Soil physical and chemical properties. Figure 1, Supplementary Table S1 and Supplementary Table S2 show that the soil properties in different habitats and different seasons. The difference in the soil temperatures (ST) at various habitats was significant in the warm season (P< 0.05). The seasonal difference in the average temperatures of the superficial layer (0~10 cm) was significant and not significant in those of the deep layer (10–20 cm) (P< 0.05) (Fig.1 a, b). The difference in soil pHs between soil layers at various habitats and between seasons were not significant (Fig. 1 e, f). The difference in soil water content (WC), total nitrogen (TN), total phosphorus (TP) and soil organic carbon (SOC) between habitats in cold season and warm season was significant (Fig. 1 c, d, g-l, Supplementary Table S1, Supplementary Table S2).
Component of soil arthropod communities. Table 2 and Supplementary Table S3 shows that the number and abundance of individual soil arthropods and groups at both larval and adult stages. We collected 7706 individuals belonging to 32 taxa, and classified them into 3 classes, 9 orders, 30 families. In the cold season, the dominant groups were Chironomidae larvae, Sejidae and Trombidiidae, accounting for 36.30% of the total individuals. The common groups included Arrhopalites, Ceratopgonidae, Doilchopodidae, Entomobrya, Isotoma, Isotomiella, Oribatella, Phlaeothripidae, Proisotoma, Sminthurus, Tabanidae and Uropodidae, accounting for 61.19% of the total individuals. The other 4 taxa were in the rare groups, accounting for 2.51% of the total individuals. In the warm season, the dominant groups were Chironomidae larva, Onychiurus, Pygmephorus and Tullbergia, accounting for 43.57% of the total individuals. The common groups included Aphididae, Cecidomyidae,Cryptopygus, Doilchopodidae, Entomobrya, Galumna, Isotoma, Limoniidae, Oribatella, Proisotoma, Staphylinidae, Tabanidae, Trichoceratidae and Trombidiidae, accounting for 46.04% of the total individuals. The other 4 groups were rare groups, accounting for 10.39% of the total individuals. In whole year, the dominant group was Chironomidae larva, accounting for 14.61% of the total individuals. The common groups included Aphididae, Ceratopgonidae, Cryptopygus, Doilchopodidae, Entomobrya, Isotoma, Isotomiella, Limoniidae, Onychiurus, Oribatella, Phlaeothripidae, Proisotoma, Pygmephorus, Sejidae, Tabanidae, Trichoceratidae, Trombidiidae, Tullbergia and Uropodidae, accounting for 81.07% of the total individuals. The other 10 groups were rare groups, accounting for 4.32% of the total individuals (Table 2). Some were only found in the cold season (Arrhopalites, Ceratopgonidae larva, Chrysomeilidae, Elateridae, Formicinae, Isotomiella, Phlaeothripidae larva, Sejidae, Sminthurus, Uropodidae), and some were only found in the warm season (Aphididae, Cecidomyidae, Cicadellidae, Coreidae, Ephydridae, Galumna, Limoniidae, Onychiurus, Pygmephorus, Tenthredinidae, Trichoceratidae, Tullbergia).
