Effects of Elevated CO2 in the Atmosphere on Soil C and N Turnover

Rising atmospheric carbon dioxide (CO2) concentration affects various soil processes especially related to carbon (C) and nutrient turnover. The methods to study the effects of elevated CO2 (eCO2) were shortly presented. All effects of eCO2 on soil are indirect: by plants through increased net primary production and belowground C inputs due to higher photosynthesis under eCO2. We summarized the impacts of eCO2 on (1) cycling of C and nitrogen (N), (2) microbial growth and enzyme activities, (3) turnover of soil organic matter and induced priming effects including N mobilization/immobilization processes, and (4) associated nutrient mobilization from organic sources. Higher C input from plants under eCO2 leads to faster C turnover due to high microbial activities including respiration, enzymatic activities, and priming effect of soil organic matter. Comparing the effects of eCO2 on changes in pools with that in fluxes we conclude that eCO2 in the atmosphere will have small (or no) effects on the C pools but will strongly increase the fluxes. The stable pools but intensified fluxes will accelerate biogeochemical cycles under elevated CO2.