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1.
ABSTRACT Prescribed fire is used widely to manage grasslands on National Wildlife Refuges and other public lands in the northern Great Plains, but its effects on habitat use or production of wildlife in the region are poorly understood. During 1998–2003, we used point counts to examine effects of prescribed fire on vegetation and passerines in a mixed-grass prairie complex in north-central North Dakota, USA (n = 7 units, each 40–70 ha). Vegetation structure and, to a lesser extent, plant community composition varied with year of study (likely related to changes in annual precipitation) and with number of growing seasons since fire. Fire altered plant structure, especially the amount of residual vegetation, which in turn influenced bird species richness and abundance. The number of indicated pairs for sedge wren (Cistothorus platensis), clay-colored sparrow (Spizella pallida), Le Conte's sparrow (Ammodramus leconteii), Savannah sparrow (Passerculus sandwichensis), and bobolink (Dolichonyx oryzivorus) were lowest during the first postfire growing season but generally increased and stabilized within 2–3 postfire growing seasons. Our results support the premise that grassland passerines are well-adapted to frequent, periodic fires, generally corresponding to those occurring prior to Euro-American settlement of the region. Prescribed fire is important for reducing tree and shrub invasion, restoring biological integrity of plant communities, and maintaining or enhancing populations of grassland-dependent bird species. Managers in the northern mixed-grass prairie region should not be overly concerned about reductions in bird abundances that are limited mostly to the first growing season after fire.  相似文献   

2.
Members of the conserved RecQ helicase family are important for the preservation of genomic stability. Multiple RecQ homologs within one organism raise the question of functional specialization. Whereas five different homologs are present in humans, the model plant Arabidopsis (Arabidopsis thaliana) carries seven RecQ homologs in its genome. We performed biochemical analysis of AtRECQ3, expanded upon a previous analysis of AtRECQ2, and compared their properties. Both proteins differ in their domain composition. Our analysis demonstrates that they are 3′ to 5′ helicases with similar activities on partial duplex DNA. However, they promote different outcomes with synthetic DNA structures that mimic Holliday junctions or a replication fork. AtRECQ2 catalyzes Holliday junction branch migration and replication fork regression, while AtRECQ3 cannot act on intact Holliday junctions. The observed reaction of AtRECQ3 on the replication fork is in line with unwinding the lagging strand. On nicked Holliday junctions, which have not been intensively studied with RecQ helicases before, AtRECQ3, but not AtRECQ2, shows a clear preference for one unwinding mechanism. In addition, AtRECQ3 is much more efficient at catalyzing DNA strand annealing. Thus, AtRECQ2 and AtRECQ3 are likely to perform different tasks in the cell, and AtRECQ3 differs in its biochemical properties from all other eukaryotic RECQ helicases characterized so far.RecQ helicases are important players in the maintenance of genomic stability in prokaryotes and eukaryotes (for reviews covering several aspects of RecQ helicases, see Bachrati and Hickson, 2003; Hickson, 2003; Opresko et al., 2004; Sharma et al., 2006; Brosh and Bohr, 2007; Hanada and Hickson, 2007; Bachrati and Hickson, 2008). Interestingly, organisms contain different numbers of RecQ homologs. In