Soil Respiration in Planted and Naturally Regenerated Castanopis carelesii Forests during Three Years Post-Establishment

Round 1

Reviewer 1 Report

I congratulate the authors for the relevant work. It has great potential for the forestry area, reinforcing environmental quality indicators. Some considerations should be pointed out by the authors:

- Indicate the relevance of carrying out the studies for 3 years of forest restoration only. Is this relevant? are considerable changes expected in soil respiration rates, especially for forest species?

- in botanical scientific names, the names of the descriptor authors must not be in italics.

- At some points in the work, the citations are in the wrong format as required by the journal.

-The statistical analysis described does not include all the analyzes that were performed in the work. Inform everything and justify the choice and form of analysis, especially adapting to the experimental design.

-The work presents specific discussions, but deserves a broader and more relevant discussion on the subject. Especially with the closing in relation to the objective of the work.

Author Response

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Reviewer 2 Report

Difference of soil respiration between reforestation through tree planting and assisted nature regeneration in the first three years.

Zhihua Wei et al.

In this paper the authors report the variations in soil respiration from three types of reforestation during  the initial stage of establishment. The topic is certainly interesting as the authors tried to investigate the effects of vegetation management on autotrophic & heterotrophic effluxes of CO2. However, I have the following major observations and need to address appropriately before further consideration by the forests:

1.      Hypotheses: The authors fixed four Hypotheses for testing during the study (Line 91-99):

a)      Due to the differences in temporal patterns of soil biotic (e.g., plant residue availability and root biomass) and abiotic (e.g., soil temperature and moisture) conditions among the forests, their differences in Rs and its components would vary through time (H1).

b)       Second, compared with the young forest established through ANR, Rs and Rh were  greater in the young C. carlesii plantation (H2) due to higher temperature and nutrient  availability favourable for soil respiration.

c)      Third, the response to different reforestation approaches is different between Ra and Rh (H3) due to their differences in substrate.

d)     Fourth, the rates of Rs, Ra and Rh recovered more rapidly in the young forest established via ANR than the forest plantation (H4) due to its greater vegetation cover and more rapid vegetation growth in the first few years [23].

There are many overlapping issues between these four statements, which basically derived from same explanation. In first hypothesis the overlapping issues are:

1.      Differences in plant residues & root biomass- which are consequences of “different reforestation approaches” termed as “differences in substrate” in hypothesis three (overlapped with hypothesis three). Therefore if you explain impacts of “plant residues & root biomass” on soil respiration, it would be same as mentioned in hypothesis three.

2.      Similarly “abiotic (e.g., soil temperature and moisture) conditions” in first hypothesis is same as “due to higher temperature and nutrient  availability” in second hypothesis.

3.      “differences in Rs and its components” in First hypothesis is same as “Ra and Rh” in hypothesis two and three.

4.      In hypothesis four, same thing (differences in Rs, Ra and Rh between ANR & forest plantation which already compared in previous hypothesis).

I suggest to develop one or two hypotheses by combining these statements.

2.      Experimental designs are not appropriate to compare soil respiration

a)       Natural secondary forest (NSF)- Tree density & composition-unknown, understory vegetation-unknown; CONTROL

b)      ANR forest (YNR)- Density & composition 300–400/ha; C. carlesii (22%) and Litsea cubeba (32%) (so dominated by Litsea cubeba !); shrub & herb layers (grass ?); residues spread.

(some with Douglas fir but not in results ? Line 116)

c)       C. carlesii plantation (YCP)- density 2,400/ha; C. Carlesii 82 %, residues spread +burnt; understory & grass unknown

As autotrophic respiration is mostly from plant root, so tree density, dominancy, understory plants should be assessed before comparing respiration (some times more CO2 from grass soil than tree!). The above three treatments are not identical in stand characteristics except regeneration types. Therefore measured respiration is not comparable because unknown factors may affect the CO2 emission. It’s not clear why YCP retained residues spread (Line 134) –as this practice is generally followed in ANR. Burning can also affect soil respiration in plantation plots (YCP), therefore when we compared Rs between YNR and YCP, the variation may not be due to ANR, it’s may be due to burning of soil microorganisms or differences in tree density!

3.      Lack of supporting parameters: Soil respiration a very sensitive characteristic of soil and many soil properties (i.e. soil pH, texture, clay content, soil organic matter, bulk density, soil porosity, microbial biomass etc.) can affect it, but there is no measurement of soil properties in the present study. Soil organic matter, litter fall and biomass have been mentioned in the discussions as the main variables in different regeneration approaches but none of it was measured. Therefore only measuring soil respiration accompanied by temperature and moisture can’t establish the hypotheses of the study. Particularly hypothesis four (line 98), where greater vegetation cover and more rapid vegetation growth were claimed as the causes of Rs variations between YNR and YCP but vegetation cover or growth was not estimated in these plots.

4.      Comparison with previous studies: Line 323, the results of previous study (Xu et al. 2019) were referred- is it the same experiment site? If so,  it showed that the seedling density in ANR plots was 4500-6000/ha but in the present study it was 300-400/ha (?).              

Author Response

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Round 2

Reviewer 2 Report

Although the authors added one paragraph on limitations of the study, the methodological weakness ( in appropriate experimental design) and lack of supporting soil information made the manuscript technically weak, hence was not been recommended for further consideration. 

Author Response

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