the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 May 2025
Field-deployable branch enclosure system for biogenic volatile organic compounds emitted from conifers
Abstract. Biogenic volatile organic compounds (BVOCs), emitted primarily from terrestrial plants, significantly influence atmospheric chemistry and climate change. Conifers are major sources of BVOCs in temperate regions. However, their unique physiology, particularly the storage of terpenes within their tissues, makes accurate measurements of BVOC emissions challenging owing to contact-induced release. We developed a portable dynamic branch enclosure system specifically optimized for BVOC measurement in conifers, which enables measurements of multiple trees in a single day. The system uses filtered ambient air as a purge gas to reduce logistical challenges and features a foldable bag design to minimize excessive BVOC release induced by physical contact. It provides BVOC- and ozone-free air, maintains stable internal temperature and humidity conditions closely approximating those of natural environments, and ensures repeatable measurements of BVOC emissions. Field testing with Japanese cedar (Cryptomeria japonica) revealed significant individual variations in BVOC emission rates and compositions. These findings demonstrate the system's reliability and applicability for assessing BVOC emissions under field conditions, offering a practical solution for advancing our understanding of BVOC dynamics in diverse ecosystems.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-2063', Arnaud P. Praplan, 16 Jun 2025
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RC2: 'Additional comment', Arnaud P. Praplan, 16 Jun 2025
In addition to my previous comments, I would like to add that, for the dataset published, it would be good to have for the BVOC data the inclusion as metadata of what units apply the numbers that are reported.
Citation: https://doi.org/10.5194/egusphere-2025-2063-RC2 - AC1: 'Reply on RC2', Yuki Ota, 10 Aug 2025
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RC2: 'Additional comment', Arnaud P. Praplan, 16 Jun 2025
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RC3: 'Comment on egusphere-2025-2063', Anonymous Referee #2, 29 Jun 2025
The study by Ota et al. introduces a portable branch enclosure system for in-situ measurements of BVOC emissions from trees. This approach is both timely and important, as it aims to improve spatial coverage of ecosystem measurements, reduce mechanical disturbance during sampling, and enable high throughput monitoring across multiple trees in a single day. Conifers, due to their high terpene storage and sensitivity to mechanical stress, pose particular challenges for emission studies. A reliable, field-deployable system would therefore be a valuable tool for extending BVOC measurements across a wider range of tree species. That said, the current version of the manuscript does not yet provide sufficient evidence to support the robustness and real-world applicability of the system. While the technical design is clearly described, the study relies heavily on laboratory validation using cut branches, and the field deployment remains ambiguous. As a result, the system's suitability for its primary purpose (reliable, in-situ measurements of rooted trees under natural conditions) is not convincingly demonstrated. I therefore recommend major revisions, aimed at clarifying the conditions of the field deployment, presenting more rigorous validation data, and addressing interpretative limitations in the results.
General Comments
- System validation and applicability. The central claim of the manuscript is that the system enables portable measurements from multiple trees within a single day. However, most of the performance evaluations (e.g., reproducibility and stabilization time) are based on measurements from cut branches, which do not represent intact physiological conditions. Cut branches are known to alter emission profiles, especially in species with large internal storage pools such as conifers. Given that this system is meant to overcome such limitations, a convincing demonstration under field conditions using live, rooted trees is essential. Otherwise, this system would not differ significantly from simple, well-stablished chamber-based measurements in laboratory. The authors should also clarify whether the system is designed to be reused across trees or if multiple enclosure collars need to be installed in advance. Discussing a field-based example of multi-tree sampling in practice would help substantiate this important advantage.
- Ambiguity in field deployment. The field deployment data show emission rates spanning up to six orders of magnitude among individuals of the same species. While biological variability is expected, such a wide range raises questions about system consistency. The authors attribute this variability to individual differences, but without clearer evidence that the technique itself is not contributing to it (e.g. via consistently different handling of the samples from the three areas - perhaps this is why the same tree species are so consistently different among the different locations), this interpretation remains uncertain. If the final field deployment data were also based on detached branches, then the system has not yet been demonstrated under its intended real-world conditions, and the results would not validate the system's field applicability as claimed.
- Lack of environmental response validation. A core requirement for validating a new BVOC enclosure system is demonstrating that it can reproduce known patterns such as diurnal variations and emission responses to temperature and light. The manuscript does not include any environmental-driven validation. Without observing characteristic temporal emission patterns (e.g. the temperature and light-driven increases during day), it is difficult to distinguish between physiological emissions and stress-induced pulses caused by handling or storage depletion. At least a clear diurnal cycle from a rooted field-grown tree is required for validating such new measurement technique.
