Seasonal shifts in the importance of bottom–up and top–down factors on stream periphyton community structure

We examined the importance of temporal variability in top–down and bottom–up effects on the accumulation of stream periphyton, which are complex associations of autotrophic and heterotrophic microorganisms. Periphyton contributes to primary production and nutrient cycling and serves as a food resource for herbivores (grazers). Periphyton growth is often limited by the availability of nitrogen and phosphorus, and biomass can be controlled by grazers. In this study we experimentally manipulated nutrients and grazers simultaneously to determine the relative contribution of bottom–up and top–down controls on periphyton over time. We used nutrient diffusing substrates to regulate nutrient concentrations and an underwater electric field to exclude grazing insects in three sequential 16–17 day experiments from August to October in montane Colorado, USA. We measured algal biomass, periphyton organic mass, and algal community composition in each experiment and determined densities of streambed insect species, including grazers. Phosphorus was the primary limiting nutrient for algal biomass, but it did not influence periphyton organic mass across all experiments. Effects of nutrient additions on algal biomass and community composition decreased between August and October. Grazed substrates supported reduced periphyton biomass only in the first experiment, corresponding to high benthic abundances of a dominant mayfly grazer (Rhithrogena spp.). Grazed substrates in the first experiment also showed altered algal community composition with reduced diatom relative abundances, presumably in response to selective grazing. We showed that top–down grazing effects were strongest in late summer when grazers were abundant. The effects of phosphorus additions on algal biomass likely decreased over time because temperature became more limiting to growth than nutrients, and because reduced current velocity decreased nutrient uptake rates. These results suggest that investigators should proceed with caution when extending findings based on short‐term experiments. Furthermore, these results support the need for additional seasonal‐scale field research in stream ecology.     

