bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulated protein–protein interaction between aPKC and PAR‐3 plays an essential role in the polarization of epithelial cells
Authors: Nagai‐Tamai Yoko , Mizuno Keiko , Hirose Tomonori , Suzuki Atsushi , Ohno Shigeo
Published: March 2003

Background: Recent studies have revealed that aPKC (atypical protein kinase C), PAR‐3 and PAR‐6 play indispensable roles in the regulation of various cell polarization events, from worms to mammals, suggesting that they comprise an evolutionarily conserved protein machinery which is essential for cell polarization. The three proteins interact with each other to form a ternary complex and thus mutually regulate their functionality and localization. Here, we investigated the biochemical nature of the aPKC–PAR‐3 interaction in detail to clarify its functional importance in cell polarity.

Results: The highly conserved 26 amino acid sequence 816–841, in PAR‐3 was found to be necessary and sufficient for the tight association with aPKC. Among several conserved serine/threonine residues within the region, aPKC preferentially phosphorylates serine‐827 in vitro, and this phosphorylation reduces the stability of the PAR‐3–aPKC interaction. Several analyses using a phospho‐serine 827 specific antibody have established that this phosphorylation by aPKC occurs in vivo. Over‐expression of a point mutant of PAR‐3 (S827A), which is predicted to form a stable complex with aPKC, causes defects in the cell‐cell contact‐induced cell polarization of epithelial MDCK cells, similarly to a dominant negative mutant of aPKC.

Conclusions: These results imply that serine 827 in the aPKC binding site of PAR‐3 is a target of aPKC and that the regulated interaction between a protein kinase, aPKC, and its substrate, PAR‐3, plays an essential role in the establishment of cell polarity.
Interaction of the chromatin compaction‐inducing domain (LR domain) of Ki‐67 antigen with HP1 proteins
Authors: Kametaka Ai , Takagi Masatoshi , Hayakawa Tomohiro , Haraguchi Tokuko , Hiraoka Yasushi , Yoneda Yoshihiro
Published: March 2003

Background: The LR domain of marsupial chmadrin is defined by its C‐terminal amino acid sequence, which contains several pairs of leucine (L) and arginine (R) residues. The LR domain of chmadrin causes a significant compaction of chromatin over the entire length of chromosomes when it is overproduced. The possible human homologue of chmadrin, Ki‐67 antigen (pKi‐67), also has a stretch of LR pairs, but with no obvious overall similarity, at its C‐terminus.

Results: The LR domain of human pKi‐67 also induced chromatin compaction, both in human and marsupial cells. A yeast two‐hybrid assay and an in vitro binding assay demonstrated that the human LR domain binds to heterochromatin protein 1 (HP1), a well‐characterized molecule as a mediator of heterochromatin formation. In fixed cells stained with specific antibodies, the pKi‐67 was found to be co‐localized partially with HP1 at foci on chromosomes in an early G1 phase. Time‐lapse observation in living cells co‐expressing the fluorescently tagged proteins showed that the LR domain formed foci on chromosomes over a limited period of the cell cycle from the telophase to early G1 phase and that HP1 subsequently accumulated at these foci of the LR domain.

Conclusions: Marsupial chmadrin and human pKi‐67 induce chromatin compaction across species, possibly via the interaction of its LR domain with HP1.
The upstream regulator, Rsr1p, and downstream effectors, Gic1p and Gic2p, of the Cdc42p small GTPase coordinately regulate initiation of budding in Saccharomyces cerevisiae
Authors: Kawasaki Ryosuke , Fujimura‐Kamada Konomi , Toi Hirofumi , Kato Hiroyuki , Tanaka Kazuma
Published: March 2003

Background: Cdc42p, a Rho family small GTPase, is essential for budding initiation in the yeast Saccharomyces cerevisiae. The homologous proteins Gic1p and Gic2p (Gic1/2p) are effectors of Cdc42p, but their precise functions remain unknown. Rsr1p/Bud1p is a Ras family small GTPase that controls the selection of the budding site. Previous observations suggested that Rsr1p‐GTP recruits Cdc24p, a GDP/GTP exchange factor for Cdc42p, at the incipient bud site. However, this model only addresses how Rsr1p determines the budding site, because the rsr1 mutant normally initiates budding.

