the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 30 Jul 2026
Canopy processing of atmospheric dust creates a short-term phosphorus pathway in a tropical forest
Abstract. Phosphorus (P) availability constrains productivity in many humid tropical forests, where highly weathered soils retain P in poorly available forms and external inputs are needed to offset long-term losses. Caribbean forests receive new P through trans-Atlantic Saharan dust and episodic African biomass-burning particles, however how this particulate P enters forest nutrient cycling remains poorly understood. Here, we examined the fate and uptake of particulate P in the Luquillo Experimental Forest, Puerto Rico, using a foliar dust-application experiment and soil incubations with mineral dust and wildfire ash. In soils, both materials increased P supply to ion-exchange membranes, but mineral dust-derived P was rapidly transferred into Fe- and Al-associated pools, whereas wildfire ash generated greater short-term P availability. On leaves, mineral dust exposure resulted in foliar uptake of dust-derived Fe and P, with P uptake quantified using Fe as a conservative anchor. Particles recovered from leaf surfaces contained more bicarbonate-extractable P than the applied dust, indicating that contact with leaves increased the lability of P remaining in deposited particles. Together, these findings identify two complementary canopy pathways: direct foliar uptake of dust-derived P and leaf-surface processing that increases the fraction potentially available for subsequent uptake, either from foliage or, following redistribution in throughfall, by roots. By revealing a pre-soil pathway for atmospheric P, our results highlight a process not explicitly represented in most terrestrial nutrient-cycle frameworks that may affect how models represent the biological availability of dust-derived P and its coupling to tropical forest carbon cycling.
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Status: open (until 17 Oct 2026)
- CC1: 'Comment on egusphere-2026-4320', Charles T. Driscoll, 03 Sep 2026 reply
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RC1: 'Comment on egusphere-2026-4320', Anonymous Referee #1, 04 Sep 2026
reply
The manuscript (MS No.: egusphere-2026-4320) “Canopy processing of atmospheric dust creates a short-term phosphorus pathway in a tropical forest” by A. Gross et al. describes an interesting experimental study in which the authors (sort of) compare foliar uptake of phosphorus (P) from atmospheric particles with soil processing of P from atmospheric particles applied to soil. The authors are comparing apples with oranges but that notwithstanding, this is a challenging question to address. I like the paper and the authors should be commended for taking this research on. The authors provide a unique perspective on the important role of foliage in the processing and assimilation of atmospheric particles to obtain P. A challenge for the authors is to present a clear and coherent description of a complex experiment which contrasts foliar processing with soil processing of atmospheric particles using contrasting methods. Although I like the paper and think it should be ultimately published, I had much difficulty following the author’s text. I found myself going back and forth through the text trying to follow their experimental approach. I don’t think there is any way around this problem. The authors have undertaken a complex experiment and there are clear limitations, but the results are interesting and the paper could ultimately be published in EGU Sphere.
One of the big issues I have with the paper is understanding how the dust is “applied” to the leaves. The authors state that they “use a fine sieve to apply uniform coverage” But how is this done? The dust is a dry material. What keeps it from falling off the leaf after it is applied? Of the mass of dust applied to the leaves what fraction remains on the leaf? This experimental application should be clarified on p. 9, line 242.
Another concern that I have is that it seems that the mass of dust applied experimentally is quite large; approximately 70 g m-2 of leaf surface. The authors state that is approximately equivalent to 3 years of deposition. I understand that the authors would like to apply a large dose to observe a plant response, but could there be limitations associated with over dosing? If so these limitations should be discussed in the Discussion section of the paper.
I don’t like the fact that the authors made two separate applications of two different types of dust to the same leaves. I think this is a serious flaw in the experiment. How can the authors determine if one type of dust reacts substantially differently to the leaf than the other type. I understand that the authors had limited quantity of atmospheric dust, but this approach is a clear limitation to interpreting the experimental observations.
In various sections of the Discussion the authors address some of the limitations of the experiment. However, they don’t discuss the two limitations which I mention above and I consider these to be major limitations of the study. I think these limitations should be addressed in a separate “limitations” section of the Discussion which would include all the other limitations mentioned throughout the Discussion section.
I have a number of smaller points and comments which should be addressed before the manuscript is suitable for publication.
Line 133 I don’t understand “dry deposition is approximately 53 -73%”. Of what? Is this percent as P or total mass? If it is total mass, how is total mass expressed? Dry mass of wet plus dry deposition? The authors need to clarify what they are trying to say here.
Lines 177-180 How are the local dust and ash collected. Are these surface soil deposits? What depth? Some additional detail on the collection of these materials is needed. How soon after the fire was the ash collected?
Lines 261, 270, 379 and probably others elsewhere The authors cite Lokshin et al. 2026 and Lokshin et al. 2026a in the text. In the references they provide Lokshin et al. 2026a and 2026b. However this seems to be the same article cited twice. Something is incorrect and the authors should fix it.
Line 302 The authors should clarify here that the greenhouse experiment is Starr et al. 2023.
Line 393 It appears that the authors cite Figure 3a here is the text before they cite Figure 2. If I am correct the authors should probably switch the order of Figures 2 and 3.
Line 405 Should equation 3 be %ΔPest ?
Line 476 Why do the authors use ppm to express concentration units here when they use mg P g-1 elsewhere in the paper?
