Table 1.
The total biomasses (g) (means ± SE) and the results of paired-t test of Eisenia fetida and Metaphire guillelmi in each pot at the beginning and end of the experiment (n = 15, T-test).
Fig 1.
The aboveground and belowground biomasses (dry weight g) of winter wheat under two earthworm species (Eisenia fetida, Metaphire guillelmi), and the different density of Eisenia fetida and Metaphire guillelmi treatments.
+1E1, +2E1, and +4E1 represents added 1, 2, and 4 Eisenia fetida earthworm individuals, respectively; +1E2, +2E2, and +4E2 represents added 1, 2, and 4 Metaphire guillelmi earthworm individuals, respectively. Different uppercase letters indicate significant difference in different earthworm species. Different lowercase letters indicate significant difference in different density under each earthworm species, relative to the control treatments (replicates = 15).
Table 2.
The physical indices (Mean ± se) of two earthworm species including Eisenia fetida (105 individuals) and Metaphire guillelmi (105 individuals) at the end of the experiment.
Table 3.
Results of linear mixed models examining effects of earthworm species, the different earthworm density addition, and the nested density of earthworm species on soil physical and chemical properties.
Table 4.
Soil physical and chemical properties (means ± SE) under the different density Eisenia fetida and Metaphire guillelmi addition treatments (n = 15).
Fig 2.
The biomass of soil total microorganism (a), bacteria (b), fungi (c), gram-negative bacteria (d), gram-positive bacteria (e), actinomycetes (f), AMF (arbuscular mycorrhizal fungi) (g), and protozoa (h) under two earthworm species (Eisenia fetida, Metaphire guillelmi), and the different density of Eisenia fetida and Metaphire guillelmi treatments. C, control (no added earthworm); +1E1, +2E1, and +4E1 represents added 1, 2, and 4 Eisenia fetida earthworm individuals, respectively; +1E2, +2E2, and +4E2 represents added 1, 2, and 4 Metaphire guillelmi earthworm individuals, respectively. Different uppercase letters indicate significant difference in different earthworm species. Different lowercase letters indicate significant difference in different density under each earthworm species, relative to the control treatments (replicates = 15).
Table 5.
Results of linear mixed models examining effects of earthworm species, the different earthworm density addition, and the nested density of earthworm species on soil microorganism biomasses including total microorganism, bacteria, fungi, the ratio of gram-positive bacteria to gram-negative bacteria, gram-negative bacteria, gram-positive bacteria, the ratio of gram-positive to gram-negative bacteria, actinomycete, arbuscular mycorrhizal fungi (AMF), protozoa.
Fig 3.
Principle components analysis (PCA) of soil microbial and nematode communities under two earthworm species (Eisenia fetida, Metaphire guillelmi), and the different density of Eisenia fetida and Metaphire guillelmi treatments (Ba, bacterivores; Fu, fungivores; Pp, plant parasites; Om, omnivore-predators; Actinomy, actinomycetes; G+, gram-positive bacteria; G-, gram-negative bacteria; AMF, arbuscular mycorrhizal fungi).
+1E1, +2E1, and +4E1 represents added 1, 2, and 4 Eisenia fetida earthworm individuals, respectively; +1E2, +2E2, and +4E2 represents added 1, 2, and 4 Metaphire guillelmi earthworm individuals, respectively.
Fig 4.
The abundance of soil total nematode (a) and bacterivores (b), fungivores (c), plant parasites (d), and omnivore-predators (e) (individuals / 100 g dry soil weight) under two earthworm species (Eisenia fetida, Metaphire guillelmi), and the different density of Eisenia fetida and Metaphire guillelmi treatments. C, control (no added earthworm); +1E, +2E, and +4E represents added 1, 2, and 4 earthworm individuals, respectively. Different uppercase letters indicate significant difference in different earthworm species. Different lowercase letters indicate significant difference in different density under each earthworm species, relative to the control treatments (replicates = 15).
Table 6.
Results of linear mixed models examining the effects of earthworm species, the different earthworm density addition, and the nested density of earthworm species on soil nematode indexes.
Fig 5.
Redundancy analysis (RDA) showing the relationship between soil biota ((a) soil microbial community; (b) nematode community) and soil parameters. NH4+N, ammonium nitrogen; NO3-N, nitrate nitrogen; TP, total phosphorus; TN, total nitrogen; SOC, organic carbon; Availabl, available phosphorus. Actinomy, actinomycetes; G+, gram-positive bacteria; G-, gram-negative bacteria; AMF, arbuscular mycorrhizal fungi. Ba, bacterivores; Fu, fungivores; Pp, plant parasites; Om, omnivore-predators.
Fig 6.
Structural equation models showing the feeding relationship in the food web (soil microorganism, and soil nematode communities) in response to the addition of the different density earthworms (Eisenia fetida) (n = 60) (χ2 = 43.913, df = 56, P = 0.879, CFI = 1.000, GFI = 0.907, RMSEA = 0.000).
Numbers on arrows are standardized path coefficients. Solid arrows suggested the effects were significant (P < 0.05) and the thickness represents the magnitude of the path coefficients. Dashed arrows represent the effects were nonsignificant (P > 0.05). BG, the belowground biomasses of winter wheat.
Fig 7.
Structural equation models showing the feeding relationship in the food web (soil microorganism, and soil nematode communities) in response to the addition of the different density earthworms (Metaphire guillelmi) (n = 60) (χ2 = 55.998, df = 64, P = 0.919, CFI = 1.000, GFI = 0.889, RMSEA = 0.000).
Numbers on arrows are standardized path coefficients. Solid arrows suggested the effects were significant (P < 0.05) and the thickness represents the magnitude of the path coefficients. Dashed arrows represent the effects were nonsignificant (P > 0.05). BG, the belowground biomasses of winter wheat.