the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Potassium-limitation of forest productivity, part 2: CASTANEA-MAESPA-K shows a reduction in photosynthesis rather than a stoichiometric limitation of tissue formation
Guerric le Maire
Jean-Paul Laclau
Joannès Guillemot
Yann Nouvellon
Nicolas Delpierre
Abstract. Potassium availability constrains forest productivity. Brazilian eucalypt plantations are a good example of the K-limitation of wood production. Here, we built upon a previously described model (CASTANEA-MAESPA-K) and used it to understand whether the simulated decline in C-source under K deficiency was sufficient to explain the K-limitation of wood productivity in Brazilian eucalypt plantations. We developed allocation schemes for both C and K and included into CASTANEA-MAESPA-K. No direct limitations of the C-sink activity, nor direct modifications of the C-allocation by K availability were included in the model. Simulation results show that the model was successful in replicating the observed patterns of wood productivity, growth, NPP limitation by K deficiency. Simulations also show that the response of NPP is not linear with increasing K fertilisation. Simulated stem carbon use and water use efficiencies decreased with decreasing levels of K availability. Simulating a direct stoichiometric limitation of wood productivity, growth, NPP was not necessary to reproduce the observed decline of productivity under K limitation, suggesting that K stoichiometric plasticity could be different than that of N and P. Confirming previous results from the literature, the model simulated an intense recirculation of K in the trees, suggesting that retranslocation processes were essential for tree functioning. Optimal K fertilisation levels calculated by the model were similar to nutritional recommendations currently applied in Brazilian eucalypt plantations, paving the way for validating the model at a larger scale and this approach to develop decision-making tools to improve fertilisation practices.
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Ivan Cornut et al.
Status: closed
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RC1: 'Comment on egusphere-2022-884', Anonymous Referee #1, 19 Oct 2022
General comments
The manuscript submitted to Biogeosciences by Cornut et al. studies the impact of a potassium limitation on wood productivity and in particular on the allocation of carbon and potassium towards trunk, branches and bark, through the modelling and evaluation of the CASTENEA-MAESPA-K model. This is the Part2 of a two-part paper, Part1 being dedicated to the impact of K limitation on the C-source activity (GPP). The split in the 2 parts is relatively well done, and the present manuscript (Part 2) is sufficiently self-supporting, without the need of reading the Part 1 first.
The overall objectives of the manuscript are relevant; and the “Results” and “Discussion” sections report fairly on the model capacities at simulating biomass of each compartment (organ) for different K availability scenarios.
However, the manuscript needs a strong revision of the Methods section and some restructuration. Currently, this section contains too many inconsistencies in several equations, variable units, ... There is not a particular major deficiency but an accumulation of inaccuracies, which really prevents to access at the content of the manuscript. I address many of them in the Technical comments below.
Technical comments
Line 1: After “Potassium” add “(K)”.
Line 9: Please rephrase “of wood productivity, growth, NPP” as it is unclear
Line 21: rephrase “from plots with trunk wood (every 6-7 years) from the stands”.
Line 39: WUEGPP to be defined prior to use it.
Line 48: “various” not “Various”.
Lines 48-51: a bit unclear to me. Are the roles of K as enzyme co-factor and in cell turgor pressure, two “processes” you list here? If so, mention them in a single sentence, or in two separate ones but without using the colon (“:”). Are the two processes not potentially related to K stoichiometry, not only enzyme cofactor. If so, maybe add “in order to preserve K stoichiometry” line 49 after “K deficiency”.
Line 62: add “see Part 1” after “obtained”
Line 70: replace “year-1” by “yr-1”
Line 73: Remove one of the 2 “two”.
Line 74: Replace “, which consisted in” by “:”
Line 74-75: Replace “K fertilisation:+K (” by “K fertilisaton (+K treatment) with”
Line 76: Remove the end parenthesis (“)”)
Line 76: Replace “: oK” by (oK)
Line 80: Replace “at 1, 2, 3, 4, 5 and 6 years in each fertilisation treatment” by “in each fertilisation treatment at year 1, 2, 3, 4, 5 and 6 after planting”
Line 89: Replace “Cornut et al., submitted” by “Part 1”
Line 95: I would suggest using the present tense in the Methods section when describing the model features, instead of the past tense.
Line 100-108: As far as I understood, the allocation coefficients presented in subsections 2.3.2 and after are applied over “NPP - C allocated in leaves” not NPP. If this is correct, this should be clarified here. To my understanding, the sentence “The growth of all organs was a fraction of the daily NPP” does not reflect the way it is modelled. If “all organs” include leaves, it is in contradiction with the sentence “the generation of leaves ... was not directly dependant on NPP”. If “all organs” means “all organs except leaves”, their growth is a fraction of NPPorg, not NPP. To my opinion, NPPorg should be defined here and not line 200 of the current manuscript.
Line 105: To my opinion, the subsection 2.3.1 can be removed and its content merges with the paragraph right above (lines 100-104).
Line 110-111: The sentence is a bit unclear to me. Could you rephrase it ?
Line 113: GSSmax is not defined
Line 114: add “(unitless)” after “GSS” ; remove “(daily)”
Line 117: add “(GCR, unitless)” after “roots”
Line 121: add “(GFR, unitless)” after “roots”
Line 124: Remove “GFR was the allocation coefficient to fine roots,”, and add “were” after “GSS”
Line 131: add “(unitless)” after “GW”. You can remove the end of the sentence from “, and GFR ...”
Line 138: add “(unitless)” after GBr
Line 144: the line may be removed
Line 151-152: Could you give slightly more information on how the growth respiration is computed?
Line 153 and after: Description of the maintenance respiration modelling is quite difficult to follow. This section needs clarifications (see below).
Line 155: maintenance respiration is a “function of their respective respiration rate per nitrogen unit, nitrogen content and surface temperature”. Equation (9), in which we divide by Ntrunk, defines the respiration rate per nitrogen unit (MRNtrunk). Equation (10) defines the maintenance respiration from MRNtrunk by multiplying it by Ntrunk. So, RMtrunk (or more generally RMorgan) does not seeem to be a function of the nitrogen content.
