Rhizosphere effects on N mineralization and
availability. The obtained data supported our hypothesis
that N mineralization in the rhizosphere
would be promoted by rhizosphere effects of all
tree species. The simultaneous increases in potential
net N mineralization rate and MBN in rhizosphere
soil suggest that tree roots stimulated gross
N mineralization, as net N mineralization rate is the
difference between gross N mineralization and N
immobilization (which went to the MBN). In general,
enhanced gross N mineralization in rhizosphere
soil primarily resulted from the rhizosphere ‘priming
effects’ on soil organic matter decomposition
(Ehrenfeld et al. 1997, Phillips and Fahey 2006).
Nitrogen transformation is tightly coupled with soil
organic matter decomposition that can be strongly
accelerated by rhizodeposition (i.e., root exudates)
activated microbial growth (Jackson et al. 2008). In
addition, release of NH4
+ by soil faunal grazing of
rhizosphere microbes has been proposed as another
important mechanism for increased rhizosphere N
availability.