Incorporating Shrub Neighborhood Dynamics to Predict Forest Succession Trajectories in an Altered Fire Regime

Ecosystems - As fire regimes shift in western North America, patches of stand-replacing fire are becoming larger. Forest succession in these patches is not well understood. There is concern that...     

How do riparian woody seedlings survive seasonal drought?

In semi-arid regions, a major population limitation for riparian trees is seedling desiccation during the dry season that follows annual spring floods. We investigated the stress response of first-year pioneer riparian seedlings to experimental water table declines (0, 1 and 3 cm day⁻¹), focusing on the three dominant cottonwood and willows (family Salicaceae) in California’s San Joaquin Basin. We analyzed growth and belowground allocation response to water stress, and used logistic regression to determine if these traits had an influence on individual survival. The models indicate that high root growth (>3 mm day⁻¹) and low shoot:root ratios (<1.5 g g⁻¹) strongly predicted survival, but there was no evidence that plants increased belowground allocation in response to drawdown. Leaf δ¹³C values shifted most for the best-surviving species (net change of +3.5 per mil from −30.0 ± 0.3 control values for Goodding’s willow, Salix gooddingii), implying an important role of increased water-use efficiency for surviving water stress. Both S. gooddingii and sandbar willow (S. exigua) reduced leaf size from controls, whereas Fremont cottonwood (Populus fremontii) sustained a 29% reduction in specific leaf area (from 13.4 to 9.6 m² kg⁻¹). The functional responses exhibited by Goodding’s willow, the more drought-tolerant species, may play a role in its greater relative abundance in dry regions such as the San Joaquin Basin. This study highlights the potential for a shift in riparian forest composition. Under a future drier climate regime or under reduced regulated river flows, our results suggest that willow establishment will be favored over cottonwood.     

Preferential alcoholic embryopathy: effects of liquid diets.

Our initial report of a preferential expression of experimental alcoholic embryopathy affecting the male offspring contiguous in utero to male siblings of Long-Evans rats was based on gavage administration of alcohol to pregnant rats without regard to isocaloric, pair-fed exposure paradigms. In this study, pregnant Long-Evans rats were given 35% ethanol-derived calories (EDC) in one of two different liquid diets: 1) a liquid alcohol diet based on Sustacal, a flavored liquid food formulated for human nutritional standards; and 2) a high-protein liquid rodent diet devised by Lieber and DeCarli (L&D). The diets were administered from day 6 to 15 of gestation. Pregnant rats were pair-fed liquid diets containing 0% EDC, but isocalorically balanced to 35% EDC with either sucrose (Sustacal) or maltose-dextrin (L&D). A fifth group of pregnant rats was given access ad libitum to standard certified laboratory rodent diet and served as free-fed controls. On day 20 of gestation, all pregnant rats were euthanized and the products of conception examined by standard teratologic techniques. Pregnant animals fed Sustacal-based diets consistently consumed fewer calories per kilogram body weight per day from day 6 to 15 of gestation (i.e., they were significantly calorie-deprived during pregnancy) as compared with the standard laboratory-diet-fed controls or those consuming L&D diets. Body weights of rats consuming Sustacal diets (both 0 and 35% EDC) were significantly lower throughout gestation when compared with all other groups. Higher (> 150 mg/dl) blood alcohol levels were attained by rats consuming 35% EDC in Sustacal diet as compared with L&D (100 mg/dl) diets.(ABSTRACT TRUNCATED AT 250 WORDS)     

Five birds,one stone: Neutralization of α-hemolysin and 4 bi-component leukocidins of Staphylococcus aureus with a single human monoclonal antibody

