Data from: Mycelia-derived C contributes more to nitrogen cycling than root-derived C in ectomycorrhizal alpine forests

1. 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. 2. 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. 3. 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. 4. 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.

1. 植物根系及其相关的共生微生物（microbial symbionts）可调控生态系统中的碳（C）与养分循环，但针对根系与微生物来源的动态碳输入的相对贡献的估算尚存极大不确定性。根系可通过释放根系分泌物与组织周转（即根系来源碳）将碳输入土壤，同时还会将碳分配至菌根真菌菌丝体（mycorrhizal fungal mycelia），而菌丝体自身也会通过释放分泌物与组织周转贡献碳（即菌丝体来源碳）。鉴于根系与菌丝体来源的碳输入的相对贡献尚不明确，当前的核心知识空白不仅在于厘清二者的相对贡献比例，更在于理解这些碳通量对养分循环的具体影响。
2. 本研究借助根系生长芯（ingrowth cores）技术与稳定同位素分析（stable isotope analyses），在中国四川西部的两类外生菌根（ectomycorrhizal）高山森林中，定量解析了根系与菌丝体来源的碳向土壤的输入通量，以及二者对氮（N）循环的相对贡献：分别为70年生云杉人工林，以及200年生以云杉、冷杉为优势种的森林。
3. 在两个研究样地中，外生菌根真菌的外延菌丝体（extramatrical mycelia）占土壤新输入根系碳的比例最高可达三分之二，且贡献了约80%的诱导氮矿化（stimulated N mineralization）。此外，每克（per gram）的菌丝体来源碳输入对土壤氮循环多项指标的刺激效应显著高于同单位的根系来源碳输入，在两个森林样地中均贡献了约70%的诱导氮矿化过程。
4. 综合来看，本研究结果表明，在外生菌根主导的高山针叶林中，菌根真菌对土壤碳、氮循环的调控效应可能超过根系，这凸显了将菌根真菌碳输入纳入生态系统生物地球化学模型（biogeochemical models）的必要性。