  We study the X-ray spectral variability of the Narrow Line Seyfert 1 galaxy
NGC 4051 as observed during two XMM-Newton observations. The data show evidence
for a neutral and constant reflection component and for constant emission from
photoionized gas, which are included in all spectral models. The nuclear
emission can be modelled both in terms of a ``standard model'' (pivoting power
law plus a black body component for the soft excess) and of a two--component
one (power law plus ionized reflection from the accretion disc). The standard
model results indicate that the soft excess does not follow the standard black
body law. Moreover, although the spectral slope is correlated with flux, which
is consistent with spectral pivoting, the hardest photon indexes are so flat as
to require rather unusual scenarios. These problems can be solved in terms of
the two-component model in which the soft excess is not thermal, but due to the
ionized reflection component. The variability of the reflection component from
the inner disc closely follows the predictions of the light bending model,
suggesting that most of the primary nuclear emission is produced in the very
innermost regions, only a few gravitational radii from the central black hole.
(abridged)
