One of the major controls on soil N dynamics is the availability of C to soil microorganisms. Although many indices of the C quality of a substrate in terms of its effect on N dynamics have been proposed (e.g., the N or lignin concentration), we still have a relatively equivocal understanding of the impact of these factors on soil N dynamics, and how native soil fertility interacts with litter quality in altering soil N turnover. We conducted a novel long-term litter decomposition to help elucidate C controls on soil N dynamics in two tropical soils that had contrasting N availability and C concentrations in the mineral soil. We added ground litter from a dominant overstory tree (Metrosideros polymorpha) with three contrasting qualities (low lignin, low N; high lignin, low N; and high lignin, high N) to separate subsamples of each soil, increasing the mineral soil C content by 25%. We continuously monitored microbial respiration and periodically measured microbial biomass, inorganic N pools, gross N transformation rates, and the propensity of soil microorganisms to directly assimilate glutamic acid, as the microbial metabolism switched from N- to C-limitation during extended incubation. We found that microbial respiration from the added litter was highest when both lignin and N concentrations were low, intermediate when both lignin and N concentrations were high, and lowest when lignin concentration was high and N concentration was low, irrespective of mineral soil N availability. However, microbial respiration from added litter was about 1/3^rd higher in the high N availability soil than in the low N availability soil, irrespective of litter quality. Gross rates of soil N mineralization were more strongly influenced by the lignin concentration of added litter than litter N concentration. Our results suggest that, during the N-limited phase of decomposition, the organic constituent composition of litter has a greater influence on decomposition dynamics than the N concentration of the litter, and native soil fertility interacts with litter quality in determining the strength of C-N connections.