Photosynthetic rates and nitrogen use efficiencies in plants of different functional groups in the open savannas of Gran Sabana, Canaima National Park, Venezuela
Bibiana
Alejandra
Bilbao, Departamento de Estudios Ambientales, Universidad Simón Bolívar, Caracas, Venezuela, bibiana_bilbao@hotmail.com
(Presenting)
Carlos
Luis
Méndez, Departamento de Estudios Ambientales, Universidad Simón Bolívar, Caracas, Venezuela, carlosmendez@etheron.net
Eduardo
Zambrano, Departamento de Estudios Ambientales, Universidad Simón Bolívar, Caracas, Venezuela, ezambrano@usb.ve
Rosana
Castillo, Departamento de Estudios Ambientales, Universidad Simón Bolívar, Caracas, Venezuela, rosanacastillo@cantv.net
Mercedes
Jaffé, Departamento de Estudios Ambientales, Universidad Simón Bolívar, Caracas, Venezuela, mechejaffe@yahoo.com
José
Manuel
Moreno, Facultad de Ciencias del Medio Ambiente, Universidad de Castilla- La Mancha, Toledo, España,, JoseM.Moreno@uclm.es
The Gran Sabana, Canaima National Park (30000 km2), Venezuela, is a region characterized by a mosaic of forest, shrubs and savannas. The presence of open savannas has been attributed to the Holocene dry climatic phases, but more recently anthropogenic fires have become the prevailing factor. Among the dominant herbaceous savanna species we find Axonopus anceps and Trachypogon plumosus (Poaceae, C4), Lagenocarpus rigidus and Hypolytrum pulchrum (Cyperaceae, C4), among woody plants, Byrsonima verbascifolia (Malpighiacaea) (C3, a stemless tree). A question of interest in this particular type landscape is to evaluate to what extent fires interact with soil nutrient deficiencies to result in different seasonal net photosynthesis (Pn) and N use efficiencies (NUE) between different herbs and trees and in relation to their C4/C3 nature. The highest Pn were observed in grasses T. plumosus and A. anceps (20-25 and 15-20 micromol CO2 m-2 s-1 respectively). All other species had Pn values lower than 14 micromol CO2 m-2 s-1. The sedges (group with higher biomass in the savannas) showed comparable values of PnW (Pn expressed in weight bases: micromol CO2 g-1 s-1) and NUE, in respect to the C3 woody species. Although all species had similar low values of leaf nitrogen contents, the sedges and the woody species displayed lower SLA than grasses. Our results support the idea that the expansion of savannas (promoted by fire) over the forest, plus the low performance of the herbaceous components in CO2 assimilation, could have a deep impact on the C balance in the region.
Submetido por Bibiana Alejandra Bilbao em 24-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)