Biogeochemistry

  • Letter |

    The net balance of terrestrial biogenic greenhouse gases produced as a result of human activities and the climatic impact of this balance are uncertain; here the net cumulative impact of the three greenhouse gases, methane, nitrous oxide and carbon dioxide, on the planetary energy budget from 2001 to 2010 is a warming of the planet.

    • Hanqin Tian
    • , Chaoqun Lu
    •  & Steven C. Wofsy
  • Letter |

    A climate modelling experiment is used to identify where ocean carbon uptake should change as a result of anthropogenic climate change and to distinguish these changes from internal climate variability; we may be able to detect changing uptake in some oceanic regions between 2020 and 2050, but until then, internal climate variability will preclude such detection.

    • Galen A. McKinley
    • , Darren J. Pilcher
    •  & Nicole S. Lovenduski
  • Letter |

    A reconstruction of changes in ocean oxygenation throughout the last glacial cycle shows that respired carbon was removed from the deep Southern Ocean during deglaciation and Antarctic warm events, consistent with a prominent role of reduced iron fertilization and enhanced ocean ventilation, modifying atmospheric carbon dioxide concentrations over the past 80,000 years.

    • Samuel L. Jaccard
    • , Eric D. Galbraith
    •  & Robert F. Anderson
  • Letter |

    Core isotope measurements in the equatorial Pacific Ocean reveal that although atmospheric dust deposition during the last ice age was higher than today’s, the productivity of the equatorial Pacific Ocean did not increase; this may have been because iron-enabled greater nutrient consumption, mainly in the Southern Ocean, reduced the nutrients available in the equatorial Pacific Ocean, and hence also productivity there.

    • K. M. Costa
    • , J. F. McManus
    •  & A. C. Ravelo
  • Article |

    Until now, the oxidation steps necessary for complete nitrification have always been observed to occur in two separate microorganisms in a cross-feeding interaction; here, together with the study by van Kessel et al., Daims et al. report the enrichment and characterization of Nitrospira species that encode all of the enzymes necessary to catalyse complete nitrification, a phenotype referred to as “comammox” (for complete ammonia oxidation).

    • Holger Daims
    • , Elena V. Lebedeva
    •  & Michael Wagner
  • Perspective |

    Careful management of nitrogen fertilizer usage is required to ensure world food security while limiting environmental degradation; an analysis of historical nitrogen use efficiency reveals socio-economic factors and technological innovations that have influenced a range of past national trends and that suggest ways to improve global food production and environmental stewardship by 2050.

    • Xin Zhang
    • , Eric A. Davidson
    •  & Ye Shen
  • Perspective |

    Instead of containing stable and chemically unique ‘humic substances’, as has been widely accepted, soil organic matter is a mixture of progressively decomposing organic compounds; this has broad implications for soil science and its applications.

    • Johannes Lehmann
    •  & Markus Kleber
  • Letter |

    Particulate organic carbon export from the terrestrial biosphere is primarily controlled by physical erosion, and tectonic and climatic forcing of physical erosion may favour biospheric particulate organic carbon sequestration over silicate weathering as a long-term atmospheric carbon dioxide sink.

    • Valier Galy
    • , Bernhard Peucker-Ehrenbrink
    •  & Timothy Eglinton
  • Review Article |

    A large amount of organic carbon stored in frozen Arctic soils (permafrost) could be released as carbon dioxide and methane in a warming climate, which would accelerate the pace of climate change; this review suggests that release of greenhouse gas emissions will be gradual but prolonged.

    • E. A. G. Schuur
    • , A. D. McGuire
    •  & J. E. Vonk
  • Perspective |

    Formal criteria must be met to define a new human-driven epoch; the geological evidence appears to do so, with 1610 and 1964 both likely to satisfy the requirements for the start of the Anthropocene.

    • Simon L. Lewis
    •  & Mark A. Maslin
  • Letter |

    Nitrogen isotope ratios from rocks between 3.2 and 2.75 billion years old are most readily explained by biological nitrogen fixation, most probably using the metal molybdenum as a cofactor, showing that nitrogen fixation is at least 3.2 billion years old and suggesting that molybdenum was available to organisms long before the Great Oxidation Event.

    • Eva E. Stüeken
    • , Roger Buick
    •  & Matthew C. Koehler
  • Article |

    As incomes grow, diets change, with varying impacts on human health and the environment; here the links are examined and suggestions made for diets that both improve health and minimize environmental impacts.

