bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seasonal variation in energy fluxes and carbon dioxide exchange for a broad‐leaved semi‐arid savanna (Mopane woodland) in Southern Africa
Authors: Veenendaal Elmar M. , Kolle Olaf , Lloyd Jon 
Published: December 2004

AbstractWe studied the seasonal variation in carbon dioxide, water vapour and energy fluxes in a broad‐leafed semi‐arid savanna in Southern Africa using the eddy covariance technique. The open woodland studied consisted of an overstorey dominated by Colophospermum mopane with a sparse understorey of grasses and herbs. Measurements presented here cover a 19‐month period from the end of the rainy season in March 1999 to the end of the dry season September 2000.During the wet season, sensible and latent heat fluxes showed a linear dependence on incoming solar radiation (I) with a Bowen ratio (β) typically just below unity. Although β was typically around 1 at low incoming solar radiation (150 W m−2) during the dry season, it increased dramatically with I, typically being as high as 4 or 5 around solar noon. Thus, under these water‐limited conditions, almost all available energy was dissipated as sensible, rather than latent heat.Marked spikes of CO2 release occurred at the onset of the rainfall season after isolated rainfall events and respiration dominated the balance well into the rainfall season. During this time, the ecosystem was a constant source of CO2 with an average flux of 3–5 μmol m−2 s−1 to the atmosphere during both day and night. But later in the wet season, for example, in March 2000 under optimal soil moisture conditions, with maximum leaf canopy development (leaf area index 0.9–1.3), the peak ecosystem CO2 influx was as much as 10 μmol m−2 s−1. The net ecosystem maximum photosynthesis at this time was estimated at 14 μmol m−2 s−1, with the woodland ecosystem a significant sink for CO2. During the dry season, just before leaf fall in August, maximum day‐ and night‐time net ecosystem fluxes were typically −3 μmol m−2 s−1 and 1–2 μmol m−2 s−1, respectively, with the ecosystem still being a marginal sink.Over the course of 12 months (March 1999–March 2000), the woodland was more or less carbon neutral, with a net uptake estimated at only about 1 mol C m−2 yr−1. The annual net photosynthesis (gross primary production) was estimated at 32.2 mol m−2 yr−1.
Soil 13C–15N dynamics in an N2‐fixing clover system under long‐term exposure to elevated atmospheric CO2
Authors: Van Groenigen Kees‐Jan , Six Johan , Harris David , Blum Herbert , Van Kessel Chris 
Published: December 2004

AbstractReduced soil N availability under elevated CO2 may limit the plant's capacity to increase photosynthesis and thus the potential for increased soil C input. Plant productivity and soil C input should be less constrained by available soil N in an N2‐fixing system. We studied the effects of Trifolium repens (an N2‐fixing legume) and Lolium perenne on soil N and C sequestration in response to 9 years of elevated CO2 under FACE conditions. 15N‐labeled fertilizer was applied at a rate of 140 and 560 kg N ha−1 yr−1 and the CO2 concentration was increased to 60 Pa pCO2 using 13C‐depleted CO2. The total soil C content was unaffected by elevated CO2, species and rate of 15N fertilization. However, under elevated CO2, the total amount of newly sequestered soil C was significantly higher under T. repens than under L. perenne. The fraction of fertilizer‐N (fN) of the total soil N pool was significantly lower under T. repens than under L. perenne. The rate of N fertilization, but not elevated CO2, had a significant effect on fN values of the total soil N pool. The fractions of newly sequestered C (fC) differed strongly among intra‐aggregate soil organic matter fractions, but were unaffected by plant species and the rate of N fertilization. Under elevated CO2, the ratio of fertilizer‐N per unit of new C decreased under T. repens compared with L. perenne. The L. perenne system sequestered more 15N fertilizer than T. repens: 179 vs. 101 kg N ha−1 for the low rate of N fertilization and 393 vs. 319 kg N ha−1 for the high N‐fertilization rate. As the loss of fertilizer‐15N contributed to the 15N‐isotope dilution under T. repens, the input of fixed N into the soil could not be estimated. Although N2 fixation was an important source of N in the T. repens system, there was no significant increase in total soil C compared with a non‐N2‐fixing L. perenne system. This suggests that N2 fixation and the availability of N are not the main factors controlling soil C sequestration in a T. repens system.
Elevated CO2decreases leaf fluctuating asymmetry and herbivory by leaf miners on two oak species
Authors: Cornelissen Tatiana , Stiling Peter , Drake Bert 
Published: December 2004

