Increased Forest Soil CO2 and N2O Emissions During Insect Infestation

Abstract

Forest soils are major sinks of terrestrial carbon, but this function may be threatened by mass outbreak events of forest pests. Here, we measured soil CO2-C and N2O-N fluxes from a Scots pine (Pinus sylvestris L.) forest that was heavily infested by the nun moth (Lymantria monacha L.) and an adjacent noninfested (control) forest site during one year. In the infested forest, net emissions of CO2-C were higher during main defoliation, summer and autumn, while indications of increased N2O-N emissions were found at one sampling date. On basis of this, a microcosm incubation experiment with different organic matter treatments was conducted. Soil treatments with needle litter, insect feces plus needle litter, and insect feces showed 3.7-, 10.6-, and 13.5-fold higher CO2-C emissions while N2O-N of the insect feces plus needle litter, and insect feces treatment was 8.9-, and 10.4-fold higher compared with soil treatments without added organic matter (control). Hence, the defoliation in combination with high inputs of organic matter during insect outbreaks distinctly accelerate decomposition processes in pine forest soils, which in turn alters forests nutrient cycling and the functioning of forests as carbon sinks.

Below‐ground responses to insect herbivory in ecosystems with woody plant canopies: A meta‐analysis

“…Insect herbivory increased overall C and N mineralization (H 3 , Figure ), which was expected due to higher input of more labile substrates to the soil (e.g. Grüning, Germeshausen, Thies, & le‐Mellec‐Arnold, ; Grüning et al, ; Lovett et al, ). However, following severe outbreaks, decreased soil respiration has been observed in subarctic systems (Parker et al, ; Sandén et al, ).…”

“…In a global change perspective, this implies that particularly in high latitude systems, where the climate models predict warmer and wetter climates (ACIA, ), which in turn allows insect herbivores to expand their ranges (Jepsen et al, ), immediate below‐ground responses to insect herbivory might cause a positive climate warming feedback (e.g. Grüning et al, ; Heliasz et al, ; Kristensen et al, ).…”

Black Soldier Fly Diet Impacts Soil Greenhouse Gas Emissions From Frass Applied as Fertilizer

“…Application of manure with a larger content of easily degradable organic C substrates tended to generate higher N 2 O emissions than those with more recalcitrant organic C, confirming that both C and N are major controls of N 2 O emissions from agricultural soils (Zhou et al, 2017). Increased losses of greenhouse gases from soils after frass application are likely, due to its high share of easily available N and C. Accordingly, increased CO 2 and N 2 O fluxes from forest soil amended with feces of the nun moth (Lymantria monacha L.) or feces and Scots pine needles (Pinus sylvestris L.) have been measured under laboratory conditions (Grüning et al, 2018). Information about CO 2 and N 2 O emissions of frass from commercially reared insects applied to soils is lacking.…”

Larvae of an invasive scarab increase greenhouse gas emissions from soils and recruit gut mycobiota involved in C and N transformations

“…These inputs to an ~8% decrease in total soil carbon, a 13% increase in microbial biomass carbon, and a 16% increase in microbial biomass nitrogen (Gan et al, 2018). Moreover, deposition of insect frass, which is generally described as high in organic matter and nutrient content (Frost and Hunter, 2004;Watson et al, 2021), can create hot spots of high soil microbial activity with an increase in decomposition of soil organic matter (Kuzyakov et al, 2000;Filser et al, 2016;Gan et al, 2018;Watson et al, 2021), leading to subsequent increases in release of CO 2 , CH 4 , and N 2 O (Kammann et al, 2009;Fielding et al, 2013;Kammann et al, 2017;Grüning et al, 2018;Rummel et al, 2021;Watson et al, 2021). Larval movement in soil apparently represents another indirect effect.…”