bluuebunny/crossref_metadata_2025_split huggingface dataset:
A generalized, bioclimatic index to predict foliar phenology in response to climate
Authors: Jolly William M. , Nemani Ramakrishna , Running Steven W. 
Published: April 2005

AbstractThe phenological state of vegetation significantly affects exchanges of heat, mass, and momentum between the Earth's surface and the atmosphere. Although current patterns can be estimated from satellites, we lack the ability to predict future trends in response to climate change. We searched the literature for a common set of variables that might be combined into an index to quantify the greenness of vegetation throughout the year. We selected as variables: daylength (photoperiod), evaporative demand (vapor pressure deficit), and suboptimal (minimum) temperatures. For each variable we set threshold limits, within which the relative phenological performance of the vegetation was assumed to vary from inactive (0) to unconstrained (1). A combined Growing Season Index (GSI) was derived as the product of the three indices. Ten‐day mean GSI values for nine widely dispersed ecosystems showed good agreement (r>0.8) with the satellite‐derived Normalized Difference Vegetation Index (NDVI). We also tested the model at a temperate deciduous forest by comparing model estimates with average field observations of leaf flush and leaf coloration. The mean absolute error of predictions at this site was 3 days for average leaf flush dates and 2 days for leaf coloration dates. Finally, we used this model to produce a global map that distinguishes major differences in regional phenological controls. The model appears sufficiently robust to reconstruct historical variation as well as to forecast future phenological responses to changing climatic conditions.
Gross primary production is stimulated for three Populus species grown under free‐air CO2 enrichment from planting through canopy closure
Authors: Wittig Victoria E. , Bernacchi Carl J. , Zhu Xin‐Guang , Calfapietra Carlo , Ceulemans Reinhart , Deangelis Paolo , Gielen Birgit , Miglietta Franco , Morgan Patrick B. , Long Stephen P. 
Published: April 2005

AbstractHow forests will respond to rising [CO2] in the long term is uncertain, most studies having involved juvenile trees in chambers prior to canopy closure. Poplar free‐air CO2 enrichment (Viterbo, Italy) is one of the first experiments to grow a forest from planting through canopy closure to coppice, entirely under open‐air conditions using free‐air CO2 enrichment technology. Three Populus species: P. alba, P. nigra and P. x euramericana, were grown in three blocks, each containing one control and one treatment plot in which CO2 was elevated to the expected 2050 concentration of 550 ppm. The objective of this study was to estimate gross primary production (GPP) from recorded leaf photosynthetic properties, leaf area index (LAI) and meteorological conditions over the complete 3‐year rotation cycle. From the meteorological conditions recorded at 30 min intervals and biweekly measurements of LAI, the microclimate of leaves within the plots was estimated with a radiation transfer and energy balance model. This information was in turn used as input into a canopy microclimate model to determine light and temperature of different leaf classes at 30 min intervals which in turn was used with the steady‐state biochemical model of leaf photosynthesis to compute CO2 uptake by the different leaf classes. The parameters of these models were derived from measurements made at regular intervals throughout the coppice cycle. The photosynthetic rates for different leaf classes were summed to obtain canopy photosynthesis, i.e. GPP. The model was run for each species in each plot, so that differences in GPP between species and treatments could be tested statistically. Significant stimulation of GPP driven by elevated [CO2] occurred in all 3 years, and was greatest in the first year (223–251%), but markedly lower in the second (19–24%) and third years (5–19%). Increase in GPP in elevated relative to control plots was highest for P. nigra in 1999 and for P. x euramericana in 2000 and 2001, although in 1999 P. alba had a higher GPP than P. x euramericana. Our analysis attributed the decline in stimulation to canopy closure and not photosynthetic acclimation. Over the 3‐year rotation cycle from planting to harvest, the cumulative GPP was 4500, 4960 and 4010 g C m−2 for P. alba, P. nigra and P. x euramericana, respectively, in current [CO2] and 5260, 5800 and 5000 g C m−2 in the elevated [CO2] treatments. The relative changes were consistent with independent measurements of net primary production, determined independently from biomass increments and turnover.
Elevated atmospheric CO2 effects on biomass production and soil carbon in conventional and conservation cropping systems
Authors: Prior Stephen A. , Brett Runion G. , Rogers Hugo H. , Allen Torbert H. , Wayne Reeves D. 
Published: April 2005

