Timing of Drought and Severity of Induced Leaf Desiccation Affect Recovery, Growth and Autumnal Leaf Senescence in Fagus sylvatica L. Saplings

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors!

You have conducted long-term experiments. The text of the manuscript is clear, relevant for the scientific field and presented in a well-structured manner.  

More than a half (63%) of the cited references are not within the last 5 years, but they are relevant. I didn`t noticed the excessive number of self-citations.

The manuscript is scientifically sound and the experimental design is appropriate to test the hypothesis. However, I think you should check English of the manuscript. For example, a major European tree species (lines 16-17).

The setting of the experiments is described in detail. The manuscript’s results are reproducible based on the details given in the methods section. What is ß? You should add this information.

The figures are appropriate, they properly show the data. They are easy to interpret and understand. The data is interpreted appropriately and consistently throughout the manuscript. I think you should increase the size of Table 9. Probably, you can add correlation matrix (lines 438-439).

The conclusions are consistent with the evidence and arguments presented.

I didn`t notice any statistical and ethical mistakes.

Author Response

Reviewer 1

• check English of the manuscript. For example, amajor European tree species (lines 16-17).

We changed this to: “… one of the major European tree species…” The whole manuscript has been checked and adjusted for the English language.

• The manuscript’s results are reproducible based on the details given in the methods section. What is ß? You should add this information.

We added: “In the presented model formulas, each β is an indication of the effect of each independent variable on the response variable.”

• I think you should increase the size of Table 9. Probably, you can add correlation matrix (lines 438-439).

We increased the size of the table in Figure 9. We did not calculate correlation coefficients, as the summary presented is based on the outcomes of the statistical modelling. We moved now Figure 9 to a separate paragraph in the Results section.

Reviewer 2 Report

Comments and Suggestions for Authors

Comments are attached.

Comments for author File: Comments.pdf

Author Response

Reviewer 2

• In Table 3, explain what each variable represents in the foot note. For example, what are Daycat, Des, DiaO and other variables shown in the table 3?

We made this more clear by using bold text in the description column of the table and indicating this in the caption: “Abbreviations of the variables are explained in the description using bold text.”

We also adjusted the names of the variables to make them more clear. We did this in Table 3 and accordingly also in the model formulas and in the tables with the test statistics.

• In Figure 9, some groups are shown in blue and and others in grey colour. Which one of them is significantly differing or not differing? Please mention in the foot note.

We adapted the caption of Figure 9: “Schematic representation of the results from the modelling of the response variables for the spring and summer treatments. The saplings were in a control (C) or drought group (D) in the spring treatment or in the combined spring and summer treatment (separated by a hyphen). The spring drought caused less than half or more than half of the leaves to desiccate (D<50 or D>50). Italic: response variable specific to either spring or summer treatment; grey background: not measured; arrows: increase or decrease; equality sign: no change; green: standard group to which the others are compared; blue: significantly different from the standard group; grey: no significant difference with regard to the standard group.”

• But how drought improves diameter increment in the later part of the growing season? It is not known and not explained. A mechanistic explanation may be added in the discussion if known.

 

Apart from what we already mentioned in the discussion (see below) we are not aware of any literature describing in a more physiological, molecular or mechanistic way how radial growth can be improved later on in the growing season.

“It can be hypothesized that in the here described experiment, the late-season radial growth represented a specific response to hydraulic impairment. Research suggested that the primary response to hydraulic impairment in trees is the regeneration of xylem through active vascular cambium [40], and not the refilling of embolised conduits [4].”

 

• Line 50: Change the word “live” to “life”. OK

 

• Line 323: Put a full point (.) after (Figure 4). OK

 

• Line 391: It should be “spring drought”, not “pring drought”. OK

 

Reviewer 3 Report

Comments and Suggestions for Authors

Thanks for the opportunity to review the interesting and quite written manuscript.

Extreme drought events will lead to the cessation of tree growth and individual mortality, which will trigger forest degradation and weaken the ecological functions of forests. Therefore, understanding the adaptive capacity of trees to climate extremes in the context of climate change is an important theoretical basis for forest management. Understanding the response of tree growth to extreme drought will help assess species distribution and vegetation dynamics, and provide an important basis for forest ecological assessment and forest ecosystem management, conservation and restoration. This will provide an important basis for forest ecological assessment and forest ecosystem management, protection and restoration. The authors' controlled simulation experiment from the perspective of the recovery process and focused on the timing of autumnal leaf senescence and the influence on growth traits is novel.

