The factors influencing chemical evolution of galaxies are poorly understood .
Both gas inflow and gas outflow reduce a gas-phase abundance of heavy elements ( metallicity ) whereas the ongoing star formation continuously increases it .
To exclude the stellar nucleosynthesis from consideration , we analyze for the sample of 14 spiral galaxies the radial distribution of the effective yield of oxygen y _ { eff } , which would be identical to the true stellar yield ( per stellar generation ) y _ { o } if the evolution followed the closed box model .
As the initial data for gas-phase abundance we used the O/H radial profiles from , based on two different calibrations ( ( PT2005 ) and ( KK2004 ) methods ) .
In most of galaxies with the PT2005 calibration , which we consider as a preferred one , the yield y _ { eff } in the main disk ( R \geq 0.2 \leavevmode \nobreak R _ { 25 } , where R _ { 25 } is the optical radius ) increases with radius , remaining lower than the empirically found true stellar yield y _ { o } .
This may indicate the inflow of low-enriched gas predominantly to the inner disk regions , which reduces y _ { eff } .
We show that the maximal values of the effective yield in the main disks of galaxies , y _ { eff,max } , anti-correlate with the total mass of galaxies and with the mass of their dark halo enclosed within R _ { 25 } .
It allows to propose the higher role of gas accretion for galaxies with massive halos .
We also found that the radial gradient of oxygen abundance normalized to R _ { 25 } has a tendency to be shallower in the systems with lower dark halo to stellar mass ratio within the optical radius , which , if confirmed , gives evidences of the effective radial mixing of gas in galaxies with the relatively light dark matter halo .