Fotossintese e acumulo de biomassa em plantas jovens de duas especies arboreas de diferentes grupos ecologicos (pioneira x climacica) de uma floresta estacional semidecidual

AUTOR(ES)
DATA DE PUBLICAÇÃO

2000

RESUMO

Tropical tree species present different adaptative strategies according to the micro habitat where they live or according to their ecological group. The objective of this research was to evaluate the photosynthetic responses and accumulation and allocation of biomass of seedlings of Trema micrantha (L.) Blum. (pioneer) and Hymenaea courbaril (L.) varo stilbocarpa (Hayne) Lee &Langenh. (climax) grown for 4 months under low radiation (LR) (daily PFD of 4,0 :t: 0,2 moI. m-2.day-1 and maximum PFD of 260 :t: 26 !J.mol. m-2. S-1) and high radiation (HR) (daily PFD 50 :t: 4 moI. m-2.dai1 and maximum PFD of 2347 :t: 117 !J.mol. m-2. S-1). Afier this period, seedlings grown under LR were transfered to HR to estimate the acclimation of these two species to a sudden change of radiation intensity, simulating an opening of the canopy. Data of biomass accumulation and allocation, rates of CO2 assimilation, chlorophyll a fluorescence, chlorophyll and carotenoid content were recorded. Under HR, T. micrantha showed higher light saturated rates of photosynthesis with saturation occurring at a higher PFD, higher light compensation point and higher photosynthetic efficiency than H. courbaril. Under LR, lower values were found for T. micrantha with the exception of photosynthetic efficiency that was tended to be greated for this specie. High chlorophyll (Ca+Cb) and carotenoid contents were found in H. courbaril under LR. The Ca:Cb ratio was higher in T. micrantha under both treatments. H. courbaril produced higher amounts of biomass under LR and HR. In the acclimation experiment, accumulation and biomass allocation, rates of CO2 assimilation, chlorophyll a fluorescence and pigment content were recorded up to 190 days afier the transfer to HR. Both species presented reduced rates of assimilation and symptorns of chronic photoinhibition in expanded leaves while under LR. T. micrantha presented total recovery of assimilation and photoprotection mechanisms in their expanded leaves after HR condition. H. courbaril showed partial acclimation and was more sensitive to this new HR condition than T. micrantha. Besides lower photosynthetic rates in relation to the pioneer species, seedlings of H. courbaril presented morphological and physiological changes after transfer to HR thus showing an adjustment to the new condition. This fact suggets an acclimation potential of H. courbaril to a sudden change of light in a new gap formation

ASSUNTO(S)

fotossintese biomassa sucessão ecologica

ACESSO AO ARTIGO

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