ALBERT

Notizen: In 1990 and 1991, 40 ditch plugs were constructed to restore a more natural hydroperiod (i.e., duration and depth of flooding) on portions of the 8,900-ha Dupuis Reserve in south Florida. Vegetation transects and digital water level recorders were installed at three sites to monitor changes in vegetation relative to improved hydrologic conditions. Increased hydroperiod resulted in the elimination of Paspalum notatum (bahia grass), an exotic species introduced for cattle forage. Panicum repens (torpedo grass), another introduced species, formed dense monotypic stands in response to increased hydroperiod, but was unable to penetrate areas where Panicum hemitomon (maidencane) already existed. Frequency of occurrence and density of two desirable species, Pontederia cordata (pickerelweed) and maidencane, increased relative to higher inundation frequencies, although maidencane preferred more moderate water depths. Pickerelweed density increased significantly after the second year and was well established on two sites by the fourth year of monitoring.

Notizen: Arbuscular-mycorrhizal (AM) fungi stabilize the soil and enhance plant growth by alleviating nutrient and drought stress. Their contributions to agriculture are well known, but their role in desert ecosystems has received less attention. The AM status of perennial plants in disturbed and undisturbed plots were investigated in the Sonoran Desert near La Paz, Baja California Sur, Mexico to determine if AM fungi contribute to resource-island stability and plant establishment. All perennial plants (46 species) in the study plots were AM, but root colonization varied widely (〈10 to〉 70%). Roots of plants that established in greatest numbers in plant-free zones (colonizers) of disturbed areas were highly AM. Plants with trace (〈10%) root colonization (cacti of the tribe Pachycereae: Pachycereus pringlei, Machaerocereus gummosus, and Lemaireocereus thurberi; and Agave datilyo) established preferentially in association with nurse trees. The pachycereid cacti grew under Prosopis articulata and A. datilyo under Olneya tesota canopies. Of the nine species of trees and arborescent shrubs in the area, the mature (〉20 yr) nurse-legumes P. articulata and O. tesota supported the largest number of under-story plants. Younger plants had only occasional associates. AM propagule densities in plant-free areas were lower than under plant canopies (40 vs. 280 propagules/kg soil). Occurrence of soil mounds (islands) under plants owing to soil deposition was related to the nature of the canopies and to the AM status of the roots. Island soils were enmeshed with AM-fungal hyphae, especially in the upper layer (approximately 10 cm). Seedlings of P. pringlei, growing in a screenhouse for six months in soil collected under P. articulata, had a biomass ten times greater than plants growing in bare-area soil. The results are consistent with the proposition that AM fungi contributed to the plant-soil system of our study area by: (1) helping to stabilize windborne soil that settles under dense plant canopies; (2) enhancing the establishment of colonizer plants in bare soils of disturbed areas; and (3) influencing plant associations through differences in the mycotrophic status of the associates.

Notizen: We tested the effects of fall burning and protection from livestock grazing as management to enhance native grasses on a coastal grassland in central California. Plants from the Mediterranean, introduced beginning in the late 1700s, have invaded and now dominate most of California's grasslands. Coastal grasslands are generally less degraded than those inland and have higher potential for restoration and conservation. Productivity of the experimental plots varied annually and declined over the course of the study because of rainfall patterns. Foliar cover of the native Danthonia californica (California oatgrass) increased more under grazing than grazing exclusion and did not respond to burning. Two other natives, Nassella pulchra (purple needlegrass) and Nassella lepida (foothill needlegrass), responded variably to treatments. The response of N. pulchra differed from that reported on more inland sites in California. Restoring these grasslands is complicated by differing responses of target species to protection from grazing and burning. The current practice of managing to enhance single species of native plants (e.g., N. pulchra) may be detrimental to other equally important native species.

Notizen: The biodiversity of coal slurry ponds can be inhibited, at least in part, by dense stands of Phragmites australis. In this study, we demonstrate that species richness can be increased in coal slurry ponds if the dominant species (P. australis and Typha latifolia) are removed and that underwater herbivory simulated by cutting will kill emergents. The study was conducted in the greenhouse and the field in both flooded and drawndown conditions. Stems of plants of P. australis and T. latifolia were cut in a greenhouse and the cut plants of both species showed a decline in survivorship (25 and 42% survival, respectively) whereas all uncut plants survived. In a reclaimed coal pond at Pyramid State Park, Illinois, neither P. australis nor T. latifolia survived cutting underwater, but all of the uncut plants survived. Regrowth measured as total biomass of stems was less among flooded versus freely drained plants (0.3 and 2.6 g biomass, respectively). Cut versus uncut plants, combining freely drained and flooded, had less below-ground biomass (99.4 and 254.4 g, respectively). In the greenhouse study, oxygen levels in rhizomes subsequent to cutting were measured using an oxygen electrode and millivolt meter. Oxygen levels in P. australis were lower in cut versus uncut plants both in flooded (15.0 vs. 16.3% ambient O2, respectively) and freely drained conditions (14.5 vs. 15.0%, ambient O2, respectively). Similar responses to cutting were demonstrated by T. latifolia. In an unreclaimed coal slurry pond with monospecific stands of P. australis, plant species richness increased in cut plots as compared to uncut plots (29 vs. 2 species, respectively) between March and September, 1995. This study demonstrated that species richness can be increased in coal ponds by mechanical cutting and this potentially by herbivory; however, the additional species were mostly exotics.

Notizen: Attributes of 25 headwater streams and their associated wetlands were quantitatively sampled in the inner coastal plain of eastern North Carolina. Data from these sites were used to construct and test one functional assessment model (biogeochemical cycling) using the hydrogeomorphic (HGM) approach. Of the 25 sites sampled, 16 unaltered sites were used to establish standards against which field indicators could be compared (indexed). Nine altered sites were used to examine the sensitivity of the model to assess the types of alterations typically inflicted upon headwater ecosystems in eastern North Carolina: channelization, logging, construction of cross-floodplain ditches to shunt water directly from uplands to the main stream channel, and conversion of stream floodplains and buffer zones to cropland. Of 30 field indicators measured that potentially could be used to model alterations to hydrologic regime and biomass stocks, we found six were robust in assessing conditions related to biogeochemical cycling. Hydrologic indicators used in the model included: (1) presence/absence of channelization, (2) presence/absence of cross-floodplain ditches, and (3) a measure of buffer condition (using width and quality). Biomass indicators included: (4) total basal area of trees, (5) percent litter cover, and (6) volume of coarse woody debris. Our preliminary biogeochemical cycling model using these six variables was sensitive to alterations in nine altered sites and to a suite of hypothetical restorations of the most altered site. However, in order to improve accuracy of our preliminary model, it should be validated with studies designed to measure how alterations of various types and magnitudes affect biogeochemical processes.

Notizen: The study objective was to determine the fuelwood harvesting rotation and magnitude of nutrient accumulation by the sodic tolerant species Dalbergia sissoo and Prosopis juliflora for the rehabilitation of sodic wastelands. Mean annual increment and current annual increment growth of these trees reached a peak in six-year-old stands. Leaves dominated the litter of these species and contained high concentrations of most nutrients. N, Ca, Mg, and Fe were present in larger concentrations than other nutrients. Organic carbon additions at harvest after six years averaged 16 Mg ha−1, while soil pH was reduced from 9.8 to 8.6. Exchangeable sodium percentage (ESP) values decreased 65 and 29% under P. juliflora and D. sissoo, respectively, after harvest. These tree species produced significant root spread and deep penetration and were able to rehabilitate sodic soil effectively.

Notizen: Successional development at abandoned farmlands in southern Queensland, formerly occupied by sub-tropical rain forest is centred around scattered, isolated trees. Soil seed banks contain few woody plants and most tree species appear to be recruited from seed dispersed into the site by birds or bats. Scattered, low-growing trees 〈3 m in height act as the initial focus for the activities of seed-dispersing birds, but this process is accelerated by the development of taller trees〉 6 m in height that act as bird perches. The identity of these trees and whether or not they offer a fruit reward appears to matter less than their structure and suitability as a bird perch. The process of seedling recruitment may be accelerated when two or more trees form a cluster. The proportion of seedlings that survive and grow beyond 150 cm in height appears to be very small. Most of those that do can be classed as secondary rather than primary forest species, even though many primary forest species initially colonize the site. These observations were used to develop guidelines to accelerate the recovery of rainforest at degraded sites. The guidelines promote the early establishment of species that are usually poorly dispersed (e.g., large-fruited species), planted in scattered clumps. The guidelines should be suitable for situations where relatively large areas are in need of rehabilitation.

Notizen: The success of restoration plantings in restoring indigenous forest vascular plant and ground invertebrate biodiversity was assessed on previously grass-covered sites in the eastern South Island, New Zealand. The composition and structure of grassland, three different aged restoration plantings (12, 30, and 35 years old), a naturally regenerating forest (100 years old), and a remnant of the original old-growth forest of the area were measured. The restoration plantings are dominated by the native tree Olearia paniculata, which is not indigenous to the study area. Despite this, indigenous forest invertebrate and plant species are present in all three restoration sites and with increasing age the restoration sites become compositionally more similar to the naturally regenerating and mature forest sites. In particular the regenerating vegetation of the restoration sites is very similar floristically to the regenerating vegetation of the naturally regenerating and mature forest sites, despite marked differences in the current canopy vegetation reflecting the presence of the planted O. paniculata. The presence of regeneration in all three restoration sites indicates that the functional processes that initiate regeneration, such as dispersal, are present. The majority of regenerating tree species (71%) are bird dispersed and it is clear that birds play an important role in the recolonization of plant species at these sites despite the absence of edible fruit attractive to frugivorous birds on O. paniculata, a wind-dispersed species. The strong correlations between plant and invertebrate community composition and study-site age (r = 0.80, −0.24, −0.68 for plants, beetles, and spiders, respectively) suggest that the restoration site plant and invertebrate communities are undergoing change in the direction of the naturally regenerating and mature forest communities. Without restoration, colonization of grassland by forest plants is very slow in the study area and the restoration plantings studied here have been successful because they have considerably accelerated the return to forest at these sites.

Notizen: Rehabilitation of mangrove habitat has become common practice, but few studies have investigated the growth and survival of mangrove on artificial substrates. Managers attempting to plant mangrove in sites containing artificial substrates must remove substrates or risk poor performance of rehabilitation efforts. This study compared propagule retention, early survival, growth, flowering success, and nutrient concentrations of Avicennia marina (grey mangrove) grown on sand, naturally occurring substrate, and rock blast furnace slag over two growing seasons at an experimental site near Newcastle, Australia. Nutrient concentrations of experimental plants were also compared to those of naturally occurring plants. Experimental results showed significant differences (p 〈 0.05) in short-term survival, growth over the two growing seasons, and carbon and nitrogen concentrations between plants grown on different substrates. Comparison of plants grown in slag and plants from reference sites suggests, however, that slag does not lead to anomalies in nutrient concentrations of young mangroves. Although the results identified some differences between plants grown on river sand, naturally occurring substrate, and slag substrate, the absence of consistent differences suggests that mangroves planted in slag are under no greater risk of future failure than mangroves planted in naturally occurring substrate.

