116,761 research outputs found
Zonal Soil Type Determines Soil Microbial Responses to Maize Cropping and Fertilization.
Soil types heavily influence ecological dynamics. It remains controversial to what extent soil types shape microbial responses to land management changes, largely due to lack of in-depth comparison across various soil types. Here, we collected samples from three major zonal soil types spanning from cold temperate to subtropical climate zones. We examined bacterial and fungal community structures, as well as microbial functional genes. Different soil types had distinct microbial biomass levels and community compositions. Five years of maize cropping (growing corn or maize) changed the bacterial community composition of the Ultisol soil type and the fungal composition of the Mollisol soil type but had little effect on the microbial composition of the Inceptisol soil type. Meanwhile, 5 years of fertilization resulted in soil acidification. Microbial compositions of the Mollisol and Ultisol, but not the Inceptisol, were changed and correlated (P < 0.05) with soil pH. These results demonstrated the critical role of soil type in determining microbial responses to land management changes. We also found that soil nitrification potentials correlated with the total abundance of nitrifiers and that soil heterotrophic respiration correlated with the total abundance of carbon degradation genes, suggesting that changes in microbial community structure had altered ecosystem processes. IMPORTANCE Microbial communities are essential drivers of soil functional processes such as nitrification and heterotrophic respiration. Although there is initial evidence revealing the importance of soil type in shaping microbial communities, there has been no in-depth, comprehensive survey to robustly establish it as a major determinant of microbial community composition, functional gene structure, or ecosystem functioning. We examined bacterial and fungal community structures using Illumina sequencing, microbial functional genes using GeoChip, microbial biomass using phospholipid fatty acid analysis, as well as functional processes of soil nitrification potential and CO2 efflux. We demonstrated the critical role of soil type in determining microbial responses to land use changes at the continental level. Our findings underscore the inherent difficulty in generalizing ecosystem responses across landscapes and suggest that assessments of community feedback must take soil types into consideration. Author Video: An author video summary of this article is available
Mass-Radius Relations and Core-Envelope Decompositions of Super-Earths and Sub-Neptunes
Many exoplanets have been discovered with radii of 1-4 Earth radii, between
that of Earth and Neptune. A number of these are known to have densities
consistent with solid compositions, while others are "sub-Neptunes" likely to
have significant hydrogen-helium envelopes. Future surveys will no doubt
significantly expand these populations. In order to understand how the measured
masses and radii of such planets can inform their structures and compositions,
we construct models both for solid layered planets and for planets with solid
cores and gaseous envelopes, exploring a range of core masses, hydrogen-helium
envelope masses, and associated envelope entropies. For planets in the
super-Earth/sub-Neptune regime for which both radius and mass are measured, we
estimate how each is partitioned into a solid core and gaseous envelope,
associating a specific core mass and envelope mass with a given exoplanet. We
perform this decomposition for both "Earth-like" rock-iron cores and pure ice
cores, and find that the necessary gaseous envelope masses for this important
sub-class of exoplanets must range very widely from zero to many Earth masses,
even for a given core mass. This result bears importantly on exoplanet
formation and envelope evaporation processes.Comment: 26 pages, 21 figures, 16 tables, accepted to Ap
Integrating trait-based empirical and modeling research to improve ecological restoration
A global ecological restoration agenda has led to ambitious programs in environmental policy to mitigate declines in biodiversity and ecosystem services. Current restoration programs can incompletely return desired ecosystem service levels, while resilience of restored ecosystems to future threats is unknown. It is therefore essential to advance understanding and better utilize knowledge from ecological literature in restoration approaches. We identified an incomplete linkage between global change ecology, ecosystem function research, and restoration ecology. This gap impedes a full understanding of the interactive effects of changing environmental factors on the long-term provision of ecosystem functions and a quantification of trade-offs and synergies among multiple services. Approaches that account for the effects of multiple changing factors on the composition of plant traits and their direct and indirect impact on the provision of ecosystem functions and services can close this gap. However, studies on this multilayered relationship are currently missing. We therefore propose an integrated restoration agenda complementing trait-based