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Aims: Photodegradation acts as a direct contributor to litter decomposition in arid and semi-arid ecosystems. However, its indirect effects are unclear. Does photodegradation condition litter for subsequent microbial decomposition? Methods: We conditioned litter of Bromus diandrus with ambient or reduced ultraviolet (UV) radiation and three periods of exposure (summer, summer-winter, and 1 year) in a California annual grassland. We then investigated how field UV exposure affected subsequent microbial decomposition of litter using a controlled laboratory incubation. Results: Surprisingly, microbial decomposition was decreased by UV radiation when the exposure occurred during summer but was unaffected by UV treatment for exposure longer than summer. Litter lignin concentrations did not explain these results, as they were not affected by UV radiation for any of the exposure periods. However, for the summer period exposure, UV radiation was associated with decreased litter N concentration, which corresponded with lowered subsequent microbial activity. Conclusions: Our results suggest a new mechanism through which photodegradation interacts with litter microbial decomposition: photodegradation may decrease microbial decomposition through inhibition of microbial N immobilization. Our results imply that solar radiation can interact with litter N cycling dynamics to influence litter decomposition processes.

Litter chemistry is one of the most studied controls on decomposition in terrestrial ecosystems. Solar radiation has been shown to increase litter decomposition rates in arid ecosystems through the process of photodegradation. However, it remains unclear how photodegradation affects litter chemistry, especially the abundance and composition of lignin, which is thought to play a key role in photodegradation. Using two-dimensional nuclear magnetic resonance (2D NMR) spectroscopic methods, we quantified the molecular-level changes in litter chemistry associated with photodegradation. Litter of Bromus diandrus was exposed in the field to two levels of radiation [with and without ultraviolet (UV) wavelengths] and two durations of exposure (2.5 months during summer, and 1 year). Through fiber analysis by sequential digestion, we found that the litter hemicellulose fraction decreased significantly from 31.6 to 24.9 % after 1 year of decomposition. In litter exposed for 1 year, the hemicellulose fraction was significantly lower in litter with UV exposure compared to litter without UV exposure (23.8 vs. 25.9 %). These results indicate that UV photodegradation has a small but significant effect on litter chemistry compared to other decomposition processes. Even though fiber analysis showed no loss of total lignin, 2D NMR analysis demonstrated that UV exposure reduced the major lignin structural units containing β-aryl ether inter-unit linkages by 9 % and decreased the relative abundance of lignin p-hydroxyphenyl units by 20 %. The 2D NMR analysis also revealed that lignin guaiacyl units were preferentially lost after 1 year of decomposition relative to the reference material, but no effects of UV exposure on guaiacyl units were observed. These results suggest that photodegradation causes partial degradation, not necessarily complete breakdown, of lignin structures. Our data also demonstrate that applications of 2D NMR methods are valuable for acquiring detailed information on lignin and polysaccharide chemistry during both biotic and abiotic decomposition processes.

The importance of photodegradation in surface litter decomposition has recently been recognized in arid and semi-arid terrestrial ecosystems, yet its importance in decomposing dense litter and the mechanisms through which it acts remain unclear. We investigated how ultraviolet (UV) radiation exposure and litter position affected decomposition processes in a California annual grassland. In a split-plot design, we exposed Bromus diandrus litter to two levels of UV radiation (UV pass and UV block) at two aboveground locations (at the top, suspended above the litter layer, and at the bottom of the litter layer) for 1 year. We found that UV radiation increased the litter decay constant by 23% at the top location over 1 year, consistent with the occurrence of photodegradation. Surprisingly, UV radiation also increased the litter decay constant by 30% at the bottom location over 1 year. We speculate that photodegradation indirectly increased microbial decomposition through priming effects. Overall, litter in the top location had a 29% higher decay constant than litter in the bottom location. In terms of litter chemistry, exposure to UV radiation increased loss of hemicellulose by 26%, but not loss of lignin. Litter in the bottom location exhibited greater loss of the cell solubles fraction and greater nitrogen immobilization, but lower loss of hemicellulose than litter in the top location. Our results demonstrate that litter position significantly regulates the contribution of photodegradation to overall decomposition, both through direct (top location) and indirect (bottom location) effects. Therefore, better quantification of both direct and indirect effects of photodegradation can greatly improve understanding of biogeochemical cycling in grasslands. © 2013 Springer Science+Business Media New York.