Arthropod
|
Cold season
|
Warm season
|
Whole year
|
Individuals
|
%
|
A
|
Individuals
|
%
|
A
|
Individuals
|
%
|
A
|
Aphididae
|
|
|
|
31.00±9.83
|
1.06
|
++
|
31.00±9.83
|
0.40
|
+
|
Arrhopalites
|
240.53±10.50
|
5.04
|
++
|
|
|
|
240.53±10.50
|
3.12
|
++
|
Cecidomyidae
|
|
|
|
65.28±0.83
|
2.22
|
++
|
65.28±0.83
|
0.85
|
+
|
Ceratopgonidae larva
|
223.11±3.72
|
4.68
|
++
|
|
|
|
223.11±3.72
|
2.90
|
++
|
Chironomidae larva
|
480.99±0.24
|
12.18
|
+++
|
644.63±3.42
|
18.56
|
+++
|
1125.62±0.15
|
14.61
|
+++
|
Chrysomeilidae
|
20.64±9.27
|
0.43
|
+
|
|
|
|
20.64±9.27
|
0.27
|
+
|
Cicadellidae
|
|
|
|
6.96±0.84
|
0.24
|
+
|
6.96±0.84
|
0.08
|
+
|
Coreidae
|
|
|
|
6.39±1.55
|
0.22
|
+
|
6.39±1.55
|
0.08
|
+
|
Cryptopygus
|
122.34±0.92
|
2.56
|
++
|
43.94±4.61
|
1.50
|
++
|
166.28±6.18
|
2.16
|
++
|
Doilchopodidae larva
|
396.90±4.15
|
8.32
|
++
|
243.27±4.55
|
8.29
|
++
|
640.17±2.47
|
8.31
|
++
|
Elateridae
|
41.39±0.05
|
0.87
|
+
|
|
|
|
41.39±0.05
|
0.54
|
+
|
Entomobrya
|
137.38±2.83
|
2.88
|
++
|
84.51±0.22
|
2.88
|
++
|
221.89±3.62
|
2.88
|
++
|
Ephydridae
|
|
|
|
22.29±0.82
|
0.76
|
+
|
22.29±0.82
|
0.29
|
+
|
Formicinae
|
20.55±3.91
|
0.43
|
+
|
|
|
|
20.55±3.91
|
0.27
|
+
|
Galumna
|
|
|
|
58.94±4.18
|
2.01
|
++
|
58.94±4.18
|
0.76
|
+
|
Isotoma
|
414.27±1.85
|
8.68
|
++
|
59.41±0.66
|
2.02
|
++
|
473.68±7.35
|
6.15
|
++
|
Isotomiella
|
343.37±8.44
|
7.20
|
++
|
|
|
|
343.37±8.44
|
4.46
|
++
|
Limoniidae
|
|
|
|
43.27±4.18
|
1.47
|
++
|
43.27±4.18
|
0.56
|
+
|
Onychiurus
|
|
|
|
417.69±3.88
|
14.23
|
+++
|
417.69±3.88
|
5.42
|
++
|
Oribatella
|
123.29±3.16
|
2.58
|
++
|
56.74±2.65
|
1.93
|
++
|
180.03±3.55
|
2.34
|
++
|
Phlaeothripidae larva
|
90.29±3.52
|
1.89
|
++
|
|
|
|
90.29±3.52
|
1.18
|
++
|
Proisotoma
|
454.57±1.91
|
9.53
|
++
|
99.17±3.28
|
3.38
|
++
|
553.74±6.58
|
7.19
|
++
|
Pygmephorus
|
|
|
|
535.25±6.11
|
18.24
|
+++
|
535.25±6.11
|
6.95
|
++
|
Sejidae
|
651.52±9.42
|
13.65
|
+++
|
|
|
|
651.52±9.42
|
8.45
|
++
|
Sminthurus
|
141.37±6.19
|
2.96
|
++
|
|
|
|
141.37±6.19
|
1.83
|
++
|
Staphylinidae
|
37.51±0.08
|
0.79
|
+
|
47.23±5.66
|
1.61
|
++
|
84.74±0.57
|
1.10
|
+
|
Tabanidae larva
|
53.38±5.62
|
1.12
|
++
|
65.83±0.69
|
2.24
|
++
|
119.21±6.55
|
1.55
|
++
|
Tenthredinidae
|
|
|
|
16.17±4.72
|
0.55
|
+
|
16.17±0.33
|
0.21
|
+
|
Trichoceratidae
|
|
|
|
99.17±3.41
|
3.38
|
++
|
99.17±3.41
|
1.29
|
++
|
Trombidiidae
|
499.37±5.53
|
10.47
|
+++
|
71.25±0.38
|
2.43
|
++
|
570.62±2.53
|
7.40
|
++
|
Tullbergia
|
|
|
|
316.54±8.19
|
10.79
|
+++
|
316.54±8.19
|
4.11
|
++
|
Uropodidae
|
178.81±0.18
|
3.75
|
++
|
|
|
|
178.81±0.18
|
2.32
|
++
|
Table 2. Composition of soil arthropod in Gannan section of Daxia River wetland. Note: A: abundance, +++: dominant groups (percentage of individual number>10 %), ++: common groups (1 %<percentage of individual number<10 %), +: rare groups (0.1 %<percentage of individual number<1 %).
