Distribution and characterisation of phenolic compounds in macaranga pruinosa and associated soils in a tropical peat swamp forest

Phenolic compounds are abundant in tropical peat swamp forests and peat mostly comprises lignin and other phenolics. Water in these forests is darkened by tannins and humic acids and the flora exhibit high total phenolic contents (TPC). To further understand the functions of phenolics in peat swamp forests we investigated phenolic compounds (Folin Ciocalteu assays, HPLC) in a common tree, Macaranga pruinosa (Euphorbiaceae), over 18 months. We simultaneously studied peat phenolics with respect to composition, depth and season. TPC were highest in mature leaves compared with trunks, branches and roots, probably relating to their role in defence against herbivory and pathogens in low nutrient environments. Relative concentrations of low (phenolic acids, flavonoids) to high (tannins, derivatives) molecular weight phenolics decreased as leaves matured indicating conversion within leaves. TPC increased significantly at the peat surface and during the wet seasons. TPC of mature leaves were significantly higher during the wet season. This implies either plants synthesise phenolic compounds in response to flooding or phenolics are more readily available during the wet season due to increased detrital leaching and plants can absorb phenolics via their roots. Waterlogged conditions may not be stressful to adapted plants but may facilitate recycling of protective phenolic compounds.