AbstractIncreasing atmospheric CO2 concentration has led to concerns about potential effects on production agriculture as well as agriculture's role in sequestering C. In the fall of 1997, a study was initiated to compare the response of two crop management systems (conventional and conservation) to elevated CO2. The study used a split‐plot design replicated three times with two management systems as main plots and two CO2 levels (ambient=375 μL L−1 and elevated CO2=683 μL L−1) as split‐plots using open‐top chambers on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudults). The conventional system was a grain sorghum (Sorghum bicolor (L.) Moench.) and soybean (Glycine max (L.) Merr.) rotation with winter fallow and spring tillage practices. In the conservation system, sorghum and soybean were rotated and three cover crops were used (crimson clover (Trifolium incarnatum L.), sunn hemp (Crotalaria juncea L.), and wheat (Triticum aestivum L.)) under no‐tillage practices. The effect of management on soil C and biomass responses over two cropping cycles (4 years) were evaluated. In the conservation system, cover crop residue (clover, sunn hemp, and wheat) was increased by elevated CO2, but CO2 effects on weed residue were variable in the conventional system. Elevated CO2 had a greater effect on increasing soybean residue as compared with sorghum, and grain yield increases were greater for soybean followed by wheat and sorghum. Differences in sorghum and soybean residue production within the different management systems were small and variable. Cumulative residue inputs were increased by elevated CO2 and conservation management. Greater inputs resulted in a substantial increase in soil C concentration at the 0–5 cm depth increment in the conservation system under CO2‐enriched conditions. Smaller shifts in soil C were noted at greater depths (5–10 and 15–30 cm) because of management or CO2 level. Results suggest that with conservation management in an elevated CO2 environment, greater residue amounts could increase soil C storage as well as increase ground cover.
Decomposition of soybean grown under elevated concentrations of CO2 and O3
Authors: Booker Fitzgerald L. , Prior Stephen A. , Torbert H. Allen , Fiscus Edwin L. , Pursley Walter A. , Hu Shuijin 
Published: April 2005

AbstractA critical global climate change issue is how increasing concentrations of atmospheric CO2 and ground‐level O3 will affect agricultural productivity. This includes effects on decomposition of residues left in the field and availability of mineral nutrients to subsequent crops. To address questions about decomposition processes, a 2‐year experiment was conducted to determine the chemistry and decomposition rate of aboveground residues of soybean (Glycine max (L.) Merr.) grown under reciprocal combinations of low and high concentrations of CO2 and O3 in open‐top field chambers. The CO2 treatments were ambient (370 μmol mol−1) and elevated (714 μmol mol−1) levels (daytime 12 h averages). Ozone treatments were charcoal‐filtered air (21 nmol mol−1) and nonfiltered air plus 1.5 times ambient O3 (74 nmol mol−1) 12 h day−1. Elevated CO2 increased aboveground postharvest residue production by 28–56% while elevated O3 suppressed it by 15–46%. In combination, inhibitory effects of added O3 on biomass production were largely negated by elevated CO2. Plant residue chemistry was generally unaffected by elevated CO2, except for an increase in leaf residue lignin concentration. Leaf residues from the elevated O3 treatments had lower concentrations of nonstructural carbohydrates, but higher N, fiber, and lignin levels. Chemical composition of petiole, stem, and pod husk residues was only marginally affected by the elevated gas treatments. Treatment effects on plant biomass production, however, influenced the content of chemical constituents on an areal basis. Elevated CO2 increased the mass per square meter of nonstructural carbohydrates, phenolics, N, cellulose, and lignin by 24–46%. Elevated O3 decreased the mass per square meter of these constituents by 30–48%, while elevated CO2 largely ameliorated the added O3 effect. Carbon mineralization rates of component residues from the elevated gas treatments were not significantly different from the control. However, N immobilization increased in soils containing petiole and stem residues from the elevated CO2, O3, and combined gas treatments. Mass loss of decomposing leaf residue from the added O3 and combined gas treatments was 48% less than the control treatment after 20 weeks, while differences in decomposition of petiole, stem, and husk residues among treatments were minor. Decreased decomposition of leaf residues was correlated with lower starch and higher lignin levels. However, leaf residues only comprised about 20% of the total residue biomass assayed so treatment effects on mass loss of total aboveground residues were relatively small. The primary influence of elevated atmospheric CO2 and O3 concentrations on decomposition processes is apt to arise from effects on residue mass input, which is increased by elevated CO2 and suppressed by O3.
Stripping Bacillus: ComK auto‐stimulation is responsible for the bistable response in competence development
Authors: Smits Wiep Klaas , Eschevins Caroline C. , Susanna Kim A. , Bron Sierd , Kuipers Oscar P. , Hamoen Leendert W. 
Published: April 2005