Bacteria on leaves: a previously unrecognised source of N2O in grazed pastures

Nitrous oxide (N₂O) emissions from grazed pastures are a product of microbial transformations of nitrogen and the prevailing view is that these only occur in the soil. Here we show this is not the case. We have found ammonia-oxidising bacteria (AOB) are present on plant leaves where they produce N₂O just as in soil. AOB (Nitrosospira sp. predominantly) on the pasture grass Lolium perenne converted 0.02–0.42% (mean 0.12%) of the oxidised ammonia to N₂O. As we have found AOB to be ubiquitous on grasses sampled from urine patches, we propose a ‘plant'' source of N₂O may be a feature of grazed grassland.In terms of climate forcing, nitrous oxide (N₂O) is the third most important greenhouse gas (Blunden and Arndt, 2013). Agriculture is the largest source of anthropogenic N₂O (Reay et al., 2012) with about 20% of agricultural emissions coming from grassland grazed by animals (Oenema et al., 2005).Grazed grassland is a major source of N₂O because grazers harvest nitrogen (N) from plants across a wide area but recycle it back onto the pasture, largely as urine, in patches of very high N concentration. The N in urine patches is often in excess of what can be used by plants resulting in losses through leaching as nitrate, as N₂O and through volatilisation as ammonia (NH₃) creating a high NH₃ environment in the soil and plant canopy; an important point that we will return to later. The established wisdom is that N₂O is generated exclusively by soil-based microbes such as ammonia-oxidising bacteria (AOB). This soil biology is represented in models designed to simulate N₂O emissions and the soil is a target for mitigation strategies such as the use of nitrification inhibitors.We have previously shown that pasture plants can emit N₂O largely through acting as a conduit for emissions generated in the soil, which are themselves controlled to some degree by the plant (Bowatte et al., 2014). In this case the origin of the emission is still the soil microbes. However, AOB have been found on the leaves of plants, for example, Norway spruce (Papen et al., 2002; Teuber et al., 2007) and weeds in rice paddies (Bowatte et al., 2006), prompting us to ask whether AOB might be present on the leaves of pasture species and contribute to N₂O emissions as they do in soil.We looked for AOB on plants in situations where NH₃ concentrations were likely to be high, choosing plants from urine patches in grazed pastures and plants from pastures surrounding a urea fertiliser manufacturing plant. DNA was extracted from the leaves (including both the surface and apoplast) and the presence of AOB tested using PCR. AOB were present in all the species we examined—the grasses Lolium perenne, Dactylis glomerata, Anthoxanthum odoratum, Poa pratensis, Bromus wildenowii and legumes Trifolium repens and T. subterraneum.To measure whether leaf AOB produce N₂O, we used intact plants of ryegrass (L. perenne) lifted as cores from a paddock that had been recently grazed by adult sheep. The cores were installed in a chamber system designed to allow sampling of above- and belowground environments separately (Bowatte et al., 2014). N₂O emissions were measured from untreated (control) plants and from plants where NH₃ was added to the aboveground chamber and leaves were either untreated or sterilised by wiping twice with paper towels soaked in 1% hypoclorite (Sturz et al., 1997) and then with sterile water. We tested for the presence and abundance of AOB on the leaves by extracting DNA and using PCR and real-time PCR targeting the ammonia monoxygenase A (amoA) gene, which is characteristic of AOB. AOB identity was established using cloning and DNA sequencing. Further details of these experiments can be found in the Supplementary Information.The addition of NH₃ to untreated plants significantly stimulated N₂O emissions (P<0.001) compared with the controls; by contrast, the plants with sterilised leaves produced significantly less N₂O than controls (P<0.001) even with NH₃ added (Figure 1) providing strong evidence for emissions being associated with bacteria on the leaves. Control plants did emit N₂O suggesting there was either sufficient NH₃ available for bacterially generated emissions and/or other plant-based mechanisms were involved (Bowatte et al., 2014).Open in a separate windowFigure 1Effect of an elevated NH₃ atmosphere and surface sterilisation of leaves on leaf N₂O emissions measured over 1-h periods on three occasions during the day. Values are means (s.e.m.), where n=7.The major AOB species identified was Nitrosospira strain III7 that has been previously shown to produce N₂O (Jiang and Bakken, 1999). We measured 10⁹ AOB cells per m² ryegrass leaf, assuming a specific leaf area of 250 cm² g⁻¹ leaf.The rate of production of N₂O (0.1–0.17 mg N₂O-N per m² leaf area per hour) can be translated to a field situation using the leaf area index (LAI)—1 m² leaf per m² ground would be an LAI of 1. LAI in a pasture can vary from <1 to >6 depending on the management (for example, Orr et al., 1988). At LAI of 1, the AOB leaf emission rate would equate to a N₂O emission rate of about 0.1–0.3 mg N₂O-N per m² ground per hour. By comparison, the emission rates measured after dairy cattle urine (650 kg N ha⁻¹) was applied to freely and poorly drained soil were 0.024–1.55 and 0.048–3.33 mg N₂O-N per m² ground per hour, respectively (Li and Kelliher, 2005).The fraction of the NH₃ that was converted to N₂O by the leaf AOB was 0.02–0.42% (mean 0.12%). The mean value is close to that measured for Nitrosospira strains including strain III7 isolated from acidic, loamy and sandy soils where values ranged from 0.07 to 0.10% (Jiang and Bakken, 1999). This is good evidence that the AOB on leaves have the capacity to produce N₂O at the same rate as AOB in soils. We do not suggest that leaf AOB will produce as much N₂O as soil microbes; however, because leaf AOB have access to a source of substrate—volatilised NH₃—that is unavailable to soil microbes and may constitute 26% (Laubach et al., 2013) to 40% (Carran et al., 1982) of the N deposited in the urine, N₂O emissions from these aboveground AOB are additional to soil emissions. Further research is required to identify the situations in which leaf AOB contribute to total emissions and to quantify this contribution.     

Non-Toxic Metabolic Management of Metastatic Cancer in VM Mice: Novel Combination of Ketogenic Diet,Ketone Supplementation,and Hyperbaric Oxygen Therapy

The Warburg effect and tumor hypoxia underlie a unique cancer metabolic phenotype characterized by glucose dependency and aerobic fermentation. We previously showed that two non-toxic metabolic therapies – the ketogenic diet with concurrent hyperbaric oxygen (KD+HBOT) and dietary ketone supplementation – could increase survival time in the VM-M3 mouse model of metastatic cancer. We hypothesized that combining these therapies could provide an even greater therapeutic benefit in this model. Mice receiving the combination therapy demonstrated a marked reduction in tumor growth rate and metastatic spread, and lived twice as long as control animals. To further understand the effects of these metabolic therapies, we characterized the effects of high glucose (control), low glucose (LG), ketone supplementation (βHB), hyperbaric oxygen (HBOT), or combination therapy (LG+βHB+HBOT) on VM-M3 cells. Individually and combined, these metabolic therapies significantly decreased VM-M3 cell proliferation and viability. HBOT, alone or in combination with LG and βHB, increased ROS production in VM-M3 cells. This study strongly supports further investigation into this metabolic therapy as a potential non-toxic treatment for late-stage metastatic cancers.     

