Pedosphere 17(5): 611–618, 2007
ISSN 1002-0160/CN 32-1315/P
c 2007 Soil Science Society of China
°
Published by Elsevier Limited and Science Press
Nematode Faunal Response to Grassland Degradation
in Horqin Sandy Land∗1
LIANG Wen-Ju1 , ZHONG Shuang1,3 , HUA Jian-Feng1,3 , CAO Cheng-You2 and JIANG Yong1
1 Institute
of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016 (China). E-mail: [email protected]
of Sciences, Northeastern University, Shenyang 110004 (China)
3 Graduate School of the Chinese Academy of Sciences, Beijing 100049 (China)
2 College
(Received April 1, 2007; revised July 17, 2007)
ABSTRACT
The responses of soil nematode communities to grassland degradation were studied under undegraded grassland (UG),
degraded grassland (DG), and improved grassland (IG), in Horqin Sandy Land, Inner Mongolia, Northeast China. Soil
samples were collected at depths of 0–10, 10–20, and 20–30 cm. Total organic carbon (TOC) and total nitrogen (TN)
exhibited positive effects on the total number of nematodes and trophic groups. Significant treatment effects were found
in the total number of nematodes, plant parasites, and omnivores-predators. Measures taken in the improved grassland
could improve the number of omnivore-predators, especially in the deeper soil layers. Nematode richness was lower in the
DG treatment than in the IG and UG treatments. The food web structure index (SI) was significantly higher in the UG
and IG treatments than in the DG treatment. A higher SI suggested a food web with more trophic linkages and relatively
healthy ecosystems.
Key Words:
functional groups, grassland degradation, Horqin Sandy Land, soil nematodes
Citation: Liang, W. J., Zhong, S., Hua, J. F., Cao, C. Y. and Jiang, Y. 2007. Nematode faunal response to grassland
degradation in Horqin Sandy Land. Pedosphere. 17(5): 611–618.
INTRODUCTION
Grassland is a large terrestrial ecosystem in China. However, about 90% of the total production
grassland in China is degraded to some extent (Nan, 2005). Grassland degradation has become a serious
environmental problem in semiarid areas, where it is responsible for land degradation and declines in
livestock production (Feng et al., 2003). Therefore, grassland improvement has now become an urgent
task for local economic development. In Horqin Sandy Land, Northeast China, desertification is being
controlled and grassland productivity has been enhanced in recent decades by planting indigenous
grasses, returning degraded farmland to grassland and fencing degraded grassland. Reseeding fine
quality leguminous herb species in combination with plowing-harrowing of degraded alkaline meadow
grassland has proved to be a good alternative to increasing the biomass and quality of the vegetation
and improving soil physiochemical and biological properties in this region (Jiang et al., 2003).
Nematode community structure analysis is currently gaining interest as a tool in ecological studies,
to assess the functioning of soils and for biomonitoring. Various kinds of soil perturbations, such as,
addition of mineral nitrogen fertilizers, cultivation and different land uses, affect species richness, trophic
structure, and the succession status of nematode communities. Their fauna composition, together with
its ecological indices, has emerged as a useful monitor for environmental conditions and soil ecosystem
function (Bongers and Ferris, 1999; Ferris et al., 2001; Neher, 2001; Berkelmans et al., 2003).
Recent studies on the effects of grazing management on vegetation dynamics have been carried out
in the Horqin sandy and alkaline grasslands (Li et al., 2000). However, no information exists on the
∗1 Project
supported by the National Key Technologies R & D Program of China (No. 2005BA517A-8).
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responses of soil nematode communities to grassland management in this region. The objectives of this
study were to determine the effects of grassland management on the nematode community structure
and to assess the interrelations between soil characteristics and soil nematodes under different grassland
managements.
MATERIALS AND METHODS
Experimental site
This study was conducted at the western Horqin Sandy Land (43◦ 020 N, 119◦ 390 E) in Inner
Mongolia, Northeast China, which is an experimental demonstration site of the Wulan’aodu Station
of Desertification Research, Chinese Academy of Sciences. The area is characterized by a temperate
continental semiarid monsoon climate. The mean annual temperature is 6.3 ◦ C, annual precipitation is
340 mm with over 70% occurring from July to September, and annual evaporation is around 2 514 mm.
