

MI = [summation] V(i) x f(i),

where (i) was the individual taxon, f(i) was the frequency of free-living nematode taxa in a sample, V(i) was the cp value from 1 to 5 according to Bongers (1990), from colonisers to persisters (r- to K-strategists).

Guild/composition indices:

El, enrichment index, EI - 100 x (e/(e + b)),

and SI, structure index, SI = 100 x (s/(s + b)),

where b, e, s represent basal, enrichment, structure food web components; b was calculated as [summation][k.sub.b] [n.sub.b], [k.sub.b] was the weightings assigned to guilds that indicated basal characteristics of the food web, [n.sub.b] was the abundance of nematodes in those guilds, and e and s were calculated similarly (Ferris et al. 2001).

Statistical analysis

All of the nematode data were analysed through 2-way ANOVA with the age of stabilised sand dunes (treatment) and soil depth as main effect factors. Soil characteristics were also analysed with 2-way ANOVA, with treatment and soil depth as main effect factors. Tukey's multiple range test was conducted as a post-hoc test for the soil characteristics from different treatments at 2 soil depths. Partial correlation with Bonferroni adjustment between nematodes and soil characteristics was quantified by controlling for soil depth. All statistic analyses were performed using SPSS version 13.0 software (SPSS Inc., Chicago, IL). Differences obtained at levels of P= 0.05 were considered significant.

Redundancy analysis (RDA) was conducted using CANOCO version 4.5 software (Wageningen, The Netherlands). The following environment factors were included: age of stabilised sand dunes, coarse particles, fine particles, pH, organic matter, total nitrogen, electric conductivity, and moisture. Depth thought to affect the vertical distribution of nematodes on a site was treated as covariate.

All data on abundances of nematode assemblages were log(x+ 1) transformed and proportions were transformed as the arcsine of square root to normalise data before analysis. MI, H', J' values were not transformed because they already met the assumption of normality.

Results

Variation in soil properties with age was less pronounced at 100-200mm depth than 0-100mm. Soil moisture increased with dune age at 0-100mm and decreased with dune age at 100 200mm soil depth. Fine particles, pH, organic matter, total nitrogen, and electric conductivity at both soil depths increased significantly with increasing time after stabilisation. In contrast, coarse particles decreased (Table 2).

In total, 22 nematode taxa were found in the dune soil samples. Bacterivorous genera included Acrobeloides, Acrobeles, Cervidellus, Chiloplacus, Panagrolaimus, and Plectus. Fungivorous genera included Aphelenchus, Aphelenchoides, Ditylenchus, and Nothotylenchus. Plant feeder genera included Filenchus, Tylenchorhynchus, Psilenchus, and Rotylenchus. Ominivorous genera included Leptonchus, Eudorylaimus, Ecumenicus, and Thorneella.

Predator genera included Discolaimus, Discolaimium, Labronema, and Miconchus. In sand dunes stabilised for increasing time from 0 to 51 years, 3, 13, 22, 20, and 18 genera, respectively, existed at 0-100mm soil depth, while 3, 13, 19, 15, and 11 occurred at 100 200mm soil depth. Acrobeles, Acrobeloides, Chiloplacus, Aphelenchus, Aphelenchoides, and Miconchus were eudominants (>10%) in at least 1 sampling site.

Nematode abundance increased with age to a greater degree at 0-100mm than at 100 200mm soil depth, and overall was greater at 0-100 mm than 100-200 mm soil depth. There was a significant difference between sand dunes stabilised or not at both soil depths (Table 3). A positive correlation was observed between nematode abundance and dune age, fine particles, pH, organic matter, total nitrogen, and electric conductivity. Conversely, there was a negative correlation between nematode abundance and coarse particles (Table 4). The proportion of fungivores was higher on stabilised sand dunes than on shifting sand dunes, and the proportion of predators and omnivores increased with sand dune age at both soil depths (P<0.05) (Table 3). The proportions of fungivores and predators were correlated with dune age and soil characteristics in a similar pattern, except for organic matter and pH. The proportion of omnivores was positive correlated with dune age, pH, total nitrogen, and electric conductivity, and negative correlated with coarse particles (Table 4).

