Estresses abióticos na germinação de sementes e no desenvolvimento de mudas florestais
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2022-02-16
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Universidade Estadual Paulista (Unesp)
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Estresses abióticos prejudicam a germinação e o desenvolvimento de mudas em espécies florestais, em áreas comerciais ou de recomposição. Frente às mudanças climáticas, estudos podem melhorar as estratégias para a conservação da biodiversidade autóctone e fortalecer projetos de reflorestamento comercial ou de recomposição ambiental. Objetivou-se avaliar os efeitos dos estresses térmico, hídrico e salino na germinação de sementes e do estresse hídrico no crescimento de plantas de Corymbia citriodora, uma espécie exótica com interesse comercial crescente no Brasil, e de Zeyheria tuberculosa, uma espécie nativa do Brasil com potencial econômico e para uso em trabalhos de recomposição ambiental. Para as duas espécies foram conduzidos experimentos em laboratório e em casa de vegetação. Em laboratório avaliou-se o processo germinativo das sementes das duas espécies sob diferentes temperaturas, potenciais hídricos simulados com polietilenoglicol (PEG 6000) e potenciais osmóticos simulados com NaCl. Em casa de vegetação, mudas das duas espécies foram submetidas a cinco regimes hídricos (20, 35, 50, 65 e 80% da capacidade máxima de retenção de água no solo), avaliando-se características de crescimento, fisiológicas e bioquímicas. Para as duas espécies, as temperaturas de 25 e 30 °C favorecem o potencial fisiológico das sementes. Para C. citriodora a porcentagem e a velocidade de germinação das sementes diminuíram com o aumento do estresse hídrico e salino, mas de forma mais acentuada sob déficit hídrico a 30 ºC e o limite de tolerância das sementes ao déficit hídrico está entre -0,6 e -0,8 MPa, tanto a 25 quanto a 30 ºC, e ao estresse salino entre -1,4 e -1,6 MPa, a 25 ºC, e entre -1,2 e -1,4 MPa, a 30 ºC. Portanto, a germinação de sementes de C. citriodora apresenta sensibilidade diferenciada ao déficit hídrico e salino, sendo mais prejudicada pelo déficit hídrico. Para Z. tuberculosa, o aumento do estresse reduziu a germinação e IVG das sementes a partir de -0,6 MPa, porém de forma diferenciada entre os tipos de estresse, sendo mais sensível ao estresse salino. As mudas de C. citriodora apresentaram aumento nos teores de clorofila, carotenoides, prolina e MDA e redução no potencial hídrico foliar e nos parâmetros de trocas gasosas e crescimento com a diminuição da disponibilidade hídrica e quando cultivadas em níveis inferiores a 50% da capacidade máxima de retenção de água no solo houve redução significativa nas características de crescimento. Observou-se, também, que os regimes de irrigação mais restritivos proporcionaram diferenças, que com o aumento da idade e crescimento das mudas, se acentuaram de forma mais severa. As temperarturas de 25 e 30 ºC porpocionaram o maior potencial fisiológico em ambas as espécies. O limite de tolerância das sementes de C. citriodora ao déficit hídrico está entre -0,6 e -0,8 MPa, tanto a 25 quanto a 30 ºC, e ao estresse salino entre -1,4 e -1,6 MPa, a 25 ºC, e entre -1,2 e -1,4 MPa, a 30 ºC. Portanto, a germinação de sementes de C. citriodora tem sensibilidade diferenciada ao déficit hídrico e salino, sendo mais prejudicada pelo déficit hídrico. As sementes de Z. tuberculosa são mais sensíveis ao estresse salino do que ao estresse hídrico. Potenciais hídricos inferiores a -0,6 MPa e salinos a -0,4 MPa comprometem o potencial fisiológico das sementes. Os regimes hídricos mais restritivos reduziram os parâmetros fisiológicos e morfológicos das mudas de C. citriodora, sendo o desenvolvimento de mudas comprometido a níveis de umidade inferiores a 50% da capacidade de campo. Regimes de irrigação que proporcionam 50% ou menos de retenção de água no substrato prejudicam o crescimento de plantas de Z. tuberculosa e alta umidade (80%) no substrato prejudica o crescimento radicular.
