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Elevated CO2 Stimulates the Competitive Abilities of a Tropical Tree Species

Paper Reviewed
Melo, N.M.J., Rosa, R.-E.G., Pereira, E.G. and Souza, J.P. 2018. Rising [CO2] changes competition relationships between native woody and alien herbaceous Cerrado species. Functional Plant Biology 45: 854-864.

The Brazilian Cerrado is a diverse tropical savanna region covering approximately 2,000,000 square kilometers. It is an area of high species richness and is characterized by intense competition for resources among inhabiting plant species and invasive alien species.

One such invasive plant is the C4 grass Melinis minutiflora. Its introduction and march into the Cerrado is a cause for concern, given its propensity to outcompete and displace native woody and herbaceous vegetation. Recently, however, the research team of Melo et al. (2018) surmised that the rise in atmospheric CO2 might provide a competitive advantage for native C3 woody species over M. minutiflora by inducing larger increases in net photosynthesis and plant water use efficiency than that observed by this invasive C4 grass. And so it was that the four Brazilian scientists designed an experiment to test this hypothesis.

Their experiment consisted of an open-top-chamber CO2-enrichment study conducted at the Federal University of Vicosa in Minas Gerais, Brazil, where the researchers grew an endemic C3 woody tree species (Hymenaea stigonocarpa) for one year under ambient (380 ppm) and elevated (700 ppm) levels of atmospheric CO2 and three densities of M. minutiflora (0%, 50% and 100%). At different stages of the study, Melo et al. collected photosynthetic and growth-related measurements of the plants in the different chamber conditions to evaluate their hypothesis. And what did those measurements reveal?

In the words of the authors, "H. stigonocarpa plants responded to high [CO2] with increased leaf production, length, and stem diameter in the first year of the experiment." Additionally, they allocated "proportionally more biomass to stems and leaves," which shift they viewed to be advantageous for the C3 tree, as it "could resprout more easily after fire events or herbivory and emerge above the fire zone." Furthermore, Melo et al. report finding that, "under high [CO2], woody young plants will be more competitive for light, but not at the expense of root production, so H. stigonocarpa plants under rising [CO2] should become superior competitors for light as well as for water and soil nutrients. In contrast, M. minutiflora plants experienced delayed leaf development under elevated CO2.

Given these several findings, it should come as welcomed news that the Brazilian scientists conclude that "these changes in growth patterns under elevated [CO2] will modify allocation of resources, improving the competition potential of the [endemic] woody species over the alien grass species in the Cerrado."

Posted 1 October 2018