Plant residue biochemistry regulates soil carbon cycling and carbon sequestration

Substrate composition is one of the most important factors influencing the decomposition of plant residues in soils. The interaction of organic residu e biochemistry with residue decomposition rates, soil aggregation and soil humus composition was determined in a laboratory experiment. Addition of se ven different organic residues (2% w/w alfalfa, oat, canola, clover, soybea n, corn and prairie grasses) to a Webster soil resulted in a rapid, transie nt increase in aggregate mean weight diameters (MWD) when incubated for 9 d with residues with low phenolic acid content (alfalfa, canola and clover) and was inversely correlated with soil carbohydrate content (r = -0.63). Mo re pronounced improvement in aggregate size was noted upon increased incuba tion to 84 d with organic residues higher in phenolic acid content (corn, p rairie grasses, oat and soybean) and was related to soil phenolic acid (r = 0.65) and soil carbohydrate content (r = 0.70). Total plant residue phenol ic acid content was related to MWD measured after incubation for 84 d by a quadratic response and plateau function (r = 0.96) and the MWD quadraticall y increased with an increase in vanillin-vanillic acid concentrations in th e plant residues (r = 0.997). Soil organic C after 84 d was related to the MWD (r = 0.82) and the residue's vanillin-vanillic acid content (r = 0.86), suggesting that C remaining in the soil following decomposition maybe rela ted to the specific phenolic acid content. The results suggest that transie nt aggregate stability initiated by microbial decomposition of the carbohyd rate and amino acid content of the residue, is then strengthened by the int eraction with phenolic acids such as vanillin or vanillic acid released by microbial decomposition from residues structural components. Published by E lsevier Science Ltd.