Litter decomposition contributes to one of the largest fluxes of carbon (C) in the terrestrial biosphere and is a primary control on nutrient cycling. The inability of models using climate and litter chemistry to predict decomposition in dry environments has stimulated investigation of non-traditional drivers of decomposition, including photodegradation, the abiotic decomposition of organic matter via exposure to solar radiation. Recent work in this developing field shows that photodegradation may substantially influence terrestrial C fluxes, including abiotic production of carbon dioxide, carbon monoxide and methane, especially in arid and semi-arid regions. Research has also produced contradictory results regarding controls on photodegradation. Here we summarize the state of knowledge about the role of photodegradation in litter decomposition and C cycling and investigate drivers of photodegradation across experiments using a meta-analysis. Overall, increasing litter exposure to solar radiation increased mass loss by 23% with large variation in photodegradation rates among and within ecosystems. This variation was tied to both litter and environmental characteristics. Photodegradation increased with litter C to nitrogen (N) ratio, but not with lignin content, suggesting that we do not yet fully understand the underlying mechanisms. Photodegradation also increased with factors that increased solar radiation exposure (latitude and litter area to mass ratio) and decreased with mean annual precipitation. The impact of photodegradation on C (and potentially N) cycling fundamentally reshapes our thinking of decomposition as a solely biological process and requires that we define the mechanisms driving photodegradation before we can accurately represent photodegradation in global C and N models. © 2012 US Government.

We investigated a possible mechanism underlying observed correlation between net ecosystem carbon dioxide exchange and methane emission. Using the technique of 14C pulse-labeling, we traced the movement of carbon fixed by photosynthesis as it moved through wet sedge and moist tussock tundra plant-soil mesocosms and was emitted as methane to the atmosphere. The 14C tracer provided a definitive way of quantifying the fate of recently fixed carbon. Carbon fixed by photosynthesis was measured as emitted methane from both moist tussock and wet sedge tundra mesocosms within 2 hours after labeling. Integration of time series measurements of methane emission showed that recent photosynthates are an important source of carbon for methane production. Approximately 2% of carbon fixed by photosynthesis at peak growing season was subsequently emitted as methane from moist tussock tundra, and approximately 3% was emitted as methane from wet sedge tundra. Measurements of soil pore water carbon pools demonstrate rapid transfer of 14C from plant carbon to dissolved forms and subsequently to the atmosphere as carbon dioxide or methane.

We conducted a 14C pulse-labeling experiment under field conditions to estimate the contribution of recent photosynthates to methane (CH4) emission in arctic wet sedge tundra dominated by Carex aquatilis and Eriophorum angustifolium. The average CH4 emission rate from plant-soil mesocosms in this study was 0.45 g C m-2 d-1. Carbon assimilated by plants via photosynthesis during pulse-labeling turned over rapidly and appeared as emitted CH4 within 24 h. Integration of flux measurements made over a 2-week period shows that the contribution of recent photosynthates to mid-season CH4 emission is relatively low. Less than 1% of the 14C-labeled carbon dioxide taken up through photosynthesis was emitted as 14CH4 during this study. © 2002 Elsevier Science Ltd. All rights reserved.

To increase our understanding of carbon (C) cycling and storage in soils, we used 14C to trace C from roots into four soil organic matter (SOM) fractions and the movement of soil microbes in arctic wet sedge and tussock tundra. For both tundra types, the proportion of 14C activity in the soil was 6% of the total 14C-CO2 taken up by plants at each of the four harvests conducted 1, 7, 21, and 68 days after labeling. In tussock tundra, we observed rapid microbial transformation of labile C from root exudates into more stable SOM. In wet sedge tundra, there appears to be delayed or indirect microbial use of root exudates. The net amount of 14C label transfered to SOM by the end of the season in both tundra types was approximately equal to the amount transferred to soils 1 day after labeling, suggesting that transfer of 14C tracer from roots to soils continued through the growing season. Overall, C inputs from living roots contributes 24 g C m-2 yr-1 in tussock tundra and 8.8 g C m-2 yr-1 in wet sedge tundra. These results suggest rapid belowground allocation of C by plants and subsequent incorporation of much of this C into storage in the SOM.