Line 159, equation (9): There is a problem with the 2 terms of the max functions (in brackets). Both terms are constants without any variable.
Line 159, equation (9): why expressing MRNtrunk in “mol CO2” and not in “gC” . In all cases, you may put the different conversion factors in the terms of the max function.
Line 159, equation (9): Mention that MRNtrunk and more generally MRNorgan are respiration rate per unit nitrogen, at reference temerature TMR
Line 161: add “C” between “unit” and “mass”.
Line 164-166: Mention that the Nbranches and Ntrunk were defined assuming a Carbon content per biomass unit of 50% (0.5).
Line 167-168, equation (10): For clarification, you may rewrite 0.005 as 0.01 x 0.5 and inject the “0.01” into the min function terms.
Line 168: The terms “0.256”, “-0.00854” and “0.0759” don’t match with the values reported on Figure S2b while those of the equation for Nbranches do match with values of on Figure S2a.
Line 173: RMorgan (CO2 hr-1). Do you mean “mol CO2”. You may express it in “gC”. Isn’t there a “m-2” missing in the units of RMorgan ?
Line 173: Borgan is “(gC m-2)” not “(gC)”
Line 174: “Norgan” not “Norgan”
Lines 176-177: I can’t find any information on Rd in Part 1 manuscript.
Line 183: “The realised lifespan of leaves was influenced by their K status (see Part 1)”. I could not find in Part 1 any information of the equation that relates LLSrealised to K status.
Line 186: remove one of the 2 “the”.
Line 192-268, Section 2.6: I think you can re-structure this section in two, one dedicated to ‘K allocation’ and another to ‘K remobilization’ (currently subsection 2.6.5). Paragraphs between line 225 and line 237 should be moved in the section on ‘K remobilization’.
Line 198: “flexible” not “flexivle”
Linr 199: I think you should replace Kwoodopti by Ktrunkopti as the branches are also made of wood. There are many places in the manuscript (and some figure captions) indeed, where you should replace “wood” by “trunk”
Line 210, equation (14): What’s the link between eq (14) and eq. (21) of Part1. To my understanding, the use of LimKorg assumes that Kphloem->leaf has been deduced first from Kavailable,phloem which is not mention in the text. Would not be more consistent with Part 1 and clearer, to use LK in Part 2 as well, and not LimKorg ?
Line 214 and after, section 2.6.1 Wood: it is the only section where you deal with the cohort level. Is it really needed ? If so, you should better explain the cohorts principle. For instance, line 217-218: “trunk NPP was allocated daily to a cohort of wood”. How is this cohort selected among all ?
Line 218-219: “optimal K concentration of newly formed wood was constant and to the maximum trunk concentration measured”. In this respect, why equation (15) includes LimorgK which tends to reduce Ktrunkopti
Line 229: equation (16) is not homogeneous.
Line 230-231: Unit of Ktrunk→xylemi gK m-2 day-1 instead of gK m-2 ? Unit of Ktrunki: gK (gC)-1 ? Unit of TKTrunk : (unitless) ?
Line 247-250: I think you can rephrase the sentences to gain in clarity.
Line 257: Replace “there no measurements were available” by “no measurement was available”.
Line 267: add “(unitless) after RKbranches
Line 267: maybe replace “rate” by “fraction”
Line 272: “m-2”
Line 272: Add an end parenthesis after “planting”
Line 281: “blocks” instead of “blocs”
Lines 285 to 305: There is probably a problem with the numbering of section 2.9 and subsections 2.9.1 to 2.9.3: 2.9 -> 2.8.1 ; 2.9.1 -> 2.8.2 ; 2.9.2 -> 2.8.3 ; 2.9.3 -> 2.8.4
Line 285-287: name explicitly and define the different CUE you use in the Results section : CUENPP, CUEtrunk, ; I think you only report CUE values in the Result for the full rotation period by computed a mean CUE as the cumulated NPP divided by the cumulated GPP. If this is correct, specify it here (and also for WUE).
Line 289-290: define also here WUEGPP for which you report values in the Results section.
Line 293: “C-based metric” may refer to CUE; you may replace it by “C flux”
Line 295, equation (20): as it is defined, KUENPP seems to be a function of the length of the rotation. Is it really expected? It does not appear to be a very handy metric to compare experiments with different rotation length. You could use the mean daily C flux over the length of the rotation instead of the cumulated one. This would imply to express KUENPP in gC day-1 (gK)-1
Line 295: As “i” index refers to time, you could replace it by “t”.
Line 307: replace “and dividing it” by “divided”
Line 309, equation (21): Kfertiliseradded should be sum for i=0 to k as well, in particular to account for the fertiliser regime with 4 applications.
Line 317-320: I think it is sufficient to report the five-year mean annual GPP values (those in parenthesis), not the cumulated fluxes.
Line 321: “Table 2”, I think you want to refer to “Table 3” of Part 1, not Table 2
Line 323: replace “trunk NPPtrunk” by “NPPtrunk”
Line 325: add an end parenthesis after “Fig. 2e”
Line 325: add a “,” after “stand”.
Line 326: give units to the RMSE values. Replace “for” by “of simulated”
Line 328: replace “age 59 months” by “month 59 after planting”
Line 333: replace “carbon use efficiency (defined as the ration of NPP to GPP)” by “CUENPP”
Line 334: replace “0.52 vs 0.40” by “0.40 vs 0.52”
Line 336: replace “CUE” by “CUENPP”
Line 338: add “relative” before “increase”
Line 339-340: “This was further amplified by leaf NPP representing 13% of GPP in oK compared to 7% in +K”. Is this remark related to the difference in CUEtrunk, only (and not CUENPP)? If so, please specify.
Line 345: replace “0, 3, 10 and 20 moths of age” by “month 0, 3, 10 and 20 after planting”
Line 353: add “located in” between “were” and “the”.
Line 363: add a comma after “model”.
Line 393: “Potassium concentrations in trunk wood and branches are correctly simulated”. Could you provide a quantitative metric for this “correct simulation performance” ? In addition, you should probably highlight that for branches at least, there is a large spread in the measurements in particular for low biomass values.
