We tested the hypothesis that the biogeochemical effect of the role of CO2 change is interactively linked with soil moisture availability for all the General Circulation Model (GCM) based vegetation types. A 1D atmospheric model dynamically coupled with a prognostic soil moisture / soil temperature scheme including a photosynthesis based vegetation sub-model was used in this study. The objective was to analyze the biogeochmical effects of CO2 doubling, under high as well as limiting soil moisture conditions, over different terrestrial biomes. Results for all the nine global biomes, as defined through the SiB2 land cover classification, were analyzed for coupled feedbacks such as evapotranspiration and net carbon assimilation. Results confirm that simultaneous CO2 and soil moisture changes are significant for both the C3 and C4 plants. In particular the study highlights the role of soil moisture (and its feedback effects with CO2) as a first – order effect of the terrestrial ecosystem. Our results also indicate that (a) explicit resolution of the direct and interactive effects associated with the changes in input variables are useful measures for assessing the effects and variability due to CO2 changes; (b) resolving the interactions explicitly, both C3 and C4 vegetation, appear to be significantly affected by the CO2 changes; (c) studies linking CO2 effects in a sensitivity type analysis both in observational as well as numerical experiments should explicitly resolve the interactions. Thus, impacts associated with CO2 increase cannot be assessed without considering the soil moisture status. In that, each vegetation type has a different strategy to account for CO2 changes with regard to soil moisture availability. The hydrological feedback needs to be thus explicitly considered in any comprehensive future assessment. Often, despite significant dramatic impacts due to a variable change, the natural ecosystem appears to be buffered and does not show a dramatic response. Our analysis suggests that the interactive feedbacks between the biotic and abiotic changes tend to have a compensatory response. This reduces the effect of the variable change on the overall system response. Additional studies considering both the radiative as well as biogeochemical feedbacks of CO2 and soil moisture changes are needed using observations and coupled models.