On the causes of trends in the seasonal amplitude of atmospheric CO2

No consensus has yet been reached on the major factors driving the observed increase in the seasonal amplitude of atmospheric CO₂ in the northern latitudes. In this study, we used atmospheric CO₂ records from 26 northern hemisphere stations with a temporal coverage longer than 15 years, and an atmospheric transport model prescribed with net biome productivity (NBP) from an ensemble of nine terrestrial ecosystem models, to attribute change in the seasonal amplitude of atmospheric CO₂. We found significant (p < .05) increases in seasonal peak‐to‐trough CO₂ amplitude (AMP_P‐T) at nine stations, and in trough‐to‐peak amplitude (AMP_T‐P) at eight stations over the last three decades. Most of the stations that recorded increasing amplitudes are in Arctic and boreal regions (>50°N), consistent with previous observations that the amplitude increased faster at Barrow (Arctic) than at Mauna Loa (subtropics). The multi‐model ensemble mean (MMEM) shows that the response of ecosystem carbon cycling to rising CO₂ concentration (eCO₂) and climate change are dominant drivers of the increase in AMP_P‐T and AMP_T‐P in the high latitudes. At the Barrow station, the observed increase of AMP_P‐T and AMP_T‐P over the last 33 years is explained by eCO₂ (39% and 42%) almost equally than by climate change (32% and 35%). The increased carbon losses during the months with a net carbon release in response to eCO₂ are associated with higher ecosystem respiration due to the increase in carbon storage caused by eCO₂ during carbon uptake period. Air‐sea CO₂ fluxes (10% for AMP_P‐T and 11% for AMP_T‐P) and the impacts of land‐use change (marginally significant 3% for AMP_P‐T and 4% for AMP_T‐P) also contributed to the CO₂ measured at Barrow, highlighting the role of these factors in regulating seasonal changes in the global carbon cycle.     

Geothermally warmed soils reveal persistent increases in the respiratory costs of soil microbes contributing to substantial C losses

Increasing temperatures can accelerate soil organic matter decomposition and release large amounts of CO₂ to the atmosphere, potentially inducing positive warming feedbacks. Alterations to the temperature sensitivity and physiological functioning of soil microorganisms may play a key role in these carbon (C) losses. Geothermally active areas in Iceland provide stable and continuous soil temperature gradients to test this hypothesis, encompassing the full range of warming scenarios projected by the Intergovernmental Panel on Climate Change for the northern region. We took soils from these geothermal sites 7 years after the onset of warming and incubated them at varying temperatures and substrate availability conditions to detect persistent alterations of microbial physiology to long-term warming. Seven years of continuous warming ranging from 1.8 to 15.9 °C triggered a 8.6–58.0% decrease on the C concentrations in the topsoil (0–10 cm) of these sub-arctic silt-loam Andosols. The sensitivity of microbial respiration to temperature (Q₁₀) was not altered. However, soil microbes showed a persistent increase in their microbial metabolic quotients (microbial respiration per unit of microbial biomass) and a subsequent diminished C retention in biomass. After an initial depletion of labile soil C upon soil warming, increasing energy costs of metabolic maintenance and resource acquisition led to a weaker capacity of C stabilization in the microbial biomass of warmer soils. This mechanism contributes to our understanding of the acclimated response of soil respiration to in situ soil warming at the ecosystem level, despite a lack of acclimation at the physiological level. Persistent increases in the respiratory costs of soil microbes in response to warming constitute a fundamental process that should be incorporated into climate change-C cycling models.     

Smoke aldehyde component influences pulmonary edema.

The pulmonary edema of smoke inhalation is caused by the toxins of smoke and not the heat. We investigated the potential of smoke consisting of carbon in combination with either acrolein or formaldehyde (both common components of smoke) to cause pulmonary edema in anesthetized sheep. Seven animals received acrolein smoke, seven animals received a low-dose formaldehyde smoke, and five animals received a high-dose formaldehyde smoke. Pulmonary arterial pressure, pulmonary capillary wedge pressure, and cardiac output were not affected by smoke in any group. Peak airway pressure increased after acrolein (14 +/- 1 to 21 +/- 2 mmHg; P less than 0.05) and after low- and high-dose formaldehyde (14 +/- 1 to 21 +/- 1 and 20 +/- 1 mmHg, respectively; both P less than 0.05). The partial pressure of O2 in arterial blood fell sharply after acrolein [219 +/- 29 to 86 +/- 9 (SE) Torr; P less than 0.05] but not after formaldehyde. Only acrolein resulted in a rise in lung lymph flow (6.5 +/- 2.2 to 17.9 +/- 2.6 ml/h; P less than 0.05). Lung lymph-to-plasma protein ratio was unchanged for all three groups, but clearance of lymph protein was increased after acrolein. After acrolein, the blood-free extravascular lung water-to-lung dry weight ratio was elevated (P less than 0.05) compared with both low- and high-dose formaldehyde groups (4.8 +/- 0.4 to 3.3 +/- 0.2 and 3.6 +/- 0.2, respectively). Lymph clearance (ng/h) of thromboxane B2, leukotriene B4, and the sulfidopeptide leukotrienes was elevated after acrolein but not formaldehyde.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genome annotation and antimicrobial properties of Bacillus toyonensis VU‐DES13, isolated from the Folsomia candida gut

