Effects of elevated CO₂ on the C:N stoichiometry of plants, soils, and microorganisms in terrestrial ecosystems

The stoichiometry of carbon to nitrogen ratio (C:N) plays an important role in biogeochemical cycling in terrestrial ecosystems. As time goes by, the increase in atmospheric CO2 levels is expected; however, the impact of elevated atmospheric CO2 on the C:N stoichiometry of soils, plants, and microorganisms remains largely unclear. The results of the meta-analysis that included 174 studies with 1009 observations demonstrated that above- and below-ground C concentrations and C:N ratio increased under elevated CO2 regimes, whereas N concentrations decreased. Importantly, these responses were more pronounced with rising CO2 concentrations and longer experimental durations. Moreover, the responses of C, N, and C:N to elevated CO2 were similar across croplands, forests, and grasslands ecosystems with varying climates. Our results revealed that the C:N stoichiometry of soils, plants, and microorganisms responded consistently to the rising global CO2 levels, which indicated that terrestrial ecosystems might have the capacity to mitigate increased atmospheric CO2 concentrations by increasing C sequestration in plants, soils, and microorganisms in future.