AbstractFluctuating asymmetry (FA) represents small, random variation from symmetry in otherwise bilaterally symmetrical characters. Significant increases in FA have been found for several species of plants and animals in response to various stresses, including environmental and genetic factors. In this study, we investigated the effects of elevated CO2on leaf symmetry of two oak species,Quercus geminataandQ. myrtifolia, and the responses of three species of leaf miners and one gall‐making species to random variation in leaf morphology. Leaf FA decreased with an increase in CO2concentration. There were fewer asymmetric leaves and lower levels of asymmetry on leaf width and leaf area on elevated CO2compared with ambient CO2. Leaf miners responded to leaf asymmetry, attacking asymmetric leaves more frequently than expected by chance alone. Differences in secondary chemistry and nitrogen (N) content between symmetric and asymmetric leaves may be responsible for these results due to lower levels of tannins and higher levels of N found on asymmetric leaves ofQ. myrtifoliaandQ. geminata.
Reduced water repellency of a grassland soil under elevated atmospheric CO2
Authors: Newton Paul C. D. , Carran R. A , Lawrence Erin J. 
Published: December 2004

AbstractWater repellency is a widespread characteristic of soils that can modify soil moisture content and distribution and is implicated in important processes such as aggregation and carbon sequestration. Repellency arises as a consequence of organic matter inputs; as elevated atmospheric CO2 is known to modify such inputs, we tested the repellency of a grassland soil after 5 years of exposure to elevated CO2 in a free air carbon dioxide enrichment experiment. Using a water droplet penetration time test, we found a significant reduction in repellency at elevated CO2 in samples at field moisture content. As many of the processes potentially influenced by repellency have been shown to be modified at elevated CO2 (e.g. soil aggregation, C sequestration, recruitment from seed), we suggest that further exploration of this phenomenon could enhance our understanding of CO2 effects on ecosystem function. The mechanism responsible for the change in repellency has not been identified.
Simulation and scaling of temporal variation in gross primary production for coniferous and deciduous temperate forests
Authors: Wang Q. , Tenhunen J. , Falge E. , Bernhofer Ch. , Granier A. , Vesala T. 
Published: December 2004

AbstractObservations of ecosystem net carbon dioxide exchange obtained with eddy covariance techniques over a 4‐year period at spruce, beech and pine forest sites were used to derive time series data for gross primary production (GPP) and ecosystem respiration (Reco). A detailed canopy gas exchange model (PROXELNEE) was inverted at half‐hour time step to estimate seasonal changes in carboxylation capacity and light utilization efficiency of the forest canopies. The parameter estimates were then used further to develop a time‐dependent modifier of physiological activity in the daily time step gas exchange model of Chen et al. (1999), previously used for regional simulations in BOREAS. The daily model was run under a variety of assumptions and the results emphasize the need in future analyses: (1) to focus on time‐dependent seasonal changes in canopy physiology as well as in leaf area index, (2) to compare time courses of physiological change in different habitats in terms of recognizable cardinal points in the seasonal course, and (3) to develop methods for utilizing information on seasonal changes in physiology in regional and continental carbon budget simulations. The results suggest that the daily model with appropriate seasonal adjustments for physiological process regulation should be an efficient tool for use in conjunction with remote sensing for regional evaluation of global change scenarios.
Summer warming and increased winter snow cover affect Sphagnum fuscum growth, structure and production in a sub‐arctic bog
Authors: Dorrepaal Ellen , Aerts Rien , Cornelissen Johannes H. C. , Callaghan Terry V. , Van Logtestijn Richard S. P. 
Published: December 2004

