  Using the replica method, we analyze the mass dependence of the QCD3
partition function in a parameter range where the leading contribution is from
the zero momentum Goldstone fields. Three complementary approaches are
considered in this article. First, we derive exact relations between the QCD3
partition function and the QCD4 partition function continued to half-integer
topological charge. The replica limit of these formulas results in exact
relations between the corresponding microscopic spectral densities of QCD3 and
QCD4. Replica calculations, which are exact for QCD4 at half-integer
topological charge, thus result in exact expressions for the microscopic
spectral density of the QCD3 Dirac operator. Second, we derive Virasoro
constraints for the QCD3 partition function. They uniquely determine the
small-mass expansion of the partition function and the corresponding sum rules
for inverse Dirac eigenvalues. Due to de Wit-'t Hooft poles, the replica limit
only reproduces the small mass expansion of the resolvent up to a finite number
of terms. Third, the large mass expansion of the resolvent is obtained from the
replica limit of a loop expansion of the QCD3 partition function. Because of
Duistermaat-Heckman localization exact results are obtained for the microscopic
spectral density in this way.
