the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 May 2026
Long-term throughfall exclusion reduced soil organic carbon towards higher soil microbial carbon use efficiency and lower microbial enzyme activities in Phyllostachys edulis plantations
Abstract. Soil microbial carbon utilization efficiency (CUE) serves as a crucial metric for evaluating the effectiveness with which microbes assimilate organic carbon, acting as a vital benchmark for assessing the potential of soil carbon sequestration. Previous studies have shown that drought can significantly affect microbial CUE, which is crucial for the carbon cycle in forest ecosystems. However, the mechanisms of microbial CUE on soil carbon stability under drought conditions are not well understood. In this study, a throughfall exclusion experiment was conducted in subtropical Phyllostachys edulis plantations (The control, CK; throughfall exclusion, T). The results showed that drought increased microbial CUE by 9.12% (p<0.05) and 2.56% in 0–10 cm and 10–20 cm soil layers, respectively. Soil organic carbon (SOC), soil particulate organic carbon (POC), soluble organic carbon (DOC), and easily oxidized organic carbon (EOC) all significantly decreased, while the proportion of mineral-associated organic carbon (MAOC) in SOC increased by 4.1% and 6.3% (p<0.05) at two layers, respectively. Microbial CUE was positively correlated with POC/SOC ratio and MAOC/SOC ratio, indicating that variation of SOC components substrate quality was an important factor driving microbial physiological changes. Structural equation model (SEM) further showed that soil polyphenol oxidase (PPO) and cellobiohydrolase (CBH) enzymes were the main factors driving changes in microbial CUE. Our results suggested that drought indirectly regulates the storage and transformation of SOC by affecting microbial community structure and function, which would have a profound impact on the carbon cycle of forest ecosystems.
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RC1: 'Comment on egusphere-2026-2229', Anonymous Referee #1, 25 Jun 2026
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This manuscript by Mao et al. investigated the effects of long-term throughfall exclusion on soil organic carbon (SOC) fractions and their relationships with microbial carbon use efficiency (CUE).The authors found that long-term drought significantly decreased SOC, particulate organic carbon (POC), dissolved organic carbon (DOC), and easily oxidizable carbon (EOC), while significantly increasing microbial CUE in the 0–10 cm soil layer. The results suggest that drought indirectly regulates the storage and transformation of SOC by altering microbial community structure and function, which may have profound implications for carbon cycling in forest ecosystems.Overall, this study is interesting and timely in the context of global climate change and may attract considerable attention from readers interested in soil carbon stability under long-term drought conditions.However, several aspects of the manuscript could be improved. In particular, the hypotheses presented in the Introduction should be articulated more clearly to better guide readers through the study objectives and expected outcomes. In addition, some findings discussed in the Discussion section, especially those concerning the responses of CUE and SOC fractions across different soil depths, require further clarification and interpretation. Detailed comments are provided below.L31–33: This sentence should be revised to clearly indicate the percentage decreases observed in the various carbon fractions.L39–42: It is recommended to specify that these findings were obtained under long-term drought conditions.Keywords: Replace “Drought” with “Long-term drought” to better reflect the study focus.L51: Replace “such as vegetation and composition” with “such as vegetation and community composition”.L72–74: The logical relationship between these two sentences is unclear. Please reorganize them to improve coherence and readability.L75–76: This sentence is difficult to understand and should be rewritten for clarity.L104–106: The sentence is obscure and requires substantial revision to improve its clarity and logical flow.L242–252: Please provide a more detailed description of the structural equation modeling (SEM) analysis, including model construction, variable selection, model evaluation criteria, and software used.In addition, the calculation method for carbon pool activity (CA) is not described. Please provide the relevant equation and calculation procedure in an appropriate section of the manuscript.L256–257: The statement “Throughfall exclusion significantly reduced SOC, POC, DOC and ROC (p > 0.05), but did not affect MAOC” is inaccurate because a p-value greater than 0.05 does not indicate a significant effect.L270–272: Please specify which soil layer(s) exhibited significant changes rather than providing a generalized description. Similar revisions are recommended throughout the Results section to improve accuracy and clarity.L339–340: This sentence is confusing and should be completely rewritten to clearly convey the intended meaning.L365–372: The discussion regarding the response of POC to long-term drought across different soil depths is insufficient. It would be valuable to further discuss how soil depth influences POC dynamics under prolonged drought, particularly through mechanisms such as changes in microbial metabolism, litter decomposition and nutrient return, and extracellular enzyme activities. Reduced litter inputs are generally expected to primarily affect POC accumulation. Therefore, a more in-depth analysis of these mechanisms would strengthen the interpretation of the results.L463–465: The conclusion should be revised to specify the soil depth(s) associated with the observed responses rather than using ambiguous descriptions. In addition, the logical relationships among the key findings should be clarified to improve the overall coherence and impact of the conclusion.ReplyCitation: https://doi.org/
10.5194/egusphere-2026-2229-RC1 -
AC1: 'Reply on RC1', Xiaogai Ge, 11 Jul 2026
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The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2229/egusphere-2026-2229-AC1-supplement.zip
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AC1: 'Reply on RC1', Xiaogai Ge, 11 Jul 2026
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RC2: 'Comment on egusphere-2026-2229', Anonymous Referee #2, 15 Jul 2026
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The manuscript “Long-term throughfall exclusion reduced soil organic carbon towards higher soil microbial carbon use efficiency and lower microbial enzyme activities in Phyllostachys edulis plantation” investigates responses of soil microbial CUE and organic carbon stability to throughfall exclusion in subtropical bamboo (Phyllostachys edulis) plantations. The manuscript shows that drought increases microbial CUE, while depleting the more labile carbon pools. These findings are relevant for the Biogeosciences readership; however, several aspects of the manuscript need a very thorough revision. The English and overall clarity of the manuscript should be carefully re-checked, as several unclear sentences currently hinder comprehension. I have provided some examples below (but not exhaustive) of unclear sentences.