Integrated annual methane fluxes measured from 1994 to 1996 at sites representing specific tundra vegetation and land cover types were weighted areally using a vegetation map [Auerbach et al., 1997] for the Kuparuk River basin and subareas. Wetland and open water CH4 emissions dominate the Kuparuk River basin emission estimate. Areal weighting of site fluxes resulted in a regional CH4 emission estimate of 2.09 x 1010 g CH4 yr-1 for the Kuparuk River basin. The global CH4 emission obtained by extending areally weighted annual fluxes from this study to global tundra area (7.34 x 1012 m2) is 5.83 Tg CH4 yr-1. This is about 15% of the Fung et al. [1991] atmospheric tracer model estimate and indicates that the vegetation distribution of the Kuparuk River Basin is not typical of the entire Arctic. Reconciling results from atmospheric tracer model estimates and areally weighted field flux measurements will require accurate high-resolution circumpolar estimates of wetland and open water areas and fluxes. Copyright 1998 by the American Geophysical Union.

Methane flux and below-ground methane profile studies were conducted in a wet meadow vegetation manipulation site at the Toolik Lake Long-Term Ecological Research (LTER) site during the summers of 1995 and 1996. Control plots, moss-removal plots, and sedge-removal plots were studied to determine the role of these vegetation types in wetland methane emission and to study the gas transport mechanism. Methane emission was greatest from plots with intact sedges. Depth distributions of root density collected in 1995 showed a strong inverse relationship to pore water methane concentration. Results on insertion of arrays of gas-permeable silicone rubber tubing into the soil indicate that they are reasonable analogs for the physical process of gaseous diffusion through plants. The observed differences in flux between plots with and without sedges cannot be fully explained by differences in methane production or dissolved organic carbon concentrations in our measurements. Copyright 1998 by the American Geophysical Union.

Within electrical contacts, poor electrical conductivity of lubricants can lead to triboelectric charging, causing electrostatic currents and thermal effects, which accelerate lubrication failure. This study aimed to address these challenges by producing and testing three greases with different base oils: ionic liquid ([Oley][Oleic]), synthetic oil (PAO4), and vegetable oil-based synthetic ester (trimethylolpropane oleate). Each grease was prepared with polytetrafluoroethylene powder as the thickener. The greases were tested using a custom-made tribometer, integrated with a grounded electrical current system, with friction tests conducted with up to a 2 A electrical current flow at a constant voltage supply of 4.5 V. Under triboelectric friction testing, [Oley][Oleic] grease outperformed a commercial perfluoropolyether grease by 27.7% in friction and 16.3% in wear. This grease also showed better performance than formulated lithium grease with extreme pressure additives. The study demonstrates that greases with low interfacial resistance can retain their lubrication capacity under triboelectric conditions. These results indicate that [Oley][Oleic] grease, with its ionic liquid base oil, offers a promising solution for applications involving electrical contacts. This study highlights the potential of using advanced base oils and thickeners to enhance the performance and sustainability of lubricants in demanding environments.

Mixed-mode delamination is one of the common failures of composites which has not been studied under low-impact loading. This paper studies the influence of displacement rate on mixed-mode I/II delamination of unidirectional carbon/epoxy composites. Single leg bending test is performed at displacement rates of 1, 10, 100, and 500 mm/min. Experimental results reveal that the mixed-mode I/II fracture toughness is invariant with the displacement rate. In addition, scanning electron micrographs shows that shear cusps are more obvious at 1, 10, and 100 mm/min. At 500 mm/min, significant matrix debris is noticed. Furthermore, the proposed three-dimensional rate-dependent fracture criterion is found to well predict the fracture toughness. Numerical simulation using cohesive zone model suggests that the lower numerical peak load is due to lower damage dissipated energy. In addition, the theoretical and numerical traction-separation responses show significant differences, which is also reflected in the numerical phase angle. This implies that the local mixed-mode ratio is not constant throughout the simulation process.

