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Terrestrial biosphere models (TBMs) are highly sensitive to model representation of photosynthesis, in particular the parameters maximum carboxylation rate and maximum electron transport rate at 25°C (V

The significance of the development of nodular liver lesions in rodents following the administration of test agents raises several questions which could be placed in one of two general categories: diagnostic and interpretational. From a diagnostic point of view, the proper classification of liver tumors into a benign and malignant category has to be based on the direct correlation between the morphology and the biologic behavior of the lesions. Therefore, extreme care should be taken to separate the malignant tumors from the benign and the benign neoplasia from the hyperplasia. The substitution of the term “neoplastic nodule” for hyperplastic nodule in rats is misleading. Most of these nodules, when induced under special experimental conditions, may regress or remodel and thus they are not neoplastic in nature. Chronic carcinogenicity bioassays should include “stop” type of treatment leaving enough of the observational time to establish the fate of induced nodular lesions. The induction of histochemically changed foci can serve only as an indication of potential hepatocarcinogenicity and should not be equated with the induction of bona fide cancer. The biologic interpretation of nodular liver lesions, especially in mice, needs further scrutiny because these lesions have a tendency to develop spontaneously with high incidence in some strains. This characteristic then raises the question as to the mechanism by which various agents augment and/or accelerate the development of such tumors. Is this action primarily promoting or initiating in nature or does it represent the induction of tumors de novo? The answer to this dilemma may have a decisive bearing on carcinogenic risk assessment and the type of regulatory action, since the promoting agents possess a threshold effect and the promoted changes may regress following withdrawal of treatment. The interpretation of hepatocarcinogenesis is further complicated by the fact that several factors, such as sex hormonal environment, increased mitotic activity following an excessive loss of parenchymal cells, degree of caloric intake, enzymatic complement, and animals’ age at the time of the exposure to a test agent, may influence the outcome of liver tumor development by modulating “initiation” and/or “promotion” of carcinogenesis. Broad fluctuation in the historic incidence of liver tumors further compounds the complexity of the proper bioassay interpretation. The specifically designed experiments may have the objective to explore predominantly the initiating or promoting effects of the agent. Such protocols should be used whenever necessary to differentiate between these two mechanisms of action. In the Caucasians, the “spontaneous” development of the primary hepatocellular tumors is rare. The majority of these tumors are malignant and rapidly fatal. According to some human pathologists, the benign variety of liver tumors is rare and it does not represent necessarily a premalignant stage in tumor development. Carcinoma of the liver may occur in infancy, especially in males before the age of 2 years. This suggests a genetic causation or carcinogenic exposure in utero. One of the geographic factors which significantly enhances the incidence of hepatocellular carcinoma in humans is exposure to aflatoxin B1 which is apparently potentiated by concurrent liver cirrhosis. Because many more agents have been found to be hepatocarcinogenic in mice and rats than in men, a question arises as to the direct relevance of rodent studies to humans. A balanced assessment of the carcinogenicity of the agent could only be reached in considering both the pharmacokinetics and the development of malignant neoplasia in other organs. In the case of positive carcinogenicity assessment, the outcome of the mutagenicity bioassays can suggest genic (genotoxic) or paragenic (epigenetic) mode of action in mammalian systems.

The few prethaw observations of tundra carbon fluxes suggest that there may be large spring releases, but little is known about the scale and underlying mechanisms of this phenomenon. To address these questions, we combined ecosystem eddy flux measurements from two towers near Barrow, Alaska, with mechanistic soil-core thawing experiment. During a 2 week period prior to snowmelt in 2014, large fluxes were measured, reducing net summer uptake of CO2 by 46% and adding 6% to cumulative CH4 emissions. Emission pulses were linked to unique rain-on-snow events enhancing soil cracking. Controlled laboratory experiment revealed that as surface ice thaws, an immediate, large pulse of trapped gases is emitted. These results suggest that the Arctic CO2 and CH4 spring pulse is a delayed release of biogenic gas production from the previous fall and that the pulse can be large enough to offset a significant fraction of the moderate Arctic tundra carbon sink.

We consider a convection-diffusion model with linear fractional diffusion in the sub-critical range. We prove that the large time asymptotic behavior of the solution is given by the unique entropy solution of the convective part of the equation. The proof is based on suitable a-priori estimates, among which proving an Oleinik type inequality plays a key role.

