Hymenaea Courbaril l. (leguminosae): A Model Tree to Understand Pathways for Carbon Sequestration Into Cellulose in the Rain Forest
Marcos
Silveira
Buckeridge, Inst.de Botânica, Seç. Fis.Bioq.Plts, msbuck@usp.br
(Presenting)
Marcos
P.M.
Aidar, Instituto de Botânica, Seç.de Fis.Bioq. Plantas, maidar@uol.com.br
Marilia
Gaspar, Instituto de Botânica, Seç.de Fis.Bioq. Plantas, gasparmarilia@yahoo.com.br
Solange
C.M.
Viveiros, Instituto de Botânica, Seção de Anatomia, billysol@uol.com.br
Carlos
Alberto
Martinez, USP, Depto de Biologia, Ribeirão Preto, carlosamh@ffclrp.usp.br
Paula
M.F.
Costa, Instituto de Botânica, Seç.de Fis.Bioq. Plantas, paulacosta@uol.com.br
Marco
A.S.
Tiné, Instituto de Botânica, Seç.de Fis.Bioq. Plantas, matine@ig.com.br
Sonia
M.C.
Dietrich, Instituto de Botânica, Seç.de Fis.Bioq. Plantas, smcdietrich@aol.com.br
Beatriz
J.
Lopes, Instituto de Botânica, Seç.de Fis.Bioq. Plantas, lopes@yahoo.com.br
Most work performed to understand how tropical plant respond to higher atmospheric CO2 concentrations focus on how much more phototosynthesis (CO2 assimilation) and accumulation of mass they acquire after growth under elevated CO2. With few exceptions, little is known about the biochemical responses of plants to high CO2. After carbon dioxide is assimilated by the leaves, it is transformed into sucrose that can be further metabolised for 1) cell respiration ; 2) starch synthesis, which can be used for respiration within the next day or week; 3) as a source of carbon for proteins, nucleic acids and secondary metabolites and 4) as a source of carbon for synthesis of cell wall polysaccharides, which will stay in the plant body for much longer. In this work we used Hymenaea courbaril, a late secondary species that occur throughout the rain forests in the neotropics, as a model to study morphological, physiological and biochemical landmarks that characterise the behaviour of seedlings of H. courbaril under 720ppm of CO2. Under this condition: 1) Leaves altered their stomata, decreasing their frequency; 2) Leaves collected in 1919, 1929 and 1956 confirmed that H. courbaril has been responding to the increase in CO2 concentration by decreasing stomata indexes since industrial revolution; 3) Sucrose and starch levels were higher in the leaves; 4) Stem and leaves of the seedlings accumulated respectively 19 and 30 % more cellulose. These effects were all buffered when storage mobilisation took place. These results suggest that the CO2 assimilated by the leaves are partitioned through a pathway that leads to accumulation of carbon into cellulose. We speculate that when plants use their “internal” stored reserves as a source of carbon, a common event in seasonal environment, another carbon pathway becomes active and competes with the photosynthetic path so that carbon sequestration becomes lower. This confirms previous observations that regions with higher seasonality have a lower potential for carbon sequestration. FAPESP, CNPq.
Submetido por Marcos Silveira Buckeridge em 17-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)