The changes of extractive contents of young Swietenia mahagoni (L.) Jacq trees during heartwood formation

We investigated the distribution of extractive, phenolic, and polysaccharides content of young S. mahagoni trees aged 1 to 5 years. The wood powder materials in two vertical positions (bottom and top) were successively extracted using n-hexane, methanol, and hot water solutions. The results showed that there was a significant interaction between the tree age and axial position in all parameters. The methanol and total extractive content decreased significantly from 1 to 3-year-old at the top part. In contrast, the amount of hot water and total extractive increased significantly from 3 to 4-year-old trees at the bottom part. Furthermore, a significant increase was also found at the bottom heartwood for hexane, methanol, and the total extractive from 4 to 5-year-old trees. The reverse trend was observed in the polar fractions (methanol and hot water) at the top of the trees. Generally, the extractive pattern tends to decrease from bottom to top with the highest proportion of methanol extract (70% based on the total extractive weight), and it increased from sapwood to heartwood. The total phenolic content (TPC) and total soluble polysaccharides (TSP) generally increase with tree age (except for TSP from 2 to 3-year-old trees at the top part). The high content of TPC in the heartwood and TSP in the sapwood indicated the process of heartwood formation. In addition, a drastic decrease in the methanol extract and TSP at the age of 3 years at the top indicated that the TSP was transferred from top to bottom for the heartwood formation at the bottom part of 4-year-old trees.