humans, mutations in three of the five RecQ helicases have been linked to distinct, cancer-associated genetic diseases. Consequently, the human RecQ helicases have been intensively studied. All RecQ helicases share a characteristic helicase domain, due to which they are classified as RecQ helicases. In addition, a RecQ C-terminal (RQCt) and/or a Helicase and RNAseD C-terminal (HRDC) domain can be identified in some RecQ helicases. The possible functions of the latter in protein stability and DNA and protein binding are summarized, for example, in a recent review (Chu and Hickson, 2009). From the enzymatic point of view, most RecQ helicases both unwind DNA and promote the opposite reaction, called strand annealing. In addition, some RecQ homologs combine these activities to catalyze branch migration.One of the central questions regarding RecQ helicases is the extent to which the homologs have unique or overlapping functions (Ellis et al., 2008). This question originally raised for the human RecQ helicases is of equal importance for other organisms, such as plants. Analysis of plant RecQ homologs could reveal species- or kingdom-specific tasks, and such comparisons could shed light on evolutionary questions, such as how selection pressures induce multiple homologs within a single species.In the dicotyledonous model plant Arabidopsis (Arabidopsis thaliana), seven RecQ helicase homologs have been identified (Hartung et al., 2000; Hartung and Puchta, 2006). A biochemical comparative analysis may provide information about the molecular basis of their cellular functions, which are likely to be different. As has been shown, sequence homology does not necessarily imply functional homology (Hartung et al., 2007).Previously, we were able to characterize basic biochemical properties of the helicase RECQ2 of the model plant Arabidopsis (Kobbe et al., 2008). In this study, we chose to study AtRECQ3 as a RecQ helicase that differs in the domain structure from AtRECQ2, lacking the HRDC domain and the winged helix subdomain of the RQCt domain (Fig. 1A). AtRECQ3 has the same domain structure as human RECQ5β. AtRECQ3 was expressed in Escherichia coli, purified, and biochemically characterized. The specificity of AtRECQ2 and AtRECQ3 was compared with several substrates, extending the analyzed spectrum of substrates for AtRECQ2 and for RecQ helicases in general. We identified several differences in the enzymatic properties of AtRECQ2 and AtRECQ3, suggesting that these two enzymes might play different roles in vivo.Open in a separate windowFigure 1.Domain structure, purification, and directionality of AtRECQ2 and AtRECQ3. A, Schematic drawing of the domain structure of AtRECQ2 and AtRECQ3. In the helicase domain, the different helicase motifs (0, I, Ia, II, III, IV, V, and VI) are depicted in dark gray. B, 10% SDS-PAGE analysis stained with colloidal Coomassie Brilliant Blue of representative purifications of AtRECQ2-K117M (lane 1, 0.5 pmol), AtRECQ2 (lane 2, 0.8 pmol), AtRECQ3-K64M (lane 3, 0.9 pmol), and AtRECQ3 (lane 4, 1.25 pmol). The proteins were overexpressed in E. coli and purified by nickel-immobilized metal ion affinity chromatography and Calmodulin affinity chromatography. The gray arrow indicates AtRECQ2/-K117M with a predicted molecular mass of 85.5 kD, and the black arrow indicates AtRECQ3/-K64M with a predicted molecular mass of 86 kD. C, AtRECQ2 (8 nm), AtRECQ3 (8 nm), AtRECQ3-K64M (8 nm), and AtRECQ2-K117M (5 nm) were incubated with 150 pm of the indicated substrates for 30 min at 37°C. Error bars indicate sd of the mean of three independent experiments.  相似文献   

