Abstract
Above- and belowground herbivory represents a major challenge to crop productivity and sustainable agriculture worldwide. How this threat from multiple herbivore pests will change under anthropogenic climate change, via altered trophic interactions and plant response traits, is key to understanding future crop resistance to herbivory. In this study, we hypothesized that atmospheric carbon enrichment would increase the amount (biomass) and quality (C:N ratio) of crop plant resources for above- and belowground herbivore species. In a controlled environment facility, we conducted a microcosm experiment using the large raspberry aphid (Amphorophora idaei), the root feeding larvae of the vine weevil (Otiorhynchus sulcatus), and the raspberry (Rubus idaeus) host-plant. There were four herbivore treatments (control, aphid only, weevil only and a combination of both herbivores) and an ambient (aCO2) or elevated (eCO2) CO2 treatment (390 versus 650 ± 50 μmol/mol) assigned to two raspberry cultivars (cv Glen Ample or Glen Clova) varying in resistance to aphid herbivory. Contrary to our predictions, eCO2 did not increase crop biomass or the C:N ratio of the plant tissues, nor affect herbivore abundance either directly or via the host-plant. Root herbivory reduced belowground crop biomass under aCO2 but not eCO2, suggesting that crops could tolerate attack in a CO2 enriched environment. Root herbivory also increased the C:N ratio in leaf tissue at eCO2, potentially due to decreased N uptake indicated by lower N concentrations found in the roots. Root herbivory greatly increased root C concentrations under both CO2 treatments. Our findings confirm that responses of crop biomass and biochemistry to climate change need examining within the context of herbivory, as biotic interactions appear as important as direct effects of eCO2 on crop productivity.
Highlights
Root herbivory is very damaging to plants, especially when combined with multiple biotic and abiotic stresses (Zvereva and Kozlov, 2012) that can lead to substantial losses of crop yields (Villani and Wright, 1990; Blossey and Hunt-Joshi, 2003; Blackshaw and Kerry, 2008)
In this study we investigate how elevated atmospheric CO2 (eCO2) influences plant growth and primary chemistry when under attack from an aboveground and belowground herbivore
There was no indication of any effect of herbivore treatment on aboveground biomass (F3,173 = 0.44 p = 0.7275), root herbivory consistently reduced root biomass with treatments where weevil larvae were present yielding significantly less root biomass than treatments without weevils
Summary
Root herbivory is very damaging to plants, especially when combined with multiple biotic and abiotic stresses (Zvereva and Kozlov, 2012) that can lead to substantial losses of crop yields (Villani and Wright, 1990; Blossey and Hunt-Joshi, 2003; Blackshaw and Kerry, 2008). The direct and indirect (mediated by host-plant plasticity) interactions among plants and herbivores occupying different guilds or niches, are key to understanding crop resistance and resilience to herbivory (Johnson et al, 2009; Huang et al, 2013; McKenzie et al, 2013; Hagenbucher et al, 2014) Environmental stressors such as drought, elevated atmospheric CO2 (eCO2) and temperature can modify these trophic interactions (Johnson et al, 2011b; Stevnbak et al, 2012; Ryalls et al, 2013; Johnson et al, 2016a,b). Johnson and Riegler (2013) showed concomitant increases in root herbivory in Eucalyptus seedlings, reversed several of the effects of elevated CO2 on plant growth and chemistry
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