Notizen: Industrial barrens replacing coniferous forests around the Severonikel smelter in the Kola Peninsula, northwestern Russia, have recently expanded over 3000 ha or more. Total concentrations of metal contaminants in the upper soil layers approach 3000–5000 μg/g, and maximum hourly concentrations of sulphur dioxide in ambient air exceed 1000 μg/m3. To monitor possibilities for vegetation recovery in the denuded landscapes continuously affected by industrial emissions, we conducted several experiments with 4- to 15-year-old (1–25 cm tall) seedlings of Betula pubescens ssp. czerepanovi (mountain birch), replanted to two barren sites. Specifically, we investigated the effects of wind-sheltering, watering, and fertilization on seedling performance in the polluted sites. Sheltered and watered seedlings had more symmetrical leaves than control seedlings, suggesting less environmental stress. Consistently, sheltering and (to a lesser extent) watering improved the survival of seedlings compared with controls. The beneficial effects of watering and sheltering were most pronounced the first 2–4 weeks following planting and were greatest in the most polluted site. We conclude that the revegetation of industrial barrens can be significantly promoted by inexpensive treatments such as wind sheltering and watering, even under current emissions.

Notizen: The revegetation of sedge meadows has been problematic because natural recolonization does not occur under many circumstances and because planted propagules often fail to reestablish successfully. In this study, detached rhizomes of Carex lacustris Willd. and Carex stricta Lam. were transplanted in both fall (September) and spring (May) into three experimental wetlands to determine the effects of both planting season and hydrology on survival and establishment. Each experimental wetland had the same mean water depth across 5% slopes, but one had a constant water depth (0.5 m) throughout the growing season, another fell from a mean depth of 0.75 m to 0.25 m, and a third rose from a mean depth of 0.25 m to 0.75 m. Initial rhizome survival, shoot growth, and soil characteristics were recorded over 2 years. Neither planting proved successful (6.9% versus 0.5%) for C. stricta, a tussock-forming sedge. For C. lacustris, a sedge with spreading rhizomes, spring planting had greater rhizome survival (53.2% survival) than fall planting (0.7%). Since both species initiate new shoots in the fall, they are susceptible to transplant failure during this season. The highest survival rates (71–100%) and plant production (736.0 and 494.5 g/m2) for C. lacustris occurred near the water’s edge in both the constant and falling basins. In the rising basin, establishment and growth of this species was high at all water depths (71–96%; 399 g/m2). C. lacustris grew optimally at the same elevations where rhizome survival was greatest, suggesting that shoots are more sensitive to early-season than late-season water levels.

Notizen: Restoration of riparian vegetation along large rivers is complicated by the patchiness of the habitat and by conflicts with the societal need to control flooding. The Sacramento River Project, led by The Nature Conservancy in northern California, is testing whether it is possible to restore native forest along a large river without removing flood control. We conducted a post-hoc analysis of monitoring data collected by the project on 1–4-year old plantings of 10 native trees and shrubs at five sites. Two questions of general interest were: Can one identify types of species or sites that are especially suitable for restoration in such riparian habitats? To what degree must sites be treated as mosaics of patches, with different types of patches that are suited to different species? Plant performance as measured by height was better in species of Salicaceae or in species planted as cuttings than in species of other families or in species planted as seedings or seeds. Three within-site factors, land form, soil depth to a buried layer of sand or gravel, and soil texture, affected the growth of several species, indicating that sites do need to be treated as patchy. However, there was little evidence that different species performed better on different types of patches. Instead, areas with deep or fine soils seemed to be favorable for a number of species. Results suggest that it is feasible to re-establish native trees and shrubs along large, regulated rivers, at least at certain sites for an initial period of several years with the aid of weed control and irrigation. Shallowly buried layers or lenses of gravel or sand are a hidden, fine-scale factor that can reduce plant growth on river terraces.

Notizen: Efforts to reforest tropical pasture with native tree species have increased in recent years, yet little is known about the physiology of most tropical trees. The goal of this study was to assess the effect of habitat on photosynthetic responses to light for seedlings of four native rainforest species (Calophyllum brasiliense, Ocotea glaucosericea, Ocotea whitei, and Sideroxylon portoricense) planted to facilitate tropical rainforest recovery in southern Costa Rica. Seedlings were planted in primary forest, in open abandoned pasture, and in the shade of remnant trees within the pasture. Growth, morphology, photosynthetic gas exchange responses to light, and chlorophyll fluorescence (an indication of the integrity of photosynthetic processes) were measured in the three habitats. Height and leaf area were generally greater for seedlings in tree shade compared to those in the forest and open pasture. Photosynthetic rates were higher for plants in open pasture and tree shade compared to those in the forest for two of the four species. Chlorophyll fluorescence results indicated flexibility in the photosynthetic processing of light energy that may help plants tolerate the bright light of the pasture. This study demonstrates that, for certain species, seedlings under remnant pasture trees do not exhibit the level of photosynthetic stress experienced in open abandoned pasture. Seedling responses to light, in combination with other factors such as increased nutrient input through litterfall, help explain the enhanced growth of seedlings under remnant pasture trees. Planting seedlings under remnant trees may increase the success of future efforts to restore tropical forest in abandoned agricultural land.

Notizen: In the late 1800s, fire suppression, livestock grazing, and a wet and warm climate led to an irruption of pine regeneration in Pinus ponderosa Laws. (ponderosa pine) forests of the southwestern United States. Pines invaded bunchgrass openings, causing stand structure changes that increased the number of stand-replacing fires. Ecological restoration, via thinning and prescribed burning, is being used to decrease the risk of stand-replacing fires and ameliorate other effects of pine invasion. The effects of aboveground restoration on belowground processes are poorly understood. We used a hydrologic model and soil water nutrient concentrations, measured monthly below the rooting zone, to estimate restoration effects on nutrient losses by leaching from a mature ponderosa pine forest near Flagstaff, Arizona. Replicated restoration treatments included thinning to pre-1880 stand densities (partial restoration), thinning plus forest floor fuel reduction followed by a prescribed burn (complete restoration), and an untreated control. Water outflow occurred only between January and May and was lowest from the control (47 and 28 mm in 1995 and 1996) and highest from the partial restoration treatment (67 and 59 mm in 1995 and 1996). The concentrations (typically 〈0.10 mg/ L) and estimated annual losses (〈0.02 kg/ha) of NH4+-N, PO43−-P, and organic P were similar among treatments. Nitrate and organic N concentrations were as high as 0.80 mg N/L; however, these concentrations and estimated annual losses (〈0.13 kg N/ha) were similar among treatments. Our results suggest that restoration will not enhance nutrient loss by leaching or alter stream chemistry in ponderosa pine forests.

Notizen: A series of five grasslands of differing agricultural productivity and species diversity was chosen for this study. Four of these areas were divided into three sub-plots, each under a different management regime (either mown, sheep, or cattle grazed). Each sub-plot was inoculated with 180 transplants comprised of 12 individuals of 15 perennial species. These species were chosen to provide a spectrum of ‘phytometers’ to evaluate the receptivity of the grasslands to species introduction. Half of the plants were 9-cm pot-grown transplants, the other half, 2-cm plug plants. One-third of each of the transplant sizes was inserted into either 0-cm, 15-cm, or 30-cm-diameter gaps. Evaluation of species enrichment success was made by monitoring the survivorship of the transplants over a three-year study period. The fifth grassland was already species-rich and, therefore, left untreated and used as a reference community. The species could be classified into three main groups on the basis of their survivorship: (a) species with higher survivorship for pot than plug transplants; (b) species that established significantly better as plug than as pot transplants; and (c) species that suffered equally high mortalities as either pot or plug transplants. For three out of the four grasslands, the size of competition-free gaps was not significant in enhancing survivorship for either pot or plug transplants. Gap creation only aided survivorship for the set of plug plants inserted into the most productive grassland. Transplant survival was strongly negatively correlated with soil P and K concentrations, and peak biomass. In this, the establishment phase, the three management treatment regimes did not have a significant differential effect on transplant survival. The results are discussed in relation to practical techniques for restoring species-poor grasslands using transplants.

Notizen: We evaluated forest structure and composition in 9- to 13-year-old stands established on a bauxite-mined site at Trombetas (Pará), Brazil, using four different reforestation techniques following initial site preparation and topsoil replacement. These techniques included reliance on natural forest regeneration, mixed commercial species plantings of mostly exotic timber trees, direct seeding with mostly native early successional tree species, and mixed native species plantings of more than 70 tree species (the current operational restoration treatment at this site). Replicated fixed-radius plots in each treatment and in undisturbed primary forest were used to quantify the canopy and understory structure and the abundance and diversity of all vascular plant species. Treatment comparisons considered regeneration density, species richness and diversity for all floristic categories, and, for trees and shrubs, the relative contribution of initial planting and subsequent regeneration from soil seed banks and seed inputs from nearby primary forests. With the possible exception of the stands of mixed commercial species, which were superior to all others in terms of tree basal-area development but relatively poor in species richness, all treatments were structurally and floristically diverse, with a high probability of long-term restoration success. Of these, the mixed native species plantings appeared to be at least risk of arrested succession due to the dominance of a broader range of tree species of different successional stages or expected life spans. In all treatments, several locally important families of primary forest trees (Annonaceae, Chrysobalanaceae, Lauraceae, Palmae and Sapotaceae) were markedly underrepresented due to a combination of poor survival of initial plantings and limitations on seed dispersal from the surrounding primary forest.

Notizen: The goal of the study was to learn whether native prairie grasses and, eventually, a diverse mixture of native forbs could be incorporated in permanent pastures by means of rotational grazing by cattle. An experiment was established on a farm in northeastern Iowa on a pasture that had never been plowed but had been grazed since the 1880s. One treatment was protected from grazing to test for the presence of remnant vegetation. Andropogon gerardii, Sorghastrum nutans, Panicum virgatum, and Desmanthus illinoensis were introduced in plots first treated with glyphosate; seeds were either drilled (DR) or hand-broadcast and incorporated by controlled cattle trampling (BT). Seedling establishment and aboveground biomass were followed over 3 years. There was no evidence for remnant native plants on uplands, but seven species of native forbs and four native graminoids flowered in exclosures erected within waterways. D. illinoensis initially established up to 12 seedlings/m2 but had disappeared from all but one plot by the third year. Variation in native grass establishment among replicate plots within treatments was very high, ranging initially from 0.2 to 9.9 plants/m2. In August of the second year, native grasses made up only 8% of the available forage in DR plots and 1% of BT plots. One year later, however, native grasses made up 56% of the available forage in DR plots and 37% of BT plots, and these differences were significant (p= 0.05). A pilot study seeded in late winter (frost seeding) suggested that seeds spread after cattle trampling produced five times more seedlings (2.5/m2) than seeds spread before cattle trampling (0.5/m2). Frost seeding had advantages because it did not require herbicide for sod suppression or tractor access to the site. New plantings could be safely grazed in early spring and late fall, before and after most native grass growth, to offset the negative economic impact of protecting new plantings from burning during the growing season. But this practice precluded subsequent prescribed burning. I propose a strategy for incorporating native wildflowers into the pasture over time with minimum cost.

