Effect of Living Roots on Soil Organic Matter Decomposition

Published information is contradictory about the inhibitory or stimulatory effect of living roots on soil organic matter d~m~sition. In this study, i4C-labelled rye straw was exposed in fertilii or unfertilized soil with or without plants (winter rye, Se&e cereuIe) for 49 days under semi-controlled conditions. Our objective was to study the effect of roots on soil organic matter mineralization under different mineral nutrient conditions. The planted treatment had a higher “CO, loss and a higher efficiency of 14C-labelled material utilization by microorganisms. Fertilization decreased “CO2 loss. Percent “C in microbial biomass was positively correlated with percent “C respired. Total microbial biomass, ‘C-labelled microbial biomass and total “C remaining of the rhiiosphere soil were higher compared to bulk soil. Living roots had a stimulatory effect on soil organic matter decom@tion due to the higher microbial activity induced by the roots. This stimulatory effect was reduced by application of fertilizer.