Moreover, the research gap and hypotheses are not clearly phrased and integrated with existing literature. Specifically, the mechanisms linking soil fractions (POC and MAOC) to CUE need deeper explanation, and the rationale behind the expected drought responses (and differences across soil depths) must be justified. Moreover, the formulated hypotheses are not discussed in light of the observed results in the discussion section. Contrary to the hypotheses, higher CUE was observed under throughfall exclusion, and lower enzyme activity, and the reasons behind these discrepancies are not clearly addressed in the manuscript.
Several key experimental information regarding the experimental setup are missing, specifically the exact percentage of throughfall reduction achieved and the resulting differences in soil moisture between treatments. This information is necessary to understand the effectiveness of the throughfall exclusion treatment, allow comparability across studies, and ultimately to interpret microbial CUE and soil fractions responses.
The statistical approach used requires clarification; a one-way ANOVA is insufficient for testing both depth and treatment effects simultaneously and the actual statistical results (including p-values) must be reported rather than just letter-groupings on figures. Depth and treatment can be used as predictors if a two-way (not one way) anova would be used, for instance also including their interaction. Have you tested the use of this statistical model as well, and how would this affect your results?
Additionally, the Structural Equation Modeling methodology must be described in the methods section, as well as several soil properties and their abbreviations that are reported in the result section but not described in the methods. Without this information, the manuscript lacks the necessary information for a complete evaluation.
Pay also attention at the terminology used to refer to different SOC pool, as several terms are employed throughout the manuscript, which are not synonyms and possibly misleading if their meaning is not well defined (e.g. volatile, active, labile / inert, resilient, stable…).
Specific comments
- The conclusion of the abstract (Line 40-41): “by affecting microbial community structure”, is not substantiated by presented results as analysis of microbial community structure is not presented in the manuscript.
- Line 49: more generally, it can be stated that precipitation patterns are altered, with some regions getting drier while other wetter.
- The introduction feels a bit repetitive: for instance, it is repeated at line 52 and 57 that drought affects the carbon cycle.
- The classification of SOC into active and inert SOC (line 65) is not defined in the manuscript, and no reference to existing literature is made. Can you define more specifically what you mean with active and inert fractions (citing the relavant literature)? It is mentioned then in the manuscript that DOC, EOC and MBC are active fractions. Do you also consider particulate organic matter as the active fraction?
- The research gap is not well defined in the introduction see lines 84-91, and the writing is really unclear in this section. See especially sentence 86-88:” MAOC increased proportionally with microbial biomass and POC, fungal necromass carbon had a more contributed to MAOC in Qinling Mountains”.
- How far are the three forest stands from each other? It would help show a map of the locations of the three stands.
- What is the type of soil i.e., according to WRB classification; the basic soil characteristics such as pH, texture (% clay, sand, silt) are not presented.
- Can you clarify what it is meant that the litter was gathered and allocated to the plots (line 155-157), please provide a motivation of this choice and the amount of litter allocated per plot per year.
- The description of how the sampling was performed is lacking important information: was soil coring performed, and if so, diameter of the corer?
- Discussion at Line 428 (and 433-434) “microbial CUE demonstrated a significant and positive correlation with SOC, DOC and POC” is not substantiated by results shown in the Fig. 6, and result section that shows that high CUE linked to a decrease in POC under throughfall exclusion.
- How were DOC and DON were obtained from the soil samples, by extraction with water? If so, specify and provide references. How was the DON measured (was the TN measured, not clear). See line 172-174.
- The abbreviations ROC, EOC, PPO, CBH, carbon pool activity index (CA) are introduced for the first time in the results section, while are not mentioned in the methods. Clarify their meaning and the methods used for their measurement in the method section.
- How have you selected the predictor variables to include in the SEM model? Have you also considered the SOC%, C/N ratio (not included), pH (not reported in the manuscript) and microbial biomass as possible predictors?
- Is the reduction of POC under drought related to a decrease in litter input to the throughfall exclusion (with PVC plates), or has this been taken into account?
- The conclusion section is not straightforward to understand, please improve clarity.
Technical comments
- The abstract is unclear at line 27: “the mechanisms of microbial CUE on soil carbon stability under drought conditions are not well understood”.
- Use consistently only 1 decimal in the abstract (e.g. CUE is reported as 9.12% while increases in SOC are reported as 4.1%)
- The graphical abstract is not well readable; can you improve the quality?
- Line 51: what do you mean with “composition”?
- Line 63: what do you mean with “which varies with..:, with varying?
- Line 81-83 and 86-88: not understandable, rephrase
- Line 135: replace “were first delineated” with “are presented”
- Table 1: provide the meaning of all abbreviations in the table caption (TE, CK, TN etc..). In the text the abbreviations T and CK are provided. Please ensure consistency with those used in the table (TE and CK?)
- Line 144: clarify the meaning of the sentence (CK and T were three repetitions)
- Line 153: unclear sentence, rephrase
- Line 153-155: unclear sentence
- Line 160: what is meant by 5-point sampling?
- Line 164: check the soundness of the writing.
- Line 186: rephrase and check for correctness e.g. measurement of SOC fractionation
- Line 200-202: four soil enzymes activities are mentioned, but only 3 are listed (BG, POX, PER), please double check for correctness.
- Line 236-237, not clear, rephrase
- Fig.2 : is AMOC correct, or do you mean MAOC? Please define abbreviations in the caption.
- All figures: define abbreviations in the caption.
- Fig.5 is not readable.
- Lines 390, 395, 448-449 are unclear.
Citation: https://doi.org/10.5194/egusphere-2026-2229-RC2
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