Notizen: Measuring the success of wetland restoration efforts requires an assessment of the wetland plant community as it changes following restoration. But analyses of restored wetlands often include plant community data from only one time period. We studied the development of plant communities at 13 restored marshes in northern New York for 4 years, including 1 year prior to restoration and 3 years afterwards. Restored wetlands ranged in size from 0.23 to 1.70 ha. Four reference wetlands of similar basin morphology, soil type, and size (0.29–0.48 ha) that occurred naturally in the same area were studied as comparisons. Dike construction to restore hydrology disturbed the existing vegetation in some parts of the restored sites, and vegetation was monitored in both disturbed and undisturbed areas. Undisturbed areas within the restored sites, which were dominated by upland field grasses before restoration, developed wetland plant communities with lower wetland index values but comparable numbers of wetland plant species than the reference wetlands, and they lagged behind the reference sites in terms of total wetland plant cover. There were significantly more plant species valuable as food sources for wetland birds, and a significantly higher percent cover of these species, at the undisturbed areas of the restored sites than at the reference wetlands. Areas of the restored sites that were disturbed by dike construction, however, often developed dense, monospecific cattail stands. In general, the plant communities at restored sites became increasingly similar to those at the reference wetlands over time, but higher numbers of herbaceous plants developed at the restored sites, including food plants for waterfowl, rails, and songbirds. Differences in shrub cover will probably lessen as natural recolonization increases shrub cover at the restored sites. Natural recolonization appears to be an effective technique for restoring wetlands on abandoned agricultural fields with established plant cover, but it is less successful in areas where soil has been exposed by construction activity.

Notizen: Reinstatement of vegetation to a similar condition to that prior to disturbance is often required in industrial restoration schemes. Seeding with specially prepared seed mixes containing species suited to local soils is often the preferred option on grounds of practicality and cost. Turf translocation is more difficult and costly but, if successful, meets the reinstatement requirement more precisely. In a pilot study at a proposed opencast coal site in Wales, we compared the effectiveness of whole-turf translocation of herb-rich mesic grassland communities, with a less technically demanding and more cost-effective technique involving spreading turf over twice the area at the receiver site and rotovating it into the underlying soil. The translocated whole turf and rotovated turf plots were cut annually and the vegetation removed to simulate grazing that had occurred prior to translocation. Both the whole-turf and rotovated turf transplant techniques gave successful re-establishment of 50% or more of the species originally present. After three years, the cover and species composition were similar in “whole-turf” and “spread and rotovated” plots. This suggests that the “spread and rotovate” technique provides a satisfactory ecological alternative to whole-turf translocation. However, plant communities changed, in some cases substantially, after translocation using either technique. Altered soil hydrology and nutrition combined with the substitution of cutting for grazing are probably the main causes of these changes.

Notizen: Only about 2.8 million ha of an estimated original 10 million ha of bottomland hardwood forests still exist in the Lower Mississippi River Alluvial Valley (LMAV) of the United States. The U.S. Fish and Wildlife Service, the U.S. Forest Service, and state agencies initiated reforestation efforts in the late 1980s to improve wildlife habitat. We surveyed restorationists responsible for reforestation in the LMAV to determine the magnitude of past and future efforts and to identify major limiting factors. Over the past 10 years, 77,698 ha have been reforested by the agencies represented in our survey and an additional 89,009 ha are targeted in the next 5 years. Oaks are the most commonly planted species and bare-root seedlings are the most commonly used planting stock. Problems with seedling availability may increase the diversity of plantings in the future. Reforestation in the LMAV is based upon principles of landscape ecology; however, local problems such as herbivory, drought, and flooding often limit success. Broad-scale hydrologic restoration is needed to fully restore the structural and functional attributes of these systems, but because of drastic and widespread hydrologic alterations and socioeconomic constraints, this goal is generally not realistic. Local hydrologic restoration and creation of specific habitat features needed by some wildlife and fish species warrant attention. More extensive analyses of plantings are needed to evaluate functional success. The Wetland Reserve Program is a positive development, but policies that provide additional financial incentives to landowners for reforestation efforts should be seriously considered.

Notizen: Gold Creek, in western Montana, lost complexity and diversity of fish habitat following riparian logging activities, removal of instream wood, and subsequent scouring. In the 4.8-km study area, the stream was almost totally void of large woody debris (4.2 pieces/km) and associated pools (1.3 pools/km). We constructed 66 structures made of natural materials (rock and wood) that resulted in 61 new pools in the study area in an attempt to restore salmonid habitat in the fall of 1996. An estimated 50-year recurrence interval flood occurred in the following spring. Of the original 66 structures, 55 (85%) remained intact and stable. Laterally confined reaches retained significantly more pools than laterally extended reaches. Owing to a history of anthropogenic impacts in forested streams in the intermountain west, restoration efforts are needed. If instream structures are tailored to specific morphologic channel types, fish habitat restoration can be successful and withstand major floods.

Notizen: In restoration experiments it is imperative to consider the study of mechanisms of how species are maintained and preserved in a system. This paper reports on the results of a field experiment examining the growth and survival of seedlings of Schizachyrium scoparium, a dominant perennial bunchgrass member of the Quercus havardii (sand shinnery oak) communities of semiarid western Texas, on mounds of displaced soil produced by Sylvilagus auduboni (rabbit). The central question posed is: does environmental heterogeneity created by small mammals influence seedling survival and growth? The specific questions addressed are: (1) Does seedling survival, growth, and nutrient uptake vary when grown on mounds, off-mound soils, and artificially created mounds?; (2) What is the influence of the microbial and litter components of mound soils on seedling survival?; and (3) In communities where animal disturbances create environmental heterogeneity and may impact seedling establishment, is it possible to artificially create mounds that could serve a similar function? Results show that characteristics of mound soils increase seedling survival, shoot and root biomass, root length, number of tillers, mycorrhizal infection, and nutrient uptake more in plants grown on mounds than off mounds. Both the microbial and litter components of mound soils are essential components of this effect. Artificial mounds generated from soils associated with the herbaceous community were more similar to intact rabbit mounds than artificial mounds generated from soils associated with the oaks. The results indicate that rabbits produce rich patches (both nutrient and microbial) favorable to the growth of seedlings of the dominant bunchgrass, and point to the potential importance of rabbit disturbances in shaping the dynamics of this plant community. Thus, rabbit-generated disturbances produce environmental heterogeneity in the sand shinnery oak community, similar to that produced by harvester ants in this community as shown by an earlier study. Small animal activity that results in soil displacement, and influences soil characteristics, may indirectly contribute to the persistence of certain plant species within a community. Thus, disturbances may well operate in semiarid communities to produce nutrient and microbe rich microsites which may function to maintain diversity.

Notizen: South African fynbos ecosystems are under threat from alien plant invasions and transformations to alternative land uses. If large-scale habitat loss and species extinction are to be halted, restoration actions are urgently required. We postulate that by adopting an approach in which an understanding of community and ecosystem dynamics is applied to restoration practices, protocols can be developed which will lead to more efficient restoration. This understanding is based on a review of the relevant ecological literature, focusing on recruitment dynamics, community structure, and ecosystem function, which are particularly relevant to restoration. We develop a conceptual framework for restoration and apply our protocols to a case study area on the Cape Peninsula. Before ecological restoration can begin, the cause of transformation must first be removed or ameliorated. The next step is to ensure that the important ecological processes are functioning. We contend that a fully functioning community requires a good balance of the major growth-form, regeneration, and nutrient acquisition guilds. Fire is the natural disturbance event initiating recruitment in fynbos. It is, therefore, essential to either burn a site or provide fire-related germination cues in order to stimulate recruitment. Where guilds are under-represented, corrective reintroductions will further improve the long-term resilience of the restored community. Many taxa have persistent soil-stored seed banks, so it is important to conserve topsoil and optimize use of this local species pool. Seed dispersal distances are generally very short, and in highly transformed sites it will be necessary to reintroduce seed of the major guilds in order to restore community structure and functioning. Post-fire succession in fynbos begins with the full complement of species; species gradually die out from the vegetation according to their respective life spans. In order to stimulate germination and promote successful establishment, it is important to sow seed after fire or site clearing in late summer or autumn. Introducing seed or plants at a later stage in the succession is very likely to fail. Because of the localized distributions of many taxa, extreme care must be taken when selecting species for reintroduction if local gene pools are to be conserved.

Notizen: To more thoroughly understand the ecological effects of harvesting geophytes for food by American Indians, an investigation of the ethnobotany and population dynamics of Dichelostemma capitatum (blue dicks), an attractive source of nutrition to many California Indian groups was undertaken. Some cultural groups harvest the corms and replant the cormlets, spare plants, and harvest after seeding to ensure replenishment of seed. Some Indian elders equate judicious harvesting with the maintenance and enhancement of field populations of this geophyte. A field experiment was conducted to determine the degree to which differences in intensity and timing of harvest, with and without replanting of cormlets, have any effect on corm and cormlet production. We found that harvesting at 100% intensity, through digging up all plants and corms, and without replanting cormlets at the seed stage, significantly reduces numbers of corms and cormlets compared to the controls (no harvest). However, harvesting at 50% intensity, through digging up half of all plants and corms at the flowering or seed stages, without replanting cormlets, was not significantly different from the controls (no harvest). The results suggest that harvesting blue dicks corms with a digging stick in the latter way could yield a sustainable level of harvest. Indigenous harvesting and management regimes may offer some of the best examples of long-term uses and management of the regional flora without detriment to its biodiversity. Restorationists are urged to study and experimentally mimic indigenous disturbance regimes and their ecological effects known to occur historically in various ecosystems. In some cases, areas will greatly benefit from the reintroduction of management and harvesting regimes that authentically simulate ancient indigenous interactions.

Notizen: Aristida stricta (wiregrass), a perennial bunchgrass, quickly accumulates dead leaves, which along with the shed needles of Pinus palustris (longleaf pine) provide the fuel for frequent surface fires. Thus, historically, wiregrass played a key role in many longleaf communities where it significantly influenced the natural fire regime and thereby the composition of the plant community. Reestablishment of wiregrass is, therefore, critical to restoring the native understory of Atlantic Coastal Plain longleaf pine ecosystems. This study measured the effects of different site preparations and fertilizer application on the survival and growth of wiregrass seedlings. Two-month–old seedlings were underplanted in existing longleaf pine stands on dry Lakeland soils at the Savannah River Site in South Carolina. Survival was acceptable at 51% after four years, although reduced owing to drought and small seedling size. Survival and growth could both be increased by using older seedlings with an initial height of at least 6 cm. Wiregrass leaves grew quite rapidly and attained an average length of 48 cm in four years on control plots. Basal area growth rate was greater than expected, averaging 40% on control treatments and 55% on cultivated and fertilized plots. If growth rates during the first four seasons continue, wiregrass will attain mature size on cultivated and fertilized plots at six years, while non-fertilized control plots will take eight years. A planting density of one seedling per m2 is recommended to provide sufficient wiregrass foliar cover to influence fire regimes in a reasonable length of time (i.e., 5–7 years).

Notizen: The loss and fragmentation of habitat is a major threat to the continued survival of many species. We argue that, by including spatial processes in restoration management plans, the effects of habitat loss and fragmentation can be offset. Yet few management plans take into account spatial effects of habitat conservation/restoration despite the importance of spatial dynamics in species conservation and recovery plans. Tilman et al. (1997) found a “restoration lag” in simulations of species restoration when randomly selecting habitat for restoration. Other studies have suggested that the placement of restored habitat can overcome effects of habitat loss and fragmentation. Here we report the findings of simulations that examine different regional management strategies, focusing on habitat selection. We find that nonrandom restoration practices such as restoring only habitat that is adjacent to those occupied by the target species can dramatically reduce or negate any restoration lag. In fact, we find that the increase in patch occupancy of the landscape can be greater than two-fold in the adjacent versus the random scenarios after only two restoration events, and this increase can be as great as six-fold during the early restoration phase. Many restoration efforts have limitations on both funds and available sites for restoration, necessitating high potential success on any restoration efforts. The incorporation of spatial analyses in restoration management may drastically improve a species' chance of recovery. Therefore, general principles that incorporate spatial processes and sensible management are needed to guide specific restoration efforts.