3.
Individual blastospores of Candida albicans were deposited on the surface of 50-mm membranes (Millipore Corp.) and placed within sealed glass chambers at various relative humidities (RH). After 48 hr, virtually all cells maintained at 100 and 10% RH had survived, but 84% of the cells maintained at 60% RH failed to develop into colonies when transferred to Sabouraud medium. No morphological abnormalities could be observed in cells surviving low RH values, but their initial rate of multiplication after transfer to Sabouraud medium was greatly reduced, compared to that demonstrated by cells maintained at 100% RH. At 60% RH, the exposure time required to kill 50% of the blastospores was 2 to 3.5 days. The inimical effect of 60% RH was confirmed in a total of 21 isolates of C. albicans. No deleterious effect was noted when 12 other species of yeasts were subjected to 10, 60, and 100% RH. The single isolate of Candida brumptii and 1 out of the 20 isolates of Cryptococcus neoformans tested also failed to grow after blastospores had been exposed to 60% RH for 4 days.  相似文献   

4.
Long-term (10 years) growth responses of residual trees to prescribed fire and thinning were evaluated using standard dendrochronological protocols to understand the broader effects of the treatments on mixed-oak forest ecosystems in southern Ohio. Analysis of 696 increment cores (348 trees ≥ 25 cm DBH; five species) from 80 0.1 ha permanent plots distributed evenly across four treatments (control, thin, thin + burn, burn) indicated substantial increase in tree basal area increment (BAI) following the treatment. Post-treatment mean BAI of trees from the three active treatments ranged from 20.52 to 23.55 cm2 y?1 compared with pre-treatment values of 16.86–17.07 cm2 y?1. BAI rates (averaging 15.13 and 16.33 cm2 y?1, respectively, for pre- and post-treatments) in the control plots did not change much over time. Mechanical treatments were more effective than prescribed fire at enhancing BAI of trees. However, basal area growth depended to some degree on the severity of prescribed fire. Analysis of percent BAI change revealed an interesting temporal trend with moderate to major growth releases during the first 5-year post-treatment period, and a slight attenuation thereafter, suggesting the need for periodic application of treatments to sustain growth over a longer timescale. Growth responses varied greatly among species, with yellow-poplar and hickories exhibiting the highest and lowest post-treatment BAI rates of 31.11 and 15.71 cm2 y?1, respectively. Given their variable growth responses, integrating residual trees into current monitoring programs may help in elucidating the consequences of prescribed fire and thinning on forest dynamics and development.  相似文献   

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Forest openings, also known as glades, arise through a variety of mechanisms including disturbance (fire and blow downs) and local variation in soil or bedrock geology. They are common in many forest types and are often dominated by locally rare herbaceous species. Prescribed burning is increasingly used as a management approach for maintaining glades although little is known about the effects of fire on these habitats. Of particular concern is the potential for nutrient loss during and after fire because glades are often characterized by nutrient‐poor soils. We quantitated nutrient losses through combustion and leaching for glade and adjacent forest habitats subjected to a prescribed burn. Our findings suggest that spring burns do not result in appreciable loss of nutrient capital from glades in comparison with those observed in the surrounding forest. Fire resulted in a substantial loss of litter mass (37%) in the forest but no measurable loss in the glade. Nitrogen losses through combustion were significant in the forest and were equivalent to 4.5 years of atmospheric inputs. Fire significantly increased soil nitrate pools in forest but not in glade plots. No detectable increases in nitrogen, phosphorus, or base cation leaching were observed in either forest or glade habitats within 4 months after the burn. These findings suggest that plant and microbial nutrient uptake rapidly reestablish control over leaching losses when burns are conducted at the start of the growing season. Biotic retention minimizes fire impacts on nutrient loss from the ecosystem.  相似文献   

7.
One of the largest and rarest Bebb willow (Salix bebbiana) communities in the United States occurs at Hart Prairie, Arizona. Low recruitment of the willow over the past several decades has been linked to inadequate soil water content for seed germination and seedling establishment. We tested a hypothesis that a prescribed burn would reduce biomass of and evapotranspiration by herbaceous plants, thereby increasing soil water content. Three treatments (unburned control, early‐growing season burned, late‐growing season burned) were applied in year 2001 to replicated plots in fern‐ and grass‐dominated herbaceous communities. Soil water content (0–30 cm) was measured weekly in plots during the 2001, 2002, and 2003 growing seasons. Both early‐ and late‐season burning reduced herbaceous biomass in the fern‐dominated community in 2002 and 2003 and reduced biomass in the grass‐dominated community in 2002 but not in 2003. Soil water content increased for approximately four weeks in 2001 following the early‐season burn, but the early‐season and late‐season burns reduced soil water content in both communities over much of the 2002 and 2003 growing seasons. Thus, early‐season burning may benefit willow seed germination by increasing soil water content immediately following burning but be detrimental to germination in the second and third growing seasons after burning because of drier soil. Large temporal variation in the effect of prescribed burning on soil water content will complicate the use of fire as a restoration tool to manage soil water available for threatened plants such as Bebb willow and for recharge of groundwater.  相似文献   

8.
Changes in structural and compositional attributes of shinnery oak (Quercus havardii Rydb.) plant communities have occurred in the twentieth century. These changes may in part relate to altered fire regimes. Our objective was to document effects of prescribed fire in fall (October), winter (February), and spring (April) on plant composition. Three study sites were located in western Oklahoma; each contained 12, 60 × 30‐m plots that were designated, within site, to be seasonally burned, annually burned, or left unburned. Growing season canopy cover for herbaceous and woody species was estimated in 1997–1998 (post‐treatment). At one year post‐fire, burning in any season reduced shrub cover, and spring burns reduced cover most. Winter and annual fires increased cover of rhizomatous tallgrasses, whereas burning in any season decreased little bluestem cover. Perennial forbs increased with fall and winter fire. Shrub stem density increased with fire in any season. Communities returned rapidly to pre‐burn composition with increasing time since fire. Fire effects on herbaceous vegetation appear to be manifested through increases in bare ground and reduction of overstory shrub dominance. Prescribed fire can be used as a tool in restoration efforts to increase or maintain within and between community plant diversity. Our data suggest that some plant species may require or benefit from fire in specific seasons. Additional research is needed to determine the long‐term effects of repeated fire over time.  相似文献   

