Different from the alteration of leaf internal soft tissues, the cuticle membrane covering the epidermal cell layer is morphologically intact through the whole duration of decay, which is consistent with chemical analysis results. Both carbon and hydrogen isotope compositions of n-alkanes of these leaves change little during the decay process with an average fluctuation of 0.8‰ for δ13C and 8‰ for δD respectively.
Our data indicate that: (1) although not obvious in morphological and anatomical observation, major N-containing biomolecules experience decay through senescence before leaves reach to the ground. (2) The negative shift of bulk carbon isotope value was due to the loss of liable biomolecules such as polysaccharides. (3) When reach to the lake, lake water facilitates decay process, resulting in the destruction of internal tissue probably through the loss of polysaccharide compounds. (4) The stability of decay resistant components such as cuticle and associated waxes render molecular carbon and hydrogen isotope signals that are affected little during early diagenesis.
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