Mecanismos de regulação hídrica associados à redução na fotossíntese em árvores de dossel na Amazônia Central

Abstract

The Amazon rainforest is main tropical forest in the world and keeper large of the terrestrial carbon. Climate change and increased extreme drought (e. g. El Niño), the forest can show a decline in primary productivity and increased tree mortality. Mortality has great impact on the global carbon balance and current leading hypotheses of plant mortality mechanisms are based on understanding of plant water relations. The plants are susceptible to death by hydraulic failure or carbohydrate depletion in response to stomatal closure. We study the differences in water relations and drought tolerance in canopy trees in the central Amazon in the year El Niño (2015-2016). We measure daily water potentials, morphological and anatomical characteristics, water characteristics of leaf tissue, parameters of gas exchange, non-structural carbohydrates and osmoregulators solute. Analyses were during the year 2015, El Nino's year, in seasonal periods (May, July, September and October). This study involve eleven species classified from dynamics leaf production in non-flush group and flush group (leaf fall timing). The stomatal behavior has minimum water potential (Ψmin) occurring at different times of the day along the year. The groups differ in seasonal water relationship, to maintain Ψ min above critical thresholds, the group with flush peaked leaf fall before dry season (July-August). In addition, this group has good capacity for water recovery from soil with stability in Ψ6:00 during the dry season. On the other hand, the non-flush group changes the state of hydration in dry season, and this was associated with lower in Ψ6:00 (more negative). Wood density is lower in flush group and had the positive relationship with Ψmin. The morphological and anatomical characteristics had no influence in responses seasonal and between the groups. Photosynthesis reduced from 33.6% in response to stomatal limitation due to the hydration status of the species, on the other hand there were reductions in the levels of starch, but there was no consumption of soluble sugars. Unable to detect seasonal differences between the groups and the potassium accumulation, but proline accumulation in flush grup has higher concentrations trend in the dry season. Do not exist differences in water characteristics of leaf tissues (Ψπ, Ψ TLP and ε) between the groups, however the increase in diameter of trees was correlated to the reduction of ΨTLP. The results suggest that wood density plays an important role in water ralations of the trees. The general behavior of the species is isohydric, which led to limiting the consumption of CO 2 in dry season. The two groups have different mechanisms of use and conservation of water convergent in physiological acclimation hence photosynthesis is reduced equally in the dry season, and lastly the large canopy trees can be more sensitive to extreme drought event.