Changes in turnover rather than production regulate biomass of ectomycorrhizal fungal mycelium across a Pinus sylvestris chronosequence

Abstract

SummaryIn boreal forest soils, ectomycorrhizal fungi are fundamentally important for carbon (C) dynamics and nutrient cycling. Although their extraradical mycelium (ERM) is pivotal for processes such as soil organic matter build-up and nitrogen cycling, very little is known about its dynamics and regulation.In this study, we quantified ERM production and turnover, and examined how these two processes together regulated standing ERM biomass in seven sites forming a chronosequence of 12-to 100-yr-old managed Pinus sylvestris forests. This was done by determining ERM biomass, using ergosterol as a proxy, in sequentially harvested in-growth mesh bags and by applying mathematical models.Although ERM production declined with increasing forest age from 1.2 to 0.5 kg ha À1 d À1 , the standing biomass increased from 50 to 112 kg ha À1 . This was explained by a drastic decline in mycelial turnover from seven times to one time per year with increasing forest age, corresponding to mean residence times from 25 d up to 1 yr. Our results demonstrate that ERM turnover is the main factor regulating biomass across differently aged forest stands. Explicit inclusion of ERM parameters in forest ecosystem C models may significantly improve their capacity to predict responses of mycorrhiza-mediated processes to management and environmental changes.

Melanin mitigates the accelerated decay of mycorrhizal necromass with peatland warming

“…; Hagenbo et al . ) and will be important to include to better understand the mycorrhizal biomass production dynamics in these systems.…”

“…Unlike aboveground inputs, and even root inputs, estimating mycorrhizal fungal inputs is incredibly challenging to obtain because of the fineness of the fungal hyphae and their heterogenous distribution in soils. However, methods using in-growth cores or bags filled with sterile sand have been used to estimate mycorrhizal biomass production and turnover (death) (Wallander et al 2001;Hagenbo et al 2017) and will be important to include to better understand the mycorrhizal biomass production dynamics in these systems.…”

Complex effects of mammalian grazing on extramatrical mycelial biomass in the Scandes forest‐tundra ecotone

“…It is possible that browsing and removal of B. nana biomass in ambient plots at the beginning of summer cause dieback and subsequent regrowth of EMM hyphae and that this increased mycelial turnover is the reason that we found more EMM biomass in grazed plots than in exclosures. In P. sylvestris forests, mycelia turnover time has been found to be higher in younger than older forest stands, possibly due to total belowground C flux being lower and N immobilization being higher in older forest stands (Hagenbo et al., 2017). The same could perhaps be true of exclosures compared to ambient plots at the Långfjället site, where in the absence of grazing, B. nana was allowed to proliferate, increasing the competition for resources.…”

Mycorrhizal types differ in ecophysiology and alter plant nutrition and soil processes

“…By contrast, ergosterol accumulation and standing fungal biomass suggest that EcM fungal hyphae turn over in 28-36 days in temperate coniferous forest soil Hendricks et al, 2016). More recent estimates indicate EcM hyphal turnover in 25-500 days in a strong negative correlation with stand age (Hagenbo et al, 2017). Longevity of EcM fungal rhizomorphs has been estimated at 7-22 months , which roughly corresponds to the median age of roots (McCormack et al, 2012).…”

“…In EcM and AM systems, respectively, 7-30% and 2-20% of photosynthetically fixed C is allocated to fungi within 6-72 h after initiation of 13 CO 2 labelling, with an average twofold difference among mycorrhizal types (reviewed in Leake et al, 2004). Notably, these experiments were performed in the exponential growth phase of the extraradical mycelium, which does not necessarily represent natural conditions with high standing mycelium biomass Hagenbo et al, 2017).…”