Efeito da submersão em espécies reófitas utilizadas em obras de engenharia natural no sul do Brasil

Abstract

Natural Engineering is a discipline that has technical, ecological, aesthetic and economic objectives and takes advantage of the multiple functions of plants for his works. Among the applications of Natural Engineering, there is the revegetation of lake slopes, who naturally face the adverse effects caused by water level fluctuations and by the waves that imprint energy on its banks. To study the effects that submersion causes in species used in Natural Engineering works in southern Brazil, the species Caliandra brevipes (Benth.), Gymnanthes schottiana Müll. Arg., Mimosa pigra L. and Phyllanthus sellowiannus (Klotzsch) Müll. Arg. were submitted to four levels of simulated submersion: TE – control (normal irrigation); CO - Water layer at the level of the lap of the seedling; SP – Partial submersion, water depth covering 50% of the seedling; ST – Total submersion, water layer covering 100% of the plant, during three distinct periods: 15, 30 and 45 days. The experimental design was completely causalized with two factors: level and period of submersion. The analyses performed were: survival rate (%), height (cm), diameter (mm), green leaf mass (MFV) (g), green root mass (MRV) (g), initial fluorescence (Fo), maximum fluorescence in light (Fm), maximum quantum yield of PSII (Fv/Fm), maximum fluorescence in dark (Fm'), chlorophyll a (Chl a), b (Chl b), total (total Chl) and carotenoid content. It was observed, at 45 days in the total submersion treatment, a sharp fall of leaves in C. brevipes and M. pigra.Therefore, the analyses of chlorophyll a fluorescence and photosynthesizing pigment content could not be continued. In M. pigra, there was 62.5% mortality in the ST treatment. At 30 days, MRV was stimulated in C. brevipes, with the highest averages observed in the PS treatment. G. schottiana and P. sellowiannus maintained 100% survival rates. The attribute Chl a decreased with increasing water layer, along with Fo and Fm levels, indicating that light uptake may have been affected by the submersion. However, Fv/Fm levels remained undifferentiated, indicating that energy production was not affected by stress. The results indicate that C. brevipes and M. pigra can be used at higher elevations, where the water layer reaches at most 50% of the plant height, for up to 45 days, while G. schottiana and P. sellowiannus can be used at lower elevations, and can withstand submergence stress for 45 days with the level of the water layer covering 100% of the seedlings.