Results: Here we show that a rsr1 gic1 gic2 mutant fails to initiate budding, resulting in unbudded, large, and multinucleated cells. Expression of a dominant active or dominant negative mutant of RSR1 also inhibited the growth of the gic1 gic2 mutant, suggesting that cycling of Rsr1p between the GTP‐ and GDP‐bound forms is required for budding initiation in the gic1 gic2 mutant. Among the mutations in effectors of CDC42, only the gic1 gic2 mutation demonstrated a synthetic lethal interaction with rsr1. Increased gene dosage of CDC42 suppressed defects in budding initiation of rsr1 gic1 gic2 mutants containing additional mutations in other effectors of CDC42, including BNI1, CLA4 or STE20. The polarized localization of Bni1p‐GFP (green fluorescent protein) and Cla4p‐GFP was lost after depletion of Gic1p in the rsr1 gic2 mutant.

Conclusion: We propose that Gic1/2p may stabilize or maintain a complex consisting of Cdc42p‐GTP and its effectors at the budding site, which are assembled by the action of the Rsr1p‐Cdc24p system.
The geology of Worbarrow, Dorset
Authors: Nowell D. A. G.
Published: March 2003

A classic hidden geological locality in Britain is revealed.
Sinking cities
Authors: Waltham Tony
Published: March 2003

When water supplies are abstracted from alluvial sands, interbedded clays compact and cause ground subsidence. Entire cities are being gently lowered, with serious consequences for those on low coastal sites.
Inversion for multiple parameter classes
Authors: Kennett B. L. N. , Sambridge M.
Published: March 2003

Many geophysical data, such as the frequencies of the free oscillations of the Earth, depend on more than one type of model parameter. For inverse problems depending on multiple parameter classes, an iterative solution procedure is introduced in which each parameter class can be treated in the same way. This approach has considerable advantages where a large number of parameters are employed, but can still be useful for smaller systems.

The iteration by parameter class commences by solving for the direct dependence on a particular parameter class, and at subsequent iterations the cross-dependences between classes are introduced. The update affects only the right-hand side of the equations, and, because the same sets of equations have to be solved at each iteration, an efficient computational implementation can be made. The largest set of equations that has to be solved at a time corresponds to the number of variables in an individual parameter class rather than the full set of parameters, which confers substantial computational benefits for very large problems.
Interpreting non‐orthogonal split shear waves for seismic anisotropy in multicomponent VSPS
Authors: Li Xiang‐Yang , MacBeth Colin , Crampin Stuart
Published: March 2003

There are two main sources of non‐orthogonality in multicomponent shear‐wave seismics: inherent non‐orthogonal split shear waves arising from substantial ray deviation in off‐symmetry planes due to strong anisotropy or complex overburden, and apparent non‐orthogonal split shear waves in the horizontal plane due to variation of the angle of incidence even if the two shear waves along the raypath are orthogonal. Many techniques for processing shear‐wave splitting in VSP data ignore these kinds of non‐orthogonality of the split shear waves.

Assuming inherent non‐orthogonality in zero‐offset VSPs, and apparent non‐orthogonality in offset VSPs, we derive equations for the four‐component data matrix. These can be solved by extending the linear‐transform technique (LTT) to determine the shear‐wave polarizations in zero‐offset and offset VSPs. Both full‐wave synthetic and field data are used to evaluate the technique and to examine the effects of non‐orthogonal polarized split shear waves.

