Ectomycorrhizas and tipping points in forest ecosystems

Abstract

The resilience of forests is compromised by human-induced environmental influences pushing them towards tipping points resulting in major shifts in ecosystem state that might be difficult to reverse, are difficult to predict and manage, and can have vast ecological, economic and social consequences. The literature on tipping points has grown rapidly, but almost exclusively based on aquatic and aboveground systems. So far little effort has been made to make links to soil systems, where change is not as drastically apparent, timescales may differ, and recovery may be slower.Predicting belowground ecosystem state transitions and recovery, and their impacts on aboveground systems, remains a major scientific, practical and policy challenge. Recently observed major changes in aboveground tree condition across European forests are likely causallylinked with ectomycorrhizal (EM) fungal changes belowground. Based on recent breakthroughs in data collection and analysis, we 1) apply tipping point theory to forests, including their belowground component, focusing on EM fungi, 2) link environmental thresholds for EM fungi with nutrient imbalances in forest trees, 3) explore the role of phenotypic plasticity in EM fungal adaptation to, and recovery from, environmental change, and 4) propose major positive feedback mechanisms to understand, address and predict forest ecosystem tipping points.

Forest tree growth is linked to mycorrhizal fungal composition and function across Europe

“…S6 ). Thus, proportions of different EMF soil exploration types in communities may be an underlying mechanism to explain variation in tree growth as they have also been linked to a tipping point in tree mineral nutrition in the same forests [ 103 ]. How this may apply to older forests with different proportions of EMF exploration types remains uncertain.…”

Identifying thresholds of nitrogen enrichment for substantial shifts in arbuscular mycorrhizal fungal community metrics in a temperate grassland of northern China

“…Natural ecosystems can respond to environmental disturbance gradually until a threshold at which an abrupt shift in the community occurs, and beyond which it will be difficult to reverse effects (Scheffer et al ., 2001; Hillebrand et al ., 2020; Lever et al ., 2020; Suz et al ., 2021). When environmental stress reaches a threshold that soil microbial communities can no longer resist, the community is likely to lose species diversity, stability and ecological functions (Jassey et al ., 2018; Bardgett & Caruso, 2020; Liu et al ., 2020).…”

Phosphorus regulates ectomycorrhizal fungi biomass production in a Norway spruce forest

“…Indeed, in the study performed by Almeida et al (2019) in the same experimental plots as the current experiment, it was reported that P fertilization enhanced tree growth. Moreover, the authors reported that the foliar N : P ratios measured in the unfertilized control plots corresponded to suggested tipping points where the ecosystem shifts towards P limitation (see Suz et al, 2021, andvan der Linde et al, 2018). The results of the current pa-per suggest that this shift is linked to changes in EMF growth as shown by the reduction of EMF biomass production when P fertilization alleviates the nutrient limitation.…”