Agriculture is a major source of NO x pollution in California.

Nitrogen oxides (NO x = NO + NO2) are a primary component of air pollution-a leading cause of premature death in humans and biodiversity declines worldwide. Although regulatory policies in California have successfully limited transportation sources of NO x pollution, several of the United States' worst-air quality districts remain in rural regions of the state. Site-based findings suggest that NO x emissions from California's agricultural soils could contribute to air quality issues; however, a statewide estimate is hitherto lacking. We show that agricultural soils are a dominant source of NO x pollution in California, with especially high soil NO x emissions from the state's Central Valley region. We base our conclusion on two independent approaches: (i) a bottom-up spatial model of soil NO x emissions and (ii) top-down airborne observations of atmospheric NO x concentrations over the San Joaquin Valley. These approaches point to a large, overlooked NO x source from cropland soil, which is estimated to increase the NO x budget by 20 to 51%. These estimates are consistent with previous studies of point-scale measurements of NO x emissions from the soil. Our results highlight opportunities to limit NO x emissions from agriculture by investing in management practices that will bring co-benefits to the economy, ecosystems, and human health in rural areas of California

Extrapolation of point measurements and fertilizer-only emission factors cannot capture statewide soil NO x emissions.

Maaz et al. argue that inconsistencies across scales of observation undermine our working hypothesis that soil NO x emissions have been substantially overlooked in California; however, the core issues they raise are already discussed in our manuscript. We agree that point measurements cannot be reliably used to estimate statewide soil NO x emissions-the principal motivation behind our new modeling/airplane approach. Maaz et al.'s presentation of fertilizer-based emission factors (a nonmechanistic scaling of point measures to regions based solely on estimated nitrogen fertilizer application rates) includes no data from California or other semiarid sites, and does not explicitly account for widely known controls of climate, soil, and moisture on soil NO x fluxes. In contrast, our model includes all of these factors. Finally, the fertilizer sales data that Maaz et al. highlight are known to suffer from serious errors and do not offer a logically more robust pathway for spatial analysis of NO x emissions from soil

Guided flows in coronal magnetic flux tubes

There is evidence for coronal plasma flows to break down into fragments and to be laminar. We investigate this effect by modeling flows confined along magnetic channels. We consider a full MHD model of a solar atmosphere box with a dipole magnetic field. We compare the propagation of a cylindrical flow perfectly aligned to the field to that of another one with a slight misalignment. We assume a flow speed of 200 km/s, and an ambient magnetic field of 30 G. We find that while the aligned flow maintains its cylindrical symmetry while it travels along the magnetic tube, the misaligned one is rapidly squashed on one side, becoming laminar and eventually fragmented because of the interaction and backreaction of the magnetic field. This model could explain an observation of erupted fragments that fall back as thin and elongated strands and end up onto the solar surface in a hedge-like configuration, made by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The initial alignment of plasma flow plays an important role in determining the possible laminar structure and fragmentation of flows while they travel along magnetic channels.Comment: 11 pages, 8 figures, accepted for publication, movies available upon request to the first autho

Biogeographic Distribution Patterns of Bacteria in Typical Chinese Forest Soils

Microbes are widely distributed in soils and play a very important role in nutrient cycling and ecosystem services. To understand the biogeographic distribution of forest soil bacteria, we collected 115 soil samples in typical forest ecosystems across eastern China to investigate their bacterial community compositions using Illumina MiSeq high throughput sequencing based on 16S rRNA. We obtained 4,667,656 sequences totally and more than 70% of these sequences were classified into five dominant groups, i.e. Actinobacteria, Acidobacteria, Alphaproteobacteria, Verrucomicrobia and Planctomycetes (relative abundance > 5%). The bacterial diversity showed a parabola shape along latitude and the maximum diversity appeared at latitudes between 33.50°N and 40°N, an area characterized by warm-temperate zones and moderate temperature, neutral soil pH and high substrate availability (soil C and N) from dominant deciduous broad-leaved forests. Pairwise dissimilarity matrix in bacterial community composition showed that bacterial community structure had regional similarity and the latitude of 30°N could be used as the dividing line between southern and northern forest soils. Soil properties and climate conditions (MAT and MAP) greatly accounted for the differences in the soil bacterial structure. Among all soil parameters determined, soil pH predominantly affected the diversity and composition of the bacterial community, and soil pH = 5 probably could be used as a threshold below which soil bacterial diversity might decline and soil bacterial community structure might change significantly. Moreover, soil exchangeable cations, especially Ca2+ (ECa2+) and some other soil variables were also closely related to bacterial community structure. The selected environmental variables (21.11%) explained more of the bacterial community variation than geographic distance (15.88%), indicating that the edaphic properties and environmental factors played a more important role than geographic dispersal limitation in determining the bacterial community structure in Chinese forest soils

