General comments.

The manuscript “The Loobos ecosystem first tower dataset: meteorology, turbulent fluxes and net ecosystem exchange (1996 to 2021)” by Zhao et al. describes an impressive bulk of data collected over 25 years at one of the earliest micrometeorological towers installed in Europe for the systematic monitoring of CO2 and energy fluxes. The dataset includes, beyond flux variables, numerous parallel measurements of biophysical parameters and biological processes of the forest ecosystem such as LAI, foliage chemistry, biomass carbon stocks, sap flow density and water table depth.

A dedicated section explains in detail the flux data processing pipeline and the quality check procedures for flux and partly for meteorological variables. Finally, a synthesis of the dataset is illustrated by plots showing the consistency of the flux data, the mean diurnal variation and in particular the mean monthly NEE fluxes from which the trend towards a stronger carbon sequestration can be observed.

The presented dataset is undoubtedly of interest to the readers of ESSD and the well-structured manuscript delivers an overall clear and detailed description of it. Said that, I recommend the publication of the manuscript but only after a minor revision mainly to : (i)fix some issues concerning the terminology used to describe the ecosystem-atmosphere CO₂ exchanges,; (ii) provide more information about the quality of meteorological measurements and the instruments maintenance routines.

Specific comments.

Introduction section (ca. L60): I suggest including a map of the area showing the location of the measurements (eddy covariance, meteorological, forest transects, sap flow, etc.).

Introduction – par 2.1.1: Some instruments were operated continuously for long periods of time (eg. pyranometers, quantum sensors, etc.). Report about the maintenance routine and its frequency to ensure accurate measurements, mentioning if the sensors were periodically calibrated and if the calibration drift was accounted for in processing the data.

L223: I guess that the “depth of 15 cm” refers to insertion of the collar into the soil and not to the depth of the chamber which would be placed on top of the collar. Please confirm.

L444:  the negative storage at sunrise should not be associated only to a “release of carbon dioxide” to the atmosphere, but also to the photosynthetic uptake of CO₂ by the vegetation below the eddy covariance sensors height.

L460: fig. 8 shows mean monthly NEE, that is, by definition, the net flux resulting from the difference between the processes of photosynthesis and respiration. Therefore, in the case of this evergreen needle forest, I would not talk about a decrease of “winter respiration” but rather of the intensity of the CO₂ source.

Appendix (L570-571): Replace “left photo” and “ right photo” with “photo on the right” and “photo on the left” respectively.

Zhao et al gives a thorough description of the data collection and processing for data collected at the first Loobos tower. Data users will find this to be a comprehensive presentation of the sensor characteristics, location, and calibration. 

It would be helpful to present the information about instrument changeover in a more easily digested way. For the eddy covariance measurements this is noted in the narrative text and Table 1, but showing this graphically would be easier for readers to absorb. Could you also comment on whether there was any overlap when sensor types were changed so that the data from each sensor could be compared. If there was no overlap, then note that in the text.

It is helpful to see some graphical examples of the typical diel patterns of CO2 flux.  Could you include some examples of a mean CO2 concentration profile, which would help assess whether the selected sampling heights were suitable for representing the profile shape and calculating the column integral?

Other than that I just note a few typographical errors

Some instances at line 152 and thereafter where mole should replace model

line 444 carbon dioxide should be singular

Use of subscript in CO₂ should be consistent