The average annual wind velocity varies between 3.2 and 4.5 m s−1 , with frequent occurrences of gales
(wind speeds > 20 m s−1 ) in winter and spring. The landscape is characterized by gently undulating,
shifting, and semi-shifting sand dunes with interdune bottomlands. The soil in the study site is an
Aquic-Sandic Primosol (Chinese Soil Taxonomy), and chemical and physical properties of the soil in
the study site are presented in Liu et al. (2005). The dominant plant species in these grasslands, based
on their relative abundance, are: Aneurolepidium chinense, Arundinella hirta, Spodiopogon sibiricus,
Phragmites communis, Hemarthria japonica, Adenophora tetraphylla, Thalictrum simplex, Artemisia
japonica, Trigonella korshinskyi, Astragalus adsurgens, Sanguisorba officinalis, Vicia cracca, Chloris
virgata, Galium verum, Stellera chamaejasme, Galium verum, and Artemisia laciniata (Jiang et al.,
2003).
Three treatments were imposed on these grasslands: relatively undegraded grassland (UG) and
degraded grassland (DG) imposed in 1990, and improved grasslands (IG) imposed in 2002. Replicates
of each treatment were fenced and allocated in a randomized block design. In the undegraded grassland,
the varieties of grass were relatively abundant and vegetation covering was relatively high. In the
degraded grassland there was lower vegetation covering and a single variety of grass. The improved
grassland was a three-year improvement of degraded grassland. Astragalus adsurgens is a perennial
herbal legume and is used in China as forage (Gao et al., 2001).
A. adsurgens can not only improve soil fertility, but it also serves as a high quality forage, and can
grow in Horqin grasslands (Jiang et al., 2003). A. adsurgens has been re-seeded in the IG treatment by
plowing-harrowing (30 cm depth), with a seeding rate of 15 kg ha−1 . A. adsurgens was drilled and the
row spacing was 30–40 cm (Liu et al., 2005).
Soil sampling
Soil samples were collected from four plots (25 m2 each) of every treatment at depths of 0–10, 10–20,
and 20–30 cm in May 2005. Each soil sample was comprised of five cores (5 cm diameter) that were
bulked into one composite sample. Subsamples were taken from each composite sample for nematode
analyses. The subsamples were placed in individual plastic bags and kept in cold storage at 4 ◦ C until
processed.
Nematode extraction, identification, and faunal analyses
Nematodes were extracted from 100 g (fresh weight) of soil from each sample using sugar flotation
and centrifugation (Liang et al., 2005). The nematode populations were expressed per 100 g dry weight
soil. After counting the number of total nematodes, 100 nematodes per sample were selected randomly
and identified for genus, and divided into trophic groups, which were, bacterivores, fungivores, plantparasites, and omnivores-predators (Yeates et al., 1993).
NEMATODE FAUNAL RESPONSE TO GRASSLAND DEGRADATION
613
The structure index (SI) and enrichment index (EI) were calculated, and the nematode faunal
profiles representing the structure-enrichment conditions of the food web were interpreted according to
Ferris et al. (2001). The following ecological indices were calculated: enrichment index (EI) = 100 ×
(e/(e + b)), structure index (SI) = 100 × (s/(b + s)), where e is the abundance of individuals in guilds in
the enrichment component weighted by their respective ke values, b is the abundance of individuals in
the basal component weighted by their kb values, and s is the abundance of individuals in the structural
component weighted by their ks values (Ferris et al., 2001). ke is the weighting assigned to guilds Ba1
and Fu2, kb the weighting assigned to guilds Ba2 and Fu2, and ks the weighting assigned to guilds
Ba3–Ba4, Fu3–Fu5, Om4–Om5 (Wu et al., 2002).
Statistical analysis
The effects of treatment and soil depth were analyzed by two-way analysis of variance (ANOVA).