MI and H' were greater in stabilised sand dunes than in shifting sand dunes, whereas J' only exhibited a similar pattern at 100-200mm soil depth (Table 3). MI was positively correlated with dune age, fine particles, pH, organic matter, total nitrogen, and electric conductivity, and it was negatively correlated with coarse particles. Similarly, H' was correlated with soil characteristics except fine particles and organic matter. jr was only correlated with dune age, pH, and electric conductivity (Table 4).

Mean values for S1 and EI are shown in Fig. 1. SI increased significantly with dune age at both soil depths (P<0.05) (Table 3); higher SI occurred on sand dune successions at later stages than at early stages (Fig. 1). SI was positively correlated with dune age, fine particles, pH, organic matter, total nitrogen, and electric conductivity (Table 4).

The RDA showed that axis 1 and axis 2 explained 81.4% of the total species-environment variance and 36.3% of the variation in the total species data. Scatter plot for samples showed that shifting sand dunes were clearly separated from stabilised sand dunes; sand dunes stabilised for 43 years and 5 l years were separated by the first axis from those stabilised for 16 years and 26 years to a lesser degree. RDA suggested 2 main gradients affecting the nematode communities: the initial stabilisation effect and the dune age effect (Fig. 2). There were no taxa that were unique to shifting sand dunes; the first colonisers after planting vegetation since sand dune stabilisation were Tylenchorhynchus, Nothotylenchus, Panagrolaimus, and Psilenchus; colonisers after 26 years were Acrobeloides, Acrobeles, Aphelenchoides, Cervidellus, Discolaimus, Eudorylaimus, Leptonchus, and Thorneella; colonisers in sand dunes stabilised for 43 years and 51 years were Aphelenchus, Chiloplacus, Discolaimium, Ditylenchus, Ecumenicus, Filenchus, Labronema, Miconchus, Plectus, and Rotylenchus (Fig. 2). In contrast to nematode taxa colonised on sand dunes stabilised for a shorter time period, these taxa on sand dunes stabilised for a longer time were characterised by high total nitrogen, organic matter, fine particles, pH, and more moisture, and less coarse particles (Fig. 3).

[FIGURE 1 OMITTED]

Discussion

After using straw checkerboards and xerophytic shrubs, shifting sand dunes have been stabilised on the south-eastern edge of the Tengger Desert, China (Li et al. 2007). Compared to shifting sand dunes, the edaphic factors changed to different degrees with dune age. In our study, the moisture was very low, and only increased slightly. None of the nematode indices or trophic groups was correlated with soil moisture. Soil moisture was not a differentiating factor for nematode communities under stabilised soils. Soil pH increased significantly when stabilisation was initially established, then it remained more or less constant. The pH did not differ greatly between soil layers, whereas nematode abundance did; pH did not play a major role in our system. Organic matter, total nitrogen, and electric conductivity increased with dune age and were positively correlated with nematode abundance, MI, and SI. The variation in soil texture in terms of fine particles and coarse particles affected pore size distribution and provided inhabitable pore spaces for nematodes (Gorres et al. 1999). These physical and chemical characteristics were important edaphic factors which differentiated between habitats in stabilised sand dunes. Our results provide support that the changes in abiotic factors led to the variations in nematode abundance and community composition (Goralczyk 1998; Wall et al. 2002). As we expected, nematode abundance, diversity, and MI increased, and omnivores and predators were more abundant with dune age. RDA indicated 2 main gradients affecting the nematode communities: the initial stabilisation effect and the dune age effect.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Extremely low numbers of nematodes (0-7 individuals/100 g dry soil) were found in the shifting sand dunes. Similar results were obtained in previous works in Negev Desert ecosystems (Liang and Steinbergcr 2001; Pen-Mouratov et al. 2003, 2004a), and there were <10 nematode individuals/100 g dry soil, even empty samples. Because no predators other than nematodes were found in our study area (Liu et al. 1999), it might be due to harsh environmental conditions and severe food resource limitation. Once sand dunes stabilised after straw checkerboard application and artificial vegetation input, nematode abundance sharply increased and a significant initial stabilisation effect could be detected.

The trend of increasing nematode abundance along the stabilisation of sand dunes was identified with previous studies of coastal sand dune succession (Goralczyk 1998; Wall et al. 2002). In addition, our results revealed that the main statistically significant differences among nematode abundances, the proportions of fungivores, Shannon index, and evenness were between dune age of 0 year and all other ages. If shifting sand dunes were excluded from statistical analysis, these parameters were not affected any more by dune age. This could be explained by the initial stabilisation effect at the early stage of sand dune succession.