    • David Tilman
    •  & Michael Clark
  • Letter |

    The abundance of key microbial lineages can be used to predict atmospherically relevant patterns in methane isotopes and the proportion of carbon metabolized to methane during permafrost thaw, suggesting that microbial ecology may be important in ecosystem-scale responses to global change.

    • Carmody K. McCalley
    • , Ben J. Woodcroft
    •  & Scott R. Saleska
  • Letter |

    A global, observation-based assessment of whole-ecosystem carbon turnover times shows that the overall mean global carbon turnover time is about 23 years and that locally its spatial variability depends on precipitation at least as strongly as on temperature.

    • Nuno Carvalhais
    • , Matthias Forkel
    •  & Markus Reichstein
  • Letter |

    Microbial community responses in soils from the Arctic to the Amazon often enhance the longer-term temperature sensitivity of respiration, particularly in soils with high carbon-to-nitrogen ratios and in soils from cold regions, suggesting that carbon stored in Arctic and boreal soils could be more vulnerable to climate warming than currently predicted.

    • Kristiina Karhu
    • , Marc D. Auffret
    •  & Iain P. Hartley
  • Letter |

    Distinct groups of microorganisms have been thought to grow on methane and on short-chain alkanes; now, the methanotroph Methylocella silvestris is shown to express two distinct soluble di-iron centre monooxygenases that allow it to use either methane or propane as a carbon and energy source.

    • Andrew T. Crombie
    •  & J. Colin Murrell
  • Letter |

    The discrepancy between the components of the oceanic carbon budget — export of carbon from the surface and its conversion into carbon dioxide by water-column biota at depth — is reconciled using field data and a steady-state model which indicates that synergy between microbes and zooplankton is an important factor.

    • Sarah L. C. Giering
    • , Richard Sanders
    •  & Daniel J. Mayor
  • Letter |

    Meta-analyses show that the temperature dependence of methane fluxes scales consistently across populations of methanogens, microbial communities and whole ecosystems, and that this temperature dependence is higher than for respiration and photosynthesis; this indicates that global warming may impact the relative contributions of CO2 and CH4 to total greenhouse gas emissions.

    • Gabriel Yvon-Durocher
    • , Andrew P. Allen
    •  & Paul A. del Giorgio
  • Letter |

    The long-term record of atmospheric carbon dioxide growth rate shows that the sensitivity of this growth rate to tropical temperature variability has increased by a factor of about two in the past five decades, and was greater when tropical land regions experienced drier conditions, implying that moisture regulates this sensitivity.

    • Xuhui Wang
    • , Shilong Piao
    •  & Anping Chen
  • Letter |

    Escherichia coli K-12 performs sulphoglycolysis; heterologous expression of enzymes encoded in a ten-gene cluster present in almost all (>91%) available E. coli genomes is used to show that sulphoquinovose is catabolised through four reactions to produce dihydroxyacetone phosphate, which powers energy conservation and growth, and a sulphonate product, which is excreted.

    • Karin Denger
    • , Michael Weiss
    •  & David Schleheck
  • Letter |

    A global analysis shows that for most tree species the largest trees are the fastest-growing trees, a finding that resolves conflicting assumptions about tree growth and that has implications for understanding forest carbon dynamics, resource allocation trade-offs within trees and plant senescence.

    • N. L. Stephenson
    • , A. J. Das
    •  & M. A. Zavala
  • Letter |

    Global carbon budgets reveal that inland waters emit substantial amounts of carbon, which is believed to originate from the terrestrial biosphere; however, here the carbon emitted from the Amazon River system is shown to originate from temporary wetlands in the flooded area itself, such as flooded forests.

    • Gwenaël Abril
    • , Jean-Michel Martinez
    •  & Fabio Roland
  • Article |

    An analysis of regional variations in global inland water surface area, dissolved CO2 and gas transfer velocity yields a global CO2 evasion rate of 2.1 × 1015 grams of carbon per year, which is higher than previous estimates owing to a larger contribution from streams and rivers.

    • Peter A. Raymond
    • , Jens Hartmann
    •  & Peter Guth
  • Letter |

    Soil samples collected from 224 dryland sites around the world show that aridity affects the concentration of organic carbon and total nitrogen differently from the concentration of inorganic phosphorus, suggesting that any predicted increase in aridity with climate change could uncouple the carbon, nitrogen and phosphorus cycles in drylands and negatively affect the services provided by these ecosystems.

