ABSTRACT Changes in atmospheric CO2 levels are accompanied by ecological interactions involving other environmental factors, such as drought, which can severely alter the water balance of plants, thereby influencing sap flow, gas exchange, and plant growth. The objective of this study was to evaluate the water use economy, leaf gas exchange, and growth of young plants of the species Lafoensia pacari subjected to high concentrations of atmospheric CO2 ([CO2]) and soil water deficit. Increased vapor pressure deficit was observed from 1200 to 1800 hours. Plants under elevated [CO2] exhibited increased leaf photosynthesis, resulting in improved growth. Specific leaf area was lower in plants under high [CO2], mainly after soil water deficit treatment. Daily irrigated plants growing under ambient [CO2] had higher stem sap flow velocity (cm h-1) and hourly sap flow (kg h-1), mainly during the hottest hours of the day, than plants under high [CO2]. Improved water use by plants growing under high [CO2] may result in increased availability of water in the soil, partially offsetting future drought events and extending the growth period.

ABSTRACT Water availability is the main factor that explains current patterns of palm abundance. However, the interaction between water stress and increasing atmospheric CO2 concentrations caused by climatic change and its effects on palm physiology remain poorly known. Macauba palm is a widespread Neotropical species commonly found in ecosystems subjected to seasonal drought and has potential use in oil production. The present work investigated the influence of increased CO2 concentrations on photosynthetic responses to drought in macauba palm plants. Exposure to increased CO2 concentrations led to up-regulation of photosynthesis through higher stomatal conductance and improved light and water use efficiency. Macauba palm plants under water stress, irrespective of CO2 concentration, were able to maintain constant levels of proline and chlorophyll, while preventing oxidative damage. Plants grown at higher CO2 concentrations were more capable of recovering from drought due to higher Rubisco carboxylation rate (Vc max) and electron transport rate (J max), which prevented a reduction in total dry mass at the end of the stress period. Stomatal control of photosynthesis, coupled with the prevention of severe damage under stress, would allow efficient biomass production by the macauba palm under future scenarios of climate change.

ABSTRACT Fire is an abiotic disturbance that regulates vegetation structure and biodiversity. Some plant species have adapted to fire prone environments by evolving protective structures. Acrocomia aculeata (macaw palm) is widely distributed throughout tropical America, and is found in environments continuously influenced by anthropogenic fire. We aimed to determine whether the fruit characteristics of A. aculeata enable seeds to resist the effects of fire and also the consequent effects of fire on fruit biometric traits and embryo viability. After a fire event in a region of pasture-forest transition, we marked 30 individuals of A. aculeata. The trees were separated by UPGMA analysis into 5 groups according to fire exposure, ranging from trees with no exposure to trees with fruit completely exposed to fire. Fruit exposure to high temperatures led to lower values in fruit fresh weight, length, density, and processable mass.Fire had no significant effect on seed biometric variables, because of the structures of the fruit, including its lignified endocarp and its insulating and mucilaginous mesocarp. These structures helped to maintain the embryos viability by preventing oxidative damage. In conclusion, the fruit structure of the macaw palm may facilitate seed persistence, even when subject to increasingly frequent fire events.