Inter-sand dune desert sites are known to be among the most prominent locations for generating playa surfaces characterized by compact floors, salt pavements, carbonate surfaces, and a high percentage (50 % or more) of clay lacking microbiotic crusts (Breckle
Soil nematode community is known to be among the important components of soil fauna, by being of great abundance (>3 million m-2 at some sites) (Yeates, 2003; Liu
Most of the studies on sand dune ecosystems have been oriented toward costal sand dunes. For example, Goralczyk (1998) studied the nematode population as bioindicators in a coastal sand dune elucidating their importance as good indicators in the plant succession process in bare dunes. Wall
An important gap in the knowledge on the soil free living nematode community structure in desert inter-sand dune ecosystem raised our interest, due to a unique combination between a xeric environment and sandy soil physical characteristics. Furthermore, two main biotopes can be found in this unique inter-dune area: the playa system is characterized by a thick crust with low water infiltration and the sandy system with high water infiltration rates. Moreover, due to the lack of moisture, unpredictability followed by different rates of water infiltration between the two systems, the food randomness availability for the nematode community becomes even more critical. Therefore, the vertical distribution of the nematode community and its trophic composition aspect were found to be even more inspiring.
The aim of this study was to determine the vertical distribution of soil free living nematode community representing a playa and a loessial plain area in a desert inter-sand dune ecosystem under two – wet and dry – extreme environmental conditions in the North-Western Negev Desert, Israel.
Study site (30º53’14’’N, 34º25’15’’E) is located at the Nizzana sand dune site within the Hallamish dune field eastern extension of the northern Sinai dune field – western Negev Desert, Israel (Yair, 1990). The dune field comprises longitudinal dunes aligned west-east, are 15 to 20 m high and are separated by a 50 m to 200 m wide interdune. The Nizzana experimental site is located about 45 km inland from the Mediterranean Sea. Mean annual precipitation is 95 mm and occurs during the winter months (November – April) and the average monthly temperatures are 9 oC in January and 25oC in August. Potential annual evaporation is in the order of 2200 mm (Kidron, 2001; Kidron & Yair, 2001; Keck
The playa area is a geomorphological inter-sand dune desert site unit comprised of thin, dense layers (1 – 2 mm thick) covered with dark brown clay skins, followed by 3 cm of angular blocky, deeper down, single grained sandy layers, with very few tubules and holes, alternating with loamy units, having a massive blocky structure (Kidron
Soil samples were collected at the study site at the end of the summer season, representing the driest period and in the middle of the winter season, representing the wet season, using a 7-cm diameter soil auger. Soil samples from the 0 to 50 cm at 10 cm intervals (corresponding to 0 – 10, 10 – 20, 20 – 30, 30 – 40, and 40 – 50 cm depths, four replicates) were randomly collected from both playa and loessial plain areas (as control). Each of the soil samples was deposited in an individual plastic bag which was placed in an insulated container and transported to the laboratory. These soil samples were kept in cold storage at 4 oC until processing. All soil samples were sieved (2 mm mesh size) before biological and chemical analysis in order to remove root particles and other organic debris.
Soil moisture – was determined gravimetrically by drying the samples at 105 oC for 48 h. The values were expressed as percentage of dry weight.
Organic matter concentration – was determined by oxidization dry soil sample with dichromate in the presence of H2SO4, without application of external heat (Rowell, 1994).
Electrical conductivity – was determined on a 5 g subsample that was agitated (half-hour at room temperature) with 50 ml distilled water. The filtrated solution was analyzed using a TH-2400 conductivity meter (ms cm-1).
Soil free-living nematodes – were extracted from 100 g fresh soil samples using the Baermann funnel procedure (Cairns, 1960) and nematode populations were expressed per 100 g dry mass soil. The recovered organisms were counted and preserved in formalin (Steinberger & Sarig, 1993). Total one hundred individuals from each samples were randomly picked and used for identification to genus level, according to esophageal and morphology characteristics using an inverted compound microscope (Mal & Lyon, 1975; Ying, 1998).