Figure 2: You may put x- and y-labels bigger. Add “Measured and” at the beginning of the figure legend.
Figure S2 b), replace “wood” by “trunk” in the Y-label
Citation: https://doi.org/10.5194/egusphere-2022-884-RC1 -
AC1: 'Reply on RC1', Ivan Cornut, 28 Dec 2022
General comments
The manuscript submitted to Biogeosciences by Cornut et al. studies the impact of a potassium limitation on wood productivity and in particular on the allocation of carbon and potassium towards trunk, branches and bark, through the modelling and evaluation of the CASTENEA-MAESPA-K model. This is the Part2 of a two-part paper, Part1 being dedicated to the impact of K limitation on the C-source activity (GPP). The split in the 2 parts is relatively well done, and the present manuscript (Part 2) is sufficiently self-supporting, without the need of reading the Part 1 first.
The overall objectives of the manuscript are relevant; and the “Results” and “Discussion” sections report fairly on the model capacities at simulating biomass of each compartment (organ) for different K availability scenarios.
However, the manuscript needs a strong revision of the Methods section and some restructuration. Currently, this section contains too many inconsistencies in several equations, variable units, ... There is not a particular major deficiency but an accumulation of inaccuracies, which really prevents to access at the content of the manuscript. I address many of them in the Technical comments below.
We thank Reviewer one for these general comments. We take notice that our two-part approcah is acknowledged and accepted here. We appreciate that these comments are thorough and relevant to our work. They were very useful when revising our manuscript. We have attempted to answer some of the most important concern below. We hope that our answers can alleviate some of the mis-comprehensions that have stemmed from reading our manuscript. This will feed into the restructuration of the methods section.
Technical comments
I would suggest using the present tense in the Methods section when describing the model features, instead of the past tense.
Line 100-108: As far as I understood, the allocation coefficients presented in subsections 2.3.2 and after are applied over “NPP - C allocated in leaves” not NPP. If this is correct, this should be clarified here. To my understanding, the sentence “The growth of all organs was a fraction of the daily NPP” does not reflect the way it is modelled. If “all organs” include leaves, it is in contradiction with the sentence “the generation of leaves ... was not directly dependant on NPP”. If “all organs” means “all organs except leaves”, their growth is a fraction of NPPorg, not NPP. To my opinion, NPPorg should be defined here and not line 200 of the current manuscript.
Thank you for the detailed review, we used a shortcut in our description but yes allocation coefficients are NPP – C allocated to leaves. The production of leaves had priority over the production of all other organs. Meaning that NPP was first allocated to leaves then allocated to the other organs (following their respective allocation ratios). The production of leaves can be limited by NPP in our model but this was very rarely the case in our simulations.
Line 151-152: Could you give slightly more information on how the growth respiration is computed?
Growth respiration was computed by using parameters measured in eucalypt plantations (Ryan et al., 2009). The growth respiration was modelled as in the original CASTANEA model (Dufrêne et al., 2005).
Line 153 and after: Description of the maintenance respiration modelling is quite difficult to follow. This section needs clarifications (see below).
Thank you for this comment. This will be clarified in the manuscript as explained below..
Line 155: maintenance respiration is a “function of their respective respiration rate per nitrogen unit, nitrogen content and surface temperature”. Equation (9), in which we divide by Ntrunk, defines the respiration rate per nitrogen unit (MRNtrunk). Equation (10) defines the maintenance respiration from MRNtrunk by multiplying it by Ntrunk. So, RMtrunk (or more generally RMorgan) does not seeem to be a function of the nitrogen content.
This is true (for the trunk only). We used this since the N content of trunks in Ryan et al., 2009 there were no concurrent measurements of N trunk. Instead we resorted to use a maintenance respiration rate of biomass that was a function of said biomass (to be able to use these published measurements) and a constant Ntrunk for MRN_trunk. This is unclear and will be clarified in the manuscript.
Line 159, equation (9): There is a problem with the 2 terms of the max functions (in brackets). Both terms are constants without any variable.
Yes, there was an error in the transcription of this equation. Thank you for seeing this. The equation should read:
max(0.00047,0.0073-0.00000116*B_trunk)*1/1e6*3600*1/12*1/0.001
Line 168: The terms “0.256”, “-0.00854” and “0.0759” don’t match with the values reported on Figure S2b while those of the equation for Nbranches do match with values of on Figure S2a.
This will be changed. We will use direct model outputs instead for this figure, that will help clarify the values.
Line 183: “The realised lifespan of leaves was influenced by their K status (see Part 1)”. I could not find in Part 1 any information of the equation that relates LLSrealised to K status.
This is presented in the companion paper Part 1 (Cornut et al., 2022). Since leaves fall when their K concentration is below a threshold value, their “true” lifespan can be strongly reduced by K availability.
Line 214 and after, section 2.6.1 Wood: it is the only section where you deal with the cohort level. Is it really needed ? If so, you should better explain the cohorts principle. For instance, line 217-218: “trunk NPP was allocated daily to a cohort of wood”. How is this cohort selected among all ?
Wood cohorts correspond to daily productions of wood. Trunk NPP is allocated to the cohort created on that day. This was necessary for our wood remobilisation model.
Line 218-219: “optimal K concentration of newly formed wood was constant and to the maximum trunk concentration measured”. In this respect, why equation (15) includes LimorgK which tends to reduce Ktrunkopti
Because optimal (when K is present in sufficient quantities) and realized (after computation of offer vs demand of K) concentrations are different.
Line 295, equation (20): as it is defined, KUENPP seems to be a function of the length of the rotation. Is it really expected? It does not appear to be a very handy metric to compare experiments with different rotation length. You could use the mean daily C flux over the length of the rotation instead of the cumulated one. This would imply to express KUENPP in gC day-1 (gK)-1
Yes. It is true that this means that KUE is a function of rotation length and that this should not be the focus of this metric. We will thus recalculate its value by using it divided by the number of days in the rotation. This should not change the discussion of the results since we simulated rotations with all the same length.