In contrast to the shifting sand dunes, the planting of artificial vegetation was the most distinctive difference at the initial phase of sand dune stabilisation. Plants can act on soil environment by shading or accumulation of organic matter, which influence bacteria and fungi, then nematodes. Thereafter, shrubs degraded, annual herbs invaded, and plant community biomass deceased with dune age (Li et al. 2003, 2007). The variation of plant community biomass was not clearly mirrored by soil nematode abundance in our system. It could result from the biological crusts which established and developed gradually with dune age. Well-developed biological crust could not only directly provide more food available, in quantity and quality, for nematodes, but also act as a boundary over the soil surface to keep the soil environment stable (Darby et al. 2007). Nematode abundance showed no statistical increment with dune age. Possibly, it could be explained by resource limitation (bottom-up limitation), which apparently regulated nematode abundance according to Thornton and Matlack (2002). Moreover, top-down regulation by predators (Holtkamp et al. 2008) could also be an explanation. Predators do show an increase with dune age.

Plants can affect plant feeders directly because they use plant roots as food sources (Viketoft et al. 2005). Hence, when the shifting sand dunes were excluded from statistical analysis, the proportion of plant feeders was expected to decrease significantly with plant community biomass reducing in an age sequence. Although plant feeders remained at a very low level, plant feeders responded to the changes of vegetation succession. Tylenchorhynchus and Psilenchus appeared on sand dunes with shrub input at early succession and Rotylenchus and Filenchus occurred on sand dunes with annual herbs at later succession. During the sand dune succession, Acrobeloides and Aphelenchoides, as general opportunists due to ability to colonise food resource limitation environments (Hohberg 2003; Dmowska and Krassimira 2006), were more abundant in the sand dunes stabilised for 26 years. With dune age increasing, bacteria, actinomyces, and fungi increased in number (Wang et al. 2006); algae and moss gradually increased in number of species and cover in the dunes stabilised for a longer time (Li et al. 2003). Fine particles increased and coarse particles decreased; the pore size distribution might provide inhabitable pore spaces for nematodes in the older stabilised dunes. Sand dunes stabilised earlier have been reported to be characteristics of more inhabitable conditions (Li et al. 2004). Persisters Miconchus began to colonise in 43-year-old dunes successfully and Ecumenicus until 51 years after stabilisation.

Higher trophic levels of predators and omnivores were recorded at later stages of dune succession, suggesting a more complex functional composition of the soil food web incremental with the abundances of predators and omnivores. In fact, sand dunes stabilised for a longer time could provide more appropriate environments with more water retention, less thermal fluctuation, and more abundant and diverse food sources for nematodes (Li et al. 2004; Wang et al. 2006). Moreover, structure-enrichment plots representing sand dunes stabilised for 43 and 51 years indicated that the habitats provided more favourable conditions, SI kept increasing with dune age, and the food webs were close to mature or structured (Fig. 1). However, low SI values in combination with low EI values reflected a basal food web due to limitation of resources and adverse environmental conditions (Ferris et al. 2001). With regard to our system on the south-eastern edge of the Tengger Desert, habitats for nematodes show extreme desiccation, strong radiation, large fluctuation of temperature, and poor nutrients. Although those harsh environmental conditions lessened after the stabilisation of sand dunes, the faunal profile revealed that both El and SI were low in our system, suggesting that the environments of the present study were still extreme, and the food webs showed basal or poor structure. They did not have sufficient food resources to support onmivores and predators. Probably, they will gradually become more structured as food resources increase.

Maturity index, which reflects the maturation of the nematode community, was positively correlated with fine particles, pH, organic matter, total nitrogen, and electric conductivity along stabilised sand dune succession. MI has been proposed as a useful indicator of ecosystem development and disturbance response (Bongers 1990; Neilson et al. 1996), and it has been reported to increase with succession (Wasilewska 1994; Hanel 2003). Although there were no differences between sand dunes stabilised from 16 to 51 years, the MI did tend to increase gradually with stabilised sand dune age; when the shifting sand dunes were excluded from statistical analysis, MI was still significantly affected by dune age (P<0.05). This indicates that nematode communities are more mature in old sand dunes stabilised than in young sand dunes stabilised and MI could be used as an indicator of stabilised sand dune succession in our system.