A world of cobenefits : solving the global nitrogen challenge

Houlton, Benjamin Z. University of California. John Muir Institute of the Environment. Davis, CA, USA.Houlton, Benjamin Z. University of California. Department of Land, Air and Water Resources. Davis, CA, USA.Almaraz, Maya. University of California. Department of Land, Air and Water Resources. Davis, CA, USA.Aneja, Viney. North Carolina State University at Raleigh. Department of Marine, Earth, and Atmospheric Sciences. Raleigh, NC, USA.Austin, Amy T. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA). Buenos Aires, Argentina.Austin, Amy T. CONICET – Universidad de Buenos Aires. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA). Buenos Aires, Argentina.Bai, Edith. Chinese Academy of Sciences. Institute of Applied Ecology. CAS Key Laboratory of Forest Ecology and Management. Shenyang, China.Bai, Edith. Northeast Normal University. School of Geographical Sciences. Changchun, China.Cassman, Kenneth. University of Nebraska – Lincoln. Department of Agronomy and Horticulture. Lincoln. NE, USA.Compton, Jana E. Environmental Protection Agency. Western Ecology Division. Washington, DC, USA.Davidson, Eric A. University of Maryland Center for Environmental Science. Appalachian Laboratory. Cambridge, MD, USA.865-872Nitrogen is a critical component of the economy, food security, and planetary health. Many of the world's sustainability targets hinge on global nitrogen solutions, which, in turn, contribute lasting benefits for (i) world hunger; (ii) soil, air, and water quality; (iii) climate change mitigation; and (iv) biodiversity conservation. Balancing the projected rise in agricultural nitrogen demands while achieving these 21st century ideals will require policies to coordinate solutions among technologies, consumer choice, and socioeconomic transformation

Quality of fresh organic matter affects priming of soil organic matter and substrate utilization patterns of microbes

Changes in biogeochemical cycles and the climate system due to human activities are expected to change the quantity and quality of plant litter inputs to soils. How changing quality of fresh organic matter (FOM) might influence the priming effect (PE) on soil organic matter (SOM) mineralization is still under debate. Here we determined the PE induced by two (13)C-labeled FOMs with contrasting nutritional quality (leaf vs. stalk of Zea mays L.). Soils from two different forest types yielded consistent results: soils amended with leaf tissue switched faster from negative PE to positive PE due to greater microbial growth compared to soils amended with stalks. However, after 16 d of incubation, soils amended with stalks had a higher PE than those amended with leaf. Phospholipid fatty acid (PLFA) results suggested that microbial demand for carbon and other nutrients was one of the major determinants of the PE observed. Therefore, consideration of both microbial demands for nutrients and FOM supply simultaneously is essential to understand the underlying mechanisms of PE. Our study provided evidence that changes in FOM quality could affect microbial utilization of substrate and PE on SOM mineralization, which may exacerbate global warming problems under future climate change

Thresholds in decoupled soil-plant elements under changing climatic conditions

Background and aims: aridity has increased in the past decades and will probably continue to increase in arid and semiarid regions. Here we decipher the plant and soil capacity to retain metal cations when climate evolves to more arid conditions. - Methods: we analyzed K, Na, Ca, Mg, Fe, Mn, Zn and Cu concentrations in 580 soil samples and 666 plant (shoot and root) samples along a 3600 km aridity gradient in northern China. - Results: the concentrations of soil exchangeable K, Mg, Mn, Fe and Cu clearly decreased with increasing aridity due to the relationships of aridity with soil clay content and soil pH. Increases in exchangeable Na and Ca concentrations at mid- and high-aridity levels are probably due to the soil salinization, whereas increased exchangeable Fe concentrations at extreme levels of aridity may be more related to a reduced pH. Element concentrations in both plant shoots and roots were unrelated to soil exchangeable element concentrations; instead they increased monotonously with increasing aridity, corresponding with decreases in plant size and shoot/root ratios. The shoot/root mineralomass ratios in general increased with increasing aridity. The proportional higher element contents in shoots than in roots with increasing aridity are related to increased water uptake and/or use efficiency. - Conclusions: the extractability of soil elements in response to changing climate varied with the nature of specific elements that are controlled by biological and geochemical processes, i.e., some decreased linearly with increasing aridity, whereas others first decreased and then increased with different thresholds. These contrasting effects of aridity on nutrient availability could further constrain plant growth and should be incorporated into biogeochemical models. The prevailing paradigm of a positive relationship between concentrations of plant and soil elements needs to be reconsidered under changing climatic condition

