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Pulse Release of Sugars and Polyols from Canopy Bryophytes in Tropical Montane Rain Forest (Guadeloupe, French West Indies)

D. S. Coxson, D. D. McIntyre and H. J. Vogel
Biotropica
Vol. 24, No. 2, Part A (Jun., 1992), pp. 121-133
DOI: 10.2307/2388665
Stable URL: http://www.jstor.org/stable/2388665
Page Count: 13
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Pulse Release of Sugars and Polyols from Canopy Bryophytes in Tropical Montane Rain Forest (Guadeloupe, French West Indies)
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Abstract

Nonvascular epiphytes within the canopy of tropical montane rain forest in Guadeloupe (French West Indies) are exposed to episodes of severe desiccation on more than 30 percent of all days each year. This exposure to wetting/drying cycles induces the accumulation of more than 950 kg ha$^{-1}$ of sugars and polyols by epiphytic bryophytes within the cloud forest canopy. These sugars are then released in pulse form during rewetting episodes and subsequently translocated by throughflow precipitation within the canopy. Sugars and polyols were measured by high-performance liquid chromatography and one- and two-dimensional proton and carbon-13 nuclear magnetic resonance spectroscopy Total sugar and polyol reserves equivalent to 17 percent of the dry weight were seen for the upper canopy liverwort Frullania atrata (Sw.) Nees. In contrast, standing reserves of the lower canopy moss Phyllogonium fulgens (Hedw.) Brid. were less than 6 percent of the dry weight. Exposure to simulated wetting/drying cycles resulted in the substantial loss of sugars. Among sugars and polyols detected in throughflow solution were fructose and mannitol, as well as glucose, erythritol, glycerol and sucrose. Mean release of sugars and polyols during rewetting episodes was greatest for lower canopy bryophyte mats, at 0.9 g m$^{-2}$, compared to 0.3 g m$^{-2}$ in the upper canopy. These release patterns were verified under field conditions, where net annual release of sugars from bryophytes epiphytic within the upper canopy was estimated at 122 kg ha$^{-1}$ These release episodes are postulated to have significant impact on nutrient cycling in the tropical montane rain forest environment, particularly for processes of microbial decomposition and asymbiotic nitrogen fixation, which are readily influenced by supply of exogenous sugars.

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