Impactos de fatores do solo e da competição com Cryptostegia madagascariensis sobre as respostas ecofisiológicas de plantas jovens e adultas de Copernicia prunifera

Abstract

The global biota has been modified by biological invasions, reducing biodiversity and causing economic losses. Copernicia prunifera (carnauba), a palm tree native to Caatinga ecosystem (Northeastern Brazil), has been impacted by invasive C.madagascariensis (viúva alegre), causing death of hundreds of carnauba trees. In this study we evaluated physiological, biochemical, and nutritional responses in adult plants of C. prunifera and C. madagascariensis, seeking a better understanding of the interaction between these two species. The study was divided into two stages: the first carried out in the field with mature plants and the second with young plants in a greenhouse. The field study was carried out in two areas, in the municipality of Caucaia, Ceará, Brazil: District of Catuana (intense water deficit during dry season) and Minguaú Farm (salinity, sodicity and excess water throughout the year). Our results show that the native species C. prunifera is better adapted to severe water deficit conditions, but this ecophysiological performance is not sufficient to maintain the carnauba populations after introduction of the C. madagascariensis. The invader becomes more competitive under waterlogging in salt-affected soils, and its ecophysiological responses are not severely impacted even with high sodium accumulation in the leaves. The results also show that the negative impacts on the native palm tree occur only in the final stage of infestation, when the shading caused by the invasive species restricts access to solar radiation and accelerates the leaf senescence process, confirmed by the reduction of nitrogen content and photosynthetic rate. The experiment carried out in a greenhouse aimed to evaluate the establishment of young plants of C. prunifera and C.madagascariensis, exposed to periods of excess water in the soil. The experiment was carried out under a randomized block statistical design, in a split-plot arrangement with five replications. The treatments in the plots were formed by five periods of stress by flooding (0, 8, 12, 16 and 20 days) and the subplots by the two species. For some variables the time was considered as a sub-subplot. Non-destructive evaluations (leaf gas exchange, fluorescence and relative chlorophyll content) were carried out at 8, 12,16 and 20 days of flooding, as well as at 32 and 40 days. The growth rates in height and diameter were estimated for the period from 0 to 20 and from 20 to 40 days. Plants were harvested at 40 days, and leaf samples were used for biochemical and nutritional analyses. Young plants of C. prunifera. and C. madagascariensis showed tolerance to flooding, surviving periods up to 20 days of stress and with good recovery capacity afterdraining excess water. In response to flooding, the invasive species reduces the root/shoot ratio, promotes the formation of adventitious roots and concentrates its roots in the topsoil (0 to 8 cm). Conversely, the native species has a higher root/shoot ratio, which is slightly increased under flood stress, and has better root distribution in the soil.The net photosynthesis rate in mature leaves is higher and less impacted by flooding in the invasive species, despite the greater accumulation of sodium in the leaves. However, biomass accumulation is less impacted on native species, indicating that leaf characteristics, especially low specific leaf area, and morphological and anatomical adaptations of the root system can ensure greater capacity for net carbon assimilation in the whole plant, in flooded environments temporary, in relation to C. madagascariensis. The results reinforce the vulnerability of carnauba populations in the Caatinga ecosystem, which can be severely impacted without the development of technologies to mitigate the impacts in the invaded areas.