Multiple comparisons were made based on Tukey’s honest significant difference (HSD) test. Linear
correlations between nematodes and selected soil chemical properties were quantified using Pearson’s
correlation coefficients in the SPSS statistical package. Differences with P < 0.05 were considered
significant.
RESULTS AND DISCUSSION
Nematode richness
Nematode richness, as indicated by the number of genera (Ekschmitt et al., 2001), reflects the
biodiversity of soil habitats. Forty-five nematode genera were identified in this study (Table I). The
highest number of genera (32) was found in the UG treatment at a 10–20 cm depth, whereas, the lowest
number of genera (20) was found in the DG treatment at a 20–30 cm depth. Significant treatment
effects and interaction effects of treatments and depths were found in the numbers of genera (P < 0.05).
This suggested that grassland management could affect the biodiversity of soil nematodes, with higher
values in the UG and IG treatments and lower values in the DG treatment. It is generally accepted
that undisturbed systems have more diverse communities of soil organisms (Kandji et al., 2001). This
reflects a higher diversity that is derived from greater basal resource inputs. The significant effects of
the treatments on the number of nematodes genera indicate that grasslands with more groundcover
vegetation often support the most diverse assemblages of nematodes, possibly as a result of a greater
heterogeneity of resources, added during the return of residues and root-exudates (Ou et al., 2005).
Total number of nematodes
The total number of nematodes ranged from 222 to 792 individuals per 100 g dry weight soil (Table II). The highest abundance was found in the UG treatment at the 0–10 cm depth, whereas, the
lowest abundance was found in the DG treatment at the 20–30 cm depth. Significant differences in
the total number of nematodes were found between different treatments (P < 0.05) (Table III). Significant correlations were observed between the total number of nematodes and the soil TOC (r = 0.505,
P < 0.01) and TN (r = 0.537, P < 0.01). According to the previous study, the TOC in the improved
and undegraded grasslands were 1.6–2.6 times greater than that in the degraded grasslands. Similar
trends were also observed in the TN, that is, the TN in the improved and undegraded grasslands were
3.0–5.9 times greater than that in the degraded grasslands (Liu et al., 2005). As nematode diversity
and abundance in grasslands were dependent upon variations in environmental conditions (Wasilewska,
1994), the changes in TOC and TN following the different treatments might contribute to the changes in
the total number of nematodes among improved, degraded, and undegraded grasslands. Similar results
were also reported by Popovici and Ciobanu (2000), who found that relevant environmental variables,
such as soil pH, total nitrogen and humus content, could explain the variations in the composition of
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TABLE I