Specific Comments
L24-26. Please note that observing significant individual variation cannot not demonstrate system reliability (quite the opposite actually). This should be reworded to avoid conflating biological variation with instrument performance.
L37-42. Please consider expanding this paragraph and referencing recent review articles covering emission behaviour of monoterpenes (eg. https://doi.org/10.1038/s43247-023-01175-9) , sesquiterpenes (e.g. https://doi.org/10.1111/gcb.70258), and diterpenes (e.g. https://doi.org/10.21203/rs.3.rs-5407662/v1), to provide more context on their chemical properties and relevance.
L154-163. A. The emission rate equation differs from more commonly used formulations (e.g., E = F × (Cout − Cin)/(dry weight mass)). Please elaborate on the reasoning behind this approach and its comparability. B. The use of basal emission rate (ES) calculated using fixed β values from the literature assumes consistent temperature sensitivity across all conditions. This approach is not appropriate in a study designed to evaluate natural emissions. Empirical derivation of temperature responses would provide more convincing validation.
L195-196. The statement that the system reduces "desiccation stress" based on chamber humidity is incorrect. Drought stress is primarily soil-driven, and relative humidity in the enclosure does not replicate root water availability. Please rephrase or remove this statement.
L204/Table 2. With the flows used, one would have expected higher humidity inside the chamber as the result of evapotranspiration from a living branch.
L210-216. The orders of magnitude of phyllocladane stronger emissions is perhaps an indication that we are seeing the effects of stress and not natural emissions.
Chapter 3.4 / Figure 3. The sharp emission peak followed by exponential decay likely reflects the depletion of storage pools in a severed branch rather than natural stabilization. Comparing late-stage emissions to initial peaks does not validate reproducibility but rather shows a system with low emission rates as the storage pools are emptying. Demonstrating that with isoprene, which is mainly de novo produced, would have been more convincing.
Chapter 4. As mentioned above, please clarify whether the field deployment involved measurements from branches still attached to living trees. This is a key point for assessing whether the system has been tested in realistic conditions.
Citation: https://doi.org/10.5194/egusphere-2025-2063-RC3 - AC2: 'Reply on RC3', Yuki Ota, 10 Aug 2025
Data sets
Data from: Field-deployable branch enclosure system for biogenic volatile organic compounds emitted from conifers Yuki Ota https://doi.org/10.5281/zenodo.14965367
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The manuscript titled 'Field-deployable branch enclosure system for biogenic volatile organic compounds emitted from conifers' by Ota et al. describe in detail their portable dynamic branch enclosure system design for the collection of emissions from conifers. The system is well designed and described so that others will be able to make similar systems for their own research, benefiting the community. The validation of the method is well documented and its use on the field demonstrated, yielding a valuable dataset of the emissions of Japanese cedar trees. The manuscript itself is well-written, well-structured, and easy to follow. In addition, the underlying data has been published in open access.
As the manuscript is of good quality, I recommend its publication in Atmospheric Measurement Techniques with only small technical corrections.
- lines 211-212: 'After trimming its base, we cut the branch under water to maintain it vascular integrity.' Could the author explain a little bit more how the branch was cut under water and possibly provide a reference demonstrating how vascular integrity is maintained by doing so?
- lines 226-227: 'at least one terpene was detected in each category'. Why did the author decided not to included all the detected terpenes (one in each category) in Fig. 2? There seems to be only MTs and one DT.
- FIgure 4: I am not sure to understand the boxplot (panel (a)) as there are datapoints scattered horizontally (why?) and some blue dots are on the same levels as gray crosses. It is not clear from the caption if the crosses are outliers, but if they are, why are there blue dots (not outliers?) at the same height? In panel (b), the three colors used for MTs are very similar and make it difficult to see what compounds are present in the emissions from the figure.
- lines 296-303: The authors mention the possible effect of stress, but state that it is not the objective of their study to look closer at the factors determining BVOCs emissions. The sample size, they argue, is 'not large enough', but I believe that it is still a decent enough sample size as they have shown using various statistical tools. As a suggestion (more than a request for revision), I think that it would be nice to include something about the environmental conditions (e.g. temperature and its effect on the emission rates) as the sensors (for temperature, radiation, etc.) are part of the dynamic branch enclosure system and it would be good to demonstrate what conclusions could be made with the acquired dataset. I understand, however, if the authors have planned to demonstrate this in a subsequent manuscript with a larger dataset and more solid conclusions.