Vegetable-oil-based biolubricants are an excellent alternative to conventional lubricants. Instead of focusing on novel feedstocks, these biolubricants should be further elucidated based on their fatty acid composition, which influences their tribological properties. Therefore, the study utilises gene expression programming (GEP) to derive a boundary lubricity model for vegetable-oil-derived trimethylolpropane (TMP) esters, considering the fatty acid composition (saturation and monounsaturation levels), load and speed. Neat vegetable oil and blends from seven feedstocks are selected following a wide range of fatty acid profiles to synthesise TMP esters using a two-stage transesterification process. The TMP esters are spin-coated on wear discs that are subsequently rotated against a ball using a purpose-built tribometer. The frictional performance of the TMP esters with balanced saturation and monounsaturation levels of fatty acid are measured to improve it at higher speeds. The GEP model is statistically evaluated by adopting the friction data, a showing good generalisation and predictability capability. The model demonstrates that friction decreases with increasing saturation levels of the TMP ester. The GEP model for vegetable oil TMP esters allows for the tribological performance prediction of TMP esters following the fatty acid profile, providing a platform to optimise such biolubricant for desired applications.

This study investigates the quasi-static axial crushing tests of eco-hybrid composites based on flax and E-glass fibres strengthened with polyester resin. Five different configurations of self-supporting webs were fabricated to investigate the crushing behaviours of this eco-hybrid composite with different stacking sequences based on intercalation and sandwich-like sequences. The effect of different open-section web profiles was also investigated. The results were plotted in load-displacement curves and the specific energy absorption (SEA), as well as the crushing force efficiency (CFE), were calculated to evaluate the crushing response of each configuration. The test results verified the crushing mechanisms related to the energy absorption depending on the stacking sequence as well as the frontal profile. In this study, all specimens with the intercalation stacking sequence have achieved higher SEA and CFE than specimens with a sandwich-like stacking sequence. In terms of the frontal profile, the sine wave hat shape had the highest CFE, up to 80% compared to other web profiles. Thus, it demonstrated the capability of a sine wave hat-shape eco-composite based on flax fibre to be applied as a crashworthy material.

The role of Na+-K+-ATPase in increasing the aerobic glycolysis in skeletal muscles has been studied. The effects of epinephrine and amylin on the Na+-K+ pump activity has also been examined. Glycolysis was correlated with the Na+-K+-ATPase activity in resting rat digitorum longus and soleus muscles incubated at 30 degrees C. Results indicate that increasing amounts of epinephrine and amylin increased lactate production three to four times but decreased the intracellular Na+-to-K+ ratio. Glycolysis was suppressed by as much as 70% by ouabain in muscles exposed to epinephrine at high concentrations.

Accurately predicting frictional performance of lubrication systems requires mathematical predictive tools with reliable lubricant shear-related input parameters, which might not be easily accessible. Therefore, the study proposes a semi-empirical framework to predict accurately the friction performance of lubricant systems operating across a wide range of lubricant regimes. The semi-analytical framework integrates laboratory-scale experimental measurements from a pin-on-disk tribometer with a unified numerical iterative scheme. The numerical scheme couples the effect of hydrodynamic pressure generated from the lubricant and interacting asperity pressure, essential along the mixed lubrication regime. The lubricant viscosity-pressure coefficient is determined using a free-volume approach, requiring only the lubricant viscosity-temperature relation as the input. The simulated rough surface contact shows transition in lubricant regimes, from the boundary to the elastohydrodynamic lubrication regime with increasing sliding velocity. Through correlation with pin-on-disk frictional measurements, the slope of the limiting shear stress-pressure relation γ and the pressure coefficient of boundary shear strength m for the studied engine lubricants are determined. Thus, the proposed approach presents an effective and robust semi-empirical framework to determine shear properties of fully-formulated engine lubricants. These parameters are essential for application in mathematical tools to predict more accurately the frictional performance of lubrication systems operating across a wide range of lubrication regimes.

