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AOBPreview published online on March 24, 2006
Annals of Botany, doi:10.1093/aob/mcl064
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© The Author 2006. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received October 3, 2005
Revised November 11, 2005
Accepted February 9, 2006

Article

Factors Contributing to Dwarfing in the Mangrove Avicennia marina

G. NAIDOO 1 *

1 School of Biological and Conservation Sciences, University of KwaZulu-Natal, P/B X 54001, Durban, 4000, South Africa

* To whom correspondence should be addressed.
G. NAIDOO, E-mail: naidoogn{at}ukzn.ac.za


  Abstract

• Background and Aims In Richards Bay, South Africa, Avicennia marina frequently exhibits a distinct productivity gradient, with tree height decreasing markedly from 6-10 m in the fringe zone to <1·5 m in the dwarf zone which is 120 m inland at a slightly higher elevation. In this investigation, soil physico-chemical conditions between fringe and dwarf A. marina were compared and the constraints imposed by any differences on mangrove ecophysiology and productivity determined.

• Methods Soil and plant samples were analysed for inorganic ions using spectrophotometry. Gas exchange measurements were taken with an infrared gas analyser and chlorophyll fluorescence with a fluorometer. Xylem {psi} was determined with a pressure chamber and chlorophyll content with a chlorophyll absorbance meter.

• Results In the dwarf site, soil salinity, total cations, electrical conductivity and soil concentrations of Na+, K+, Ca2+, Mg2+, Zn2+, Mn2+ and Cu2+ were significantly higher than those in the fringe zone. Soil water potential and the concentration of soil P, however, were significantly lower in the dwarf site. In the leaves, Na+ was the predominant ion and its concentration was 24 % higher in dwarf than fringe mangroves. Leaf concentrations of K+, Ca2+, Mg2+, Mn2+ and P, however, were significantly lower in dwarf mangroves. Photosynthetic performance, measured by gas exchange and chlorophyll fluorescence, was significantly reduced in the dwarf plants.

• Conclusions The results suggest that hydro-edaphic factors contribute to high soil salinities, low water potentials, water stress and ion imbalance within tissues including P deficiency, which in interaction, contribute to dwarfing in Avicennia marina.

Keywords: Avicennia marina, hypersalinity, dwarfing, mangrove, photosynthesis, water stress.
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