the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Jan 2026
Plant-soil interactions drive GHG dynamics in organic soils under variable water tables: a case study with poplar
Abstract. Organic soils provide a substantial capacity for carbon storage both in below- and above-ground biomass, but they are also a significant contributor to natural terrestrial Greenhouse gas (GHG) emissions. Organic soil melioration, carried out to increase the primary productivity, often leads to increased CO2 emissions. By monitoring a controlled environment, it is possible to determine how organic soil management practices influence the carbon cycle, including plant vitality and productivity, and consequently shape future carbon sequestration potential.
The aim of this study was to develop a system under semi-controlled conditions to assess the impact of different groundwater levels on GHG emissions, accumulated biomass, and tree vitality. We conducted experiments in semi-controlled conditions to determine the effects of different groundwater levels (-2 cm; -15 cm; -25 cm; -35 cm) on CH4 and CO2 emission, soil chemical analyses, and plant morphological (biomass, root and leaf area, shoot length) and physiological (leaf chlorophyll a and b content) parameters. Temporal and diurnal variation strongly impacted GHG fluxes due to the changes in temperature, moisture, and plant growth activity. During soil temperature extremes, extremely high CH4 emissions occurred at a -2 cm groundwater level. Higher plant productivity had a greater influence on GHG fluxes: it decreased both CH4 and CO2 emissions during the day compared to bare soil. Therefore, the autotrophic respiration rate increased with increased productivity, but the primary determinant was heterotrophic respiration.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-4493', Anonymous Referee #1, 01 Mar 2026
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RC2: 'Comment on egusphere-2025-4493', Anonymous Referee #2, 15 Mar 2026
General comments
This paper presents the effect of different groundwater levels on GHG emissions in the case of bare soils vs cultivated soils (poplar + F. ovina). The experimental design is smart, and the semi-controlled conditions allow for precise adjustment of the groundwater levels which of course wouldn’t be possible in an open environment.
The results show that even for tree species that benefit from high water content, water-saturated soils (groundwater level at -2 cm especially) prevent efficient growth of the vegetation. Also, high groundwater levels reduce CO2 emissions but enhance CH4 emissions through anaerobic processes.
Although I acknowledge the difficulty of conducting long term experiments and managing the material aspect (need for space, etc.), the lack of replicates may be an issue, as well as the short duration of the experiment (less than 3 months), especially to derive long term trends.
However, while not perfect, the experiment and manuscript still give a great insight in the way the plants and environmental conditions interact and generate GHG, especially in the context of worldwide peatlands degradation.
Specific comments
L84: 'Water regulation system was installed inside each of the five hydroisolated boxes at four different levels depending on the depth from the soil surface: -2 cm, -15 cm, -25 cm, and -35 cm' → so, out of the five boxes, there was one at -2 cm, one at -15 cm, one at -25 cm and one at -35 cm? Was the fifth one a control box? If so, please write it. Sorry if I’m misunderstanding something here.
L137: why not monitor temperature all along the experiment? Same for chlorophyll.
L177: why '1/Date' (and not just 'Date')?
L205: the -2 cm trees did not show any root development? Also, did you correct the below-ground biomass with the mass of the stems you planted at t=0? If not, did you make sure all stems were initially around the same width and mass?
L207: the sentence seems unclear to me, as I would interpret 'shallow' as -2 cm. However, given your statement, I suppose it rather refers to -35 cm. Please clarify this, at least once, so that you can then use shallow without risking misinterpretation. Also, accumulation does not only depend on biomass production but also on biomass degradation…which might be lower in -2 cm (water-saturated environment) than in -35 cm conditions.
L223: To me, 'high weekly variability' means that there is a weekly pattern with high variability along the week. I suppose you rather mean it varies greatly along the weeks, from one measurement to the other. If so, this sentence may need rephrasing. You should also rephrase the caption of Figure 4 the same way.
L231: what do you mean by 'the most important' and 'the most significant'? The days with the highest chlorophyll concentrations? If so, this may not be the most adequate wording.
L238: 'on soil respiration depth'? I don’t think 'depth' belongs here, does it?
L327: is 'per year' a good unit as you are specifically talking about huge differences in GHG emissions from one month to the other? While the overall conclusion will be the same, wouldn’t 'per month' or 'per day' make more sense?
L353: diurnal or daily?
The whole discussion section might benefit from slight changes, such as adding subsections with clear titles, to help structure the reflection and guide the reader along.
Technical corrections
All along: please be careful with overall English, punctuation and wording: some sentences are unclear, and many would be improved with (adequate) use of commas. The sentences tend to be long. Also, the way you introduce statistical results and p-values along the text may benefit from a change. It lacks punctuation between the different groundwater levels, and globally lowers the readability of the text where it is introduced.
L31: 'decreasing CH4' I guess.
L33: 'Although these are the main threats after peat drainage, recent studies show that whether the ecosystem on organic soil acts as a carbon source or sink is significantly determined by local environmental conditions, vegetation, land use, chemical and physical properties […]' → to me it feels a bit strange to put 'land use' in this list, as you are precisely explaining before that peat drainage is a problem, and I interpret peat drainage as a land use change in itself.