Relative abundance of nematode taxa in different grasslands at sampling depths of 0–10 cm (A), 10–20 cm (B) and
20–30cm (C)
Genus
Cuticularia
Mesorhabditis
Protorhabditis
Acrobeles
Acrobeloides
Cephalobus
Cervidellus
Chiloplacus
Eucephalobus
Plectus
Heterocephalobus
Odontolaimus
Prismatolaimus
Alaimus
Aphelenchoides
Aphelenchus
Ditylenchus
Nothotylenchus
Paraphelenchus
Diphtherophora
Tylencholaimus
Eudorylaimus
Microdorylaimus
Longidorella
Thonus
Aporcelaimellus
Discolaimium
Discolaimus
Dorylaimellus
Nygolaimus
Boleodorus
Filenchus
Paratylenchus
Psilenchus
Macroposthonia
Bitylenchus
Helicotylenchus
Hemicycliophora
Heterodera
Hirschmanniella
Merlinius
Paratrichodorus
Pratylenchus
Rotylenchulus
Rotylenchus
No. of genera
Guilda)
Ba1b)
Ba1
Ba1
Ba2
Ba2
Ba2
Ba2
Ba2
Ba2
Ba2
Ba2
Ba3
Ba3
Ba4
Fu2
Fu2
Fu2
Fu2
Fu3
Fu4
Fu4
Om4
Om4
Om4
Om4
Om5
Om5
Om5
Om5
Om5
H2
H2
H2
H2
H3
H3
H3
H3
H3
H3
H3
H3
H3
H3
H3
Undegraded grassland
Degraded grassland
Improved grassland
A
B
C
A
B
C
A
B
C
0.0
0.1
0.1
3.2
6.5
3.2
0.0
1.6
0.2
0.0
0.9
0.0
0.0
0.0
0.6
4.0
0.0
0.0
0.1
0.0
5.0
0.9
0.4
0.1
0.5
1.7
0.0
0.0
2.9
0.0
0.4
13.6
28.6
0.0
0.6
3.2
10.7
0.0
0.0
0.0
2.8
0.0
2.2
0.0
5.9
27
0.0
0.5
0.4
3.3
3.8
2.1
0.4
1.1
0.4
0.5
0.9
0.0
0.0
0.0
1.0
0.3
0.0
1.0
0.3
1.1
5.9
0.5
1.7
0.0
0.7
1.7
0.0
0.0
1.0
0.0
0.7
17.1
28.5
0.8
1.6
4.7
9.5
2.0
0.0
0.0
2.0
0.0
1.8
0.0
2.7
32
0.0
0.1
1.0
1.2
4.4
2.2
0.3
1.4
0.0
0.2
1.1
0.0
0.0
0.2
0.8
1.4
0.0
0.0
0.4
0.0
1.7
0.5
0.0
0.4
0.5
0.2
0.0
0.0
0.2
0.0
0.4
25.6
28.1
0.4
2.2
6.3
8.7
3.1
0.0
0.0
1.9
0.9
0.5
0.0
3.7
31
0.0
0.3
0.0
12.5
4.7
0.4
1.6
1.7
1.4
0.0
4.4
1.1
0.0
0.0
2.7
3.3
0.3
0.6
0.3
0.0
2.9
0.3
0.0
0.0
1.5
0.3
0.0
0.3
0.5
0.0
0.0
4.9
5.4
0.0
0.0
32.1
12.8
0.3
0.0
0.0
1.7
0.0
0.3
0.0
1.4
28
%
0.0
0.0
7.4
3.9
0.7
0.4
0.8
1.5
0.6
0.5
4.1
0.0
0.0
0.0
1.4
1.0
0.0
0.0
1.1
0.0
6.9
0.0
0.4
0.0
0.8
0.3
0.0
0.0
0.4
0.0
0.0
13.6
30.6
0.0
0.3
12.6
7.9
0.3
0.0
0.0
2.5
0.0
0.0
0.0
0.0
24
0.0
0.0
7.5
3.6
1.0
0.5
0.6
0.2
0.0
0.0
2.2
0.0
0.0
0.0
2.2
0.8
0.0
0.0
0.0
0.0
2.0
0.4
0.0
0.0
0.6
0.4
0.0
0.0
0.0
0.0
0.0
9.0
56.6
0.4
1.2
6.9
2.4
0.0
0.0
0.0
1.5
0.0
0.0
0.0
0.0
20
0.0
0.0
0.0
9.3
6.8
0.6
1.8
1.2
0.5
0.5
2.9
0.5
0.5
0.0
0.2
3.0
0.5
0.0
1.2
0.0
10.3
0.3
5.3
0.5
0.5
0.2
0.0
0.0
0.0
1.1
0.0
5.0
21.0
0.0
3.5
3.9
13.4
0.5
0.5
0.0
0.0
0.0
0.0
0.0
4.5
29
0.5
0.6
0.0
6.7
2.3
1.3
0.3
0.0
1.0
0.0
1.9
0.0
0.0
0.0
0.0
2.1
0.0
0.0
0.5
0.0
0.5
1.6
0.6
0.2
0.3
0.6
0.0
0.0
0.0
0.0
0.0
7.3
58.5
0.0
3.4
2.2
3.4
0.0
0.0
0.2
0.0
0.0
0.0
2.1
1.9
24
0.0
0.7
0.7
10.2
3.2
2.3
0.8
1.6
0.3
0.0
1.8
0.0
0.0
0.0
0.3
2.7
0.0
0.0
0.4
0.0
4.1
0.3
6.2
0.0
0.0
1.6
0.0
0.3
0.5
0.5
0.5
5.6
28.9
0.0
3.6
1.2
15.6
0.0
0.4
0.0
0.0
0.0
0.0
0.0
5.7
27
a) Functional
guilds of free-living nematodes characterized by feeding habits and life-history characteristics along a colonizerpersister (cp) scale. Ba, Fu, Om and H represent bacterial feeders, fungal feeders, omnivorous nematodes, and plant feeders,
respectively; b) The number following the letters represent the cp values of each genus (adapted from Bongers and Bongers,
1998).