empirical studies with simulation modeling. We introduce an ongoing case study to demonstrate how this framework could allow systematic assessment of the impacts of interacting environmental factors on long-term service provisioning. Our proposed agenda will benefit restoration programs by suggesting plant species compositions with specific traits that maximize the supply of multiple ecosystem services in the long term. Once the suggested compositions have been implemented in actual restoration projects, these assemblages should be monitored to assess whether they are resilient as well as to improve model parameterization. Additionally, the integration of empirical and simulation modeling research can improve global outcomes by raising the awareness of which restoration goals can be achieved, due to the quantification of trade-offs and synergies among ecosystem services under a wide range of environmental conditions
A Map of the Inorganic Ternary Metal Nitrides
Exploratory synthesis in novel chemical spaces is the essence of solid-state
chemistry. However, uncharted chemical spaces can be difficult to navigate,
especially when materials synthesis is challenging. Nitrides represent one such
space, where stringent synthesis constraints have limited the exploration of
this important class of functional materials. Here, we employ a suite of
computational materials discovery and informatics tools to construct a large
stability map of the inorganic ternary metal nitrides. Our map clusters the
ternary nitrides into chemical families with distinct stability and
metastability, and highlights hundreds of promising new ternary nitride spaces
for experimental investigation--from which we experimentally realized 7 new Zn-
and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity,
and covalency of solid-state bonding from the DFT-computed electron density, we
reveal the complex interplay between chemistry, composition, and electronic
structure in governing large-scale stability trends in ternary nitride
materials
Spontaneous Octahedral Tilting in the Cubic Inorganic Caesium Halide Perovskites CsSnX and CsPbX (X = F, Cl, Br, I)
The local crystal structures of many perovskite-structured materials deviate
from the average space group symmetry. We demonstrate, from lattice-dynamics
calculations based on quantum chemical force constants, that all the
caesium-lead and caesium-tin halide perovskites exhibit vibrational
instabilities associated with octahedral titling in their high-temperature
cubic phase. Anharmonic double-well potentials are found for zone-boundary
phonon modes in all compounds with barriers ranging from 108 to 512 meV. The
well depth is correlated with the tolerance factor and the chemistry of the
composition, but is not proportional to the imaginary harmonic phonon
frequency. We provide quantitative insights into the thermodynamic driving
forces and distinguish between dynamic and static disorder based on the
potential-energy landscape. A positive band gap deformation (spectral
blueshift) accompanies the structural distortion, with implications for
understanding the performance of these materials in applications areas
including solar cells and light-emitting diodes
Fe-C and Fe-H systems at pressures of the Earth's inner core
The solid inner core of the Earth is predominantly composed of iron alloyed
with several percent Ni and some lighter elements, Si, S, O, H, and C being the
prime candidates. There have been a growing number of papers investigating C
and H as possible light elements in the core, but the results are
contradictory. Here, using ab initio simulations, we study the Fe-C and Fe-H
systems at inner core pressures (330-364 GPa). Using the evolutionary structure
prediction algorithm USPEX, we have determined the lowest-enthalpy structures
of possible carbides (FeC, Fe2C, Fe3C, Fe4C, FeC2, FeC3, FeC4 and Fe7C3) and
hydrides (Fe4H, Fe3H, Fe2H, FeH, FeH2, FeH3, FeH4) and have found that Fe2C
(Pnma) is the most stable iron carbide at pressures of the inner core, while
FeH, FeH3 and FeH4 are stable iron hydrides at these conditions. For Fe3C, the
cementite structure (Pnma) and the Cmcm structure recently found by random
sampling are less stable than the I-4 and C2/m structures found here. We found
that FeH3 and FeH4 adopt chemically interesting thermodynamically stable
structures, in both compounds containing trivalent iron. The density of the
inner core can be matched with a reasonable concentration of carbon, 11-15
mol.percent (2.6-3.7 wt.percent) at relevant pressures and temperatures. This
concentration matches that in CI carbonaceous chondrites and corresponds to the
average atomic mass in the range 49.3-51.0, in close agreement with inferences
from the Birch's law for the inner core. Similarly made estimates for the
maximum hydrogen content are unrealistically high, 17-22 mol.percent (0.4-0.5
wt.percent), which corresponds to the average atomic mass in the range
43.8-46.5. We conclude that carbon is a better candidate light alloying element
than hydrogen.Comment: Published in Physics-Uspekhi: full text will soon appear at
http://ufn.ru/en/articles/2012/5/c/ (currently, only abstract is available
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