Towards a consistent benchmark for plant mycorrhizal association databases: a reply to FungalRoot: global online database of plant mycorrhizal associations.

Mycorrhizal symbiosis, comprising functionally distinctive plant-fungus associations, mediates key plant population and community processes, and ultimately the functioning of terrestrial ecosystems (Tedersoo et al., 2020). It is estimated that about 90% of the world's vascular flora forms mycorrhizal symbioses with soil fungi (Smith & Read, 2008; Brundrett & Tedersoo, 2018). While this general estimate is probably adequate, there is a severe shortage of empirical information about mycorrhizal associations at the plant species level, with only around 5% of the world's flora explored (Moora, 2014; Bueno et al., 2019b). Several database developments have emerged since the seminal work of Harley & Harley (1987; HH); extending both the number and the geography of plant species covered (Wang & Qiu, 2006, WQ; Akhmetzhanova et al., 2012, MID) and defining and describing some key mycorrhizal traits of plant species - "mycorrhizal type" and "mycorrhizal status" (Hempel et al., 2013, MF; Moora, 2014). Nonetheless, this expansion poses new challenges connected with the compilation of global data based on heterogeneous sources with different practical and conceptual frameworks (Bueno et al., 2019b; Kattge et al., 2020). Careful work developing consistent definitions and standardizing field and lab protocols is essential for harmonizing database content and avoiding critical inconsistencies (Perez-Harguindeguy et al., 2013; Schneider et al., 2019).