bluuebunny/crossref_metadata_2025_split huggingface dataset:
Do dams and levees impact nitrogen cycling? Simulating the effects of flood alterations on floodplain denitrification
Authors: Gergel Sarah E. , Carpenter Stephen R. , Stanley Emily H. 
Published: July 2005

AbstractA fundamental challenge in understanding the global nitrogen cycle is the quantification of denitrification on large heterogeneous landscapes. Because floodplains are important sites for denitrification and nitrogen retention, we developed a generalized floodplain biogeochemical model to determine whether dams and flood‐control levees affect floodplain denitrification by altering floodplain inundation. We combined a statistical model of floodplain topography with a model of hydrology and nitrogen biogeochemistry to simulate floods of different magnitude. The model predicted substantial decreases in NO3‐N processing on floodplains whose overbank floods have been altered by levees and upstream dams. Our simulations suggest that dams may reduce nitrate processing more than setback levees. Levees increased areal floodplain denitrification rates, but this effect was offset by a reduction in the area inundated. Scenarios that involved a levee also resulted in more variability in N processing among replicate floodplains.Nitrate loss occurred rapidly and completely in our model floodplains. As a consequence, total flood volume and the initial mass of nitrate reaching a floodplain may provide reasonable estimates of total N processing on floodplains during floods. This finding suggests that quantifying the impact of dams and levees on floodplain denitrification may be possible using recent advances in remote sensing of floodplain topography and flood stage. Furthermore, when considering flooding over the long‐term, the cumulative N processed by frequent smaller floods was estimated to be quite large relative to that processed by larger, less frequent floods. Our results suggest that floodplain denitrification may be greatly influenced by the pervasive anthropogenic flood‐control measures that currently exist on most majors river floodplains throughout the world, and may have the potential to be impacted by future changes in flood probabilities that will likely occur as a result of climate shifts.
Tree photosynthesis modulates soil respiration on a diurnal time scale
Authors: Tang Jianwu , Baldocchi Dennis D. , Xu Liukang 
Published: July 2005

AbstractTo estimate how tree photosynthesis modulates soil respiration, we simultaneously and continuously measured soil respiration and canopy photosynthesis over an oak‐grass savanna during the summer, when the annual grass between trees was dead. Soil respiration measured under a tree crown reflected the sum of rhizosphere respiration and heterotrophic respiration; soil respiration measured in an open area represented heterotrophic respiration. Soil respiration was measured using solid‐state CO2 sensors buried in soils and the flux‐gradient method. Canopy photosynthesis was obtained from overstory and understory flux measurements using the eddy covariance method. We found that the diurnal pattern of soil respiration in the open was driven by soil temperature, while soil respiration under the tree was decoupled with soil temperature. Although soil moisture controlled the seasonal pattern of soil respiration, it did not influence the diurnal pattern of soil respiration. Soil respiration under the tree controlled by the root component was strongly correlated with tree photosynthesis, but with a time lag of 7–12 h. These results indicate that photosynthesis drives soil respiration in addition to soil temperature and moisture.
Growth of Eastern Cottonwoods (Populus deltoides) in elevated [CO2] stimulates stand‐level respiration and rhizodeposition of carbohydrates, accelerates soil nutrient depletion, yet stimulates above‐ and belowground biomass production
Authors: Barron‐Gafford Greg , Martens Dean , Grieve Katie , Biel Karl , Kudeyarov Valery , McLain Jean E. T. , Lipson David , Murthy Ramesh 
Published: July 2005

