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The biogeochemical consequences of litter transformation by insect herbivory in the Subarctic : a microcosm simulation experiment

Kristensen, Jeppe A. LU ; Metcalfe, Daniel B. LU and Rousk, Johannes LU (2018) In Biogeochemistry
Abstract

Warming may increase the extent and intensity of insect defoliations within Arctic ecosystems. A thorough understanding of the implications of this for litter decomposition is essential to make predictions of soil-atmosphere carbon (C) feedbacks. Soil nitrogen (N) and C cycles naturally are interlinked, but we lack a detailed understanding of how insect herbivores impact these cycles. In a laboratory microcosm study, we investigated the growth responses of heterotrophic soil fungi and bacteria as well as C and N mineralisation to simulated defoliator outbreaks (frass addition), long-term increased insect herbivory (litter addition at higher background N-level) and non-outbreak conditions (litter addition only) in soils from a Subarctic... (More)

Warming may increase the extent and intensity of insect defoliations within Arctic ecosystems. A thorough understanding of the implications of this for litter decomposition is essential to make predictions of soil-atmosphere carbon (C) feedbacks. Soil nitrogen (N) and C cycles naturally are interlinked, but we lack a detailed understanding of how insect herbivores impact these cycles. In a laboratory microcosm study, we investigated the growth responses of heterotrophic soil fungi and bacteria as well as C and N mineralisation to simulated defoliator outbreaks (frass addition), long-term increased insect herbivory (litter addition at higher background N-level) and non-outbreak conditions (litter addition only) in soils from a Subarctic birch forest. Larger amounts of the added organic matter were mineralised in the outbreak simulations compared to a normal year; yet, the fungal and bacterial growth rates and biomass were not significantly different. In the simulation of long-term increased herbivory, less litter C was respired per unit mineralised N (C:N of mineralisation decreased to 20 ± 1 from 38 ± 3 for pure litter), which suggests a directed microbial mining for N-rich substrates. This was accompanied by higher fungal dominance relative to bacteria and lower total microbial biomass. In conclusion, while a higher fraction of foliar C will be respired by insects and microbes during outbreak years, predicted long-term increases in herbivory linked to climate change may facilitate soil C-accumulation, as less foliar C is respired per unit mineralised N. Further work elucidating animal-plant-soil interactions is needed to improve model predictions of C-sink capacity in high latitude forest ecosystems.

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author
organization
publishing date
type
Contribution to journal
publication status
epub
subject
keywords
Biogeochemistry, Herbivory, Nitrogen mineralisation, Soil microbial ecology, Soil respiration, Subarctic birch forest
in
Biogeochemistry
pages
14 pages
publisher
Springer
external identifiers
  • scopus:85046488756
ISSN
0168-2563
DOI
10.1007/s10533-018-0448-8
language
English
LU publication?
yes
id
b0cd4749-263d-4b29-bfdb-38358ef2867d
date added to LUP
2018-05-15 10:41:05
date last changed
2018-05-15 10:41:05
@article{b0cd4749-263d-4b29-bfdb-38358ef2867d,
  abstract     = {<p>Warming may increase the extent and intensity of insect defoliations within Arctic ecosystems. A thorough understanding of the implications of this for litter decomposition is essential to make predictions of soil-atmosphere carbon (C) feedbacks. Soil nitrogen (N) and C cycles naturally are interlinked, but we lack a detailed understanding of how insect herbivores impact these cycles. In a laboratory microcosm study, we investigated the growth responses of heterotrophic soil fungi and bacteria as well as C and N mineralisation to simulated defoliator outbreaks (frass addition), long-term increased insect herbivory (litter addition at higher background N-level) and non-outbreak conditions (litter addition only) in soils from a Subarctic birch forest. Larger amounts of the added organic matter were mineralised in the outbreak simulations compared to a normal year; yet, the fungal and bacterial growth rates and biomass were not significantly different. In the simulation of long-term increased herbivory, less litter C was respired per unit mineralised N (C:N of mineralisation decreased to 20 ± 1 from 38 ± 3 for pure litter), which suggests a directed microbial mining for N-rich substrates. This was accompanied by higher fungal dominance relative to bacteria and lower total microbial biomass. In conclusion, while a higher fraction of foliar C will be respired by insects and microbes during outbreak years, predicted long-term increases in herbivory linked to climate change may facilitate soil C-accumulation, as less foliar C is respired per unit mineralised N. Further work elucidating animal-plant-soil interactions is needed to improve model predictions of C-sink capacity in high latitude forest ecosystems.</p>},
  author       = {Kristensen, Jeppe A. and Metcalfe, Daniel B. and Rousk, Johannes},
  issn         = {0168-2563},
  keyword      = {Biogeochemistry,Herbivory,Nitrogen mineralisation,Soil microbial ecology,Soil respiration,Subarctic birch forest},
  language     = {eng},
  month        = {05},
  pages        = {14},
  publisher    = {Springer},
  series       = {Biogeochemistry},
  title        = {The biogeochemical consequences of litter transformation by insect herbivory in the Subarctic : a microcosm simulation experiment},
  url          = {http://dx.doi.org/10.1007/s10533-018-0448-8},
  year         = {2018},
}