© 2017 Yang, Yang, Van Nostrand, Zhou, Fang, Qi, Liu, Wullschleger, Liang, Graham, Yang and Gu. Microbial decomposition of soil organic carbon (SOC) in thawing Arctic permafrost is important in determining greenhouse gas feedbacks of tundra ecosystems to climate. However, the changes in microbial community structure during SOC decomposition are poorly known. Here we examine these changes using frozen soils from Barrow, Alaska, USA, in anoxic microcosm incubation at -2 and 8°C for 122 days. The functional gene array GeoChip was used to determine microbial community structure and the functional genes associated with SOC degradation, methanogenesis, and Fe(III) reduction. Results show that soil incubation after 122 days at 8°C significantly decreased functional gene abundance (P < 0.05) associated with SOC degradation, fermentation, methanogenesis, and iron cycling, particularly in organic-rich soil. These observations correspond well with decreases in labile SOC content (e.g., reducing sugar and ethanol), methane and CO2 production, and Fe(III) reduction. In contrast, the community functional structure was largely unchanged in the -2°C incubation. Soil type (i.e., organic vs. mineral) and the availability of labile SOC were among the most significant factors impacting microbial community structure. These results demonstrate the important roles of microbial community in SOC degradation and support previous findings that SOC in organic-rich Arctic tundra is highly vulnerable to microbial degradation under warming.

There is wide breadth of root function within ecosystems that should be considered when modeling the terrestrial biosphere. Root structure and function are closely associated with control of plant water and nutrient uptake from the soil, plant carbon (C) assimilation, partitioning and release to the soils, and control of biogeochemical cycles through interactions within the rhizosphere. Root function is extremely dynamic and dependent on internal plant signals, root traits and morphology, and the physical, chemical and biotic soil environment. While plant roots have significant structural and functional plasticity to changing environmental conditions, their dynamics are noticeably absent from the land component of process-based Earth system models used to simulate global biogeochemical cycling. Their dynamic representation in large-scale models should improve model veracity. Here, we describe current root inclusion in models across scales, ranging from mechanistic processes of single roots to parameterized root processes operating at the landscape scale. With this foundation we discuss how existing and future root functional knowledge, new data compilation efforts, and novel modeling platforms can be leveraged to enhance root functionality in large-scale terrestrial biosphere models by improving parameterization within models, and introducing new components such as dynamic root distribution and root functional traits linked to resource extraction.

Plant roots play a critical role in ecosystem function in arctic tundra, but root dynamics in these ecosystems are poorly understood. To address this knowledge gap, we synthesized available literature on tundra roots, including their distribution, dynamics and contribution to ecosystem carbon and nutrient fluxes, and highlighted key aspects of their representation in terrestrial biosphere models. Across all tundra ecosystems, belowground plant biomass exceeded aboveground biomass, with the exception of polar desert tundra. Roots were shallowly distributed in the thin layer of soil that thaws annually, and were often found in surface organic soil horizons. Root traits - including distribution, chemistry, anatomy and resource partitioning - play an important role in controlling plant species competition, and therefore ecosystem carbon and nutrient fluxes, under changing climatic conditions, but have only been quantified for a small fraction of tundra plants. Further, the annual production and mortality of fine roots are key components of ecosystem processes in tundra, but extant data are sparse. Tundra root traits and dynamics should be the focus of future research efforts. Better representation of the dynamics and characteristics of tundra roots will improve the utility of models for the evaluation of the responses of tundra ecosystems to changing environmental conditions.

Properly quantifying evapotranspiration (ET) is a critical step in determining water and energy balances, especially in Arctic landscapes where spatial and temporal heterogeneity in soil water content and inundation is pronounced. Although the eddy covariance technique has gained popularity as an approach for estimating ET at aggregate scales, obtaining ET estimates at finer spatial scales remains problematic. Thus, ET is poorly estimated for highly variable tundra landscapes, despite the importance of this process for parameterization and validation of models. To overcome this methodological limitation, we developed an approach to measure diurnal ET by modifying a LI-8100A (LI-COR, Lincoln, NE, USA), a chamber-based instrument typically used for measuring soil CO2 fluxes. To enable the use of the LI-8100A for ET determinations, a calibration method was designed and implemented through laboratory and independent field measurements in Arctic and semi-arid locations. Once calibrated, the instrument was deployed June–September 2013 for diel measurements of ET on the Arctic coastal plain near Barrow, Alaska, USA. We validated the system by comparison to four adjacent plots measured by a LI-6400-09 soil CO2 flux system that was also calibrated to calculate water vapour flux. In conclusion, we determined that with calibration, the LI-8100A can make long-term, high-frequency measurements of ET, even in low flux, continuous-permafrost landscapes. This technique provides an opportunity to assess fine-scale ET and its topographic controls across low-centre and high-centre polygons and to rigorously compare such measurements with aggregate fluxes obtained with eddy covariance. Copyright © 2014 John Wiley & Sons, Ltd.

