Hiram M. Falcão

Caatinga, the Brazilian dry tropical forest: can it tolerate climate changes?

Our review focuses on the projections of climate change in the Brazilian semiarid region, the Caatinga, based on recent publications about global climate change and biology. We found several vulnerable points in the initial estimates, the main one being that the data were collected and analyzed without a multidisciplinary knowledge. This review discusses several studies that show the current knowledge in many semiarid regions around the world. Some of these studies argue for the increase in vegetation greenness responses even under severe and prolonged drought, based on the high resilience the Caatinga native species show under severe drought conditions over the years. Additionally, we include in this review recent data produced by our group on key ecophysiological variables under drought conditions. We also show successful examples of deforested areas recovery in the semiarid region of the Central America. It is critical that the recovery of semiarid areas is coupled with the implementation of socio-environmental policies, engaging the local population and providing subsidies for life wealth improvement. These are key aspects for a long-term recovery and conservation of the Brazilian dry tropical forest.

Stress tolerance and ecophysiological ability of an invader and a native species in a seasonally dry tropical forest.

Ecophysiological traits of Prosopis juliflora (Sw.) DC. and a phylogenetically and ecologically similar native species, Anadenanthera colubrina (Vell.) Brenan, were studied to understand the invasive species’ success in caatinga, a seasonally dry tropical forest ecosystem of the Brazilian Northeast. To determine if the invader exhibited a superior resource-capture or a resource-conservative strategy, we measured biophysical and biochemical parameters in both species during dry and wet months over the course of two years. The results show that P. juliflora benefits from a flexible strategy in which it frequently outperforms the native species in resource capture traits under favorable conditions (e.g., photosynthesis), while also showing better stress tolerance (e.g., antioxidant activity) and water-use efficiency in unfavorable conditions. In addition, across both seasons the invasive has the advantage over the native with higher chlorophyll/carotenoids and chlorophyll a/b ratios, percent N, and leaf protein. We conclude that Prosopis juliflora utilizes light, water and nutrients more efficiently than Anadenanthera colubrina, and suffers lower intensity oxidative stress in environments with reduced water availability and high light radiation.

Leaf phytohormone levels and stomatal control in an evergreen woody species under semiarid environment in a Brazilian seasonally dry tropical forest

Phytohormones are essential for controlling abilities of plant species to overcome stress conditions, and influence some aspects of stomatal control, preventing excessive water loss. This study investigates the correlation between foliar phytohormones levels, water status and stomatal conductance in an evergreen woody species (Cynophalla flexuosa) throughout dry and rainy seasons, and the transition between them. We measured stomatal conductance (gs), xylem branch water potential (Ѱx), and leaf concentration of abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA) and trans-zeatin (tZ). Stomatal conductance was more sensitive to atmospheric conditions, such as VPD than to soil water balance. However, we found correlation between gs and Ѱx, suggesting that these direct water availability measures were a good proxy to explain gs in C. flexuosa. Moreover, ABA leaf concentration had no effect on gs, but ABA and tZ interaction was important to the phenological behaviour of this species. Cytokinins act in delaying leaf senescence, which is crucial to evergreen species, and it is opposite to ABA’s action. JA also showed a significant interaction to ABA, and kept high foliar level during wet season. ABA levels varied throughout the year, and its concentration itself was less important to gs than the interaction to other phytohormones, such as tZ and JA. In conclusion, although ABA did not directly affect stomatal conductance in C. flexuosa, the interaction between ABA, tZ and JA likely played a role in the regulation of stomatal behavior in this species.

Estratégias para tolerar o estresse salino em duas espécies lenhosas tropicais

This study aimed to evaluate the leaf primary metabolism in two woody species, Sterculia foetida and Bombacopsis glabra. Both species have seeds rich in oil and they are largely found in regions with irregularities in water availability. Seedlings were grown in a greenhouse from seeds. At 140 days after emergence, 50% of the plants were subjected to salt stress for 23 days, daily receiving 100 mM of NaCl solution. In both species, leaf stomata conductance and water potential decreased quickly under salt stress. The two species showed different strategies in photosynthetic pigment concentration and components of nitrogen metabolism. S. foetida kept the pigment concentration unchanged after 23 days of stress, while B. glabra increased concentration of chlorophyll a and carotenoids. S. foetida showed a high leaf concentration of K+ in stressed plants and a Na+/K+ ratio without differences when compared to control. Thus, S. foetida presented a better ionic balance, while B. glabra invested in photoprotection. Therefore, both species present potential to be planted in Brazilian Northeast, where water deficit and salt stress are challenging for annual crops. Estratégias para tolerar o estresse salino em duas espécies lenhosas tropicais Resumo O estudo teve como principal objetivo avaliar o metabolismo primário foliar de duas espécies lenhosas, Sterculia foetida e Bombacopsis glabra, de sementes ricas em óleo e amplamente encontradas em regiões com disponibilidade hídrica irregular. As duas espécies foram cultivadas em casa de vegetação a partir de sementes. Aos 140 dias após a emergência, 50% das plantas foram submetidas ao estresse salino durante 23 dias, recebendo diariamente uma solução de 100 mM de NaCl. As duas espécies rapidamente reduziram a sua condutância estomática e o potencial hídrico foliar, em relação às plantas controle. S. foetida e B. glabra apresentaram estratégias diferentes quanto ao conteúdo de pigmentos fotossintéticos e componentes do metabolismo do nitrogênio. S. foetida manteve seus pigmentos intactos após 23 dias de estresse, enquanto B. glabra aumentou o conteúdo de clorofila a e carotenoides. S. foetida apresentou alto teor foliar de K+ e uma relação Na+/K+ sem diferença nas plantas estressadas comparadas com as do controle. Portanto, S. foetida apresentou um melhor em balanço iônico, enquanto B. glabra investiu em fotoproteção. Assim, as duas espécies são alternativa potencial para serem cultivadas no Nordeste brasileiro, onde condições de estresse hídrico e salinidade são restritivas para culturas anuais. ISSN: 1983-2605 (online)