Acclimation to Elevated CO2 Increases Constitutive Glucosinolate Levels of Brassica Plants and Affects the Performance of Specialized Herbivores from Contrasting Feeding Guilds

Abstract

Plants growing under elevated CO2 concentration may acclimate by modifying chemical traits. Most studies have focused on the effects of environmental change on plant growth and productivity. Potential effects on chemical traits involved in resistance, and the consequences of such effects on plant-insect interactions, have been largely neglected. Here, we evaluated the performance of two Brassica specialist herbivores from contrasting feeding guilds, the leaf-feeding Pieris brassicae and the phloem-feeding Brevicoryne brassicae, in response to potential CO2-mediated changes in primary and major secondary metabolites (glucosinolates) in Brassica oleracea. Plants were exposed to either ambient (400 ppm) or elevated (800 ppm) CO2 concentrations for 2, 6, or 10 weeks. Elevated CO2 did not affect primary metabolites, but significantly increased glucosinolate content. The performance of both herbivores was significantly reduced under elevated CO2 suggesting that CO2-mediated increases in constitutive defense chemistry could benefit plants. However, plants with up-regulated defenses could also be subjected to intensified herbivory by some specialized herbivores, due to a chemically-mediated phagostimulatory effect, as documented here for P. brassicae larvae. Our results highlight the importance of understanding acclimation and responses of plants to the predicted increases in atmospheric CO2 concentrations and the concomitant effects of these responses on the chemically-mediated interactions between plants and specialized herbivores.

Health‐promoting compounds of broccoli (Brassica oleracea L. var. italica) plants as affected by nitrogen fertilisation in projected future climatic change environments

“…The N:S ratio was not significantly affected by the [CO 2 ], alone or in combination with other factors, which indicates a predominant effect of salt stress, whereas the C:N ratio was influenced by the N form and [CO 2 ]. A similar dependence was observed for the total GSL levels, and a correlation between the total GSL content and C:N ratio was found at ambient ( R = 0.71) and elevated ( R 2 = 0.81) [CO 2 ], indicating that the atmospheric CO 2 enrichment enhanced the plants' carbon supply and that the increasing C:N ratio affected the GSL content . Not only the GSL content but also the AA content was modified according to the C:N ratio, with a redistribution of N from AAs such as Glu to those with lower C:N ratios, such as Asn or Arg, characteristic of high NH 4 + concentrations .…”

“…These results are in agreement with the fact that these AAs act as S donors in the synthesis of aliphatic GSLs, and both total AAs and total GSLs were highly influenced by the N form and [CO 2 ]. However, the interaction of these two factors, N × CO 2 , affected indolic rather than aliphatic GSLs; only the former were more abundant under enhanced plant C supply . An understanding of the ecological implications for plant–herbivore interactions of chemical changes in these C‐containing secondary metabolites under individual or combined environmental conditions is necessary.…”

Phytochemical changes in milkweed induced by elevated CO2 alter wing morphology but not toxin sequestration in monarch butterflies

“…Plants grown under eCO 2 produce tissues with lower nitrogen concentrations (Drake, Gonzalez‐Meler, & Long, ; Robinson, Ryan, & Newman, ), causing herbivores to increase the amount of foliage they consume (Docherty et al, ; Johnson, Lopaticki, & Hartley, ). Moreover, eCO 2 also changes the composition and concentration of plant secondary metabolites (PSMs) (Klaiber, Dorn, & Najar‐Rodriguez, ; Ryan, Rasmussen, & Newman, ). Because catabolizing PSMs is energetically costly, changes in these compounds affect the ecology of herbivores (Hunter, ).…”

Will chemical defenses become more effective against specialist herbivores under elevatedCO2?

“…Klaiber et al . () report that elevated CO 2 increased glucosinolate concentrations in B. oleracea and consumption rates of P. brassicae , but were unable to separate whether decreased leaf nutritional quality or increased feeding stimulant was driving increased consumption rates. Our SEM was able to isolate the direct effect of leaf nitrogen on consumption from its indirect effects mediated through glucosinolates, consider the effects of leaf nitrogen on glucosinolate concentrations, and determine if those relationships differed at different CO 2 concentrations.…”

“…These results support Klaiber et al . ()'s interpretation that increased P. brassicae consumption rates on B. oleracea var. gemmifera under elevated CO 2 was driven by increased concentrations of glucosinolate feeding stimulants.…”