Landscape attributes that vary with microtopography, such as active layer thickness (ALT), are labor intensive and difficult to document effectively through in situ methods at kilometer spatial extents, thus rendering remotely sensed methods desirable. Spatially explicit estimates of ALT can provide critically needed data for parameterization, initialization, and evaluation of Arctic terrestrial models. In this work, we demonstrate a new approach using high-resolution remotely sensed data for estimating centimeter-scale ALT in a 5 km2 area of ice-wedge polygon terrain in Barrow, Alaska. We use a simple regression-based, machine learning data-fusion algorithm that uses topographic and spectral metrics derived from multisensor data (LiDAR and WorldView-2) to estimate ALT (2 m spatial resolution) across the study area. Comparison of the ALT estimates with ground-based measurements, indicates the accuracy (r2 = 0.76, RMSE ±4.4 cm) of the approach. While it is generally accepted that broad climatic variability associated with increasing air temperature will govern the regional averages of ALT, consistent with prior studies, our findings using high-resolution LiDAR and WorldView-2 data, show that smaller-scale variability in ALT is controlled by local eco-hydro-geomorphic factors. This work demonstrates a path forward for mapping ALT at high spatial resolution and across sufficiently large regions for improved understanding and predictions of coupled dynamics among permafrost, hydrology, and land-surface processes from readily available remote sensing data.

Background Earth system models describe the physical, chemical and biological processes that govern our global climate. While it is difficult to single out one component as being more important than another in these sophisticated models, terrestrial vegetation is a critical player in the biogeochemical and biophysical dynamics of the Earth system. There is much debate, however, as to how plant diversity and function should be represented in these models. Scope Plant functional types (PFTs) have been adopted by modellers to represent broad groupings of plant species that share similar characteristics (e.g. growth form) and roles (e.g. photosynthetic pathway) in ecosystem function. In this review, the PFT concept is traced from its origin in the early 1800s to its current use in regional and global dynamic vegetation models (DVMs). Special attention is given to the representation and parameterization of PFTs and to validation and benchmarking of predicted patterns of vegetation distribution in high-latitude ecosystems. These ecosystems are sensitive to changing climate and thus provide a useful test case for model-based simulations of past, current and future distribution of vegetation. Conclusions Models that incorporate the PFT concept predict many of the emerging patterns of vegetation change in tundra and boreal forests, given known processes of tree mortality, treeline migration and shrub expansion. However, representation of above- and especially below-ground traits for specific PFTs continues to be problematic. Potential solutions include developing trait databases and replacing fixed parameters for PFTs with formulations based on trait co-variance and empirical trait-environment relationships. Surprisingly, despite being important to land-atmosphere interactions of carbon, water and energy, PFTs such as moss and lichen are largely absent from DVMs. Close collaboration among those involved in modelling with the disciplines of taxonomy, biogeography, ecology and remote sensing will be required if we are to overcome these and other shortcomings. © 2014 Published by Oxford University Press on behalf of the Annals of Botany Company 2014. This work is written by (a) US Government employee(s) and is in the public domain in the US.

With predicted global changes in temperature and precipitation, drought will increasingly impose a challenge to biomass production. Most of the bioenergy crops have some degree of drought susceptibility as revealed for example through measures of low water-use efficiency (WUE). It is imperative to improve drought tolerance and WUE in bioenergy crops for sustainable biomass production in arid and semi-arid regions. Genetics and functional genomics can play critical roles in generating knowledge to inform and aid genetic improvement for drought tolerance in bioenergy crops. The molecular aspects of drought response have been extensively investigated in model plants like Arabidopsis, yet our understanding of the molecular mechanisms underlying drought tolerance in bioenergy crops is limited. Plants in general exhibit various responses to drought stress depending on species and genotype. A rational strategy for studying drought tolerance in bioenergy crops is to translate the knowledge from model plants relat...

