Paper Reviewed
Maia, R.A., Fernandes, G.W., Silva, A.I.S. and Souza, J.P. 2019. Improvement in light utilization and shoot growth in Hymenaea stigonocarpa under high CO2 concentration attenuates simulated leaf herbivory effects. Acta Botanica Brasilica 33: 558-571.

Insect herbivory can cause considerable damage to plants, including reduced growth and reproduction, thus having the potential to alter ecosystem structure and diversity. Although a number of studies have investigated the effects of elevated CO2 on insect herbivory, much remains to be learned on this topic. And so it was that Maia et al. (2019) set out to examine the impact of simulated herbivory events on the photochemical responses of photosystem II and the growth of Hymenaea stigonocarpa (Jatobá do cerrado), an abundant leguminous tree species in the Brazilian Cerrado that is of considerable economic value for its high quality wood, resin and edible fruits.

Their experiment was conducted at the Federal University of Vicosa, Minas Gerais, Brazil. H. stigonocarpa seedlings were grown in open-top chambers for nearly two years under either ambient (390 ppm) or elevated (1000 ppm) CO2 concentrations. After approximately 10 months of growth in these conditions, a subset of plants in each CO2 treatment were subjected to herbivory simulation, which included removal of approximately 50% of leaf area present in the basal or apical portions of the stem.

In describing their findings, Maia et al. report that under simulated herbivory, elevated CO2 improved the electron transport rate, effective quantum yield of photosystem II and chlorophyll contents in the apical part of the stem, whereas in the basal portion it stimulated "plant height, branch and root length, leaf number, leaf area, node number, and leaf expansion rate." Additionally, they report that "despite the increase in leaf area in H. stigonocarpa subjected to high CO2 treatment, no effect of nutrient dilution was noted on the leaves after herbivory events." What is more, Maia et al. note that "the concentration of nutrients analyzed in [the] study was either equal or greater in the leaves of plants grown under high CO2 that appeared after simulated herbivory events, indicating a better absorption and allocation of these nutrients in the leaves of those plants that grew in environments enriched with CO2," likely associated "with the formation of fine and long roots, evidenced by greater root length and volume."

In light of all the above, the researchers who conducted this study conclude the increase of atmospheric CO2 "attenuated the adverse effects of leaf removal on H. stigonocarpa plants by inducing photosynthetic improvement and growth after the loss of leaf tissue." Consequently, they add, "H. stigonocarpa could benefit from the greater availability of CO2 in the atmosphere against herbivory events." And that is good news for this important leguminous tree species on the Brazilian Cerrado!