Notizen: We conducted a survey of ants in April 1997 in seven rehabilitated (2- to 20-year-old) and three native heathland reference sites of the Renison Goldfields Corporation (RGC) Mineral Sands operations at Eneabba, Western Australia. We employed a variety of collecting methods, including pitfall trapping, litter and soil sampling, sweeping and beating of vegetation, and collecting by hand in the day and after dark, replicating those used by previous researchers in a similar study conducted in the same area in 1980. We found a total of 96 ant species representing 30 genera in 1997, compared with 46 species from 18 genera in 1980. Ant species richness increased with age of rehabilitation and exceeded that of heath controls by the time it reached 11 years. Ant species richness related to rehabilitation age was represented by a logarithmic curve, and the slope for current rehabilitation was steeper than that for the earlier rehabilitation studied in 1980. This probably reflects improved rehabilitation practices. Ordination of the sites in terms of ant species composition indicated differences between ant species in the rehabilitated sites studied in 1980 and 1997, and also between all rehabilitated sites and heath controls. Classification of the sites in terms of the distribution of ants across functional groups also indicated differences between rehabilitation and heath control sites. According to species composition and functional group profiles from rehabilitated and control sites, we concluded that although the current rehabilitation allows for a rapid return of ant species, even after 20 years the fauna still had not attained the composition of the original heath fauna.

Notizen: In the 100 years following the arrival of Euro-American settlers in northern Arizona, Pinus ponderosa (ponderosa pine) forests changed from open, low-density stands to closed, high-density stands. The increase in tree density has been detrimental to the vigor of old-growth trees that established before settlement (presettlement trees). In this study, we examined whether the vigor of presettlement trees could be improved by restoring the original stand structure by thinning the ponderosa pines that established after settlement (postsettlement trees). The restoration treatment caused the following changes in the presettlement trees and their environment in the first year following thinning: an increase in volumetric soil water content between May and August, an increase in predawn xylem water potential in July and August, a decrease in midday xylem water potential in June and August, an increase in net photosynthetic rate in August, an increase in foliar nitrogen concentration in July and August, and an increase in bud and needle size. The results show that the thinning restoration treatment improved the condition of presettlement ponderosa pines by increasing canopy growth and the uptake of water, nitrogen, and carbon.

Notizen: Establishment of native riparian communities through natural seedfall may be a viable reclamation alternative at some alluvial sand and gravel mines where water level can be controlled in the abandoned pit. We experimented with this approach at a pit in Fort Collins, Colorado, where a drain culvert equipped with a screw gate allows water levels to be manipulated. From 1994 to 1996 we conducted a series of annual drawdowns during the period of natural seedfall of Populus deltoides subsp. monilifera (plains cottonwood), Salix amygdaloides (peachleaf willow), and S. exigua (sandbar willow), thus providing the bare, moist substrate conducive to establishment of these species. Establishment was highly variable from year to year; in the fall following establishment, frequency of occurrence on 0.5-m2 sample plots ranged from 8.6% to 50.6% for cottonwood, 15.9% to 22.0% for peachleaf willow, and 21.7% to 50.0% for sandbar willow. Mean densities, however, were comparable to those reported for other locations. Concurrent establishment of the undesirable exotic Tamarix ramosissima (saltcedar) was a problem, but we were able to eradicate most saltcedar seedlings by reflooding the lower elevations of the annual drawdown zones each fall. At the end of the 3-year period, at least one of the three native woody species survived on 41.1% of the plots, while saltcedar was present on only 6.1%. In addition to the potential for establishing valuable native habitats, adaptations of the techniques described may require less earth moving than other reclamation approaches.

Notizen: The morphometry of tidal channels in a back-barrier salt marsh in New Jersey was investigated. Characteristics of the tidal channel drainage network plan form (order, bifurcation ratio, length, sinuosity) and cross section channel form (width:depth ratio, hydraulic geometry) are compared with data from other studies. Drainage patterns follow Horton’s Law of Stream Numbers and Law of Stream Lengths. Mitigation sites should be designed in accordance with these laws. The degree to which site-specific substrate, vegetation, and flow conditions constrain or facilitate the development of sinuous, meandering channel reaches should be estimated to provide information for the design of tidal channel geometries and dimensions that will accommodate predicted discharges. Drainage networks in created and restored wetlands should reflect the spatial distribution of width and depth properties (width:depth ratios, cross-sectional areas, longitudinal slopes, hydraulic geometry) found in similar natural systems. Reproducing these characteristics will lessen the practice of oversizing channels. Hydraulic geometry relationships can facilitate the sizing of channels at Atlantic coast salt marsh mitigation sites. Recommendations are given to promote the development of drainage networks that function like the coastal back-barrier Avalon/Stone Harbor marsh in New Jersey.

Notizen: Detailed information, both quantitative and observational, on the course of vegetation succession in various human-disturbed habitats in Central Europe was used to construct an expert system named SUCCESS. Using the system, it is possible to predict tentatively the sequence of seral stages and dominant species exchange in successional seres initiated on bare ground and lasting up to 50 years. Simple information on geographical position, type of substratum, relief, moisture, nutrient content, character of surrounding vegetation, and size of the disturbed area is taken into consideration to predict site-specific succession in the particular habitats. The expert system is supposed to help landscape managers, nature conservationists, and environmental impact assessment experts in decision-making procedures to take into account the development of vegetation in man-made sites. Moreover, it also summarizes scientific information on the pattern of vegetation change in human-disturbed habitats in the geographical area considered.

Notizen: We studied the cumulative effects of 3 years of carbon amendments on previously disturbed mixed-grass prairie sites near Boulder, Colorado. Analysis of soil inorganic nitrogen during the third field season indicated statistically significant but short-term nitrogen reduction in response to addition of a combination of sugar and sawdust treatments. Plant foliage production was significantly reduced by these carbon amendments and averaged 377 g/m2/year on control plots versus 219 g/m2/year on treated plots. Undesirable species such as Centaurea diffusa (diffuse knapweed) exhibited a similar biomass response. But after three years of treatment there is little evidence to suggest a relative increase in desirable, reseeded species such as Agropyron smithii (western wheatgrass). We suggest that the carbon amendment treatment alone is an inadequate remediation technique in areas exposed to extensive seed rain by exotic species.

Notizen: The goal of revegetation projects on degraded or polluted lands is to create a near-natural, stable, and quick-response ecosystem that does not require particular management after establishment and that is compatible with the surrounding landscape. Municipal waste compost (MWC) is commonly used in revegetation projects as a source of organic matter. The aim of this study was to investigate the germination percentage and average time of germination of 23 species (12 cultivated grasses and legumes and 11 native herbs) as affected by the leachates from soil, three different mixtures of soil-compost, and pure compost. The treatments influenced the average time of germination (ATG); legumes were the most affected species, followed by grasses and wild herbs. The percentage of germination of Festuca arundinacea was not affected by the presence of compost leachate, while Lolium multiflorum was the most sensitive species. A higher content of compost in the mixture caused a delay in germination of all the grasses. Most of the legumes were able to germinate in the leachate of the soil-compost mixtures, but their germination was delayed; Trifolium pratense had the highest sensitivity in terms of average time of germination. The native herbs Lepidium sativum, Matricaria chamomilla, and Sanguisorba officinalis germinated without any adverse effect when treated with leachate from high levels of MWC; the germination of Amaranthus cruentus was influenced by all levels of MWC in substrates, suggesting a high specific sensitivity for toxic components of leachate from MWC-soil mixtures.

Notizen: Flow regulation, which has largely eliminated flooding along the Rio Grande in central New Mexico, has substantially changed the riparian ecosystem. We investigated managed flooding as a means of restoring ecosystem function. After collecting baseline data during 1991 and 1992 in two riparian forest sites that had not flooded for about 50 years, we flooded an experimental site for 27–32 days during late spring of 1993, 1994, and 1995, leaving the reference site unflooded. During the final year of the study we compared these sites to two additional sites located within the riverside levee, one of which has been flooding naturally while the second remained largely unflooded. Three years of experimental flooding did not change the total biomass of either woody debris or forest-floor litter at the experimental flood site. Both woody debris and forest-floor litter, however, were significantly lower at the natural flood site than at the experimental flood site and two unflooded sites. Leaf and wood decomposition rates increased with flooding. The decay rate for cottonwood logs at the unflooded site (0.010 per year) predicted a half-life of 69.3 years, while the decay rate of 0.065 per year after 3 years of experimental flooding predicted a half-life of 10.6 years. This suggests that a decade of annual flooding may be used to restore the organic debris to pre-regulation levels. Flooding may also have caused an increase in litter production. These results suggest that experimental flooding has initiated a process of restoring ecosystem function within the riparian forest.

Notizen: The reestablishment of native shrubs is part of the mandate under which mining companies extract mineral resources in Wyoming and other western states. Post-mining shrub density and species mixtures have been topics debated by various mine reclamation stake holders. By law, coal-mined lands in Wyoming must now meet a post-mining shrub density of 1 shrub/m2 on 20% of the affected area. To better understand the long-term results of shrub reclamation methods, we measured shrub density by species in 14 pre-1985 seedings at eight mines in three geographic regions of Wyoming. The sites studied were selected as Atriplex canescens (Pursh) Nutt. (fourwing saltbush) and grass or as Artemisia tridentata Nutt. ssp. wyomingensis (Beetle and Young) (Wyoming big sagebrush), fourwing saltbush, and grass post-mining communities. Shrub density and composition varied by site but typically reflected the seed mixtures used. Seedings that used a diversity of shrub species generally had greater 1994 shrub densities. Seeding rates between 60 and 1000 shrub seeds/m2 had a positive, linear relationship with shrub density up to 0.6 shrubs/m2 when sagebrush was part of the shrub seed mixture. We conclude that the likelihood of meeting the shrub standard can be enhanced by seeding diverse shrub mixtures at high seeding rates.

Notizen: We present a conceptual framework for choosing native plant material to be used in restoration projects on the basis of ecological genetics. We evaluate both the likelihood of rapid establishment of plants and the probability of long-term persistence of restored or later successional communities. In addition, we consider the possible harmful effects of restoration projects on nearby ecosystems and their native resident populations. Two attributes of the site to be restored play an important role in determining which genetic source will be most appropriate: (1) degree of disturbance and (2) size of the disturbance. Local plants or plants from environments that “match” the habitat to be restored are best suited to restore sites where degree of disturbance has been low. Hybrids or “mixtures” of genotypes from different sources may provide the best strategy for restoring highly disturbed sites to which local plants are not adapted. Cultivars that have been modified by intentional or inadvertent selection have serious drawbacks. Nevertheless, cultivars may be appropriate when the goal is rapid recovery of small sites that are highly disturbed.