The data were analyzed using the following approaches: (1) total nematode number in 100 g-1 dry soil (TN); (2) trophic groups, including bacterivores (BF), fungivores (FF), plant parasites (PP), omnivores–predators (OP) (Yeates,
All obtained data were subjected to statistical analysis of variance (ANOVA) using the SAS model (GLM, Duncan’s multiple range test and Pearson correlation coefficient) and were used to evaluate differences between separate means. CANOCO redundancy analysis (ter Braak & Prentice 1996; ter Braak & Smilauer 2002) were used to evaluate the relationship among nematode trophic groups, soil depths and environmental variables. Differences obtained at levels of
This study is neither related to human nor animals use.
Soil moisture reached a maximum value of 7.2 % in the 0 – 10 cm soil layer at the playa site in the wet season, whereas a minimum value of 0.1 % was found in the dry season in the 0 to 20 cm soil layer in the loessial plain area. Soil moisture in the playa area was significantly (
Soil physico-chemical propertites in the playa and loessial plain areas (as control) under the dry and wet seasons.
Treatment | Dry season | Wet season | ||||
---|---|---|---|---|---|---|
SM SM: soil moisture; OM: soil organic matter content; EC: electrical conductivity. |
OM (%) | EC (ms cm-1) | SM (%) | OM (%) | EC (ms cm-1) | |
playa | 1.28±0.73a Means and standard deviation from four replicates, different letters at each soil layer in a column denote significant differences as assessed by |
0.25±0.05a | 2.20±1.15a | 7.16±1.70a | 0.14±0.07a | 1.97±0.63a |
loessial plain | 0.11±0.05b | 0.07±0.04b | 0.05±0.00b | 1.93±0.54b | 0.05±0.04b | 0.08±0.01b |
playa | 2.42±0.68a | 0.18±0.03a | 3.35±0.59a | 5.44±0.53a | 0.16±0.13a | 1.77±0.32a |
loessial plain | 0.09±0.03b | 0.07±0.04b | 0.05±0.00b | 1.14±0.15b | 0.04±0.03a | 0.07±0.01b |
playa | 3.08±0.95a | 0.13±0.03a | 3.03±0.75a | 6.75±0.89a | 0.14±0.07a | 2.85±0.97a |
loessial plain | 0.13±0.03b | 0.06±0.06b | 0.05±0.00b | 0.84±0.17b | 0.02±0.00b | 0.07±0.01b |
playa | 3.81±1.05a | 0.10±0.02a | 2.99±0.68a | 5.69±0.90a | 0.15±0.08a | 2.63±0.39a |
loessial plain | 0.16±0.06b | 0.03±0.02b | 0.06±0.01b | 0.80±0.17b | 0.02±0.00b | 0.06±0.00b |
playa | 1.23±1.35a | 0.04±0.04a | 1.09±0.75a | 3.47±1.65a | 0.10±0.05a | 1.83±0.80a |
loessial plain | 0.42±0.40a | 0.05±0.05a | 0.06±0.03b | 0.80±0.12b | 0.04±0.01b | 0.07±0.01b |
Univariate analysis of variance of the soil properties, nematode population and ecological indices.
