Vegetation types shape the soil micro-food web compositions and soil multifunctionality in Loess Plateau

Abstract

Introduction: Vegetation degradation and soil erosion are severe problems in the Loess hilly region, rendering it one of the most ecologically vulnerable areas in China and globally. Vegetation restoration has been recognized as an effective approach to amending the fragile ecological environment and restoring degraded ecosystems.

Methods: The effects of different vegetation types: Caragana korshinskii, Prunus armeniaca L., Pinus tabuliformis Carrière, Medicago sativa L., and the control vegetation Stipa bungeana on soil micro-food webs and soil multifunctionality, as well as their response mechanisms to soil environmental drivers, were investigated using High-throughput sequencing technology.

Results: C. korshinskii significantly enhanced soil physicochemical properties and soil enzyme activities by facilitating the stability of the soil micro-food web structure driven by soil bacteria and fungi and increasing the soil multifunctionality in contrast to S. bungeana. Prunus armeniaca also improved soil multifunctionality by promoting soil organic carbon and alkaline phosphatase activity. However, the stability of the soil micro-food web structure and soil multifunctionality were suboptimal in P. tabuliformis and M. sativa. Soil pH, along with carbon, nitrogen, and phosphorus cycling nutrients and enzymes, profoundly influences the structure of the soil micro-food web and soil multifunctionality; among these factors, those related to the carbon and phosphorus cycles are identified as key influencing factors.

Discussion: Therefore, a vegetation restoration strategy prioritizing C. korshinskii as the dominant vegetation type, supplemented by P. armeniaca, significantly impacts restoring soil multifunctionality and stabilizing the soil micro-food web in Loess hill regions and comparable ecological areas.

Keywords: Loess hilly area; multifunctionality; soil micro-food web; soil nematode; vegetation type.

FIGURE 1

Alpha (A–C) and beta (D–F) diversity and structure characteristics of soil microorganism and nematode communities under different vegetation types. Different lowercase letters indicate significant differences at P < 0.05 based on one-way ANOVA. AV, Prunus armeniaca L.; PT, Pinus tabuliformis Carrière; CK, Caragana korshinskii; MS, Medicago sativa L.; SB, Stipa bungeana. The horizontal and vertical coordinates denote the relative distances. (G–I) The relative abundance of soil microorganisms and nematode communities (greater than 1%) under different vegetation types. OP, omnivorous-predatory nematodes; PP, plant parasitic nematodes; FF, fungi-feeding nematodes. The asterisk (*) indicates a significant difference between treatments (P < 0.05). (J–L) Significance test analyses of the differences in dominant genera of soil microorganisms and nematode communities between different vegetation types based on one-way ANOVA analysis. *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001.

FIGURE 2

Correlation network diagram of the interaction intensity within the soil micro-food web under different vegetation types. The size of each node is proportionate to its centrality, and genera with higher centrality represent the keystone species of each network. The lines between nodes signify strong positive (yellow) or negative (dashed gray) interactions, and the thickness of the lines indicates the intensity of these correlations. (A–E) The interaction intensity among the top 50 most abundant bacterial, fungal, and nematode genera in the soil micro-food web under five distinct vegetation types. (F–J) The interaction intensity between bacteria, fungi, and nematodes with different feeding characteristics in the soil micro-food web under five distinct vegetation types. AV, Prunus armeniaca L.; PT, Pinus tabuliformis Carrière; CK, Caragana korshinskii; MS, Medicago sativa L.; SB, Stipa bungeana.

FIGURE 3

Path analysis model of the degradation pathway of the soil micro-food web under different vegetation types. Prunus armeniaca L. (AV), X² = 0.165, df = 3, p = 0.983, CFI = 1.000, GFI = 0.991, RMSEA = 0.000, NFI = 0.998, TLI = 1.147; Pinus tabuliformis Carrière (PT), X² = 0.294, df = 2, p = 0.863, CFI = 1.000, GFI = 0.977, RMSEA = 0.000, NFI = 0.996, TLI = 1.084; Caragana korshinskii (CK), X² = 3.845, df = 4, p = 0.427, CFI = 1.000, GFI = 0.852, RMSEA = 0.000, NFI = 0.965, TLI = 1.004;Medicago sativa L. (MS), X² = 0.388, df = 2, p = 0.824, CFI = 1.000, GFI = 0.970, RMSEA = 0.000, NFI = 0.992, TLI = 1.122;Stipa bungeana (SB), X² = 0.066, df = 2, p = 0.967, CFI = 1.000, GFI = 0.997, RMSEA = 0.000, NFI = 0.999, TLI = 1.192. The width of the arrows is proportional to the strength of the path coefficients. The red and blue arrows denote positive and negative relationships, respectively, while the solid and dashed lines represent significant and non-significant relationships. BFC, the carbon metabolic footprint of bacterial feeders; FFC, the carbon metabolic footprint of fungal feeders; OPC, the carbon metabolic footprint of omnivores-predators; SOC, soil organic carbon. **P ≤ 0.01, ***P ≤ 0.001.