Line 393: “Potassium concentrations in trunk wood and branches are correctly simulated”. Could you provide a quantitative metric for this “correct simulation performance” ? In addition, you should probably highlight that for branches at least, there is a large spread in the measurements in particular for low biomass values.
It is true that this sentence was overly optimistic. We have no hypotheses regarding the large spread of values at low biomasses. It could be an effect due to the large proportion of very young branches. In tne manuscript we will highlight the discrepancies between modelled concentrations in branches and simulated ones.
References:
Cornut, I., Delpierre, N., Laclau, J. P., Guillemot, J., Nouvellon, Y., Campoe, O., ... & le Maire, G. (2022). Potassium-limitation of forest productivity, part 1: A mechanistic model simulating the effects of potassium availability on canopy carbon and water fluxes in tropical eucalypt stands. EGUsphere, 1-37.
Dufrêne, E., Davi, H., François, C., Le Maire, G., Le Dantec, V., & Granier, A. (2005). Modelling carbon and water cycles in a beech forest: Part I: Model description and uncertainty analysis on modelled NEE. Ecological Modelling, 185(2-4), 407-436.
Ryan, M. G., Cavaleri, M. A., Almeida, A. C., Penchel, R., Senock, R. S., & Luiz Stape, J. (2009). Wood CO2 efflux and foliar respiration for Eucalyptus in Hawaii and Brazil. Tree Physiology, 29(10), 1213-1222.
Citation: https://doi.org/10.5194/egusphere-2022-884-AC1
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AC1: 'Reply on RC1', Ivan Cornut, 28 Dec 2022
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RC2: 'Comment on egusphere-2022-884', Anonymous Referee #2, 31 Oct 2022
Here I review the 2nd part of the work submitted by Cornut et al., focusing on simulating growth limitation induced by K deficiency. Overall, I find this manuscript well-written. I have one comment regarding the model structure. Here, the authors indicated that the model structure accounts for additional processes relating to K allocation, remobilization and turnover. I do not understand why the model structure is different in this paper as compared to the model structure of the first paper. I know two papers have different focus, but it would be valuable to justify the reason as to why the authors decided to omit processes described here in the first paper. Particularly, does it mean that the results of the two papers are not directly comparable even if they were used to simulate processes for the same site? Apart from this comment, I think the manuscript is generally well presented.
Specific comments:
L64: no hypothesis on sink limitation was previously introduced yet. It would be great to make it explicit. And, it would be useful to describe what you meant by parsimony principle.
L 91 – 93: Why these modules on carbon allocation and K effect on organ growth not important in the first manuscript? In particular, why the model structure of the two papers different? Does it mean the results of the two papers are not directly comparable, even if simulated for the same site?
L199: incorrect spelling, should be “flexible”.
Figure 1: The color scheme makes it hard to see the difference between +K and oK treatment, especially for the dots. Can the authors please revise them to more distinguishable colors?
Figure 4b: Why litter K content starts so high and declines over time?
Equation 8: Btrunk should be biomass, not in unit of g C m-2, right?
Equation 12: Knpp in the unit of gK m-2? Shouldn’t it be in the unit of gK m-2 d-1? But if this is the case, what’s the correct unit for Kavailable in equation 14?
Citation: https://doi.org/10.5194/egusphere-2022-884-RC2 -
AC2: 'Reply on RC2', Ivan Cornut, 28 Dec 2022
Here I review the 2nd part of the work submitted by Cornut et al., focusing on simulating growth limitation induced by K deficiency. Overall, I find this manuscript well-written. I have one comment regarding the model structure. Here, the authors indicated that the model structure accounts for additional processes relating to K allocation, remobilization and turnover. I do not understand why the model structure is different in this paper as compared to the model structure of the first paper. I know two papers have different focus, but it would be valuable to justify the reason as to why the authors decided to omit processes described here in the first paper. Particularly, does it mean that the results of the two papers are not directly comparable even if they were used to simulate processes for the same site? Apart from this comment, I think the manuscript is generally well presented.
We thank reviewer two for the positive remarks and the constructive criticisms that they bring to the mansucript. These remarks will be thouroughly taken into account when improving the manuscript. The model structure that was used is the same in the two papers. In the first paper we chose to focus the description on the canopy and the processes related to leaves and C acquisition. In the second paper we focus instead on allocation of K and C in the trees. The schematic attempted to show this but our explanations lack clarity. The results of the two papers are thus comparable. This was an attempt to avoid redundancy between the two papers. We will thus improve the description of this aspect in the manuscript.
Specific comments:
L64: no hypothesis on sink limitation was previously introduced yet. It would be great to make it explicit. And, it would be useful to describe what you meant by parsimony principle.
We are not sure to understand the first comment. Sink limitation was introduced line 49. By sink limitation (which also include carbohydrate transport mlimitations) we include processes that could limit wood production by affecting sugar transport from source organs to sink organs (or from sap to sink organs) or direct limitation of sink organ functionning by K deficiency (by affecting cell expansion, metabolism or lifespan).
By parsimony principle means that we did not introduce more processes in the model if the ones that were already included in the model could explain the observed patterns (here, K limitation). This was to limit hypothesis on functionning and focus on using only available information.
Both these clarifications will be added to the manuscript.
L 91 – 93: Why these modules on carbon allocation and K effect on organ growth not important in the first manuscript? In particular, why the model structure of the two papers different? Does it mean the results of the two papers are not directly comparable, even if simulated for the same site?
The structure of the model is exactly the same between the two manuscripts. The Part 1 (Cornut et al., 2022) is focused mainly on the canopy, carbon assimilation and the calibration of theses processes. Part 2 is focused mainly on the allocation of this carbon and the validation of the model using measures of biomass production. We therefore just change the focus on different processes in Part 1 and in Part 2.
Figure 4b: Why litter K content starts so high and declines over time?
This was due to the presence of ground litter on the soil following the clear-cutting of the previous plantation corresponding both to litter that was present on the gorund at cutting and branches, leaves and bark of the cut trees that were added to the soil as litter.
Equation 8: Btrunk should be biomass, not in unit of g C m-2, right?
