Impact of intra- versus inter-annual snow depth variation on water relations and photosynthesis for two Great Basin Desert shrubs

Snowfall provides the majority of soil water in certain ecosystems of North America. We tested the hypothesis that snow depth variation affects soil water content, which in turn drives water potential (Ψ) and photosynthesis, over 10 years for two widespread shrubs of the western USA. Stem Ψ (Ψ stem) and photosynthetic gas exchange [stomatal conductance to water vapor (g s), and CO2 assimilation (A)] were measured in mid-June each year from 2004 to 2013 for Artemisia tridentata var. vaseyana (Asteraceae) and Purshia tridentata (Rosaceae). Snow fences were used to create increased or decreased snow depth plots. Snow depth on +snow plots was about twice that of ambient plots in most years, and 20 % lower on -snow plots, consistent with several down-scaled climate model projections. Maximal soil water content at 40- and 100-cm depths was correlated with February snow depth. For both species, multivariate ANOVA (MANOVA) showed that Ψ stem, g s, and A were significantly affected by intra-annual variation in snow depth. Within years, MANOVA showed that only A was significantly affected by spatial snow depth treatments for A. tridentata, and Ψ stem was significantly affected by snow depth for P. tridentata. Results show that stem water relations and photosynthetic gas exchange for these two cold desert shrub species in mid-June were more affected by inter-annual variation in snow depth by comparison to within-year spatial variation in snow depth. The results highlight the potential importance of changes in inter-annual variation in snowfall for future shrub photosynthesis in the western Great Basin Desert

Elevated nitrogen effects on Bromus tectorum dominance and native plant diversity in an arid montane ecosystem

Questions: Dominance of the widespread fire-altering invasive grass, Bromus tectorum, is markedly reduced at upper elevations in the Great Basin Desert. Here, we evaluated whether increased anthropogenic nitrogen (N) deposition would have an effect on species composition and ecosystem invasibility by B. tectorum at high elevations, and whether B. tectorum cover was associated with decreased native plant diversity. Location: Sagebrush steppe of the eastern Sierra Nevada, CA, US, at the western edge of the Great Basin Desert. Methods: We set up 54 paired plots, half of which were exposed to elevated N deposition (50 kg·ha-1·yr-1 at the time of snowmelt for 4 yr) and half acted as controls, in areas differing in disturbance history (grazed, burned and grazed-burned). We monitored species composition each summer from 2008 to 2011 and then compared species richness, Shannon's diversity (H'), Simpson's dominance (D'), Simpson's evenness (E1/D), B. tectorum dominance and community similarity (with ANOSIM and SIMPER analyses) by N treatment and disturbance history. Results: Species composition differed by disturbance history in all years (ANOSIM, P < 0.05), and the grazed-burned plots consistently had the highest levels of B. tectorum dominance (P ≤ 0.0003) and cover (P ≤ 0.0001). Bromus tectorum cover was inversely related to native forb species richness (r = -0.44, P < 0.0001), H'(rs = -0.73, P < 0.0001), -ln(D') (rs = -0.75, P < 0.0001) and E1/D'(rs = -0.49, P < 0.0001). We found no evidence that increased N deposition would affect native plant diversity after 4 yr in this arid montane ecosystem, but the possibility of longer-term effects cannot be eliminated. Conclusions: Results suggest that high-elevation plant communities are already experiencing invasion impacts even though changes to the fire cycle have not yet occurred. In the most disturbed areas, B. tectorum cover is approaching the threshold for increased fire risk, which could result in more severe impacts at high elevations. © 2013 International Association for Vegetation Science

The first agmatine/cadaverine aminopropyl transferase: Biochemical and structural characterization of an enzyme involved in polyamine biosynthesis in the hyperthermophilic archaeon Pyrococcus furiosus

