In vivo micro-CT imaging of liver lesions in small animal models

Three-dimensional micro computed tomography (microCT) offers the opportunity to capture images liver structures and lesions in mice with a high spatial resolution. Non-invasive microCT allows for accurate calculation of vessel tortuosity and density, as well as liver lesion volume and distribution. Longitudinal monitoring of liver lesions is also possible. However, distinguishing liver lesions from variations within a normal liver is impossible by microCT without the use of liver- or tumor-specific contrast-enhancing agents. The combination of microCT for morphologic imaging with functional imaging, such as positron emission tomography (PET) or single photon emission tomography (SPECT), offers the opportunity for better abdominal imaging and assessment of structure discrepancies visible by functional imaging.This paper describes methods of current microCT imaging options for imaging of liver lesions compared to other imaging techniques in small animals.     

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

Biogeochemistry - 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...     

Seasonal and episodic moisture controls on plant and microbial contributions to soil respiration

Moisture inputs drive soil respiration (SR) dynamics in semi-arid and arid ecosystems. However, determining the contributions of root and microbial respiration to SR, and their separate temporal responses to periodic drought and water pulses, remains poorly understood. This study was conducted in a pine forest ecosystem with a Mediterranean-type climate that receives seasonally varying precipitation inputs from both rainfall (in the winter) and fog-drip (primarily in the summer). We used automated SR measurements, radiocarbon SR source partitioning, and a water addition experiment to understand how SR, and its separate root and microbial sources, respond to seasonal and episodic changes in moisture. Seasonal changes in SR were driven by surface soil water content and large changes in root respiration contributions. Superimposed on these seasonal patterns were episodic pulses of precipitation that determined the short-term SR patterns. Warm season precipitation pulses derived from fog-drip, and rainfall following extended dry periods, stimulated the largest SR responses. Microbial respiration dominated these SR responses, increasing within hours, whereas root respiration responded more slowly over days. We conclude that root and microbial respiration sources respond differently in timing and magnitude to both seasonal and episodic moisture inputs. These findings have important implications for the mechanistic representation of SR in models and the response of dry ecosystems to changes in precipitation patterns.     

Influence of shape-memory stent grafts on local aortic compliance

The effect of repair techniques on the biomechanics of the aorta is poorly understood, resulting in significant levels of postoperative complications for patients worldwide. This study presents a computational analysis of the influence of Nitinol-based devices on the biomechanical performance of a healthy patient-specific human aorta. Simulations reveal that Nitinol stent-grafts stretch the artery wall so that collagen is stretched to a straightened high-stiffness configuration. The high-compliance regime (HCR) associated with low diastolic lumen pressure is eliminated, and the artery operates in a low-compliance regime (LCR) throughout the entire cardiac cycle. The slope of the lumen pressure–area curve for the LCR post-implantation is almost identical to that of the native vessel during systole. This negligible change from the native LCR slope occurs because the stent-graft increases its diameter from the crimped configuration during deployment so that it reaches a low-stiffness unloading plateau. The effective radial stiffness of the implant along this unloading plateau is negligible compared to the stiffness of the artery wall. Provided the Nitinol device unloads sufficiently during deployment to the unloading plateau, the degree of oversizing has a negligible effect on the pressure–area response of the vessel, as each device exerts approximately the same radial force, the slope of which is negligible compared to the LCR slope of the native artery. We show that 10% oversizing based on the observed diastolic diameter in the mid descending thoracic aorta results in a complete loss of contact between the device and the wall during systole, which could lead to an endoleak and stent migration. 20% oversizing reaches the Dacron enforced area limit (DEAL) during the pulse pressure and results in an effective zero-compliance in the later portion of systole.

     

Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms

? It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. ? Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of net ecosystem exchange (NEE), an ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. ? We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of ecosystem respiration. ? Ecosystem-level thermal optimality is a newly revealed ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within ecosystems, and has the potential to significantly regulate ecosystem-climate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of ecosystems in changing environments and benchmarking global models.     

A Plasmodium falciparum copper-binding membrane protein with copper transport motifs

Formerly known as a hypoendemic malaria country, the Republic of Djibouti declared the goal of pre-eliminating malaria in 2006. The aim of the present study was to evaluate the prevalence of Plasmodium falciparum, Plasmodium vivax and mixed infections in the Djiboutian population by using serological tools and to identify potential determinants of the disease and hotspots of malaria transmission within the country. The prevalence of P. falciparum and P. vivax within the districts of the capital city and the rest of the Republic of Djibouti were assessed using 13 and 2 serological markers, respectively. The relationship between the immune humeral response to P. falciparum and P. vivax and variables such as age, gender, wealth status, urbanism, educational level, distance to rivers/lakes, living area, having fever in the last month, and staying in a malaria-endemic country more than one year was estimated and analysed by questionnaires administered to 1910 Djiboutians. Multivariate ordinal logistic regression models of the immune humeral response were obtained for P. falciparum and P. vivax. The P. falciparum and P. vivax seroprevalence rates were 31.5%, CI95% [29.4-33.7] and 17.5%, CI95% [15.8-19.3], respectively. Protective effects against P. falciparum and P. vivax were female gender, educational level, and never having visited a malaria-endemic area for more than one year. For P. falciparum only, a protective effect was observed for not having a fever in the last month, living more than 1.5 km away from lakes and rivers, and younger ages. This is the first study that assessed the seroprevalence of P. vivax in the Republic of Djibouti. It is necessary to improve knowledge of this pathogen in order to create an effective elimination programme. As supported by recent observations on the subject, the Republic of Djibouti has probably demonstrated a real decrease in the transmission of P. falciparum in the past seven years, which should encourage authorities to improve efforts toward elimination.     