Bacterial sepsis is frequently accompanied by increased blood concentration of lactic acid, which traditionally is attributed to poor tissue perfusion, hypoxia and anaerobic glycolysis. Therapy aimed at improving oxygen delivery to tissues often does not correct the hyperlactatemia, suggesting that high blood lactate in sepsis is not due to hypoxia. Various tissues, including skeletal muscle, demonstrate increased lactate production under well-oxygenated conditions when the activity of the Na+–K+ ATPase is stimulated. Although both muscle Na+–K+ ATPase activity and muscle plasma membrane content of Na+, K+-ATPase subunits are increased in sepsis, no studies in vivo have demonstrated correlation between lactate production and changes in intracellular Na+ and K+ resulting from increased Na+–K+ pump activity in sepsis. Plasma concentrations of lactate and epinephrine, a known stimulator of the Na+–K+ pump, were increased in rats made septic by E. coli injection. Muscle lactate content was significantly increased in septic rats, although muscle ATP and phosphocreatine remained normal, suggesting oxygen delivery remained adequate for mitochondrial energy metabolism. In septic rats, muscle intracellular ratio of Na+:K+ was significantly reduced, indicating increased Na+–K+ pump activity. These data thus demonstrate that increased muscle lactate during sepsis correlates with evidence of elevated muscle Na+–K+ ATPase activity, but not with evidence of impaired oxidative metabolism. This study also further supports a role for epinephrine in this process. [Copyright &y& Elsevier]

Solar radiation in general and UV radiation in particular have been recognized to stimulate plant litter decomposition through photochemical mineralization of organic molecules such as lignin and through facilitation of microbial decomposition in dryland ecosystems. However, little is known about how photodegradation may influence decomposition in other ecosystems not subject to moisture limitations and under what conditions photodegradation may be favored. Decomposition in humid tropical ecosystems is a complex process, and it can be influenced by a number of environmental factors that are distinct from arid and semi-arid ecosystems. To assess the mechanisms underlying photodegradation by ultraviolet B (UV-B) radiation in a humid tropical ecosystem, we designed a 300-day field experiment in a tropical site in Brazil with high levels of annual precipitation, compared to arid ecosystems, and exposed litter to three levels of radiation (full sun, UV-B removed, and shade) combined with a biocide treatment. Results show that after nearly one year of exposure, the microbial biomass was not affected by UV-B incidence, and this effect has not yet been fully understood for tropical ecosystems. Modeled using an exponential deceleration equation, the removal of UV-B radiation decelerated the plant litter decomposition rate for the control conditions by 21% compared to litter exposed to full sun. Interestingly, shaded litter exhibited similar mass loss compared to litter exposed to full sun. Furthermore, differences in the decay constant among radiation treatments due to the UV-B effect were independent of lignin loss. Overall, our study suggests that UV-B radiation contributed to plant litter decomposition through carbon losses but had no discernible effect on nitrogen, lignin, or cellulose loss specifically. Importantly, our results demonstrate that photodegradation occurs under humid tropical conditions, and further studies are necessary to examine the mechanisms of carbon loss., Competing Interests: Declaration of competing interest The authors have no competing interests to declare., (Copyright © 2020. Published by Elsevier B.V.)

