Ciclo diário de carboidratos não estruturais em espécies C3, C4 e CAM de restinga e suas relações com a fotossíntese e temperatura foliar
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Data
2023-03-20
Autores
Andrade, João Pedro Zanardo de
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Universidade Federal do Espírito Santo
Resumo
Divergent species occur in the restinga ecosystem in terms of photosynthetic metabolism (C3, C4 and CAM). The type of CO2 assimilation mechanism and daily environmental variations can influence the concentrations of photoassimilates in the form of non-structural carbohydrates (sugars and starch) during the day and night. In the case of ecophysiological studies with native species, correlations between gas exchange variables with CNE concentrations and microclimatic variations such as luminosity and leaf temperature can help in understanding the adaptive strategies in restinga species that differ in terms of photosynthetic metabolism. We hypothesize that C3 and C4 metabolism species increase their CNE concentrations throughout the day and decline during the night, while the CAM species shows the opposite response. Another hypothesis is that the CNE contents of the C3, C4 and CAM species are directly related to the CO2 assimilation rate. The objective of this study was to characterize the dynamics of CNE and gas exchange in Protium icicariba (C3), Panicum trinii (C4) and Clusia hilariana (CAM) in a 24-hour cycle, and to correlate these variables with each other and with leaf temperature. Leaves were collected every 2 hours for CNE analyses, and gas exchange variables were measured every 4 hours. Fructose and glucose concentrations in C3 and CAM metabolism species increased from 7:00 am, reaching their maximum values at 3:00 pm, and then declining to the lowest values between 1:00 am and 5:00 am. The dynamics of sucrose contents in C3 and C4 showed an inverse response to that of monosaccharides, showing low values during the day and higher values between 21:00 h and 7:00 h the next day. Gas exchanges in C3 and C4 show similar trends, while in CAM it showed inverse responses for photosynthetic assimilation (A) and transpiration (E). The A and E rates of the C3 and C4 metabolism species showed higher values between 10:00-17:00h, while the CAM showed higher values between 17:00-7:00h. The highest levels of monosaccharides between 13:00 and 15:00 hours in species C3 and C4 were attributed to greater photosynthetic activity in this period confirmed by the positive correlation between A and glucose/fructose in these two groups of photosynthetic metabolism. Species of C3 and C4 metabolism also showed positive correlations of A and E with leaf temperature. The CAM showed negative correlations between these variables. The low levels of sucrose in the three species in the light and dark phases of the day may be a reflection of the strong demand on their drain. We conclude that the hypotheses raised at the beginning of the study were partially validated since both species showed similar variations in CNE concentrations throughout the day. Despite this similarity, the CAM metabolism species was the only one that showed no correlation between CNE and A.
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Açúcares , Amido , Ciclo circadianos , Sacarose , Trocas gasosas