What are mycorrhizal traits?

Background/Question/Methods

Traits are inherent properties of organisms, but how are they defined for organismal networks such as mycorrhizas? A trait is defined as any morphological, physiological or phenological feature measurable from the subcellular to the whole-organism or system level. Mycorrhizas are complex and diverse belowground symbiotic networks between plants and fungi that have proved challenging to fit into a unified and coherent trait framework. Disparate definitions across a diversity of trait-based mycorrhizal research efforts hinder productive scientific discourse and can lead to disagreement, miscommunication, and misunderstanding among researchers. Often, different definitions of mycorrhizal traits are specific to mycorrhizal type, focused on either a plant- or fungal-centric perspective, or borrowed from existing ecological theories based on distinct unitary organisms that cause confusion for network-based modular organisms. A unified language for mycorrhizal traits that spans mycorrhizal types and morpho-physio-phenological functions is sorely needed.

Results/Conclusions

We propose an inclusive mycorrhizal trait framework that defines and classifies mycorrhizal traits as morphological, physiological, or phenological characteristics of mycorrhizal fungi, plant hosts, and mycorrhizal associations which have functional implications for the symbiosis. We further qualify mycorrhizal traits using language that references their physical location within mycorrhizal networks such that mycorrhizal traits are either plant-mycorrhizal traits (plant-MT), fungal-mycorrhizal traits (fungal-MT), or symbiotic-mycorrhizal traits (symbiotic-MT). Plant-MT are largely driven by the morphological, physiological, or phenological characteristics of plant hosts. Fungal-MT are mycorrhizal traits that are dependent on the morphological, physiological, or phenological characteristics of fungal partners. And symbiotic-MT are traits that are dependent on both the plant host and fungal partners present. We highlight and define numerous examples of morphological, physiological, and phenological traits in all of these categories and highlight new questions to stimulate research and discourse in trait-based mycorrhizal ecology. This new framework is an opportunity for researchers to interrogate their data to identify novel insights and gaps in our understanding of mycorrhizal systems.