Soil organic carbon and nitrogen pools as influenced polyphenols in different particle size fractions under tropical conditions

Abstract

Soil organic carbon (SOC) and nitrogen (N) pools are highly dependent on physico-chemical quality and composition of plant litter. Polyphenols are widely spread in the plant kingdom and found in plant litter. They are known to affect the chemical and biological processes in the soil. The objective of this study was to examine the effects of polyphenols on the soil organic matter (SOM) pools in different particle size fractions under tropical conditions. Soils were collected from 19 different sites in wet, dry and intermediate zones of Sri Lanka. The bulk soil was fractionated into three particle size fractions (coarse sand, 2-0.25 mm; fine sand, 0.25-0.05 mm; clay + silt, < 0.05 mm) by dry sieving. Total SOC, total N, labile SOC and polyphenol contents were determined in each fraction. The SOC and N pools were mainly associated with clay + silt fraction. More correlations between the variables were present in clay + silt and fine sand fractions than the coarse sand fraction. Labile SOC decreased with the increase of polyphenol/N ratio in the clay + silt fraction, suggesting the presence of a negative response of polyphenols on microbial growth. Labile SOC, total N and stable SOC increased with polyphenols in fine sand and clay + silt fractions, which indicates a positive response of polyphenols on C sequestration and N accumulation owing to reduced decomposition and chemical immobilization, respectively. However, further studies are necessary to investigate the role played by polyphenols on the SOM decomposition and nutrient cycling of tropics.