the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Nov 2023
Direct foliar phosphorus uptake from wildfire ash
Abstract. Atmospheric particles originating from combustion byproducts (burned biomass or wildfire ash) are highly enriched in nutrients such as P, K, Ca, Mg, Fe, Mn, Zn, and others. Over long timescales, deposited wildfire ash particles contribute to soil fertility by replenishing soil nutrient reservoirs. However, the immediate nutritional effects of freshly deposited fire ash on plants are mostly unknown. Here we study the influence of fire ash on plant nutrition by applying particles separately on a plant’s foliage or onto its roots. We conducted experiments on chickpea model plants under ambient and elevated CO2 levels, 412 and 850 ppm, that reflect current and future climate scenarios. We found that plants can uptake fire ash P only through their leaves, by a direct nutrient uptake from particles captured on their foliage, but not via their roots. In a future climate scenario, foliar nutrient uptake pathway may be even more significant for plants, due to the partial inhibition of key root uptake mechanism. Our findings highlight the effectiveness of the foliar nutrient uptake mechanism under both ambient and elevated CO2 levels, with fire ash P being the sole nutrient absorbed by the foliage. These findings demonstrate the substantial contribution of fire ash to the nutrition of plants. Furthermore, the role of fire ash is expected to increase in the future world, thus giving a competitive advantage to plants that can utilize fire ash P from the foliar pathway.
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RC1: 'Comment on egusphere-2023-2617', Anonymous Referee #1, 18 Dec 2023
An important contribution to the community, but some sections need clarity. See pdf for full comments. I am willing to review the revised manuscript.
- AC1: 'Reply on RC1', Anton Lokshin, 11 Feb 2024
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RC2: 'Comment on egusphere-2023-2617', Anonymous Referee #2, 12 Jan 2024
This paper is a nice illustration of the potential P-fertilising effect of ash deposited on plant surfaces. It has been known for a long time that P can be taken up by leaves, but this paper quantifies the importance of this P uptake for a crop species in an experimental setting. While the broader conclusions (that our future world will see more ash deposition and that this may make this biogeochemical pathway quantitatively more important than it has been) is true, I feel that the authors ‘over-sell’ the idea that it is going to be highly significant for plants. The experiment has done several things that maximise the effect of ash: high ash loads, complete burning of ash to remove organic residues, and importantly, choosing a species that is covered in hairs that contain high concentrations of acids, and that (being a legume) is quite responsive to P fertilisation. I would suggest that the conclusions are toned down.
I agree with (most of) the comments provided by Reviewer 1, and have avoided repeating the same points. Whilst this manuscript does not have many major issues, I believe that the cited manuscript (Palchan et al., in review) should have been made available to the reviewers. Everything indicates that this manuscript is a companion paper based on the same (or parallel experiment). The amount of data presented in this paper is not large. Whilst I have ticked the box ‘minor revision’, it is possible that a major revision that includes combining Palchan’s manuscript to publish it as a single paper may be better advice.
L5: I suggest that the species (chickpea) is included in the title.
L18 and L76: ash applied to the roots or rather to the soil surface?
L21: You have not demonstrated that plants cannot take up P through their roots. It didn’t happen in your experiment, but it is the main pathway under normal circumstances. The way you formulate it here suggests that they don’t.
L25: This is quite far extrapolated from one unique species to all plants. I’d add the word ‘potentially’ as a minimum, and would suggest to tone this down.
L68: “impair” is quite a strong word in “… impair plant’s mechanisms of nutrient uptake …”. “… reduce plant nutrient uptake …” may be appropriate?
L68: explain that eCO2 and aCO2 are elevated and ambient CO2.
L77: “Fire ash impacts will be higher than that of other atmospheric sources due to the higher P concentrations and increased solubility in comparison to desert dust and volcanic ash”. You cannot test this hypothesis as the experimental design does not include desert dush and volcanic ash treatments. This hypothesis seems to be formulated for the combined experiments of this paper and that of Palchan et al (in review) …
L108: fire ash, not fire as.
L102: bonfire I assume?
L113: further burning at 550 C reduces the ash to mineral-only ash, but is that the type of ash that is dispersed and deposited in the real world, or is that the less-completely burned ash?
