Peloton density shows species-specific associations with plant condition and reproduction in three co-occurring epiphytic orchids

This Zenodo deposit contains the field data and analysis code for a study of peloton density and reproduction in three co-occurring epiphytic orchids in central Puerto Rico. The associated manuscript (Tremblay et al.) is being prepared for submission to Annals of Botany; this record will be updated with the article DOI once available.

Background and Aims. Orchid roots commonly harbour intracellular fungal coils (pelotons), yet the functional significance of peloton density in adult epiphytic plants remains poorly resolved, and it is unclear whether peloton density provides a consistent indicator of mycorrhizal benefit across species or environmental contexts. We examined whether peloton density covaries with plant condition, reproductive allocation and microhabitat variables in three co-occurring epiphytic orchids that differ in morphology and photosynthetic strategy.

Methods. Adult plants of Campylocentrum fasciola (leafless), Ionopsis satyrioides (small, leafy) and I. utricularioides(larger, leafy) were sampled in a coffee–orange agroforestry system in Puerto Rico (n = 100 per species). Peloton density was quantified microscopically from cortical cells in actively growing root tips. Plant size, reproductive output (flowers, fruits, floral scars) and canopy closure were recorded in situ. Associations were modelled within a fully Bayesian hierarchical framework using beta regression for peloton proportions and negative binomial regression for reproductive counts, with weakly informative priors and within-species centering.

Key Results. Associations between peloton density and reproductive allocation varied markedly among species, both in direction and magnitude. Two species showed a directional tendency toward reduced reproductive allocation at higher peloton densities, whereas in the third species peloton density covaried positively with both reproductive allocation and canopy closure, a convergent pattern consistent with greater reliance on fungal-derived resources under reduced light. Relationships with light environment were similarly species-specific. In one species, peloton density was largely unrelated to plant size, reproduction or microhabitat.

Conclusions. Peloton density does not have a uniform functional meaning in adult epiphytic orchids and should not be interpreted as a general proxy for mycorrhizal benefit. It instead reflects context-dependent associations shaped by species-specific physiology, life history and microhabitat conditions, underscoring the need for cautious interpretation of root colonisation metrics in studies of adult orchid–fungus interactions.

The deposit contains a cleaned dataset (Pelotons_Mixed.csv, 300 individuals × 7 variables), five R scripts that reproduce all Bayesian regression analyses reported in the manuscript and Supplementary Material, a CC0 license file, and a README with full data dictionary and reproduction instructions.