Biodegradability of dissolved organic matter derived from rice straw

This study characterized chemical and structural properties and biodegradability of dissolved organic matter (DOM) derived from rice straw decay to evaluate the stabilization of DOM in soil systems. Five different DOM samples were obtained at different times of straw decay under laboratory conditions. The biodegradation rates of these five DOM samples were measured using a microcosm technique. The DOM before and after degradation tests was characterized using different chemical and spectroscopic methods. The results showed that the DOM production from straw decay decreased initially, then increased linearly as a function of time, and finally leveled off beyond 63 days. The biodegradation rates of DOM harvested at different decay times were adequately quantified using a two-compartment kinetics equation. The model fitting results showed that the relative content of the biologically resistant DOM fraction increased from 7% in the DOM obtained at Day 0 of decay to about 63% in the DOM at Day 180 of decay. The half lives of the labile and the resistant DOM fractions were 1.22 to 3.07 days and 36 to 630 days, respectively. Fourier transform infrared spectra, H-nuclear magnetic resonance spectra, and C-nuclear magnetic resonance spectra indicated that carbohydrates may be the major components of the labile DOM fraction, and that lignin-derived aromatic organic compounds may be the major components of the resistant DOM fraction. The increased resistance of DOM to further biodegradation may suggest enhanced carbon sequestration in soils.