Volatile responses of dwarf birch to mimicked insect herbivory and experimental warming at two elevations in Greenlandic tundra

Abstract

Plants release a complex blend of volatile organic compounds (VOCs) in response to stressors. VOC emissions vary between contrasting environments and increase with insect herbivory and rising temperatures. However, the joint effects of herbivory and warming on plant VOC emissions are understudied, particularly in high latitudes, which are warming fast and facing increasing herbivore pressure. We assessed the individual and combined effects of chemically mimicked insect herbivory, warming, and elevation on dwarf birch (Betula glandulosa) VOC emissions in high‐latitude tundra ecosystems in Narsarsuaq, South Greenland. We hypothesized that VOC emissions and compositions would respond synergistically to warming and herbivory, with the magnitude differing between elevations. Warming increased emissions of green leaf volatiles (GLVs) and isoprene. Herbivory increased the homoterpene, (E)‐4,8‐dimethyl‐1,3,7‐nonatriene, emissions, and the response was stronger at high elevation. Warming and herbivory had synergistic effects on GLV emissions. Dwarf birch emitted VOCs at similar rates at both elevations, but the VOC blends differed between elevations. Several herbivory‐associated VOC groups did not respond to herbivory. Harsher abiotic conditions at high elevations might not limit VOC emissions from dwarf birch, and high‐elevation plants might be better at herbivory defense than assumed. The complexity of VOC responses to experimental warming, elevation, and herbivory are challenging our understanding and predictions of future VOC emissions from dwarf birch‐dominated ecosystems.

Seasonal and Elevational Variability in Dwarf Birch VOC Emissions in Greenlandic Tundra

“…Previous studies on dwarf birch showed no effects of warming on the VOC blend (Rieksta et al., 2021, 2023a) when analyzed using random forests, a simple machine learning technique. However, using ASCA, which allows for the investigation of interaction effects on VOC blends, we were able to detect differences in the VOC blends.…”

“…Climate manipulation experiments at high latitudes generally show positive warming effects on VOC emissions (Faubert et al., 2010; Ghirardo et al., 2020; Kramshøj et al., 2016; Lindwall et al., 2016; Rinnan et al., 2020; Valolahti et al., 2015). However, weak or complex effects of warming on VOC emissions have also been reported (Rieksta et al., 2021, 2023a; Rinnan et al., 2011; Schollert et al., 2015). In our data, most VOCs were unaffected by warming, but GLV emission rates doubled in response to warming and this response remained even when emissions were standardized by temperature.…”

“…(2022) and Rieksta et al. (2023a). Chromatograms were analyzed using PARADISe v. 6.0 software (https://ucphchemometrics.com/); Johnsen et al., 2017; Quintanilla‐Casas et al., 2022).…”

“…In short, cartridges were desorbed at 250°C for 10 min (TD100-xr, Markes International Ltd, Llantrisant, UK) and introduced to an HP-5 capillary column (50 m length, 0.2 mm diameter, 0.33 μm film thickness, Agilent Technologies, Santa Clara, CA) with a split flow of 20 ml min −1 . VOCs were separated and analyzed as in Simin et al (2022) and Rieksta et al (2023a). Chromatograms were analyzed using PARADISe v. 6.0 software (https://ucphchemometrics.com); Johnsen et al, 2017;Quintanilla-Casas et al, 2022).…”

“…VOC emission rates were calculated according to Ortega and Helmig (2008) and expressed on the basis of leaf dry mass (ng g −1 dw h −1 ). More details of the classification of the VOCs in different VOC groups can be seen in Methods S1 in Rieksta et al (2023a).…”