Reply on RC1

This study updates an existing ecosystems model (TEM 5.0) to account for mosses including moss photosynthesis and respiration, and the influence of the moss layer on soil temperature, moisture and ecosystem N dynamics. The updated model (TEM-Moss) is then used to simulate future carbon dynamics for northern high latitudes, and by comparing the TEM-Moss simulations to those from TEM 5.0, the authors aim to understand the role of mosses in determining the future carbon balance of the region.

This is an important topic -forecasting northern high latitude C dynamics is critical for understanding global change, and mosses are an important component of northern vegetation. Attempting to understand the role of mosses on such a broad scale is novel; there has been some work incorporating the thermal properties of mosses in land-surface models, but I'm not aware of any similar analyses at this scale. It's an ambitious study and in general the manuscript is well structured and logically presented.
My main criticism is around how the TEM-Model is calibrated and validated, and whether the comparison to TEM 5.0 is valid. It may be that I haven't understood the methods fully, but it seems TEM-Moss is based on ecosystem-level calibrations of the 'moss parameters', but TEM 5.0 is not based on representative ecosystem level calibrations. If this is the case, it doesn't make sense to compare the performance of the two models. It also means that the calibrated 'moss parameters' will be compensating for un-calibrated 'non-moss parameters' i.e. the optimal moss parameters for an ecosystem will likely reflect differences in the properties of the higher plant vegetation which have not been captured by the 'default' version of TEM 5.0.
In conclusion, I think the aims of the study are worthwhile, and the general approach to update TEM 5.0 is valid, but a more robust model analysis is needed.
Specific comments I've made line by line comments below which I hope will be helpful in revising the paper.
Line 41: Define northern high latitudes and the types of ecosystems that are included in the study.
Response: Thanks for your comments and suggestions. We changed the sentence to "Northern high latitude ecosystems, which refers to the land ecosystems (>45 ºN) in northern temperate, boreal, grassland and tundra regions".
Line 43. Add some text to highlight the uncertainty around the 1024 Pg figure.
Response: We revised the sentence as "contain as much as 1024 Pg soil organic carbon from 0 to 3 m depth".
Line 44-47. "This large amount of carbon is potentially responsive to ongoing global warming". The references supporting this statement are quite old, please cite some more recent literature (e.g. Burke et al., 2017, Koven et al., 2015, Comyn-Platt et al., 2018 Response: Following suggestions, we updated the references. Line 154: Please provide more detail on the function f(NA).

Response:
We added "which is a scalar function that depends on monthly N available for incorporation into plant production of new tissue" to describe f(NA).

Response: We revised it.
Line 238: Did you use a single set of default parameters for the standard TEM model? I'm not sure I follow the reasoning here. Zha and Zhuang 2018 is an arctic study, yet you are using data from temperate forests and grasslands to calibrate TEM-Moss. Did you use the same set of default parameters across all sites? And did you use any other site-level information -apart from the NEP data -when calibrating the model?
Response: For TEM 5.0 simulations, we used different sets of default parameters for each vegetation type. Zha and Zhuang (2018) focused on the same region, but we parameterized that TEM version with site level information. In this study, we used site level data to parameterize TEM_Moss, but use the default parameterization of TEM 5.0 to compare with TEM-Moss simulations. Site-level parameterization was conducted based NEP data in addition to site level vegetation and soil information. Some site level data of NEP were used for model validation. Additionally, soil temperature and moisture at validation sites were also evaluated.
Line 247: I don't fully understand how the posterior parameter distributions were generated. As I understand it, the SCE algorithm provides a point-estimate for each parameter, then you treat the 50 independent point estimates as samples from a posterior parameter distribution? Is this correct? Please provide some clarification on this in the text. Please also update the legend in figure 4 -what probabilities do the boxes and tails represent?
Response: Yes, the posterior parameter distribution is just the distribution for the 50 independent point estimates. We added the explanation to boxes and whiskers into the figure caption "Boxes represent the range between the first quartile and the third quartile of the parameter values, the red line within box represents the second quartile or the mean of the values. The bottom and top whiskers represent minimum and maximum parameter values, respectively."