Microbial Carbon Use Efficiency and Growth Rates in Soil: Global Patterns and Drivers.

Carbon use efficiency (CUE) of microbial communities in soil quantifies the proportion of organic carbon (C) taken up by microorganisms that is allocated to growing microbial biomass as well as used for reparation of cell components. This C amount in microbial biomass is subsequently involved in microbial turnover, partly leading to microbial necromass formation, which can be further stabilized in soil. To unravel the underlying regulatory factors and spatial patterns of CUE on a large scale and across biomes (forests, grasslands, croplands), we evaluated 670 individual CUE data obtained by three commonly used approaches: (i) tracing of a substrate C by C (or C) incorporation into microbial biomass and respired CO (hereafter C-substrate), (ii) incorporation of O from water into DNA (O-water), and (iii) stoichiometric modelling based on the activities of enzymes responsible for C and nitrogen (N) cycles.

Changes in above- versus belowground biomass distribution in permafrost regions in response to climate warming.

Permafrost regions contain approximately half of the carbon stored in land ecosystems and have warmed at least twice as much as any other biome. This warming has influenced vegetation activity, leading to changes in plant composition, physiology, and biomass storage in aboveground and belowground components, ultimately impacting ecosystem carbon balance. Yet, little is known about the causes and magnitude of long-term changes in the above- to belowground biomass ratio of plants (η).

Whole-soil-profile warming does not change microbial carbon use efficiency in surface and deep soils.

The paucity of investigations of carbon (C) dynamics through the soil profile with warming makes it challenging to evaluate the terrestrial C feedback to climate change. Soil microbes are important engines driving terrestrial biogeochemical cycles; their carbon use efficiency (CUE), defined as the proportion of metabolized organic C allocated to microbial biomass, is a key regulator controlling the fate of soil C. It has been theorized that microbial CUE should decline with warming; however, empirical evidence for this response is scarce, and data from deeper soils are particularly scarce.

Effects of experimental nitrogen deposition on soil organic carbon storage in Southern California drylands.

Atmospheric nitrogen (N) deposition is enriching soils with N across biomes. Soil N enrichment can increase plant productivity and affect microbial activity, thereby increasing soil organic carbon (SOC), but such responses vary across biomes. Drylands cover ~45% of Earth's land area and store ~33% of global SOC contained in the top 1 m of soil.

Beyond bulk: Density fractions explain heterogeneity in global soil carbon abundance and persistence.

Understanding the controls on the amount and persistence of soil organic carbon (C) is essential for predicting its sensitivity to global change. The response may depend on whether C is unprotected, isolated within aggregates, or protected from decomposition by mineral associations. Here, we present a global synthesis of the relative influence of environmental factors on soil organic C partitioning among pools, abundance in each pool (mg C g  soil), and persistence (as approximated by radiocarbon abundance) in relatively unprotected particulate and protected mineral-bound pools.

A holistic framework integrating plant-microbe-mineral regulation of soil bioavailable nitrogen.

Unlabelled: Soil organic nitrogen (N) is a critical resource for plants and microbes, but the processes that govern its cycle are not well-described. To promote a holistic understanding of soil N dynamics, we need an integrated model that links soil organic matter (SOM) cycling to bioavailable N in both unmanaged and managed landscapes, including agroecosystems. We present a framework that unifies recent conceptual advances in our understanding of three critical steps in bioavailable N cycling: organic N (ON) depolymerization and solubilization; bioavailable N sorption and desorption on mineral surfaces; and microbial ON turnover including assimilation, mineralization, and the recycling of microbial products.

Amino acids dominate diffusive nitrogen fluxes across soil depths in acidic tussock tundra.

Organic nitrogen (N) is abundant in soils, but early conceptual frameworks considered it nonessential for plant growth. It is now well recognised that plants have the potential to take up organic N. However, it is still unclear whether plants supplement their N requirements by taking up organic N in situ: at what rate is organic N diffusing towards roots and are plants taking it up? We combined microdialysis with live-root uptake experiments to measure amino acid speciation and diffusion rates towards roots of Eriophorum vaginatum.

Long live A(me)rica! An examination of the interplay between nationalistic-symbolic immortality striving and belief in life after death.

Terror management theory (TMT) proposes that the awareness of our eventual death is at odds with our evolved desire to live and that humans attempt to resolve this psychological conflict by investing in cultural worldviews that grant symbolic or literal immortality. The present studies examine the interplay between symbolic and literal immortality striving. Three studies show that, following a death reminder, only individuals who did not have a route to literal immortality (belief in an afterlife) increased how long they believe their culture (Canada in Studies 1 and 2, the United States in Study 3), will last by thousands of years.

Soybeans Grown with Carbonaceous Nanomaterials Maintain Nitrogen Stoichiometry by Assimilating Soil Nitrogen to Offset Impaired Dinitrogen Fixation.

Engineered nanomaterials (ENMs) can enter agroecosystems because of their widespread use and disposal. Within soil, ENMs may affect legumes and their dinitrogen (N) fixation, which are critical for food supply and N-cycling. Prior research focusing on end point treatment effects has reported that N-fixing symbioses in an important food legume, soybean, can be impaired by ENMs.

