O papel ecológico de eventos de molhabilidade foliar na resposta de plantas à seca: Respostas funcionais entre ecossistemas e cenários climáticos

Abstract

Investigating the mechanisms behind organism vulnerability to drought remains one intriguing and increasing topic in ecology. However, the impact of drought, natural or intensified by climate change on vegetation, is still focused on precipitation fluctuations. In this sense, the ecological role of wetting events (i.e. complementary resources of water uptake via leaves, such as fog or dew) in vegetation is still neglected. This thesis aimed to evaluate the ecological role of complementary resources of water in plant vulnerability to drought in different ecosystems and climate change scenarios. To achieve this goal, the first chapter assessed the benefits and costs of leaf wetting events in vegetation using five cophysiological traits (i.e. leaf water potential, photosynthesis, stomatal conductance, leaf transpiration and sap flow). After analyses of 252 observations from 45 studies across eight vegetation types, we identified that leaf wetting events improved plant water status, even though that phenomenon did not influence photosynthesis and leaf transpiration. In addition, we found a progressive reduction of wetting events on plant water status with an increase of altitude and decrease of light rains, which means they were essential mediators of leaf wetting effects on vegetation. The second chapter investigated which contrasting cloud ecosystems (tropical montane forest or tropical rainforest) would be the most vulnerable vegetation to drought. Using 13 morpho-physiological traits, we found that forest plants are more sensitive to drought than grassland ones. Despite higher drought sensitivity in the forest, both environments can become more vulnerable in the future since grassland would be less exposed to fog in the following decades, based on a few fog events recorded in the study period. Finally, the third chapter showed that paleoclimatic models based on traits not only are able to reconstruct the climate in the past but also can indicate changes in vegetation in the future. Such models showed that cloud ecosystems at high altitudes under higher temperature and precipitation scenarios exhibit a higher proportion of plants with conservative traits, which suggests that an increase in precipitation cannot minimize the temperature and altitude effects in the study model. Also, we verified that the mechanisms behind the patterns found are better explained when described by ecophysiological traits. In conclusion, this thesis showed evidence that leaf wetting events influence the plant vulnerability to drought between environments and climate scenarios. In this sense, such events should not be neglected, but considered in plant vulnerability to drought evaluation and development of more realistic climate models.