Index | Location (L) | Depth (D) | Season (S) | L×D | L×S | D×S | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Soil Properties | ||||||||||||
SM SM: soil moisture; OM: organic matter; EC: electrical conductivity; TN: total number of nematodes; BF: bacterivores; FF: fungivores; PP: plant-parasite nematodes; OP: omnivore-predator nematodes; F/B: fungivores/bacterivores ratio; NCR: nematode channel ratio T: trophic diversity; H’: Shannon index; λ: genus dominance; SR: species richness; MI: maturity index; MMI: modified maturity index; EI: enrichment index; SI: structure index. NS: no significant. |
139.81 | < 0.0001 | 6.36 | 0.0002 | 139.81 | < 0.0001 | 7.12 | < 0.0001 | 45.04 | < 0.0001 | 6.80 | 0.0001 |
OM | 1.16 | < 0.0001 | 4.95 | 0.0016 | 1.16 | NS | 2.72 | 0.0376 | 0.54 | NS | 1.64 | NS |
EC | 1.73 | < 0.0001 | 5.25 | 0.0011 | 1.73 | NS | 5.35 | 0.0009 | 2.02 | NS | 2.45 | NS |
Trophic Group | ||||||||||||
TN | 69.36 | < 0.0001 | 6.42 | 0.0002 | 8.88 | 0.0042 | 6.21 | 0.0003 | 7.63 | 0.0076 | 1.08 | NS |
BF | 49.67 | < 0.0001 | 4.39 | 0.0035 | 6.80 | 0.0115 | 4.17 | 0.0048 | 5.48 | 0.0226 | 1.24 | NS |
FF | 24.00 | < 0.0001 | 3.67 | 0.0097 | 4.44 | 0.0394 | 3.65 | 0.0100 | 4.22 | 0.0443 | 0.92 | NS |
PP | 36.87 | < 0.0001 | 3.63 | 0.0102 | 1.87 | NS | 3.63 | 0.0103 | 1.87 | NS | 2.10 | NS |
OP | 45.42 | < 0.0001 | 3.68 | 0.0096 | 4.22 | 0.0442 | 3.66 | 0.0099 | 4.14 | 0.0462 | 0.69 | NS |
Ecological Indices | ||||||||||||
F/B | 8.71 | 0.005 | 0.76 | NS | 0.48 | NS | 0.34 | NS | 1.19 | NS | 0.52 | NS |
NCR | 17.50 | 0.0001 | 0.66 | NS | 0.63 | NS | 0.39 | NS | 1.16 | NS | 0.63 | NS |
T | 55.27 | < 0.0001 | 0.57 | NS | 0.78 | NS | 0.51 | NS | 0.53 | NS | 0.50 | NS |
H' | 618.16 | < 0.0001 | 1.29 | NS | 22.40 | < 0.0001 | 1.69 | NS | 23.27 | < 0.0001 | 0.76 | NS |
Λ | 177.50 | < 0.0001 | 0.93 | NS | 2.82 | NS | 1.79 | NS | 20.50 | < 0.0001 | 0.41 | NS |
SR | 139.82 | < 0.0001 | 0.36 | NS | 3.39 | NS | 1.25 | NS | 8.16 | 0.0062 | 0.45 | NS |
MI | 22.25 | < 0.0001 | 1.74 | NS | 1.24 | NS | 2.71 | 0.0417 | 5.07 | 0.0292 | 1.84 | NS |
MMI | 12.18 | 0.001 | 1.27 | NS | 0.95 | NS | 2.20 | NS | 0.33 | NS | 0.51 | NS |
EI | 9.75 | 0.0032 | 1.69 | NS | 5.78 | 0.0206 | 0.41 | NS | 0.01 | NS | 0.14 | NS |
SI | 22.56 | < 0.0001 | 0.56 | NS | 1.66 | NS | 3.08 | 0.0253 | 11.82 | 0.0013 | 1.85 | NS |
Soil organic matter content was found to reach a maximum value in the 0 – 10 cm layer in the playa site under dry the season and a minimum in the 20 – 40 cm soil layer in the loessial plain area during the wet season. Moreover, general high values were in the playa soil samples (Table 1). Significant difference in soil organic matter content were found by location (
Soil electrical conductivity was found to follow the soil organic matter trend, with significantly (
Total number of nematode in the playa area ranged from 1 to 15 individuals per 100 g dry soil, while total number of nematode in the loessial plain area was many fold higher, ranging from 60 to 631 individuals per 100 g dry soil and resulting in significant (
Correlation coefficients between soil properties and soil nematode indices.