Conclusion

The planting of shrubs led to sand dune stabilisation; deep-rooted shrubs gradually degraded and annual herbs invaded. At the initial phase of sand dune stabilisation, biological soil crusts established and developed gradually. With increasing dune age, our results showed that soil particle size decreased, while total nitrogen, organic matter, pH, and electric conductivity increased. Soil physical and chemical properties were correlated with nematode abundance, the proportion of fungivores, omnivores, and predators, maturity index, Shannon index, evenness, and structure index to different degrees. RDA suggested 2 main gradients affecting the nematode communities: the initial stabilisation effect and dune age effect. The planting of artificial vegetation could exert an initial stabilisation influence on nematode communities. Further, vegetation succession and the variation of soil physical and chemical characteristics were responsible for the dune age effect on nematode communities. Response to sand dune succession, nematode abundance, the proportion of fungivores, and H' only showed a clear initial stabilisation effect but did not indicate a dune age effect. MI, and especially SI, were robust indicators of dune age effect.

Acknowledgement

This work was supported by the Chunhui Plan and Program for Changjiang Scholars and Innovative Research Team at University. The authors are very grateful to the faculty of the Shapotou Station of Desert Research, Chinese Academy of Science, for their help in our sample collection. Special thanks to Dr Ni Yongqing and laboratory mate Liu Hetao for their assistance in collecting samples.

Manuscript received 28 August 2008, accepted 26 March 2009

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Dejuan Zhi (A), Wenbin Nan (A), Xiaoxia Ding (A), Qinjian Xie (A), and Hongyu Li (A,B)

(A) MOE Key Laboratory of Arid and Grassland Ecology, School of Life Sciences, Lanzhou University, Lanzhou 730000, P.R. China.

(B) Corresponding author. Email: lihy@lzu.edu.cn
Table 1. Characteristics of sand dunes stabilised
for 0, 16, 26, 43, and 51 years

Year is time sites established; RSS, remaining shrub species in
2005 of the planting vegetation; NIPS, native invasion dominant
plant species; S(H), shrub cover % (herbaceous cover %); AGB, above
ground biomass of the planting vegetation (t/ha); CT, soil crusts
thickness (ram); Alg (tot.), total species of algae (total species
of moss); Alg (%), algal cover % (moss cover %); Bacteria,
[10.sup.6] individuals/g soil; Actinomyces, [10.sup.3]
individuals/g soil; Fungi, [10.sup.3] individuals/g soil. Soil
microbe numbers were determined by plate-count techniques; -, not
detected

       Dune age:    0 year              16 years
           Year:    Control             1991

RSS (A)             No                  Amorpha fruticosa,
                                          Artemisia ordosica,
                                          Artemisia whaerocephala,
                                          Caragana korshinskii,
                                          Caragana microphylla,
                                          Calligonum arboresscens,
                                          H. scoparium

NIPS (A)            Hedysarum           H. scoparium,
                      scoparium,          A. squarrosum,
                      Agriophyllum        Bassia dasyplzvlla,
                        squarrosum        Echinos gmelinii,
                                          Eragrostis poaeoides

S(H) (A)                 1 (<1)                  22(12)
AGB (B)                     0                     4.6
CT (B)                      0                      3
Alg (tot.) (B)              0                     3(1)
Alg (%) (B)                 0                     1/10
Soil microbes (C)
  Bacteria                15.7
  Actinomyces              1.6
  Fungi                    0.1

       Dune age:    26 years            43 years
           Year:    1981                1964

RSS (A)             A. ordosica,        A. ordosica,
                      C. korshinskii,     C. korshinskii,
                      C. microphylla,     H. scoparium
                      H. scoparium

NIPS (A)            A. ordosica.        A. ordosica,
                      H. scoparium.       B. dasyphylla,
                      B. dasyphylla,      E. poaeoides,
                      E. poaeoides,       Sonchus arvensis,
                      Corispermum         Scorzonera mongolica,
                        patelliforme      Euphorbia humifusa

S(H) (A)                 20(21)                  9(19)
AGB (B)                    3.6                    1.3
CT (B)                      4                      l0
Alg (tot.) (B)            14(2)                  22(3)
Alg (%) (B)               9/25                   30/75
Soil microbes (C)
  Bacteria                20.2                    63.8
  Actinomyces             44.1                    35.9
  Fungi                    5.2                    6.2