No, the biomasses inside the model are all in grams of caron per square meters of soil (gC.m-2)
Equation 12: Knpp in the unit of gK m-2? Shouldn’t it be in the unit of gK m-2 d-1? But if this is the case, what’s the correct unit for Kavailable in equation 14?
The correct unit for K _NPPin equation should be gK.m-2.d-1 And this should also be the unit for K_available.
References :
Cornut, I., Delpierre, N., Laclau, J. P., Guillemot, J., Nouvellon, Y., Campoe, O., ... & le Maire, G. (2022). Potassium-limitation of forest productivity, part 1: A mechanistic model simulating the effects of potassium availability on canopy carbon and water fluxes in tropical eucalypt stands. EGUsphere, 1-37.
Citation: https://doi.org/10.5194/egusphere-2022-884-AC2
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AC2: 'Reply on RC2', Ivan Cornut, 28 Dec 2022
Status: closed
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RC1: 'Comment on egusphere-2022-884', Anonymous Referee #1, 19 Oct 2022
General comments
The manuscript submitted to Biogeosciences by Cornut et al. studies the impact of a potassium limitation on wood productivity and in particular on the allocation of carbon and potassium towards trunk, branches and bark, through the modelling and evaluation of the CASTENEA-MAESPA-K model. This is the Part2 of a two-part paper, Part1 being dedicated to the impact of K limitation on the C-source activity (GPP). The split in the 2 parts is relatively well done, and the present manuscript (Part 2) is sufficiently self-supporting, without the need of reading the Part 1 first.
The overall objectives of the manuscript are relevant; and the “Results” and “Discussion” sections report fairly on the model capacities at simulating biomass of each compartment (organ) for different K availability scenarios.
However, the manuscript needs a strong revision of the Methods section and some restructuration. Currently, this section contains too many inconsistencies in several equations, variable units, ... There is not a particular major deficiency but an accumulation of inaccuracies, which really prevents to access at the content of the manuscript. I address many of them in the Technical comments below.
Technical comments
Line 1: After “Potassium” add “(K)”.
Line 9: Please rephrase “of wood productivity, growth, NPP” as it is unclear
Line 21: rephrase “from plots with trunk wood (every 6-7 years) from the stands”.
Line 39: WUEGPP to be defined prior to use it.
Line 48: “various” not “Various”.
Lines 48-51: a bit unclear to me. Are the roles of K as enzyme co-factor and in cell turgor pressure, two “processes” you list here? If so, mention them in a single sentence, or in two separate ones but without using the colon (“:”). Are the two processes not potentially related to K stoichiometry, not only enzyme cofactor. If so, maybe add “in order to preserve K stoichiometry” line 49 after “K deficiency”.
Line 62: add “see Part 1” after “obtained”
Line 70: replace “year-1” by “yr-1”
Line 73: Remove one of the 2 “two”.
Line 74: Replace “, which consisted in” by “:”
Line 74-75: Replace “K fertilisation:+K (” by “K fertilisaton (+K treatment) with”
Line 76: Remove the end parenthesis (“)”)
Line 76: Replace “: oK” by (oK)
Line 80: Replace “at 1, 2, 3, 4, 5 and 6 years in each fertilisation treatment” by “in each fertilisation treatment at year 1, 2, 3, 4, 5 and 6 after planting”
Line 89: Replace “Cornut et al., submitted” by “Part 1”
Line 95: I would suggest using the present tense in the Methods section when describing the model features, instead of the past tense.
Line 100-108: As far as I understood, the allocation coefficients presented in subsections 2.3.2 and after are applied over “NPP - C allocated in leaves” not NPP. If this is correct, this should be clarified here. To my understanding, the sentence “The growth of all organs was a fraction of the daily NPP” does not reflect the way it is modelled. If “all organs” include leaves, it is in contradiction with the sentence “the generation of leaves ... was not directly dependant on NPP”. If “all organs” means “all organs except leaves”, their growth is a fraction of NPPorg, not NPP. To my opinion, NPPorg should be defined here and not line 200 of the current manuscript.
Line 105: To my opinion, the subsection 2.3.1 can be removed and its content merges with the paragraph right above (lines 100-104).
Line 110-111: The sentence is a bit unclear to me. Could you rephrase it ?
Line 113: GSSmax is not defined
Line 114: add “(unitless)” after “GSS” ; remove “(daily)”
Line 117: add “(GCR, unitless)” after “roots”
Line 121: add “(GFR, unitless)” after “roots”
Line 124: Remove “GFR was the allocation coefficient to fine roots,”, and add “were” after “GSS”
Line 131: add “(unitless)” after “GW”. You can remove the end of the sentence from “, and GFR ...”
Line 138: add “(unitless)” after GBr
Line 144: the line may be removed
Line 151-152: Could you give slightly more information on how the growth respiration is computed?
Line 153 and after: Description of the maintenance respiration modelling is quite difficult to follow. This section needs clarifications (see below).
Line 155: maintenance respiration is a “function of their respective respiration rate per nitrogen unit, nitrogen content and surface temperature”. Equation (9), in which we divide by Ntrunk, defines the respiration rate per nitrogen unit (MRNtrunk). Equation (10) defines the maintenance respiration from MRNtrunk by multiplying it by Ntrunk. So, RMtrunk (or more generally RMorgan) does not seeem to be a function of the nitrogen content.
Line 159, equation (9): There is a problem with the 2 terms of the max functions (in brackets). Both terms are constants without any variable.
Line 159, equation (9): why expressing MRNtrunk in “mol CO2” and not in “gC” . In all cases, you may put the different conversion factors in the terms of the max function.
Line 159, equation (9): Mention that MRNtrunk and more generally MRNorgan are respiration rate per unit nitrogen, at reference temerature TMR
Line 161: add “C” between “unit” and “mass”.
Line 164-166: Mention that the Nbranches and Ntrunk were defined assuming a Carbon content per biomass unit of 50% (0.5).
Line 167-168, equation (10): For clarification, you may rewrite 0.005 as 0.01 x 0.5 and inject the “0.01” into the min function terms.
Line 168: The terms “0.256”, “-0.00854” and “0.0759” don’t match with the values reported on Figure S2b while those of the equation for Nbranches do match with values of on Figure S2a.
