Influência da luminosidade do sub-bosque no crescimento e características foliares de espécies arbóreas da Amazônia na fase juvenil
The objectives of this study were to determine the effect of availability of light in the forest understorey (inferred from irradiance above the canopy and the understorey fraction of visible sky - FCV values) on growth and leaf traits (specific leaf area and leaf thickness), and on the photosynthet...
| Autor principal: | Nascimento, Helena Cristina Santos |
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| Grau: | Dissertação |
| Idioma: | por |
| Publicado em: |
Instituto Nacional de Pesquisas da Amazônia - INPA
2020
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| Acesso em linha: |
https://repositorio.inpa.gov.br/handle/1/12724 http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4247034T9 |
| Resumo: |
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The objectives of this study were to determine the effect of availability of light in the forest understorey (inferred from irradiance above the canopy and the understorey fraction of visible sky - FCV values) on growth and leaf traits (specific leaf area and leaf thickness), and on the photosynthetic characteristics of ten tree species in the juvenile stage. I also studied the effect of diurnal variation on photosynthetic rates (A), and the relationship between A and growth rates of saplings. The study was conducted at the Experimental Station of Tropical Forestry (ZF2 base) of the National Institute for Research in the Amazon. I utilized tree species in the juvenile stage with up to 3 m height. Gas exchange rates were measured with a portable photosystem system using two leaves per plant and three plants per species. Growth data were collected in 2007 and 2008, whereas the other variables were collected in the rainy and dry seasons of 2008. Light-saturated photosynthesis (Amax) and potential photosynthesis (Apot) were measured at light saturation and CO2 concentrations of 380 and 2000 μmol mol-1, respectively. The effect of time of day in stomatal movement and the photosynthetic rates (Amax) was assessed by collecting data between 06:00 and 18:00 h. Chlorophyll and nitrogen content were obtained by the Arnon and Kjeldahl´s methods, respectively. Finally, I assessed the effect of understorey irradiance on the study variables. Average annual increase in diameter (IAD) was 0.64 mm, while mean annual increase in height (IAA) did not exceed 0.08 m. Amax and stomatal conductance (gs) showed a strong diurnal variation, suggesting that stomatal opening in these plants is modulated by endogenous factors. Apot remained relatively constant throughout the day, showing little sensitivity to variation in gs. No effect of Apot on IAD and IAA was observed. The rainy pattern (dry and rainy season) had effect on Amax, leaf area index (IAF) and chlorophyll content. In the study area mean IAF was 5.1, with higher values being observed in the rainy season. Amax was higher in the rainy season. Availability of light in the understorey had a positive (p < 0,05) effect on IAA, Apot, and leaf chlorophyll content. There was no effect of understorey light levels on leaf thickness, specific leaf area, and IAD. It was concluded that small variations in light levels at the forest unsderstorey influence growth rates in height, but that the small changes observed in the understorey irradiance were not large enough as to trigger any anatomical changes in leaves, particularly, specific leaf area and leaf thickness. |