       Dune age:    51 years
           Year:    1956

RSS (A)             A. ordosica,
                      C. korshinskii,
                      H. scoparium

NIPS (A)            A. ordosica,
                      S. mongolica,
                      S. arvensis,
                      Chloris virgata,
                      Aristida adscensionis,
                      Semris viridis,
                      B. dasyphylla,
                      Chenopodium
                        aristatum
S(H) (A)                  9(40)
AGB (B)                    1.7
CT (B)                     21
Alg (tot.) (B)            24(5)
Alg (%) (B)               35/80
Soil microbes (C)
  Bacteria                32.3
  Actinomyces             48.3
  Fungi                    4.3

(A) Cited from Li et al. (2007). (B) Cited from Li et al. (2003).
(C) Cited from Wang et al. (2006).

Table 2. Soil physical and chemical properties (mean [+ or -]
s.e., n = 4) of sand dunes stabilised for 0, 16, 26, 43, and
51 years Within a column, values followed by the same letter are
not statistically different at P-0.05 by Tukey's multiple range
test. A, Age of stabilised sand dunes, D, depth; 2-way interaction
effects (A x D)

             Coarse particles        Fine particles
                   (%)                    (%)

                             0-100 mm

0 year     98.2 [+ or -] 0.2a     0.2 [+ or -] 0.0c
16 years   95.6 [+ or -] 1.5b     1.3 [+ or -] 0.3c
26 years   90.6 [+ or -] 1.5c     3.4 [+ or -] 0.9b
43 years   86.3 [+ or -] 1.2cd    6.3 + 0.7a
51 years   84.7 [+ or -] 0.7d     6.2 [+ or -] 0.6a

                            100-200 mm

0 year     98.7 [+ or -] 0.3a     0.4 [+ or -] 0.0b
16 years   96.8 [+ or -] 0.2ab    1.0 [+ or -] 0.1ab
26 years   96.2 [+ or -] 1.1ab    1.2 [+ or -] 0.3ab
43 years   95.7 [+ or -] 1.5ab    1.4 [+ or -] 0.2a
51 years   95.3 [+ or -] 1.2b     1.5 [+ or -] 0.6a

                      2-way ANOVA summary

               A, D, A x D            A, D, A x D

                    pH               Organic matter
                   (%)                   (g/kg)

                            0-100 mm

0 year     7.73 [+ or -] 0.0lb    1.7 [+ or -] 0.0c
16 years   8.36 [+ or -] 0.02a    1.9 [+ or -] 0.2c
26 years   8.32 [+ or -] 0.02a    2.4 [+ or -] 0.2b
43 years   8.33 [+ or -] 0.02a    4.1 [+ or -] 0.1a
51 years   8.32 [+ or -] 0.02a    4.2 [+ or -] 0.1a

                           100-200 mm

0 year     7.92 [+ or -] 0.02b    0.2 [+ or -] 0.0b
16 years   8.37 [+ or -] 0.04a    0.6 [+ or -] 0.1a
26 years   8.44 [+ or -] 0.03a    0.7 [+ or -] 0.1a
43 years   8.43 [+ or -] 0.02a    0.8 [+ or -] 0.0a
51 years   8.45 [+ or -] 0.02a    0.7 [+ or -] 0.0a

                      2-way ANOVA summary

               A, D, A x D            A, D, A x D

              Total nitrogen         Soil moisture
                 (mg/kg)                  (%)

                            0-100 mm

0 year       7.7 [+ or -] 0.5d    1.4 [+ or -] 0.2b
16 years    52.7 [+ or -] 2.4c    1.6 [+ or -] 0.1ab
26 years    73.0 [+ or -] 0.6b    1.6 [+ or -] 0.1ab
43 years   169.2 [+ or -] 2.1a    1.7 [+ or -] 0.1ab
51 years   180.0 [+ or -] 2.1a    1.8 [+ or -] 0.1a

                           100-200 mm

0 year     25.0 [+ or -] 0.8b     2.4 [+ or -] 0.1a
16 years   24.2 [+ or -] 0.8b     2.2 [+ or -] 0.2ab
26 years   39.3 [+ or -] 2.3a     2.2 [+ or -] 0.1ab
43 years   35.0 [+ or -] 0.6a     2.0 [+ or -] 0.2ab
51 years   35.4 [+ or -] 0.9a     1.8 [+ or -] 0.1b

