Moving beyond the black-box: fungal traits, community structure, and carbon sequestration in forest soils.

More carbon (C) is stored globally in soils than biotic and atmospheric pools combined (Lal, 2004). As such, the biogeochemical processes affecting the amount of C sequestered in soil have major implications for global climate change. Despite the fact that most plants associate with mycorrhizal fungi and allocate significant amounts of C to these symbionts in order to gain access to soil nutrients and water (Godbold et al., 2006; Hobbie, 2006; Allen & Kitajima, 2014), the input of mycorrhizal fungal biomass, its turnover, and potential contribution to C sequestration in soil organic matter (SOM) has been largely overlooked until recently (Langley & Hungate, 2003). The significance of mycorrhizal fungal inputs, however, was convincingly demonstrated by Clemmensen et al. (2013), who used bomb carbon-14 (C) modeling coupled with biomarker analysis to show that the majority of C stored in SOM in a boreal forest system was of root and fungal origin. In this issue of New Phytologist, Clemmensen et al. (2015, pp. 1525–1536) explore the link between community composition of mycorrhizal fungi and soil C sequestration in the same study system. Their results clearly indicate that simplistic ‘black-box’ approaches to studying soil fungal communities miss important ecological patterns and that shifts in species traits, both within and among fungal guilds, may be key determinants of C sequestration in forest soils.