The Dominant Factor Affecting Soil Organic Carbon in Subtropical Phyllostachys edulis Forests Is Climatic Factors Rather Than Soil Physicochemical Properties
Round 1
Reviewer 1 Report
The dominant factor affecting soil organic carbon in subtropical Phyllostachys edulis forests is climatic factors rather than soil physicochemical properties
Li et al.
In this manuscript the authors report the findings on effects of temperature, rainfall and soil physico-chemical properties on soil organic C accumulation and assessed which factors are dominant in C accumulation under moso-bamboo systems in subtropical China. Although very common research topic (i.e., climate & soil impact on C stocks in soil), the article might be interesting to the readers of forests, because of moso-bamboo systems.
1) Introduction should contain more specific review how soil properties (particularly soil maximum/minimum water holding capacity, soil water capacity etc.).
2) The manuscript need specific objectives and hypothesis, because from title it seems that the research examine the effects of moso- bamboo plants on distribution of SOC, but your analyses are comparison between climatic factors and soil factors. As in the experiment design, there is no control plot (plot without moso-bamboo), so we can´t say this SOC distribution pattern attributed to moso-bamboo vegetation. This should be clear in objectives and hypothesis.
3) Secondly, as the whole region is under subtropical climate zone, temperature variation in different locations is only 5degree, precipitation patterns are not clear from the ranges given in Line: 75. Because MAT and MAP are the climatic factors considered here, I would suggest to provide annual temperature and precipitation graphs to see the climatic variations in three regions.
4) The study considered two types of factors 1) Climate and 2) soil physico-chemical properties. In Materials & Methods Line 105-113: four similar water related parameters (Soil water capacity (SWC), maximum water holding capacity (WHCmax), minimum water holding capacity (WHCmin) and capillary water capacity (CWC)) were considered but very important soil properties that affect SOC such as: soil organic matter (SOM), soil micro/macro aggregates, soil texture (especially clay content), microbial biomass and enzyme activities etc. were not investigated.
5) Methods of analysis should be described more details with references. Line 107: “capillary water capacity (CWC) were determined by the drying weighing” This is not a scientific method for maximum water holding capacity, more details description is necessary. Similarly Line 95: “Stand biomass was estimated by allometry equation modelling” needs details of models and how it was used in current study.
6) Structural Equation Modelling (SEM) is main analysis of this study but in Materials and Methods there is nothing about SEM, how it was performed, which equations were used to evaluate the fitness of the models with references.
7) Data on stand density (Table 1) showed considerable variations in different locations, are these data represent only moso bamboo or bamboo+ other trees. This is important because tree density was the highest in Southern Subtropics (Table 1) but SOC stock was the lowest (Table 2)! As vegetation is the major source of SOC, it is necessary to describe the details of vegetation cover (including herb and shrub layers) of 6 locations.
8) In Results section Line 149-166 is just language version of Table 3. My suggestion is please put all p values (P<0.01) by the side of respective values in Table 3, and describe very precisely.
Language:
The overall language of the manuscript is poor with a lot of grammatical and structural mistakes and use of excess words. Below is the first paragraph of Introduction (for example) with language errors. I recommend for thorough revision of manuscript with qualified English proof reader.
Line 33-44: Accounting for one-third of the global land area, forests play a key role in the global carbon cycle as they account for 40% of the global soil carbon pool [1,2]. Forest soil carbon pools account for more than two-thirds of the forest carbon pool, and small changes in their capacity can have a large impact on the global carbon balance, thus changing the global carbon allocation pattern [3]
a) Word repetition in same sentence (Account-2, global-3, pool-2, global-2)
b) “and small changes in their capacity” what capacity?
Soil organic carbon (SOC) is an important indicator of soil quality dynamics, which can directly affect soil fertility and vegetation productivity, thus its distribution characteristics and influential mechanism have received much attention from scholars.
a) Excess words: “vegetation”, “characteristics”
b) Grammatical: “influential mechanism” should be influencing mechanism, “from scholars” should be “of researchers”
Xie et al. [4] used data from the second soil census of China to estimate the overall changes in SOC stocks from the 1980s to 2000s, and found that forest SOC showed an increasing trend with large regional differences during the last two decades of the 20th century. Forest SOC is affected by various factors, such as climate, altitude, soil type, forest age, and elevation.
a) Inappropriate words: “soil census” appropriate word “soil survey”
b) Excess words: “during the last two decades of the 20th century” - already mentioned “from 1980s to 2000s” (i.e. last two decades of the 20th century), altitude and elevation mean same.