Spatio and temporal variations of community composition
Distribution of soil arthropods between seasons. Figure 2, Supplementary Table S4, Supplementary Table S5 show that the soil arthropod communities showed significant differences among the habitats (P < 0.05) and between the seasons. In the cold season, Tumenguan of the habitat 6 had a greater abundance than the other habitats (P < 0.05), accounting for 41.39% of the total individuals. Sejidae and Trombidiidae were dominant groups in Tumenguan. Sangke of the habitat 1 had less arthropods than Tumenguan and more than other habitats, accounting for 21.55% of the total individuals. Chironomidae larva was the dominant group. In the warm season, Tumenguan also had a greater abundance than the other habitats (P < 0.05), accounting for 37.92% of the total individuals. Tullbergia was the dominant group. Sangke was nearly essentially equal Tumenguan, accounting for 37.83 % of the total individuals. Chironomidae larva and Onychiurus were dominant groups. Quao of the habitat 5 had less arthropods than Sangke and more than other habitats, accounting for 12.32% of the total individuals. Pygmephorus was the dominant group. In whole year, Chironomidae larva was the only dominate group. Tumenguan and Sangke had a greater abundance than the other habitats, accounting for 30.00% and 29.49% of the total individuals.
Fig. 2 c, d, Supplementary Table S4, Supplementary Table S5 show that distribution differences exist in the groups among the habitats and seasons. In the cold season, Quao had a greater abundance than the other habitats (P < 0.05), accounting for 59.38% of the total groups. The arthropods in Sangke and Tumenguan accounted for 56.25% and 46.88% of the total groups, respectively. In the warm season, Sangke had a greater abundance than the other habitats (P<0.05), accounting for 65.63% of the total groups. The arthropods in Quao and Tumenguan accounted for 62.50% and 56.25% of the total groups, respectively.
Distribution of soil arthropod between soil layers. Figure 2 shows that the warm season had a higher abundance than the cold season in the 0–10 cm soil layer (P < 0.05), accounting for 87.55% of the total individuals. The cold season had a higher abundance than the warm season in the 10–20 cm soil layer (P < 0.05) (Fig. 2), accounting for 82.44% of the total individuals. In cold season the number of individuals in the 0~10 cm soil layer was less than in 10–20 cm soil layer, accounting for 12.45% of the total individuals. In the 0–10 cm soil layer Chironomidae larva and Sejidae were the dominant groups. Nine groups were common, i.e., Arrhopalites, Ceratopgonidae larva, Chironomidae, Cryptopygus, Entomobrya, Isotomiella, Onychiurus, Phlaeothripidae larva, Sminthurus. In the 10–20 cm soil layer Doilchopodidae larva, Isotoma, Proisotoma were the dominant groups. Eleven groups were common, i.e., Arrhopalites, Entomobrya, Oribatella, Phlaeothripidae larva, Pygmephorus, Sejidae, Sminthurus, Tabanidae larva, Trombidiidae, Tullbergia, Uropodidae. In general, in the cold season the dominant groups increased as the soil layer deepened.
However, in the warm season the number of individuals in the 0–10 cm soil layer was more than 10–20 cm soil layer, accounting for 94.83% of the total individuals. Chironomidae larva, Doilchopodidae larva, Pygmephorus, Trombidiidae were the dominant groups in the 0–10 cm soil layer. Fifteen groups were common, i.e., Arrhopalites, Cecidomyidae larva, Ceratopgonidae larva, Cryptopygus, Entomobrya, Ephydridae, Isotoma, Oribatella, Proisotoma, Phlaeothripidae larva, Sejidae, Staphylinidae larva, Tenthredinidae, Trichoceratidae larva, Tullbergia. In the 10–20 cm soil layer Limoniidae larva, Tabanidae larva, Trichoceratidae larva were the dominant groups. Nine groups were common, i.e., Chironomidae, Cryptopygus, Isotomiella, Isotoma, Onychiurus, Proisotoma, Sminthurus, Trichoceratidae larva, Tullbergia.
Spatio-temporal variations of the community abundance and diversity. Figure 2 shows that the community abundance and diversity varied among the habitats and sampling seasons. Figure 3 shows that the Shannon index, Pielou index and Simple index were sensitive to the sampling seasons (P < 0.01). The multiple-comparison tests showed that the abundance (Table 2) responded significantly to habitats variation in cold season and warm season. The richness (Table 2) , Shannon index, Pielou index and Simple index varied significantly among habitats in cold season and warm season (Fig. 3). The temporal variations in the community abundance and richness were sensitive to the sampling period in all six habitats.