nematode communities in grasslands. Such relevant correlations with environmental factors (Yeates,
NEMATODE FAUNAL RESPONSE TO GRASSLAND DEGRADATION
615
TABLE II
Absolute abundance (means±standard deviation, n = 4) of total nematodes and trophic groups in different grasslands at
different depths
Nematode
Total nematodes
Plant-parasites
Bacterivores
Fungivores
Omnivores-predators
Depth
cm
0–10
10–20
20–30
0–10
10–20
20–30
0–10
10–20
20–30
0–10
10–20
20–30
0–10
10–20
20–30
Undegraded grassland
Degraded grassland
Improved grassland
g−1
792±152 Aaa)
328±294 Ab
315±140 Bb
552±201 Aa
264±277 Aa
268±144 Aa
126±66 Aa
37±22 Ab
33±13 Ab
71±37 Aa
20±9 Ab
12±7 Bb
43±34 Aab
10±11 Aa
6±3 Bb
Individuals 100
dry weight soil
403±87 Ba
447±254 ABa
284±59 Aab
480±93 Aa
222±53 Bb
662±309 Aa
241±84 Ba
241±161 Ba
198±78 Aa
380±52 Aa
177±64 Aa
419±218 Aa
113±31 Aa
124±124 Aa
53±21 Ab
71±30 Aa
32±27 Ab
150±149 Aa
37±21 Aa
56±32 Aa
28±24 Aa
16±13 Ab
11±6 Ba
46±20 Aab
13±8 Aa
27±20 Aab
6±10 Aa
16±6 Ab
3±3 Ba
47±11 Aa
a) Different
uppercase letters in a row indicate significant differences between different treatments for each soil depth and
different lowercase letters in a column indicate significant differences between soil depths for each treatment as determined
by Tukey’s multiple range test (P < 0.05).
TABLE III
Analysis of variance for soil nematodes and ecological indices in different grasslands at different depths
Nematode
Treatment
Depth
Treatment×depth
F
P
F
P
F
P
Total nematodes
Plant-parasites
Bacterivores
Fungivores
Omnivores-predators
Enrichment index
Structure index
No. of genera
4.819
3.501
1.943
1.304
7.117
1.022
3.400
3.929
0.015
0.044
0.163
0.288
0.003
0.373
0.048
0.032
3.281
0.575
2.884
9.304
3.691
2.652
0.110
1.706
0.053
0.570
0.073
0.001
0.038
0.089
0.896
0.201
3.898
2.616
0.995
2.559
4.356
0.494
0.351
2.972
0.013
0.057
0.427
0.061
0.008
0.740
0.841
0.037
1984), with either biotic or abiotic variables (De Goede and Bongers, 1994), could elucidate causal
relationships between nematode fauna and the physical parameters of terrestrial habitats.
Trophic groups
Plant parasites were found to be the most dominant group in this investigation, exhibiting similar
trends to those of the total nematodes. Significant differences in the number of plant parasites were
found among different treatments (P < 0.05). As the changes in a plant-parasites’ abundance are usually
related to primary production, the changes in the plant-parasites in this study might be because of the
relatively higher vegetation cover and the increasing of grass production in the improved grassland
(Liu et al., 2005). Paratylenchus was found to be the most dominant genus in the three treatments
at the 10–20 cm and 20–30 cm depths. Filenchus was only found to be a dominant genus in the UG
treatment at different depths, and it increased with depth. Paratylenchus increased with depth in the
DG treatment (Table I). As Paratylenchus has a relatively shorter life cycle, more generations per year
would be expected (Verschoor et al., 2001), which might contribute to the relatively higher abundance in
the three treatments. Verschoor et al. (2001) found that Paratylenchus dominated the 0–10 cm depth in
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W. J. LIANG et al.
some Dutch grasslands. This is inconsistent with the findings in the present study, where Paratylenchus
was found to be distributed evenly in the different soil depths. The discrepancy between the two studies
may be because of differences in root distribution.
