Crown humus: Part I-The chemistry of the canopy organic matter of rain forests in Costa Rica

Abstract

<span style="font-size:14.5pt;mso-bidi-font-size:8.5pt">In some tropical rain forests organic matter, derived from epiphytic plants accumulates as heavy mats on tall tree tops (Crown), trunks and branches. Upon microbial and abiotic (chemical, geological) interactions, the canopy organic matter (COM) is transformed into Crown humus. Detailed chemical, chromatographic and spectroscopic analyses of seven COM samples (COM-1 to -7), collected from five different tree tops, and one soil sample collected from the corresponding forest floor (FF-1 ), from Monte Verde Reserve Forest, in Costa Rica, have been carried out in respect of their low M_w organic compounds and the contained humus. The nature and chemical characteristics of these arboreal humic substances are compared with those of their terrestrial and aquatic counterparts. Some striking similarities, particularly in the core structures of fulvic acids (FAs), occurring in three different natural habitats (arboreal, terrestrial and aquatic), are observed. Like those of terrestrial and aquatic –Fas, the molecular architecture of the Crown-FAs constitute metallo-organic complexes of mono-, di- and oligomeric oxygenated dibenzo-<img src='/image/spc_char/alpha.gif' border=0>-pyrones (<b style="mso-bidi-font-weight:normal">1-4, 9a, b, 11, Chart 1</b>). However, the ecological and geochemical conditions of the arboreal miniecosystem being different, are reflected in the simpler structures of large variety of its secondary metabolites (<b style="mso-bidi-font-weight:normal">Tables I </b><b style="mso-bidi-font-weight: normal">& II</b><span style="font-size:14.5pt; mso-bidi-font-size:8.5pt;font-family:" times="" new="" roman";mso-fareast-font-family:="" "times="" roman";mso-ansi-language:en-us;mso-fareast-language:en-us;="" mso-bidi-language:ar-sa"=""> ) entrapped in the inner core and outer-surface of the Crown humus. The role of these compounds in the microbial (chemoheterotroph) metabolic sequence enroute to Crown humus is appraised.</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>