Natural atmospheric deposition of molybdenum: a global model and implications for tropical forests

Wong, Michelle Y.; Mahowald, N. M.; Marino, Roxanne; Williams, Earle; Chellam, Shankararaman; Howarth, Robert W.

doi:10.1007/s10533-020-00671-w

Cited by 19 publications

(26 citation statements)

References 87 publications

(137 reference statements)

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“…Terrestrial regions where Mo limitation have been found, which include several temperate, tropical, and boreal ecosystems (Dynarski & Houlton, 2018; Wong et al., 2020b; and references therein), may be particularly sensitive to anthropogenic Mo inputs. Other regions that may be similarly sensitive to anthropogenic perturbations of the Mo cycle are regions where N limitation is strong and new inputs of Mo from weathering or natural atmospheric deposition are low.…”

Section: Discussionmentioning

confidence: 99%

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Anthropogenic Perturbations to the Atmospheric Molybdenum Cycle

Wong

Rathod

Marino

et al. 2021

Global Biogeochemical Cycles

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Molybdenum (Mo) is a key cofactor in enzymes used for nitrogen (N) fixation and nitrate reduction, and the low availability of Mo can constrain N inputs, affecting ecosystem productivity. Natural atmospheric Mo aerosolization and deposition from sources such as desert dust, sea‐salt spray, and volcanoes can affect ecosystem function across long timescales, but anthropogenic activities such as combustion, motor vehicles, and agricultural dust have accelerated the natural Mo cycle. Here we combined a synthesis of global atmospheric concentration observations and modeling to identify and estimate anthropogenic sources of atmospheric Mo. To project the impact of atmospheric Mo on terrestrial ecosystems, we synthesized soil Mo data and estimated the global distribution of soil Mo using two approaches to calculate turnover times. We estimated global emissions of atmospheric Mo in aerosols (<10 μm in diameter) to be 23 Gg Mo yr−1, with 40%–75% from anthropogenic sources. We approximated that for the top meter of soil, Mo turnover times range between 1,000 and 1,000,000 years. In some industrialized regions, anthropogenic inputs have enhanced Mo deposition 100‐fold, lowering the soil Mo turnover time considerably. Our synthesis of global observational data, modeling, and a mass balance comparison with riverine Mo exports suggest that anthropogenic activity has greatly accelerated the Mo cycle, with potential to influence N‐limited ecosystems.

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Section: Discussionmentioning

confidence: 99%

“…Volcanic aerosols can be important local sources from noneruptive volcanoes (Wong et al, 2020b). Eruptive volcanoes could also be important, however, no appropriate long-term data set is available, so we focused on noneruptive emissions using the same approach as Wong et al (2020b) but with CAM6.…”

Section: Volcanoesmentioning

confidence: 99%

Anthropogenic Perturbations to the Atmospheric Molybdenum Cycle

Wong

Rathod

Marino

et al. 2021

Global Biogeochemical Cycles

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“…Together, this suggests that nutrient limitation might be site‐specific, reminiscent of studies carried out in Panama that found both Mo and P and Mo co‐limitation along a soil P and soil Mo gradient (Barron et al., 2009; Wurzburger et al., 2012), but contrast to Central Brazil where no effect of P and Mo addition was found on soil BNF (Wong, Neill, et al., 2020). It is noteworthy that Panamanian and Brazilian soils in these studies had lower (0.3–0.9 and 0.09 ppm, respectively) total soil Mo than the soils here in French Guiana (Table 1), a discrepancy that among other reasons could be linked to the influence of transatlantic atmospheric mineral dust transported from the North African Bodélé Depression (Wong, Mahowald, et al., 2020).…”

Section: Discussionmentioning

confidence: 67%

Impact of Nutrient Additions on Free‐Living Nitrogen Fixation in Litter and Soil of Two French‐Guianese Lowland Tropical Forests

et al. 2021

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Biological nitrogen (N) fixation (BNF) is a major natural source of new N to unmanaged terrestrial ecosystems worldwide (Cleveland et al., 1999;Reed et al., 2011;Vitousek et al., 2013) and in tropical evergreen forests, N input through free-living BNF has been found to vary between 0.1 and 60 kg N ha −1 yr −1 (Reed et al., 2011). During BNF, inert dinitrogen (N 2 ) is reduced to ammonia by N 2 fixing microorganisms,