Woody Plant Encroachment into Grasslands: Spatial Patterns of Functional Group Distribution and Community Development

Woody plant encroachment into grasslands has been globally widespread. The woody species invading grasslands represent a variety of contrasting plant functional groups and growth forms. Are some woody plant functional types (PFTs) better suited to invade grasslands than others? To what extent do local patterns of distribution and abundance of woody PFTs invading grasslands reflect intrinsic topoedaphic properties versus plant-induced changes in soil properties? We addressed these questions in the Southern Great Plains, United States at a subtropical grassland known to have been encroached upon by woody species over the past 50-100 years. A total of 20 woody species (9 tree-statured; 11 shrub-statured) were encountered along a transect extending from an upland into a playa basin. About half of the encroaching woody plants were potential N(2)-fixers (55% of species), but they contributed only 7% to 16 % of the total basal area. Most species and the PFTs they represent were ubiquitously distributed along the topoedaphic gradient, but with varying abundances. Overstory-understory comparisons suggest that while future species composition of these woody communities is likely to change, PFT composition is not. Canonical correspondence analysis (CCA) ordination and variance partitioning (Partial CCA) indicated that woody species and PFT composition in developing woody communities was primarily influenced by intrinsic landscape location variables (e.g., soil texture) and secondarily by plant-induced changes in soil organic carbon and total nitrogen content. The ubiquitous distribution of species and PFTs suggests that woody plants are generally well-suited to a broad range of grassland topoedaphic settings. However, here we only examined categorical and non-quantitative functional traits. Although intrinsic soil properties exerted more control over the floristics of grassland-to-woodland succession did plant modifications of soil carbon and nitrogen concentrations, the latter are likely to influence productivity and nutrient cycling and may, over longer time-frames, feed back to influence PFT distributions

A World of Cobenefits: Solving the Global Nitrogen Challenge

Nitrogen is a critical component of the economy, food security, and planetary health. Many of the world\u27s sustainability targets hinge on global nitrogen solutions, which, in turn, contribute lasting benefits for (i) world hunger; (ii) soil, air, and water quality; (iii) climate change mitigation; and (iv) biodiversity conservation. Balancing the projected rise in agricultural nitrogen demands while achieving these 21st century ideals will require policies to coordinate solutions among technologies, consumer choice, and socioeconomic transformation

A Holistic Perspective on the Dynamics of G035.39-00.33 : The Interplay between Gas and Magnetic Fields

Magnetic field plays a crucial role in shaping molecular clouds and regulating star formation, yet the complete information on the magnetic field is not well constrained owing to the limitations in observations. We study the magnetic field in the massive infrared dark cloud G035.39-00.33 from dust continuum polarization observations at 850 mu m with SCUBA-2/POL-2 at JCMT for the first time. The magnetic field tends to be perpendicular to the densest part of the main filament (F-M), whereas it has a less defined relative orientation in the rest of the structure, where it tends to be parallel to some diffuse regions. A mean plane-of-the-sky magnetic field strength of similar to 50 mu G for F-M is obtained using the Davis-Chandrasekhar-Fermi method. Based on (CO)-C-13 (1-0) line observations, we suggest a formation scenario of F-M due to large-scale (similar to 10 pc) cloud-cloud collision. Using additional NH3 line data, we estimate that F-M will be gravitationally unstable if it is only supported by thermal pressure and turbulence. The northern part of F-M, however, can be stabilized by a modest additional support from the local magnetic field. The middle and southern parts of F-M are likely unstable even if the magnetic field support is taken into account. We claim that the clumps in F-M may be supported by turbulence and magnetic fields against gravitational collapse. Finally, we identified for the first time a massive (similar to 200 M-circle dot, collapsing starless clump candidate, "c8," in G035.39-00.33. The magnetic field surrounding "c8" is likely pinched, hinting at an accretion flow along the filament.Peer reviewe