 

Here I would like to highlight my comments and suggestions,

1.     Because different plants have different wilt coefficients. What is the author's basis for setting the degree of drought as well as the period of drought?

2.     Experimental details need to be added, e.g., size and dimensions of pots, water retention and porosity of nursery potting soil. line102 is the “1.5 kg/m3” unit correct?

3.     Whether the models and formulas covered in the section “2.3. Statistical analysis” are corroborated by references.

4.     I don't think fig 9 should be in the discussion section.

5.     The conclusion part should be revised , this part should have more quantitative data and less qualitative inferences.

Comments on the Quality of English Language

 The English could be improved to more clearly express the research.

Author Response

Reviewer 3 

Here I would like to highlight my comments and suggestions,

1. Because different plants have different wilt coefficients. What is the author's basis for setting the degree of drought as well as the period of drought?

 

In the last paragraph of the introduction we added: “In the experiment, we aimed to subject saplings to varying levels of drought stress, ranging from mild to severe, which was assessed based on the visual symptoms that developed during the drought periods.”

2. Experimental details need to be added, e.g., size and dimensions of pots, water retention and porosity of nursery potting soil.

We added: “In the winter of 2019-2020, we transferred the saplings to 4 l pots (height 17 cm and diameter 21 cm). All pots were filled with standard nursery potting soil (1.5 kg/m3 NPK 12 + 14 + 24, organic matter 20%, pH 5.0 – 6.5, E.C. 450 µS/cm and dry matter 25%) without additional fertiliser. The organic matter content and the pH range promote the water-holding capacity of the potting soil, while a dry matter content of 25% indicates a relatively aerated mixture. An important aspect of this experiment is that all plants had access to the same type and amount of potting soil. Plants remained in the pots during the experiment.

line102 is the “1.5 kg/m3” unit correct?

Yes, 1.5 kg/m³ NPK 12 + 14 + 24 refers to a fertilizer mix included in the potting soil at a concentration of 1.5 kilograms per cubic meter of soil.

2. Whether the models and formulas covered in the section “3. Statistical analysis”are corroborated by references.

Yes, we added two references in the text at line 223: “In the context of experimental studies on tree seedlings and saplings, growth traits are often analysed using (general) linear mixed models, whereas phenological data can be effectively processed with cumulative logistic regression (e.g., [30,31]).”

30. Vander Mijnsbrugge, K.; Turcsan, A.; Maes, J.; Duchene, N.; Meeus, S.; Steppe, K.; Steenackers, M. Repeated Summer Drought and Re-watering during the First Growing Year of Oak (Quercus petraea) Delay Autumn Senescence and Bud Burst in the Following Spring. Frontiers in Plant Science 2016, 7, doi:10.3389/fpls.2016.00419.
31. Mariën, B.; Dox, I.; De Boeck, H.J.; Willems, P.; Leys, S.; Papadimitriou, D.; Campioli, M. Does drought advance the onset of autumn leaf senescence in temperate deciduous forest trees? Biogeosciences 2021, 18, 3309-3330, doi:10.5194/bg-18-3309-2021.

In addition, we also adjusted the names of the variables to make them more clear. We did this in Table 3 and accordingly also in the model formulas and in the tables with the test statistics.

4. I don't think fig 9 should be in the discussion section.

We moved figure 9 to a separate paragraph in the Results section: “3.5 Summary modelling results”

5. The conclusion part should be revised, this part should have more quantitative data and less qualitative inferences.

We added quantitative data in the conclusions: “….Earlier leaf senescence (e.g., 3 days earlier for a group of saplings that experienced spring drought) can be viewed as an acclimation strategy aimed at preventing impairments from putative new drought events. Delayed leaf senescence (e.g., 7 days later and more for different groups of drought treated saplings) likely provided essential time for recovery from drought-induced damage. This result likely reflects a trade-off between minimizing risks and prioritizing necessary life-saving repair processes. Saplings subjected to summer drought did not resprout but formed additional secondary xylem: they performed up to 65 % of their diameter increment in the second part of the growing season compared to 17 % for the control plants.  …”

 

 

 The English could be improved to more clearly express the research.

The whole text was now thoroughly revised and many (small) adjustments were made to improve the English language.