    • Manuel Delgado-Baquerizo
    • , Fernando T. Maestre
    •  & Eli Zaady
  • Letter |

    The distribution of chromium isotopes and redox-sensitive metals in the Nsuze palaeosol and in the Ijzermyn iron formation from the Pongola Supergroup, in South Africa, suggests that there were appreciable levels of atmospheric oxygen about three billion years ago, some 300–400 million years earlier than previous indications for Earth surface oxygenation.

    • Sean A. Crowe
    • , Lasse N. Døssing
    •  & Donald E. Canfield
  • Letter |

    In tropical moist forests, nitrogen-fixing tree species can supply a large proportion of the nitrogen required for net forest growth in the first 12 years of recovery after human or natural perturbation, with nitrogen-fixing trees accumulating carbon up to nine times faster per individual than non-fixing trees, and species-specific differences in the amount and timing of fixation.

    • Sarah A. Batterman
    • , Lars O. Hedin
    •  & Jefferson S. Hall
  • Letter |

    Correlations between the maximum and minimum daily temperatures and a vegetation index in the Northern Hemisphere suggest that asymmetric diurnal warming (faster warming of the land surface during the night than during the day) produces several different vegetation and carbon storage effects.

    • Shushi Peng
    • , Shilong Piao
    •  & Hui Zeng
  • Perspective |

    The effects of climate extremes such as droughts or storms on the carbon cycle of ecosystems are investigated; such extremes can decrease regional carbon stocks.

    • Markus Reichstein
    • , Michael Bahn
    •  & Martin Wattenbach
  • Letter |

    The amount of greenhouse gas emissions that will limit the risks from such emissions has been set by the goal of keeping global warming below two degrees Celsius above preindustrial, but this study sets thresholds for sea level rise, ocean acidification and agricultural productivity as well as warming and shows that emissions need to be lowered even further.

    • Marco Steinacher
    • , Fortunat Joos
    •  & Thomas F. Stocker
  • Letter |

    Two decades of summer warming in an Alaskan tundra ecosystem increased plant biomass and woody dominance, indirectly increased winter soil temperature, homogenized the soil trophic structure and suppressed surface-soil-decomposer activity, but did not change net soil carbon or nitrogen storage.

    • Seeta A. Sistla
    • , John C. Moore
    •  & Joshua P. Schimel
  • Letter |

    A global synthesis of stable nitrogen isotopic values in lacustrine sediments indicates a period of declining enrichment from 15,000 to 7,000 years before present, probably in response to terrestrial carbon sequestration.

    • Kendra K. McLauchlan
    • , Joseph J. Williams
    •  & Elizabeth S. Jeffers
  • Letter |

    A comparative assessment of six alternative cropping systems over 20 years shows that, once well established, successional herbaceous vegetation grown on marginal lands has a direct greenhouse gas emissions mitigation capacity that rivals that of purpose-grown crops.

    • Ilya Gelfand
    • , Ritvik Sahajpal
    •  & G. Philip Robertson
  • Letter |

    Critical transitions in experimental and theoretical systems can be anticipated on the basis of specific warning signs, with ‘critical slowing down’ being the best studied; long-term data from a real system, a Chinese lake, now show that a flickering phenomenon can be observed up to 20 years before the critical transition to a eutrophic state.

    • Rong Wang
    • , John A. Dearing
    •  & Marten Scheffer
  • Article |

    Methane oxidation under anaerobic conditions coupled to sulphate reduction is thought to be carried out by a consortium of methanotrophic archaea (ANME) and sulphate-reducing Deltaproteobacteria; here it is shown that ANME alone can mediate the reaction and that the associated bacteria perform disulphide disproportionation, a new microbial sulphur transformation.

    • Jana Milucka
    • , Timothy G. Ferdelman
    •  & Marcel M. M. Kuypers
  • Letter |

    On the basis of data from other subglacial environments and simulations of the accumulation of methane hydrate in Antarctic sedimentary basins, it seems there could be unsuspected, large stores of methane beneath the Antarctic Ice Sheet.

    • J. L. Wadham
    • , S. Arndt
    •  & C. E. H. Butler
  • Article |

    The study of an iron-fertilized phytoplankton bloom dominated by diatoms, which takes up carbon dioxide from the atmosphere, shows that a substantial proportion of the bloom eventually sinks to the deep-sea floor, sequestering the carbon for timescales of centuries or more.

    • Victor Smetacek
    • , Christine Klaas
    •  & Dieter Wolf-Gladrow
  • Letter |

    About one-fifth of organic carbon in sediments is bound to reactive iron phases, which are metastable over geological timescales and may therefore serve as a sink for the long-term storage of organic carbon.

    • Karine Lalonde
    • , Alfonso Mucci
    •  & Yves Gélinas