9.
Surface area, chlorophyll concentration and stomatal size anddensity were measured for all green components of floral clusterson Cox's Orange Pippin apple trees to assess their relativepotential for photosynthesis. Before flower opening, sepalsand receptacles had chlorophyll concentrations similar to thosefound in the laminae of rosette leaves. But, whereas the concentrationin rosette leaves continued to increased until fruit set, thosein the sepals and receptacles decreased. Sepals had a greater mature stomatal density than leaf laminaeshortly after bud burst; although both densities increased,that on the laminae later exceeded that on sepals. Flowers contributed significantly to the green surface are (40%),chlorophyll content (30%) and mature stomatal number (25%) offloral clusters at the green cluster stage, but these contributionsthen decreased. Cox apple flowers appear to have the potentialfor contributing significantly to their carbohydrate requirementat a time when the rosette leaves are not thought to be exportersof photosynthate.Copyright 1993, 1999 Academic Press Malus pumila, apples flowers, chlorophyll, stomata, surface area, flower photosynthesis  相似文献   

10.
Elephant and fire are considered to be among the most important agents that can modify the African savanna ecosystem. Although the synergistic relationship between these two key ecological drivers is well documented, it has proved much more difficult to establish the relative effects they have on savanna vegetation structure at a fine-scale over time. In this study, we explore the comparative impacts of fire and elephant on 2,522 individually identified large trees (≥5 m in height) in the Kruger National Park, South Africa. Data were collected from 21 transects first surveyed in April 2006 and resurveyed in November 2008, to determine the relative importance of past damage by these agents on subsequent impacts and mortality. The occurrence of fire or elephant damage in 2006 affected the amount of tree volume subsequently removed by both these agents; elephant removed more tree volume from previously burned trees and the impact of subsequent fire was higher on previously burned or elephant-utilized trees than on undamaged trees. Mortality was also affected by an interaction between previous and recent damage, as the probability of mortality was highest for trees that suffered from fire or elephant utilization after being pushed over. Subsequent fire damage, but not elephant utilization, on debarked trees also increased the probability of mortality. Mortality was twice (4.6% per annum) that of trees progressing into the ≥5 m height class, suggesting an overall decline in large tree density during the 30-month study period. The responses of large trees were species and landscape-specific in terms of sensitivity to elephant and fire impacts, as well as for levels of mortality and progression into the ≥5 m height class. These results emphasize the need for fine-scale site-specific knowledge for effective landscape level understanding of savanna dynamics.  相似文献   

11.
Abstract: Woodpecker damage to homes and buildings is a widespread and locally severe problem in vertebrate pest control. Woodpeckers may cause an average of $300 (United States currency) in damage to affected houses, resulting in millions of dollars of property damage annually in the United States. However, there is no known, practical, consistently effective technique to prevent woodpecker damage. We tested the effectiveness of 6 woodpecker control techniques available commercially, used anecdotally by homeowners, and recommended by wildlife specialists in different Cooperative Extension publications. These deterrents included Prowler Owls, Irri-TapeTM, the Bird Pro Sound System, Scare-Eyes (all manufactured by Bird-X, Inc., Chicago, IL), suet feeders, and roost boxes. We conducted our study in late spring and autumn during August 2003 through December 2004 in the Town of Ithaca, Tompkins County, New York, USA. We evaluated 16 homes with active woodpecker damage, and visited each house about 3 times per week to determine a rate of new woodpecker holes per day. We then placed a deterrent at the house and monitored the rate of new holes per day. Although none of the deterrents that we tested was completely successful in keeping woodpeckers from creating new holes in house siding, homes where Irri-Tape was installed exhibited the greatest reduction in woodpecker damage. Avoiding earth-tone stain and paint colors may be the best long-term solutions for preventing woodpecker damage in wooded areas. Homeowners should avoid using natural-colored stains, as brightly painted houses (white, light blue, pastels) were less likely to attract woodpeckers.  相似文献   

