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Conditions Promoting Mycorrhizal Parasitism Are of Minor Importance for Competitive Interactions in Two Differentially Mycotrophic Species

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ABSTRACT

Interactions of plants with arbuscular mycorrhizal fungi (AMF) may range along a broad continuum from strong mutualism to parasitism, with mycorrhizal benefits received by the plant being determined by climatic and edaphic conditions affecting the balance between carbon costs vs. nutritional benefits. Thus, environmental conditions promoting either parasitism or mutualism can influence the mycorrhizal growth dependency (MGD) of a plant and in consequence may play an important role in plant-plant interactions. In a multifactorial field experiment we aimed at disentangling the effects of environmental and edaphic conditions, namely the availability of light, phosphorus and nitrogen, and the implications for competitive interactions between Hieracium pilosella and Corynephorus canescens for the outcome of the AMF symbiosis. Both species were planted in single, intraspecific and interspecific combinations using a target-neighbor approach with six treatments distributed along a gradient simulating conditions for the interaction between plants and AMF ranking from mutualistic to parasitic. Across all treatments we found mycorrhizal association of H. pilosella being consistently mutualistic, while pronounced parasitism was observed in C. canescens, indicating that environmental and edaphic conditions did not markedly affect the cost:benefit ratio of the mycorrhizal symbiosis in both species. Competitive interactions between both species were strongly affected by AMF, with the impact of AMF on competition being modulated by colonization. Biomass in both species was lowest when grown in interspecific competition, with colonization being increased in the less mycotrophic C. canescens, while decreased in the obligate mycotrophic H. pilosella. Although parasitism-promoting conditions negatively affected MGD in C. canescens, these effects were small as compared to growth decreases related to increased colonization levels in this species. Thus, the lack of plant control over mycorrhizal colonization was identified as a possible key factor for the outcome of competition, while environmental and edaphic conditions affecting the mutualism-parasitism continuum appeared to be of minor importance.

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Relative neighbor effect (RNE) in mycorrhizal (A) and non-mycorrhizal (B) plants of Hieracium pilosella (HP, white) and Corynephorus canescens (CC, gray) in intraspecific (intra, open bars) and interspecific (inter, dotted bars) competition under conditions along a theoretical scale of mycorrhizal parasitism potential (parasitism scale) with I standing for hypothesized strong mutualism to V standing for hypothesized parasitism. Although, the parasitism scale can only be applied to mycorrhizal plants, the results for non-mycorrhizal plants were arranged in the same way for reasons of clarity. For calculation of RNE please see Materials and Methods Section. Different letters indicate significant differences at P = 0.05 (ANOVA). Means ± s.e., n = 5.
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Figure 2: Relative neighbor effect (RNE) in mycorrhizal (A) and non-mycorrhizal (B) plants of Hieracium pilosella (HP, white) and Corynephorus canescens (CC, gray) in intraspecific (intra, open bars) and interspecific (inter, dotted bars) competition under conditions along a theoretical scale of mycorrhizal parasitism potential (parasitism scale) with I standing for hypothesized strong mutualism to V standing for hypothesized parasitism. Although, the parasitism scale can only be applied to mycorrhizal plants, the results for non-mycorrhizal plants were arranged in the same way for reasons of clarity. For calculation of RNE please see Materials and Methods Section. Different letters indicate significant differences at P = 0.05 (ANOVA). Means ± s.e., n = 5.

Mentions: Biomass in AM C. canescens in the interspecific competition treatment decreased with increasing parasitism potential from 3.82 to 0.29 mg (Supplementary Table S1) as indicated by score distribution on the first and second component of the PLS (Figure 1A). Consequently, plant N and plant P showed the same trend. In the NM treatments, this trend was less pronounced (Figure 1B). X-loadings in the PLS plots showed that AM plants in intraspecific competition exhibited least biomass (Figure 1A), with reductions of ~68%, respectively, 71% compared to plants in interspecific competition and single plants (Supplementary Table S1). Hence, AM plants in intraspecific competition had significantly higher RNE (0.52–0.88; p < 0.05) than plants in interspecific competition (−0.19 to 0.68), except from shaded plants with high parasitism potential, where RNE values were similar in both intra- and interspecific competition treatments (Figure 2A). Competition and single treatments were significant predictors for biomass (Table 1). Biomass, plant P, and plant N in NM C. canescens were highest in interspecific competition (~5.06 g, ~11.84 mg, ~91.78 mg) and lowest in intraspecific competition (~0.81 g, ~1.51 mg, ~11.13 mg; Supplementary Table S1), indicated by opposite X-loadings (Figure 1B). Component 1 explained 48.1% of Y-variance (Table 2). Both interspecific and intraspecific competition were significant predictors for biomass, plant P and plant N (Table 1). Similar to the AM plants, NM plants in intraspecific competition had significantly higher RNE (0.70–0.92; p < 0.05) than plants in interspecific competition (−0.26 to 0.49; Figure 2B).