Staphylococcus aureus is a major human pathogen associated with high mortality. The emergence of antibiotic resistance and the inability of antibiotics to counteract bacterial cytotoxins involved in the pathogenesis of S. aureus call for novel therapeutic approaches, such as passive immunization with monoclonal antibodies (mAbs). The complexity of staphylococcal pathogenesis and past failures with single mAb products represent considerable barriers for antibody-based therapeutics. Over the past few years, efforts have focused on neutralizing α-hemolysin. Recent findings suggest that the concerted actions of several cytotoxins, including the bi-component leukocidins play important roles in staphylococcal pathogenesis. Therefore, we aimed to isolate mAbs that bind to multiple cytolysins by employing high diversity human IgG1 libraries presented on the surface of yeast cells. Here we describe cross-reactive antibodies with picomolar affinity for α-hemolysin and 4 different bi-component leukocidins that share only ∼26% overall amino acid sequence identity. The molecular basis of cross-reactivity is the recognition of a conformational epitope shared by α-hemolysin and F-components of gamma-hemolysin (HlgAB and HlgCB), LukED and LukSF (Panton-Valentine Leukocidin). The amino acids predicted to form the epitope are conserved and known to be important for cytotoxic activity. We found that a single cross-reactive antibody prevented lysis of human phagocytes, epithelial and red blood cells induced by α-hemolysin and leukocidins in vitro, and therefore had superior effectiveness compared to α-hemolysin specific antibodies to protect from the combined cytolytic effect of secreted S. aureus toxins. Such mAb afforded high levels of protection in murine models of pneumonia and sepsis.     

Giant Sequoia (Sequoiadendron giganteum) Regeneration in Experimental Canopy Gaps

Restoration of giant sequoia populations is a high priority for managers, but few experimental studies have examined the efficacy of restoration treatments. To inform giant sequoia restoration treatment options, we assessed the response of giant sequoia regeneration (germination, mortality, and growth) to experimental gaps within a native giant sequoia grove. We created experimental gaps, ranging in size from 0.05 to 0.4 ha. Following gap creation, we sowed seeds and planted seedlings along north‐south transects across gaps. Transects were planted on paired burned and unburned substrates. The seed‐sowing treatment did not result in a cohort of established seedlings, although the amount of seeds sowed was far short of the potential amount released during intense fires. Mortality of planted seedlings did not vary with gap size (average 25% mortality). However, there was a distinct relationship between gap size and second year seedling growth. The relationship was best modeled with an asymptotic curve for both burned and unburned substrates. Relative seedling growth more than doubled as gap size increased from 0.05 to 0.2 ha, then increases in growth diminished. Growth rates of giant sequoia seedlings saturated above 70% light availability while increasing linearly with belowground resource availability. Long‐lived pioneer species such as giant sequoia require restoration treatments that involve relatively severe disturbances to facilitate cohort establishment and recruitment.     

The Role of Abandoned Channels as Refugia for Sustaining Pioneer Riparian Forest Ecosystems

In disturbance-prone ecosystems, organisms often persist in spatial refugia during stressful periods. A clear example is the colonization of abandoned river channels by pioneer riparian trees. Here, we examine the prominence of this establishment pathway for a foundation tree species (Fremont cottonwood, Populus fremontii) within the riparian corridor of a large river, the Sacramento River in central California. We quantified the total proportion of forest that initiated as a result of channel abandonment for a 160-km reach, analyzed concurrent patterns of tree establishment with floodplain accretion and sedimentation history, and developed a conceptual model of biogeomorphic evolution of abandoned channels. Historical air photo analysis indicated that stands associated with abandoned channels comprised more than 50% of the total extant cottonwood forest area. Tree-ring evidence showed that cottonwood stands commonly developed immediately following abandonment, and the recruitment window ranged from 4 to 40 years, but was less than 10 years at most sites. Rates of floodplain rise and fine sediment accumulation were high in young sites and decreased logarithmically over time. Together, these results suggest that abandoned channels are an important refuge for cottonwood recruitment, that the greatest opportunity for colonization occurs within a short period after the cutoff event, and that sedimentation processes influence the duration of the colonization window. On rivers where tree recruitment along the active channel is severely limited by hydrologic regulation and/or land management, abandoned channel refugia may play an even more important role in sustaining an ecologically functional riparian corridor. Preserving bank erosion, active meander corridors and forest regeneration zones created by cutoff events are therefore key conservation measures on shifting rivers.     