SummaryIn Bacillus subtilis competence for genetic transformation develops only in a subpopulation of cells in an isogenic culture. The molecular mechanisms underlying this phenotypic heterogeneity are unknown. In this study, we stepwise simplify the signal transduction cascade leading to competence, yielding a strain devoid of all regulatory inputs for this process that have been identified so far. We demonstrate that auto‐stimulation of ComK, the master regulator for competence development, is essential and in itself can be sufficient to generate a bistable expression pattern. We argue that transcriptional regulation determines the threshold of ComK to initiate the auto‐stimulatory response, and that the basal level of ComK (in a wild‐type strain governed by MecA‐mediated proteolytic control) determines the fraction of cells that reach this threshold, and thus develop competence.
Control of speed modulation (chemokinesis) in the unidirectional rotary motor of Sinorhizobium meliloti
Authors: Attmannspacher Ursula , Scharf Birgit , Schmitt Rüdiger 
Published: April 2005

SummarySwimming cells of Sinorhizobium meliloti are driven by flagella that rotate only clockwise. They can modulate rotary speed (achieve chemokinesis) and reorient the swimming path by slowing flagellar rotation. The flagellar motor is energized by proton motive force, and torque is generated by electrostatic interactions at the rotor/stator (FliG/MotA‐MotB) interface. Like the Escherichia coli flagellar motor that switches between counterclockwise and clockwise rotation, the S. meliloti rotary motor depends on electrostatic interactions between conserved charged residues, namely, Arg294 and Glu302 (FliG) and Arg90, Glu98 and Glu150 (MotA). Unlike in E. coli, however, Glu150 is essential for torque generation, whereas residues Arg90 and Glu98 are crucial for the chemotaxis‐controlled variation of rotary speed. Substitutions of either Arg90 or Glu98 by charge‐neutralizing residues or even by their smaller, charge‐maintaining isologues, lysine and aspartate, resulted in top‐speed flagellar rotation and decreased potential to slow down in response to tactic signalling (chemokinesis‐defective mutants). The data infer a novel mechanism of flagellar speed control by electrostatic forces acting at the rotor/stator interface. These features have been integrated into a working model of the speed‐modulating rotary motor.
A bZIP transcription factor from Phytophthora interacts with a protein kinase and is required for zoospore motility and plant infection
Authors: Blanco Flavio A. , Judelson Howard S. 
Published: April 2005

SummaryZoospores are critical in the disease cycle of Phytophthora infestans, a member of the oomycete group of fungus‐like microbes and the cause of potato late blight. A protein kinase induced during zoosporogenesis, Pipkz1, was shown to interact in the yeast two‐hybrid system with a putative bZIP transcription factor. This interaction was confirmed in vitro using a pull‐down assay. The transcription factor gene, Pibzp1, was single copy and expressed in all tissues. Transformants of P. infestans stably silenced for Pibzp1 were generated using plasmids expressing its coding region in sense or antisense orientations. A protoplast transformation method induced silencing more efficiently than transformation by an electroporation scheme. Wild‐type and silenced strains exhibited no differences in hyphal growth or morphology, mating, sporangia production or zoospore release. However, zoospores from the mutants spun in tight circles, instead of exhibiting the normal pattern of straight swimming punctuated by turns. Zoospore encystment was unaffected by silencing, but cysts germinated more efficiently than controls. Germinated cysts from the mutants failed to develop appressoria and were unable to infect plants; however, they could colonize wounded tissue. These phenotypes indicate that Pibzp1 is a key regulator of several stages of the zoospore‐mediated infection pathway.
Seeing is believing: the role of videoconferencing in distance learning
Authors: Martin Marie 
Published: April 2005

