The manuscript by Gonzales-Armas et al. investigates the drivers of diurnal dynamics of land-atmosphere carbon and water exchange in an alfalfa field using one clear-sky observation day from the LIAISE field campaign and a modelling framework. What stands out in this study is the wide range of observations from leaf- to ecosystem- to planetary boundary layer scale that are used in combination with a model that explicitly represents all these scales. Finally, they introduce the concept of tendency equations to analyse the model output with the aim to better understand the underlying drivers of diurnal land-atmosphere exchange dynamics. In my opinion, the manuscript can be an important contribution to further our understanding of and extend our tool set to analyse land-atmosphere interactions. The manuscript is generally well written, and the methodology is described in sufficient detail. However, I have to main comments that the authors could address:

The tendency equations represent a powerful tool to “make sense” of modelling output. Often in the literature, modelling outputs (or differences in modelling outputs) are not sufficiently explained and tendency equations might help in this regard. I was wondering if a framework could be developed to apply this concept to observations or at least to use observations to validate these tendencies in models. In the current study, observations are shown to demonstrate that the model can reproduce the diurnal dynamics in the observations. However, it would for example be even more insightful to test if the opposing A_n responses at the leaf- and canopy-scale in the VPD-ENT experiment can be validated against field observations. These questions could also be discussed as part of the Discussion.

The authors mention the potential effects of diffuse and direct radiation on carbon and water exchange. I think this is an important issue and should be more discussed in the Discussion section. The authors could go further than just mentioning potential effects and discuss how for example cloud cover and the associated changes in direct and diffuse radiation could affect their results.

Please see below a few more specific comments.

Specific comments

Line 41: Explain what the “phase lag” is.

Line 44-52: The authors refer here to “surface” and “canopy”. Is there a difference between these two definitions?

Line 83: Why do the authors only focus on diurnal dynamics? The model could also be validated against multi-day simulations to explore day-to-day variations in meteorological conditions and their impacts.

Figure 1: This is a great figure conceptualising their research approach.

Line 133: How was it tested if the ABL started to be a CBL?

Line 146: The authors mention here that the initial CO2 jump was chosen to reproduce the diurnal variability in observed CO2. Later, they validate the model against diurnal CO2 dynamics. Would this not by default improve the model output? Is it then justified to compare the model CO2 output to observations.

Line 186: How was the soil respiration derived from the chamber measurements? A reference could be sufficient here.

Line 276: It could be helpful here to also show the actual observation in addition to the idealised modelling experiments.

Line 308 & 309: I am not sure if “acquiring” and “excepting” are the right choice of words here.

Section 3.1.3: Slope and intercept could be also shown for the model validation section.

Line 384-397: It seems as if the different responses described in this paragraph are due to different model representation of photosynthesis. Is there any way to assess which representation is more accurate in this case?

Line 436: The authors could add more details on how the sensitivity analysis was conducted and what the results were.

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