Seasonal Cambial Activity and Formation of Secondary Phloem and Xylem in White Oaks (Quercus alba L.)

Round 1

Reviewer 1 Report

 

General Impression

The seasonal formation of xylem and phloem in white oak under conditions of a typical northern-continental climate was chosen as a research topic. Sampling was carried out during two growing seasons. Samples from four trees were analyzed using conventional light microscopy techniques. Such studies are very time-consuming, since the preparation of a large number of samples for microscopy takes a long time. As far as I know, detailed studies of the seasonal activity of the cambium and the formation of conductive tissues of the trunk have been carried out only for a relatively small number of tree species, which makes it difficult to conduct comparative studies in tree physiology and ecology, including those related to the influence of a changing climate on the phases of cambial growth. For this reason, the presented work is of undoubted scientific interest. Another strength of the work is the large number of photographs illustrating the various stages of cambial growth.

At the same time, I have many comments and questions about this work, which I will outline below. These remarks are mainly related to the presentation of the work and do not detract from its scientific significance.

 

Specific notes

Introduction

1) The Introduction lacks a clearly formulated research goal or working hypothesis. This makes it difficult to evaluate the results obtained. In lines 46-61 it is indicated that it is necessary to obtain more data on the seasonal formation of the conducting tissues of the trunk. However, this is too general a phrase. I believe that the relevance of this study should be more clearly defined. Also, in my opinion, it is necessary to indicate how the results of this study can contribute to other works from the field of forest science or biology (for example, in comparative studies of the response of the cambium to a changing climate).

2) In my opinion, the choice of the object of study is not sufficiently substantiated in the text of the manuscript. Please describe in more detail the studied species: its range, biological features, ecological and/or economic importance. Perhaps the authors could add some photos of the appearance of the tree, its bark and wood. This is optional, but readers from other regions could more easily get an idea of the species under study.

Has the seasonal development of phloem and xylem been previously studied in other deciduous oak species? If seasonal cambium activity in other tree species was studied in the same area (Madison, USA) or in an area with similar climatic conditions, please indicate this and write how the results of this study can complement previously obtained data.

 3) At the end of the Introduction, it is desirable to make a brief description of the design of the study, namely, the study area, the sampling period, the chosen research method. Since the tissue samples were taken in 1961-1962 (60 years ago), please state this.

 

Materials and Methods

I strongly encourage the authors to write this section in more detail. I propose the following clarifications to be made:

1) Please give the geographical coordinates of the area where the study was conducted. This will facilitate comparative studies on the phenology of cambial growth in the future.

2) Data on climatic features of the study years (Figure 1) should be transferred to this section, because they describe the study area and are not their own data obtained by the authors in the course of the study. Perhaps, on the same diagrams, it is possible to designate the periods of sampling (weekly and monthly samplings)? The latter is at the discretion of the authors.

3) It is necessary to give a more precise description of the selected trees: their age, height, diameter at breast height. The timing of cambial activity may vary in trees of different ages and sizes.

Please specify whether the samples were taken all the time from the same trees (4 trees were examined in total) or they were different trees in each sampling date (4 trees for each date of sampling). In the case that samples were taken all the time from the same trees, please indicate at what distance from each other the sampling points were located on the trunk and whether there was a wound effect from wounds inflicted during previous selections.

4) What equipment (microscope, camera, software) was used to take photographs and analyze sections? Please indicate it.

5) Please write in detail the criteria that were used to determine the stages of development of elements (differentiating and mature). Was it the size or condition of the cell walls? If different criteria were used for xylem and phloem elements, please indicate this.

The authors also use the words "functional state" and "non-functional state" in relation to sieve elements. In winter, as well as late autumn and early spring, in the northern-continental climate, I believe, phloem transport is absent and sieve elements do not perform a transport function. Therefore, it is necessary to clarify what the authors call "functional state" or use another word to indicate that the sieve elements are potentially capable of performing a transport function.

 

Results

The general description of the bark and wood and of the seasonal formation of tissues is done at a high level. I would like to separately note a large number of good photographs taken on sections of different planes (transverse, tangential, radial) to illustrate different developmental phases - this is a very strong point of this work.

1) At the same time, I strongly recommend that the main measurable characteristics of tissues and cells be included in the results, namely:

- width of annual increments of xylem and phloem,

- diameters of elements of early and late xylem and early and late phloem when they reached their final sizes.

I believe that it will be also good to give the results of measurements at least for some critical dates related to the beginning and end of the described phases. This will give the reader a clearer idea of the progress of each phase.

2) Since the results are further discussed in connection with changes in environmental factors during the growing season, I propose to also indicate the range of values of the average daily temperature (or sum of effective temperatures above +5 °C) and the length of the photoperiod for each phase (cell division in the cambium, the formation of early phloem and early xylem, the formation of late phloem and late xylem).

I also had a question about whether the beginning and/or end of different phases in 1961 and 1962 differed. Figure 1 shows that the average monthly temperature in May 1961 was much lower than in May 1962. Please indicate in the text how the two years studied differed from each other.

