Invasive and Native Plants Differentially Respond to Exogenous Phosphorus Addition in Root Growth and Nutrition Regulated by Arbuscular Mycorrhizal Fungi

Abstract

Plant invasion has severely damaged ecosystem stability and species diversity worldwide. The cooperation between arbuscular mycorrhizal fungi (AMF) and plant roots is often affected by changes in the external environment. Exogenous phosphorus (P) addition can alter the root absorption of soil resources, thus regulating the root growth and development of exotic and native plants. However, it remains unclear how exogenous P addition regulates the root growth and development of exotic and native plants mediated by AMF, affecting the exotic plant invasion. In this experiment, the invasive plant Eupatorium adenophorum and native plant Eupatorium lindleyanum were selected and cultured under intraspecific (Intra-) competition and interspecific (Inter-) competition conditions, involving inoculation with (M⁺) and without AMF (M^-) and three different levels of P addition including no addition (P₀), addition with 15 mg P kg^-1 soil (P₁₅), and addition with 25 mg P kg^-1 soil (P₂₅) for the two species. Root traits of the two species were analyzed to study the response of the two species' roots to AMF inoculation and P addition. The results showed that AMF significantly promoted the root biomass, length, surface area, volume, tips, branching points, and carbon (C), nitrogen (N), and P accumulation of the two species. Under M⁺ treatment, the Inter- competition decreased the root growth and nutrient accumulation of invasive E. adenophorum but increased the root growth and nutrient accumulation of native E. lindleyanum relative to the Intra- competition. Meanwhile, the exotic and native plants responded differently to P addition, exhibiting root growth and nutrient accumulation of invasive E. adenophorum increased with P addition, whereas native E. lindleyanum reduced with P addition. Further, the root growth and nutrition accumulation of native E. lindleyanum were higher than invasive E. adenophorum under Inter- competition. In conclusion, exogenous P addition promoted the invasive plant but reduced the native plant in root growth and nutrient accumulation regulated by AMF, although the native plant outcompeted the invasive plant when the two species competed. The findings provide a critical perspective that the anthropogenic P fertilizer addition might potentially contribute to the successful invasion of exotic plants.

Keywords: arbuscular mycorrhizal fungi; competition; phosphorus addition; plant invasion; root trait.

Figure 1

The root mycorrhizal colonization of alien plant E. adenophorum and indigenous plant E. lindleyanum. The subgraph (a,b) indicate the root mycorrhizal colonization of alien plant E. adenophorum and indigenous plant E. lindleyanum, respectively. Abbreviations: Intra- = intraspecific, Inter- = interspecific; P₀ = without P addition of 0 mg·kg⁻¹, P₁₅ = with P addition of 15 mg·kg⁻¹, P₂₅ = with P addition of 25 mg·kg⁻¹. Different Greek letters (α, β) above the bars indicate significant differences between Intra- and Inter- treatments; different lowercase letters (a, b) above the bars indicate significant differences between P₀, P_15, and P₂₅ treatments (p < 0.05). Note: As the uninoculated plant roots were observed to be colonized by AMF, meaning that the root mycorrhizal colonization under the M⁻ treatment was considered to be zero, we only show the root mycorrhizal colonization under AMF inoculation in the figure.

Figure 2

The root biomass of alien plant E. adenophorum and indigenous plant E. lindleyanum. The subgraph (a,b) indicate the root biomass of alien plant E. adenophorum and indigenous plant E. lindleyanum, respectively. Abbreviations: M⁺ = with AMF; M⁻ = without AMF; Intra- = intraspecific, Inter- = interspecific; P₀ = without P addition of 0 mg·kg⁻¹, P₁₅ = with P addition of 15 mg·kg⁻¹, P₂₅ = with P addition of 25 mg·kg⁻¹. Different capital letters (X, Y) above the bars indicate significant differences between M⁺ and M⁻ treatments; different Greek letters (α, β) above the bars indicate significant differences between Intra- and Inter- treatments; different lowercase letters (a–c) above the bars indicate significant differences between P₀, P₁₅, and P₂₅ treatments (p < 0.05).

Figure 3

The root traits of alien plant E. adenophorum. The subgraph (a–f) indicate the root length, root surface, root volume, root average diameter, root tips, root branching points of alien plant E. adenophorum, respectively. Abbreviations: M⁺ = with AMF; M⁻ = without AMF; Intra- = intraspecific, Inter- = interspecific; P₀ = without P addition of 0 mg·kg⁻¹, P₁₅ = with P addition of 15 mg·kg⁻¹, P₂₅ = with P addition of 25 mg·kg⁻¹. Different capital letters (X, Y) above the bars indicate significant differences between M⁺ and M⁻ treatments; different Greek letters (α, β) above the bars indicate significant differences between Intra- and Inter- treatments; different lowercase letters (a–c) above the bars indicate significant differences between P₀, P₁₅, and P₂₅ treatments (p < 0.05).

Figure 4

The root traits of the indigenous plant E. lindleyanum. The subgraph (a–f) indicate the root length, root surface, root volume, root average diameter, root tips, root branching points of indigenous plant E. lindleyanum, respectively. Abbreviations: M⁺ = with AMF; M⁻ = without AMF; Intra- = intraspecific, Inter- = interspecific; P₀ = without P addition of 0 mg·kg⁻¹, P₁₅ = with P addition of 15 mg·kg⁻¹, P₂₅ = with P addition of 25 mg·kg⁻¹. Different capital letters (X, Y) above the bars indicate significant differences between M⁺ and M⁻ treatments; different Greek letters (α, β) above the bars indicate significant differences between Intra- and Inter- treatments; different lowercase letters (a–c) above the bars indicate significant differences between P₀, P₁₅, and P₂₅ treatments (p < 0.05).

Figure 5

The specific root traits of alien plant E. adenophorum and indigenous plant E. lindleyanum. The subgraph (a–c) indicate the specific root length, specific root area, root tissue density of alien plant E. adenophorum and subgraph (d–f) indicate the specific root length, specific root area, root tissue density of indigenous plant E. lindleyanum, respectively. Abbreviations: M⁺ = with AMF; M⁻ = without AMF; Intra- = intraspecific, Inter- = interspecific; P₀ = without P addition of 0 mg·kg⁻¹, P₁₅ = with P addition of 15 mg·kg⁻¹, P₂₅ = with P addition of 25 mg·kg⁻¹. Different capital letters (X, Y) above the bars indicate significant differences between M⁺ and M⁻ treatments; different Greek letters (α, β) above the bars indicate significant differences between Intra- and Inter- treatments; different lowercase letters (a, b) above the bars indicate significant differences between P₀, P₁₅, and P₂₅ treatments (p < 0.05).

Figure 6

The root C, N, P accumulation of alien plant E. adenophorum and indigenous plant E. lindleyanum. The subgraph (a–c) indicate the root C, N, P accumulation of alien plant E. adenophorum and subgraph (d–f) indicate the root C, N, P accumulation of indigenous plant E. lindleyanum, respectively. Abbreviations: M⁺ = with AMF; M⁻ = without AMF; Intra- = intraspecific, Inter- = interspecific; P₀ = without P addition of 0 mg·kg⁻¹, P₁₅ = with P addition of 15 mg·kg⁻¹, P₂₅ = with P addition of 25 mg·kg⁻¹. Different capital letters (X, Y) above the bars indicate significant differences between M⁺ and M⁻ treatments; different Greek letters (α, β) above the bars indicate significant differences between Intra- and Inter- treatments; different lowercase letters (a–c) above the bars indicate significant differences between P₀, P₁₅, and P₂₅ treatments (p < 0.05).