Ideas and perspectives: Heat stress: more than hot air

De Boeck, Hans J.; Van De Velde, Helena; De Groote, Toon; Nijs, Ivan

doi:https://doi.org/10.5194/bg-13-5821-2016

Articles | Volume 13, issue 20

https://doi.org/10.5194/bg-13-5821-2016

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

https://doi.org/10.5194/bg-13-5821-2016

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

Articles | Volume 13, issue 20

Ideas and perspectives

|

24 Oct 2016

Ideas and perspectives |

| 24 Oct 2016

Ideas and perspectives: Heat stress: more than hot air

Hans J. De Boeck, Helena Van De Velde, Toon De Groote, and Ivan Nijs

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Final revised paper (published on 24 Oct 2016)
Supplement to the final revised paper
Preprint (discussion started on 21 Mar 2016)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC1: '"Ideas and perspectives: Heat stress: more than hot air", by De Boeck et al.', Anonymous Referee #1, 28 Apr 2016
- SC1: 'Reply to referee 1', Hans J. De Boeck, 15 May 2016
RC2: '"Ideas and perspectives: Heat stress: more than hot air", by De Boeck et al.', Anonymous Referee #2, 09 May 2016
- SC2: 'Reply to referee 2', Hans J. De Boeck, 15 May 2016
AC1: 'Final response to referees', Hans De Boeck, 02 Jun 2016

Peer-review completion

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

ED: Reconsider after major revisions (08 Jun 2016) by Anja Rammig

AR by Hans De Boeck on behalf of the Authors (08 Jun 2016)

ED: Referee Nomination & Report Request started (27 Jun 2016) by Anja Rammig

RR by Anonymous Referee #1 (05 Jul 2016)

RR by Anonymous Referee #2 (26 Jul 2016)

Suggestions for revision or reasons for rejection

The revised manuscript addresses some of the raised concerns but the use of an inappropriately complex model in favor of a thorough theoretical reasoning remains the fundamental flaw of the paper.

In their response, the authors justify the use of their model by claiming that the calculation of leaf temperature “requires iterative computation and decision schemes.” This alone wouldn’t justify the replacement of theory by numerical simulations. But it is not even true. An excellent example of a concise theoretical discussion of the topic including an explicit equation to determine leaf temperature from air temperature, radiation, wind speed, and vapor deficit can be found in Campbell and Norman (1998). It is not the only example. In fact, the issue is a standard topic covered by almost every textbook on the matter. Further examples include Geiger (1950), Oke (1987), Lambers, Chapin III, and Pons (2008), Monteith and Unsworth (2009), and Jones (2013), to name just a few.

Given the fact that knowledge about the difference between leaf and air temperature and its importance is so well established, it is indeed surprising that leaf temperature is not routinely used when assessing plant responses to heat waves and environmental conditions in general. One probable reason might be that leaf temperature is not a standard meteorological variable and cannot be easily measured on the landscape scale. On the other hand, estimation of leaf temperature from standard climate variables is data intensive and entails potentially large uncertainties. Additional problems arise from temperature gradients within canopies leading to non-uniform distribution of heat stress. Practical guidance on how to address these problems is required to lower the barrier for including leaf temperature in ecological and agronomic studies.

In my view, the manuscript by De Boeck et al. fails to provide any new ideas and perspectives on the issue of leaf temperature and heat stress. It merely states that using air temperature instead of leaf temperature as a measure for heat stress is inappropriate. The attempt to identify the drivers for leaf temperature remains superficial and consequently ignores the vast body of literature on the topic. The paper does not provide any practical suggestions for improving studies on heat waves nor does it line out a way towards addressing the problem more appropriately in the future.

References

Geiger R. (1950) The Climate Near the Ground, Harvard University Press, Cambridge.

Jones H.G. (2013) Plants and Microclimate: A Quantitative Approach to Environmental Plant Physiology: Third Edition. Cambridge Univ. Press, Cambridge.

Campbell G.S. and J.M. Norman (1998) An Introduction to Environmental Biophysics, 2nd Edn. Springer, New York.

Lambers H., F.S. Chapin III and T.L. Pons (1998): Plant physiological ecology, 2nd Edn. Springer, New York.

Monteith J.L. and M.H. Unsworth (1990) Principles of Environmental Physics, 2nd Edn. Edward Arnold, London.

Oke T.R. (1987) Boundary Layer Climates, 2nd Edn. Routledge, New York.

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ED: Reconsider after major revisions (09 Aug 2016) by Anja Rammig

AR by Hans De Boeck on behalf of the Authors (25 Aug 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (07 Sep 2016) by Anja Rammig

RR by Anonymous Referee #1 (15 Sep 2016)

Suggestions for revision or reasons for rejection

I would like to thank the authors for the revision of their manuscript. I understand their struggle with two opposing sets of comments, and think that the current version of the manuscript is a well-balanced compromise between these. I have a few minor suggestions (below), and I recommend publication of this manuscript to support the discussion and usage of leaf temperature (measurements and models) in our analysis of heat wave impacts.

- p. 1/l. 9: replace "Climate change models" with "Climate models"
- p. 1/l. 15: the sentence "in excess of 10C ... to even 20C" could be misunderstood: The range is not between 10 and 20 degrees, but rather between 0 and 10/20. Also, the given upper limits (10/20 degrees) are obtained only when taking rather extreme (and possibly very unlikely) conditions (such as high RH and closed stomata, Fig. S9) into the comparisons. I do not think that this is within the scope of something the user would understand as a "fluctuation" (p. 1/l. 15), the conditions that need to be met to obtain these differences are so extreme that they will rarely occur within a short period of time. I would recommend a more moderate statement that better reflects real conditions.
- p. 3/l. 12: The addition "via stomatal responses" is unnecessary here, the authors cannot exclude other impacts (e.g. a change in near-surface RH resulting from the change in irrigation).
- p. 4/l. 30: replace "such as used here" with "as used here", or "such as the one used here".
- p. 4/l. 30: I do not think that model and IR observations exclude each other: We will need more IR observations to evaluate model performance (e.g. to perform a more direct comparison under heat wave conditions). But in general I like the addition of the statement on availability/possibility of IR measurements.

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ED: Publish subject to minor revisions (Editor review) (21 Sep 2016) by Anja Rammig

AR by Hans De Boeck on behalf of the Authors (21 Sep 2016) Author's response Manuscript

ED: Publish as is (12 Oct 2016) by Anja Rammig

AR by Hans De Boeck on behalf of the Authors (13 Oct 2016)

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Short summary

Considering air temperature as a direct predictor of heat stress is misleading as physiological consequences from heat depend on tissue temperatures. This study helps to clarify more fundamentally when and how heat waves may lead to plant stress by demonstrating how several environmental variables contribute to tissue temperatures. This renders it easier for ecologists and agronomists to predict when the dangers of heat stress occurring are highest.