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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 138(3). p.323-336
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
published
subject
keywords
Biogeochemistry, Herbivory, Nitrogen mineralisation, Soil microbial ecology, Soil respiration, Subarctic birch forest
in
Biogeochemistry
volume
138
issue
3
pages
323 - 336
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
2019-03-12 04:10:00
@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},
  number       = {3},
  pages        = {323--336},
  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},
  volume       = {138},
  year         = {2018},
}