## 5 Conclusions  
We describe the calibration technique, observational setup of the measurement campaign, aspects of the data analysis, and instrument field analysis of the recorded time series of soil gases and auxiliaries data within the study area. This soil gas measurement infrastructure combining borehole measurement with micrometeorological measurement offers excellent possibilities for long-term in-situ and continuous gas monitoring to derive the vertical distribution of CO2. Thus, this infrastructure allowed the observation of the temporal dynamics in soil-gas CO2 research. Relatively short-term events could be monitored, notably those associated with pressure and temperature at a deep soil layer, which is difficult to measure using a conventional method. Besides, the long-term data set of soil gas baseline will contribute to understanding better the influence of short-term events, including (i) spikes of short-term event, (ii) magnitudes of change caused by the suspected driving variables, (iii) the duration of the changing circumstances, and (iv) indirect variables influencing these short-term events. Such a metrology approach will contribute to the definition of good practice for the state of studies related to subsoil CO2 molar fraction in conjunction with the soil-air pressure and temperature. Even though this approach has been applied to the forest ecosystem, it can be extended to any other natural or anthropic systems. Even though CH4 concentration was always below our IR sensor's sensibility limit, this infrastructure might still be applied in CH4-rich site. Furthermore, this study shows substantial empirical pieces of evidence that the increase of temperature leads to higher respiration rates, which further produced CO2 stored in deep soil layers. However, this factor related to biological activity cannot fully explain the variation. We hypothesize pressure pumping effects also play a role, especially during dry summer. The decreases of CO2 molar fraction in the subsoil coincided with high turbulence, resulting in increased CO2 storage in deep soil during low turbulence. This study also demonstrates that permeability significantly reduced during wet periods diminishing the molecular diffusion and advection. All of these highlight the importance of spatial and temporal dynamics of deep soil CO\({}_{2}\) dynamics that reach a value of up to 100 times larger than atmospheric CO\({}_{2}\). This empirical evidence also challenges the current assumption that the influence of PPE is only significant on a topsoil layer. However, it is still uncertain whether this strong relationship is site-specific or not since it is highly likely that the soil porosity, soil texture, stand type, and canopy height play roles. As flux tower establishment expands, there is a strong need to apply borehole measurement underneath to understand better the relationships between friction velocity and subsoil CO\({}_{2}\) dynamics on various sites. Conceptualization, D.A., P.D.D., L.S.-A., and O.B. ; methodology, O.B., C.G., G.N., M.P., and M.D. ; software, D.A. ; validation, O.B., G.N. ; formal analysis, D.A. ; investigation, D.A., P.D.D., and O.B. ; resources, C.G., M.P., and M.D. ; data curation, D.A. ; writing--original draft preparation, D.A. ; writing--review and editing, P.D.D., L.S.-A., and O.B. ; visualization, D.A. ; supervision, P.D.D., L.S.-A. ; project administration, P.D.D., L.S.-A. ; funding acquisition, P.D.D., L.S.-A. All authors have read and agreed to the published version of the manuscript. This work was supported partly by the French PIA project \"_Lorraine Universite d'Excellence_\", reference ANR-15-IDEX-04-LUE. Not applicable. The data presented in this study are available on request from GeoResources Laboratory. We wish to thank [PERSON] for his excellent technical assistance on the calibration experiment. Special thanks go to [PERSON] for his technical assistance in managing the flux tower data. We also thank [PERSON] and [PERSON] for their meticulous work on gas chromatography calibration.