Capacidade fotossintética de duas espécies invasoras do Pantanal e do Cerrado

Abstract

In southeast of Brazil there is one of the most extensive wetlands on the planet known as Pantanal. Its geographic location lets it in touch with different types of surrounding vegetation, in which the Cerrado that occupies large portion of the central Brazil. The changes occurred in the last few years in the Pantanal and in the Cerrado whether in climate, hydrology or land use and occupation have contributed to the invasion of undesirable plants, among them Vochysia divergens, a species adapted to flooding that has expanded to the Cerrado. In contrast, Curatella Americana, a native species of the Brazilian Cerrado, is colonizing the lower regions of the Pantanal. Thus, there was an interest in assessing photosynthetic capacity of V. divergens and C. americana in order to verify possible physiological adaptations that justify their success in colonizing new areas in the Cerrado and Pantanal, respectively. Thus, two hypothesis were made: a) in the Pantanal, the photosynthetic capacity of C. americana cannot be lower than that observed for V. divergens, and b) the photosynthetic capacity of both V. divergens and C. americana could not significantly differ between biomes. To test these hypotheses, it was measured the photosynthetic response to light (A/PPFD) and CO2 (A/Cc), nitrogen (N) and phosphorus (P) concentrations in the leaves, and specific leaf area (SLA) of both species during one year, in that different biomes. Confirming the first hypothesis, in the Pantanal it was found no significant differences in the photosynthesis rate between species. The physiological performance of both species was strongly related to N and P leaves content, but the limitation imposed by P appeared to be more important than that imposed by N for both species and biomes. Both species are tolerant to flooding from the point of view of CO2 assimilation. This physiological plasticity, especially for C. Americana, can be a key feature for its ability to survive and persist in the Pantanal. Contrary of the second hypothesis, the results showed significant declines in photosynthesis of C. americana in Pantanal in relation to Cerrado, accompanied by a reduction in the leaves N and P contents. C. americana also maintained a conservative strategy in relation to the water use, which usually is associated with an intrinsic feature of a slower growth rate, and may be a problem in years with longer periods of flooding. Thus, the C. americana colonizing process seems to depend mainly on the flooding pulse, rather than their physiological adaptations, being beneficiated in drier years. On the other hand, V. divergens, as expected, showed no decline in the maximum photosynthesis rate in the Cerrado. Such evidence suggests a greater physiological plasticity of this species, that allows an expansion into drier environments.