Paper Reviewed
de Rezende, F.M., Souza, A.P., Buckeridge, M.S. and Furlan, C.M. 2015. Is guava phenolic metabolism influenced by elevated atmospheric CO2? Environmental Pollution 196: 483-488.

Psidium guajava is described by de Rezende et al. (2015) as an important tropical crop that is used for the production of fruit in Brazil, where it also is employed in popular medicine, primarily because of its anti-diarrheal effect, as described by Gutierrez et al. (2008). More specifically, they state that the tannins and flavonoids produced by this species -- as described by Park et al. (2012), Mailoa et al. (2013) and Yousaf et al. (2013) -- have a therapeutic activity that has been further reported by Meckes et al. (1996) and Shaheen et al. (2000). And they add that tannins are also "an important anti-herbivore substance."

In further studying P. guajava, the four Brazilian researchers grew 30-cm-tall seedlings of the species in pots filled with well-watered and fertilized soil within open-top chambers maintained at atmospheric CO2 concentrations of either 390 or 780 ppm for a period of 90 days, after which the plants were harvested and a number of different plant properties determined.

This work revealed only a slight increase in plant dry mass in the CO2-enriched chambers at the end of the experiment; but there was what de Rezende et al. call "a significant accumulation of tannins after 90 days of exposure" in the leaves of the plants, while the plant roots showed even higher concentrations of total phenolic compounds. And in light of these facts, the four scientists conclude that the higher accumulation of plant tannins "may result in higher protection of this species against herbivores and pathogens," which is something that has often been found to occur in other plants as well. See Tannins in our Subject Index.

References
Gutierrez, R.M.P., Mitchell, S. and Solis, R.V. 2008. Psidium guajava; a review of its traditional uses, phytochemistry and pharmacology. Journal of Ethnopharmacology 117: 1-27.

Mailoa, M.N., Mahendradatta, M., Laga, A. and Djide, N. 2013. Tannin extract of guava leaves (Psidium guajava L) variation with concentration organic solvents. International Journal of Science and Technology Research 2: 106-110.

Meckes, M., Calzada, F., Tortoriello, J., Gonzalez, J.L. and Martinez, M. 1996. Terpenoids isolated from Psidium guajava hexane extract with depressant activity on central nervous system. Phytotherapy Research 10: 600-603.

Park, B.J., Matsuta, T., Kanazawa, T., Park, C.H., Chang, K.J. and Onjo, M. 2012. Phenolic compounds from the leaves of Psidium guajava II. Quercetin and its glycosides. Chemistry of Natural Compounds 48: 477-479.

Shaheen, H.M., Ali, B.H., Alqarawi, A.A. and Bashir, A.K. 2000. Effect of Psidium guajava leaves on some aspects of the central nervous system in mice. Phytother Research 14: 107-111.

Yousaf, M., Zahoor, A.F., Ali, K.G., Anjum, A., Shahzadi, H., Mubeen, Z., Awais, M. and Purveen, S. 2013. Qualitative determination of allelochemicals in Psidium guajava L leaves for their effect against wheat and canary grass. Pakistan Journal of Weed Science Research 19: 239-256.