Abstract Sphagnum mosses form a major component of northern peatlands, which are expected to experience substantially higher increases in temperature and winter precipitation than the global average. Sphagnum may play an important role in the responses of the global carbon cycle to climate change. We investigated the responses of summer length growth, carpet structure and production in Sphagnum fuscum to experimentally induced changes in climate in a sub‐arctic bog. Thereto, we used open‐top chambers (OTCs) to create six climate scenarios including changes in summer temperatures, and changes in winter snow cover and spring temperatures. In winter, the OTCs doubled the snow thickness, resulting in 0.5–2.8°C higher average air temperatures. Spring air temperatures in OTCs increased by 1.0°C. Summer warming had a maximum effect of 0.9°C, while vapor pressure deficit was not affected. The climate manipulations had strong effects on S. fuscum. Summer warming enhanced the length increment by 42–62%, whereas bulk density decreased. This resulted in a trend (P<0.10) of enhanced biomass production. Winter snow addition enhanced dry matter production by 33%, despite the fact that the length growth and bulk density did not change significantly. The addition of spring warming to snow addition alone did not significantly enhance this effect, but we may have missed part of the early spring growth. There were no interactions between the manipulations in summer and those in winter/spring, indicating that the effects were additive. Summer warming may in the long term negatively affect productivity through the adverse effects of changes in Sphagnum structure on moisture holding and transporting capacity. Moreover, the strong length growth enhancement may affect interactions with other mosses and vascular plants. Because winter snow addition enhanced the production of S. fuscum without affecting its structure, it may increase the carbon balance of northern peatlands.
Long‐term ecosystem level experiments at Toolik Lake, Alaska, and at Abisko, Northern Sweden: generalizations and differences in ecosystem and plant type responses to global change
Authors: Van Wijk M. T. , Clemmensen K. E. , Shaver G. R. , Williams M. , Callaghan T. V. , Chapin F. S. , Cornelissen J. H. C. , Gough L. , Hobbie S. E. , Jonasson S. , Lee J. A. , Michelsen A. , Press M. C. , Richardson S. J. , Rueth H. 
Published: December 2004

AbstractLong‐term ecosystem‐level experiments, in which the environment is manipulated in a controlled manner, are important tools to predict the responses of ecosystem functioning and composition to future global change. We present the results of a meta‐analysis performed on the results of long‐term ecosystem‐level experiments near Toolik Lake, Alaska, and Abisko, Sweden. We quantified aboveground biomass responses of different arctic and subarctic ecosystems to experimental fertilization, warming and shading. We not only analysed the general patterns but also the differences in responsiveness between sites and regions. Aboveground plant biomass showed a broad similarity of responses in both locations, and also showed some important differences. In both locations, aboveground plant biomass, particularly the biomass of deciduous and graminoid plants, responded most strongly to nutrient addition. The biomass of mosses and lichens decreased in both locations as the biomass of vascular plants increased. An important difference between the two regions was the smaller positive aboveground biomass response of deciduous shrubs in Abisko as compared with Toolik Lake. Whereas in Toolik Lake Betula nana increased its dominance and replaced many of the other plant types, in Abisko all vascular plant types increased in abundance without major shifts in relative abundance. The differences between the responses of the dominant vegetation types of the Toolik Lake region, i.e. tussock tundra systems, and that of the Abisko region, i.e. heath systems, may have important implications for ecosystem development under expected patterns of global change. However, there were also large site‐specific differences within each region. Several potential mechanistic explanations for the differences between sites and regions are discussed. The response patterns show the need for analyses of joint data sets from many regions and sites, in order to uncover common responses to changes in climate across large arctic regions from regional or local responses.
The SAFARI 2000 – Kalahari Transect Wet Season Campaign of year 2000
Authors: Shugart H. H. , Macko S. A. , Lesolle P. , Szuba T. A. , Mukelabai M. M. , Dowty P. , Swap R. J. 
Published: December 2004

AbstractOver 50 scientists from eight different countries coordinated research efforts in the Kalahari sand mass in Zambia and Botswana during the 2000 wet season as a part of the Southern African Regional Science Initiative – Kalahari Transect Wet Season Campaign (S2K‐KT Wet Season Campaign). The work focused on change in ecological processes along the International Geosphere–Biosphere Programme‐designated Kalahari Transect (KT). Topics included ecosystem structure, function, biogeochemistry, and modeling at the patch, landscape and regional scale. The KT of southern and central Africa follows a sharp precipitation gradient within an otherwise climatically and geographically similar region that contains a widely distributed, physically uniform soil and relatively little variation in elevation. This paper outlines the focus of the SAFARI 2000 research campaign as it relates to this study area and provides references to archived data sets generated during the study. It also describes vegetation patterns, climate, and 2000 wet season meteorological conditions for the region.
Genetic variation in Sanguisorba minor after 6 years in situ selection under elevated CO2
Authors: Wieneke Silvia , Prati Daniel , Brandl Roland , Stöcklin Jürg , Auge Harald 
Published: December 2004

