The production and turnover of extramatrical mycelium of ectomycorrhizal fungi in forest soils: role in carbon cycling

Abstract

There is growing evidence of the importance of extramatrical mycelium (EMM) of mycorrhizal fungi in carbon (C) cycling in ecosystems. However, our understanding has until recently been mainly based on laboratory experiments, and knowledge of such basic parameters as variations in mycelial production, standing biomass and turnover as well as the regulatory mechanisms behind such variations in forest soils is limited. Presently, the production of EMM by ectomycorrhizal (EM) fungi has been Plant Soil (2013) at~140 different forest sites to be up to several hundreds of kg per ha per year, but the published data are biased towards Picea abies in Scandinavia. Little is known about the standing biomass and turnover of EMM in other systems, and its influence on the C stored or lost from soils. Here, focussing on ectomycorrhizas, we discuss the factors that regulate the production and turnover of EMM and its role in soil C dynamics, identifying important gaps in this knowledge. C availability seems to be the key factor determining EMM production and possibly its standing biomass in forests but direct effects of mineral nutrient availability on the EMM can be important. There is great uncertainty about the rate of turnover of EMM. There is increasing evidence that residues of EM fungi play a major role in the formation of stable N and C in SOM, which highlights the need to include mycorrhizal effects in models of global soil C stores.

Attributing functions to ectomycorrhizal fungal identities in assemblages for nitrogen acquisition under stress

“…In our study, the aforementioned species were also present but were rare, suggesting that beech trees may foster fungal species without immediate benefits because the supply with NH 4 þ does not require the degradation of organic matter. Furthermore, long distance transport of N via fungal rhizomorphs is carbohydrate demanding (Ekblad et al, 2013). Therefore, long distance EMF are probably less favored by small plants with limited light resources than short distance EMF.…”

Maintaining connectivity: understanding the role of root order and mycelial networks in fine root decomposition of woody plants

“…Such small mesh sizes exclude macro and meso-fauna that would normally condition plant litter in ways that lead to faster microbial decomposition (González and Seastedt 2001;Sun et al 2015;Frouz et al 2015). Collembolans are known to feed on fungal hyphae which leads to fragmentation of roots tips, which in turn can disrupt the hydrophobic nature of hyphal coverings and increase decomposer access (Ekblad et al 2013). Minirhizotron studies generally report that the finest roots with shorter longevity disappear from images (i.e., decompose) more quickly than larger diameter, higher order roots (Guo et al 2008a;Fan and Guo 2010).…”

The decomposition of ectomycorrhizal fungal necromass

“…The influence of EM fungi on nutrient uptake has been well documented, and its implications for ecosystem processes are now generally appreciated (Read, 1991;Read and Perez-Moreno 2003;Courty et al, 2010;Orwin et al, 2011). In addition, we are beginning to recognize the significance to biogeochemical cycles of inputs resulting from the death of EM fungal tissues (Fogel, 1980;Fogel and Hunt, 1983;Treseder and Allen, 2000;Langley and Hungate, 2003;Godbold et al, 2006;Cairney, 2012;Clemmenssen et al, 2013;Ekblad et al, 2013). Until recently, little attention has been paid to EM fungal necromass inputs due to the fact that microbial necromass inputs have been considered to be relatively insignificant as standing pools of microbial biomass are often relatively small compared to those of standing plant biomass.…”

“…Using data from both lab and field studies, Hobbie (2006) found that C allocation to EM fungi ranged from 1 to 22% of annual net primary productivity. Ekblad et al (2013) suggested that approximately 7% allocation of NPP to EM fungi is a reasonable estimate. More recently, Allen and Kitajima (2014) estimated that 27% of NPP allocated to EM fungi in a Californian mixed conifer-deciduous forest using minirhizotron techniques and 34% of NPP using an isotopic fractionation model proposed by Hobbie and Hobbie (2006).…”