Changes in fatty acid and hydrocarbon composition of leaves during decomposition in a southeastern blackwater stream

Fatty acid and hydrocarbon composition were determined in decomposing leaf packets of sweetgum (Liquidambar styraciflua) and water oak (Quercus nigra) from a snag habitat in a southeastern blackwater stream. The initial total fatty acid and hydrocarbon concentrations in sweetgum leaves were significantly greater than in the oak species. Higher concentrations of unsaturated fatty acids and dicyclic diterpenoid hydrocarbons accounted for most of this difference. Both of these biochemical subgroups are preferentially degraded relative to the bulk leaf material and other compounds within their respective lipid classes. No significant differences remained after 70 days of decomposition. Cuticular fatty acids are selectively preserved and thus, increased relative to noncuticular components during decomposition. The bacterially derived iso- and anteiso-branched-chain fatty acids increased markedly after 23 days. The results of this study suggest that qualitative differences in lipid composition may contribute to the observed difference in overall decomposition rate of leaves between these species.