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Marine nitrogen fixers mediate a low latitude pathway for atmospheric CO₂ drawdown.

ABSTRACT: Roughly a third (~30?ppm) of the carbon dioxide (CO₂) that entered the ocean during ice ages is attributed to biological mechanisms. A leading hypothesis for the biological drawdown of CO₂ is iron (Fe) fertilisation of the high latitudes, but modelling efforts attribute at most 10 ppm to this mechanism, leaving ~20?ppm unexplained. We show that an Fe-induced stimulation of dinitrogen (N₂) fixation can induce a low latitude drawdown of 7-16?ppm CO₂. This mechanism involves a closer coupling between N₂ fixers and denitrifiers that alleviates widespread nitrate limitation. Consequently, phosphate utilisation and carbon export increase near upwelling zones, causing deoxygenation and deeper carbon injection. Furthermore, this low latitude mechanism reproduces the regional patterns of organic ?¹⁵N deposited in glacial sediments. The positive response of marine N₂ fixation to dusty ice age conditions, first proposed twenty years ago, therefore compliments high latitude changes to amplify CO₂ drawdown.

SUBMITTER: Buchanan PJ

PROVIDER: S-EPMC6787065 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Marine nitrogen fixers mediate a low latitude pathway for atmospheric CO2 drawdown.

Buchanan Pearse J PJ Chase Zanna Z Matear Richard J RJ Phipps Steven J SJ Bindoff Nathaniel L NL

Nature communications 20191010 1

Roughly a third (~30 ppm) of the carbon dioxide (CO2) that entered the ocean during ice ages is attributed to biological mechanisms. A leading hypothesis for the biological drawdown of CO2 is iron (Fe) fertilisation of the high latitudes, but modelling efforts attribute at most 10 ppm to this mechanism, leaving ~20 ppm unexplained. We show that an Fe-induced stimulation of dinitrogen (N2) fixation can induce a low latitude drawdown of 7-16 ppm CO2. Thi ...[more]

PMID: 31601810

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Project description:Photosynthesis of wheat and maize declined when grown with NH4 + as a nitrogen (N) source at ambient CO2 concentration compared to those grown with a mixture of NO3 - and NH4 +, or NO3 - as the sole N source. Interestingly, these N nutritional physiological responses changed when the atmospheric CO2 concentration increases. We studied the photosynthetic responses of wheat and maize growing with various N forms at three levels of growth CO2 levels. Hydroponic experiments were carried out using a C3 plant (wheat, Triticum aestivum L. cv. Chuanmai 58) and a C4 plant (maize, Zea mays L. cv. Zhongdan 808) given three types of N nutrition: sole NO3 - (NN), sole NH4 + (AN) and a mixture of both NO3 - and NH4 + (Mix-N). The test plants were grown using custom-built chambers where a continuous and desired atmospheric CO2 (C a ) concentration could be maintained: 280 μmol mol-1 (representing the pre-Industrial Revolution CO2 concentration of the 18th century), 400 μmol mol-1 (present level) and 550 μmol mol-1 (representing the anticipated futuristic concentration in 2050). Under AN, the decrease in net photosynthetic rate (P n ) was attributed to a reduction in the maximum RuBP-regeneration rate, which then caused reductions in the maximum Rubisco-carboxylation rates for both species. Decreases in electron transport rate, reduction of electron flux to the photosynthetic carbon [Je(PCR)] and electron flux for photorespiratory carbon oxidation [Je(PCO)] were also observed under AN for both species. However, the intercellular (C i ) and chloroplast (C c ) CO2 concentration increased with increasing atmospheric CO2 in C3 wheat but not in C4 maize, leading to a higher Je(PCR)/ Je(PCO) ratio. Interestingly, the reduction of P n under AN was relieved in wheat through higher CO2 levels, but that was not the case in maize. In conclusion, elevating atmospheric CO2 concentration increased C i and C c in wheat, but not in maize, with enhanced electron fluxes towards photosynthesis, rather than photorespiration, thereby relieving the inhibition of photosynthesis under AN. Our results contributed to a better understanding of NH4 + involvement in N nutrition of crops growing under different levels of CO2.

Project description:Models of species response to climate change often assume that physiological traits are invariant across populations. Neglecting potential intraspecific variation may overlook the possibility that some populations are more resilient or susceptible than others, creating inaccurate predictions of climate impacts. In addition, phenotypic plasticity can contribute to trait variation and may mediate sensitivity to climate. Quantifying such forms of intraspecific variation can improve our understanding of how climate can affect ecologically important species, such as invasive predators. Here, we quantified thermal performance (tolerance, acclimation capacity, developmental traits) across seven populations of the predatory marine snail (Urosalpinx cinerea) from native Atlantic and non-native Pacific coast populations in the USA. Using common garden experiments, we assessed the effects of source population and developmental acclimation on thermal tolerance and developmental traits of F1 snails. We then estimated climate sensitivity by calculating warming tolerance (thermal tolerance - habitat temperature), using field environmental data. We report that low-latitude populations had greater thermal tolerance than their high latitude counterparts. However, these same low-latitude populations exhibited decreased thermal tolerance when exposed to environmentally realistic higher acclimation temperatures. Low-latitude native populations had the greatest climate sensitivity (habitat temperatures near thermal limits). In contrast, invasive Pacific snails had the lowest climate sensitivity, suggesting that these populations are likely to persist and drive negative impacts on native biodiversity. Developmental rate significantly increased in embryos sourced from populations with greater habitat temperature but had variable effects on clutch size and hatching success. Thus, warming can produce widely divergent responses within the same species, resulting in enhanced impacts in the non-native range and extirpation in the native range. Broadly, our results highlight how intraspecific variation can alter management decisions, as this may clarify whether management efforts should be focused on many or only a few populations.

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Marine nitrogen fixers mediate a low latitude pathway for atmospheric CO₂ drawdown.

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Marine nitrogen fixers mediate a low latitude pathway for atmospheric CO<sub>2</sub> drawdown.

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