Dead fungal mycelium (necromass) represents a critical component of soil carbon (C) and nutrient cycles. Assessing how the microbial communities associated with decomposing fungal necromass change as global temperatures rise will help in determining how these belowground organic matter inputs contribute to ecosystem responses. In this study, we characterized the structure of bacterial and fungal communities associated with multiple types of decaying mycorrhizal fungal necromass incubated within mesh bags across a 9°C whole ecosystem temperature enhancement in a boreal peatland. We found major taxonomic and functional shifts in the microbial communities present on decaying mycorrhizal fungal necromass in response to warming. These changes were most pronounced in hollow microsites, which showed convergence towards the necromass‐associated microbial communities present in unwarmed hummocks. We also observed a high colonization of ericoid mycorrhizal fungal necromass by fungi from the same genera as the necromass. These results indicate that microbial communities associated with mycorrhizal fungal necromass decomposition are likely to change significantly with future climate warming, which may have strong impacts on soil biogeochemical cycles in peatlands. Additionally, the high enrichment of congeneric fungal decomposers on ericoid mycorrhizal necromass may help to explain the increase in ericoid shrub dominance in warming peatlands.
Fungi represent a rapidly cycling pool of carbon (C) and nitrogen (N) in soils. Understanding of how this pool impacts soil nutrient availability and organic matter fluxes is hindered by uncertainty regarding the dynamics and drivers of fungal necromass decomposition. Here we assessed the generality of common models for predicting mass loss during fungal necromass decomposition and linked the resulting parameters to necromass substrate chemistry. We decomposed 28 different types of fungal necromass in laboratory microcosms over a 90‐day period, measuring mass loss on all types, and N release on a subset of types. We characterised the initial chemistry of each necromass type using: (a) fibre analysis methods commonly used for plant tissues, (b) initial melanin and nitrogen (N) concentrations and (c) Fourier transform infrared (FTIR) spectroscopy to assess the presence of bonds associated with common biomolecules. We found universal support for an asymptotic model of decomposition, which assumes that fungal necromass consists of an exponentially decomposing ‘fast’ pool, and a ‘slow’ pool that decomposes at a rate approaching zero. The strongest predictor of the fast pool decay rate ( Collectively, our results indicate that the decomposition of fungal necromass in soils can be described as having two distinct stages that are driven by different components of substrate C chemistry, with implications for rates of N availability and organic matter accumulation in soils.
A free
- PAR ID:
- 10442935
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Functional Ecology
- Volume:
- 35
- Issue:
- 3
- ISSN:
- 0269-8463
- Page Range / eLocation ID:
- p. 796-806
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary Interactions between symbiotic ectomycorrhizal (EM) and free‐living saprotrophs can result in significant deceleration of leaf litter decomposition. While this phenomenon is widely cited, its generality remains unclear, as both the direction and magnitude of EM fungal effects on leaf litter decomposition have been shown to vary among studies.
Here we explicitly examine how contrasting leaf litter types and EM fungal communities may lead to differential effects on carbon (C) and nitrogen (N) cycling. Specifically, we measured the response of soil nutrient cycling, litter decay rates, litter chemistry and fungal community structure to the reduction of EM fungi (via trenching) with a reciprocal litter transplant experiment in adjacent
Pinus ‐ orQuercus ‐dominated sites.We found clear evidence of EM fungal suppression of C and N cycling in the
Pinus ‐dominated site, but no suppression in theQuercus ‐dominated site. Additionally, in thePinus ‐dominated site, only thePinus litter decay rates were decelerated by EM fungi and were associated with decoupling of litter C and N cycling.Our results support the hypothesis that EM fungi can decelerate C cycling via N competition, but strongly suggest that the ‘Gadgil effect’ is dependent on both substrate quality and EM fungal community composition. We argue that understanding tree host traits as well as EM fungal functional diversity is critical to a more mechanistic understanding of how EM fungi mediate forest soil biogeochemical cycling.
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Abstract Ecosystem functional responses such as soil CO2emissions are constrained by microclimate, available carbon (C) substrates and their effects upon microbial activity. In tropical forests, phosphorus (P) is often considered as a limiting factor for plant growth, but it is still not clear whether P constrains microbial CO2emissions from soils. In this study, we incubated seven tropical forest soils from Brazil and Puerto Rico with different nutrient addition treatments (no addition, Control; C, nitrogen (N) or P addition only; and combined C, N and P addition (CNP)). Cumulative soil CO2emissions were fit with a Gompertz model to estimate potential maximum cumulative soil CO2emission (
C m ) and the rate of change of soil C decomposition (k ). Quantitative polymerase chain reaction (qPCR) was conducted to quantify microbial biomass as bacteria and fungi. Results showed that P addition alone or in combination with C and N enhancedC m , whereas N addition usually reducedC m , and neither N nor P affected microbial biomass. Additions of CNP enhancedk , increased microbial abundances and altered fungal to bacterial ratios towards higher fungal abundance. Additions of CNP, however, tended to reduceC m for most soils when compared to C additions alone, suggesting that microbial growth associated with nutrient additions may have occurred at the expense of C decomposition. Overall, this study demonstrates that soil CO2emission is more limited by P than N in tropical forest soils and those effects were stronger in soils low in P.Highlights A laboratory incubation study was conducted with nitrogen, phosphorus or carbon addition to tropical forest soils. Soil CO2emission was fitted with a Gompertz model and soil microbial abundance was quantified using qPCR. Phosphorus addition increased model parameters
C m and soil CO2emission, particularly in the Puerto Rico soils. Soil CO2emission was more limited by phosphorus than nitrogen in tropical forest soils. -
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Abstract Greater tree density and forest productivity at the tundra–taiga ecotone (TTE) are expected with climate warming, with potential feedbacks to the climate system. Yet, competition for nitrogen (N) may impact TTE dynamics. Greater tree density will likely increase N demand, while reducing N supply through soil shading and slower decomposition rates. We explored whether characteristics of roots and root‐associated fungi important to N acquisition responded to changes in density at the TTE and were related to above‐ground stand productivity and N cycling.
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Abstract Decomposition is a major component of global carbon cycling. However, approximately 50% of wood necromass and a small proportion of leaf litter do not contact the forest floor, and the factors that regulate the decomposition above the forest floor are largely untested. We hypothesized that separation from soil resources causes slower decomposition rates above the forest floor. Specifically, we tested whether slower decomposition results from decreased nutrient availability (the nutrient limitation hypothesis) and/or microbial dispersal limitation (the dispersal limitation hypothesis) in the absence of soil resources.
We tested these hypotheses by combining experimental manipulations of epiphytes and macronutrient fertilization with elemental analyses and community metabarcoding (fungi and prokaryotes). Specifically, we compared wood stick and cellulose decomposition among three treatments: an unaltered trunk section, an epiphyte mat, and a ‘removal treatment’ where an epiphyte mat was removed to test the effect of soil resources. We also performed a factorial fertilization experiment to test the effects of nitrogen (N) and phosphorus (P) on the decomposition of suspended cellulose.
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These experiments show that slowed decomposition above the forest floor is caused, in part, by separation from soil resources. Moreover, our findings provide support for both the nutrient limitation and dispersal limitation hypotheses and indicate that mechanisms regulating canopy‐level decomposition differ from those documented on the forest floor. This demonstrates the need for a holistic approach to decomposition that considers the vertical position of necromass as it decomposes. Further experimentation is necessary to quantify interactions between community assembly processes, nutrient availability, substrate traits, and microclimate.
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