AbstractWe took advantage of the distinctive system‐level measurement capabilities of the Biosphere 2 Laboratory (B2L) to examine the effects of prolonged exposure to elevated [CO2] on carbon flux dynamics, above‐ and belowground biomass changes, and soil carbon and nutrient capital in plantation forest stands over 4 years. Annually coppiced stands of eastern cottonwoods (Populus deltoides) were grown under ambient (400 ppm) and two levels of elevated (800 and 1200 ppm) atmospheric [CO2] in carbon and N‐replete soils of the Intensive Forestry Mesocosm in the B2L. The large semiclosed space of B2L uniquely enabled precise CO2 exchange measurements at the near ecosystem scale. Highly controllable climatic conditions within B2L also allowed for reproducible examination of CO2 exchange under different scales in space and time. Elevated [CO2] significantly stimulated whole‐system maximum net CO2 influx by an average of 21% and 83% in years 3 and 4 of the experiment. Over the 4‐year experiment, cumulative belowground, foliar, and total aboveground biomass increased in both elevated [CO2] treatments. After 2 years of growth at elevated [CO2], early season stand respiration was decoupled from CO2 influx aboveground, presumably because of accelerated fine root production from stored carbohydrates in the coppiced system prior to canopy development and to the increased soil carbohydrate status under elevated [CO2] treatments. Soil respiration was stimulated by elevated [CO2] whether measured at the system level in the undisturbed soil block, by soil collars in situ, or by substrate‐induced respiration in vitro. Elevated [CO2] accelerated depletion of soil nutrients, phosphorus, calcium and potassium, after 3 years of growth, litter removal, and coppicing, especially in the upper soil profile, although total N showed no change. Enhancement of above‐ and belowground biomass production by elevated [CO2] accelerated carbon cycling through the coppiced system and did not sequester additional carbon in the soil.
Remote sensing of heterogeneity in photosynthetic efficiency, electron transport and dissipation of excess light in Populus deltoides stands under ambient and elevated CO2 concentrations, and in a tropical forest canopy, using a new laser‐induced fluorescence transient device
Authors: Ananyev Gennady , Kolber Zbigniew S. , Klimov Dennis , Falkowski Paul G. , Berry Joseph A. , Rascher Uwe , Martin Robin , Osmond Barry 
Published: July 2005

AbstractDetermining the spatial and temporal diversity of photosynthetic processes in forest canopies presents a challenge to the evaluation of biological feedbacks needed for improvement of carbon and climate models. Limited access with portable instrumentation, especially in the outer canopy, makes remote sensing of these processes a priority in experimental ecosystem and climate change research. Here, we describe the application of a new, active, chlorophyll fluorescence measurement system for remote sensing of light use efficiency, based on analysis of laser‐induced fluorescence transients (LIFT). We used mature stands of Populus grown at ambient (380 ppm) and elevated CO2 (1220 ppm) in the enclosed agriforests of the Biosphere 2 Laboratory (B2L) to compare parameters of photosynthetic efficiency, photosynthetic electron transport, and dissipation of excess light measured by LIFT and by standard on‐the‐leaf saturating flash methods using a commercially available pulse‐modulated chlorophyll fluorescence instrument (Mini‐PAM). We also used LIFT to observe the diel courses of these parameters in leaves of two tropical forest dominants, Inga and Pterocarpus, growing in the enclosed model tropical forest of B2L. Midcanopy leaves of both trees showed the expected relationships among chlorophyll fluorescence‐derived photosynthetic parameters in response to sun exposure, but, unusually, both displayed an afternoon increase in nonphotochemical quenching in the shade, which was ascribed to reversible inhibition of photosynthesis at high leaf temperatures in the enclosed canopy. Inga generally showed higher rates of photosynthetic electron transport, but greater afternoon reduction in photosynthetic efficiency. The potential for estimation of the contribution of outer canopy photosynthesis to forest CO2 assimilation, and assessment of its response to environmental stress using remote sensing devices such as LIFT, is briefly discussed.
The effect of elevated CO2 on diel leaf growth cycle, leaf carbohydrate content and canopy growth performance of Populus deltoides
Authors: Walter Achim , Christ Maja M. , Barron‐gafford Greg A. , Grieve Katie A. , Murthy Ramesh , Rascher Uwe 
Published: July 2005

