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Dryad

Foliar phosphorus concentration modulates the defensive mutualism of an endophytic fungus in a perennial host grass

Cite this dataset

Decunta, Facundo; Perez, Luis; Graff, Pamela; Gundel, Pedro (2024). Foliar phosphorus concentration modulates the defensive mutualism of an endophytic fungus in a perennial host grass [Dataset]. Dryad. https://doi.org/10.5061/dryad.c2fqz61jd

Abstract

Grasses hosting Epichloë endophytes are protected against herbivores due to the production of various fungal alkaloids. Previous research has found that high foliar phosphorus concentrations reduce the level of the alkaloid ergovaline, thereby reducing the endophyte-mediated herbivore resistance. Yet, the impact of phosphorus on ergovaline biosynthesis versus its influence on endophyte growth and synthesis of other fungal alkaloids remains unresolved. Our objective was to elucidate these relationships. We grew endophyte-symbiotic and non-symbiotic Festuca arundinacea plants and fertilized them with different doses of phosphorus. Later, half of the plants from each treatment were challenged with larvae of the generalist chewing insect Spodoptera frugiperda. We assessed the relationships between foliar phosphorus levels, fungal mycelium, and alkaloid concentrations, as well as their impacts on larvae performance, herbivore-caused damage, and plant biomass. Endophyte mycelial biomass in plant tissue was found to be independent of foliar phosphorus concentration. The alkaloids lolines and peramine showed a linear relationship with mycelial biomass but no correlation with foliar phosphorus. Surprisingly, high ergovaline concentrations were positively associated with an interaction between endophyte mycelial biomass and foliar phosphorus concentration. Although herbivory increased loline concentration, only high concentrations of ergovaline and peramine were related to reduced S. frugiperda larvae weight gain. However, endophyte presence did not reduce herbivory damage to plants. Contrary to expectation, we did not find a negative but a positive association between concentrations of foliar phosphorus and ergovaline alkaloid, through its interaction with endophyte mycelial biomass. Alternatively, our findings suggest that phosphorus plays a crucial role in modulating the Epichloë-mediated defensive mutualism, primarily through its effects on ergovaline rather than on endophyte concentration or production of other alkaloids.

README: Foliar phosphorus concentration modulates the defensive mutualism of an endophytic fungus in a perennial host grass

https://doi.org/10.5061/dryad.c2fqz61jd

We conducted an experiment to study how phosphorus fertilization modulates the production of anti-herbivory alkaloids in grasses associated with Epichloë endophytes. We used Lolium arundinaceum plants, either associated with the fungal endophyte Epichloë coenophiala or not. The plants were treated with four different levels of phosphorus fertilization (no fertilization, low, medium, and high) and exposed half of the plants to larvae of the insect herbivore Spodoptera frugiperda.

This repository contains the data produced by this experiment.

Description of the data

The data is contained in a single CSV file. Each column represents a factor or a variable, and each row contains data from an individual plant.

Experimental factors

  • endo: Epichloë endophyte presence (E+) or absence (E-)
  • trat: Phosphorus fertilization treatment (Control: no fertilization; T1: low; T2: medium; T3: high)
  • herb: Herbivory by Spodoptera frugiperda (H+, herbivore presence; H-, herbivore absence)

Response variables

  • aboveground_biomass: Plant aboveground biomass (g)
  • C_foliar_percentage: Carbon concentration in foliar tissues (%)
  • N_foliar_percentage: Nitrogen concentration in foliar tissues (%)
  • P_foliar_ppm: Phosphorus concentration in foliar tissues (ppm)
  • C_N_ratio: Carbon-to-nitrogen ratio in foliar tissues
  • N_P_ratio: Nitrogen-to-phosphorus ratio in foliar tissues
  • Mycelial_mass: Epichloë endophyte mycelial biomass in foliar tissues
  • Ergovaline_ppm: Ergovaline concentration in foliar tissues (ppm)
  • Peramine_ppm: Peramine concentration in foliar tissues (ppm)
  • TotalLolines_ppm: Lolines concentration in foliar tissues (ppm)
  • spodoptera_weight_gain: Mean weight gained by Spodoptera frugiperda (%)
  • herbivory_index: Herbivory index to estimate the damage caused by herbivores to plants (see the Methods section for more detail)

Methods

Herbivory index

We used an herbivory index to estimate the damage caused by herbivores to plants (Boege & Dirzo, 2004; Salgado-Luarte et al., 2023). Plants not exposed to herbivores were not included in this calculation as they did not show signs of damage (personal observation). For each estimation, five leaves were randomly selected and photographed. Then, the damaged area was estimated using the software ImageJ (Abràmoff et al., 2004). As in Boege & Dirzo (2004), each leaf was scored according to the level of damage: 0 = no damage, 1 = 1-6% damage, 2 = 6-12% damage, 3 = 12-25% damage, 4 = 25-50% damage, and 5 = more than 75% of damage. These categories were selected because low levels of damage were most frequent and high levels of damage were less common. Thus, categories with narrower ranges were needed in the lower part of the range to capture differences in plant damage (Boege & Dirzo, 2004). Adapted from Boege and Dirzo (2004), the herbivory index for each plant was calculated as: Herbivory index = d/N ⨯ ∑ ni ⨯ Ci, where d is the number of leaves with damage, N the total number of evaluated leaves, i is the ith damage score, ni the number of leaves with the ith damage score, Ci is the midpoint of the ith damage score (i.e., C0 = 0, C1 = 3.5, C2 = 9.0, C3 = 18.5, C4 = 37.5, and C5 = 87.5).

References
  • Abràmoff, M. D., Magalhães, P. J., & Ram, S. J. (2004). Image processing with ImageJ. Biophotonics International, 11(7), 36-42.

  • Boege, K., & Dirzo, R. (2004). Intraspecific variation in growth, defense and herbivory in Dialium guianense (Caesalpiniaceae) mediated by edaphic heterogeneity. Plant Ecology, 175(1), 59-69. https://doi.org/10.1023/B:VEGE.0000048092.82296.9a

  • Salgado‐Luarte, C., González‐Teuber, M., Madriaza, K., & Gianoli, E. (2023). Trade‐off between plant resistance and tolerance to herbivory: Mechanical defenses outweigh chemical defenses. Ecology, 104(1): e3860. https://doi.org/10.1002/ecy.3860

Funding

APNCyT , Award: PICT 2019-02304

University of Buenos Aires, Award: UBACYT 20020130100423BA