A color-based stable multi-copy integrant selection system for Pichia pastoris using the attenuated ADE1 and ADE2 genes as auxotrophic markers

The methylotropic yeast Pichia pastoris has been used for more than two decades to successfully produce a large number of recombinant proteins. Currently, a wide variety of auxotrophic and drug based selection markers are employed to screen for clones expressing the protein of interest. For most proteins an increased copy number of the integrated plasmid results in higher levels of expression, but these multi-copy integrants can be unstable due to the propensity of P. pastoris for homologous recombination. Here we describe a multi-copy selection system based on ade1 and ade2 auxotrophic parent strains and the respective attenuated markers with truncated promoter regions. We show that for all four proteins we tested, the use of the attenuated markers leads to increased protein expression when compared with selection based on the full strength markers. The fact that the adenine auxotrophic strains grow more slowly than the complemented counterparts essentially ensures the stability of multi-copy integration. At the same time, the accumulation of a red dye in the auxotrophic strains also provides an easy, color-based selection for transformants with multiple copies.     

Nitrogen deposition,distribution and cycling in a subalpine spruce-fir forest in the Adirondacks,New York,USA

Nitrogen inputs, fluxes, internal generation and consumption, and outputs were monitored in a subalpine spruce-fir forest at approximately 1000-m elevation on Whiteface Mountain in the Adirondacks of New York, USA. Nitrogen in precipitation, cloudwater and dry deposition was collected on an event basis and quantified as an input. Throughfall, stemflow, litterfall and soil water were measured to determine fluxes within the forest. Nitrogen mineralization in the forest floor was estimated to determine internal sources of available N. Lower mineral horizon soil water was used to estimate output from the ecosystem. Vegetation and soil N pools were determined.During four years of continuous monitoring, an average of 16 kg N ha^–1 yr^–1 was delivered to the forest canopy as precipitation, cloudwater and dry deposition from the atmosphere. Approximately 30% of the input was retained by the canopy. Canopy retention is likely the result of both foliar uptake and immobilization by bark, foliage and microorganisms. Approximately 40 kg of N was made available within the forest floor from mineralization of organic matter. Virtually all the available ammonium (mineralized plus input from throughfall) is utilized in the forest floor, either by microorganisms or through uptake by vegetation. The most abundant N component of soil water solutions leaving the system was nitrate. Net ecosystem fluxes indicate accumulation of both ammonium and nitrate. There is a small net loss of organic N from the ecosystem. Some nitrate leaves the bottom of the B horizon throughout the year. Comparisons with other temperate coniferous sites and examination of the ecosystem N mass balance indicate that N use efficiency is less at our site, which suggests that the site is not severely limited by N.     

Immunological characterization of the gag gene products of bovine immunodeficiency virus.

The bovine immunodeficiency virus (BIV) gag gene encodes a 53-kDa precursor (Pr53gag) that is involved in virus particle assembly and is further processed into the putative matrix (MA), capsid (CA), and nucleocapsid (NC) functional domains in the mature virus. Gag determinants are also found in the Gag-Pol polyprotein precursor. To immunologically identify the major precursors and processed products of the BIV gag gene, monospecific rabbit sera to recombinant BIV MA protein and Pr53gag and peptides predicted to correspond to the CA and NC proteins and the MA-CA cleavage site were developed and used in immunoprecipitations and immunoblots of BIV antigens. Monospecific antisera to native and recombinant human immunodeficiency virus type 1 proteins were also used to identify analogous BIV Gag proteins and to determine whether cross-reactive epitopes were present in the BIV Gag precursors or processed products. The BIV MA, CA, and NC Gag proteins were identified as p16, p26, and p13, respectively. In addition to BIV Pr53gag, the major Gag precursor, two other Gag-related precursors of 170 and 49 kDa were identified that have been designated pPr170gag-pol and Pr49gag, respectively; pPr170gag-pol is the Gag-Pol polyprotein precursor, and Pr49gag is the transframe Gag precursor present in pPr170gag-pol. Several alternative Gag cleavage products were also observed, including p23, which contains CA and NC determinants, and p10, which contains a peptide sequence conserved in the CA proteins of most lentiviruses. The monospecific antisera to human immunodeficiency virus type 1 CA (p24) and NC (p7) proteins showed cross-reactivity to and aided in the identification of analogous BIV proteins. Based on the present data, a scheme for the processing of BIV Gag precursors is proposed.