the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Jan 2025
Litter biomass as a driver of soil VOC fluxes in a Mediterranean forest
Abstract. Soil biogenic volatile organic compound (BVOC) emissions have been studied in different biomes, showing that their emissions are not negligible. However, previous studies have so far neglected the role of litter accumulation on soil BVOC fluxes, and most of them refer to coniferous and evergreen forests, while litter emissions from Mediterranean deciduous forests remain poorly explored. To fill these gaps, the present work aimed to study BVOC fluxes in a Mediterranean deciduous forest, with a particular attention to the relationship between soil BVOC fluxes and litter biomass accumulation on soils. Measurements were performed in southern France, in the downy oak (Quercus pubescens Willd.) forest of the Observatoire de Haute Provence (O3HP), during the late spring of 2023, using dynamic chambers coupled to an on-line PTR-ToF-MS. We investigated in-situ daily BVOC fluxes from soil alone and different litter biomasses mimicking low, current, high, and very high litter production, respectively, as both decreases and increases of litter accumulation are expected in the Mediterranean region under the current context of climate change and greening management policies. The results showed a high BVOC diversity with more than 135 emitted compounds. For a large majority of the measured compounds, the BVOC fluxes were negative, suggesting that soil (bare soil covered by litter) uptakes compounds through biochemical and/or physical processes. Some compounds, such as acetone, methanol or sesquiterpenes, increased with increasing litter biomass, suggesting the importance of considering litter accumulation when assessing soil BVOC emissions from Mediterranean deciduous forests. Microbial abundance was highlighted as a potential driver of this relation between litter biomass and VOC fluxes.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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Supplement
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1229 KB) - Metadata XML
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Supplement
(403 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-54', Anonymous Referee #1, 25 Feb 2025
This study investigates how litter biomass influences soil biogenic volatile organic compound (VOC) fluxes in a Mediterranean deciduous forest dominated by Quercus pubescens at the Observatoire de Haute Provence (O3HP) in southern France. The authors measured in situ VOC fluxes using dynamic soil chambers coupled with a PTR-ToF-MS. The experiment compared bare soil with soils amended with four different amounts of fresh litter over daily 24-hour measurement cycles. Additionally, phospholipid fatty acid (PLFA) analyses were conducted to characterize the microbial communities associated with each treatment. The results show a high diversity of VOCs (over 135 compounds) and indicate that for some compounds—such as methanol, acetone, oxygenated monoterpenes, cyclohexanecarboxylic acid, and sesquiterpenes—the net flux shifts from negative (a sink) in bare soil to positive (a source) with increasing litter mass. The experimental design is generally sound and the manuscript is well presented, there are several key points that may require further clarification.
Major Comments
The authors filter VOC ions using a Welch t-test with a threshold p-value of 0.001. Conventionally, a p-value below 0.001 would be considered significant, so it is unclear whether the intended criterion was p < 0.001. In addition, given the large number of comparisons made across numerous VOC ions, it is important to know whether any corrections for multiple testing (e.g., Bonferroni or FDR adjustments) were applied.
The use of a 20-meter Teflon tube to connect the chambers to the PTR-ToF-MS could potentially lead to VOC adsorption or saturation on the tube walls, especially for compounds with high boiling points or sticky properties. I would like know if there were any measures taken to mitigate these effects and to prevent residual contamination between measurements. Moreover, the flux calculation formula referenced around line 125 is a critical part of the method. Including the full formula, along with a more detailed description of the calibration procedure and the role of the 14 calibration gases, would greatly enhance reproducibility.
Since the fresh litter was used and replaced daily (if I understand this correctly), the study only captures a snapshot of VOC emissions from fresh litter. One of the conclusions drawn is that no clear relationship between litter accumulation and VOC fluxes can be established, which should be considered with caution. A time series analysis covering the litter decomposition process would be necessary to fully evaluate how VOC emissions evolve over time (could be at least mentioned in the conclusion for future suggestions).
The study presents a correlation matrix to explore relationships among VOC fluxes, environmental factors, and microbial parameters. It is not clear whether the analysis was performed using individual replicate values or chamber averages. Clarification on how replicates were handled would provide insight into how variability across measurements was managed.
Additionally, Figure 3 may require improvement in its presentation. It would be beneficial to highlight key compounds described around line 195 and consider splitting the figure into subfigures (e.g., categorizing compounds as emission-only, immission-only, or fluctuating, or grouping them by source/sink characteristics). Also, please include the number of replicates in the figure captions and consider presenting statistical analyses comparing soil versus litter treatments.
Minor Comments
Line 107: "Time of Life" vs. "Time-of-Flight"
Line 100: Please specify the origin of the ambient air used for the measurements (e.g., is it drawn from within the forest canopy?) and provide details on the background VOC levels and their temporal fluctuations.
Line 130: How the outlet concentration was calculated? And curious to know how stable it was? (e.g., whether the outlet concentrations initially increased or decreased before stabilizing).
Line 143: "actinobacteria" should be italicized.
Lines 166–167: The description in these lines is unclear; additional details explaining what is being measured or described would improve understanding.
Line 312 – I've noticed that several sections (e.g., also around Line 353) suggest that the observed flux patterns might be due to different environmental conditions. Could the authors be more specific about this reasoning? Which could be the environmental factors/mechanisms driving these patterns?
Abstract: Species’ Latin names should be italicized, and spell out PTR-ToF-MS.