AbstractImage sequence processing methods were applied to study the effect of elevated CO2 on the diel leaf growth cycle for the first time in a dicot plant. Growing leaves of Populus deltoides, in stands maintained under ambient and elevated CO2 for up to 4 years, showed a high degree of heterogeneity and pronounced diel variations of their relative growth rate (RGR) with maxima at dusk. At the beginning of the season, leaf growth did not differ between treatments. At the end of the season, final individual leaf area and total leaf biomass of the canopy was increased in elevated CO2. Increased final leaf area at elevated CO2 was achieved via a prolonged phase of leaf expansion activity and not via larger leaf size upon emergence. The fraction of leaves growing at 30–40% day−1 was increased by a factor of two in the elevated CO2 treatment. A transient minimum of leaf expansion developed during the late afternoon in leaves grown under elevated CO2 as the growing season progressed. During this minimum, leaves grown under elevated CO2 decreased their RGR to 50% of the ambient value. The transient growth minimum in the afternoon was correlated with a transient depletion of glucose (less than 50%) in the growing leaf in elevated CO2, suggesting diversion of glucose to starch or other carbohydrates, making this substrate temporarily unavailable for growth. Increased leaf growth was observed at the end of the night in elevated CO2. Net CO2 exchange and starch concentration of growing leaves was higher in elevated CO2. The extent to which the transient reduction in diel leaf growth might dampen the overall growth response of these trees to elevated CO2 is discussed.
The impact of recent increases in atmospheric CO2 on biomass production and vegetative retention of Cheatgrass (Bromus tectorum): implications for fire disturbance
Authors: Ziska L. H. , Reeves J. B. , Blank B. 
Published: July 2005

AbstractCheatgrass (Bromus tectorum) is a recognized, invasive annual weed of the western United States that reduces fire return times from decades to less than 5 years. To determine the interaction between rising carbon dioxide concentration ([CO2]) and fuel load, we characterized potential changes in biomass accumulation, C : N ratio and digestibility of three cheatgrass populations from different elevations to recent and near‐term projections in atmospheric [CO2]. The experimental CO2 values (270, 320, 370, 420 μmol mol−1) corresponded roughly to the CO2 concentrations that existed at the beginning of the 19th century, that during the 1960s, the current [CO2], and the near‐term [CO2] projection for 2020, respectively. From 25 until 87 days after sowing (DAS), aboveground biomass for these different populations increased 1.5–2.7 g per plant for every 10 μmol mol−1 increase above the 270 μmol mol−1 preindustrial baseline. CO2 sensitivity among populations varied with elevational origin with populations from the lowest elevation showing the greatest productivity. Among all populations, the undigestible portion of aboveground plant material (acid detergent fiber ADF, mostly cellulose and lignin) increased with increasing [CO2]. In addition, the ratio of C : N increased with leaf age, with [CO2] and was highest for the lower elevational population. These CO2‐induced qualitative changes could, in turn, result in potential decreases in herbivory and decomposition with subsequent effects on the aboveground retention of cheatgrass biomass. Overall, these data suggest that increasing atmospheric [CO2] above preambient levels may have contributed significantly to cheatgrass productivity and fuel load with subsequent effects on fire frequency and intensity.
Quantification of survivin mRNA in testes of infertile patients and in testicular germ cell tumours: high levels of expression associated with normal spermatogenesis
Authors: WEIKERT STEFFEN , SCHRADER MARK , CHRISTOPH FRANK , SCHULZE WOLFGANG , KRAUSE HANS , MÜLLER MARKUS , MILLER KURT 
Published: July 2005

SummaryDeregulated apoptosis of germ cells may contribute to male infertility as well as malignant transformation. Survivin, an inhibitor of apoptosis (IAP), is overexpressed in all the most common human malignancies, but barely detectable in normal tissues. We used real‐time polymerase chain reaction (PCR) to quantify survivin mRNA expression in normal testes (n = 22), testes with defective spermatogenesis (n = 26) and testicular germ cell tumours (TGCTs; n = 16). Survivin was expressed at high levels in normal testes. Testicular survivin levels in infertile patients were related inversely to the severity of spermatogenic failure (p < 0.001), with a lack of expression in most specimens with pre‐meiotic spermatogenic arrest and in all those with germ cell aplasia. Lower levels of expression were observed in TGCTs than in normal testes. While survivin expression was detected in most TGCTs with undifferentiated components (12 of 13), it was absent in all mature teratomas (n = 3). These data show that survivin is expressed in normal and transformed germ cells. Its downregulation in spermatogenic disorders indicates that survivin may contribute to the normal balance between germ cell proliferation and apoptosis. In TGCTs, survivin expression appears to be lost with somatic differentiation.
Intraguild omnivory in predatory stream insects
Authors: LANCASTER JILL , BRADLEY DAVID C. , HOGAN ANITA , WALDRON SUSAN 
Published: July 2005