Notizen: At a salt marsh restoration site, fertilizer trials to improve height growth of Spartina foliosa (a C4 perennial grass that can reach 140 cm) appeared to favor Salicornia bigelovii (an annual C3 succulent under 40 cm tall) where the two species co-occurred on the marsh plain. This observation prompted a field experiment to examine the potential for nitrogen (N) addition to shift community composition. Without N addition, total stem length and stem density of S. foliosa did not respond to the presence or absence of S. bigelovii. But where N was added, S. foliosa growth increased only where S. bigelovii was removed from plots. S. bigelovii responded strongly to fertilizer, with mean heights matching those of S. foliosa and 600% increases in biomass, branching, and seed production (to more than 1 million seeds/m2). Soil N also increased seasonally where S. bigelovii was present, suggesting that this species may aid accumulation of N at restoration sites with poor soils. S. foliosa growth is greatest at lower elevations along tidal creeks where it occurs alone. Beyond creek edges, where S. bigelovii and other potential competitors occur, S. foliosa is unlikely to grow tall even with N addition. Thus, there is little point in trying to force mixed-species stands to provide tall S. foliosa for nesting by an endangered bird, Rallus longirostris levipes (the Light-footed Clapper Rail). A marsh construction design that maximizes tidal creek edges is thus recommended when restoration goals include providing habitat for clapper rails.

Notizen: Successful restoration of sedge meadow wetlands is limited by lack of information regarding reintroduction of sedge (Carex) propagules. While restoration from seed is common for prairie restorations, little is known about the germination characteristics of many wetland plants, including sedges. We present the results of a 2.5-year study on seed germination and viability for five species of Carex common to sedge meadow and prairie pothole wetlands in temperate North America. Seed storage and germination conditions were investigated to determine the optimum combination for maintaining seed viability and stimulating germination rates over time. Seeds were germinated under seven different temperature and three moisture regimes after storage for 4, 10, and 14 months under one of four different storage regimes (dry-warm, dry-cold, moist-cold, and wet-cold). The efficacy of short-term wet-cold stratification to stimulate germination of 2.5-year-old seed after long-term dry storage was also investigated. Carex stricta, Carex comosa, and Carex lacustris showed the greatest germination response after wet-cold or moist-cold storage, while Carex lasiocarpa and Carex rostrata showed similar rates of germination after either wet-cold or dry-warm storage. Wet-cold long-term storage was associated with a high level of viability in all five species after 2.5 years. Viability and germination rates were reduced in Carex stricta, Carex comosa, and Carex lasiocarpa after long-term dry-cold storage. Germination rates of seeds stored dry for 2.5 years are not improved by short-term wet-cold treatment in any species tested. Carex seeds should be stored under wet-cold conditions to maintain seed viability over time, thus increasing the likelihood of seeding success for sedge meadow restoration.

Notizen: I describe a 1.5-ha riverine headwater forest (Hall Branch) that was created 11 years earlier on phosphate-mined and reclaimed land near Tampa, Florida, U.S.A. Favorable hydrologic and edaphic conditions were realized, owing to the proper positioning of the project site in an effectively reclaimed landscape. The soil had developed a distinct A horizon and an incipient B horizon. Planted trees, mainly species of Acer, Fraxinus, Ilex, Liquidambar, Magnolia, Persea, Quercus, Taxodium, and Ulmus, shared dominance with short-lived volunteer willows (Salix caroliniana) that had already begun to senesce. The tree canopy exhibited 85% cover, and some trees had grown to 12.5 m tall. Basal area reached 8.31 m2/ha for trees 10 cm or more in diameter at breast height. Ten planted tree species produced seeds and yielded seedlings. The floristic composition over the decade consisted of 22 species of trees and 208 shrubs, vines, epiphytes, ferns, graminoids, and forbs. Thirty-eight non-arboreal species were directly transplanted, others arose from a seed bank in muck that was amended on wetter sites, and the rest volunteered via natural dissemination. The frequency of non-arboreal plants was collectively 98%. Seventy-three species at the restoration site were characteristic of the mature, undisturbed reference ecosystem. A corresponding area within the reference ecosystem contained essentially the same number of species and the same array of life forms. Copious plant reproduction has transformed the planted forest into an intact ecosystem that no longer needs restoration assistance.

Notizen: The rehabilitation of vegetation on structurally crusted soils by triggering termite activity through mulch was studied on three soil types in northern Burkina Faso, West Africa. A split-plot design was used in a fenced environment for the experiment. Insecticide (Dieldrin) was used at a rate of 500 g a.i. (active ingredient)/ha to create nontermite and termite plots. Three mulch types consisting of straw (Pennisetum pedicellatum), woody material (Pterocarpus lucens), and a composite mulch (straw and woody material) applied at a rate of 3, 6, and 4 tons/ha, respectively, were used to trigger termite activity. The grasses and woody species on the plots were surveyed. Nontermite plots responded weakly to mulch treatments, but even in the first year vegetation established on termite + mulch plots. Termite activity resulted in the increase of plant cover, plant species number, phytomass production, and rainfall use efficiency. Infiltrated water use efficiency and plant diversity were not statistically different among treatments during the first 2 years but were in the third. Woody species established only on termite plots. The three types of mulch plots showed greater vegetation development than bare plots, which remained bare throughout the experiment. Analysis of the termite and mulch interaction indicated that mulch plots without termites did not perform better than bare plots, especially in the case of woody plant regeneration. Vegetation rehabilitation was best with composite and straw mulches with termites, followed by woody mulch with termites; it was worst on bare plots.

Notizen: Hypothetical models in the scientific literature suggest that ecosystem restoration and creation sites follow a smooth path of development (called a trajectory), rapidly matching natural reference sites (the target). Multi-million-dollar mitigation agreements have been based on the expectation that damages to habitat will be compensated within 5–10 years, and monitoring periods have been set accordingly. Our San Diego Bay study site, the Sweetwater Marsh National Wildlife Refuge, has one of the longest and most detailed records of habitat development at a mitigation site: data on soil organic matter, soil nitrogen, plant growth, and plant canopies for up to 10 years from a 12-year-old site. High interannual variation and lack of directional changes indicate little chance that targets will be reached in the near future. Other papers perpetuate the trajectory model, despite data that corroborate our findings. After reviewing “trajectory models” and presenting our comprehensive data for the first time, we suggest alternative management and mitigation policies.

Notizen: High metacyclogenesis was induced when freshly-isolated Trypanosoma rangeli from humans were grown in a modified liver-infusion-tryptose medium and transferred into the medium overlaid on mouse fibroblasts at 27° C in a 5% CO2 atmosphere. Such in yitro-generated metacyclic trypomastigotes could induce a significantly high and constant parasitemia in both ICR and SCID mice for a period of about a week but thereafter the parasitemia gradually decreased. Histological examination could not detect any tissue-forms of T. rangeli in various organs of SCID mice. On the other hand, two long-maintained stocks of T. rangeli produced lower metacyclogenesis and only latent parasitemia in both strains of mice. When these populations were incubated in fibroblast cultures at 37° C in a 5% CO2 atmosphere, only trypomastigotes survived for two to three weeks without proliferation, while other forms, mainly epimastigotes, soon began to swell and degenerate. Electron microscopy showed that most surviving trypomastigotes had the basket-like conformation of the kinetoplasts. This is characteristic of the non-dividing trypomastigote stage of T. cruzi, and suggests that T. rangeli trypomastigotes may survive long periods in the blood without proliferation.

Notizen: Several transmission studies, as well as recent molecular data, have indicated that the two classes Myxosporea and Actinosporea represent different life cycle stages of Myxozoa. To evaluate the life cycles of myxozoa in catfish aquaculture systems, the small subunit (18S) ribosomal RNA gene sequences of Henneguya exilis, a myxosporean from channel catfish Ictalurus punctatus, and an actinosporean (previously designated as Aurantiactinomyxon janiszewskai) from the aquatic oligochaete Dero digitata were determined. The sequences were identical, indicating that H. exilis and the actinosporean are alternate life stages of a single species. This is the first report identifying the actinosporean stage of the genus Henneguya.

Notizen: The mechanism of stomatin-induced differentiation of Tetrahymena vorax was investigated by in vivo protease degradation of cell surface proteins, the direct measurement of products formed from the activation of phospholipase C, and the use of an array of signal transduction inhibitors/activators. The data indicate that a surface-exposed protein is required for stomatin to signal the cells to differentiate and that the cells are committed to the differentiation pathway within two hours after exposure to stomatin. Analysis of radiolabeled polyphosphoinositols and inositol lipids from control and stomatin-treated populations in the presence of 10 mM LiCl were consistent with a rapid activation of phospholipase C. Within five min following addition of stomatin, this resulted in an increase in polyphosphoinositols and a concomitant decrease in the relative amounts of phosphatidylinositol bisphosphate and phosphatidylinositol trisphosphate.

Notizen: Abstract The Raman spectrum of a protein or nucleic acid consists of numerous discrete bands representing molecular normal modes of vibration and serves as a sensitive and selective fingerprint of three-dimensional structure, intermolecular interactions, and dynamics. Recent improvements in instrumentation, coupled with innovative approaches in experimental design, dramatically increase the power and scope of the method, particularly for investigations of large supramolecular assemblies. Applications are considered that involve the use of (a) time-resolved Raman spectroscopy to elucidate assembly pathways in icosahedral viruses, (b) polarized Raman microspectroscopy to determine detailed structural parameters in filamentous viruses, (c) ultraviolet-resonance Raman spectroscopy to probe selective DNA and protein residues in nucleoprotein complexes, and (d) difference Raman methods to understand mechanisms of protein/DNA recognition in gene regulatory and chromosomal complexes.

Notizen: Abstract Transcription in eukaryotes is frequently regulated by a mechanism termed combinatorial control, whereby several different proteins must bind DNA in concert to achieve appropriate regulation of the downstream gene. X-ray crystallographic studies of multiprotein complexes bound to DNA have been carried out to investigate the molecular determinants of complex assembly and DNA binding. This work has provided important insights into the specific protein-protein and protein-DNA interactions that govern the assembly of multiprotein regulatory complexes. The results of these studies are reviewed here, and the general insights into the mechanism of combinatorial gene regulation are discussed.

Notizen: Abstract Analytical ultracentrifugation is a classical method of biochemistry and molecular biology. Because it is a primary technique, sedimentation can provide first-principle hydrodynamic and first-principle thermodynamic information for nearly any molecule, in a wide range of solvents and over a wide range of solute concentrations. For many questions, it is the technique of choice. This review stresses what information is available from analytical ultracentrifugation and how that information is being extracted and used in contemporary applications.

Notizen: Abstract Measurement of the distance between two spin label probes in proteins permits the spatial orientation of elements of defined secondary structure. By using site-directed spin labeling, it is possible to determine multiple distance constraints and thereby build tertiary and quaternary structural models as well as measure the kinetics of structural changes. New analytical methods for determining interprobe distances and relative orientations for uniquely oriented spin labels have been developed using global analysis of multifrequency electron paramagnetic resonance data. New methods have also been developed for determining interprobe distances for randomly oriented spin labels. These methods are being applied to a wide range of structural problems, including peptides, soluble proteins, and membrane proteins, that are not readily characterized by other structural techniques.

Notizen: Abstract Current computer simulations of biomolecules typically make use of classical molecular dynamics methods, as a very large number (tens to hundreds of thousands) of atoms are involved over timescales of many nanoseconds. The methodology for treating short-range bonded and van der Waals interactions has matured. However, long-range electrostatic interactions still represent a bottleneck in simulations. In this article, we introduce the basic issues for an accurate representation of the relevant electrostatic interactions. In spite of the huge computational time demanded by most biomolecular systems, it is no longer necessary to resort to uncontrolled approximations such as the use of cutoffs. In particular, we discuss the Ewald summation methods, the fast particle mesh methods, and the fast multipole methods. We also review recent efforts to understand the role of boundary conditions in systems with long-range interactions, and conclude with a short perspective on future trends.