Antibiotic resistance necessitates the search for new bioactive compounds with novel mechanisms of action. Natural products derived from bacteria and fungi are widely used in the field of medicine and new environments can be explored as sources of antimicrobials. Bacteria associated with springtails have shown high inhibitory activity against pathogens. Here, we characterized a bacterial strain with high potential for antimicrobial activity, isolated from the gut of the springtail Folsomia candida Willem (Collembola: Isotomidae). The strain was characterized using the ‘analytical profile index’ and the ‘minimal inhibitory concentration’ assay to test for antibiotic resistance. Agar overlay and agar disk diffusion assays were used to test the inhibitory activity of the strain and its extract against a variety of pathogens, and reporter assays were used to investigate the mode of action. High‐performance liquid chromatography was used to analyze and fractionate the extract of bacterial culture, followed by additional assays on the fractions. The genome of the strain was screened for presence of antibiotic resistance genes and secondary metabolite gene clusters. The isolate was identified as Bacillus toyonensis Jiménez et al., but it displayed differences in metabolic profile when compared to the type species. The isolate was highly resistant to penicillin and inhibited the growth of a variety of pathogenic microorganisms. Genome analysis revealed an enrichment of resistance genes for β‐lactam antibiotics compared to the type isolate. Also, secondary metabolite clusters involved in the production of siderophores, bacteriocins, and nonribosomal peptide synthetases were identified. In conclusion, a unique Bacillus strain was isolated from the gut of F. candida, for which we provide evidence of inhibitory activity against an array of pathogens. This, coupled with high resistance to penicillin as substantiated by the presence of resistance genes, points to the potential of B. toyonensis VU‐DES13 to provide a new source of antimicrobial compounds.     

Seasonally different response of photosynthetic activity to daytime and night‐time warming in the Northern Hemisphere

Over the last century the Northern Hemisphere has experienced rapid climate warming, but this warming has not been evenly distributed seasonally, as well as diurnally. The implications of such seasonal and diurnal heterogeneous warming on regional and global vegetation photosynthetic activity, however, are still poorly understood. Here, we investigated for different seasons how photosynthetic activity of vegetation correlates with changes in seasonal daytime and night‐time temperature across the Northern Hemisphere (>30°N), using Normalized Difference Vegetation Index (NDVI) data from 1982 to 2011 obtained from the Advanced Very High Resolution Radiometer (AVHRR). Our analysis revealed some striking seasonal differences in the response of NDVI to changes in day‐ vs. night‐time temperatures. For instance, while higher daytime temperature (T_max) is generally associated with higher NDVI values across the boreal zone, the area exhibiting a statistically significant positive correlation between T_max and NDVI is much larger in spring (41% of area in boreal zone – total area 12.6 × 10⁶ km²) than in summer and autumn (14% and 9%, respectively). In contrast to the predominantly positive response of boreal ecosystems to changes in T_max, increases in T_max tended to negatively influence vegetation growth in temperate dry regions, particularly during summer. Changes in night‐time temperature (T_min) correlated negatively with autumnal NDVI in most of the Northern Hemisphere, but had a positive effect on spring and summer NDVI in most temperate regions (e.g., Central North America and Central Asia). Such divergent covariance between the photosynthetic activity of Northern Hemispheric vegetation and day‐ and night‐time temperature changes among different seasons and climate zones suggests a changing dominance of ecophysiological processes across time and space. Understanding the seasonally different responses of vegetation photosynthetic activity to diurnal temperature changes, which have not been captured by current land surface models, is important for improving the performance of next generation regional and global coupled vegetation‐climate models.     

The likely impact of elevated [CO2], nitrogen deposition, increased temperature and management on carbon sequestration in temperate and boreal forest ecosystems: a literature review

Temperate and boreal forest ecosystems contain a large part of the carbon stored on land, in the form of both biomass and soil organic matter. Increasing atmospheric [CO2], increasing temperature, elevated nitrogen deposition and intensified management will change this C store. Well documented single-factor responses of net primary production are: higher photosynthetic rate (the main [CO2] response); increasing length of growing season (the main temperature response); and higher leaf-area index (the main N deposition and partly [CO2] response). Soil organic matter will increase with increasing litter input, although priming may decrease the soil C stock initially, but litter quality effects should be minimal (response to [CO2], N deposition, and temperature); will decrease because of increasing temperature; and will increase because of retardation of decomposition with N deposition, although the rate of decomposition of high-quality litter can be increased and that of low-quality litter decreased. Single-factor responses can be misleading because of interactions between factors, in particular those between N and other factors, and indirect effects such as increased N availability from temperature-induced decomposition. In the long term the strength of feedbacks, for example the increasing demand for N from increased growth, will dominate over short-term responses to single factors. However, management has considerable potential for controlling the C store.     

