Even underwater, plant roots can keep their fungal partners

Wetlands have their own hidden fungal communities beneath the water: AM fungal associations persist despite prolonged root flooding.

Arbuscular mycorrhizal (AM) fungi are important partners of many plants, including plants growing in wetlands. They usually live in soils around plant roots, where they help plants obtain nutrients such as phosphorus and, in return, receive carbon from the plant.

Flooded environments are very different from typical soils because water fills the spaces between soil particles and changes oxygen availability and nutrient movement. This raises an important question: can AM fungal associations persist when plant roots become submerged in flooded sediments?

This study investigated AM fungal communities associated with the common wetland plant Phragmites australis (common reed), comparing roots growing in dry soil with roots growing in flooded sediment.

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AM fungi can survive and form symbiotic associations with Phragmites australis roots even when those roots are growing in flooded sediment. Flooding did not substantially reduce fungal diversity but changed which fungal communities were present, suggesting that wetlands select for particular AM fungi adapted to water-saturated conditions.

Mycorrhizal fungi normally live around plant roots in soil, helping plants obtain nutrients in exchange for carbon. But what happens to these fungi when the soil becomes completely waterlogged?

This study looked at Phragmites australis, a common wetland plant, and compared fungi living on roots growing in relatively dry soil with those living on roots growing in flooded sediment.

The researchers found that AM fungi were still present on roots growing underwater. Surprisingly, the flooded roots did not have substantially fewer fungal species. Instead, the types of fungi changed. In particular, fungi belonging to the genus Glomus were especially common in the flooded roots.

The researchers suggest that flooding may act as a kind of environmental filter. Fungi that spend more of their growth inside plant roots may be better able to cope with flooded conditions than fungi that depend heavily on extensive networks outside the roots.

The study therefore shows that wetlands have their own distinctive belowground fungal communities and that AM fungi should be considered an important part of wetland biodiversity and ecosystem functioning.

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Summary: Arbuscular mycorrhizal fungi can persist in flooded sediments and form distinct communities on wetland plant roots. Flooding may not eliminate AM fungal diversity, but instead select for particular fungal taxa adapted to water-saturated conditions.

This is important because wetlands are highly productive ecosystems that provide important environmental services, including:

• Water purification
• Nutrient cycling
• Carbon storage
• Habitat for biodiversity
• Flood regulation

Yet AM fungal communities in wetlands remain relatively poorly studied.

This study expands our understanding of mycorrhizal fungi by showing that flooded sediments can support distinct AM fungal communities rather than simply representing environments where terrestrial mycorrhizal fungi become less abundant.

This has potential implications for wetland restoration and management because maintaining healthy fungal communities could contribute to the functioning and resilience of wetland plants.