Abiotic stresses affect the germination and development of seedlings in forest species, in commercial or recomposition areas. Faced with climate change, studies can improve strategies for the conservation of indigenous biodiversity and strengthen commercial reforestation or environmental restoration projects. The objective was to evaluate the effects of heat, water and saline stress on seed germination and of water stress on plant growth of Corymbia citriodora, an exotic species with growing commercial interest in Brazil, and Zeyheria tuberculosa, a species native to Brazil with economic potential and for use in environmental restoration work. For both species, experiments were carried out in the laboratory and in a greenhouse. In the laboratory, the germination process of the seeds of the two species was evaluated under different temperatures, water potentials simulated with polyethylene glycol (PEG 6000) and osmotic potentials simulated with NaCl. In a greenhouse, seedlings of the two species were submitted to five water regimes (20, 35, 50, 65 and 80% of the maximum soil water retention capacity), evaluating growth, physiological and biochemical characteristics. For both species, temperatures of 25 and 30 °C favor the physiological potential of the seeds. For C. citriodora, the percentage and speed of seed germination decreased with increasing water and saline stress, but more markedly under water deficit at 30 ºC and the tolerance limit of seeds to water deficit is between -0.6 and -0.8 MPa, both at 25 and 30 ºC, and to salt stress between -1.4 and - 1.6 MPa, at 25 ºC, and between -1.2 and -1.4 MPa, at 30 ºC Therefore, the germination of C. citriodora seeds presents differentiated sensitivity to water and saline deficits, being more affected by water deficits. For Z. tuberculosa, the increase in stress reduced germination and IVG of seeds from -0.6 MPa, but in a different way between the types of stress, being more sensitive to saline stress. C. citriodora seedlings showed an increase in chlorophyll, carotenoids, proline and MDA contents and a reduction in leaf water potential and in gas exchange and growth parameters with the decrease in water availability and when cultivated at levels below 50% of maximum capacity of water retention in the soil there was a significant reduction in growth characteristics. It was also observed that the more restrictive irrigation regimes provided differences, which with increasing age and seedling growth, became more severe. Temperatures of 25 and 30 ºC provided the highest physiological potential in both species. The tolerance limit of C. citriodora seeds to water deficit is between -0.6 and - 0.8 MPa, both at 25 and 30 ºC, and to salt stress between -1.4 and -1.6 MPa, at 25°C, and between -1.2 and -1.4 MPa at 30 °C. Therefore, the germination of C. citriodora seeds has differentiated sensitivity to water and saline deficits, being more affected by water deficits. The seeds of Z. tuberculosa are more sensitive to salt stress than to water stress. Water potentials below -0.6 MPa and saline at -0.4 MPa compromise the physiological potential of seeds. The most restrictive water regimes reduced the physiological and morphological parameters of C. citriodora seedlings, and seedling development was vii compromised at moisture levels below 50% of field capacity. Irrigation regimes that provide 50% or less of water retention in the substrate impair the growth of Z. tuberculosa plants and high humidity (80%) in the substrate impairs root growth.
Abiotic stresses affect the germination and development of seedlings in forest species, in commercial or recomposition areas. Faced with climate change, studies can improve strategies for the conservation of indigenous biodiversity and strengthen commercial reforestation or environmental restoration projects. The objective was to evaluate the effects of heat, water and saline stress on seed germination and of water stress on plant growth of Corymbia citriodora, an exotic species with growing commercial interest in Brazil, and Zeyheria tuberculosa, a species native to Brazil with economic potential and for use in environmental restoration work. For both species, experiments were carried out in the laboratory and in a greenhouse. In the laboratory, the germination process of the seeds of the two species was evaluated under different temperatures, water potentials simulated with polyethylene glycol (PEG 6000) and osmotic potentials simulated with NaCl. In a greenhouse, seedlings of the two species were submitted to five water regimes (20, 35, 50, 65 and 80% of the maximum soil water retention capacity), evaluating growth, physiological and biochemical characteristics. For both species, temperatures of 25 and 30 °C favor the physiological potential of the seeds. For C. citriodora, the percentage and speed of seed germination decreased with increasing water and saline stress, but more markedly under water deficit at 30 ºC and the tolerance limit of seeds to water deficit is between -0.6 and -0.8 MPa, both at 25 and 30 ºC, and to salt stress between -1.4 and - 1.6 MPa, at 25 ºC, and between -1.2 and -1.4 MPa, at 30 ºC Therefore, the germination of C. citriodora seeds presents differentiated sensitivity to water and saline deficits, being more affected by water deficits. For Z. tuberculosa, the increase in stress reduced germination and IVG of seeds from -0.6 MPa, but in a different way between the types of stress, being more sensitive to saline stress. C. citriodora seedlings showed an increase in chlorophyll, carotenoids, proline and MDA contents and a reduction in leaf water potential and in gas exchange and growth parameters with the decrease in water availability and when cultivated at levels below 50% of maximum capacity of water retention in the soil there was a significant reduction in growth characteristics. It was also observed that the more restrictive irrigation regimes provided differences, which with increasing age and seedling growth, became more severe. Temperatures of 25 and 30 ºC provided the highest physiological potential in both species. The tolerance limit of C. citriodora seeds to water deficit is between -0.6 and - 0.8 MPa, both at 25 and 30 ºC, and to salt stress between -1.4 and -1.6 MPa, at 25°C, and between -1.2 and -1.4 MPa at 30 °C. Therefore, the germination of C. citriodora seeds has differentiated sensitivity to water and saline deficits, being more affected by water deficits. The seeds of Z. tuberculosa are more sensitive to salt stress than to water stress. Water potentials below -0.6 MPa and saline at -0.4 MPa compromise the physiological potential of seeds. The most restrictive water regimes reduced the physiological and morphological parameters of C. citriodora seedlings, and seedling development was vii compromised at moisture levels below 50% of field capacity. Irrigation regimes that provide 50% or less of water retention in the substrate impair the growth of Z. tuberculosa plants and high humidity (80%) in the substrate impairs root growth.
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Eucalipto, Ipê, mudanças climáticas, Florestal