Line 173: RMorgan (CO2 hr-1). Do you mean “mol CO2”. You may express it in “gC”. Isn’t there a “m-2” missing in the units of RMorgan ?
Line 173: Borgan is “(gC m-2)” not “(gC)”
Line 174: “Norgan” not “Norgan”
Lines 176-177: I can’t find any information on Rd in Part 1 manuscript.
Line 183: “The realised lifespan of leaves was influenced by their K status (see Part 1)”. I could not find in Part 1 any information of the equation that relates LLSrealised to K status.
Line 186: remove one of the 2 “the”.
Line 192-268, Section 2.6: I think you can re-structure this section in two, one dedicated to ‘K allocation’ and another to ‘K remobilization’ (currently subsection 2.6.5). Paragraphs between line 225 and line 237 should be moved in the section on ‘K remobilization’.
Line 198: “flexible” not “flexivle”
Linr 199: I think you should replace Kwoodopti by Ktrunkopti as the branches are also made of wood. There are many places in the manuscript (and some figure captions) indeed, where you should replace “wood” by “trunk”
Line 210, equation (14): What’s the link between eq (14) and eq. (21) of Part1. To my understanding, the use of LimKorg assumes that Kphloem->leaf has been deduced first from Kavailable,phloem which is not mention in the text. Would not be more consistent with Part 1 and clearer, to use LK in Part 2 as well, and not LimKorg ?
Line 214 and after, section 2.6.1 Wood: it is the only section where you deal with the cohort level. Is it really needed ? If so, you should better explain the cohorts principle. For instance, line 217-218: “trunk NPP was allocated daily to a cohort of wood”. How is this cohort selected among all ?
Line 218-219: “optimal K concentration of newly formed wood was constant and to the maximum trunk concentration measured”. In this respect, why equation (15) includes LimorgK which tends to reduce Ktrunkopti
Line 229: equation (16) is not homogeneous.
Line 230-231: Unit of Ktrunk→xylemi gK m-2 day-1 instead of gK m-2 ? Unit of Ktrunki: gK (gC)-1 ? Unit of TKTrunk : (unitless) ?
Line 247-250: I think you can rephrase the sentences to gain in clarity.
Line 257: Replace “there no measurements were available” by “no measurement was available”.
Line 267: add “(unitless) after RKbranches
Line 267: maybe replace “rate” by “fraction”
Line 272: “m-2”
Line 272: Add an end parenthesis after “planting”
Line 281: “blocks” instead of “blocs”
Lines 285 to 305: There is probably a problem with the numbering of section 2.9 and subsections 2.9.1 to 2.9.3: 2.9 -> 2.8.1 ; 2.9.1 -> 2.8.2 ; 2.9.2 -> 2.8.3 ; 2.9.3 -> 2.8.4
Line 285-287: name explicitly and define the different CUE you use in the Results section : CUENPP, CUEtrunk, ; I think you only report CUE values in the Result for the full rotation period by computed a mean CUE as the cumulated NPP divided by the cumulated GPP. If this is correct, specify it here (and also for WUE).
Line 289-290: define also here WUEGPP for which you report values in the Results section.
Line 293: “C-based metric” may refer to CUE; you may replace it by “C flux”
Line 295, equation (20): as it is defined, KUENPP seems to be a function of the length of the rotation. Is it really expected? It does not appear to be a very handy metric to compare experiments with different rotation length. You could use the mean daily C flux over the length of the rotation instead of the cumulated one. This would imply to express KUENPP in gC day-1 (gK)-1
Line 295: As “i” index refers to time, you could replace it by “t”.
Line 307: replace “and dividing it” by “divided”
Line 309, equation (21): Kfertiliseradded should be sum for i=0 to k as well, in particular to account for the fertiliser regime with 4 applications.
Line 317-320: I think it is sufficient to report the five-year mean annual GPP values (those in parenthesis), not the cumulated fluxes.
Line 321: “Table 2”, I think you want to refer to “Table 3” of Part 1, not Table 2
Line 323: replace “trunk NPPtrunk” by “NPPtrunk”
Line 325: add an end parenthesis after “Fig. 2e”
Line 325: add a “,” after “stand”.
Line 326: give units to the RMSE values. Replace “for” by “of simulated”
Line 328: replace “age 59 months” by “month 59 after planting”
Line 333: replace “carbon use efficiency (defined as the ration of NPP to GPP)” by “CUENPP”
Line 334: replace “0.52 vs 0.40” by “0.40 vs 0.52”
Line 336: replace “CUE” by “CUENPP”
Line 338: add “relative” before “increase”
Line 339-340: “This was further amplified by leaf NPP representing 13% of GPP in oK compared to 7% in +K”. Is this remark related to the difference in CUEtrunk, only (and not CUENPP)? If so, please specify.
Line 345: replace “0, 3, 10 and 20 moths of age” by “month 0, 3, 10 and 20 after planting”
Line 353: add “located in” between “were” and “the”.
Line 363: add a comma after “model”.
Line 393: “Potassium concentrations in trunk wood and branches are correctly simulated”. Could you provide a quantitative metric for this “correct simulation performance” ? In addition, you should probably highlight that for branches at least, there is a large spread in the measurements in particular for low biomass values.
Figure 2: You may put x- and y-labels bigger. Add “Measured and” at the beginning of the figure legend.
Figure S2 b), replace “wood” by “trunk” in the Y-label
Citation: https://doi.org/10.5194/egusphere-2022-884-RC1 -
AC1: 'Reply on RC1', Ivan Cornut, 28 Dec 2022
General comments
The manuscript submitted to Biogeosciences by Cornut et al. studies the impact of a potassium limitation on wood productivity and in particular on the allocation of carbon and potassium towards trunk, branches and bark, through the modelling and evaluation of the CASTENEA-MAESPA-K model. This is the Part2 of a two-part paper, Part1 being dedicated to the impact of K limitation on the C-source activity (GPP). The split in the 2 parts is relatively well done, and the present manuscript (Part 2) is sufficiently self-supporting, without the need of reading the Part 1 first.
