Mass–metallicity relation for galaxies in protoclusters (red) and blank fields (blue), which are based on R3 calibration from C24. The S24 calibration provides similar results, which are listed in the Table B.2 for comparison. The results from other works in the literature are shown with different colors, which are also listed in the Table B.2 for reference. Higher redshift (z > 3) measurements in literature are shown in solid lines, and lower redshift (z ∼ 2 − 3) measurements are shown in dashed lines.