                       2-way ANOVA summary

               A, D, A x D            A, D, A x D

                    EC
              ([micro]S/cm)

                 0-100 mm

0 year     18.91 [+ or -] 0.78d
16 years   41.17 [+ or -] 1.34c
26 years   59.93 [+ or -] 1.15b
43 years   79.43 [+ or -] 1.10a
51 years   78.52 [+ or -] 1.31a

                100-200 mm

0 year     17.15 [+ or -] 0.08c
16 years   29.60 [+ or -] 1.92b
26 years   38.43 [+ or -] 1.07a
43 years   36.30 [+ or -] 0.46a
51 years   36.26 [+ or -] 1.24a

           2-way ANOVA summary

               A, D, A x D

Table 3. Nematode abundance (N), the proportion (%) of trophic
groups, and ecological indices (mean [+ or -] s.e., n = 4) from
stabilised sand dunes for 0, 16, 26, 43, and 51 years in the
Tengger Desert, China

Within a row, different letters at each site or depth of 0-100 or
100-200 mm indicate significant differences assessed by Tukey's
multiple range test (P < 0.05). A, Age of stabilised sand dunes;
D, depth; 2-way interaction effects (A x D)

Index
               0 year                 16 years

                   Nematode abundance

N        0.8-4 [+ or -] 0.5a    116.1 [+ or -] 53.7b

                 Trophic group composition

Ba       37.5 [+ or -] 23.9      58.0 [+ or -] 4.2
Fu               0a              31.8 [+ or -] 0.0b
P1       12.5 [+ or -] 12.5       6.6 [+ or -] 3.1
Pr               0a               0.2 [+ or -] 0.2a
Om               0a               3.4 [+ or -] 1.3ab

                  Ecological indices

H'       0.17 [+ or -] 0.1a      1.95 [+ or -] 0.11b
J'       0.25 [+ or -] 0.50      0.84 [+ or -] 0.05
MI       0.75 [+ or -] 0.47a     1.98 [+ or -] 0.09b
EI       25.0 [+ or -] 25.0      44.0 [+ or -] 10.5
SI        0.0 [+ or -] 0.0a      14.4 [+ or -] 5.3b

Index         0-100 mm
              26 years                43 years

                    Nematode abundance

N       368.7 [+ or -] 97.8b    237.7 [+ or -] 40.3b

                 Trophic group composition

Ba       47.4 [+ or -] 12.3      31.8 [+ or -] 14.3
Fu       40.8 [+ or -] 16.4b     47.2 [+ or -] 14.4b
P1        0.7 [+ or -] 0.2        1.1 [+ or -] 0.5
Pr        4.4 [+ or -] 2.9ab     17.2 [+ or -] 6.9b
Om        6.7 [+ or -] 3.1bc      2.7 [+ or -] 1.5b

                     Ecological indices

H'       1.51 [+ or -] 0.30b     1.56 [+ or -] 0.26b
J'       0.58 [+ or -] 0.10      0.60 [+ or -] 0.09
MI       2.22 [+ or -] 0.11b     2.31 [+ or -] 0.15b
EI       28.9 [+ or -] 10.0      53.4 [+ or -] 3.2
SI       29.6 [+ or -] 11.5bc    49.5 [+ or -] 9.7cd

Index
              51 years                 0 year

                   Nematode abundance

N       560.2 [+ or -] 297.5b     3.1 [+ or -] 1.4a

                Trophic group composition

Ba       58.7 [+ or -] 10.1      62.5 [+ or -] 23.9
Fu       20.4 [+ or -] 5.3b              0a
P1        3.0 [+ or -] 2.4       37.5 [+ or -] 23.9
Pr        8.2 [+ or -] 1.3b              0a
Om        9.7 [+ or -] 0.7c              0a

                    Ecological indices

H'       1.60 [+ or -] 0.16b     0.17 [+ or -] 0.17a
J'       0.67 [+ or -] 0.08      0.25 [+ or -] 0.25a
MI       2.37 [+ or -] 0.11b     1.00 [+ or -] 0.41a
EI       23.4 [+ or -] 3.7       50.0 [+ or -] 28.9
SI       46.2 [+ or -] 7.4d       0.0 [+ or -] 0.0a

