Recycling of phenolic compounds in Borneo\u2019s tropical peat swamp forests

Catherine M Yule,Yau Yan Lim,Tse Yuen Lim

doi:10.1186/s13021-018-0092-6

Abstract

BackgroundTropical peat swamp forests (TPSF) are globally significant carbon stores, sequestering carbon mainly as phenolic polymers and phenolic compounds (particularly as lignin and its derivatives) in peat layers, in plants, and in the acidic blackwaters. Previous studies show that TPSF plants have particularly high levels of phenolic compounds which inhibit the decomposition of organic matter and thus promote peat accumulation. The studies of phenolic compounds are thus crucial to further understand how TPSF function with respect to carbon sequestration. Here we present a study of cycling of phenolic compounds in five forests in Borneo differing in flooding and acidity, leaching of phenolic compounds from senescent Macaranga pruinosa leaves, and absorption of phenolics by M. pruinosa seedlings.ResultsThe results of the study show that total phenolic content (TPC) in soil and leaves of three species of Macaranga were highest in TPSF followed by freshwater swamp forest and flooded limestone forest, then dry land sites. Highest TPC values were associated with acidity (in TPSF) and waterlogging (in flooded forests). Moreover, phenolic compounds are rapidly leached from fallen senescent leaves, and could be reabsorbed by tree roots and converted into more complex phenolics within the leaves.ConclusionsExtreme conditions—waterlogging and acidity—may facilitate uptake and synthesis of protective phenolic compounds which are essential for impeded decomposition of organic matter in TPSF. Conversely, the ongoing drainage and degradation of TPSF, particularly for conversion to oil palm plantations, reverses the conditions necessary for peat accretion and carbon sequestration.

Highlights

Tropical peat swamp forests (TPSF) are globally significant carbon stores, sequestering carbon mainly as phenolic polymers and phenolic compounds in peat layers, in plants, and in the acidic blackwaters
The TPSF was flooded with acidic water with very high levels of phenolic compounds (354 ± 24 gallic acid equivalent (GAE)/100 g) in comparison with the other forest types which all had neutral to alkaline soils and water, and soil total phenolic content (TPC) several times lower (31.2–132 GAE/100 g) (Table 3)
Our results demonstrate that M. pruinosa, a common TPSF tree, is capable of a direct uptake of phenolic compounds via the root system, which supports the previous findings of Lim et al [10], in which there were high concentrations of lower molecular weight phenolics detected in the fine and thick roots of TPSF M. pruinosa

Summary

Introduction

Tropical peat swamp forests (TPSF) are globally significant carbon stores, sequestering carbon mainly as phenolic polymers and phenolic compounds ( as lignin and its derivatives) in peat layers, in plants, and in the acidic blackwaters. Previous studies show that TPSF plants have high levels of phenolic compounds which inhibit the decomposition of organic matter and promote peat accumulation. TPC varies within plants, being most abundant in the mature leaves of a common TPSF tree Macaranga pruinosa compared with young or senescent leaves, branches, trunks or buttresses. TPC and tannins vary temporally, being significantly more abundant in surface peat and in mature leaves during the wet season compared with the dry season [10], suggesting that waterlogging influences the uptake or production of phenolic compounds by plants

Methods

Results

Discussion

Conclusion