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 decomposition. In this study, 14C-labelled rye straw was exposed in fertilized or unfertilized soil with or without plants (winter rye, Secale cereale) 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 14CO2 loss and a higher efficiency of 14C-labelled material utilization by microorganisms. Fertilization decreased 14CO2 loss. Percent 14C in microbial biomass was positively correlated with percent 14C respired. Total microbial biomass, 14C-labelled microbial biomass and total 14C remaining of the rhizosphere soil were higher compared to bulk soil. Living roots had a stimulatory effect on soil organic matter decomposition due to the higher microbial activity induced by the roots. This stimulatory effect was reduced by application of fertilizer. © 1990.