Ecofisiologia em poliploides de Lippia alba sob diferentes regimes hídricos

Abstract

Lippia alba (Mill.) N. E. Br ex Britton & P. Wilson is a shrub widely used in traditional medicine as an analgesic and soothing, with wide distribution throughout South America. There is also commercial interest in this species because some cosmetics and industrialized teas use it in its composition. Thus, it becomes clear the need to study how this species responds to different growing conditions, mainly in relation to water, a scarce resource in many regions and directly impacted by global climate change. This work aimed to verify how diploid, tetraploid and hexaploid autopolyloid accessions of L. alba respond physiologically to dehydration. For that, biochemical and metabolic parameters were evaluated in L. alba plants cultivated under different irrigation conditions in two experiments. In both it was shown that polyploidy level does not influence the physiological response of L. alba under water stress. Experiment 1 had four continuous soil dewatering times after watering suspension: 0; 5; 10 or 15 days. The results of this step indicated that the water stress situation occurred only in the 15 days treatment without irrigation. In addition, stomatal conductance and transpiration were the most sensitive and stress-responsive variables, and loss in photosynthetic rates was attributed mainly to stomatal closure. Experiment 2 was planned and conducted according to the results of Experiment 1. At this stage, plants of the same ploidy from previous experiment were submitted to 0 or 15 days of total irrigation suspension and rehydrated after the period of water deficit. After 24 hours of rehydration, they were reevaluated. Furthermore, more physiological parameters were evaluated during the dehydration period in Experiment 2. The results showed that parameters of gas exchange have a high power of explanation of the total data variation in relation to the others. On rehydration, it was found that only 24 hours are not enough for L. alba plants to irrigaçãoin their water and physiological status, although some positive changes, on smaller scales, could begin to be perceived. The analysis of essential oils allowed us to infer that water stress does not influence qualitative profile production of these compounds, which is strongly regulated by genetic factors. The results indicate that L. alba is a tolerant species to water stress, which is probably one of the main factors that contribute to its high dispersion in different regions.