Index | SM | OM | EC |
---|---|---|---|
TN Abbreviations as in Table 2. NS: no significant. |
- 0.44 Correlation coefficients significant at |
- 0.23 Correlation coefficients significant at |
- 0.51 Correlation coefficients significant at |
BF | - 0.41 Correlation coefficients significant at |
NS | - 0.48 Correlation coefficients significant at |
FF | - 0.33 Correlation coefficients significant at |
NS | - 0.37 Correlation coefficients significant at |
PP | - 0.36 Correlation coefficients significant at |
- 0.2 Correlation coefficients significant at |
- 0.44 Correlation coefficients significant at |
OP | - 0.43 Correlation coefficients significant at |
- 0.25 Correlation coefficients significant at |
- 0.48 Correlation coefficients significant at |
F/B | - 0.28 Correlation coefficients significant at |
NS | NS |
NCR | 0.36 Correlation coefficients significant at |
NS | 0.35 Correlation coefficients significant at |
T | - 0.52 Correlation coefficients significant at |
- 0.44 Correlation coefficients significant at |
- 0.58 Correlation coefficients significant at |
H' | - 0.77 Correlation coefficients significant at |
- 0.54 Correlation coefficients significant at |
- 0.78 Correlation coefficients significant at |
λ | 0.74 Correlation coefficients significant at |
0.47 Correlation coefficients significant at |
0.70 Correlation coefficients significant at |
SR | - 0.6 Correlation coefficients significant at |
- 0.57 Correlation coefficients significant at |
- 0.72 Correlation coefficients significant at |
MI | - 0.56 Correlation coefficients significant at |
- 0.42 Correlation coefficients significant at |
- 0.42 Correlation coefficients significant at |
MMI | - 0.40 Correlation coefficients significant at |
- 0.35 Correlation coefficients significant at |
- 0.32 Correlation coefficients significant at |
EI | NS | NS | - 0.39 Correlation coefficients significant at |
SI | - 0.58 Correlation coefficients significant at |
- 0.44 Correlation coefficients significant at |
- 0.47 Correlation coefficients significant at |
The general pattern obtained for the changes in total soil free living nematode were found to be reflected in the trophic group abundance. Bacterivores were found to be the dominant trophic group in the present study, and they were significantly greater (
Fungivores were found in lower numbers, whereas the pattern of their behavior was found to replicate that of the bacterivores, with a relatively higher population size in the loessial plain area than in the playa area in all sampling depths and season (Fig. 2). In the upper 0 – 10 cm soil layer in the loessial plain area, the fungivores had a higher abundance during the dry and wet season. Furthermore, the overall data revealed that the sampling locations (
Plant-parasitic nematodes were the least trophic group (Fig. 2). Plant-parasitic nematodes were significantly affected by sampling locations (
Omnivores-predators were found to follow bacteria-feeding and fungi-feeding trophic groups, with a higher abundance in the loessial plain area and in the 0 – 20 cm soil layer (Fig. 2). Omnivores-predators were significantly influenced by sampling locations (
RDA analysis revealed that BF and OP were mainly distributed within the 0 – 10 cm depth and PP mainly in the 10 – 20 cm and 20 – 30 cm depths in the playa area during the dry season (Fig. 3). BF and PP were mainly distributed in the 0 – 10 cm depth in the playa area during the wet season. All trophic group of nematodes were mainly distributed within the 0 – 10 cm, 10 – 20 cm and 20 – 30 cm in the loessial plain area during the dry season, and correlated positively with soil organic matter content and negatively with soil moisture and electrical conductivity. However, the trophic group of nematodes was mainly distributed within the 0 – 10 cm and 10 – 20 cm in the loessial plain area during the wet season, and positively correlated with soil organic matter content, soil moisture and electrical conductivity.
Total of 55 genera were observed, including 19 bacterivores, 10 fungivores, 12 plant-parasites, and 14 omnivore-predators (Table 4). Total of thirteen genera (including 6 bacterivores, 1 fungivores, 5 plant-parasites, and 1 omnivore-predators) were found in the playa area, while total of fifty-five genera (including 19 bacterivores, 10 fungivores, 12 plant-parasites, and 14 omnivore-predators) were found in the loessial plain area.
Number of soil nematode (individuals per 100 g dry soils) across all soil layers in the playa and loessial plain areas during the dry and wet seasons.