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Abstract Historic fire return intervals in Artemesia tridentata (big sagebrush) ecosystems have been altered by livestock grazing, fire suppression, and other land management techniques resulting in ecological changes in these areas. Increases in abundance of woody vegetation may be causing declines in native herbaceous understory species. We examined the effects of prescribed fire on the morphology, abundance, and phenology of nine abundant forb (herbaceous dicot) species used selectively by Centrocercus urophasianus (Sage Grouse). In September 1997 prescribed fire was applied to four of eight randomly assigned 400‐ha A.t. wyomingensis (Wyoming big sagebrush) study plots at Hart Mountain National Antelope Refuge, Oregon. Livestock had not grazed experimental plots since 1991. Burning caused morphological changes such as significantly greater numbers of racemes and flowers per raceme in Astragalus malachus (shaggy milkvetch‐Legumoideae) (9 in burn vs. 6 in control; 23 in burn vs. 21 in control, respectively). Also, prescribed burning caused greater numbers of flowers in Phlox gracilis (microsteris‐Polemoniaceae) (57 vs. 13), greater numbers of umbels and umbelletts in Lomatium nevadense (Nevada desert parsley‐Umbellifereae) (4 vs. 2 and 59 vs. 31, respectively), greater numbers of flower heads in Crepis modocensis (Modoc hawksbeard‐Compositae) (32 vs. 21), and greater number of flowers/cm3 in Phlox longifolia (longleaf phlox‐Polemoniaceae) (0.11 vs. 0.06). Crown volume of Crepis modocensis (7,085 vs. 4,179 cm3) and Astragalus malachus (2,854 vs. 1,761 cm3) plants was greater in burned plots than control plots. However, burning resulted in a smaller crown area of Antennaria dimorpha (low pussytoes‐Compositae) (20 vs. 37 cm2). Phenology and time of flowering were also affected by fire. The period of active growth for each species was extended later into the summer in burned plots ( p < 0.01). In addition, Crepis modocensis and Lomatium nevadense flowered 12 to 14 days earlier in burned plots. Fire had no effect on frequency, density, and relative abundance of seven of the nine studied species. Fire reduced the frequency and relative abundance of A. dimorpha and Phlox longifolia and reduced the density of A. dimorpha.  相似文献   

14.
Abstract We investigated effects of fire frequency, seasonal timing, and plant community on patchiness and intensity of prescribed fires in subtropical savannas in the Long Pine Key region of Everglades National Park, Florida (U.S.A.). We measured patchiness and intensity in different plant communities along elevation gradients in “fire blocks.” These blocks were prescribed burned at varying times during the lightning season and at different frequencies between 1995 and 2000. Fire frequency, seasonal timing, and plant community all influenced the patchiness and intensity of prescribed fires. Fires were less patchy and more intense, probably because of drier conditions and pyrogenic fuels, in higher elevation plant communities (e.g., high pine savannas) than in lower elevation communities (e.g., long‐hydroperiod prairies). In all plant communities fires became increasingly patchy and less intense as the wet season progressed and moisture accumulated in fuels. Frequent prescribed fire resulted in increased patchiness but a wider range of intensities; higher intensities appeared to result from regrowth of more flammable vegetation. Our study suggests that frequent early lightning season prescribed fires produce a wider range of post‐fire conditions than less frequent late lightning season prescribed fires. Our study also suggests that natural early lightning season fires readily carried through pine savannas and short‐hydroperiod prairies, but lower elevation long‐hydroperiod prairies functioned as firebreaks. Natural fires probably crossed these firebreaks only during drier years, potentially producing large landscape‐level fires. Knowledge of how patchily and intensely fires burn across a savanna landscape should be useful for developing landscape‐level fire management.  相似文献   