The overall objectives of the manuscript are relevant; and the “Results” and “Discussion” sections report fairly on the model capacities at simulating biomass of each compartment (organ) for different K availability scenarios.
However, the manuscript needs a strong revision of the Methods section and some restructuration. Currently, this section contains too many inconsistencies in several equations, variable units, ... There is not a particular major deficiency but an accumulation of inaccuracies, which really prevents to access at the content of the manuscript. I address many of them in the Technical comments below.
We thank Reviewer one for these general comments. We take notice that our two-part approcah is acknowledged and accepted here. We appreciate that these comments are thorough and relevant to our work. They were very useful when revising our manuscript. We have attempted to answer some of the most important concern below. We hope that our answers can alleviate some of the mis-comprehensions that have stemmed from reading our manuscript. This will feed into the restructuration of the methods section.
Technical comments
I would suggest using the present tense in the Methods section when describing the model features, instead of the past tense.
Line 100-108: As far as I understood, the allocation coefficients presented in subsections 2.3.2 and after are applied over “NPP - C allocated in leaves” not NPP. If this is correct, this should be clarified here. To my understanding, the sentence “The growth of all organs was a fraction of the daily NPP” does not reflect the way it is modelled. If “all organs” include leaves, it is in contradiction with the sentence “the generation of leaves ... was not directly dependant on NPP”. If “all organs” means “all organs except leaves”, their growth is a fraction of NPPorg, not NPP. To my opinion, NPPorg should be defined here and not line 200 of the current manuscript.
Thank you for the detailed review, we used a shortcut in our description but yes allocation coefficients are NPP – C allocated to leaves. The production of leaves had priority over the production of all other organs. Meaning that NPP was first allocated to leaves then allocated to the other organs (following their respective allocation ratios). The production of leaves can be limited by NPP in our model but this was very rarely the case in our simulations.
Line 151-152: Could you give slightly more information on how the growth respiration is computed?
Growth respiration was computed by using parameters measured in eucalypt plantations (Ryan et al., 2009). The growth respiration was modelled as in the original CASTANEA model (Dufrêne et al., 2005).
Line 153 and after: Description of the maintenance respiration modelling is quite difficult to follow. This section needs clarifications (see below).
Thank you for this comment. This will be clarified in the manuscript as explained below..
Line 155: maintenance respiration is a “function of their respective respiration rate per nitrogen unit, nitrogen content and surface temperature”. Equation (9), in which we divide by Ntrunk, defines the respiration rate per nitrogen unit (MRNtrunk). Equation (10) defines the maintenance respiration from MRNtrunk by multiplying it by Ntrunk. So, RMtrunk (or more generally RMorgan) does not seeem to be a function of the nitrogen content.
This is true (for the trunk only). We used this since the N content of trunks in Ryan et al., 2009 there were no concurrent measurements of N trunk. Instead we resorted to use a maintenance respiration rate of biomass that was a function of said biomass (to be able to use these published measurements) and a constant Ntrunk for MRN_trunk. This is unclear and will be clarified in the manuscript.
Line 159, equation (9): There is a problem with the 2 terms of the max functions (in brackets). Both terms are constants without any variable.
Yes, there was an error in the transcription of this equation. Thank you for seeing this. The equation should read:
max(0.00047,0.0073-0.00000116*B_trunk)*1/1e6*3600*1/12*1/0.001
Line 168: The terms “0.256”, “-0.00854” and “0.0759” don’t match with the values reported on Figure S2b while those of the equation for Nbranches do match with values of on Figure S2a.
This will be changed. We will use direct model outputs instead for this figure, that will help clarify the values.
Line 183: “The realised lifespan of leaves was influenced by their K status (see Part 1)”. I could not find in Part 1 any information of the equation that relates LLSrealised to K status.
This is presented in the companion paper Part 1 (Cornut et al., 2022). Since leaves fall when their K concentration is below a threshold value, their “true” lifespan can be strongly reduced by K availability.
Line 214 and after, section 2.6.1 Wood: it is the only section where you deal with the cohort level. Is it really needed ? If so, you should better explain the cohorts principle. For instance, line 217-218: “trunk NPP was allocated daily to a cohort of wood”. How is this cohort selected among all ?
Wood cohorts correspond to daily productions of wood. Trunk NPP is allocated to the cohort created on that day. This was necessary for our wood remobilisation model.
Line 218-219: “optimal K concentration of newly formed wood was constant and to the maximum trunk concentration measured”. In this respect, why equation (15) includes LimorgK which tends to reduce Ktrunkopti
Because optimal (when K is present in sufficient quantities) and realized (after computation of offer vs demand of K) concentrations are different.
Line 295, equation (20): as it is defined, KUENPP seems to be a function of the length of the rotation. Is it really expected? It does not appear to be a very handy metric to compare experiments with different rotation length. You could use the mean daily C flux over the length of the rotation instead of the cumulated one. This would imply to express KUENPP in gC day-1 (gK)-1
Yes. It is true that this means that KUE is a function of rotation length and that this should not be the focus of this metric. We will thus recalculate its value by using it divided by the number of days in the rotation. This should not change the discussion of the results since we simulated rotations with all the same length.
Line 393: “Potassium concentrations in trunk wood and branches are correctly simulated”. Could you provide a quantitative metric for this “correct simulation performance” ? In addition, you should probably highlight that for branches at least, there is a large spread in the measurements in particular for low biomass values.
It is true that this sentence was overly optimistic. We have no hypotheses regarding the large spread of values at low biomasses. It could be an effect due to the large proportion of very young branches. In tne manuscript we will highlight the discrepancies between modelled concentrations in branches and simulated ones.
References:
Cornut, I., Delpierre, N., Laclau, J. P., Guillemot, J., Nouvellon, Y., Campoe, O., ... & le Maire, G. (2022). Potassium-limitation of forest productivity, part 1: A mechanistic model simulating the effects of potassium availability on canopy carbon and water fluxes in tropical eucalypt stands. EGUsphere, 1-37.