AbstractThe potential of videoconferencing to enrich distance learning needs to be widely recognised as well as the technology embedded in curriculum delivery and in distance learning programmes. The argument is supported by reference to a wide range of case studies from the author's experiences over a period of six years as International Officer with the Western Education and Library Board in Northern Ireland, and to exemplars of good practice from other sources in different parts of the world. As videoconferencing becomes more widely available in schools and in public libraries, it is important that there is a new awareness of its vast potential in order to ensure that this technology is fully exploited for the benefit of learning communities.
Netskills and the current state of beliefs and practices in student learning: an assessment and recommendations
Authors: Murray Liam , Hourigan Triona , Jeanneau Catherine , Chappell Dominic 
Published: April 2005

AbstractThis article analyses data from over 1000 student questionnaires dealing with how students currently use the web to support their learning. It discusses student understanding, needs, and expectations of the web and the overwhelming perception that the web now forms an integral part of their study and research practices. However, these practices require greater definition and refinement for and by the student. Evidence from some teaching staff is compared with that from students for validation purposes and has also revealed striking differences in perception and attitudes between the two groups. We identify specific needs on the part of most students in our survey who require greater guidance and study skills when using the web. These “Netskills” are described and recommendations are made concerning their acquisition and future development by students who are demanding that such skills become part of their own learning strategies.
Do two heads search better than one? Effects of student collaboration on web search behaviour and search outcomes
Authors: Lazonder Ard W. 
Published: April 2005

AbstractThis study compared Pairs of students with Single students in web search tasks. The underlying hypothesis was that peer‐to‐peer collaboration encourages students to articulate their thoughts, which in turn has a facilitative effect on the regulation of the search process as well as search outcomes. Both hypotheses were supported by the results. Pairs located the target information more often and in less time than Singles did. Pairs also employed a richer repertoire of search strategies and were more proficient in monitoring and evaluating their search behaviour. Implications of these findings for practice and further research are discussed.
What campus‐based students think about the quality and benefits of e‐learning
Authors: Concannon Fiona , Flynn Antoinette , Campbell Mark 
Published: April 2005

AbstractThere is a trend in Irish universities to utilise the benefits of the e‐learning as a mechanism to improve learning performance of campus‐based students. Whilst traditional methods, such as face‐to‐face lectures, tutorials, and mentoring, remain dominant in the educational sector, universities are investing heavily in learning technologies, to facilitate improvements with respect to the quality of learning. The technology to support reuse and sharing of educational resources, or learning objects, is becoming more stable, with interoperability standards maturing. However, debate has raged about what constitutes effective use of learning technology.This research expands upon a study carried out in 2003 examining students’ perceptions of e‐learning in a large undergraduate accounting class environment. As a result, improvements were made to the instructional design of the course, to enable students to engage interactively with content. The subsequent study, reported in this paper, adopted a broad range of techniques to understand students’ learning experience in depth. The findings of this research provide an insight into how these students really work and learn using technologies, if at all. It is hoped that our findings will improve the experience for both students and lecturers who engage in teaching and learning through this medium.
Causes and Consequences of Changes in Nutrient Structure in the Jiaozhou Bay
Authors: ZHAO Shu‐Jiang , JIAO Nian‐Zhi , SHEN Zhi‐Liang , WU Yu‐Lin 
Published: April 2005

Abstract: Concentrations and ratios of nutrients in Jiaozhou Bay, China, have changed much in the past decades, with trends indicating an increase in nitrogen and a decrease in silicate. Statistical analysis has shown that the long‐term variations of nutrients are associated with agricultural activities, precipitation, and anthropogenic factors. Stoichiometric calculations indicate that the nutrient structure has become more and more unbalanced. There has been almost no possibility for nitrogen limitation since the 1980s, the probability of P limitation has increased, and the probability of Si limitation has also increased markedly from the 1980s to the 1990s. As a consequence of changes in nutrient structure, a decrease in the abundance of net phytoplankton was evident, whereas total chlorophyll a, levels have remained roughly unchanged at around 3.55 g/L. Thus, it is likely that smaller species have taken the niche vacated by the larger species. Changes in phytoplankton size and species composition may ultimately lead to various functional and structural changes at the system level.(Managing editor: Ya‐Qin HAN)
OsDREB4 Genes in Rice Encode AP2‐Containing Proteins that Bind Specifically to the Dehydration‐Responsive Element
Authors: TIAN Xiu‐Hong , LI Xue‐Ping , ZHOU Hua‐Lin , ZHANG Jin‐Song , GONG Zhi‐Zhong , CHEN Shou‐Yi 
Published: April 2005