Notizen: Abstract Recent structural and biochemical studies have begun to illuminate how cells solve the problems of recognizing and removing damaged DNA bases. Bases damaged by environmental, chemical, or enzymatic mechanisms must be efficiently found within a large excess of undamaged DNA. Structural studies suggest that a rapid damage-scanning mechanism probes for both conformational deviations and local deformability of the DNA base stack. At susceptible lesions, enzyme-induced conformational changes lead to direct interactions with specific damaged bases. The diverse array of damaged DNA bases are processed through a two-stage pathway in which damage-specific enzymes recognize and remove the base lesion, creating a common abasic site intermediate that is processed by damage-general repair enzymes to restore the correct DNA sequence.

Notizen: Abstract A significant number of exciting papain-like cysteine protease structures have been determined by crystallographic methods over the last several years. This trove of data allows for an analysis of the structural features that empower these molecules as they efficiently carry out their specialized tasks. Although the structure of the paradigm for the family, papain, has been known for twenty years, recent efforts have reaped several structures of specialized mammalian enzymes. This review first covers the commonalities of architecture and purpose of the papain-like cysteine proteases. From that broad platform, each of the lysosomal enzymes for which there is an X-ray structure (or structures) is then examined to gain an understanding of what structural features are used to customize specificity and activity. Structure-based design of inhibitors to control pathological cysteine protease activity will also be addressed.

Notizen: Abstract For nuclear magnetic resonance determinations of the conformation of oligosaccharides in solution, simple molecular mechanics calculations and nuclear Overhauser enhancement measurements are adequate for small oligosaccharides that adopt single, relatively rigid conformations. Polysaccharides and larger or more flexible oligosaccharides generally require additional types of data, such as scalar and dipolar coupling constants, which are most conveniently measured in 13C-enriched samples. Nuclear magnetic resonance relaxation data provide information on the dynamics of oligosaccharides, which involves several different types of internal motion. Oligosaccharides complexed with lectins and antibodies have been successfully studied both by X-ray crystallography and by nuclear magnetic resonance spectroscopy. The complexes have been shown to be stabilized by a combination of polar hydrogen bonding interactions and van der Waals attractions. Although theoretical calculations of the conformation and stability of free oligosaccharides and of complexes with proteins can be carried out by molecular mechanics methods, the role of solvent water for these highly polar molecules continues to present computational problems.

Notizen: Abstract Proteasomes are large multisubunit proteases that are found in the cytosol, both free and attached to the endoplasmic reticulum, and in the nucleus of eukaryotic cells. Their ubiquitous presence and high abundance in these compartments reflects their central role in cellular protein turnover. Proteasomes recognize, unfold, and digest protein substrates that have been marked for degradation by the attachment of a ubiquitin moiety. Individual subcomplexes of the complete 26S proteasome are involved in these different tasks: The ATP-dependent 19S caps are believed to unfold substrates and feed them to the actual protease, the 20S proteasome. This core particle appears to be more ancient than the ubiquitin system. Both prokaryotic and archaebacterial ancestors have been identified. Crystal structures are now available for the E. coli proteasome homologue and the T. acidophilum and S. cerevisiae 20S proteasomes. All three enzymes are cylindrical particles that have their active sites on the inner walls of a large central cavity. They share the fold and a novel catalytic mechanism with an N-terminal nucleophilic threonine, which places them in the family of Ntn (N terminal nucleophile) hydrolases. Evolution has added complexity to the comparatively simple prokaryotic prototype. This minimal proteasome is a homododecamer made from two hexameric rings stacked head to head. Its heptameric version is the catalytic core of archaebacterial proteasomes, where it is sandwiched between two inactive antichambers that are made up from a different subunit. In eukaryotes, both subunits have diverged into seven different subunits each, which are present in the particle in unique locations such that a complex dimer is formed that has six active sites with three major specificities that can be attributed to individual subunits. Genetic, biochemical, and high-resolution electron microscopy data, but no crystal structures, are available for the 19S caps. A first step toward a mechanistic understanding of proteasome activation and regulation has been made with the elucidation of the X-ray structure of the alternative, mammalian proteasome activator PA28.

Notizen: Abstract Ubiquitous among eukaryotes, the ADF/cofilins are essential proteins responsible for the high turnover rates of actin filaments in vivo. In vertebrates, ADF and cofilin are products of different genes. Both bind to F-actin cooperatively and induce a twist in the actin filament that results in the loss of the phalloidin-binding site. This conformational change may be responsible for the enhancement of the off rate of subunits at the minus end of ADF/cofilin-decorated filaments and for the weak filament-severing activity. Binding of ADF/cofilin is competitive with tropomyosin. Other regulatory mechanisms in animal cells include binding of phosphoinositides, phosphorylation by LIM kinases on a single serine, and changes in pH. Although vertebrate ADF/cofilins contain a nuclear localization sequence, they are usually concentrated in regions containing dynamic actin pools, such as the leading edge of migrating cells and neuronal growth cones. ADF/cofilins are essential for cytokinesis, phagocytosis, fluid phase endocytosis, and other cellular processes dependent upon actin dynamics.

Notizen: Abstract Endoderm, one of the three principal germ layers, contributes to all organs of the alimentary tract. For simplicity, this review divides formation of endodermal organs into four fundamental steps: (a) formation of endoderm during gastrulation, (b) morphogenesis of a gut tube from a sheet of cells, (c) budding of organ domains from the tube, and (d) differentiation of organ-specific cell types within the growing buds. We discuss possible mechanisms that regulate how undifferentiated endoderm becomes specified into a myriad of cell types that populate the respiratory and gastrointestinal tracts.

Notizen: Abstract Information can be transferred between the nucleus and the cytoplasm by translocating macromolecules across the nuclear envelope. Communication of extracellular or intracellular changes to the nucleus frequently leads to a transcriptional response that allows cells to survive in a continuously changing environment. Eukaryotic cells have evolved ways to regulate this movement of macromolecules between the cytoplasm and the nucleus such that the transfer of information occurs only under conditions in which a transcriptional response is required. This review focuses on the ways in which cells regulate movement of proteins across the nuclear envelope and the significance of this regulation for controlling diverse biological processes.

Notizen: Abstract In Dictyostelium amoebae, cell-type differentiation, spatial patterning, and morphogenesis are controlled by a combination of cell-autonomous mechanisms and intercellular signaling. A chemotactic aggregation of ~105 cells leads to the formation of a multicellular organism. Cell-type differentiation and cell sorting result in a small number of defined cell types organized along an anteroposterior axis. Finally, a mature fruiting body is created by the terminal differentiation of stalk and spore cells. Analysis of the regulatory program demonstrates a role for several molecules, including GSK-3, signal transducers and activators of transcription (STAT) factors, and cAMP-dependent protein kinase (PKA), that control spatial patterning in metazoans. Unexpectedly, two component systems containing histidine kinases and response regulators also play essential roles in controlling Dictyostelium development. This review focuses on the role of cAMP, which functions intracellularly to mediate the activity of PKA, an essential component in aggregation, cell-type specification, and terminal differentiation. Cytoplasmic cAMP levels are controlled through both the regulated activation of adenylyl cyclases and the degradation by a phosphodiesterase containing a two-component system response regulator. Extracellular cAMP regulates G-protein-dependent and -independent pathways to control aggregation as well as the activity of GSK-3 and the transcription factors GBF and STATa during multicellular development. The integration of these pathways with others regulated by the morphogen DIF-1 to control cell fate decisions are discussed.

Notizen: Abstract Cotranslational protein translocation across and integration into the membrane of the endoplasmic reticulum (ER) occur at sites termed translocons. Translocons are composed of several ER membrane proteins that associate to form an aqueous pore through which secretory proteins and lumenal domains of membrane proteins pass from the cytoplasm to the ER lumen. These sites are not passive holes in the bilayer, but instead are quite dynamic both structurally and functionally. Translocons cycle between ribosome-bound and ribosome-free states, and convert between translocation and integration modes of operation. These changes in functional state are accompanied by structural rearrangements that alter translocon conformation, composition, and interactions with ligands such as the ribosome and BiP. Recent studies have revealed that the translocon is a complex and sophisticated molecular machine that regulates the movement of polypeptides through the bilayer, apparently in both directions as well as laterally into the bilayer, all while maintaining the membrane permeability barrier.

Notizen: Abstract Synaptic vesicles, which have been a paradigm for the fusion of a vesicle with its target membrane, also serve as a model for understanding the formation of a vesicle from its donor membrane. Synaptic vesicles, which are formed and recycled at the periphery of the neuron, contain a highly restricted set of neuronal proteins. Insight into the trafficking of synaptic vesicle proteins has come from studying not only neurons but also neuroendocrine cells, which form synaptic-like microvesicles (SLMVs). Formation and recycling of synaptic vesicles/SLMVs takes place from the early endosome and the plasma membrane. The cytoplasmic machinery of synaptic vesicle/SLMV formation and recycling has been studied by a variety of experimental approaches, in particular using cell-free systems. This has revealed distinct machineries for membrane budding and fission. Budding is mediated by clathrin and clathrin adaptors, whereas fission is mediated by dynamin and its interacting protein SH3p4, a lysophosphatidic acid acyl transferase.

Notizen: Abstract A decade of research on adaptive mutation has revealed a plethora of mutagenic mechanisms that may be important in evolution. The DNA synthesis associated with recombination could be an important source of spontaneous mutation in cells that are not proliferating. The movement of insertion elements can be responsive to environmental conditions. Insertion elements not only activate and inactivate genes, they also provide sequence homology that allows large-scale genomic rearrangements. Some conjugative plasmids can recombine with their host's chromosome, and may acquire chromosomal genes that could then spread through the population and even to other species. Finally, a subpopulation of transient hypermutators could be a source of multiple variant alleles, providing a mechanism for rapid evolution under adverse conditions.

Notizen: Abstract Lentiviruses are associated with chronic diseases of the hematological and neurological systems in animals and man. In particular, human immunodeficiency virus type 1 (HIV-1) is the etiological agent of the global AIDS epidemic. The genomes of lentiviruses are complex, encoding a number of regulatory and accessory proteins not found in other retroviruses. This complexity is reflected in their replication cycle, which reveals intricate regulatory pathways and unique mechanisms for viral persistence. In this review, we highlight some of these unique features for HIV-1, with particular focus on the transcriptional and posttranscriptional control of gene expression. Although our understanding of the biology of HIV-1 is far from complete, the knowledge gained thus far has already led to novel strategies for both virus intervention and exploiting the lentiviruses for therapeutic applications.

Notizen: Abstract The stability of mRNA in prokaryotes depends on multiple factors and it has not yet been possible to describe the process of mRNA degradation in terms of a unique pathway. However, important advances have been made in the past 10 years with the characterization of the cis-acting RNA elements and the trans-acting cellular proteins that control mRNA decay. The trans-acting proteins are mainly four nucleases, two endo- (RNase E and RNase III) and two exonucleases (PNPase and RNase II), and poly(A) polymerase. RNase E and PNPase are found in a multienzyme complex called the degradosome. In addition to the host nucleases, phage T4 encodes a specific endonuclease called RegB. The cis-acting elements that protect mRNA from degradation are stable stem-loops at the 5' end of the transcript and terminators or REP sequences at their 3' end. The rate-limiting step in mRNA decay is usually an initial endonucleolytic cleavage that often occurs at the 5' extremity. This initial step is followed by directional 3' to 5' degradation by the two exonucleases. Several examples, reviewed here, indicate that mRNA degradation is an important step at which gene expression can be controlled. This regulation can be either global, as in the case of growth rate-dependent control, or specific, in response to changes in the environmental conditions.