Solar radiation plays an important role in carbon cycling by increasing the decomposition rates of plant litter and soil organic matter (i.e. photodegradation). Previous work suggests that exposure to radiation can facilitate microbial decomposition of litter by altering litter chemistry and consequently litter degradability (i.e. photopriming). However, it remains unclear to what extent photopriming contributes to litter decomposition processes and on what timescale photopriming operates. We conducted laboratory experiments to compare the effects of UV photopriming at two temporal scales (months versus days). In one experiment, we found that four months of UV exposure induced a significant but small (3-4%) mass loss in two of three litter species commonly found in California oak savanna; however, UV exposure did not alter litter degradability as measured by microbial respiration in an incubation experiment. We also found that UV exposure had limited effects on lignin and other cell wall structures, but one month of microbial decomposition (in absence of UV exposure) significantly reduced lignin β-aryl ether inter-unit linkages and acetylated xylans. These results indicate that abiotic photodegradation alone was ineffective at breaking down lignin. In another experiment, litter of a common grass was exposed to either alternating UV radiation and dark conditions or constant darkness for 128days. We found that the alternating UV exposure increased litter CO 2 production in both dark and UV phases over that observed in constant darkness. This led to a 35% greater release of CO 2 from the alternating UV exposure treatment between days 65 and 128 of the experiment. These results demonstrate that alternating UV exposure with dark conditions is key to enabling photopriming on a timescale of days. Overall, we identify short-term photopriming as a novel mechanism behind photodegradation. Our results also challenge the conventional hypothesis that abiotic processes are primarily responsible for degrading lignin during photodegradation., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Fog-drip to the soil is the most obvious contribution of fog to the water budget of an ecosystem, but several studies provide convincing evidence that foliar absorption of fog water through leaf wetting events is also possible. The focus of our research was to assess the relative importance of fog drip and fog immersion (foliar wetting) on leaf gas-exchange rates and photosynthetic capacity of a coastal pine species, Bishop pine (Pinus muricata D.Don), a drought-sensitive species restricted to the fog belt of coastal California and offshore islands. In a controlled experiment, we manipulated fog water inputs to potted Bishop pine saplings during a 3 week dry-down period. Ten saplings were randomly assigned one of two fog treatments: (1) fog drip to the soil and canopy fog immersion, or (2) fog immersion alone. Five saplings were assigned the 'control' group and received no fog water inputs. We found that fog immersion alone significantly increased carbon assimilation rates and photosynthetic capacity of saplings as soil moisture declined compared with those that received no fog at all. The highest carbon assimilation rates were observed in saplings that also received fog drip. Soil moisture was 40% higher in the fog immersion compared with the control group during the dry-down, indicating a reduced demand for soil water in saplings that had only leaves wetted by canopy interception of fog. Leaf-level physiology is more strongly enhanced by fog drip compared with fog immersion, although the results of this study provide evidence that foliar absorption is a viable mechanism by which Bishop pines use fog water and that it can enhance instantaneous plant carbon gain and potentially whole plant productivity.

Fog water inputs can offset seasonal drought in the Mediterranean climate of coastal California and may be critical to the persistence of many endemic plant species. The ability to predict plant species response to potential changes in the fog regime hinges on understanding the ways that fog can impact plant physiological function across life stages. Our study uses a direct metric of water status, namely plant water potential, to understand differential responses of adult versus sapling trees to seasonal drought and fog water inputs. We place these measurements within a water balance framework that incorporates the varying climatic and soil property impacts on water budgets and deficit. We conducted our study at a coastal and an inland site within the largest stand of the regionally endemic bishop pine (Pinus muricata D. Don) on Santa Cruz Island. Our results show conclusively that summer drought negatively affects the water status of sapling more than adult trees and that sapling trees are also more responsive to changes in shallow soil moisture inputs from fog water deposition. Moreover, between the beginning and end of a large, late-season fog drip event, water status increased more for saplings than for adults. Relative to non-foggy conditions, we found that fog water reduces modeled peak water deficit by 80 and 70 % at the inland and coastal sites, respectively. Results from our study inform mechanistically based predictions of how population dynamics of this and other coastal species may be affected by a warmer, drier, and potentially less foggy future.

Rapid worldwide urbanization calls for a better understanding of the biogeochemical cycling of those macroelements that have large environmental impacts in cities. This study, part of the Twin Cities Household Ecosystem Project, quantified fluxes of carbon (C), nitrogen (N), and phosphorus (P) at the scale of individual households in the Minneapolis-Saint Paul metropolitan area in Minnesota, USA. We estimated input and output fluxes associated with several components of household activities including air and motor vehicle travel, food consumption, home energy use, landscape, pets, and paper and plastic use for 360 owner-occupied, stand-alone households. A few component fluxes dominated total input fluxes of elements. For instance, air and motor vehicle transportation, together with home energy use, accounted for 85% of total C consumption and emissions. All total and component fluxes were skewed to varying degrees, suggesting that policies targeting disproportionately high fluxes could be an effective and efficient way to reduce pollution. For example, 20% of households contributed 75% of air travel emissions and 40% of motor vehicle emissions. Home energy use was more nearly normally distributed. Nitrogen fluxes were dominated by human diet and lawn fertilizer applications, which together accounted for 65% of total household N inputs. The majority of P inputs were associated with human diet, use of detergents, and pet food. A large portion of the variation among household fluxes of C, N, and P was related to a few biophysical variables. A better understanding of the biophysical, demographic, and behavioral drivers of household activities that contribute to C, N, and P fluxes is pivotal for developing accurate urban biogeochemical models and for informing policies aimed at reducing sources of pollution in urban ecosystems.