Enhanced root-exudate inputs can stimulate decomposition of soil carbon (C) by priming soil microbial activity, but the mechanisms controlling the magnitude and direction of the priming effect remain poorly understood. With this study we evaluated how differences in soil C availability affect the impact of simulated root exudate inputs on priming. We conducted a 60-day laboratory incubation with soils collected (60 cm depth) from under six switchgrass (Panicum virgatum) cultivars. Differences in specific root length (SRL) among cultivars were expected to result in small differences in soil C inputs and thereby create small differences in the availability of recent labile soil C; whereas soil depth was expected to create large overall differences in soil C availability. Soil cores from under each cultivar (roots removed) were divided into depth increments of 0–10, 20–30, and 40–60 cm and incubated with addition of either: (1) water or (2) 13C-labeled synthetic root exudates (0.7 mg C/g soil). We measured CO2 respiration throughout the experiment. The natural difference in 13C signature between C3 soils and C4 plants was used to quantify cultivar-induced differences in soil C availability. Amendment with 13C-labeled synthetic root-exudate enabled evaluation of SOC priming. Our experiment produced three main results: (1) switchgrass cultivars differentially influenced soil C availability across the soil profile; (2) small differences in soil C availability derived from recent root C inputs did not affect the impact of exudate-C additions on priming; but (3) priming was greater in soils from shallow depths (relatively high total soil C and high ratio of labile-to-stable C) compared to soils from deep depths (relatively low total soil C and low ratio of labile-to-stable C). These findings suggest that the magnitude of the priming effect is affected, in part, by the ratio of root exudate C inputs to total soil C and that the impact of changes in exudate inputs on the priming of SOC is regulated differently in surface soil compared to subsoil.

For the first time, we report integration of air spacers with FinFET technology at 10nm node dimensions. The benefit of parasitic capacitance reduction by air spacers has been successfully demonstrated both at transistor level (15–25% reduction in overlap capacitance (C OT )) and at ring oscillator level (10–15% reduction in effective capacitance (Cf)). Key process challenges and device implications of integrating air spacers in FinFET are identified. We propose a partial air spacer scheme, in which air spacers are formed only above fin top and sandwiched by two dielectric liners, as a viable option to adopt air spacers in FinFET technology with minimal risks to yield and reliability.

We present a 7nm technology with the tightest contacted poly pitch (CPP) of 44/48nm and metallization pitch of 36nm ever reported in FinFET technology. To overcome optical lithography limits, Extreme Ultraviolet Lithography (EUV) has been introduced for multiple critical levels for the first time. Dual strained channels have been also implemented to enhance mobility for high performance applications.

© 2015 Kole, Muthamilarasan, Henry, Edwards, Sharma, Abberton, Batley, Bentley, Blakeney, Bryant, Cai, Cakir, Cseke, Cockram, de Oliveira, De Pace, Dempewolf, Ellison, Gepts, Greenland, Hall, Hori, Hughes, Humphreys, Iorizzo, Ismail, Marshall, Mayes, Nguyen, Ogbonnaya, Ortiz, Paterson, Simon, Tohme, Tuberosa, Valliyodan, Varshney, Wullschleger, Yano and Prasad. Climate change affects agricultural productivity worldwide. Increased prices of food commodities are the initial indication of drastic edible yield loss, which is expected to increase further due to global warming. This situation has compelled plant scientists to develop climate change-resilient crops, which can withstand broad-spectrum stresses such as drought, heat, cold, salinity, flood, submergence and pests, thus helping to deliver increased productivity. Genomics appears to be a promising tool for deciphering the stress responsiveness of crop species with adaptation traits or in wild relatives toward identifying underlying genes, alleles or quantitative trait loci. Molecular breeding approaches have proven helpful in enhancing the stress adaptation of crop plants, and recent advances in high-throughput sequencing and phenotyping platforms have transformed molecular breeding to genomics-assisted breeding (GAB). In view of this, the present review elaborates the progress and prospects of GAB for improving climate change resilience in crops, which is likely to play an ever increasing role in the effort to ensure global food security.

Here we detail how Atkin and his colleagues compiled a global database (GlobResp) that details rates of leaf dark respiration and associated traits from sites that span Arctic tundra to tropical forests. This compilation builds upon earlier research (Reich et al., 1998; Wright et al., 2006) and was supplemented by recent field campaigns and unpublished data.In keeping with other trait databases, GlobResp provides insights on how physiological traits, especially rates of dark respiration, vary as a function of environment and how that variation can be used to inform terrestrial biosphere models and land surface components of Earth System Models. Although an important component of plant and ecosystem carbon (C) budgets (Wythers et al., 2013), respiration has only limited representation in models. Seen through the eyes of a plant scientist, Atkin et al. (2015) give readers a unique perspective on the climatic controls on respiration, thermal acclimation and evolutionary adaptation of dark respiration, and insights into the covariation of respiration with other leaf traits. We find there is ample evidence that once large databases are compiled, like GlobResp, they can reveal new knowledge of plant function and provide a valuable resource for hypothesis testing and model development.