L118: dispersion instead of erosion?
L155: “…whereas the chickpea grown in similar growing conditions.” Change to “… in which the chickpea was grown …”
L156: 3 g of ash (not as)
L157: “the ash was gently applied manually on the leaves”. More detail is needed. Was it evenly spread, how did you avoid spillage? Did you touch the leaf or let the ash fall on it? Touching the leaf of chickpea damages hairs which release strong acids …
L159: “applied to the roots”. I strongly request different wording, e.g. soil surface, as I’m sure you didn’t apply it to the roots in the way you applied it to the leaves. However you may not like to use ‘soil’ for perlite. “Substrate” is an alternative option.
L162: “The plants were rinsed in tap water, 0.1M HCl and three times in distilled water to remove any ash remains.” The HCl concentration seems very high, do you have evidence that this did not damage the plants? Do you also have (microscopic) evidence that all ash was effectively removed?
L175: Not dust but ash.
L188: only ash, not dust?
L189: leaf, not leave.
Figures 1 and 2: I think that these figures can be effectively combined. I would add Root biomass too. And I would prefer P concentration rather than P content. Differences in P content seem simply due to differences in biomass, but this can be verified by showing P concentration.
L273: “The depletion of the plants nutrient status is caused by the downregulation of the roots system”. This is an interpretation that should not be stated in the figure caption. Lower nutrient concentrations at eCO2 are also due to ‘dilution’ by carbon-based compounds, including higher concentrations of non-structural carbohydrates.
L291: “These results suggest that solubility tests examined by chemical extractions do not necessarily reflect actual biological availability and emphasize the importance of fertilization experiments with plants.” I agree, but the result remains puzzling, and it’s a pity that no attempts were made to look into this further. What was the pH in the perlite substrate? Was there evidence of the ash dissolving and being transported into the substrate? Were there roots throughout the substrate? Chickpea roots have the capacity to access P from poorly soluble salts, through the same mechanism that you propose for leaves.
L296: “ … promotes the release of P solubilizing metabolites, such as malic citric and oxalic acids”. As far as I know these compounds are contained in gland hairs, and only released when these break, rather than ‘exuded’. Breakge may occur naturally, but I’d suggest that you comment on this rather than suggesting that these compounds are continuously exuded.
L321: “Another possible factor could be the elevated pH level of the fire ash particles which may impact the chemical environment of the leaf surface.” But your measurements demonstrate a highly acidic environment …
Figure S1: why do the fractions not add up to 100%? Is that the soluble fraction that’s missing? Why not include it?
Citation: https://doi.org/10.5194/egusphere-2023-2617-RC2 - AC2: 'Reply on RC2', Anton Lokshin, 11 Feb 2024
- AC3: 'Comment on egusphere-2023-2617', Anton Lokshin, 14 Feb 2024
Status: closed
-
RC1: 'Comment on egusphere-2023-2617', Anonymous Referee #1, 18 Dec 2023
An important contribution to the community, but some sections need clarity. See pdf for full comments. I am willing to review the revised manuscript.
- AC1: 'Reply on RC1', Anton Lokshin, 11 Feb 2024
-
RC2: 'Comment on egusphere-2023-2617', Anonymous Referee #2, 12 Jan 2024
This paper is a nice illustration of the potential P-fertilising effect of ash deposited on plant surfaces. It has been known for a long time that P can be taken up by leaves, but this paper quantifies the importance of this P uptake for a crop species in an experimental setting. While the broader conclusions (that our future world will see more ash deposition and that this may make this biogeochemical pathway quantitatively more important than it has been) is true, I feel that the authors ‘over-sell’ the idea that it is going to be highly significant for plants. The experiment has done several things that maximise the effect of ash: high ash loads, complete burning of ash to remove organic residues, and importantly, choosing a species that is covered in hairs that contain high concentrations of acids, and that (being a legume) is quite responsive to P fertilisation. I would suggest that the conclusions are toned down.
I agree with (most of) the comments provided by Reviewer 1, and have avoided repeating the same points. Whilst this manuscript does not have many major issues, I believe that the cited manuscript (Palchan et al., in review) should have been made available to the reviewers. Everything indicates that this manuscript is a companion paper based on the same (or parallel experiment). The amount of data presented in this paper is not large. Whilst I have ticked the box ‘minor revision’, it is possible that a major revision that includes combining Palchan’s manuscript to publish it as a single paper may be better advice.