Genus | Dry season | Wet season | |||
---|---|---|---|---|---|
playa | loessial plain | playa | loessial plain | ||
Trophic groups according to Yeates |
|||||
2 | 0.8 Means from four replicates. |
74.9 | 0.3 | 42.3 | |
2 | 2.7 | 24.4 | 0.3 | 07.1 | |
4 | 0.0 | 00.0 | 0.0 | 00.1 | |
2 | 0.5 | 32.3 | 0.0 | 15.5 | |
2 | 0.0 | 04.8 | 0.0 | 00.0 | |
2 | 0.0 | 02.6 | 0.0 | 00.5 | |
2 | 0.0 | 23.9 | 0.1 | 14.4 | |
1 | 0.0 | 00.0 | 0.1 | 02.9 | |
2 | 0.0 | 00.9 | 0.0 | 02.0 | |
1 | 0.0 | 03.1 | 0.0 | 00.0 | |
3 | 3.0 | 46.8 | 0.0 | 20.7 | |
2 | 0.0 | 00.0 | 0.0 | 00.1 | |
1 | 0.0 | 00.0 | 0.0 | 00.9 | |
1 | 0.0 | 01.6 | 0.0 | 00.5 | |
2 | 0.0 | 03.4 | 0.0 | 00.1 | |
1 | 0.0 | 00.0 | 0.0 | 00.1 | |
1 | 0.0 | 01.9 | 0.0 | 00.4 | |
2 | 0.0 | 00.0 | 0.0 | 01.0 | |
2 | 0.0 | 01.3 | 0.0 | 00.0 | |
2 | 0.4 | 38.2 | 0.0 | 07.8 | |
2 | 0.0 | 08.6 | 0.0 | 09.2 | |
2 | 0.0 | 00.0 | 0.0 | 00.2 | |
3 | 0.0 | 00.0 | 0.0 | 00.7 | |
2 | 0.0 | 00.0 | 0.0 | 00.1 | |
2 | 0.0 | 01.4 | 0.0 | 00.5 | |
2 | 0.0 | 00.0 | 0.0 | 00.5 | |
4 | 0.0 | 03.2 | 0.0 | 02.2 | |
4 | 0.0 | 02.5 | 0.0 | 00.7 | |
3 | 0.0 | 00.0 | 0.0 | 00.9 | |
2 | 0.0 | 01.4 | 0.0 | 01.2 | |
3 | 0.4 | 01.1 | 0.0 | 00.0 | |
3 | 0.0 | 02.1 | 0.0 | 01.4 | |
5 | 0.0 | 05.5 | 0.0 | 00.1 | |
2 | 0.0 | 00.0 | 0.0 | 01.6 | |
3 | 0.0 | 02.1 | 0.0 | 02.9 | |
3 | 0.0 | 01.3 | 0.1 | 02.8 | |
3 | 0.0 | 01.6 | 0.1 | 02.2 | |
4 | 0.0 | 00.0 | 0.0 | 00.2 | |
3 | 0.0 | 07.7 | 0.1 | 03.2 | |
2 | 0.1 | 00.6 | 0.2 | 00.4 | |
5 | 0.0 | 02.8 | 0.0 | 00.0 | |
5 | 0.0 | 01.1 | 0.0 | 02.5 | |
5 | 0.1 | 12.8 | 0.0 | 04.4 | |
4 | 0.0 | 00.5 | 0.0 | 00.0 | |
5 | 0.0 | 00.0 | 0.0 | 00.2 | |
5 | 0.0 | 03.2 | 0.0 | 06.6 | |
5 | 0.0 | 07.6 | 0.0 | 01.4 | |
4 | 0.0 | 00.7 | 0.0 | 00.0 | |
4 | 0.0 | 03.0 | 0.0 | 00.0 | |
4 | 0.0 | 06.3 | 0.0 | 00.0 | |
4 | 0.0 | 03.7 | 0.0 | 03.8 | |
5 | 0.0 | 05.4 | 0.0 | 00.0 | |
4 | 0.0 | 00.9 | 0.0 | 00.0 | |
5 | 0.0 | 00.0 | 0.0 | 00.8 | |
4 | 0.0 | 00.0 | 0.0 | 04.5 |
F/B values at every soil layer in the loessial plain area were higher compared with the playa area during the dry and wet seasons (Table 5). Significant difference in the F/B values was found between locations (
Nematode ecological indices in different sampling sites, depths and seasons.