Index                                100-200 mm
              16 years                26 years

                     Nematode abundance

N        42.9 [+ or -] 19.0b     61.1 [+ or -] 16.2b

                  Trophic group composition

Ba       59.4 [+ or -] 5.0       67.5 [+ or -] 6.9
Fu       16.1 [+ or -] 4.6b      21.7 [+ or -] 5.5b
P1       22.8 [+ or -] 1.6        4.0 [+ or -] 1.9
Pr        1.3 [+ or -] 1.3a       1.4 [+ or -] 0.8ab
Om        0.4 [+ or -] 0.4ab      5.4 [+ or -] 2.4b

                     Ecological indices

H'       1.92 [+ or -] 0.17b     1.84 [+ or -] 0.06b
J'       0.88 [+ or -] 0.00b     0.77 [+ or -] 0.04b
MI       2.05 [+ or -] 0.06b     2.12 [+ or -] 0.05b
EI       23.7 [+ or -] 3.1       25.1 [+ or -] 6.5
SI        7.3 [+ or -] 7.3b      22.8 [+ or -] 6.0bc

Index                                                    2-way
              43 years                51 years           ANOVA

                       Nematode abundance

N        22.1 [+ or -] 8.5b      43.0 [+ or -] 12.2b    A,D, AxD

                   Trophic group composition

Ba       47.9 [+ or -] 10.6      40.7 [+ or -] 8.5
Fu       30.7 [+ or -] 12.2b     31.2 [+ or -] 10.3b       A
P1        5.8 [+ or -] 2.9        3.4 [+ or -] 1.2
Pr       10.0 [+ or -] 7.8b      10.7 [+ or -] 6.3b        A
Om        5.7 [+ or -] 4.3b      14.0 [+ or -] 7.2c        A

                     Ecological indices

H'       1.83 [+ or -] 0.11b     1.61 [+ or -] 0.06b       A
J'       0.89 [+ or -] 0.02b     0.83 [+ or -] 0.03b       A
MI       2.31 [+ or -] 0.17b     2.51 [+ or -] 0.10b       A
EI       31.2 [+ or -] 7.1       27.9 [+ or -] 6.6
SI       37.2 [+ or -] 15.7cd    55.9 [+ or -] 7.3d        A

Table 4. Partial correlation coefficients controlled for depth
between nematode indices and soil physical and chemical properties

* P < 0.05 after Bonferroni adjustment; n.s., not significant

           Age      Particles (%)            pH

                     Coarse      Fine

                    Nematode abundance

         0.686 *    0.642 *    0.833 *    0.595 *

                Trophie group composition

Ba (%)     n.s.       n.s.       n.s.     n.s.
Fu (%)   0.740 *    -0.502 *   0.440 *    0.737 *
P1 (%)     n.s.       n.s.       n.s.     n.s.
Pr (%)   0.535 *    -0.634 *   0.550 *    n.s.
Om (%)   0.627 *    -0.443 *     n.s.     0.555 *

                    Ecological indices

H'       0.827 *    0.505 *      n.s.     0.862 *
J'       0.617 *      n.s.       n.s.     0.656 *
MI       0.822 *    0.683 *    0.555 *    0.779 *

                       Guild indices

EI         n.s.       n.s.       n.s.     n.s.
SI       0.778 *    0.660 *    0.593 *    0.669 *

           Org.     Total N    Moisture        EC
          matter    (mg/kg)      (%)      ([micro]S/cm)
          (g/kg)

                    Nematode abundance

         0.816 *      n.s.                   0.877 *

                Trophie group composition

Ba (%)     n.s.       n.s.       n.s.         n.s.
Fu (%)     n.s.     0.570 *      n.s.        0.701 *
P1 (%)     n.s.       n.s.       n.s.         n.s.
Pr (%)   0.617 *    0.513 *      n.s.        0.554 *
Om (%)     n.s.     0.493 *      n.s.        0.585 *

                    Ecological indices

H'         n.s.     0.573 *      n.s.        0.734 *
J'         n.s.       n.s.       n.s.        0.496 *
MI       0.543 *    0.648 *      n.s.        0.789 *

                      Guild indices

EI         n.s.       n.s.       n.s.         n.s.
SI       0.633 *    0.660 *      n.s.        0.756 *
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