L83–84: typo (×3): 'from', not 'form'. Same L140 (×1) and 141 (×1).
L101: 'kg' not needed (it is a ratio).
L109: '-1' in superscript (×2).
L140–142: the sentence is unclear, please rephrase. Also, what does CCI stand for?
L194–197: This is already visible on the figure as you indicated significant differences with different letters. I suppose you want to emphasize that it is even smaller than 0.05, but I don’t think it’s needed. If you want to keep it, I would advise to find another way to present these statistical results (a table?).
L206: in Figure 2, '-2 cm' suddenly turned into -5 cm on the figure. Please correct all the occurrences.
L227–230: I would advise to find another way to present these statistical results (a table?).
L247: 'Nevertheless, the regression analyses showed […]' → Unclear, probably lacks punctuation.
L249: '10000 kg c' → '10000 kg C'.
L289: 'with for' → please correct.
L321: remove 'are', or make two different sentences.
L333: grammar → 'the vegetation negatively influences', or 'the vegetation negative influence on'
L345: 'in advance'? I don’t understand.
Citation: https://doi.org/10.5194/egusphere-2025-4493-RC2
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- 1
The manuscript is well-structured and addresses the important topic of CO2 and CH4 emissions from managed organic soils, with clear implications for climate-smart forestry. Strengths include the semi-controlled setup to isolate water table effects and the integration of plant physiology with GHG fluxes.
However, clarification on the replication structure is needed (n=1 box per water level, split into veg/bare sections?) and extrapolation to annual fluxes (t C ha⁻¹ year⁻¹) from ~2.5 months of data is bold, especially with seasonal spikes like June CH₄ extremes. It would be good to present GHG fluxes as short-term rates per day or hour to avoid overgeneralization, and/or please provide details on the scaling method used, including your assumptions about non-measured periods.
Specific comments:
Line 7: No need to capitalize “g” in “greenhouse”
Line 11-15: Some of the info here is repeated, like no need to tell me twice that the experiment is in semi-controlled conditions
Abstract: Some info on the effect of organic soil melioration on GHGs would be nice as this is the initial framing. Or, if the study doesn’t provide answers to this question, focus on groundwater table as that seems to be the main study factor. Maybe also inform the reader in the abstract that they are going to learn about autotrophic vs heterotrophic respiration.
Line 76: I am convinced that the light intensity in the greenhouse was consistent with the region, but the argument about shading is less convincing. Shading was consistent with which conditions exactly? Field conditions? In young poplar forest, old poplar forest, peat area? Shrub zones, the treeline?
Line 63: But no data on diurnal variability is presented in this study. Only arithmetic means per day, or day/night splits. This effectively erases any insights to diurnal variability, like duration of sunrise/sunset, how long during the day temperatures are at the optimum for given plant species, how quick temperature rises/falls etc. Maybe some diurnal plots could be added?
Line 69: Does this mean ALL studied soils were organic soils? In that case, the study does not test the effect of organic content in soil, as no control exists for this factor. So please remove from the abstract.
Line 86/117: Please clarify the replication structure: How many independent replicates for each soil organic matter content x water table x plant level?
Line 100: So, this study uses a single mixed substrate (peat + mineral soil from two depths, layered consistently across all boxes) to meet the >20% organic matter threshold for "organic soil."? It's thence not testing varying soil organic matter content as a factor, everything is presented by groundwater level only, and no significant differences in OM are analyzed or graphed. Please rewrite abstract and intro accordingly.
Line 126: I do not know how often OPUS is updated, but it seems a bit strange to me to provide the date and time stamp of the version.
Line 133/134: Why express GHG as yearly fluxes when measurements cover much shorter periods? It would be more meaningful to present data per hour or per day if it must be.
137: every 5 mins. What happened between these periods?
Line 138-142: At what time of day/light intensity was chlorophyll fluorescence measured? Were the measurements standardized for time of day/light intensity?
Line 214/15: Please rephrase
Line 222-25: Why is non-normality an “issue”?
Line 233:34: what does the R2 tell us here?
Line 241: No need to capitalize “d” in “day”
Figure 5: After reading the abstract I was really expecting a figure showing GHG-emissions as a function of soil organic C content. Since this is not possible from the experimental design, maybe rephrase abstract/intro focusing on water table instead of OM content.
Figure 4+6: I am not entirely convinced that we can assume linearity across the spare measurements.
Line 285: … can decrease productivity at the young seedling growth stages investigated here. Would it be the same for more mature trees?
Line 292: Leaf? Leaves?
Line 312: initial?
Line 339: The proportion was not really measured but only inferred from parallel measurement of unplanted soil (where the microbial community may be entirely different). Therefore, I’d be in favor of a more careful interpretation. Do you have measurements to show that microbial biomass/community composition were not significantly different between planted and unplanted soils?
Line 376: Diurnal variability was not really presented in this manuscript?