General comments

This paper is well-constructed and well-articulated. However, it would take benefit from some improvements including more quantitative/statistical data, comparisons with similar systems/facilities, clearer objectives, and better figure labelling, which are welcome for better readability.

General comments

This paper is well-constructed and well-articulated. However, to enhance the overall description of such equipment, a synthetic presentation of the extreme climates covered and simplified schematic illustration of the whole system would be appreciated. The key scientific and technical locks addressed in this paper could be more highlighted. Finally, a summary of the performances achieved after the first tests compared to those expected would be welcome.

Recommendation: Accepted with Major Revisions

Please do find below remarks and suggestions:

• Adding a summary table with performance objectives versus reached ones would be of interest for the reader.
• Regulation test results presented seems not to have been carried out with an external load (temperature, water ingress, pollutant gas episode, …) added in measurement cell. Although, the time constant of natural event are low, one would be interested in extreme event impact on long term plant growing and soil evolution.
• Introduction should explicitly state the primary goal and research gap to help understand the novelty the facility's development brings to the research domain. For instance, by better introducing the limitation of existing outdoor experiments possibilities and limitations, for instance by acting directly on soil pollution composition.
• Is global instrumentation at air level is enough sensitive to allow
• What is the typical duration of an experiment and how breakdowns or maintenance operations could be addressed?
• Could you introduce some complementary information on how your regulation system would respond to changes in the root environment, to the simulation of heat or cold wave in terms of adapting and handling heat and mass transfer management, strong rain event, air pollution puff?
• Could you detailed particular adaptation you have imagined to manage pollutants and drainage water in your large-scale testing facilities?
• Looking at the whole system, is energy harvesting and/or energy optimisation are integrated in the scheduling of your experiments?
• How do you planned to manage TDR probe calibration in front of soil composition against its potential evolution in order to maintain accurate measurements?
• Line 351, reference to fig 8 failed in the text