Respostas ecofisiológicas de mudas de manguezal a um gradiente de salinidade e desenvolvimento de sensor de baixo custo para mensuraração de salinidade do solo.

Abstract

Global climate change has caused a number of consequences for the environment. Among the most threatened ecosystems are mangroves, which are major providers of ecological and socioeconomic goods and services. One of the main factors related to climate change that can affect this ecosystem is the increase in salinity. Little is known how seedlings, which is one of the most sensitive stages of development, responded to increases in salt in the soil. A problem that may exist when conducting studies is the methodology used to estimate salinity. Our objective was to evaluate the growth and ecophysiological responses of two mangrove species (Avicennia germinans L. and Rhizophora racemosa G. Mey) to a salinity gradient, as well as to develop a practical and low-cost sensor to assess soil salinity. For each mangrove species, five salinity treatments (0, 10, 20, 40 and 55 grams of salt per liter of water) were established and we evaluated the growth trajectory and ecophysiological attributes, including: height, diameter, number of leaves, biomass, specific leaf area, leaf dry matter content, curves of vulnerability to cavitation, pressure-volume curves, water potential and gas exchange. For the calibration and testing of the sensor, soil samples were arranged in the same five treatments, which were followed up in two groups (soil with salt replacement and soil without salt replacement). The studied species proved to be quite resistant to salinity (physiological drought), since there were no major differences in growth and mortality between them during the 3-month of accompaniment. A. germinans showed better height performance, while R. racemosa invested in more resistant leaf tissues. There was little difference between treatments for growth attributes. In the hydraulic and tissue attributes R. racemosa showed less vulnerability to cavitation, less point of loss of the turgor and less osmotic potential, having greater resistance to drought before the addition of salt, but A. germinans managed to better vary the tissue attributes according to the salinity treatment, in addition to being more conservative in the use of water. In terms of time, the osmotic adjustments and the point of loss of the turgor demonstrated that they were unable to maintain acclimatization in all treatments until the end of the experiment. For the sensor, the results demonstrate that the instrument showed good sensitivity to salt loss and accumulation in different treatments and dates, presenting a satisfactory performance. Our results bring important contributions to the understanding of the growth and physiology of mangrove species and demonstrate a variation in the hydraulic, osmotic and gas exchange strategies developed by the species in a gradient of salinity. Our results also present a practical, efficient and low-cost alternative for measuring salinity when more robust instruments are not available.