Photosynthetic Pigments in Siberian Pine and Fir under Climate Warming and Shift of the Timberline
Round 1
Reviewer 1 Report
This is an interesting approach to evaluating the potential for a treeline tree species to move up in elevation with continued climate warming. However, the lack of English writing skills makes it difficult to evaluate the overall merit of this manuscript. Also, the relationship between the importance of the ratio of the pigments studied and the electron transport rate is not made clear in terms of which species will move upward. These relationships have to be clarified in terms of both insolation effects and temperature changes.
Author Response
Thank you for reviewing our manuscript.
The manuscript has been revised and the grammar errors have been corrected.
Regarding the relationship between chlorophyll content and ETR, you are right that we do not elaborate on this issue deeply. The ETR data are to some extent additional. In fact, both chlorophyll content and ETR speak more or less about the same thing, the activity of the photosynthetic system.
Reviewer 2 Report
MS Title: Which species drive the timberlines up: photosynthetic pigments in Siberian pine and Siberian fir under ongoing climate warming.
Summary of Research
Global warming is resulting in shifts of species distributions in geographic space. This phenomenon is more pronounced at the limits of the species distribution, for example alpine treeline. Here, the authors explore needle physiology in Pinus sibirica and Abies sibirica along an elevation gradient in order to assess how projected increases in temperature will alter photosynthetic processes and presumably enhance the fitness of one or the other species as the compete to move up slope.
The authors used standard measures of photosynthetic productivity in both species and then compared them to each other. Ultimately, the paper concludes with the declaration that P. sibirica will be the likely “winner” in the race up the mountain. I generally think that ecophysiological papers are important as we combine large scale models, common gardens and observational studies of treeline advance. However, I was disappointed in the overall detail of how this project was carried out and the level of synthesis of the results. On balance, the manuscript was difficult to read in places and a careful review of grammar and syntax would be warranted.
Below I provide a few detailed comments to help the authors in improving the manuscript.
Draft Main Points of Review
Title:
The title is a little cumbersome. I think a simplified title that more accurately addresses the scope of the paper is warranted. Perhaps something like “The interaction of photosynthetic pigments and climate warming in shifting timberline up in Siberian pine and fir.” – Just a suggestion.
Introduction:
First, I would expect a little more in the way of synthesizing the literature on global treeline shifts. The introduction is missing some key citations. For example, Melanie Harsch (2009) conducted a global meta-analysis of treeline position and showed that only slightly more than 50% of treelines globally are increasing in elevation. Following global trends I would expect to see the authors narrow down their discussion to how photosynthetic mechanisms may control treeline position. Bill Smith (2003) introduced an alternate explanation to treeline position (as opposed to the temperature/growth limitation of Korner) suggesting that restrictions on photosynthetic carbon gain may be more important (conceptualized as ecological facilitation away from the forest edge). The point I’m attempting to make is that I think the reseach needs to be better justified and situated in the alpine treeline literature so that statements about photosynthetic characteristics can be made.
Methods:
The methods were sparse. A section on sampling design is needed to assess the appropriateness of the study overall. There is no explanation of how sampling points were chosen or the elevational sampling units. The reader needs this information, or the rest of the analysis cannot be assessed.
The figures are difficult to interpret.
Figure one: Standard cartographical elements are missing (at a minimum a scale and inset map are needed to place the study site into a geographic context).
Results:
Again, the figures are difficult to interpret.
Figure two: axis labels are inappropriately positioned.
Table one: Caption needs additional information. What information is indicated by spi? It seems that sample points need explanation in the methods somewhere.
Some of the information in the results would be better suited for the discussion. For example, lines 244-246, put a careful reading of the results is warranted.
Discussion:
How do the findings here fit back into the global picture of alpine treeline advance? The first paragraph should stress your important findings and then place them into the broader treeline literature.
Citations still seem missing here too.
Line 265 - Harsch 2011, Treeline Form – a potential key to understanding treeline dynamics, discusses issues of climatic versus geologically controlled treelines.
Line 268 – Unless I missed it, this is the first time I’ve read about the study site as a slope with a uniform climb and minimal microrelief. This is important to include in the methods.
Overall, I expected more of a discussion of how this studies results fit into the broader scientific literature.
Concluding Thoughts:
I will close by stating that the ideas in this paper are good. I would like to see the ideas and findings from the research better situated in the literature. I would also like to see the research methods and results better described so that a reader can assess the overall merit of the research.
Author Response
Thank you for reviewing our manuscript.
The manuscript has been revised and the grammar errors have been corrected.
As you suggested, the title has been changed. We suggest "Photosynthetic pigments in Siberian pine and fir under climate warming and shifting the timberline up".
The literature that you suggested was reviewed and added to the manuscript's reference list to provide a broader scientific context.
In the Materials and Methods section, some specifications have been added regarding the slope choice and the measurements of altitudes. What concerns the choice of the specimens to sample, we had to act in a sort of ad hoc manner as the firs and pines grew a bit randomly. Not always there was an opportunity to sample a fir and a pine in the same location.
In Table, an indication of what <sp> means is added.
Figure 1 has been replaced and the necessary geographical indications have been added.
Figure 2 has been corrected as to the axis position.
All the figures have been redrawn to improve their outlook.
Round 2
Reviewer 2 Report
The manuscript has been improved following several changes. The figures are much better and the additional literature provides more in-depth context to the study. However, I am still not comfortable with the level of detail in the methods and results. In particular the description of the sampling. The authors note in their response to reviewers that the sampling is somewhat ad hoc because of the disjunct distribution of the two pine species. They did not include this information in the methods. I think this information needs to be in the paper so that readers can appropriately assess the soundness of the results and the conclusions drawn from these results. An additional reading of the manuscript and editing for clarity and consistency would be helpful.
Author Response
Thank you for your comments.
The sampling scheme was specified in more detail.
lines 170-173: The sampling points were taken at more or less equal distances from one another but taking into account the presence of trees of close age, ca. 40–50 years. The sampling of 50 cm long shoots was done from a lower part of the crowns, with only vegetative shoots were taken (no presence of female or male cones).
lines 185-188: Because Siberian pine and fir grow often disjunctively at a higher elevation, the sampling followed sometimes an ad hoc approach—where both pine and fir might have been sampled at the same location/elevation. In a few instances, however, pine and fir trees were sampled at different but still close locations (see Figure 1).
Also, a remark was inserted that relates the pigment content and ETR.
lines 275-277: These data are related to chlorophyll a content (Table 1) and give evidence that A. sibirica needles have higher photosynthetic activity at altitudes 1640 and 1660 m a.s.l.
The manuscript has been checked and a few grammar errors were corrected.