Index | Sampling depths (cm) | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
0-10 | 10-20 | 20-30 | 30-40 | 40-50 | ||||||
Playa | Control | Playa | Control | Playa | Control | Playa | Control | Playa | Control | |
F/B Abbreviations as in Table 2. |
0.25b Mean values from four replicates, different letters at each layer in a line denote significant differences as assessed by |
0.35a | 0.13a | 0.20a | 0.00b | 0.19a | 0.13a | 0.18a | 0.00b | 0.30a |
NCR | 0.88a | 0.74b | 0.92a | 0.84a | 1.00a | 0.85b | 0.90a | 0.86a | 1.00a | 0.80b |
T | 1.29b | 2.20a | 1.42b | 2.37a | 1.23b | 2.28a | 1.44b | 2.25a | 1.00b | 2.50a |
H' | 0.92b | 2.23a | 0.78b | 2.32a | 0.71b | 2.12a | 0.95b | 2.23a | 0.49b | 2.10a |
λ | 0.44a | 0.14b | 0.54a | 0.13b | 0.55a | 0.16b | 0.41a | 0.14b | 0.66a | 0.14b |
SR | 0.78b | 1.89a | 0.77b | 2.07a | 0.61b | 1.99a | 0.88b | 2.19a | 0.46b | 2.12a |
MI | 2.43a | 2.25b | 2.25b | 2.81a | 2.17b | 2.83a | 2.35b | 2.86a | 2.71a | 2.58b |
MMI | 2.43a | 2.35a | 2.25b | 2.85a | 2.48b | 2.90a | 2.39b | 2.86a | 2.71a | 2.66a |
EI | 8.25b | 34.75a | 8.33a | 14.75a | 0.00b | 11.25a | 10.50a | 15.50a | 0.00b | 22.50a |
SI | 54.50a | 41.00b | 25.00b | 70.00a | 23.00b | 71.25a | 49.50b | 73.75a | 83.25a | 62.25b |
F/B | 0.00b | 0.28a | 0.00b | 0.38a | 0.00b | 0.19a | 0.00b | 0.19a | 0.00b | 0.37a |
NCR | 1.00a | 0.82b | 1.00a | 0.73b | 1.00a | 0.84b | 1.00a | 0.85b | 1.00a | 0.78b |
T | 1.20b | 2.08a | 1.00b | 2.92a | 1.00b | 2.49a | 1.00b | 1.98a | 1.00b | 2.33a |
H' | 0.45b | 2.42a | 0.00b | 2.32a | 0.00b | 2.15a | 0.00b | 2.09a | 0.00b | 2.05a |
λ | 0.71a | 0.20b | 1.00a | 0.11b | 1.00a | 0.17b | 1.00a | 0.15b | 1.00a | 0.12b |
SR | 0.44 | 1.91 | 0.00 | 2.39 | 0.00 | 2.16 | 0.00 | 2.48 | 0.00 | 2.88 |
MI | 1.75b | 2.42a | 2.00b | 2.95a | 2.00b | 2.84a | 2.00b | 2.40a | 2.00b | 2.39a |
MMI | 2.13b | 2.47a | 2.00b | 2.93a | 2.00b | 2.85a | 2.50a | 2.46a | 2.50a | 2.53a |
EI | 40.00a | 26.00b | 0.00b | 20.25a | 0.00b | 23.50a | 0.00b | 29.25a | 0.00b | 32.50a |
SI | 0.00b | 55.00a | 0.00b | 76.75a | 0.00b | 74.75a | 0.00b | 55.25a | 0.00b | 51.75a |
NCR values at every soil layer in the playa area were higher contrasted with the loessial plain area during the dry and wet seasons (Table 5). Significant difference in the NCR values was found between locations (
T values at every soil layer in the loessial plain area were higher compared with the playa area during the dry and wet seasons (Table 5). Significant sampling locations effect was found on the T values (
H’ values at every soil layer in the loessial plain area were higher than that in the playa area during the dry and wet seasons (Table 5). Significant sampling locations and seasons effects were found on the H’ values (
The λ values at every soil layer in the loessial plain area were lower compared with the playa area during the dry and wet seasons (Table 5). Significant sampling location effect was found on the λ values (
SR values at every soil layer in the loessial plain area were higher contrasted with the playa area during the dry and wet seasons (Table 5). Significant sampling location effect was found on the SR values (
MI values at every soil layer in the loessial plain area were higher compared with the playa area during the wet season (Table 5). Significant sampling locations effect was found on the MI values (
MMI values at every soil layer in the loessial plain area were higher contrasted with the playa area, except the 30 – 40 cm layer during the wet season (Table 5). Significant sampling location effect was found on the MMI values (
EI values in every soil layer in the loessial plain area were higher compared with the playa area (except the 0 – 10 cm layer during the wet season) during the dry and the wet seasons (Table 5). Significant differences in the EI values were found between locations (
SI values in every soil layer in the loessial plain area were higher contrasted with the playa area (except for the 0 – 10 cm and 40 – 50 cm layers during the dry season) during the dry and wet seasons (Table 5). Significant difference in the SI values was found between locations (
