Split down the middle: studying arbuscular mycorrhizal and ectomycorrhizal symbioses using split-root assays

Abstract

Most land plants symbiotically interact with soil-borne fungi to ensure nutrient acquisition and tolerance to various environmental stressors. Among these symbioses, arbuscular mycorrhizal and ectomycorrhizal associations can be found in a large proportion of plants, including many crops. Split-root assays are widely used in plant research to study local and systemic signaling responses triggered by local treatments, including nutrient availability, interaction with soil microbes, or abiotic stresses. However, split-root approaches have only been occasionally used to tackle these questions with regard to mycorrhizal symbioses. This review compiles and discusses split-root assays developed to study arbuscular mycorrhizal and ectomycorrhizal symbioses, with a particular emphasis on colonization by multiple beneficial symbionts, systemic resistance induced by mycorrhizal fungi, water and nutrient transport from fungi to colonized plants, and host photosynthate allocation from the host to fungal symbionts. In addition, we highlight how the use of split-root assays could result in a better understanding of mycorrhizal symbioses, particularly for a broader range of essential nutrients, and for multi-partite interactions.

Development of split-root assays for loblolly pine (Pinus taeda L.) seedlings to study ectomycorrhizal symbioses

“…In combination with carefully designed treatment applications, this method may be useful for researchers interested in studying systemic loblolly pine responses to ECM fungi and soil environmental conditions. Indeed, split-root systems have been used in the past to explore ECM interactions with other tree species, employing a variety of techniques to determine nutrient transport, host tree carbon allocation, and competitive interactions amongst fungal species [2] . For example, a split-root system was used with 3- to 4-year-old beech trees ( Fagus sylvatica ) to determine spatial distribution of host photosynthates and fungal nitrogen in ectomycorrhizae [16] .…”

“…Plant roots interact with the soil and its biotic and abiotic components, making crucial the development of techniques to study these interactions. Split-root systems have been developed in multiple plant species and used to distinguish systemic versus local responses of roots to various environmental conditions, including resource availability, resistance to pathogens, or interactions with symbiotic microbes [1 , 2] . In split-root experiments, the roots of a single plant are divided into two relatively equal parts and grown in separate and distinct environments.…”

A snapshot of the transcriptome ofMedicago truncatula(Fabales: Fabaceae) shoots and roots in response to an arbuscular mycorrhizal fungus and the pea aphid (Acyrthosiphon pisum) (Hemiptera: Aphididae)

“…7). Mycorrhizal plants are known to activate local and/or systemic defenses that increase disease resistance (Pozo et al 2002, Liu et al 2007, Cameron et al 2013, Dreischhoff et al 2020, Kafle et al 2022). However, local and systemic susceptibility to insects and pathogens has also been reported (Bernaola et al 2018).…”

Split-root system as a useful tool to study woody plant biology

“…The disease is closely related to soil microorganisms, and the defence reactions of the roots at the biochemical level are local, as they were observed only in the part of the root exposed to apple replant disease (Balbin-Suarez et al 2021Rohr et al 2021). The use of SRS in studies of arbuscular mycorrhizal and ectomycorrhizal symbioses, including several studies on woody plants, was presented by Kafle et al (2022), so we will not discuss this issue in detail in this paper.…”