 

Discussion

The discussion is very detailed, including both old classic and recently published works. However, I would suggest changing the order of the parts a little and arrange the discussion in chronological order: from the reactivation of the cambium and the beginning of the formation of early phloem and early xylem, to the formation of late phloem and late xylem, and then to the end of the cambial growth period and the situation with overwintering sieve elements.

Perhaps the authors could make a scheme indicating the beginning and end of the discussed phases during the growing season at the end of the Results section or at the beginning of the Discussion section. This would help readers better navigate the voluminous material.

 

Small notes

Lines 21-23. Please, indicate that collection of samples was done in 1961-1962.

Line 33. “Functional sieve elements are present yearlong”. Please, rephrase.

Lines 48, 438. I don't like the phrase “cambial products”. I suggest “cambial derivatives” instead of it.

Figure 3b. White arrows are hard to see.

 

 

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The seasonal pattern of wood and phloem formation helps us understand the physiology of trees and their response to changing environmental conditions. Studies in such have become popular in recent years because of their high utility in dendroclimatic studies. This justifies undertaking such research. However, reading the manuscript, I was disappointed not to find any cambium and phloem phenology statistics.

To my surprise, the authors in this manuscript analyze material collected about sixty years ago. This also seems valuable since only some such studies are known from that period. Some of them received more attention only decades later, such as the observations on xylogenesis in Quercus rubra.

The paper would be much more valuable if the authors calculated basic descriptive statistics for the phenological phases of wood formation. It would have been worthwhile to compare the averages or medians for the phenological phases from the two seasons and describe the differences in relation to meteorological conditions in the two seasons. The authors could also present models of width growth from simple width measurements, fitting them with, for example, the Double Gompertz Curve. Curve fitting could calculate the onset of wood formation and the wood dynamic formation during the vegetation period. Note that now, many studies show that it started earlier than a few decades ago. The material the authors have at their disposal could fill a hole in this knowledge from when such models were not used. This could significantly increase the citability of this study.

This would interest many researchers involved in dendrochronology since knowledge of the mid-season responses of trees to meteorological factors allows better interpretation of wood characteristics and reading of the climate signal. As it stands, the article is addressed to a narrow group of readers concerned with plant anatomy.

 

Example studies:

Michelot, A., Simard, S., Rathgeber, C., Dufrêne, E., & Damesin, C. (2012). Comparing the intra-annual wood formation of three European species (Fagus sylvatica, Quercus petraea and Pinus sylvestris) as related to leaf phenology and non-structural carbohydrate dynamics. Tree Physiology, 32, 1033–1045. https://doi.org/10.1093/treephys/tps052

Puchałka, R., Koprowski, M., Gričar, J., & Przybylak, R. (2017). Does tree-ring formation follow leaf phenology in Pedunculate oak (Quercus robur L.)? European Journal of Forest Research, 136(2), 259–268. https://doi.org/10.1007/s10342-017-1026-7

Author Response

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Round 2

Reviewer 1 Report

The quality of the manuscript has been significantly improved. The comments made have been taken into account and corrections have been made. In cases where the authors refused to make changes to the text, their refusal was substantiated. In its present form, the manuscript can be recommended for publication. I believe that this material will be of great interest to researchers and wish the authors success in publishing other results from this collection of specimens.

However, I recommend proofreading the text carefully, as I noticed some typos (for example, Figure 7, earlyphloem instead of early phloem, late-phloem instead of late phloem). It is also necessary to make changes to the caption for Figure 3b, because the arrow color was changed from white to yellow, but the arrow color designation was not adjusted in the caption.

Reference 76 was not found in the text. Please, carefully check references in the text.

Author Response

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Reviewer 2 Report

I have read the new version of the manuscript and the authors' responses to my comments. It is not true that three growing seasons are needed for radial growth to be modeled. After all, the Gompertz/double Gompertz curve is normally fitted for observations from a single season. This model would allow one to calculate when trees start producing wood cells, and when they stop growing. According to the authors, cambium activity begins in April. The question is, when in April? The discrepancy covers as much as 30 days when the described shifts in phenological phases in other species are considered significant if they are a few days, likewise, with the offset of the cambial activity, which, according to the authors, occurs in August. Here, too, it is unclear whether at the beginning, middle or end of the month, and again the range of estimates with uncertainties of up to 30 days is larger than the scale of the phenological shift at the end of wood formation is described.

Here, too, let me note that my several years of observations on wood formation in other white oaks species show that the offset of the cambial activity is determined more by meteorological conditions than by photoperiod. In addition, the same individuals in different years stop forming the tree rings at different times, with differences exceeding a month. This is even more variable than the onset of the cambial activity. Several years of observations may not capture patterns, especially regarding the end of wood formation. Hence, the conclusions of this study are too bold. The lack of statistics, the attempt to estimate the timing of phenological phases and the link to meteorological conditions make the results of this study of little use to researchers involved in the phenology of wood and phloem formation and dendrochronology.

The advantage of this study is an excellent anatomical description of the stages of wood formation. Instead, the authors should focus on bringing these studies to readers dealing with plant anatomy. From the point of view of bioclimatology, they are of little use, and hasty conclusions can be harmful if someone starts quoting them.

Author Response

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