Environmental effects affecting phenolic production in Macaranga pruinosa in the tropical peat swamp forest

The tropical peat swamp forest (PSF) has always been perceived as an unproductive environment due to several environmental characteristics such as low pH, waterlogged conditions, anaerobic conditions, low nutrient availability and slow decomposition rate. However, these environments have been known to support unique ecosystems rich in flora and fauna diversity. This study represents the first study comparing the bioactivity of Macaranga species in peat swamp and non-peat swamp (NPS) environments. This study also represents the first systematic study to investigate the effects of certain environmental factors in the PSF on the phenolic production in PSF plants. There are a total of five studies representing various works in this project. The first study investigates the difference in phenolic content represented by total phenolic content (TPC), in several plant species collected from PSF and NPS sites. It was found that the same plant species collected from PSF had significantly higher phenolic content compared to NPS plants. RP-HPLC analysis of six PSF Macaranga species also showed a difference in certain phenolic compounds compared to NPS. In the second study, a total of five phenolic compounds were isolated, purified and determined from the mature leaf methanolic extracts collected from the North Selangor PSF population. The compounds isolated were determined to be ferulic acid, p-coumaric acid, kaempferol, quercetin and taxifolin by RP-HPLC, LC-MS and C-13 NMR analysis. Also shown in this study was the first reported isolation and quantification of quercetin in M. pruinosa in high concentrations from both PSF (783.4 ± 54.8 ug/ 100g fresh weight) and NPS (232.1 ± 22.1 ug/ 100g fresh weight) mature leaf samples from the North Selangor PSF population. The purpose of the third study was to determine if the higher concentration of phenolic compounds in PSF M. pruinosa is a naturally occurring adaptation of the plant. Findings from this study showed that the higher concentration of phenolic compounds in PSF M. pruinosa is a natural adaptation for the plants. This study also showed that the increased phenolic compounds in the PSF originate from the partially decomposed plant matter of which peat is composed of. Phenolic compounds in senescent leaves were leached out within the first 48 hours. Lastly, this study also suggests that seasonal water input into the PSF (by rainfall) changes the hydrology of the PSF which affects the phenolic production in PSF M. pruinosa. In the fourth study, the purpose was to determine if PSF plants were capable of absorbing lower molecular phenolics (LMP) into their system and using these compounds to supplement the synthesis of more complex phenolic compounds. Another purpose was to determine if acidic and waterlogged conditions in the PSF affect the amount of phenolic compounds available to the plants in the system. The findings showed that the increased phenolic content in PSF plants is a natural adaptation to the plants. The findings presented in this chapter strongly suggest that substrate acidity and waterlogged conditions have effects on the production of phenolic compounds in this ecosystem. The findings also showed that PSF seedlings were capable of converting phenolic acids (i.e. ferulic acid and p-coumaric acid) into more complex phenolic compounds (i.e. kaempferol and quercetin). The last study was to determine the relationship between the phenolic content in mature M. pruinosa leaves and the phenolic content in surface peat. Findings from this study showed general trend in which the concentration of phenolic molecules in M. pruinosa leaves decreases according to degradation level of the peat land it grows on. The more degraded and exposed the surface peat is, the lower the concentration of phenolics would be made available to the plants.