Commercial Sphagnum peat moss is a vector for exotic ectomycorrhizal mushrooms

Abstract

Sphagnum peat moss is one of the most commonly used substrates for forest plant and houseplant production. It is extracted from peat bogs in the circumboreal region and exported worldwide. Commercial peat moss is pasteurized, and is therefore believed to be free of viable ectomycorrhizal propagules. We used a bioassay with Pinus montezumae to demonstrate that commercial peat moss carries viable ectomycorrhizal spores, able to form mycorrhizae. Ectomycorrhizal fungi on seedling root-tips were sequenced for phylogenetic analyses using the ITS rDNA barcode region. We found three species: Suillus brevipes, Sphaerosporella brunnea, and Thelephora terrestris. S. brevipes and T. terrestris were found as viable inoculum transported in the peat moss, while S. brunnea was a greenhouse contaminant. S. brevipes and T. terrestris have biological characteristics (such as heat resistant and long living spores) that facilitate their survival to the extraction, transport, and storage processes of peat moss. This allows them to colonize nursery seedlings and to become potential invasive species in plantation areas. S. brevipes and T. terrestris are two of the most introduced fungi by anthropic activities; it has been argued that the vehicle for the introductions are their pine symbionts. This is the first time it has been demonstrated that peat moss is an important vehicle for the introduction of these fungi; a fact potentially related to the pattern of introduction of these ectomycorrhizal species from the northern hemisphere to elsewhere in the world.

Sympatric species develop more efficient ectomycorrhizae in the Pinus-Laccaria symbiosis

“…On the other hand, we demonstrate the efficiency of peat sterilization with Gamma rays, since both the negative control and the treatment with only P. fluorescens showed no mycorrhizae. The former means that we managed to eliminate the viability of resistant ectomycorrhizal fungi spores present in the peat (Ángeles-Argáiz et al, 2016).…”

“…Peat was sterilized with 50 kiloGrays of Gamma radiation at the Institute of Nuclear Sciences, UNAM, https://doi.org/10. 22201/ib.20078706e.2019.90.2868 as it has been shown it contains ectomycorrhizal fungi spores resistant to pasteurization (Ángeles-Argáiz et al, 2016). At the beginning of the experiment, each plant was inoculated with 10 7 spores placed in water solution added to the substrate.…”

Soil biotic and abiotic effects on seedling growth exhibit context‐dependent interactions: evidence from a multi‐country experiment on Pinus contorta invasion

“…Before planting, seeds were stored in a freezer for 1 month, and were then brought up to room temperature, and surface‐sterilized by soaking and periodically shaking them in 30% hydrogen peroxide with a few drops of Tween 20 for 20 min (Ángeles‐Argáiz et al ., 2016). Seeds were then rinsed several times in distilled water and germinated in sterile sand.…”

Towards management of invasive ectomycorrhizal fungi

“…Mycorrhizal inoculum of particular desirable species can also harbour non-target organisms, as suggested by Hall et al (2008) for the spread of Tuber indicum and T. brumale with or on sporocarps of T. melanosporum, or as a contaminant on nursery inoculated seedlings. Sphagnum peat moss, widely used in commercial nursery production, can also be a vector of invasive fungi, with heat resistant strains remaining viable even after pasteurization (Á ngeles-Argáiz et al 2015). Once introduced, ectomycorrhizal fungi can naturalize through dispersal by mammals (Nuñez et al 2013), wind, movement of soil, and by both inadvertent and deliberate spread by humans.…”