Integration of Process-based Soil Respiration Models with Whole-Ecosystem CO2 Measurements

We integrated soil models with an established ecosystem process model (SIPNET, simplified photosynthesis and evapotranspiration model) to investigate the influence of soil processes on modelled values of soil CO₂ fluxes (R _Soil). Model parameters were determined from literature values and a data assimilation routine that used a 7-year record of the net ecosystem exchange of CO₂ and environmental variables collected at a high-elevation subalpine forest (the Niwot Ridge AmeriFlux site). These soil models were subsequently evaluated in how they estimated the seasonal contribution of R _Soil to total ecosystem respiration (TER) and the seasonal contribution of root respiration (R _Root) to R _Soil. Additionally, these soil models were compared to data assimilation output of linear models of soil heterotrophic respiration. Explicit modelling of root dynamics led to better agreement with literature values of the contribution of R _Soil to TER. Estimates of R _Soil/TER when root dynamics were considered ranged from 0.3 to 0.6; without modelling root biomass dynamics these values were 0.1–0.3. Hence, we conclude that modelling of root biomass dynamics is critically important to model the R _Soil/TER ratio correctly. When soil heterotrophic respiration was dependent on linear functions of temperature and moisture independent of soil carbon pool size, worse model-data fits were produced. Adding additional complexity to the soil pool marginally improved the model-data fit from the base model, but issues remained. The soil models were not successful in modelling R _Root/R _Soil. This is partially attributable to estimated turnover parameters of soil carbon pools not agreeing with expected values from literature and being poorly constrained by the parameter estimation routine. We conclude that net ecosystem exchange of CO₂ alone cannot constrain specific rhizospheric and microbial components of soil respiration. Reasons for this include inability of the data assimilation routine to constrain soil parameters using ecosystem CO₂ flux measurements and not considering the effect of other resource limitations (for example, nitrogen) on the microbe biomass. Future data assimilation studies with these models should include ecosystem-scale measurements of R _Soil in the parameter estimation routine and experimentally determine soil model parameters not constrained by the parameter estimation routine.     

The Influence of Soil Biodiversity on Hydrological Pathways and the Transfer of Materials between Terrestrial and Aquatic Ecosystems

The boundaries between terrestrial and aquatic ecosystems, known as critical transition zones (CTZ), are dynamic interfaces for fluxes of water, sediment, solutes, and gases. Moreover, they often support unique or diverse biotas. Soils, especially those of riparian zones, have not been recognized as CTZ even though they play a critical role in regulating the hydrologic pathways of infiltration and leaching, or runoff and erosion, which can cumulatively affect biogeochemical processes and human livelihoods at landscape scales. In this review, we show how the processes that regulate hydrologic fluxes across and through soil CTZ are influenced by the activities of soil biota. Our message is fourfold. First, there are a variety of ways in which soil biodiversity, in terms of richness and dominance, can influence hydrological pathways in soil and thus the transfer of materials from terrestrial to aquatic ecosystems. Second, the influence of soil organisms on these hydrological pathways is very much interlinked with other environmental, soil biophysical, and vegetation factors that operate at different spatial and temporal scales. Third, we propose that the influence of soil biodiversity on hydrological pathways is most apparent (or identifiable), relative to other factors, in situations that lead to the dominance of certain organisms, such as larger fauna. Fourth, soils are buffered against environmental change by biophysical properties that have developed over long periods of time. Therefore, the effects of changes in soil biodiversity on hydrological processes at the ecosystem scale might be delayed and become most apparent in the long term. Received 25 February 2000; accepted 11 December 2000.     

Respiration from coarse wood litter in central Amazon forests

Respiration from coarse litter (trunks and large branches >10 cm diameter) was studied in central Amazon forests. Respiration ratesvaried over almost two orders of magnitude (1.003–0.014 µg Cg^–1 C min^–1, n = 61), and weresignificantly correlated with wood density (r² _adj= 0.42), and moisture content (r² _adj= 0.39). Additional samples taken from a nearby pasture indicatedthat wood moisture content was the most important factor controllingrespiration rates across sites (r² _adj =0.65). Based on average coarse litter wood density and moisture content,the mean long-term carbon loss rate due to respiration was estimated tobe 0.13 yr^–1 (range of 95% prediction interval(PI) = 0.11–0.15 yr^–1). Comparing meanrespiration rate with mean mass loss (decomposition) rate from aprevious study, respiratory emissions to the atmosphere from coarselitter were predicted to be 76% (95% PI =65–88%) of total carbon loss, or about 1.9 (95% PI= 1.6–2.2) Mg C ha^–1yr^–1. Optimum respiration activity corresponded toabout 2.5 g H₂O g^–1 dry wood, and severelyrestricted respiration to < 0.5 g H₂O g^–1dry wood. Respiration from coarse litter in central Amazon forests iscomparable in magnitude to decomposing fine surface litter (e.g. leaves,twigs) and is an important carbon cycling component when characterizingheterotrophic respiration budgets and net ecosystem exchange(NEE).