Could competition between plants and microbes regulate plant nutrition and atmospheric CO2 concentrations?

It has been proposed that under high CO2, soil microbes may outcompete plants for access to inorganic nutrients, leading to a negative feedback to the fertilising effects of that CO2. However, tests of the hypothesis using radioisotope tracers indicate that, in the competition for inorganic nutrients, higher CO2 concentrations may actually favour the plants rather than the microflora. The relatively lower microbial metabolism could, however, have an indirect adverse effect on plant nutrition by restricting nutrient cycling in soils, and has the potential to induce negative feedback to rising atmospheric CO2 concentrations.