Effects of carbonaceous nanomaterials on soil-grown soybeans under combined heat and insect stresses.

Because carbonaceous nanomaterials (CNMs) are expected to enter soils, the exposure implications to crop plants and plant-microbe interactions should be understood. Most investigations have been under ideal growth conditions, yet crops commonly experience abiotic and biotic stresses. Little is known how co-exposure to these environmental stresses and CNMs would cause combined effects on plants.

Limited effects of early snowmelt on plants, decomposers, and soil nutrients in Arctic tundra soils.

In addition to warming temperatures, Arctic ecosystems are responding to climate change with earlier snowmelt and soil thaw. Earlier snowmelt has been examined infrequently in field experiments, and we lack a comprehensive look at belowground responses of the soil biogeochemical system that includes plant roots, decomposers, and soil nutrients. We experimentally advanced the timing of snowmelt in factorial combination with an open-top chamber warming treatment over a 3-year period and evaluated the responses of decomposers and nutrient cycling processes.

Understanding how microbiomes influence the systems they inhabit.

Translating the ever-increasing wealth of information on microbiomes (environment, host or built environment) to advance our understanding of system-level processes is proving to be an exceptional research challenge. One reason for this challenge is that relationships between characteristics of microbiomes and the system-level processes that they influence are often evaluated in the absence of a robust conceptual framework and reported without elucidating the underlying causal mechanisms. The reliance on correlative approaches limits the potential to expand the inference of a single relationship to additional systems and advance the field.

Carbonaceous Nanomaterials Have Higher Effects on Soybean Rhizosphere Prokaryotic Communities During the Reproductive Growth Phase than During Vegetative Growth.

Carbonaceous nanomaterials (CNMs) can affect agricultural soil prokaryotic communities, but how the effects vary with the crop growth stage is unknown. To investigate this, soybean plants were cultivated in soils amended with 0, 0.1, 100, or 1000 mg kg of carbon black, multiwalled carbon nanotubes (MWCNTs), or graphene.

Shrub encroachment in Arctic tundra: Betula nana effects on above- and belowground litter decomposition.

Rapid arctic vegetation change as a result of global warming includes an increase in the cover and biomass of deciduous shrubs. Increases in shrub abundance will result in a proportional increase of shrub litter in the litter community, potentially affecting carbon turnover rates in arctic ecosystems. We investigated the effects of leaf and root litter of a deciduous shrub, Betula nana, on decomposition, by examining species-specific decomposition patterns, as well as effects of Betula litter on the decomposition of other species.

Damage assessment for soybean cultivated in soil with either CeO or ZnO manufactured nanomaterials.

With increasing use, manufactured nanomaterials (MNMs) may enter soils and impact agriculture. Herein, soybean (Glycine max) was grown in soil amended with either nano-CeO (0.1, 0.

Water balance creates a threshold in soil pH at the global scale.

Soil pH regulates the capacity of soils to store and supply nutrients, and thus contributes substantially to controlling productivity in terrestrial ecosystems. However, soil pH is not an independent regulator of soil fertility-rather, it is ultimately controlled by environmental forcing. In particular, small changes in water balance cause a steep transition from alkaline to acid soils across natural climate gradients.

Acidity and organic matter promote abiotic nitric oxide production in drying soils.

Soils are an important source of NO, particularly in dry lands because of trade-offs that develop between biotic and abiotic NO-producing processes when soils dry out. Understanding how drier climates may offset the balance of these trade-offs as soils transition toward more arid states is, therefore, critical to estimating global NO budgets, especially because drylands are expected to increase in size. We measured NO emission pulses after wetting soils from similar lithologies along an altitudinal gradient in the Sierra Nevada, CA, where mean annual precipitation varied from 670 to 1500 mm.

Older Adults and the Fear of Death: The Protective Function of Generativity.

Terror management theory (TMT) posits that cultural worldviews function to allay concerns about human mortality. Preliminary research with older adults has indicated that seniors do not respond to death reminders in the same way as their younger counterparts. The purpose of the current study was to test a developmentally relevant construct that may buffer death anxiety in later life.

Aridity and plant uptake interact to make dryland soils hotspots for nitric oxide (NO) emissions.

Nitric oxide (NO) is an important trace gas and regulator of atmospheric photochemistry. Theory suggests moist soils optimize NO emissions, whereas wet or dry soils constrain them. In drylands, however, NO emissions can be greatest in dry soils and when dry soils are rewet.

Long-Term Effects of Multiwalled Carbon Nanotubes and Graphene on Microbial Communities in Dry Soil.

Little is known about the long-term effects of engineered carbonaceous nanomaterials (ECNMs) on soil microbial communities, especially when compared to possible effects of natural or industrial carbonaceous materials. To address these issues, we exposed dry grassland soil for 1 year to 1 mg g(-1) of either natural nanostructured material (biochar), industrial carbon black, three types of multiwalled carbon nanotubes (MWCNTs), or graphene. Soil microbial biomass was assessed by substrate induced respiration and by extractable DNA.