  Understanding how the magnetic activity of low-mass stars depends on their
fundamental parameters is an important goal of stellar astrophysics. Previous
studies show that activity levels are largely determined by the stellar Rossby
number which is defined as the rotation period divided by the convective
turnover time. However, we currently have little information on the role that
chemical composition plays. In this work, we investigate how metallicity
affects magnetic activity using photometric variability as an activity proxy.
Similarly to other proxies, we demonstrate that the amplitude of photometric
variability is well parameterised by the Rossby number, although in a more
complex way. We also show that variability amplitude and metallicity are
generally positively correlated. This trend can be understood in terms of the
effect that metallicity has on stellar structure and, hence, the convective
turnover time (or, equivalently, the Rossby number). Lastly, we demonstrate
that the metallicity dependence of photometric variability results in a
rotation period detection bias whereby the periods of metal-rich stars are more
easily recovered for stars of a given mass.