Minor errors:
1. Title of article is too much descriptive, try to make it bit concise.
2. Line 12-13 “contribute significantly to the carbon sink of terrestrial ecosystems”- “terrestrial ecosystem” means something in global scale, please make it local/regional scale.
3. Line 14 “scales” scale
4. Line 75-76 no unit in temperature and precipitation values
5. Line 94 “bamboo height, height under the branch and stand density”- No data on “height under the branch” in Table 1
6. Units of values Stand density (trees•hm-2) (Table 1), stock (t·hm-2) (Line 116)- what these mean? If tree per m2 i.e. (tree m-2), ton per m2 (t m-2), g per kg (g kg-1) no point (.) after g. In the whole manuscript.
7. Line 123 “ Amos 24” what is it?
8. Table 2 No unit of values!
9. Line 227: ”Pinus massoniana” plantation -should be italic
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
Initial thoughts:
In this manuscript the authors visit natural bamboo forests in southern China and measure the soil organic carbon and factors that might influence this (climate, soil properties). The authors find a moderately strong effect of climate, in particular mean annual temperature as well as some quite nuanced and weaker effects from soil chemistry and bulk density, which are also interrelated with climate.
First of all, I would like to say how valuable this kind of fundamental research is and I would like to commend the authors on carrying out what must have been a tough field work campaign, visiting some remote and very steep bamboo forests.
I have come concerns about the data quality, which I hope the authors are able to respond to in a satisfactory way. 1) the data in Table 2 does not match Figure 2 or the description of the results in the manuscript text. This is important as it could reflect an error in the analysis and therefore the conclusions. 2) the climate data is poorly described and likely to be somewhat unreliable given the complex terrain the authors work in. See below for more details
If the authors can give satisfactory explanations for the differences in data (is this an error or a difference in units?) and discuss the climate data critically then I think the paper is fundamentally sound and should be published. Research such as this is very valuable to our understanding of the carbon cycle. Too often high-altitude and climatically extreme sites have been overlooked, despite these being large carbon stores.
Figure 2 does not match the data in Table 2: For example, the Northern Subtropics have in total 90.9 t hm-2 in the table, compared to 130 t hm-2 in in the figure. Is this an error or difference in the units? The data for the Middle Subtropics seems to match. Please check which number is correct and that the analysis has been done with the correct numbers.
The main weakness of this paper as I can see it is that the authors do not describe how the climate data was obtained, or discuss it’s quality. These sites analysed are in extremely complex terrain (gorges, steep hill slopes, high altitude etc.) unless climate is measured precisely at the coring location I cannot believe that the precipitation data, for instance, is particularly accurate. This is fine, we do the best job we can as Scientists. However, if we consider that the climate data has some large uncertainty then the climate effect could actually be stronger than claimed here. If we can get a significant R2 with what is likely to be quite imprecise climate data then just imagine how strong this effect could be if we had the exact mean annual precipitation and the exact mean annual temperature over a long time period!
I think what is needed is some discussion of how the climate data was obtained (models or nearby stations?), how long is the data representative of (are these 20 year normals or shorter?) and whether or not we expect any systemic or random error in the climate data when we extrapolate it to the research sites (for instance, it might be reasonable to assume they are wetter if they are on slopes into the direction of the prevailing wind, or to assume they are colder if they are higher altitude compared to the reference stations)
In addition to this I have some specific comments:
Line 25: It is not clear what is meant by physical properties having a significant negative effect on SOC, do the authors mean bulk density of the soil?
Line 65: Can the authors elaborate a little more on which soil physiochemical characteristics were most important?
Line 78: “soil types in these sampling plots are mainly red, yellow and yellow-brown soil” – this is extremely vague, can the authors elaborate using internationally recognisable terms i.e. loam, sand, clay rich etc.
Line 26-27: The second line contradicts the first, do the authors mean that apart from NH4 and P other soil chemical properties did not correlate with SOC?
Figure 2: please specify if the caption what depth the carbon was measured to
Table 2: units are missing
Table 3: A traditional correlation table would be clearer so we can see which factors co-correlate
It would be helpful to have a single additional figure showing the climate space of moso bamboo forests (i.e. mean annual temperature on the X axis and mean annual precipitation on the Y axis) with points which show the climate at the sites analysed, that way we can see if the data presented here convers the whole range of moso bamboo forests, or if it is skewed to one climatic extreme or another.
I wish the authors the best of luck with the revisions.
Author Response
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Author Response File: Author Response.docx