Summary

The veracity of food webs and other trophic structures derived from empirical data sets depends ultimately on our ability to identify species’ diets and, thus, to classify organisms according to their major energy source or functional feeding groups. True omnivory (mixing plant and animal food) is common among terrestrial and marine arthropods, but poorly documented in freshwater systems. In a field study, we examined a guild of six large‐bodied, lotic insects (Plecoptera and Trichoptera) that are generally considered to be predatory and that coexist in one stream. Gut contents analysis was used to characterize prey in the diet and to quantify the consumption of plant material. Nitrogen isotope ratios (δ15N) were measured in whole‐animal samples to determine whether any algae were assimilated into body tissues.
Gut contents analysis showed that all six study taxa were polyphagous with respect to their animal prey. All taxa also consumed substantial amounts of algae, but little true detritus (terrestrial plant material). Contrary to previous suggestions, an ontogenetic shift from carnivory to algivory was apparent in two species; a shift from algivory to carnivory was not observed.
Stable isotope analysis indicated that some predators assimilated algae: δ15N was lower than expected if predators were wholly carnivorous. Using a stable isotope mixing model to estimate the proportion of algae assimilated into body tissues, we suggest that three taxa are true omnivores and estimate that 40–55% of body nitrogen is derived from algae. The remaining three taxa appear to be primarily carnivorous.
Intraguild omnivory is a distinctive feature of the food web in this stream, and probably many others, and needs to be incorporated explicitly into models of stream systems. The food limitation hypothesis may explain, in part, true omnivory at this site. However, the nutritional value of algae and its role in the growth and fecundity of predatory stream insects requires further investigation before underlying mechanisms can be identified with confidence.
Relationships between taxonomic resolution and spatial scales of multivariate variation
Authors: ANDERSON MARTI J. , CONNELL SEAN D. , GILLANDERS BRONWYN M. , DIEBEL CAROL E. , BLOM WILMA M. , SAUNDERS JUSTINE E. , LANDERS TODD J. 
Published: July 2005

Summary

We investigated the effects of changes in taxonomic resolution on analyses of patterns of multivariate variation at different spatial scales for the highly diverse fauna inhabiting holdfasts of the kelp Ecklonia radiata.
Multivariate analyses were performed using several transformations to examine differences in spatial patterns of variation from metres up to hundreds of kilometres for composition vs. relative abundance in assemblages.
The greatest variability in assemblages occurred at the smallest spatial scale, from plant to plant, pointing to the existence of important small‐scale processes. The proportional amount of variation at the smallest spatial scale decreased with decreasing taxonomic resolution (i.e. from species through to phyla). For composition, the next‐greatest source of variation was at the largest spatial scale (hundreds of kilometres), while for relative abundance, the next‐greatest source of variation was at the level of sites (hundreds of metres to kilometres).
For abundance data, location‐level variation became less important and site‐level variation became more important with decreasing taxonomic resolution, while for compositional data, the opposite pattern occurred. This suggests that variation in the presence of species or taxa at a particular location along the coast is driven by large‐scale processes, while variation in relative abundances within locations is driven by medium‐scale processes.
The lack of significant variation in the proportional abundances of phyla at large spatial scales suggests that some consistency of pattern may emerge at larger scales (spatial and/or taxonomic), even in the presence of high small‐scale variability. These findings strengthen the idea that substantial local variation need not preclude the existence of broad‐scale organization in ecological patterns and biodiversity.
Predation cost of rapid growth: behavioural coupling and physiological decoupling
Authors: STOKS ROBBY , BLOCK MARJAN DE , VAN DE MEUTTER FRANK , JOHANSSON FRANK 
Published: July 2005