Laser-induced breakdown spectroscopy (LIBS) along with multivariate analysis was used to differentiate between the total carbon (C), inorganic C, and organic C in a set of 58 different soils from 5 soil orders. A 532 nm laser with 45 mJ of laser power was used to excite the 58 samples of soil and the emission of all the elements present in the soil samples was recorded in a single spectrum with a wide wavelength range of 200–800 nm. The results were compared to the laboratory standard technique, e.g., combustion on a LECO-CN analyzer, to determine the true values for total C, inorganic C, and organic C concentrations. Our objectives were: 1) to determine the characteristic spectra of soils containing different amounts of organic and inorganic C, and 2) to examine the viability of this technique for differentiating between soils that contain predominantly organic and/or inorganic C content for a range of diverse soils. Previous work has shown that LIBS is an accurate and reliable approach to measuring total carbon content of soils, but it remains uncertain whether inorganic and organic forms of carbon can be separated using this approach. Total C and inorganic C exhibited correlation with rock-forming elements such as Al, Si, Fe, Ti, Ca, and Sr, while organic C exhibited minor correlation with these elements and a major correlation with Mg. We calculated a figure of merit (Mg/Ca) based on our results to enable differentiation between inorganic versus organic C. We obtained the LIBS validation prediction for total, inorganic, and organic C to have a coefficient of regression, r2 = 0.91, 0.87, and 0.91 respectively. These examples demonstrate an advance in LIBS-based techniques to distinguish between organic and inorganic C using the full wavelength spectra.

The differential expression and secretion of the neuropeptide kisspeptin from neurons in the arcuate (Arc) and anteroventral periventricular (AVPV) nuclei of the hypothalamus coordinate the temporal release of pituitary gonadotropins that control the female reproductive cycle. However, the molecular basis for this differential regulation is incompletely understood. Here, we report that liver receptor homolog-1 (LRH-1), a member of the nuclear receptor superfamily, is expressed in kisspeptin neurons in the Arc but not in the AVPV in female mice. LRH-1 binds directly to the kisspeptin (Kiss1) promoter and stimulates Kiss1 transcription. Deletion of LRH-1 from kisspeptin neurons in mice decreased Kiss1 expression in the Arc, leading to reduced plasma FSH levels, dysregulated follicle maturation, and prolongation of the estrous cycle. Conversely, overexpression of LRH-1 in kisspeptin neurons increased Arc Kiss1 expression and plasma FSH concentrations. These studies provide a molecular basis for the differential regulation of basal kisspeptin expression in Arc and AVPV neurons and reveal a prominent role for LRH-1 in hypothalamus in regulating the female reproductive axis.

Roots regulate soil carbon (C) input, but fine root decomposition rates and root impacts on soil organic C turnover (SOC) are uncertain. This uncertainty is, partly, caused by the heterogeneity of root systems, which vary in diameter distributions and tissue chemistry. Here, we evaluated how root diameter distributions affect root and SOC decomposition. Roots from eight Panicum virgatum (switchgrass) cultivars were analyzed for root diameter size-class distribution and C:N ratio. Roots from each cultivar were mixed with C 3 soil according to five root diameter treatments: (1) 0–0.5 mm, (2) 0.5–1 mm, (3) 1–2.5 mm, (4) a 1:1:1 mixture of roots from each diameter size class, and (5) a mixture combining diameter classes in proportions representing measured size distributions for each cultivar. All treatments were incubated for 90 days under laboratory conditions. Respired CO 2 was measured throughout and the microbial community structure was measured at termination of the experiment. Carbon-13 isotope techniques were used to partition respiration into root-derived C versus native SOC-derived C. Results indicated: (1) specific root length differed among the cultivars, (2) root decomposition rates within the three size classes varied by cultivar, but were not correlated with cultivar differences in root C:N ratios, (3) root diameter size class affected root and SOC decomposition, and (4) mixing roots of different diameters did not lead to synergistic increases in decomposition. We conclude that intraspecific variation in root architecture is significant and that fine root diameter size class distribution is an important trait for shaping decomposition processes.