The relationship between soil arthropod community and environmental factors. Table 3 shows that the impacts of each soil physical and chemical factors are estimated by RDA. The importance of ST, WC, pH, TN, TP and SOC all exceed 0.21 and all pass the test of P < 0.005. Altitude (Al) is significant but less important (Table 3), so this variable is removed. Figure 4 shows that the RDA analysis results of ST, WC, pH, TN, TP and SOC variables were retained. Table 4 shows the correlation coefficient between the first two axes of RDA ranking and soil physical and chemical factors, indicating that the ranking axis reflects most of the information about the relationship between soil physical and chemical factors and soil arthropod community.
|
ST
|
WC
|
pH
|
TN
|
TP
|
SOC
|
Al
|
Importance factor
|
0.36
|
0.31
|
0.33
|
0.27
|
0.28
|
0.21
|
0.07
|
Significance level
|
0.003
|
0.002
|
0.004
|
0.003
|
0.003
|
0.003
|
0.003
|
Table 3. Importance and significance level of each variable. Note: ST: Soil temperature; WC: Water content; TN: Total nitrogen; TP: Total phosphorus; SOC: Soil organic carbon; Al: Altitude.
RDA sequencing described the correlation between the number of individuals and groups of arthropods in different soil layers and the main physicochemical factors of soil in cold season and warm season (Fig. 4). Figure 4 (a) explains the change of arthropod community in 0–10 cm soil layer in the cold season. It can be seen from the figure that the three factors (WC, TP and ST), have the greatest impact on the structural characteristics of soil arthropod community (Table 4). In general, WC, TP, ST and pH were positively correlated with the number of arthropod groups, while TN and SOC were positively correlated with the number of arthropod individuals. Figure 4 (b) explains the changes of arthropod community in the 10–20 cm soil layer in the cold season. TP, TN and pH have the greatest impact on the structural characteristics of the arthropod community(Table 4). In general, TP, WC, SOC and ST were positively correlated with the number of arthropod groups, while TN and pH were positively correlated with the number of arthropod individuals. Figure 4 (c) explains the change of arthropod community in 0–10 cm soil layer in warm season. ST, WC and TP have the greatest impact on the structural characteristics of soil arthropod community (Table 4). In general, ST, TN, SOC and pH were positively correlated with the number of arthropod groups, while WC and TP were positively correlated with the number of arthropod individuals. Figure 4 (d) explains the changes of arthropod community in the 10–20 cm soil layer in warm season. TN, SOC and pH have the greatest impact on the structural characteristics of soil arthropod community (Table 4). In general, TN, SOC and TP were positively correlated with the number of arthropod groups, while pH, ST and WC were positively correlated with the number of arthropod individuals. Thus, the RDA sequence diagram can directly reflect the impact of soil physical and chemical factors on the seasonal change of soil arthropod community and the degree of impact.
factors
|
Cold season
|
Warm season
|
0-10 cm
|
10-20 cm
|
0-10 cm
|
10-20 cm
|
R
|
1st axis
|
2nd axis
|
R
|
1st axis
|
2nd axis
|
R
|
1st axis
|
2nd axis
|
R
|
1st axis
|
2nd axis
|
ST
|
0.493
|
0.258
|
0.339
|
0.308
|
0.062
|
0.009
|
0.483
|
-0.382
|
0.191
|
0.300
|
0.348
|
-0.191
|
WC
|
0.551
|
0.537
|
0.001
|
0.466
|
0.104
|
0.231
|
0.304
|
0.317
|
0.267
|
0.285
|
0.136
|
-0.083
|
pH
|
0.036
|
0.175
|
0.280
|
0.263
|
-0.226
|
-0.194
|
0.316
|
-0.114
|
0.142
|
0.321
|
0.419
|
-0.351
|
TN
|
0.157
|
-0.268
|
0.315
|
0.271
|
-0.319
|
0.204
|
0.412
|
-0.286
|
-0.319
|
0.527
|
-0.508
|
0.262
|
TP
|
0.100
|
0.308
|
-0.100
|
0.519
|
0.436
|
-0.183
|
0.298
|
0.290
|
-0.325
|
0.381
|
-0.094
|
0.262
|
SOC
|
0.082
|
-0.296
|
-0.201
|
0.310
|
0.113
|
-0.098
|
0.390
|
-0.238
|
-0.261
|
0.499
|
-2.105
|
-0.026
|
Table 4. Correlation coefficients of first two RDA axes and physical and chemical factors of soil. Note:ST: Soil temperature; WC: Water content; TN: Total nitrogen; TP: Total phosphorus; SOC: Soil organic carbon; R: resolution.