Citation: https://doi.org/10.5194/egusphere-2025-54-RC1 -
AC1: 'Reply on RC1', Manon Rocco, 27 Mar 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-54/egusphere-2025-54-AC1-supplement.pdf
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AC1: 'Reply on RC1', Manon Rocco, 27 Mar 2025
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RC2: 'Comment on egusphere-2025-54', Anonymous Referee #2, 27 Feb 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-54/egusphere-2025-54-RC2-supplement.pdf
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AC2: 'Reply on RC2', Manon Rocco, 27 Mar 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-54/egusphere-2025-54-AC2-supplement.pdf
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AC2: 'Reply on RC2', Manon Rocco, 27 Mar 2025
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-54', Anonymous Referee #1, 25 Feb 2025
This study investigates how litter biomass influences soil biogenic volatile organic compound (VOC) fluxes in a Mediterranean deciduous forest dominated by Quercus pubescens at the Observatoire de Haute Provence (O3HP) in southern France. The authors measured in situ VOC fluxes using dynamic soil chambers coupled with a PTR-ToF-MS. The experiment compared bare soil with soils amended with four different amounts of fresh litter over daily 24-hour measurement cycles. Additionally, phospholipid fatty acid (PLFA) analyses were conducted to characterize the microbial communities associated with each treatment. The results show a high diversity of VOCs (over 135 compounds) and indicate that for some compounds—such as methanol, acetone, oxygenated monoterpenes, cyclohexanecarboxylic acid, and sesquiterpenes—the net flux shifts from negative (a sink) in bare soil to positive (a source) with increasing litter mass. The experimental design is generally sound and the manuscript is well presented, there are several key points that may require further clarification.
Major Comments
The authors filter VOC ions using a Welch t-test with a threshold p-value of 0.001. Conventionally, a p-value below 0.001 would be considered significant, so it is unclear whether the intended criterion was p < 0.001. In addition, given the large number of comparisons made across numerous VOC ions, it is important to know whether any corrections for multiple testing (e.g., Bonferroni or FDR adjustments) were applied.
The use of a 20-meter Teflon tube to connect the chambers to the PTR-ToF-MS could potentially lead to VOC adsorption or saturation on the tube walls, especially for compounds with high boiling points or sticky properties. I would like know if there were any measures taken to mitigate these effects and to prevent residual contamination between measurements. Moreover, the flux calculation formula referenced around line 125 is a critical part of the method. Including the full formula, along with a more detailed description of the calibration procedure and the role of the 14 calibration gases, would greatly enhance reproducibility.
Since the fresh litter was used and replaced daily (if I understand this correctly), the study only captures a snapshot of VOC emissions from fresh litter. One of the conclusions drawn is that no clear relationship between litter accumulation and VOC fluxes can be established, which should be considered with caution. A time series analysis covering the litter decomposition process would be necessary to fully evaluate how VOC emissions evolve over time (could be at least mentioned in the conclusion for future suggestions).
The study presents a correlation matrix to explore relationships among VOC fluxes, environmental factors, and microbial parameters. It is not clear whether the analysis was performed using individual replicate values or chamber averages. Clarification on how replicates were handled would provide insight into how variability across measurements was managed.
Additionally, Figure 3 may require improvement in its presentation. It would be beneficial to highlight key compounds described around line 195 and consider splitting the figure into subfigures (e.g., categorizing compounds as emission-only, immission-only, or fluctuating, or grouping them by source/sink characteristics). Also, please include the number of replicates in the figure captions and consider presenting statistical analyses comparing soil versus litter treatments.
Minor Comments
Line 107: "Time of Life" vs. "Time-of-Flight"
Line 100: Please specify the origin of the ambient air used for the measurements (e.g., is it drawn from within the forest canopy?) and provide details on the background VOC levels and their temporal fluctuations.
Line 130: How the outlet concentration was calculated? And curious to know how stable it was? (e.g., whether the outlet concentrations initially increased or decreased before stabilizing).
Line 143: "actinobacteria" should be italicized.
Lines 166–167: The description in these lines is unclear; additional details explaining what is being measured or described would improve understanding.
Line 312 – I've noticed that several sections (e.g., also around Line 353) suggest that the observed flux patterns might be due to different environmental conditions. Could the authors be more specific about this reasoning? Which could be the environmental factors/mechanisms driving these patterns?
Abstract: Species’ Latin names should be italicized, and spell out PTR-ToF-MS.
Citation: https://doi.org/10.5194/egusphere-2025-54-RC1 -
AC1: 'Reply on RC1', Manon Rocco, 27 Mar 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-54/egusphere-2025-54-AC1-supplement.pdf
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AC1: 'Reply on RC1', Manon Rocco, 27 Mar 2025
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RC2: 'Comment on egusphere-2025-54', Anonymous Referee #2, 27 Feb 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-54/egusphere-2025-54-RC2-supplement.pdf
-
AC2: 'Reply on RC2', Manon Rocco, 27 Mar 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-54/egusphere-2025-54-AC2-supplement.pdf
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AC2: 'Reply on RC2', Manon Rocco, 27 Mar 2025
Peer review completion
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Julien Kammer
Mathieu Santonja
Brice Temime-Roussel
Cassandra Saignol
Caroline Lecareux
Etienne Quivet
Henri Wortham
Elena Ormeno
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1229 KB) - Metadata XML
-
Supplement
(403 KB) - BibTeX
- EndNote
- Final revised paper