Abstract
The biogenic volatile organic compounds, BVOCs have a central role in ecosystem–atmosphere interactions. High-latitude ecosystems are facing increasing temperatures and insect herbivore pressure, which may affect their BVOC emission rates, but evidence and predictions of changes remain scattered. We studied the long-term effects of + 3 °C warming and reduced insect herbivory (achieved through insecticide sprayings) on mid- and late summer BVOC emissions from field layer vegetation, supplemented with birch saplings, and the underlying soil in Subarctic mountain birch forest in Finland in 2017–2018. Reduced insect herbivory decreased leaf damage by 58–67% and total ecosystem BVOC emissions by 44–72%. Of the BVOC groups, total sesquiterpenes had 70–80% lower emissions with reduced herbivory, and in 2017 the decrease was greater in warmed plots (89% decrease) than in ambient plots (34% decrease). While non-standardized total BVOC, monoterpene, sesquiterpene and GLV emissions showed instant positive responses to increasing chamber air temperature in midsummer samplings, the long-term warming treatment effects on standardized emissions mainly appeared as changes in the compound structure of BVOC blends and varied with compounds and sampling times. Our results suggest that the effects of climate warming on the total quantity of BVOC emissions will in Subarctic ecosystems be, over and above the instant temperature effects, mediated through changes in insect herbivore pressure rather than plant growth. If insect herbivore numbers will increase as predicted under climate warming, our results forecast herbivory-induced increases in the quantity of Subarctic BVOC emissions.Graphic
Highlights
Ecosystems in Subarctic and Arctic regions, while known to be sensitive to warming (Walsh 2014), are currently experiencing temperature increments twice the rate of the global average (Pachauri and others 2014)
These results suggest that the instant positive effect of warmer climate on total Biogenic volatile organic compounds (BVOCs) emission rates in Subarctic ecosystems may depend on plant phenological state and that the long-term effects may be mediated through changes in insect herbivore pressure rather than changes in plant growth
Isoprene emissions have been found to increase 1.5–6-fold with 1 - 2 °C warming (Tiiva and others 2008; Tang and others 2018). Supporting these findings, we found that the non-standardized BVOC emissions from our Subarctic vegetation showed an instant increase with increasing chamber air temperature, this response depended on plant phenological stage: while the positive response was clear in the June sampling in both years, no response was found in the August sampling in either year
Summary
Ecosystems in Subarctic and Arctic regions, while known to be sensitive to warming (Walsh 2014), are currently experiencing temperature increments twice the rate of the global average (Pachauri and others 2014). Background insect herbivory is typically low (Barrio and others 2017; Kozlov 2008; Li and others 2019), but observations of downy birch (Betula pubescens) leaf damage in Fennoscandia show that the leaf area eaten increases from 1–2 to 5–7% along a latitudinal gradient from 70° N to 60° N (Kozlov 2008) As this gradient climatically roughly represents the predicted warming in the 100 years in these areas (Ruosteenoja and others 2016), insect herbivore damages on plant leaves in Herbivory, Temperature and Subarctic BVOC Emissions the Arctic can be assumed to more than double in the near future. These predictions are supported by recent findings from the tundra, where dwarf birch (Betula nana) growing in experimentally warmed plots had fourfold leaf damages in comparison with plants growing in control plots (Li and others 2019)
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