No significant differences were observed in the number of bacterivores in both treatments and depths
(Table III). Acrobeles and Acrobeloides were more abundant than other bacterivore genera in different
grasslands at different depths. The relative abundance of Acrobeloides in the three treatments was
relatively higher at the 0–10 cm depth than at the 10–20 cm and 20–30 cm depths (Table I). The results
indicated that Acrobeloides were relatively insensitive to different grassland managements. Fungivores
and omnivores-predators were the least abundant trophic groups in this study (Table II). These results
are in agreement with those reported by Bardgett and Cook (1998), who found that omnivores and
fungivores usually comprise of smaller proportions of nematode community, and that predators are
the least abundant trophic group. Significant differences were observed in the number of fungivores at
the different depths and in the number of omnivores-predators between treatments and depths (Table
III). Significant correlations were observed between the contents of TOC and TN and the number
of plant-parasites (r = 0.462, P < 0.01; r = 0.466, P < 0.01), fungivores (r = 0.444, P < 0.01;
r = 0.532, P < 0.01) and omnivore-predators (r = 0.526, P < 0.01; r = 0.588, P < 0.01). The
composition of nematode community could reflect the different levels and distribution of their food
sources in different treatments. Of the nematode trophic groups, the omnivore-predators were found to
be relatively sensitive, exhibiting a response to different treatments and soil depths, with higher values
found in the improved grassland and lowest values in the degraded grassland at the 20–30 cm depth. Liu
et al. (2005) found that the engineering measures performed on the improved grassland could improve
soil fertility and biodiversity, especially in the deeper soil layers. These results could contribute to the
changes in the omnivores-predators group, and indicate that omnivores-predators are susceptible to soil
disturbance (Bongers and Ferris, 1999).
Faunal profile analyses
Graphical representation of nematode faunal analysis provides an integral synopsis of the food web
structure and the state of its environment (Ferris et al., 2001). No significant differences in soil food
web enrichment in the spring, as indicated by the EI (Fig. 1a), were observed between treatments and
depths (Table III). Significant differences were found in SI (P < 0.05) between the UG, DG, and IG
treatments (Table III). SI values were higher (P < 0.05) in the UG and IG treatments than in the
DG treatment (Fig. 1b). Significant positive correlations between the SI values and the TOC contents
(r = 0.445, P < 0.01) and TN (r = 0.447, P < 0.01) might contribute to the changes in SI. A higher
SI indicates a food web with more trophic linkages and relatively healthy ecosystems (Berkelmans et
Fig. 1 Enrichment index (a) and structure index (b) in different grasslands at 0–10, 10–20, and 20–30 cm depths. UG =
undegraded grassland; DG = degraded grassland; IG = improved grassland.
NEMATODE FAUNAL RESPONSE TO GRASSLAND DEGRADATION
617
al., 2003).
CONCLUSIONS
The nematode community composition and ecological indices responded to grassland management.
The TOC and TN contents, following the different treatments, exhibited positive effects on the nematode
composition. Significant treatment effects were found in the total number of nematodes, plant parasites,
and omnivores-predators. Food web SI was significantly higher in the UG and IG treatments than in
the DG treatment. A higher SI indicates a food web with more trophic linkages and relatively healthy
ecosystems.
ACKNOWLEDGMENTS
The authors appreciate the English proofing done by Prof. Yosef Steinberger in the Bar-Ilan University, Israel. They also thank Ms. Qi Li at the Institute of Applied Ecology, CAS, for technical
assistance.
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