Mycelia‐derived C contributes more to nitrogen cycling than root‐derived C in ectomycorrhizal alpine forests

Abstract

Plant roots and their associated microbial symbionts impact carbon (C) and nutrient cycling in ecosystems, but estimates of the relative contributions of root‐ versus microbe‐derived dynamic inputs are highly uncertain. Roots release C into soil via exudation and turnover (i.e., root‐derived C), but also by allocating C to mycorrhizal fungal mycelia, which exude C and undergo turnover (i.e., mycelia‐derived C). Given that the relative contributions of root‐ and mycelia‐derived C inputs are unknown, a key knowledge gap lies in understanding not only the relative contributions of root‐ versus mycelia‐derived C inputs, but also the consequences of these fluxes on nutrient cycling. Using ingrowth cores and stable isotope analyses, we quantified root‐ and mycelia‐derived C inputs into the soil and their relative contributions to nitrogen (N) cycling in two ectomycorrhizal alpine forests, a 70‐year‐old spruce plantation and a 200‐year‐old spruce‐fir dominated forest, in western Sichuan, China. Across the two forests, extramatrical mycelia of ectomycorrhizal fungi accounted for up to two‐thirds of the new root C inputs into soil and ~80% of the stimulated N mineralization. Moreover, flux‐specific (per gram) mycelia‐derived C inputs stimulated multiple indices of soil N cycling to a greater degree than the flux‐specific root‐derived C inputs, accounting for ~70% of the stimulated N mineralization in both forests. Collectively, our findings indicate that the effects of mycorrhizal fungi on soil C and N cycling may exceed those of roots in alpine coniferous forests dominated by ectomycorrhizal fungi, highlighting the need to incorporate mycorrhizal fungal inputs into biogeochemical models for ecosystems. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13236/suppinfo is available for this article.

Substrate quality drives fungal necromass decay and decomposer community structure under contrasting vegetation types

“…The amount of carbon (C) stored in soils is dependent upon the balance between soil organic matter (SOM) inputs and their subsequent rates of decomposition and C loss (Chapin, Matson, & Vitousek, 2012). While plant‐derived inputs and losses have received decades of study (Berg & McClaugherty, 2003), there is growing evidence that fungal mycelium is also a major determinant of soil C stocks (Clemmensen et al, 2013; Ekblad et al, 2013; Godbold et al, 2006; Zhang et al, 2019). Conservative estimates of fungal mycelial biomass range from 20 to 250 g/m 2 , with turnover times ranging from 9 to 48 days (Allen & Kitajima, 2014; Godbold et al, 2006; Soudzilovskaia et al, 2015).…”

“…The high nutrient content of fungal necromass compared to other organic matter (OM) inputs also makes it an important resource for a variety of decomposers (Brabcová et al, 2018; Finlay & Clemmensen, 2016). Recent studies indicate that the presence of fungal necromass significantly increases microbial enzyme activity (Brabcová, Nováková, Davidová, & Baldrian, 2016; Zeglin & Myrold, 2013) and is responsible for up to 80% of nitrogen (N) cycling associated with the decomposition of below‐ground OM inputs (Zhang et al, 2019).…”

“…Given the importance of soil fungi to C and nutrient cycling, there is a pressing need to understand the factors that control the fate of fungal necromass across diverse environments (Baskaran et al, 2017; Fernandez, Langley, Chapman, McCormack, & Koide, 2016; Smith & Wan, 2019; Zhang et al, 2019). Current knowledge of the controls on decomposition are largely derived from assessments of plant litter decay, which identify the following interrelated factors: (a) climate; (b) biochemical traits (which typically indicate resource quality for decomposers); (c) soil properties (e.g.…”

Production of Fungal Mycelia in a Temperate Coniferous Forest Shows Distinct Seasonal Patterns

“…The standing biomass of ECM mycelia in the upper 70 cm of the soil profile may be as high as 480 to 580 g m −2 [ 11 ]. Due to the rapid turnover of ectomycorrhizal mycelia [ 14 , 15 ], the rate of ECM fungal biomass production is high, reaching up to 180 g C m −2 y −2 and being considerably higher in coniferous than deciduous stands [ 12 , 16 ].…”

The contribution of arbuscular mycorrhizal fungi to ecosystem respiration and methane flux in an ephemeral plants‐dominated desert

“…Recent advances have been made in the ability to confirm the impact of AMF on the soil–plant C, N and P cycles through the use of mesh‐walled in‐growth mesocosms (MIM) (Nottingham et al, 2010; van der Heijden, 2010; Lilleskov et al, 2019; Zhang et al, 2019). However, to date, there has been little research on this in temperate desert ecosystems.…”