We report here the characterization of the first agmatine/cadaverine aminopropyl transferase (ACAPT), the enzyme responsible for polyamine biosynthesis from an archaeon. The gene PF0127 encoding ACAPT in the hyperthermophile Pyrococcus furiosus was cloned and expressed in Escherichia coli, and the recombinant protein was purified to homogeneity. P. furiosus ACAPT is a homodimer of 65 kDa. The broad substrate specificity of the enzyme toward the amine acceptors is unique, as agmatine, 1,3-diaminopropane, putrescine, cadaverine, and sym-nor-spermidine all serve as substrates. While maximal catalytic activity was observed with cadaverine, agmatine was the preferred substrate on the basis of the kcat/Km value. P. furiosus ACAPT is thermoactive and thermostable with an apparent melting temperature of 108°C that increases to 112°C in the presence of cadaverine. Limited proteolysis indicated that the only proteolytic cleavage site is localized in the C-terminal region and that the C-terminal peptide is not necessary for the integrity of the active site. The crystal structure of the enzyme determined to 1.8-Å resolution confirmed its dimeric nature and provided insight into the proteolytic analyses as well as into mechanisms of thermal stability. Analysis of the polyamine content of P. füriosus showed that spermidine, cadaverine, and sym-nor-spermidine are the major components, with small amounts of sym-nor-spermine and N-(3-aminopropyl)cadaverine (APC). This is the first report in Archaea of an unusual polyamine APC that is proposed to play a role in stress adaptation. Copyright © 2007, American Society for Microbiology. All Rights Reserved

Fluorescent Probes for Applications in Bioimaging

Optical bioimaging has played a central role in fundamental research and clinical practice. The signals emitted by biological tissues can provide molecular information about various physiological and pathophysiological processes. NIR light (650–1700 nm) can penetrate the blood and biological tissues more profoundly and effectively because, at longer wavelengths, less light is diffused and absorbed. Therefore, many probes have been developed for bioimaging in the NIR window for real-time, high-sensitivity deep tissue imaging. The library of optical probes has been expanded in recent years to include a wide range of probes with emission in the Red-NIR window. The emergence of these new contrast media has provided an essential alternative for realizing the full potential of bioimaging. The most recent advances in small molecule potential probes for detection and imaging in biological systems are examined below

Variation in phenotypic plasticity for native and invasive populations of Bromus tectorum

Phenotypic plasticity is often considered important for invasive plant success, yet relatively few studies have assessed plasticity in both native and invasive populations of the same species. We examined the plastic response to temperature for Bromus tectorum populations collected from similar shrub-steppe environments in the Republics of Armenia and Georgia, where it is native, and along an invasive front in California and Nevada. Plants were grown in growth chambers in either ‘warm’ (30/20 °C, day/night) or ‘cold’ (10/5 °C) conditions. Invasive populations exhibited greater adaptive plasticity than natives for freezing tolerance (as measured by chlorophyll a fluorescence), such that invasive populations grown in the cold treatment exhibited the highest tolerance. Invasive populations also exhibited more rapid seedling emergence in response to warm temperatures compared to native populations. The climatic conditions of population source locations were related to emergence timing for invasive populations and to freezing tolerance across all populations combined. Plasticity in growth-related traits such as biomass, allocation, leaf length, and photosynthesis did not differ between native and invasive populations. Rather, some growth-related traits were very plastic across all populations, which may help to dampen differences in biomass in contrasting environments. Thus, invasive populations were found to be particularly plastic for some important traits such as seedling emergence and freezing tolerance, but plasticity at the species level may also be an important factor in the invasive ability of B. tectorum

Nitrogen Cycling Responses to Mountain Pine Beetle Disturbance in a High Elevation Whitebark Pine Ecosystem

Ecological disturbances can significantly affect biogeochemical cycles in terrestrial ecosystems, but the biogeochemical consequences of the extensive mountain pine beetle outbreak in high elevation whitebark pine (WbP) (Pinus albicaulis) ecosystems of western North America have not been previously investigated. Mountain pine beetle attack has driven widespread WbP mortality, which could drive shifts in both the pools and fluxes of nitrogen (N) within these ecosystems. Because N availability can limit forest regrowth, understanding how beetle-induced mortality affects N cycling in WbP stands may be critical to understanding the trajectory of ecosystem recovery. Thus, we measured above- and belowground N pools and fluxes for trees representing three different times since beetle attack, including unattacked trees. Litterfall N inputs were more than ten times higher under recently attacked trees compared to unattacked trees. Soil inorganic N concentrations also increased following beetle attack, potentially driven by a more than two-fold increase in ammonium (NH(4) (+)) concentrations in the surface soil organic horizon. However, there were no significant differences in mineral soil inorganic N or soil microbial biomass N concentrations between attacked and unattacked trees, implying that short-term changes in N cycling in response to the initial stages of WbP attack were restricted to the organic horizon. Our results suggest that while mountain pine beetle attack drives a pulse of N from the canopy to the forest floor, changes in litterfall quality and quantity do not have profound effects on soil biogeochemical cycling, at least in the short-term. However, continuous observation of these important ecosystems will be crucial to determining the long-term biogeochemical effects of mountain pine beetle outbreaks