Summary

Despite its prominent role in life‐history theory, there is no direct empirical evidence for a behaviourally mediated predation cost of rapid growth. Moreover, we know little about how digestive physiology may also influence the shape of the growth/predation risk trade‐off function.
We determined the role of behaviour and digestive physiology in experiments in which damselfly larvae were induced to grow slowly or rapidly by manipulating photoperiod (time stress), and exposure to a fish predator.
We showed that larvae under time stress grew more rapidly. Rapid‐growing larvae had a higher foraging activity and a higher growth efficiency.
Under predation risk, larvae not only had a lower foraging activity but also a lower growth efficiency.
Rapid‐growing larvae (i.e. those under time stress) balanced the growth/predation risk trade‐off differently and took more risk in the presence of a predator, which resulted in a behaviourally mediated higher predation cost compared to slow‐growing larvae. Their higher growth efficiency, however, made this cost smaller compared to a completely behaviourally mediated rapid‐growth strategy.
Our results provide the first explicit experimental proof of a behaviourally mediated predation cost of rapid growth. Besides a behavioural coupling of growth and predation risk, resulting in the well‐known trade‐off, we also found a partial decoupling of these two processes by digestive physiology.
Specificity and selectivity determinants of peptide transport in Lactococcus lactis and other microorganisms
Authors: Doeven Mark K. , Kok Jan , Poolman Bert 
Published: July 2005

SummaryPeptide transport in microorganisms is important for nutrition of the cell and various signalling processes including regulation of gene expression, sporulation, chemotaxis, competence and virulence development. Peptide transport is mediated via different combinations of ion‐linked and ATP‐binding cassette (ABC) transporters, the latter utilizing single or multiple peptide‐binding proteins with overlapping specificities. The paradigm for research on peptide transport is Lactococcus lactis, in which the uptake of peptides containing essential amino acids is vital for growth on milk proteins. Differential expression and characteristics of peptide‐binding proteins in several Lactococcus lactis strains resulted in apparent conflicts with older literature. Recent developments and new data now make the pieces of the puzzle fall back into place again and confirm the view that the oligopeptide‐binding proteins determine the uptake selectivity of their cognate ABC transporters. Besides reviewing the current data on binding specificity and transport selectivity of peptide transporters in L. lactis, the possible implications for peptide utilization by other bacterial species are discussed.
NssR, a member of the Crp‐Fnr superfamily from Campylobacter jejuni, regulates a nitrosative stress‐responsive regulon that includes both a single‐domain and a truncated haemoglobin
Authors: Elvers Karen T. , Turner Sue M. , Wainwright Laura M. , Marsden Gemma , Hinds Jason , Cole Jeffrey A. , Poole Robert K. , Penn Charles W. , Park Simon F. 
Published: July 2005

SummaryConsistent with its role as a nitric oxide (NO)‐detoxifying globin in Campylobacter jejuni, Cgb (Campylobacter globin) expression is strongly and specifically induced following exposure to nitrosative stress, suggesting a previously unrecognized capacity for NO‐related stress sensing in this food‐borne pathogen. In this study, Fur and PerR have been eliminated as major regulators of cgb, and NssR (Cj0466), a member of the Crp‐Fnr superfamily, has been identified as the major positive regulatory factor that controls nitrosative stress‐responsive expression of this gene. Accordingly, disruption of nssR resulted in the abolition of inducible cgb expression, which was restored by a complementing chromosomal insertion of the wild‐type gene with its indigenous promoter at a second location. The NssR‐deficient mutant was more sensitive to NO‐related stress than a cgb mutant and this phenotype most likely arises from the failure of these cells to induce other NO‐responsive components in addition to Cgb. Indeed, analysis of global gene expression, by microarray and confirmatory real‐time polymerase chain reaction (PCR) in the wild type and nssR mutant, not only confirmed the dependence of inducible cgb expression on NssR, but also revealed for the first time a novel NssR‐dependent nitrosative stress‐responsive regulon. This regulon of at least four genes includes Cj0465c, a truncated globin. Consistent with NssR being a Crp‐Fnr superfamily member, an Fnr‐like binding sequence (TTAAC‐N4‐GTTAA) was found upstream of each gene at locations −40.5 to −42.5 relative to the centre of the binding sites and the transcription start point. Site‐directed mutagenesis confirmed that this cis‐acting motif mediates the nitrosative stress‐inducible expression of cgb.