Canalization of Gene Expression and Domain Shifts in the Drosophila Blastoderm by Dynamical Attractors

The variation in the expression patterns of the gap genes in the blastoderm of the fruit fly Drosophila melanogaster reduces over time as a result of cross regulation between these genes, a fact that we have demonstrated in an accompanying article in PLoS Biology (see Manu et al., doi:10.1371/journal.pbio.1000049). This biologically essential process is an example of the phenomenon known as canalization. It has been suggested that the developmental trajectory of a wild-type organism is inherently stable, and that canalization is a manifestation of this property. Although the role of gap genes in the canalization process was established by correctly predicting the response of the system to particular perturbations, the stability of the developmental trajectory remains to be investigated. For many years, it has been speculated that stability against perturbations during development can be described by dynamical systems having attracting sets that drive reductions of volume in phase space. In this paper, we show that both the reduction in variability of gap gene expression as well as shifts in the position of posterior gap gene domains are the result of the actions of attractors in the gap gene dynamical system. Two biologically distinct dynamical regions exist in the early embryo, separated by a bifurcation at 53% egg length. In the anterior region, reduction in variation occurs because of stability induced by point attractors, while in the posterior, the stability of the developmental trajectory arises from a one-dimensional attracting manifold. This manifold also controls a previously characterized anterior shift of posterior region gap domains. Our analysis shows that the complex phenomena of canalization and pattern formation in the Drosophila blastoderm can be understood in terms of the qualitative features of the dynamical system. The result confirms the idea that attractors are important for developmental stability and shows a richer variety of dynamical attractors in developmental systems than has been previously recognized.     

TRPV channels and modulation by hepatocyte growth factor/scatter factor in human hepatoblastoma (HepG2) cells

Using patch clamp and Ca(2+) imaging techniques, we have studied Ca(2+) entry pathways in human hepatoblastoma (HepG2) cells. These cells express the mRNA of TRPV1, TRPV2, TRPV3 and TRPV4 channels, but not those of TRPV5 and TRPV6. Functional assessment showed that capsaicin (10 microM), 4alpha-phorbol-12,13-didecanoate (4alphaPDD, 1 microM), arachidonic acid (10 microM), hypotonic stress, and heat all stimulated increases in [Ca(2+)](i) within minutes. The increase in [Ca(2+)](i) depended on extracellular Ca(2+) and on the transmembrane potential, which indicated that both driving forces affected Ca(2+) entry. Capsaicin also stimulated an increase in [Ca(2+)](i) in nominally Ca(2+)-free solutions, which was compatible with the receptor functioning as a Ca(2+) release channel. Hepatocyte growth factor/scatter factor (HGF/SF) modulated Ca(2+) entry. Ca(2+) influx was greater in HepG2 cells incubated with HGF/SF (20 ng/ml for 20 h) compared with non-stimulated cells, but this occurred only in those cells with a migrating phenotype as determined by presence of a lamellipodium and trailing footplate. The effect of capsaicin on [Ca(2+)](i) was greater in migrating HGF/SF-treated cells, and this was inhibited by capsazepine. The difference between control and HGF/SF-treated cells was not found in Ca(2+)-free solutions. 4alphaPDD also had no greater effect on HGF/SF-treated cells. We conclude that TRPV1 and TRPV4 channels provide Ca(2+) entry pathways in HepG2 cells. HGF/SF increases Ca(2+) entry via TRPV1, but not via TRPV4. This rise in [Ca(2+)](i) may constitute an early response of a signalling cascade that gives rise to cell locomotion and the migratory phenotype.     

An optimized fine root sampling methodology balancing accuracy and time investment

Aims

Tree roots are spatially highly heterogeneous and it thus requires large numbers of samples to detect statistically significant changes in root biomass. The objectives of this study were to understand and quantify the sources of error in the assessment of fine root biomass (<2 mm) during the second year of a high-density Populus plantation.

Methods

Soil cores were collected in winter (n?=?35) and in summer (n?=?20), and fine roots were picked by hand for varying lengths of time: 1, 2, 5, 20, 40, and 60 min. The root biomass data were used to identify the best combination of the time spent for root picking and the number of samples collected, that minimizes the overall uncertainty (i.e. the combination of the spatial error due to the incomplete sampling and the temporal error due to the incomplete core processing).

Results

On average, 25 min was enough time to pick 90 % of the fine root biomass in winter, while in summer only 10 min were needed. In winter fewer samples were needed, but more time for picking was necessary as compared to summer when root biomass was higher.

Conclusions

Fine root sampling can be optimized by minimizing the uncertainty of the biomass estimates and simultaneously decreasing root sampling time investment.