Abstract: Most dehydration‐responsive element‐binding (DREB) factors interact specifically with the dehydration‐responsive element (DRE) and control the expression of many stress‐inducible genes in Arabidopsis. In rice (Oryza sativa L. cv. Lansheng), we cloned three DREB homologs: OsDREB1‐1, OsDREB4‐1, and OsDREB4‐2. The deduced amino acid sequences revealed that each protein contained a potential nuclear localization signal, an AP2 DNA‐binding domain, and a possible acidic activation domain. The yeast one‐hybrid assay indicated that both OsDREB4‐1 and OsDREB4‐2 proteins specifically bound to DRE and activated expression of the dual reporter genes of histidine (HIS3) and galactosidase (LacZ). In rice seedlings, expression of OsDREB4‐1 was induced by dehydration and high salt, whereas OsDREB1‐1 and OsDREB4‐2 were expressed constitutively. Under normal growth conditions, OsDREB1‐1 was expressed strongly in the leaf, sheath, and spike, was expressed relatively weak in the stem and only faintly expressed in the roots, whereas expression of transcripts of OsDREB4‐1 and OsDREB4‐2 was higher in the roots, stem, and spike, lower in the leaf, and undetectable in the sheath. Together, these results imply that expression of the OsDREB genes could be controlled by specific aspects of differentiation or development. Thus, OsDREB4‐1 could function as a trans ‐acting factor in the DRE/DREB regulated stress‐responsive pathway.(Managing editor: Li‐Hui ZHAO)
Chemical Constituents from the Seeds of Ziziphus jujuba var. spinosa (Bunge) Hu
Authors: LI Li‐Mei , LIAO Xun , PENG Shu‐Lin , DING Li‐Sheng 
Published: April 2005

Abstract: To search for new and bioactive minor components from traditional Chinese medicines, a new compound, named jujuphenoside (1), was isolated from the seeds of Ziziphus jujuba var. spinosa (Bunge) Hu. The structure of jujuphenoside was elucidated by spectral and chemical methods, particularly two‐dimensional nuclear magnetic resonance analysis. Together with the new compound, 22 known compounds were also isolated and identified from the seeds of Z. jujuba var. spinosa, among which, epiceanothic acid (2) was first obtained from natural resources, whereas compounds 7–16 were first obtained from this plant.(Managing editor: Wei WANG)
Effects of Phosphorus Nutrient on the Hydraulic Conductivity of Sorghum (Sorghum vulgare Pers.) Seedling Roots Under Water Deficiency
Authors: SHANGGUAN Zhou‐Ping , LEI Ting‐Wu , SHAO Ming‐An , XUE Qing‐Wu 
Published: April 2005

Abstract: Hydroponic experiments were conducted in a growth chamber and changes in the hydraulic conductivity of sorghum (Sorghum vulgare Pers.) roots (Lpr) at the three‐leaf stage were measured using the pressure chamber method. Water deficiency was imposed with polyethylene glycol (PEG) 6000 and the phosphorus (P) levels were controlled by complete Hoagland solution with and without P nutrient. The objective of this study was to investigate the effect of P nutrition on root Lpr under water deficiency. The results showed that the Lpr in P deficiency treatments decreased markedly, but the Lpr recovered to the same value as that of control when sufficient P was supplied for 4–24 h. Water deficiency decreased Lpr, but the hydraulic conductivity of the roots with sufficient P supply was still higher than that of plants without P supply. When resuming water supply, the Lpr of the water‐deficient plants under P supply recovered faster than that of plants without P supply, which indicates that plants with sufficient P nutrient are more drought tolerant and have a greater ability to recover after drought. The treatment of HgCl2 indicated that P nutrient could regulate the Lpr by affecting the activity and the expression levels of aquaporins.(Managing editor: Ya‐Qin HAN)