Belowground carbon flux links biogeochemical cycles and resource‐use efficiency at the global scale

Gill, Allison L.; Finzi, Adrien C.

doi:10.1111/ele.12690

Cited by 92 publications

(101 citation statements)

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“…Modeled nutrient mineralization rates are very high for two alpine grasslands, but they are plausible given the high productivity and relatively large nutrient content of grass leaves and the fact that grass litter is left on the field in the simulations. Nitrogen use efficiency (NUE) and phosphorus use efficiency (PUE) computed as the ratio of GPP to nutrient uptake rates have the same magnitude of the values published by Gill and Finzi () even though simulated NUE is generally smaller. Simulated values are rather scattered and do not follow the pattern of increase in PUE and decrease in NUE with GPP from high‐latitude boreal ecosystems to low‐latitude tropical forests (Figures c and d).…”

Section: Resultssupporting

confidence: 61%

“…Patterns of nitrogen and phosphorus mineralization in relation to gross primary production (GPP) have been recently assessed by Gill and Finzi (). Simulations in the 20 sites are typically consistent with those values, although simulated nutrient mineralization rates tend to be slightly larger than observed for intermediate values of GPP (Figures a and b).…”

Section: Resultsmentioning

confidence: 99%

“…A few studies have quantified the global-scale relation among NPP, litterfall, SOC, soil respiration, nutrient mineralization rates, and microbial and macrofauna biomass (Fierer et al, 2009;Gill & Finzi, 2016;Raich & Nadelhoffer, 1989;Xu et al, 2013;Zak et al, 1994). Here, we compare these variables for the 20 modeled sites with the values published in literature.…”

Section: Global Scale Patterns Of Carbon Cycle Componentsmentioning

confidence: 99%

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A Mechanistic Model of Microbially Mediated Soil Biogeochemical Processes: A Reality Check

Fatichi

Manzoni

et al. 2019

Global Biogeochemical Cycles

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Present gaps in the representation of key soil biogeochemical processes such as the partitioning of soil organic carbon among functional components, microbial biomass and diversity, and the coupling of carbon and nutrient cycles present a challenge to improving the reliability of projected soil carbon dynamics. We introduce a new soil biogeochemistry module linked with a well‐tested terrestrial biosphere model T&C. The module explicitly distinguishes functional soil organic carbon components. Extracellular enzymes and microbial pools are differentiated based on the functional roles of bacteria, saprotrophic, and mycorrhizal fungi. Soil macrofauna is also represented. The model resolves the cycles of nitrogen, phosphorus, and potassium. Model simulations for 20 sites compared favorably with global patterns of litter and soil stoichiometry, microbial and macrofaunal biomass relations with soil organic carbon, soil respiration, and nutrient mineralization rates. Long‐term responses to bare fallow and nitrogen addition experiments were also in agreement with observations. Some discrepancies between predictions and observations are appreciable in the response to litter manipulation. Upon successful model reproduction of observed general trends, we assessed patterns associated with the carbon cycle that were challenging to address empirically. Despite large site‐to‐site variability, fine root, fungal, bacteria, and macrofaunal respiration account for 33%, 40%, 24%, and 3% on average of total belowground respiration, respectively. Simulated root exudation and carbon export to mycorrhizal fungi represent on average about 13% of plant net primary productivity. These results offer mechanistic and general estimates of microbial biomass and its contribution to respiration fluxes and to soil organic matter dynamics.

