ABSTRACT Popularly known as araçá-una, Psidium myrtoides is an endemic tree species in Brazil, with fruits much appreciated by the fauna. It is indicated for the composition of reforestation and for enriching the vegetation of degraded areas. This work aimed to evaluate the effects of drought, heat, and the interaction of both in the physiological attributes of Psidium myrtoides plants. Monitored fluorescence, gas exchange, and chlorophyll index in araçá-una plants induced by drought, heat, and the combination of both during 1, 3, and 7 days after treatment induction (DAT). After, the plants were returned to their initial condition, and their recovery was evaluated at 15 DAT. The results indicate that Psidium myrtoides plants reduce photosynthetic activity in the absence of water, contrary to what has been shown in other studies; in addition, they are not potentiated by the combination with heat. Therefore, we conclude that this species has a potential tolerance to heat (Tmean 30.3 °C). However, if water is available in the soil, it maintains photosynthetic activity at normal levels.

Resumo O objetivo deste trabalho foi avaliar os efeitos de quatro osmorreguladores sob diferentes concentrações na germinação de sementes e no crescimento de plântulas de Samanea tubulosa. As sementes foram dispostas em “gerbox” e umedecidas com 20 mL das seguintes soluções: manitol, PEG-6000, NaCl e KCl, nos potenciais osmóticos de 0,0; -0,3; -0,6; -0,9 e -1,2 MPa. Ao final do experimento realizaram-se os cálculos de IG e IVG. As plântulas consideradas normais foram selecionadas para medição de massa fresca, massa seca, comprimento da raiz e da parte aérea. Observou-se que o tratamento com PEG-6000 apresentou as maiores alterações no IG e IVG, obtendo uma redução de 81% da germinação já na concentração de -0,3 MPa. Com o manitol, os maiores efeitos sobre a redução na germinação só foram observados a partir de -0,9 MPa. Os tratamentos com NaCl e KCl obtiveram comportamentos semelhantes. A testemunha apresentou o maior percentual de plântulas normais, ao passo que o tratamento com -0,3 MPa de KCl apresentou o crescimento da raiz 22% e a parte aérea 14% maior que a testemunha. Ao fim do experimento, constatou-se que as sementes e plântulas se Samanea tubulosa são moderadamente tolerantes ao estresse provocado por NaCl e KCl, entretanto são levemente sensíveis ao estresse causado por manitol e extremamente sensíveis ao estresse provocado por PEG-6000. Ademais, concluiu-se que para a espécie estudada o manitol não foi eficiente em simular o estresse hídrico, sendo recomendado o PEG-6000 para simular esse estresse em estudos futuros.

Abstract The objective of this work was to evaluate the effects of four osmoregulators under different concentrations on seed germination and seedling growth of Samanea tubulosa. The seeds were placed in gerbox and moistened with 20 mL of the following solutions: mannitol, PEG-6000, NaCl and KCl, in osmotic potentials 0.0; -0.3; -0.6; -0.9 and -1.2 MPa. At the end of the experiment, GI and GIS calculations were performed. The seedlings considered normal were selected to measure fresh mass, dry mass, root and shoot length. It was observed that the treatment with PEG-6000 was the one that presented the greatest changes in the GI and GIS obtaining a reduction of 81% in the germination already in the concentration of -0.3 MPa. With mannitol, the greatest effects on the reduction in germination were only observed from -0.9 MPa. The treatments with NaCl and KCl obtained similar behaviors. The control presented the highest percentage of normal seedlings, while the treatment with -0.3 MPa of KCl showed root growth 22% and shoot 14% higher than the control. At the end of the experiment, it was observed that the seeds and seedlings of Samanea tubulosa are moderately tolerant to stress caused by NaCl and KCl, however, they are slightly sensitive to the stress caused by mannitol and extremely sensitive to the stress caused by PEG-6000. Furthermore, it was concluded that for the studied species mannitol was not efficient in simulating water stress, being recommended PEG-6000 to simulate this stress in future studies.