Rates of soil organic matter decomposition and nitrogen mineralization have been commonly assessed by incubating soil samples in the absence of live roots with an implicit assumption that rhizosphere processes have little impact on the results.  However, our studies have indicated that this implicit assumption is often invalid.  The rate of soil organic matter decomposition in the presence of live roots can be inhibited by as much as 50% or accelerated by as much as 382%, depending on the kind of plant-soil couplings and experimental conditions.  This presentation addresses the question: what are the mechanisms responsible for the rhizosphere-dependent soil organic matter decomposition?  According to recent results, we suggest that accelerated soil microbial turnover in the rhizosphere and transpiration-induced drying-rewetting cycle are two of the possible mechanisms behind rhizosphere-dependent soil organic matter decomposition.  Results from one of our greenhouse studies indicate that the levels of rhizosphere effects on soil organic matter decomposition are linked with total soil microbial turnover rates, but not with soil microbial biomass.  Our data also indicate that drying and rewetting may explain the increased CO₂ efflux and N mineralization in the presence of the rhizosphere, since CO₂ efflux originating from soil organic matter is positively correlated with total daily evapotranspiration rates in the planted treatments.  However, evapotranspiration rates are also positively correlated with leaf biomass and possibly root exudation.  It is unclear at this stage whether drying-rewetting alone, or drying-rewetting together with root exudation, or root exudation alone causes the rhizosphere effect on SOM decomposition.  The two mechanisms are also connected to each other because drying and rewetting may also accelerate soil microbial turnover.