Litter decomposition provides the primary source of mineral nitrogen (N) for biological activity in most terrestrial ecosystems. A 10-year decomposition experiment in 21 sites from seven biomes found that net N release from leaf litter is dominantly driven by the initial tissue N concentration and mass remaining regardless of climate, edaphic conditions, or biota. Arid grasslands exposed to high ultraviolet radiation were an exception, where net N release was insensitive to initial N. Roots released N linearly with decomposition and exhibited little net N immobilization. We suggest that fundamental constraints on decomposer physiologies lead to predictable global-scale patterns in net N release during decomposition.

Large-scale gene expression studies provide significant insight into genes differentially regulated in disease processes such as cancer. However, these investigations offer limited understanding of multisystem, multicellular diseases such as atherosclerosis. A systems biology approach that accounts for gene interactions, incorporates nontranscriptionally regulated genes, and integrates prior knowledge offers many advantages. We performed a comprehensive gene level assessment of coronary atherosclerosis using 51 coronary artery segments isolated from the explanted hearts of 22 cardiac transplant patients. After histological grading of vascular segments according to American Heart Association guidelines, isolated RNA was hybridized onto a customized 22-K oligonucleotide microarray, and significance analysis of microarrays and gene ontology analyses were performed to identify significant gene expression profiles. Our studies revealed that loss of differentiated smooth muscle cell gene expression is the primary expression signature of disease progression in atherosclerosis. Furthermore, we provide insight into the severe form of coronary artery disease associated with diabetes, reporting an overabundance of immune and inflammatory signals in diabetics. We present a novel approach to pathway development based on connectivity, determined by language parsing of the published literature, and ranking, determined by the significance of differentially regulated genes in the network. In doing this, we identify highly connected "nexus" genes that are attractive candidates for therapeutic targeting and followup studies. Our use of pathway techniques to study atherosclerosis as an integrated network of gene interactions expands on traditional microarray analysis methods and emphasizes the significant advantages of a systems-based approach to analyzing complex disease.

The propensity for developing atherosclerosis is dependent on underlying genetic risk and varies as a function of age and exposure to environmental risk factors. Employing three mouse models with different disease susceptibility, two diets, and a longitudinal experimental design, it was possible to manipulate each of these factors to focus analysis on genes most likely to have a specific disease-related function. To identify differences in longitudinal gene expression patterns of atherosclerosis, we have developed and employed a statistical algorithm that relies on generalized regression and permutation analysis. Comprehensive annotation of the array with ontology and pathway terms has allowed rigorous identification of molecular and biological processes that underlie disease pathophysiology. The repertoire of atherosclerosis-related immunomodulatory genes has been extended, and additional fundamental pathways have been identified. This highly disease-specific group of mouse genes was combined with an extensive human coronary artery data set to identify a shared group of genes differentially regulated among atherosclerotic tissues from different species and different vascular beds. A small core subset of these differentially regulated genes was sufficient to accurately classify various stages of the disease in mouse. The same gene subset was also found to accurately classify human coronary lesion severity. In addition, this classifier gene set was able to distinguish with high accuracy atherectomy specimens from native coronary artery disease vs. those collected from in-stent restenosis lesions, thus identifying molecular differences between these two processes. These studies significantly focus efforts aimed at identifying central gene regulatory pathways that mediate atherosclerotic disease, and the identification of classification gene sets offers unique insights into potential diagnostic and therapeutic strategies in atherosclerotic disease.