Conditions Promoting Mycorrhizal Parasitism Are of Minor Importance for Competitive Interactions in Two Differentially Mycotrophic Species
Relative neighbor effect (RNE) in mycorrhizal (A) and non-mycorrhizal (B) plants of Hieracium pilosella (HP, white) and Corynephorus canescens (CC, gray) in intraspecific (intra, open bars) and interspecific (inter, dotted bars) competition under conditions along a theoretical scale of mycorrhizal parasitism potential (parasitism scale) with I standing for hypothesized strong mutualism to V standing for hypothesized parasitism. Although, the parasitism scale can only be applied to mycorrhizal plants, the results for non-mycorrhizal plants were arranged in the same way for reasons of clarity. For calculation of RNE please see Materials and Methods Section. Different letters indicate significant differences at P = 0.05 (ANOVA). Means ± s.e., n = 5.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5037182&req=5

Figure 2: Relative neighbor effect (RNE) in mycorrhizal (A) and non-mycorrhizal (B) plants of Hieracium pilosella (HP, white) and Corynephorus canescens (CC, gray) in intraspecific (intra, open bars) and interspecific (inter, dotted bars) competition under conditions along a theoretical scale of mycorrhizal parasitism potential (parasitism scale) with I standing for hypothesized strong mutualism to V standing for hypothesized parasitism. Although, the parasitism scale can only be applied to mycorrhizal plants, the results for non-mycorrhizal plants were arranged in the same way for reasons of clarity. For calculation of RNE please see Materials and Methods Section. Different letters indicate significant differences at P = 0.05 (ANOVA). Means ± s.e., n = 5.
Mentions: Biomass in AM C. canescens in the interspecific competition treatment decreased with increasing parasitism potential from 3.82 to 0.29 mg (Supplementary Table S1) as indicated by score distribution on the first and second component of the PLS (Figure 1A). Consequently, plant N and plant P showed the same trend. In the NM treatments, this trend was less pronounced (Figure 1B). X-loadings in the PLS plots showed that AM plants in intraspecific competition exhibited least biomass (Figure 1A), with reductions of ~68%, respectively, 71% compared to plants in interspecific competition and single plants (Supplementary Table S1). Hence, AM plants in intraspecific competition had significantly higher RNE (0.52–0.88; p < 0.05) than plants in interspecific competition (−0.19 to 0.68), except from shaded plants with high parasitism potential, where RNE values were similar in both intra- and interspecific competition treatments (Figure 2A). Competition and single treatments were significant predictors for biomass (Table 1). Biomass, plant P, and plant N in NM C. canescens were highest in interspecific competition (~5.06 g, ~11.84 mg, ~91.78 mg) and lowest in intraspecific competition (~0.81 g, ~1.51 mg, ~11.13 mg; Supplementary Table S1), indicated by opposite X-loadings (Figure 1B). Component 1 explained 48.1% of Y-variance (Table 2). Both interspecific and intraspecific competition were significant predictors for biomass, plant P and plant N (Table 1). Similar to the AM plants, NM plants in intraspecific competition had significantly higher RNE (0.70–0.92; p < 0.05) than plants in interspecific competition (−0.26 to 0.49; Figure 2B).

View Article: PubMed Central - PubMed

ABSTRACT

Interactions of plants with arbuscular mycorrhizal fungi (AMF) may range along a broad continuum from strong mutualism to parasitism, with mycorrhizal benefits received by the plant being determined by climatic and edaphic conditions affecting the balance between carbon costs vs. nutritional benefits. Thus, environmental conditions promoting either parasitism or mutualism can influence the mycorrhizal growth dependency (MGD) of a plant and in consequence may play an important role in plant-plant interactions. In a multifactorial field experiment we aimed at disentangling the effects of environmental and edaphic conditions, namely the availability of light, phosphorus and nitrogen, and the implications for competitive interactions between Hieracium pilosella and Corynephorus canescens for the outcome of the AMF symbiosis. Both species were planted in single, intraspecific and interspecific combinations using a target-neighbor approach with six treatments distributed along a gradient simulating conditions for the interaction between plants and AMF ranking from mutualistic to parasitic. Across all treatments we found mycorrhizal association of H. pilosella being consistently mutualistic, while pronounced parasitism was observed in C. canescens, indicating that environmental and edaphic conditions did not markedly affect the cost:benefit ratio of the mycorrhizal symbiosis in both species. Competitive interactions between both species were strongly affected by AMF, with the impact of AMF on competition being modulated by colonization. Biomass in both species was lowest when grown in interspecific competition, with colonization being increased in the less mycotrophic C. canescens, while decreased in the obligate mycotrophic H. pilosella. Although parasitism-promoting conditions negatively affected MGD in C. canescens, these effects were small as compared to growth decreases related to increased colonization levels in this species. Thus, the lack of plant control over mycorrhizal colonization was identified as a possible key factor for the outcome of competition, while environmental and edaphic conditions affecting the mutualism-parasitism continuum appeared to be of minor importance.

No MeSH data available.


Related in: MedlinePlus