DOI: 10.5061/dryad.c2fqz61jd
title: Foliar phosphorus concentration modulates the defensive mutualism of an endophytic fungus in a perennial host grass

description: 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.
description: 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. <em>Biophotonics
 International</em>, 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
description: # Foliar phosphorus concentration modulates the defensive mutualism of an
 endophytic fungus in a perennial host grass
 [https://doi.org/10.5061/dryad.c2fqz61jd](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)