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Section: Resultssupporting

confidence: 61%

Section: Resultsmentioning

confidence: 99%

Section: Global Scale Patterns Of Carbon Cycle Componentsmentioning

confidence: 99%

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A Mechanistic Model of Microbially Mediated Soil Biogeochemical Processes: A Reality Check

Fatichi

Manzoni

et al. 2019

Global Biogeochemical Cycles

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“…Globally, fine roots account for one‐third of annual net primary production (Jackson, Mooney, & Schulze, ; Li, Han, Guo, Shao, & Xin, ), and their inputs into soil through the processes of growth, exudation and turnover have important implications for the formation, stabilization and decomposition of soil organic matter (SOM) and nutrient cycling (Moore et al., ; Schmidt et al., ). Although there is emerging consensus regarding the vital role of plant roots in ecosystem functions (Clemmensen et al., ; Moore et al., ), considerable uncertainties remain regarding the role of root‐associated microbes, including symbiotic mycorrhizal fungi, in mediating below‐ground C fluxes and nutrient turnover in soils (Gill & Finzi, ). These uncertainties have hampered efforts to incorporate below‐ground dynamics in process models that are increasingly being used to predict ecosystem responses to global changes (Brzostek, Rebel, Smith, & Phillips, ).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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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.

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“…At the ecosystem or forest stand level, TBCA is a key parameter in global C budgets and can be estimated with soil C flux and litterfall measurements (Almagro, López, Boix-Fayos, Albaladejo, & Martínez-Mena, 2010;Chen, Yang, & Robinson, 2014;Giardina & Ryan, 2002;Gill & Finzi, 2016;Litton & Giardina, 2008;Litton et al, 2007;Raich & Nadelhoffer, 1989). For individual plants, however, TBCA measurements require either isotopic C pulse-chase studies (Epron et al, 2012) or C accounting through repeated harvests along with separate above-and below-ground flux measurements (Wright et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Does plant biomass partitioning reflect energetic investments in carbon and nutrient foraging?

Kong

Fridley

2019

Functional Ecology

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Studies of plant resource‐use strategies along environmental gradients often assume that dry matter partitioning represents an individual's energy investment in foraging for above‐ versus below‐ground resources. However, ecosystem‐level studies of total below‐ground carbon allocation (TBCA) in forests do not support the equivalency of energy (carbon) and dry matter partitioning, in part because allocation of carbon to below‐ground pools and fluxes that are not accounted for by root biomass (e.g., mycorrhizal hyphae, rhizodeposition; root and soil respiration) can be substantial. Here, we apply this reasoning to individual plants in controlled environments and ask whether dry matter partitioning below‐ground (root mass fraction, RMF) accurately reflects TBCA in studies of optimal partitioning theory. We quantified the relationship between RMF and TBCA in individual plants, using 311 observations from 51 studies that simultaneously measured both allocation variables. Our analysis included tests of whether the RMF‐TBCA relationship depended on mutualist soil microbes, plant growth form, age and study methodology including isotopic pulse–chase duration. We found that RMF was a poor proxy for below‐ground energy investment. This disconnect of RMF and TBCA was driven in part by plants of low RMF (<0.4) exhibiting significantly higher rates of root and soil respiration per unit root mass than plants of high RMF. Root colonization by mutualist microbes, including arbuscular mycorrhizal fungi and nitrogen‐fixing bacteria, increased TBCA by 5%–7%, and TBCA was lower in grasses than other species by 9%–16%. These patterns were evident for relationships assessed both within and between species. We conclude that optimal partitioning studies of plants along environmental gradients are likely to underestimate plant energy allocation below‐ground if the C costs of root and soil respiration are ignored, especially under conditions favouring low RMF. Because energy rather than biomass better reflects how assimilated C supports fitness, this omission of respired C suggests existing studies misrepresent the significance of below‐ground processes to plant function. A free Plain Language Summary can be found within the Supporting Information of this article.

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Belowground carbon flux links biogeochemical cycles and resource‐use efficiency at the global scale

Cited by 92 publications

References 50 publications

A Mechanistic Model of Microbially Mediated Soil Biogeochemical Processes: A Reality Check

A Mechanistic Model of Microbially Mediated Soil Biogeochemical Processes: A Reality Check

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

Does plant biomass partitioning reflect energetic investments in carbon and nutrient foraging?

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