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“…While high rates of BNF are commonly reported for tropical forests (Cleveland et al 1999, Sullivan et al 2014), most studies have been conducted in regions that receive substantial inputs of molybdenum (Mo) from atmospheric dust and sea salt (Wong et al 2020 a ), and inputs of P from dust (Mahowald et al 2008). Even in regions that receive relatively high atmospheric inputs of Mo, low biological availability of Mo may still constrain free‐living BNF.…”

Section: Introductionmentioning

confidence: 99%

“…The southeastern Amazon is a region where Mo and P limitation may be pronounced because soils are developed from old, stable surfaces with little to no parent material contribution (Quesada et al 2011) and where atmospheric inputs are very low (Mahowald et al 2008, Wong et al 2020 a ). While a handful of studies have assessed the simultaneous effects of Mo and P on free‐living BNF rates in the tropics, such as in Hawaii, Panama, Costa Rica, and Belize (Vitousek and Hobbie 2000, Barron et al 2009, Wurzburger et al 2012, Reed et al 2013, Winbourne et al 2017, Stanton et al 2019), these regions have higher weathering and atmospheric inputs, particularly from sea‐salt aerosols (Wong et al 2020 a ). In addition, these studies have either been short‐term experiments testing the addition of Mo and or P, or longer‐term studies with Mo added as a nutrient “cocktail” where responses to Mo alone have not been examined (Vitousek and Hobbie 2000, Barron et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Molybdenum, phosphorus, and pH do not constrain nitrogen fixation in a tropical forest in the southeastern Amazon

Wong

Neill

Marino

et al. 2020

Ecology

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High rates of biological nitrogen fixation (BNF) are commonly reported for tropical forests, but most studies have been conducted in regions that receive substantial inputs of molybdenum (Mo) from atmospheric dust and sea‐salt aerosols. Even in these regions, the low availability of Mo can constrain free‐living BNF catalyzed by heterotrophic bacteria and archaea. We hypothesized that in regions where atmospheric inputs of Mo are low and soils are highly weathered, such as the southeastern Amazon, Mo would constrain BNF. We also hypothesized that the high soil acidity, characteristic of the Amazon Basin, would further constrain Mo availability and therefore soil BNF. We conducted two field experiments across the wet and dry seasons, adding Mo, phosphorus (P), and lime alone and in combination to the forest floor in the southeastern Amazon. We sampled soils and litter immediately, and then weeks and months after the applications, and measured Mo and P availability through resin extractions and BNF with the acetylene reduction assay. The experimental additions of Mo and P increased their availability and the lime increased soil pH. While the combination of Mo and P increased BNF at some time points, BNF rates did not increase strongly or consistently across the study as a whole, suggesting that Mo, P, and soil pH are not the dominant controls over BNF. In a separate short‐term laboratory experiment, BNF did not respond strongly to Mo and P even when labile carbon was added. We postulate that high nitrogen (N) availability in this area of the Amazon, as indicated by the stoichiometry of soils and vegetation and the high nitrate soil stocks, likely suppresses BNF at this site. These patterns may also extend across highly weathered soils with high N availability in other topographically stable regions of the tropics.

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Natural atmospheric deposition of molybdenum: a global model and implications for tropical forests

Cited by 19 publications

References 87 publications

Anthropogenic Perturbations to the Atmospheric Molybdenum Cycle

Anthropogenic Perturbations to the Atmospheric Molybdenum Cycle

Impact of Nutrient Additions on Free‐Living Nitrogen Fixation in Litter and Soil of Two French‐Guianese Lowland Tropical Forests

Molybdenum, phosphorus, and pH do not constrain nitrogen fixation in a tropical forest in the southeastern Amazon

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