Mesodermal and epidermal precursor cells undergo phenotypic changes during differentiation to the smooth muscle cell (SMC) lineage that are relevant to pathophysiological processes in the adult. Molecular mechanisms that underlie lineage determination and terminal differentiation of this cell type have received much attention, but the genetic program that regulates these processes has not been fully defined. Study of SMC differentiation has been facilitated by development of the P19-derived A404 embryonal cell line, which differentiates toward this lineage in the presence of retinoic acid and allows selection for cells adopting a SMC fate through a differentiation-specific drug marker. We sought to define global alterations in gene expression by studying A404 cells during SMC differentiation with oligonucleotide microarray transcriptional profiling. Using an in situ 60-mer array platform with more than 20,000 mouse genes derived from the National Institute on Aging clone set, we identified 2,739 genes that were significantly upregulated after differentiation was completed (false-detection ratio <1). These genes encode numerous markers known to characterize differentiated SMC, as well as many unknown factors. We further characterized the sequential patterns of gene expression during the differentiation time course, particularly for known transcription factor families, providing new insights into the regulation of the differentiation process. Changes in genes associated with specific biological ontology-based pathways were evaluated, and temporal trends were identified for functional pathways. In addition to confirming the utility of the A404 model, our data provide a large-scale perspective of gene regulation during SMC differentiation.

Levels of UV were manipulated in a native shortgrass steppe using open-sided structures with tops that either passed or blocked wavelengths shorter than approximately 370 nm. Precipitation was controlled to create a drought or a very wet year. Subplots were either nondefoliated or defoliated to simulate grazing by livestock, which is the primary land use. Plant community productivity and forage quality were assessed in response to the two climate change variables (UV, precipitation) and grazing stress. Productivity and seasonal standing biomass of the dominant grass species were negatively affected by passing versus blocking UV, but only in the dry year. Another species was negatively affected by passing UV in the wet year, indicating the potential for future shifts in species composition. Forage quality for ruminants increased when UV was passed compared with blocked, as determined by in vitro digestible dry matter, depending on species and precipitation. Nitrogen concentrations and soluble and fiber components of vegetation also displayed some UV effects, but they were generally small and depended on species, season or amount of precipitation (or all). Grazing treatment had large positive effects on current-year productivity only in the wet year and some small positive effects on quality in both wet and dry years. Interactions between UV and grazing treatment were not observed.

Background: Apelin is among the most potent stimulators of cardiac contractility known. However, no physiological or pathological role for apelin-angiotensin receptor-like 1 (APJ) signaling has ever been described., Methods and Results: We performed transcriptional profiling using a spotted cDNA microarray with 12 814 unique clones on paired samples of left ventricle obtained before and after placement of a left ventricular assist device in 11 patients. The significance analysis of microarrays and a novel rank consistency score designed to exploit the paired structure of the data confirmed that natriuretic peptides were among the most significantly downregulated genes after offloading. The most significantly upregulated gene was the G-protein-coupled receptor APJ, the specific receptor for apelin. We demonstrate here using immunoassay and immunohistochemical techniques that apelin is localized primarily in the endothelium of the coronary arteries and is found at a higher concentration in cardiac tissue after mechanical offloading. These findings imply an important paracrine signaling pathway in the heart. We additionally extend the clinical significance of this work by reporting for the first time circulating human apelin levels and demonstrating increases in the plasma level of apelin in patients with left ventricular dysfunction., Conclusions: The apelin-APJ signaling pathway emerges as an important novel mediator of cardiovascular control.

In 1973, the United States Congress enacted legislation requiring physicians to initiate Peer Review Organizations to monitor utilization and quality of hospital and physician services in the federally funded Medicare program. A hardly noticed provision of the statute intimated the desirability of formulating guidelines for medical treatment. What was originally intended to simplify and universalize general standards by which quality of care could be objectively measured has more recently escalated into formalized projects, subsidized by government, to create "practice parameters". The impetus to define clinical conditions and methods of treatment for specific medical conditions (practice parameters) and standards of practice to avoid or defend malpractice claims (risk management protocols) are part of the movement in the United States for tort reform. If the vague "reasonable man" standard of care in negligence law can be supplanted by a scientifically developed, particularized medical practice standard, it is anticipated that spurious claims and defensive medical practice will be discouraged, quality improved, iatrogenic injury and malpractice litigation diminished. Many U.S. states undertook tort reform in the last decade. A few have embarked on medical-legal reform. One state is conducting a five-year medical liability project that calls for the development of practice parameters and risk management protocols in four medical specialties. The parameters will have the effect of law and may be introduced as evidence in medical malpractice trials. How the parameters are established, their effect on the strategies of litigation, the resultant trial problems in the introduction of evidence and in the burden of proof and their potential for acceptance by a significant number of jurisdictions-are the issues to be explored in this paper.