AbstractGenetic variation within plant species in their response to elevated CO2 could be important for long‐term changes in plant community composition because it allows for selection of responsive genotypes. Six years of in situ CO2 enrichment in a temperate grassland offered a unique opportunity to investigate such microevolutionary changes in a common herb of that plant community, Sanguisorba minor. Plants were grown from seeds collected at the end of a 6‐year treatment in either ambient or elevated CO2. The resulting seedlings were grown under ambient or elevated CO2 and with or without interspecific competition by Bromus erectus in the greenhouse for two seasons. The effect of competition was included because we expected selection under elevated CO2 to favour increased competitive ability. Elevated CO2 in the greenhouse and competition both caused a significant reduction of the total dry mass in S. minor, by 12% and 40%, respectively, with no interaction between CO2 and competition. Genetic variation in all traits was substantial. Seed families responded differently to competition, but the family × greenhouse CO2 interaction was rather weak. There was no main effect of the field CO2 treatment on any parameter analysed in the greenhouse. However, the field CO2 treatment did significantly interact with the greenhouse CO2 treatment for the cumulative number of leaves, suggesting microevolutionary change in this plant trait. Families from ambient field CO2 produced fewer leaves under elevated greenhouse CO2, whereas families from elevated field CO2 retained constant number of leaves in either greenhouse CO2 treatment. Since this resulted in increased litter production of the families from elevated field CO2 under elevated greenhouse CO2, the microevolutionary response should, in turn, affect ecosystem functions through dry matter recycling.
Falkland Islands biogeography: converging trajectories in the South Atlantic Ocean
Authors: McDowall R. M. 
Published: December 2004

AbstractAim This paper describes the biogeographical setting of the Falkland Islands, in the context of the relationships of the islands’ biota to other sub‐Antarctic/cold temperate lands.Location The analysis focuses primarily on the Falklands biota, and explores its relationships to those of Patagonian South America and South Africa, other southern lands and the islands of the sub‐Antarctic Pacific, Indian and Atlantic Oceans.Methods The study derives largely from literature sources on the biota and geological history of the Falkland Islands.Results The animals and plants known from the Falkland Islands exhibit strong affinities with those of Patagonian South America, and especially Tierra del Fuego; additional affinities are with various remote islands of the sub‐Antarctic, as well as New Zealand and to a lesser extent Australia; often these are shared with Patagonia. While the biotic affinities might be interpreted, by some, as indicating a former Gondwanan/South American geological connection of the Falklands, geological evidence points to the Falklands formerly having a land connection to south‐eastern South Africa. Only faint hints of a South African biotic connection remain. The historical biotic and geological connections of the Falklands thus conflict. Moreover, the Falklands biota is so strongly Patagonian that derivation of that biota is best seen as resulting from dispersal, much of it probably recent. This dispersal biota appears to have replaced, and perhaps displaced, the South African biota present on the islands as they detached from South Africa and drifted across the south Atlantic Ocean, as it opened up as South America and Africa drifted apart.
Vegetation establishment, succession and microsite frost disturbance on glacier forelands within patterned ground chronosequences
Authors: Haugland Jake E. , Beatty Susan W. 
Published: December 2004