L5: I suggest that the species (chickpea) is included in the title.
L18 and L76: ash applied to the roots or rather to the soil surface?
L21: You have not demonstrated that plants cannot take up P through their roots. It didn’t happen in your experiment, but it is the main pathway under normal circumstances. The way you formulate it here suggests that they don’t.
L25: This is quite far extrapolated from one unique species to all plants. I’d add the word ‘potentially’ as a minimum, and would suggest to tone this down.
L68: “impair” is quite a strong word in “… impair plant’s mechanisms of nutrient uptake …”. “… reduce plant nutrient uptake …” may be appropriate?
L68: explain that eCO2 and aCO2 are elevated and ambient CO2.
L77: “Fire ash impacts will be higher than that of other atmospheric sources due to the higher P concentrations and increased solubility in comparison to desert dust and volcanic ash”. You cannot test this hypothesis as the experimental design does not include desert dush and volcanic ash treatments. This hypothesis seems to be formulated for the combined experiments of this paper and that of Palchan et al (in review) …
L108: fire ash, not fire as.
L102: bonfire I assume?
L113: further burning at 550 C reduces the ash to mineral-only ash, but is that the type of ash that is dispersed and deposited in the real world, or is that the less-completely burned ash?
L118: dispersion instead of erosion?
L155: “…whereas the chickpea grown in similar growing conditions.” Change to “… in which the chickpea was grown …”
L156: 3 g of ash (not as)
L157: “the ash was gently applied manually on the leaves”. More detail is needed. Was it evenly spread, how did you avoid spillage? Did you touch the leaf or let the ash fall on it? Touching the leaf of chickpea damages hairs which release strong acids …
L159: “applied to the roots”. I strongly request different wording, e.g. soil surface, as I’m sure you didn’t apply it to the roots in the way you applied it to the leaves. However you may not like to use ‘soil’ for perlite. “Substrate” is an alternative option.
L162: “The plants were rinsed in tap water, 0.1M HCl and three times in distilled water to remove any ash remains.” The HCl concentration seems very high, do you have evidence that this did not damage the plants? Do you also have (microscopic) evidence that all ash was effectively removed?
L175: Not dust but ash.
L188: only ash, not dust?
L189: leaf, not leave.
Figures 1 and 2: I think that these figures can be effectively combined. I would add Root biomass too. And I would prefer P concentration rather than P content. Differences in P content seem simply due to differences in biomass, but this can be verified by showing P concentration.
L273: “The depletion of the plants nutrient status is caused by the downregulation of the roots system”. This is an interpretation that should not be stated in the figure caption. Lower nutrient concentrations at eCO2 are also due to ‘dilution’ by carbon-based compounds, including higher concentrations of non-structural carbohydrates.
L291: “These results suggest that solubility tests examined by chemical extractions do not necessarily reflect actual biological availability and emphasize the importance of fertilization experiments with plants.” I agree, but the result remains puzzling, and it’s a pity that no attempts were made to look into this further. What was the pH in the perlite substrate? Was there evidence of the ash dissolving and being transported into the substrate? Were there roots throughout the substrate? Chickpea roots have the capacity to access P from poorly soluble salts, through the same mechanism that you propose for leaves.
L296: “ … promotes the release of P solubilizing metabolites, such as malic citric and oxalic acids”. As far as I know these compounds are contained in gland hairs, and only released when these break, rather than ‘exuded’. Breakge may occur naturally, but I’d suggest that you comment on this rather than suggesting that these compounds are continuously exuded.
L321: “Another possible factor could be the elevated pH level of the fire ash particles which may impact the chemical environment of the leaf surface.” But your measurements demonstrate a highly acidic environment …
Figure S1: why do the fractions not add up to 100%? Is that the soluble fraction that’s missing? Why not include it?
Citation: https://doi.org/10.5194/egusphere-2023-2617-RC2 - AC2: 'Reply on RC2', Anton Lokshin, 11 Feb 2024
- AC3: 'Comment on egusphere-2023-2617', Anton Lokshin, 14 Feb 2024
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