Notizen: Abstract Due to the increase of human migrations, the appearance of emerging and reemerging endemies, growing antibiotic resistance, and climatic changes, infectious diseases most probably constitute the major challenge for medicine in the next century. The advent of molecular methods of pathogen characterization has considerably improved our knowledge of the epidemiology of these diseases. However, the use of concepts of evolutionary genetics for interpreting "molecular epidemiology" data remains limited, although the application of such methods would broaden considerably the scope of this field of research, and allow epidemiologic and taxonomic approaches to be ascertained on a much firmer basis. In turn, pathogens, hosts, and vectors provide fascinating models for basic research. The artificial character of the border between "basic" and "applied" research is especially apparent with regard to the "integrated genetic epidemiology of infectious diseases" concept. The goal of this chapter is to evaluate the respective impact, on the transmission and pathogenicity of infectious diseases, of the host's, the pathogen's, and the vector's (for vector-borne diseases) genetic diversity, and the interactions between these three parameters (coevolution phenomena).

Notizen: Abstract An RNA fold is the result of packing together two or more coaxial helical stacks. To date, four RNA folds have been determined at near-atomic resolution by X-ray crystallography: transfer RNA, the hammerhead ribozyme, the P4-P6 domain of the Tetrahymena group I intron, and the hepatitis delta virus ribozyme. All four folds result in RNAs that are considerably more compact than isolated A-form duplexes. These structures illustrate, to varying degrees, three modes of fold stabilization: association of complementary molecular surfaces, stabilization of close RNA packing by binding of cations, and stabilization through pseudoknotting.

Notizen: Abstract The F0F1 ATP synthase is a large multisubunit complex that couples translocation of protons down an electrochemical gradient to the synthesis of ATP. Recent advances in structural analyses have led to the demonstration that the enzyme utilizes a rotational catalytic mechanism. Kinetic and biochemical evidence is consistent with the expected equal participation of the three catalytic sites in the alpha3beta3 hexamer, which operate in sequential, cooperative reaction pathways. The rotation of the core gamma subunit plays critical roles in establishing the conformation of the sites and the cooperative interactions. Mutational analyses have shown that the rotor subunits are responsible for coupling and in doing so transmit specific conformational information between transport and catalysis.

Notizen: Abstract Solid-state nuclear magnetic resonance (NMR) is rapidly emerging as a successful and important technique for protein and peptide structural elucidation from samples in anisotropic environments. Because of the diversity of nuclei and nuclear spin interactions that can be observed, and because of the broad range of sample conditions that can be studied by solid-state NMR, the potential for gaining structural constraints is great. Structural constraints in the form of orientational, distance, and torsional constraints can be obtained on proteins in crystalline, liquid-crystalline, or amorphous preparations. Great progress in the past few years has been made in developing techniques for obtaining these constraints, and now it has also been clearly demonstrated that these constraints can be assembled into uniquely defined three-dimensional structures at high resolution. Although much progress toward the development of solid-state NMR as a routine structural tool has been documented, the future is even brighter with the continued development of the experiments, of NMR hardware, and of the molecular biological methods for the preparation of labeled samples.

Notizen: Abstract Stably folded membrane proteins reside in a free energy minimum determined by the interactions of the peptide chains with each other, the lipid bilayer hydrocarbon core, the bilayer interface, and with water. The prediction of three-dimensional structure from sequence requires a detailed understanding of these interactions. Progress toward this objective is summarized in this review by means of a thermodynamic framework for describing membrane protein folding and stability. The framework includes a coherent thermodynamic formalism for determining and describing the energetics of peptide-bilayer interactions and a review of the properties of the environment of membrane proteins-the bilayer milieu. Using a four-step thermodynamic cycle as a guide, advances in three main aspects of membrane protein folding energetics are discussed: protein binding and folding in bilayer interfaces, transmembrane helix insertion, and helix-helix interactions. The concepts of membrane protein stability that emerge provide insights to fundamental issues of protein folding.

Notizen: Abstract Bacteriorhodopsin is the best understood ion transport protein and has become a paradigm for membrane proteins in general and transporters in particular. Models up to 2.5 A resolution of bacteriorhodopsin's structure have been published during the last three years and are basic for understanding its function. Thus one focus of this review is to summarize and to compare these models in detail. Another focus is to follow the protein through its catalytic cycle in summarizing more recent developments. We focus on literature published since 1995; a comprehensive series of reviews was published in 1995 (112).

Notizen: Abstract The [PSI+] factor of the yeast Saccharomyces cerevisiae is an epigenetic regulator of translation termination. More than three decades ago, genetic analysis of the transmission of [PSI+] revealed a complex and often contradictory series of observations. However, many of these discrepancies may now be reconciled by a revolutionary hypothesis: protein conformation-based inheritance (the prion hypothesis). This model predicts that a single protein can stably exist in at least two distinct physical states, each associated with a different phenotype. Propagation of one of these traits is achieved by a self-perpetuating change in the protein from one form to the other. Mounting genetic and biochemical evidence suggests that the determinant of [PSI+] is the nuclear encoded Sup35p, a component of the translation termination complex. Here we review the series of experiments supporting the yeast prion hypothesis and provide another look at the 30 years of work preceding this theory in light of our current state of knowledge.

Notizen: Abstract This review of plant population genetics focuses on the genetic foundations of the processes that have led to documentable improvements in cultivated plants since the earliest domestications took place perhaps 13,000 years ago. Nearly all human civilizations have depended heavily on inbreeding plants (particularly wheat, barley, soybeans and other inbreeding legumes), as well as outbreeding vegetatively propagated species (white potatoes, yams) as their dietary standbys. The principal exception is maize (corn), an annual seed-produced outbreeder in nature. It is noteworthy that maize joined wheat, rice, and barley as a truly major crop worldwide only after its conversion to self-pollination combined with hybridization between favorably interacting inbred lines increased yield of maize several-fold in the twentieth century.

Notizen: Abstract The immune response is regulated not only by cell proliferation and differentiation, but also by programmed cell death, or apoptosis. In response to various stimuli, death factors bind to their respective receptors and activate the apoptotic death program in target cells. A cascade of specific proteases termed caspases mediates the apoptotic process. The activated caspases cleave various cellular components, a process that leads to morphological changes of the cells and nuclei, as well as to degradation of the chromosomal DNA. Loss-of-function mutations in the signaling molecules involved in apoptosis cause hyper-proliferation of cells in mouse and human. In contrast, exaggeration of this death cascade causes the destruction of various tissues.

Notizen: Abstract The past decade has witnessed extraordinary progress in retinal disease gene identification, the analysis of animal and tissue culture models of disease processes, and the integration of this information with clinical observations and with retinal biochemistry and physiology. During this period over twenty retinal disease genes were identified and for many of these genes there are now significant insights into their role in disease. This review presents an overview of the basic and clinical biology of the retina, summarizes recent progress in understanding the molecular mechanisms of inherited retinal diseases, and offers an assessment of the role that genetics will play in the next phase of research in this area.

Notizen: Abstract Conservative site-specific recombination functions to create biological diversity in prokaryotes. Simple site-specific recombination systems consist of two recombination sites and a recombinase gene. The plasmid R64 shufflon contains seven recombination sites, which flank and separate four DNA segments. Site-specific recombinations mediated by the product of the rci gene between any two inverted recombination sites result in the inversion of four DNA segments independently or in groups. The shufflon functions as a biological switch to select one of seven C-terminal segments of the PilV proteins, which is a minor component of R64 thin pilus. The shufflon determines the recipient specificity in liquid matings of plasmid R64. Other multiple inversion systems as well as integrons, which are multiple insertion systems, are also described in this review.

Notizen: Abstract The synthesis of ribosomes is one of the major metabolic pathways in all cells. In addition to around 75 individual ribosomal proteins and 4 ribosomal RNAs, synthesis of a functional eukaryotic ribosome requires a remarkable number of trans-acting factors. Here, we will discuss the recent, and often surprising, advances in our understanding of ribosome synthesis in the yeast Saccharomyces cerevisiae. These will underscore the unexpected complexity of eukaryotic ribosome synthesis.

Notizen: Abstract Molecular genetic analysis of chemotaxis and thermotaxis in Caenorhabditis elegans has revealed the molecular bases of olfaction, taste, and thermosensation, which, in turn, has demonstrated that sensory signaling in C. elegans is very similar to that in vertebrates. A cyclic nucleotide-gated channel (TAX-2/TAX-4) that is highly homologous to the olfactory and photoreceptor channels in vertebrates is required for taste and thermosensation, in addition to olfaction. A cation channel (OSM-9) that is closely related to a capsaicin receptor channel is required for olfactory adaptation in one olfactory neuron and olfactory sensation in the other olfactory neuron. A novel Galpha protein (ODR-3) is essential for olfactory responses in all olfactory neurons and aversive responses in a polymodal sensory neuron. A G protein-coupled seven-transmembrane receptor (ODR-10) is the first olfactory receptor whose ligand was elucidated. Using chemotaxis and thermotaxis as behavioral paradigms, neural plasticity including learning and memory can be studied genetically in C. elegans.

Notizen: Abstract HK022 is a temperate coliphage related to phage lamba. Its chromosome has been completely sequenced, and several aspects of its life cycle have been intensively studied. In the overall arrangement, expression, and function of most of its genes, HK022 broadly resembles lamba and other members of the lamba family. Upon closer view, significant differences emerge. The differences reveal alternative strategies used by related phages to cope with similar problems and illuminate previously unknown regulatory and structural motifs. HK022 prophages protect lysogens from superinfection by producing a sequence-specific RNA binding protein that prematurely terminates nascent transcripts of infecting phage. It uses a novel RNA-based mechanism to antiterminate its own early transcription. The HK022 protein shell is strengthened by a complex pattern of covalent subunit interlinking to form a unitary structure that resembles chainmail armor. Its integrase and repressor proteins are similar to those of lamba, but the differences provide insights into the evolution of biological specificity and the elements needed for construction of a stable genetic switch.

Notizen: Abstract Recent results from ancestral (minimally derived) protists testify to the tremendous diversity of the mitochondrial genome in various eukaryotic lineages, but also reinforce the view that mitochondria, descendants of an endosymbiotic alpha-Proteobacterium, arose only once in evolution. The serial endosymbiosis theory, currently the most popular hypothesis to explain the origin of mitochondria, postulates the capture of an alpha-proteobacterial endosymbiont by a nucleus-containing eukaryotic host resembling extant amitochondriate protists. New sequence data have challenged this scenario, instead raising the possibility that the origin of the mitochondrion was coincident with, and contributed substantially to, the origin of the nuclear genome of the eukaryotic cell. Defining more precisely the alpha-proteobacterial ancestry of the mitochondrial genome, and the contribution of the endosymbiotic event to the nuclear genome, will be essential for a full understanding of the origin and evolution of the eukaryotic cell as a whole.

