  We consider the properties of soft X-ray emission lines in the reprocessed
emission from a photoionized accretion disc. Observations of these lines will
be important in determining the ionization state and metallicity of the
innermost regions of active galaxies. Calculations of reflection from a
constant-density disc with an ionization parameter between 250 and 1000 erg
cm/s show that emission from O VIII Ly\alpha will dominate the soft X-ray
emission spectrum. There is also significant emission from C VI, N VII, O VII,
as well as Fe XVII--XIX. As the ionization parameter is increased these lines
become weaker and are broadened by Compton scattering. Significantly increasing
the O abundance primarily strengthens the O VII line, making it as large or
larger than the O VIII line. The nitrogen and carbon lines are quite weak with
equivalent widths (EWs) <30 eV, even with an increase in the N abundance. A
hydrostatic ionized disc model has a more realistic density structure and shows
a similar spectrum, but with the lines weaker and broader. This is a result of
the hot ionized skin at the surface of the disc. We apply these results to the
controversial claim of soft X-ray relativistic lines in the XMM-Newton spectrum
of MCG--6-30-15. We are unable to find a situation where O VIII has the
required EW without substantial emission from O VII. Furthermore, Compton
scattering results in the blue wing of the O VIII line to be much broader than
the << 10 eV drop observed in the data. We conclude that soft X-ray accretion
disc lines will, in general, be weak and broad features and are unlikely to
produce sharp edges in the data.