15.
Abstract Prescribed fire is often used to restore grassland systems to presettlement conditions; however, fire also has the potential to facilitate the invasion of exotic plants. Managers of wildlands and nature reserves must decide whether and how to apply prescribed burning to the best advantage in the face of this dilemma. Herbicide is also used to control exotic plants, but interactions between fire and herbicides have not been well studied. Potentilla recta is an exotic plant invading Dancing Prairie Preserve in northwest Montana. We used a complete factorial design with all combinations of spring burn, fall burn, no burn, picloram herbicide, and no herbicide to determine the effects of fire, season of burn, and their interaction with herbicide on the recruitment and population growth of P. recta over a 5‐year period. Recruitment of P. recta was higher in burn plots compared with controls the first year after the fire, but this did not lead to significant population growth in subsequent years, possibly due to drier than normal conditions that occurred most years of the study. Effect of season of burn was variable among years but was higher in fall compared with spring burn plots across all years. Herbicide effectively eliminated P. recta from sample plots for 3–5 years. By the end of the study density of P. recta was greater in herbicide plots that were burned than those that were not. Results suggest that prescribed fire will enhance germination of P. recta, but this will not always lead to increased population growth. Prescribed fire may reduce the long‐term efficacy of herbicide applied to control P. recta and will be most beneficial at Dancing Prairie when conducted in the spring rather than the fall. Results of prescribed fire on exotic plant invasions in semiarid environments will be difficult to predict because they are strongly dependent on stochastic climatic events.  相似文献   

16.
Saccharomyces bailii grows in the presence of high concentrations of sorbic, benzoic and other short-chain monocarboxylic acids commonly used as preservatives. Starved cells concentrate these acids intracellularly, approximately as expected from the pH of the ceil and the p K a of the acid. On addition of glucose, the intracellular content of preservative is considerably reduced. The glucose effect is sensitive to metabolic inhibitors, and anaerobic respiration is stimulated by the preservatives. The ability to maintain a low intracellular concentration of any of the preservatives tested is induced by growth in the presence of sorbic or benzoic acid and less effectively by butyric or acetic acid. Both induced and uninduced cells are permeable to benzoic and butyric acids. Benzoate and sorbate are not metabolized at a rate significant with respect to the permeation rate. Resistance to these preservatives apparently results primarily from an inducible, energy requiring system which transports preservative from the cell.  相似文献   

17.
An attempt has been made to measure the relative risks and longevities of a group of cancer patients using a Weibull model whose parameters are function of covariatcs (viz treatment and condition of the patient). The methodology is Cox's Partial Likelihood and the Maximum Likelihood techniques for randomly censored data. The data consists of the records of 134 patients under a clinical trial in the treatment of Carcinoma of the Oro Pharynx as quoted by Kalbfleisch and Prentice (1980).  相似文献   

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Organic fertilizers can improve soil health while providing nutrients for perennial grass growth for bioenergy feedstock, particularly under marginal soil conditions. The impact of organic fertilizer application on perennial grass composition needs clarification. Our objective was to evaluate feedstock composition, and N, P, and K dynamics of switchgrass (Panicum virgatum L.), tall fescue [Lolium arundinaceum (Schreb.)], and reed canarygrass (Phalaris arundinacea L.) provided with either inorganic or organic fertilizer sources. Grasses were established on a sandy soil and a clay soil at the Cornell University Willsboro Research Farm in Willsboro, NY. The experiment was a split-split plot randomization of a randomized block design with six replicates. Sites were whole plots, grass species were subplots, and fertility treatments were sub-subplots. Six treatments were (1) 168 kg ha?1 of N fertilizer for cool-season grasses; 84 kg ha?1 for switchgrass, (2) 56 kg ha?1 of 0-46-0 P fertilizer plus N (#1), (3) 112 kg ha?1 of 0-0-60 K fertilizer plus N (#1), (4) 89.6 Mg dairy manure ha?1, (5) 44.8 Mg dairy manure compost ha?1, and (6) a control without fertilizer. Organic fertilizers produced a net positive P and K balance, while other treatments had negative balances. Organic fertilizer treatments resulted in lower lignin and gross energy values, and higher total ash and Cl, compared to inorganic fertilizer treatments. Switchgrass biomass had higher fiber and gross energy, lower total ash, and much lower Cl content under organic fertilizer applications than cool-season grasses, making switchgrass a more desirable feedstock regardless of conversion process.  相似文献   

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