Notizen: Abstract Formation of the bacterial division septum is catalyzed by a number of essential proteins that assemble into a ring structure at the future division site. Assembly of proteins into the cytokinetic ring appears to occur in a hierarchial order that is initiated by the FtsZ protein, a structural and functional analog of eukaryotic tubulins. Placement of the division site at its correct location in Escherichia coli requires a division inhibitor (MinC), that is responsible for preventing septation at unwanted sites near the cell poles, and a topological specificity protein (MinE), that forms a ring at midcell and protects the midcell site from the division inhibitor. However, the mechanism responsible for identifying the position of the midcell site or the polar sites used for spore septum formation is still unclear. Regulation of the division process and its coordination with other cell cycle events, such as chromosome replication, are poorly understood. However, a protein has been identified in Caulobacter (CtrA) that regulates both the initiation of chromosome regulation and the transcription of ftsZ, and that may play an important role in the coordination process.

Notizen: Abstract DNA mismatch repair (MMR) is one of multiple replication, repair, and recombination processes that are required to maintain genomic stability in prokaryotes and eukaryotes. In the wake of the discoveries that hereditary nonpolyposis colorectal cancer (HNPCC) and other human cancers are associated with mutations in MMR genes, intensive efforts are under way to elucidate the biochemical functions of mammalian MutS and MutL homologs, and the consequences of defects in these genes. Genetic studies in cultured mammalian cells and mice are proving to be instrumental in defining the relationship between the functions of MMR in mutation and tumor avoidance. Furthermore, these approaches have raised awareness that MMR homologs contribute to DNA damage surveillance, transcription-coupled repair, and recombinogenic and meiotic processes.

Notizen: Abstract Meiotic chromosomes have been studied for many years, in part because of the fundamental life processes they represent, but also because meiosis involves the formation of homolog pairs, a feature which greatly facilitates the study of chromosome behavior. The complex events involved in homolog juxtaposition necessitate prolongation of prophase, thus permitting resolution of events that are temporally compressed in the mitotic cycle. Furthermore, once homologs are paired, the chromosomes are connected by a specific structure: the synaptonemal complex. Finally, interaction of homologs includes recombination at the DNA level, which is intimately linked to structural features of the chromosomes. In consequence, recombination-related events report on diverse aspects of chromosome morphogenesis, notably relationships between sisters, development of axial structure, and variations in chromatin status. The current article reviews recent information on these topics in an historical context. This juxtaposition has suggested new relationships between structure and function. Additional issues were addressed in a previous chapter (551).

Notizen: Abstract In the past few years great progress has been made in identifying and characterizing plant photoreceptors active in the blue/UV-A regions of the spectrum. These photoreceptors include cryptochrome 1 and cryptochrome 2, which are similar in structure and chromophore composition to the prokaryotic DNA photolyases. However, they have a C-terminal extension that is not present in photolyases and lack photolyase activity. They are involved in regulation of cell elongation and in many other processes, including interfacing with circadian rhythms and activating gene transcription. Animal cryptochromes that play a photoreceptor role in circadian rhythms have also been characterized. Phototropin, the protein product of the NPH1 gene in Arabidopsis, likely serves as the photoreceptor for phototropism and appears to have no other role. A plasma membrane protein, it serves as photoreceptor, kinase, and substrate for light-activated phosphorylation. The carotenoid zeaxanthin may serve as the chromophore for a photoreceptor involved in blue-light-activated stomatal opening. The properties of these photoreceptors and some of the downstream events they are known to activate are discussed.

Notizen: Abstract The neural crest is a transient population of multipotent precursor cells named for its site of origin at the crest of the closing neural folds in vertebrate embryos. Following neural tube closure, these cells become migratory and populate diverse regions throughout the embryo where they give rise to most of the neurons and support cells of the peripheral nervous system (PNS), pigment cells, smooth muscle, craniofacial cartilage, and bone. Because of its remarkable ability to generate such diverse derivatives, the neural crest has fascinated developmental biologists for over one hundred years. A great deal has been learned about the migratory pathways neural crest cells follow and the signals that may trigger their differentiation, but until recently comparatively little was known about earlier steps in neural crest development. In the past few years progress has been made in understanding these earlier events, including how the precursors of these multipotent cells are specified in the early embryo and the mechanisms by which they become migratory. In this review, we first examine the mechanisms underlying neural crest induction, paying particular attention to a number of growth factor and transcription factor families that have been implicated in this process. We also discuss when and how the fate of neural crest precursors may diverge from those of nearby neural and epidermal populations. Finally, we review recent advances in our understanding of how neural crest cells become migratory and address the process of neural crest diversification.

Notizen: Abstract Proteins of the kinesin superfamily utilize a conserved catalytic motor domain to generate movements in a wide variety of cellular processes. In this review, we discuss the rapid expansion in our understanding of how eukaryotic cells take advantage of these proteins to generate force and movement in diverse functional contexts. We summarize several recent examples revealing that the simplest view of a kinesin motor protein binding to and translocating a cargo along a microtubule track is inadequate. In fact, this paradigm captures only a small subset of the many ways in which cells harness force production to the generation of intracellular movements and functions. We also highlight several situations where the catalytic kinesin motor domain may not be used to generate movement, but instead may be used in other biochemical and functional contexts. Finally, we review some recent ideas about kinesin motor regulation, redundancy, and cargo attachment strategies.

Notizen: Abstract The Drosophila phototransduction cascade has emerged as an attractive paradigm for understanding the molecular mechanisms underlying visual transduction, as well as other G protein-coupled signaling cascades that are activated and terminated with great rapidity. A large collection of mutants affecting the fly visual cascade have been isolated, and the nature and function of many of the affected gene products have been identified. Virtually all of the proteins, including those that were initially classified as novel, are highly related to vertebrate homologs. Recently, it has become apparent that most of the proteins central to Drosophila phototransduction are coupled into a supramolecular signaling complex, signalplex, through association with a PDZ-containing scaffold protein. The characterization of this complex has led to a re-evaluation of the mechanisms underlying the activation and deactivation of the phototransduction cascade.

Notizen: Abstract Subcellular asymmetry, cell polarity, is fundamental to the diverse specialized functions of eukaryotic cells. In yeast, cell polarization is essential to division and mating. As a result, this highly accessible experimental system serves as a paradigm for deciphering the molecular mechanisms underlying the generation of polarity. Beyond yeast, cell polarity is essential to the partitioning of cell fate in embryonic development, the generation of axons and their guidance during neuronal development, and the intimate communication between lymphocytes within the immune system. The polarization of yeast cells shares many features with that of these more complex examples, including regulation by both intrinsic and extrinsic cues, conserved regulatory molecules such as Cdc42 GTPase, and asymmetry of the cytoskeleton as its centerpiece. This review summarizes the molecular pathways governing the generation of cell polarity in yeast.

Notizen: Abstract At a certain stage in their life cycle, plants switch from vegetative to reproductive development. This transition is regulated by multiple developmental and environmental cues. These ensure that the plant switches to flowering at a time when sufficient internal resources have been accumulated and the environmental conditions are favorable. The use of a molecular genetic approach in Arabidopsis has resulted in the identification and cloning of many of the genes involved in regulating floral transition. The current view on the molecular function of these genes, their division into different genetic pathways, and how the pathways interact in a complex regulatory network are summarized.

Notizen: Abstract Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric basic-helix-loop-helix-PAS transcription factor consisting of HIF-1alpha and HIF-1beta subunits. HIF-1alpha expression and HIF-1 transcriptional activity increase exponentially as cellular O2 concentration is decreased. Several dozen target genes that are transactivated by HIF-1 have been identified, including those encoding erythropoietin, glucose transporters, glycolytic enzymes, and vascular endothelial growth factor. The products of these genes either increase O2 delivery or allow metabolic adaptation to reduced O2 availability. HIF-1 is required for cardiac and vascular development and embryonic survival. In fetal and postnatal life, HIF-1 is required for a variety of physiological responses to chronic hypoxia. HIF-1 expression is increased in tumor cells by multiple mechanisms and may mediate adaptation to hypoxia that is critical for tumor progression. HIF-1 thus appears to function as a master regulator of O2 homeostasis that plays essential roles in cellular and systemic physiology, development, and pathophysiology.

Notizen: Abstract Viruses are ubiquitous and dangerous obligate intracellular parasites. To facilitate recognition of virus-infected cells by the immune system, vertebrates evolved a system that displays oligopeptides derived from viral proteins on the surface of cells in association with class I molecules of the major histocompatibility complex. Here we review the mechanisms counter-evolved by viruses to interfere with the generation of viral peptides, their intracellular trafficking, or the cell surface expression of class I molecules bearing viral peptides. This topic is important in its own right because the viruses that encode these proteins represent medically important pathogens, are potential vectors for vaccines or gene therapy, and provide strategies and tools for blocking immune recognition in transplantation, autoimmunity, and gene therapy. In addition, studies on viral interference provide unique insights into unfettered antigen processing and normal cellular functions that are exploited and exaggerated by viruses.

Notizen: Abstract The compartmentation of eukaryotic cells requires all nuclear proteins to be imported from the cytoplasm, whereas, for example, transfer RNAs, messenger RNAs, and ribosomes are made in the nucleus and need to be exported to the cytoplasm. Nuclear import and export proceed through nuclear pore complexes and can occur along a great number of distinct pathways, many of which are mediated by importin beta-related nuclear transport receptors. These receptors shuttle between nucleus and cytoplasm, and they bind transport substrates either directly or via adapter molecules. They all cooperate with the RanGTPase system to regulate the interactions with their cargoes. Another focus of our review is nuclear export of messenger RNA, which apparently largely relies on export mediators distinct from importin beta-related factors. We discuss mechanistic aspects and the energetics of transport receptor function and describe a number of pathways in detail.

Notizen: Abstract A conserved mRNA degradation system, referred to as mRNA surveillance, exists in eukaryotic cells to degrade aberrant mRNAs. A defining aspect of aberrant transcripts is that the spatial relationship between the termination codon and specific downstream sequence information has been altered. A key, yet unknown, feature of the mRNA surveillance system is how this spatial relationship is assessed in individual transcripts. Two views have emerged to describe how discrimination between proper and improper termination might occur. In the first view, a surveillance complex assembles onto the mRNA after translation termination, and scans the mRNA in a 3' to 5' direction for a limited distance. If specific downstream sequence information is encountered during this scanning, then the surveillance complex targets the transcript for rapid decay. An alternate view suggests that the downstream sequence information influences how translation termination occurs. This view encompasses several ideas including: (a) The architecture of the mRNP can alter the rate of key steps in translation termination; (b) the discrimination between a proper and improper termination occurs via an internal, Upf1-dependent, timing mechanism; and (c) proper termination results in the restructuring of the mRNP to a form that promotes mRNA stability. This proposed model for mRNA surveillance is similar to other systems of kinetic proofreading that monitor the accuracy of other biogenic processes such as translation and spliceosome assembly.

Notizen: Abstract French genetics had unusual beginnings. There are clear indications that the French biological establishment resisted Mendelian genetics strenuously from about 1910 to 1940. From about 1930 to 1950 several unconventional research programs with a strongly physiological orientation paved the way for the full entrance of French biology into genetics after World War II. This review examines some salient features of this history to clarify the strengths, weaknesses, and distinctive features of French genetics until about 1965. We suggest that after that date French genetics slowly merged into the international mainstream as genetics has become a largely molecular discipline.