MZR and dependence on environment of the 259 cluster galaxies and 169 field galaxies of the mass-complete OHgals sample. For the matched SDSS sample, we indicate 16th and 84th percentiles, and the medians (50th percentiles) of the distribution of O/H values in the respective mass bin as magenta lines and symbols. The median O/Hs in the mass-complete Mhigh and Mlow mass bins are shown as big filled circles; the field median values (cyan symbols) are shown in all panels (slightly displaced in mass compared to cluster galaxies for visibility of the median symbols). The field median O/H value of Mhigh galaxies of the LoCuSS sample is similar to the SDSS median value at higher masses, while the Mlow field median value is slighty lower than the Mlow SDSS median value. The field Mlow and Mhigh median metallicities values are comparable to the respective (Mlow, Mhigh) cluster O/H medians for R >  R₂₀₀. On the other hand, the median O/H value of Mlow galaxies in the more central part of the clusters (R <  R₂₀₀) is higher than the median O/H field value, by about 0.06 dex, with a 2.4σ significance. The histograms on the right showing the offsets from the local SDSS MZR relation, ΔO/H, also clearly reveal enhanced metallicities for Mlow cluster galaxies inside R₂₀₀ (red histograms) compared to field galaxies and galaxies at R >  R₂₀₀. This indicates that the cluster environment has the effect of increasing the gas metallicities of Mlow galaxies inside R₂₀₀ compared to their field counterparts of similar masses.