Statistical analysis

Frequency of occurrence and spore abundance

The frequency of occurrence (FO%) of each arbuscular mycorrhizal fungal species was calculated as the percentage of sampling units in which the species was present relative to the total number of sampling units (n = 12). Species frequency was determined according to the following equation:

\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \begin{gathered} {\mathrm{FO}}\left( \% \right) \hfill \\ = \left( {{\mathrm{number}}\;{\mathrm{of}}\;{\mathrm{sampling}}\;{\mathrm{units}}\;{\mathrm{in}}\;{\mathrm{which}}\;{\mathrm{the}}\;{\mathrm{species}}\;{\mathrm{occurred}}/{\mathrm{total}}\;{\mathrm{number}}\;{\mathrm{of}}\;{\mathrm{sampling}}\;{\mathrm{units}}} \right) \hfill \\ \times {1}00. \hfill \\ \end{gathered} $$\end{document}

Differences in spore abundance among AMF species and olive cultivars were evaluated using generalized linear mixed models (GLMMs) with a negative binomial distribution (Brooks et al. 2017). Cultivar, AMF species, and their interaction were included as fixed effects, whereas sampling units were treated as a random effect. Model adequacy was assessed using residual diagnostics (Hartig 2026), and multiple comparisons were performed using estimated marginal means with appropriate adjustment for multiple testing (Lenth 2026).