“Hot spots” of N and C impact nitric oxide, nitrous oxide and nitrogen gas emissions from a UK grassland soil

Publication history: Accepted - 6 June 2017; Published online - 3 July 2017.Agricultural soils are a major source of nitric- (NO) and nitrous oxide (N2O), which are produced and consumed by biotic and abiotic soil processes. The dominant sources of NO and N2O are microbial nitrification and denitrification, and emissions of NO and N2O generally increase after fertiliser application. The present study investigated the impact of N-source distribution on emissions of NO and N2O from soil and the significance of denitrification, rather than nitrification, as a source of NO emissions. To eliminate spatial variability and changing environmental factors which impact processes and results, the experiment was conducted under highly controlled conditions. A laboratory incubation system (DENIS) was used, allowing simultaneous measurement of three N-gases (NO, N2O, N2) emitted from a repacked soil core, which was combined with 15N-enrichment isotopic techniques to determine the source of N emissions. It was found that the areal distribution of N and C significantly affected the quantity and timing of gaseous emissions and 15N-analysis showed that N2O emissions resulted almost exclusively from the added amendments. Localised higher concentrations, so-called hot spots, resulted in a delay in N2O and N2 emissions causing a longer residence time of the applied N-source in the soil, therefore minimising NO emissions while at the same time being potentially advantageous for plant-uptake of nutrients. If such effects are also observed for a wider range of soils and conditions, then this will have major implications for fertiliser application protocols to minimise gaseous N emissions while maintaining fertilisation efficiency.Rothamsted Research receives strategic funding by the Biotechnology and Biological Sciences Research Council (BBSRC). This study was funded by BBSRC project BB/K001051/1. D. Abalos thanks the Spanish Ministry of Science and Innovation for economic support through the Project AGL2009-08412-AGR

Kieft and Simmons Supplemental Material

Table S-1. Estimates of body masses of various animal species and sources of estimates of total number of microbes, with references. Table S-2. Diversity indices calculated from MG-RAST data

Data from: Allometry of animal-microbe interactions and global census of animal-associated microbes

Animals live in close association with microorganisms, mostly prokaryotes, living in or on them as commensals, mutualists, or parasites, and profoundly affecting host fitness. Most animal-microbe studies focus on microbial community structure; for this project, allometry (scaling of animal attributes with animal size) was applied to animal-microbe relationships across a range of species spanning 12 orders of magnitude in animal mass, from nematodes to whales. Microbial abundances per individual animal were gleaned from published literature and also microscopically counted in three species. Abundance of prokaryotes/individual vs. animal mass scales as a nearly linear power function (exponent = 1.07, R^2 = 0.94). Combining this power function with allometry of animal abundance indicates that macrofauna have an outsized share of animal-associated microorganisms. The total number of animal-associated prokaryotes in Earth’s land animals was calculated to be 1.3–1.4 x 10^25 cells and the total of marine animal-associated microbes was calculated to be 8.6–9.0 x 10^24 cells. Animal-associated microbes thus total 2.1–2.3 x 10^25 of the ~10^30 prokaryotes on Earth. Microbes associated with humans comprise 3.3-3.5% of Earth’s animal-associated microbes, and domestic animals harbor 14-20% of all animal-associated microbes, adding a new dimension to the scale of human impact on the biosphere. This novel allometric power function may reflect underlying mechanisms involving the transfer of energy and materials between microorganisms and their animal hosts. Microbial diversity indices of animal gut communities and gut microbial species richness for 60 mammals did not indicate significant scaling relationships with animal body mass; however, further research in this area is warranted

Data from: Allometry of animal-microbe interactions and global census of animal-associated microbes

Animals live in close association with microorganisms, mostly prokaryotes, living in or on them as commensals, mutualists, or parasites, and profoundly affecting host fitness. Most animal-microbe studies focus on microbial community structure; for this project, allometry (scaling of animal attributes with animal size) was applied to animal-microbe relationships across a range of species spanning 12 orders of magnitude in animal mass, from nematodes to whales. Microbial abundances per individual animal were gleaned from published literature and also microscopically counted in three species. Abundance of prokaryotes/individual vs. animal mass scales as a nearly linear power function (exponent = 1.07, R^2 = 0.94). Combining this power function with allometry of animal abundance indicates that macrofauna have an outsized share of animal-associated microorganisms. The total number of animal-associated prokaryotes in Earth’s land animals was calculated to be 1.3–1.4 x 10^25 cells and the total of marine animal-associated microbes was calculated to be 8.6–9.0 x 10^24 cells. Animal-associated microbes thus total 2.1–2.3 x 10^25 of the ~10^30 prokaryotes on Earth. Microbes associated with humans comprise 3.3-3.5% of Earth’s animal-associated microbes, and domestic animals harbor 14-20% of all animal-associated microbes, adding a new dimension to the scale of human impact on the biosphere. This novel allometric power function may reflect underlying mechanisms involving the transfer of energy and materials between microorganisms and their animal hosts. Microbial diversity indices of animal gut communities and gut microbial species richness for 60 mammals did not indicate significant scaling relationships with animal body mass; however, further research in this area is warranted

Data from: Allometry of animal-microbe interactions and global census of animal-associated microbes

Animals live in close association with microorganisms, mostly prokaryotes, living in or on them as commensals, mutualists or parasites, and profoundly affecting host fitness. Most animal–microbe studies focus on microbial community structure; for this project, allometry (scaling of animal attributes with animal size) was applied to animal–microbe relationships across a range of species spanning 12 orders of magnitude in animal mass, from nematodes to whales. Microbial abundances per individual animal were gleaned from published literature and also microscopically counted in three species. Abundance of prokaryotes/individual versus animal mass scales as a nearly linear power function (exponent = 1.07, R2 = 0.94). Combining this power function with allometry of animal abundance indicates that macrofauna have an outsized share of animal-associated microorganisms. The total number of animal-associated prokaryotes in Earth's land animals was calculated to be 1.3–1.4 × 1025 cells and the total of marine animal-associated microbes was calculated to be 8.6–9.0 × 1024 cells. Animal-associated microbes thus total 2.1–2.3 × 1025 of the approximately 1030 prokaryotes on the Earth. Microbes associated with humans comprise 3.3–3.5% of Earth's animal-associated microbes, and domestic animals harbour 14–20% of all animal-associated microbes, adding a new dimension to the scale of human impact on the biosphere. This novel allometric power function may reflect underlying mechanisms involving the transfer of energy and materials between microorganisms and their animal hosts. Microbial diversity indices of animal gut communities and gut microbial species richness for 60 mammals did not indicate significant scaling relationships with animal body mass; however, further research in this area is warranted

Ley diversity data-1

Species richness data from Ley et al., 2008 Supplemental informatio

Kieft and Simmons diversity data

Diversity data calculated from MG-RAST dat

Findings of the Mars Special Regions Science Analysis Group

In summary, within the upper 5 m most of Mars is either too cold or too dry to support the propagation of terrestrial life. However, there are regions that are in disequilibrium, naturally or induced, and could be classified as special or, if enough uncertainty exist, could not be declared as non-special. © Mary Ann Liebert, Inc