Abstract

The study investigates early leaf decay in marine and freshwater environments, using an experiment in which Arbutus menziesii (Pacific Madrona) leaves were placed at the sediment-water interface and allowed to decay for 20 days. The leaves show distinct changes at a morphological level from very early stages of decay (i.e., after 5 days). The pattern of degradation in the marine environment is different from that in freshwater. Comprehensive megascopic and microscopic examination using SEM images reveal that decay is essentially due to microbes: bacteria and fungi that form a biofilm. Degradation in water, either marine or freshwater, is more rapid than in sediment, due to oxic conditions and unrestricted mobility of microbes. The lower surface of the leaves shows greater alteration due to: (1) a thinner cuticle; (2) the presence of stomata, which act as an entry point of degradative agents; and (3) cuticular ridges that increase surface area and act as a platform for trapping microbes, detritus, and diatoms. The upper surface remains largely unaffected.

Chemical changes accompanying the morphological alterations have been assessed by molecular analysis of the whole leaves using Pyrolysis-Gas Chromatography-Mass Spectrometry. Various moieties released by the pyrolysis of polysaccharides, lignin, protein, cutin, and cutan (which account for the bulk of the leaf tissue) have been identified and changes in the relative abundances of these traced to the degraded leaves. Relative abundances of toluene and phenol (derived from protein), 2-furaldehyde, 2-hydroxymethylfuran and 2,3-dimethylcyclopenten-1-one (derived from polysaccharides), and 2-methoxyphenol and 2,6-dimethoxyphenol (derived from lignin) decrease after 20 days in both settings. All other pyrolysis products show no distinct change. This shows that, despite morphological changes, the bulk of the tissue, including proteins and carbohydrates (considered labile), survives early decay.

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