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Metabolism and distribution of grasses in tropical flooded savannas in Venezuela

Published online by Cambridge University Press:  10 July 2009

Ernesto Medina  and
Norma Motta
Ernesto Medina
Affiliation:
Centro de Ecología, Instituto Venezolano de Investigaciones Cientificas, IVICAptdo. 21827Caracas 1020-AVenezuela
Norma Motta
Affiliation:
Centro de Ecología, Instituto Venezolano de Investigaciones Cientificas, IVICAptdo. 21827Caracas 1020-AVenezuela
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Abstract

Flooded savannas in south-west Venezuela consist of seasonal, marshy and flooded grassland communities, the distribution of which depends on soil level. Seasonal grasslands are dominated by tuft-forming, rhizomatous C4-grasses (exemplified by Paspalum chaffanjonii in this study), while flooded grasslands are dominated by stoloniferous grasses which develop rooted, floating culms during the rainy season (Leersia hexandra and Hymenachne amplexi-caulis). The interface between these two communities is a marshy grassland dominated by stoloniferous grass species which tolerate flooding to a depth of 10 to 25 cm (Panicum laxum and Leersia hexandra). All perennial grass species in flooded grasslands behave as typical C3 plants, while marshy grasslands are dominated by Panicum laxum, a species with reduced photo-respiration, low RuBP/PEP-carboxylase ratios, and low absolute RuBP-carboxylase activity compared to C3 grasses. It also has lower photosynthetic rates than the other grass species. Hymenachne amplexicaulis appears to be the least drought tolerant from the species selected, in accordance with its distribution in the wettest side of the flooding gradient studied. The other species showed marked reduction in relative water content and pronounced increase in leaf proline content in drought experiments lasting 6 to 30 days. Alcohol dehydrogenase increased markedly in response to anaerobiosis in the root environment in the tuft forming grasses, while the stoloniferous species with ascending culms were least affected by this treatment, probably as a result of better aeration inside the culms and also to the production of adventitious roots in upper nodes. Nitrate reductase activity increased as a result of anaerobiosis in the roots but not in the leaves, of all species except Leersia hexandra. No difference among the species was found in malate accumulation, or the activity of malic enzyme.

Keywords

anaerobiosisdrought toleranceflooded-grasslandsphotosynthetic-intermediatestropical savannasVenezuela
Type
Research Article
Information
Journal of Tropical Ecology , Volume 6 , Issue 1 , February 1990 , pp. 77 - 89
Copyright
Copyright © Cambridge University Press 1990

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