AbstractAim The impact of microscale frost disturbance on vegetation colonization and successionary trends was examined within patterned ground features of Little Ice Age chronosequences. The goal was to investigate and compare vegetation response to micro‐site frost disturbance with that of previous studies done at a coarser landscape scale.Location The study sites occur on Little Ice Age glacier forelands within Jotunheimen, Norway (61°–62° N). The forelands of the glaciers Slettmarkbreen, Styggedalsbreen and Vestre Memurubreen have been well studied providing chronological controls for landscape studies. Sorted patterned ground features are found within the chronosequences, typically declining with frost intensity and disturbance with increasing terrain age.Methods Micro‐plots (8.3 × 8.3 cm) were placed at the inner borders and centres of patterned ground features. Species were identified and per cent species cover and per cent cover of life‐form category were noted. Nonparametric Kruskal–Wallis and Mann–WhitneyU‐tests were used to test for differences between percent cover of life‐form categories within patterned ground features as well as to identify thresholds of successional change across the chronosequences.Results Significant relationships between life‐from groups and patterned ground positions of varying ages were deduced using nonparametric statistics. Findings were then used to discuss trends of succession within patterned ground features and across the chronosequences. Vegetation establishment occurs at the border positions of young (< 30 years) patterned ground features. With time and distance from the ice margin, vegetation encroaches inwards toward the disturbed centres. Succession within patterned ground exhibits several stages: (1) bryophytes/crusts and lichens, (2) grasses/sedges and (3) woody shrubs. The occurrence of forbs was sporadic and generally non‐significant.Main conclusions Frost disturbance in patterned ground appears to delay successional trends of vegetation communities when compared with previous studies on ‘stable’ terrain, producing micro‐site lag effects. These small patches of disturbed ground are therefore important regarding vegetation assemblages across the landscape and are unlikely to be detected at the landscape scale.
Crystal structure of the cytotoxic bacterial protein colicin B at 2.5 Å resolution
Authors: Hilsenbeck Jacqueline L. , Park HaJeung , Chen Gregory , Youn Buhyun , Postle Kathleen , Kang ChulHee 
Published: December 2004

SummaryColicin B (55 kDa) is a cytotoxic protein that recognizes the outer membrane transporter, FepA, as a receptor and, after gaining access to the cytoplasmic membranes of sensitive Escherichia coli cells, forms a pore that depletes the electrochemical potential of the membrane and ultimately results in cell death. To begin to understand the series of dynamic conformational changes that must occur as colicin B translocates from outer membrane to cytoplasmic membrane, we report here the crystal structure of colicin B at 2.5 Å resolution. The crystal belongs to the space group C2221 with unit cell dimensions a = 132.162 Å, b = 138.167 Å, c = 106.16 Å. The overall structure of colicin B is dumbbell shaped. Unlike colicin Ia, the only other TonB‐dependent colicin crystallized to date, colicin B does not have clearly structurally delineated receptor‐binding and translocation domains. Instead, the unique N‐terminal lobe of the dumbbell contains both domains and consists of a large (290 residues), mostly β‐stranded structure with two short α‐helices. This is followed by a single long (≈ 74 Å) helix that connects the N‐terminal domain to the C‐terminal pore‐forming domain, which is composed of 10 α‐helices arranged in a bundle‐type structure, similar to the pore‐forming domains of other colicins. The TonB box sequence at the N‐terminus folds back to interact with the N‐terminal lobe of the dumbbell and leaves the flanking sequences highly disordered. Comparison  of  sequences  among  many  colicins has allowed the identification of a putative receptor‐binding domain.
Lesional T‐cell subset in post‐kala‐azar dermal leishmaniasis
Authors: Rathi Sanjay K. , Pandhi Ravindra K. , Chopra Prem , Khanna Neena 
Published: December 2004

AbstractBackground  The pathogenesis of post‐kala‐azar dermal leishmaniasis (PKDL) is ill understood. This study was carried out to find the percentage of T‐helper and T‐suppressor cells in lesional tissue and their probable role in the pathogenesis of PKDL.Methods  An immunoperoxidase monoclonal antibody technique was used to characterize and quantify the subsets of T lymphocytes in the infiltrate in 25 patients with PKDL.Results  The ratio of T‐helper to T‐suppressor cells was 0.87 in hypopigmented macules and 0.85 in nodule and/or plaque lesions of PKDL.Conclusions  In this study, there was a definite preponderance of T‐suppressor cells over T‐helper cells in both types of skin lesions of PKDL. Further studies should be undertaken on larger numbers of patients to compare T‐cell subsets both in skin lesions and the circulation, in order to determine the pathogenesis of PKDL.