Integrating all the data using RDA (Fig. 3) for each of the sampling sites and seasons and soil depths indicated a strong effect between the dry (Fig. 3 A, B) and wet periods (Fig. 3 C, D) of each treatment. The relatively higher values of soil moisture (SM) during the wet period were found to explain the significant difference between the sampling sites. In the playa area (Fig. 3A, B) the SM was found to move to deeper layers, whereas the SM in loessial plain area remained close to the upper soil layer (Fig. 3 C, D). Different behavior of SM between the two sites explain the importance of soil pedological characteristics. The second variable known to play an important role in basic food source availability is the OM whose behavior was found to remain stable in the upper soil layers in both cases. These main variables were found to have the greatest significant effect on the soil free living nematode community abundance, distribution and trophic groups (Fig. 3), where in the playa area the OM was found to have a great effect on TN compared with the loessial plain area. Redundancy analysis reflected that the nematode community mainly distributed in the upper soil layers (0 – 20 cm) under the playa and loessial plain area.
The playa and loessial plain area (as control) are two main geomorphological units in the inter-sand dune area in the North-Western Negev desert (Kidron
Bacterivores were the most dominant trophic group in this study, which was consistent with the findings of Rahman
Total 55 nematode genera were observed in all soil samples, which was higher than the taxa of nematode reported by Zhang
Nematode ecological indices can be used to estimate soil nematode community structure and composition (Yeates & Bongers, 1999). Ecological indexes are known to be a useful tool for helping differentiate between sampling depths and sites effect. Jiang
Fungivore/bacterivore ratio (F/B) in the loessial plain area was higher than that in the playa area, which manifested that there had much more fungi community in the loessial plain area. Mean value of F/B was higher in the wet season under the loessial plain area than in the dry season, which showed that there had much more fungi community in the wet season in contrast to the dry season. The results reported by Yu
Nematode channel ratio (NCR) reflects the soil bacterial or fungi decomposition pathway in the soil detrital food webs (Ruess, 2003). NCR values in the playa area were higher compared with loessial plain area, which manifested that bacterial decomposition pathway was predominant in the playa area. NCR values significantly negatively correlated with soil moisture and electrical conductivity in the Horqin Sandy Land of China (Zhang
Trophic diversity index (T) demonstrates the diversity of the functional groups within the nematode community. T affords greater weight to common taxa, and a higher index indicates greater diversity (Heip
Shannon index (H’) affords more weight to rare species, and a high value indicates greater diversity and Simpson index (λ) gives more weight to common species (Liang
Similarly, spieces richness (SR) values in the loessial plain area were greater than that in the playa area, and also indicating that there had abundant species in the loessial plain area. Yu
Maturity index (MI) is a measure based on the composition of the nematode community and can reflect the degree of stability of the soil ecosystem (Bongers, 1990). MI values in the loessial plain area were higher in the wet season than that in the playa area, indicating a relatively higher environmental stability compared with the playa area. MI values significantly negatively correlated with soil organic matter content and electrical conductivity, however, Jiang
Enrichment index (EI) provides an indicator of resources available to the soil food web and the response of primary decomposers to those resources (Wang
Structure index (SI) reflects the degree of trophic linkage in soil food webs and is an indicator of greater trophic links. Higher SI value indicates a food web that is more structured or stable, with more persisters (