Effect of xenon on the excited States of phototropic receptor flavin in corn seedlings

The chemically inert, water-soluble heavy atom gas, xenon, at millimolar concentrations specifically quenches the triplet excited state of flavin in solution without quenching the flavin singlet excited state. The preferential quenching of the flavin triplet over the singlet excited state by Xe has been established by showing that the flavin triplet-sensitized photooxidation of NADH is inhibited while the fluorescence intensity and lifetime of flavin are not affected by Xe.     

Adaptation to natural flow regimes

Floods and droughts are important features of most running water ecosystems, but the alteration of natural flow regimes by recent human activities, such as dam building, raises questions related to both evolution and conservation. Among organisms inhabiting running waters, what adaptations exist for surviving floods and droughts? How will the alteration of the frequency, timing and duration of flow extremes affect flood- and drought-adapted organisms? How rapidly can populations evolve in response to altered flow regimes? Here, we identify three modes of adaptation (life history, behavioral and morphological) that plants and animals use to survive floods and/or droughts. The mode of adaptation that an organism has determines its vulnerability to different kinds of flow regime alteration. The rate of evolution in response to flow regime alteration remains an open question. Because humans have now altered the flow regimes of most rivers and many streams, understanding the link between fitness and flow regime is crucial for the effective management and restoration of running water ecosystems.     

A telemedicine instrument for remote evaluation of tremor: design and initial applications in fatigue and patients with Parkinson's Disease

Introduction  

A novel system that combines a compact mobile instrument and Internet communications is presented in this paper for remote evaluation of tremors. The system presents a high potential application in Parkinson's disease and connects to the Internet through a TCP/IP protocol. Tremor transduction is carried out by accelerometers, and the data processing, presentation and storage were obtained by a virtual instrument. The system supplies the peak frequency (fp), the amplitude (Afp) and power in this frequency (Pfp), the total power (Ptot), and the power in low (1-4 Hz) and high (4-7 Hz) frequencies (Plf and Phf, respectively).     

Toward a mechanistic understanding and prediction of biotic homogenization

The widespread replacement of native species with cosmopolitan, nonnative species is homogenizing the global fauna and flora. While the empirical study of biotic homogenization is substantial and growing, theoretical aspects have yet to be explored. Consequently, the breadth of possible ecological mechanisms that can shape current and future patterns and rates of homogenization remain largely unknown. Here, we develop a conceptual model that describes 14 potential scenarios by which species invasions and/or extinctions can lead to various trajectories of biotic homogenization (increased community similarity) or differentiation (decreased community similarity); we then use a simulation approach to explore the model's predictions. We found changes in community similarity to vary with the type and number of nonnative and native species, the historical degree of similarity among the communities, and, to a lesser degree, the richness of the recipient communities. Homogenization is greatest when similar species invade communities, causing either no extinction or differential extinction of native species. The model predictions are consistent with current empirical data for fish, bird, and plant communities and therefore may represent the dominant mechanisms of contemporary homogenization. We present a unifying model illustrating how the balance between invading and extinct species dictates the outcome of biotic homogenization. We conclude by discussing a number of critical but largely unrecognized issues that bear on the empirical study of biotic homogenization, including the importance of spatial scale, temporal scale, and data resolution. We argue that the study of biotic homogenization needs to be placed in a more mechanistic and predictive framework in order for studies to provide adequate guidance in conservation efforts to maintain regional distinctness of the global biota.     

Kinetics for Phototropic Curvature by Etiolated Seedlings of Arabidopsis thaliana

An infrared-imaging system has been used to study the influence of gravity on the kinetics of first positive phototropism. The development of phototropic curvature of etiolated seedlings of Arabidopsis thaliana was measured in the absence of visible radiation. Following a pulse of blue light, stationary seedlings curved to a maximum of approximately 16° about 80 minutes after stimulation. The seedlings then curved upward again or straightened by about 6° during the subsequent 100 minutes. Seedlings rotated on a clinostat reached a similar maximum curvature following photostimulation. These seedlings maintained that curvature for 30 to 40 minutes before subsequently straightening to the same extent as the stationary seedlings. It is concluded that straightening is not a consequence of gravitropism, although gravity has some effect on the phototropism kinetics.