FIGURE 4

Metabolic footprint, floristic analysis, food web energy flow analysis, and functional structure index of soil nematodes under diverse vegetation types. (A) Metabolic footprint; (B) flora analysis; (C) food web energy flow analysis; (D–F) functional structural indices. AV, Prunus armeniaca L.; PT, Pinus tabuliformis Carrière; CK, Caragana korshinskii; MS, Medicago sativa L.; SB, Stipa bungeana. BFMF, The metabolic footprint of bacterial feeders; FFMF, The metabolic footprint of fungal feeders; PPMF, The metabolic footprint of plant-parasites; OPMF, The metabolic footprint of omnivores-predators; TNMF, The metabolic footprint of total nematodes. PPI, plant-parasitic nematode maturity index; MI, maturity index. Different lowercase letters indicate significant differences at P < 0.05 based on one-way ANOVA.

FIGURE 5

Factors influencing soil microorganisms and nematode communities. (A) The Mantel test disclosing the correlations between soil microorganisms and nematode communities, soil physicochemical properties, and soil enzymes. (B–E) Random Forest analysis exploring the explanatory factors of plant-parasitic and omnivores-predatory nematodes, bacteria, and fungi. Significance levels were indicated by *P < 0.05, **P < 0.01. (F–H) Redundancy analysis of the soil nematode, bacterial, and fungal community concerning environmental factors. SM, EC, SOC, AP, AK, TP, TN, NO₃^–-N, NH₄⁺-N, C/N, βGC, SC, UE, PPO, and ALP, respectively, correspond to soil moisture, electric conductivity, soil organic carbon, available phosphorus, available potassium, total phosphorus, total nitrogen, nitrate nitrogen, ammonium nitrogen, the ratio of carbon to nitrogen, β-1, 4-glucosidase, sucrase, urease, polyphenol oxidase and alkaline phosphatases.

FIGURE 6

Factors influencing soil multifunctionality. (A) Alterations of soil multifunctionality across diverse vegetation types. Lowercase letters denote significant differences among treatments at p < 0.05. (B) Random forest analysis exploring the explanatory factors of soil multifunctionality. AV, Prunus armeniaca L.; PT, Pinus tabuliformis Carrière; CK, Caragana korshinskii; MS, Medicago sativa L.; SB, Stipa bungeana. βGC, UE, SOC, TN, EC, AK, SC, TP, ALP, NO₃^–-N, PPO, AP, C/N, NH₄⁺-N, and SM, respectively correspond to β-1, 4-glucosidase, urease, soil organic carbon, total nitrogen, electric conductivity, available potassium, sucrase, total phosphorus, alkaline phosphatases, nitrate nitrogen, polyphenol oxidase, available phosphorus, the ratio of carbon to nitrogen, ammonium nitrogen and soil moisture. (C) The structural equation model depicting the connections among soil physicochemical factors, microorganisms, and nematode communities, as well as enzymatic properties (X² = 4.461, df = 12, P = 0.974, CFI = 1.000, GFI = 1.000, RMSEA = 0.000, NFI = 0.999, TLI = 1.125). Positive and negative paths are marked with red and blue arrows, respectively. In contrast, significant (marked by *P < 0.05, **P < 0.01, ***P < 0.001) and non-significant links were represented by solid and dashed arrows, respectively. The width of the lines represents the standardized regression weights. R² values adjacent to the variables indicate the proportion of variance explained by the other variables. (D) Standardized total effects of soil physicochemical properties and the activity of enzymes associated with C, N, and P cycling derived from the model. C nutrients, P nutrients, N nutrients, C enzymes, N enzymes, and P enzymes correspond to carbon cycling nutrients, phosphorus cycling nutrients, nitrogen cycling nutrients, nitrogen cycling enzymes, and phosphorus cycling enzymes.

FIGURE 7

The contribution of arbor, shrub, and grassland types to the structural stability of the soil micro-food web and soil multifunctionality.