Line 484 The authors are not really normalizing the P fluxes to the soil surface area, are they? Aren’t the values normalized to the soil pot surface area (0.01 m2)? The soil presumably has a relatively high specific surface area and therefore a high surface area. This description should be clarified in the revised text.
Line 490 and Figure 4a I am completely confused by the normalization of the foliar P response to the total P content of dust. Why is this done? Also why are the values normalized to the values reported by Pett-Ridge et al.? Why not use the authors measured P content in the dust they applied? This approach needs to be clarified.
I am also confused by the units shown in Figure 4a. The units shown in the figure are mg m-2, but the figure title says P uptake per gr of dust. This adds to my confusion and needs to be clarified in the revised manuscript.
Lines 500- 505 Can the authors really measure these concentrations to hundredths of µg g-1 ? This seems too precise to me; too many significant figures.
Citation: https://doi.org/10.5194/egusphere-2026-4320-RC1
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The manuscript (MS No.: egusphere-2026-4320) “Canopy processing of atmospheric dust creates a short-term phosphorus pathway in a tropical forest” by A. Gross et al. describes an interesting experimental study in which the authors (sort of) compare foliar uptake of phosphorus (P) from atmospheric particles with soil processing of P from atmospheric particles applied to soil. The authors are comparing apples with oranges but that notwithstanding, this is a challenging question to address. I like the paper and the authors should be commended for taking this research on. The authors provide a unique perspective on the important role of foliage in the processing and assimilation of atmospheric particles to obtain P. A challenge for the authors is to present a clear and coherent description of a complex experiment which contrasts foliar processing with soil processing of atmospheric particles using contrasting methods. Although I like the paper and think it should be ultimately published, I had much difficulty following the author’s text. I found myself going back and forth through the text trying to follow their experimental approach. I don’t think there is any way around this problem. The authors have undertaken a complex experiment and there are clear limitations, but the results are interesting and the paper could ultimately be published in EGU Sphere.
One of the big issues I have with the paper is understanding how the dust is “applied” to the leaves. The authors state that they “use a fine sieve to apply uniform coverage” But how is this done? The dust is a dry material. What keeps it from falling off the leaf after it is applied? Of the mass of dust applied to the leaves what fraction remains on the leaf? This experimental application should be clarified on p. 9, line 242.
Another concern that I have is that it seems that the mass of dust applied experimentally is quite large; approximately 70 g m-2 of leaf surface. The authors state that is approximately equivalent to 3 years of deposition. I understand that the authors would like to apply a large dose to observe a plant response, but could there be limitations associated with over dosing? If so these limitations should be discussed in the Discussion section of the paper.
I don’t like the fact that the authors made two separate applications of two different types of dust to the same leaves. I think this is a serious flaw in the experiment. How can the authors determine if one type of dust reacts substantially differently to the leaf than the other type. I understand that the authors had limited quantity of atmospheric dust, but this approach is a clear limitation to interpreting the experimental observations.
In various sections of the Discussion the authors address some of the limitations of the experiment. However, they don’t discuss the two limitations which I mention above and I consider these to be major limitations of the study. I think these limitations should be addressed in a separate “limitations” section of the Discussion which would include all the other limitations mentioned throughout the Discussion section.
I have a number of smaller points and comments which should be addressed before the manuscript is suitable for publication.
Line 133 I don’t understand “dry deposition is approximately 53 -73%”. Of what? Is this percent as P or total mass? If it is total mass, how is total mass expressed? Dry mass of wet plus dry deposition? The authors need to clarify what they are trying to say here.
Lines 177-180 How are the local dust and ash collected. Are these surface soil deposits? What depth? Some additional detail on the collection of these materials is needed. How soon after the fire was the ash collected?
Lines 261, 270, 379 and probably others elsewhere The authors cite Lokshin et al. 2026 and Lokshin et al. 2026a in the text. In the references they provide Lokshin et al. 2026a and 2026b. However this seems to be the same article cited twice. Something is incorrect and the authors should fix it.
Line 302 The authors should clarify here that the greenhouse experiment is Starr et al. 2023.
Line 393 It appears that the authors cite Figure 3a here is the text before they cite Figure 2. If I am correct the authors should probably switch the order of Figures 2 and 3.
Line 405 Should equation 3 be %ΔPest ?
Line 476 Why do the authors use ppm to express concentration units here when they use mg P g-1 elsewhere in the paper?
Line 484 The authors are not really normalizing the P fluxes to the soil surface area, are they? Aren’t the values normalized to the soil pot surface area (0.01 m2)? The soil presumably has a relatively high specific surface area and therefore a high surface area. This description should be clarified in the revised text.
Line 490 and Figure 4a I am completely confused by the normalization of the foliar P response to the total P content of dust. Why is this done? Also why are the values normalized to the values reported by Pett-Ridge et al.? Why not use the authors measured P content in the dust they applied? This approach needs to be clarified.
I am also confused by the units shown in Figure 4a. The units shown in the figure are mg m-2, but the figure title says P uptake per gr of dust. This adds to my confusion and needs to be clarified in the revised manuscript.
Lines 500- 505 Can the authors really measure these concentrations to hundredths of µg g-1 ? This seems too precise to me; too many significant figures.
Line 625 Here is the Discussion the authors first mention that the atmospheric acids could alter the availability of P in trans-Atlantic Saharan dust. It might be useful to mention this idea earlier in the Methods to justify using both desert soil dust and trans-Atlantic Saharan dust in the experimental design.