Challenges in modelling isoprene and monoterpene emission dynamics of Arctic plants: a case study from a subarctic tundra heath

Tang, Jing; Schurgers, Guy; Valolahti, Hanna; Faubert, Patrick; Tiiva, Päivi; Michelsen, Anders; Rinnan, Riikka

doi:https://doi.org/10.5194/bg-13-6651-2016

Articles | Volume 13, issue 24

https://doi.org/10.5194/bg-13-6651-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

Interactions between climate change and the Cryosphere: SVALI,...

https://doi.org/10.5194/bg-13-6651-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 13, issue 24

Research article

|

19 Dec 2016

Research article |

| 19 Dec 2016

Challenges in modelling isoprene and monoterpene emission dynamics of Arctic plants: a case study from a subarctic tundra heath

Jing Tang, Guy Schurgers, Hanna Valolahti, Patrick Faubert, Päivi Tiiva, Anders Michelsen, and Riikka Rinnan

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Final revised paper (published on 19 Dec 2016)
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Preprint (discussion started on 08 Apr 2016)
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Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Referee comment', Anonymous Referee #1, 09 May 2016
- AC1: 'Tang et al., replies to RC1', Jing Tang, 23 Jun 2016
RC2: 'Still some explanations to do', Anonymous Referee #2, 10 May 2016
- AC2: 'Tang et al., replies to RC2', Jing Tang, 23 Jun 2016
RC3: 'Review', Anonymous Referee #3, 13 May 2016
- AC3: 'Tang et al., replies to RC3', Jing Tang, 23 Jun 2016

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (06 Jul 2016) by Jaana Bäck

AR by Jing Tang on behalf of the Authors (12 Aug 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (15 Aug 2016) by Jaana Bäck

RR by Anonymous Referee #2 (17 Aug 2016)

Suggestions for revision or reasons for rejection

Although many comments and suggestions have been acknowledged and considered, I am sorry to say that I am not quite convinced about the argumentation not to change a thing about noon-calculations and LAI representation. This now refers to the following parts of the manuscript:

P6, L11: The seasonality function only applies to isoprene production although (L14) the model assumes that both isoprene and monoterpenes are produced in the same pathway and respond in the same way to CO2. This is an inconsistent approach. Either the seasonality should apply on monoterpenes too or the CO2 response cannot be applied on (light dependent) monoterpenes.
It is not clear from the description but do coniferous and herbaceous PFTs light-dependent and light-independent fractions at the same time? I guess not because then I would like to know how the epsilon_s parameter is derived from measurements (Had there been an a-priori assumption about the differentiation? Have I missed this piece of information?). Please clarify in the text.
Emissions from storages should depend on average daily temperature, not on daytime temperature. Therefore, the T values in Eq. 3 and 4 should not be the same. Has this been considered?

P9, L4: I am not convinced from the response regarding using only average PAR for calculating emissions because ‘the Haxeltine and Prentice approach only describes daily photosynthesis‘. Why should it not be possible ‘to compute an instantaneous flux at noon’ all the more why can an artificially calculated flux (that might be empirically increased to a reasonable degree if not calculated) not be fed into the photosynthesis model to check its response? If this would be a reason, the use of maximum temperature to calculate an upper limit for emission would also not be valid.

P10, L13/14: I don’t see any valid response, explanation or consideration of the fact that the modelled and measured LAI values are far off for most of the vegetation types. In figure 3, the forbs/lichens type (CLM) LAI is about 0.5 measured and 0.25 modelled, the evergreen shrubs (LSE+EDPS) are presented with a measured LAI of almost 0.4 while the model gives 0.2 (note the different axis). So how can this be called ‘captured by the model’?? Or was there a kind of mix up with the axis?

In addition, you might consider to modify the following:

P7, L32: Since evaluation and validation are different terms, and what has been done here is clearly ‘evaluation’, this should not be mixed up in the headline (in short: change validation into evaluation). (Check also throughout the manuscript.)

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RR by Anonymous Referee #1 (29 Aug 2016)

Suggestions for revision or reasons for rejection

I appreciate the many changes the authors have made to improve the manuscript in response to the two reviewers’ comments, but I still have two major concerns. These were both concerns that I raised during my original review which I feel have not been adequately addressed.

First, and more importantly, I am still unsatisfied with the comparison of modelled daily means and maxes with the spot measurements. I see that my concerns were also shared by the other reviewer. I do appreciate that the authors have moved past the very qualitative comparison that was employed in the first version of the manuscript. But, the authors are using a model that produces only one estimate of BVOC emissions per day, and it’s difficult to compare this to a relatively small number of measurements. My view is given the difficulty of acquiring the field data, these measurements are useful and I understand I can’t demand the perfect dataset with more complete coverage. On the other hand, modeling is much more flexible, and more sophisticated modeling approaches can be applied. The authors can run a series of different simulations using different weather inputs. For example, they could apply a Monte Carlo approach that can give information about both mean responses and variance. This is a much more appropriate response than simply doing two runs with the mean and max values. I would be more satisfied in the authors could site a previous study that used only daily means and maxes in a similar comparison.

Second, and I understand this is a more minor and somewhat picky point, but the authors should more carefully read Monson et al 2012, which they cite on page 3 of the new manuscript. In particular, see section XI (Conclusions) in that reference. The main point is that so-called ‘mechanistic’ models, based on the Niinemets approach, have an empirical gap due to the lack of knowledge about a number of critical processes. Again, I encourage the authors to add more nuisance to their comparison of the modelling approaches. Since the authors are not bringing anything new to the table in terms of the comparison of mechanistic vs empirical models, I don’t understand the necessity of disparaging empirical models. The authors can simply state what they are using, and move forward.

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ED: Reconsider after major revisions (19 Sep 2016) by Jaana Bäck

AR by Jing Tang on behalf of the Authors (13 Oct 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (07 Nov 2016) by Jaana Bäck

RR by Anonymous Referee #2 (08 Nov 2016)

RR by Anonymous Referee #1 (18 Nov 2016)

ED: Publish as is (22 Nov 2016) by Jaana Bäck

AR by Jing Tang on behalf of the Authors (29 Nov 2016) Manuscript

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Short summary

Arctic is warming at twice the global average speed and the warming-induced increases in biogenic volatile organic compound (BVOC) emissions from Arctic plants are expected to be drastic. This modelling study aims to investigate BVOC emission responses to warming. The results show that 2 °C summer warming can increase annual emissions by 56 % and the short-term warming responses are strongly impacted by leaf temperature, while the long-time responses are interacted with vegetation changes.