Dufrêne, E., Davi, H., François, C., Le Maire, G., Le Dantec, V., & Granier, A. (2005). Modelling carbon and water cycles in a beech forest: Part I: Model description and uncertainty analysis on modelled NEE. Ecological Modelling, 185(2-4), 407-436.
Ryan, M. G., Cavaleri, M. A., Almeida, A. C., Penchel, R., Senock, R. S., & Luiz Stape, J. (2009). Wood CO2 efflux and foliar respiration for Eucalyptus in Hawaii and Brazil. Tree Physiology, 29(10), 1213-1222.
Citation: https://doi.org/10.5194/egusphere-2022-884-AC1
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AC1: 'Reply on RC1', Ivan Cornut, 28 Dec 2022
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RC2: 'Comment on egusphere-2022-884', Anonymous Referee #2, 31 Oct 2022
Here I review the 2nd part of the work submitted by Cornut et al., focusing on simulating growth limitation induced by K deficiency. Overall, I find this manuscript well-written. I have one comment regarding the model structure. Here, the authors indicated that the model structure accounts for additional processes relating to K allocation, remobilization and turnover. I do not understand why the model structure is different in this paper as compared to the model structure of the first paper. I know two papers have different focus, but it would be valuable to justify the reason as to why the authors decided to omit processes described here in the first paper. Particularly, does it mean that the results of the two papers are not directly comparable even if they were used to simulate processes for the same site? Apart from this comment, I think the manuscript is generally well presented.
Specific comments:
L64: no hypothesis on sink limitation was previously introduced yet. It would be great to make it explicit. And, it would be useful to describe what you meant by parsimony principle.
L 91 – 93: Why these modules on carbon allocation and K effect on organ growth not important in the first manuscript? In particular, why the model structure of the two papers different? Does it mean the results of the two papers are not directly comparable, even if simulated for the same site?
L199: incorrect spelling, should be “flexible”.
Figure 1: The color scheme makes it hard to see the difference between +K and oK treatment, especially for the dots. Can the authors please revise them to more distinguishable colors?
Figure 4b: Why litter K content starts so high and declines over time?
Equation 8: Btrunk should be biomass, not in unit of g C m-2, right?
Equation 12: Knpp in the unit of gK m-2? Shouldn’t it be in the unit of gK m-2 d-1? But if this is the case, what’s the correct unit for Kavailable in equation 14?
Citation: https://doi.org/10.5194/egusphere-2022-884-RC2 -
AC2: 'Reply on RC2', Ivan Cornut, 28 Dec 2022
Here I review the 2nd part of the work submitted by Cornut et al., focusing on simulating growth limitation induced by K deficiency. Overall, I find this manuscript well-written. I have one comment regarding the model structure. Here, the authors indicated that the model structure accounts for additional processes relating to K allocation, remobilization and turnover. I do not understand why the model structure is different in this paper as compared to the model structure of the first paper. I know two papers have different focus, but it would be valuable to justify the reason as to why the authors decided to omit processes described here in the first paper. Particularly, does it mean that the results of the two papers are not directly comparable even if they were used to simulate processes for the same site? Apart from this comment, I think the manuscript is generally well presented.
We thank reviewer two for the positive remarks and the constructive criticisms that they bring to the mansucript. These remarks will be thouroughly taken into account when improving the manuscript. The model structure that was used is the same in the two papers. In the first paper we chose to focus the description on the canopy and the processes related to leaves and C acquisition. In the second paper we focus instead on allocation of K and C in the trees. The schematic attempted to show this but our explanations lack clarity. The results of the two papers are thus comparable. This was an attempt to avoid redundancy between the two papers. We will thus improve the description of this aspect in the manuscript.
Specific comments:
L64: no hypothesis on sink limitation was previously introduced yet. It would be great to make it explicit. And, it would be useful to describe what you meant by parsimony principle.
We are not sure to understand the first comment. Sink limitation was introduced line 49. By sink limitation (which also include carbohydrate transport mlimitations) we include processes that could limit wood production by affecting sugar transport from source organs to sink organs (or from sap to sink organs) or direct limitation of sink organ functionning by K deficiency (by affecting cell expansion, metabolism or lifespan).
By parsimony principle means that we did not introduce more processes in the model if the ones that were already included in the model could explain the observed patterns (here, K limitation). This was to limit hypothesis on functionning and focus on using only available information.
Both these clarifications will be added to the manuscript.
L 91 – 93: Why these modules on carbon allocation and K effect on organ growth not important in the first manuscript? In particular, why the model structure of the two papers different? Does it mean the results of the two papers are not directly comparable, even if simulated for the same site?
The structure of the model is exactly the same between the two manuscripts. The Part 1 (Cornut et al., 2022) is focused mainly on the canopy, carbon assimilation and the calibration of theses processes. Part 2 is focused mainly on the allocation of this carbon and the validation of the model using measures of biomass production. We therefore just change the focus on different processes in Part 1 and in Part 2.
Figure 4b: Why litter K content starts so high and declines over time?
This was due to the presence of ground litter on the soil following the clear-cutting of the previous plantation corresponding both to litter that was present on the gorund at cutting and branches, leaves and bark of the cut trees that were added to the soil as litter.
Equation 8: Btrunk should be biomass, not in unit of g C m-2, right?
No, the biomasses inside the model are all in grams of caron per square meters of soil (gC.m-2)
Equation 12: Knpp in the unit of gK m-2? Shouldn’t it be in the unit of gK m-2 d-1? But if this is the case, what’s the correct unit for Kavailable in equation 14?
The correct unit for K _NPPin equation should be gK.m-2.d-1 And this should also be the unit for K_available.
References :
Cornut, I., Delpierre, N., Laclau, J. P., Guillemot, J., Nouvellon, Y., Campoe, O., ... & le Maire, G. (2022). Potassium-limitation of forest productivity, part 1: A mechanistic model simulating the effects of potassium availability on canopy carbon and water fluxes in tropical eucalypt stands. EGUsphere, 1-37.
Citation: https://doi.org/10.5194/egusphere-2022-884-AC2
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AC2: 'Reply on RC2', Ivan Cornut, 28 Dec 2022
Ivan Cornut et al.
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