If orthogonality is incorrectly assumed, errors in polarization measurements increase with the degree of non‐orthogonality, which introduces a consistent decreasing trend in the polarization measurements. However, the effect of non‐orthogonality on the estimation of geophone orientation and time delays of the two split shear waves is small and negligible in most realistic cases. Furthermore, for most cases of weak anisotropy (less than 5% shear‐wave anisotropy) apparent non‐orthogonality is more significant than inherent non‐orthogonality. Nevertheless, for strong anisotropy (more than 10% shear‐wave anisotropy) with complicated structure (tilted or inclined symmetry axis), inherent non‐orthogonality may no longer be negligible.

Applications to both synthetic and real data show that the extended linear‐transform techniques permit accurate recovery of polarization measurements in the presence of both significant inherent and apparent non‐orthogonality where orthogonal techniques often fail.
Estimation of reservoir fracturing from marine VSP using local shear‐wave conversion
Authors: MacBeth Colin , Boyd Mark , Rizer William , Queen John
Published: March 2003

A marine VSP is designed to estimate the orientation and density of fracturing within a gas‐producing dolomite layer in the southern North Sea. The overburden anisotropy is firstly estimated by analysing shear waves converted at or just below the sea‐bed, from airgun sources at four fixed offset azimuths. Full‐wave modelling helps confirm that the background has no more than 3% vertical birefringence, originating from TIH anisotropy with a symmetry axis orientated perpendicular to the maximum horizontal compressive stress of NW–SE. This finding concurs with current hypotheses regarding the background rock matrix in the upper crust. More detailed anisotropy estimates reveal two thin zones with possible polarization reversals and a stronger anisotropy. The seismic anisotropy of the dolomite is then determined from the behaviour of locally converted shear waves, providing a direct link with the physical properties of its fractures. It is possible to utilize this phenomenon due to the large seismic velocity contrast between the dolomite and the surrounding evaporites. Two walkaway VSPs at different azimuths, recorded on three‐component receivers placed inside the target zone, provide the appropriate acquisition design to monitor this behaviour. Anisotropy in the dolomite generates a transverse component energy which scales in proportion to the degree of anisotropy. The relative amplitudes, for this component, between the different walkaway azimuths relate principally to the orientation of the anisotropy. Full‐wave modelling confirms that a 50% vertical birefringence from TIH anisotropy with a similar orientation to the overburden is required to simulate the field observations. This amount of anisotropy is not entirely unexpected for a fine‐grained brittle dolomite with a potentially high fracture intensity, particularly if the fractures contain fluid which renders them compliant to the shear‐wave motion.
Appraisal of equivalence and suppression problems in 1D EM and DC measurements using global optimization and joint inversion*
Authors: Sharma S.P. , Kaikkonen P.
Published: March 2003

Global optimization with very fast simulated annealing (VFSA) in association with joint inversion is performed for 1D earth structures. The inherent problems of equivalence and suppression in electromagnetic (EM) and direct current (DC) resistivity methods are studied. Synthetic phase data from multifrequency sounding using a horizontal coplanar coil system and synthetic apparent resistivity data from Schlumberger DC resistivity measurements are inverted individually and jointly over different types of layered earth structures. Noisy data are also inverted. The study reveals that global optimization of individual data sets cannot solve inherent equivalence or suppression problems. Joint inversion of EM and DC measurements can overcome the problem of equivalence very well. However, a suppression problem cannot be solved even after combination of data sets. This study reveals that the K‐type earth structure is easiest to resolve while the A‐type is the most difficult. We also conclude that the equivalence associated with a thin resistive layer can be resolved better than that for a thin conducting layer.
GPR modelling by the Fourier method: improvement of the algorithm
Authors: Carcione  , Lenzi  , Valle
Published: March 2003

We improve two aspects of the modelling scheme for the simulation of electromagnetic radio waves, based on the Fourier pseudospectral method.

When there are large contrasts in the material properties, use of the standard algorithm (regular grid) causes a series of artefacts, as, for instance, ringing and acausal events. These problems, due to the non‐locality of the differential operator, are solved by using the staggered Fourier method (staggered grid).

Realistic radiation patterns can be obtained from simple combinations of magnetic and electric sources. If the directivity pattern of the antenna is known, from either a finite‐difference simulation or an analytic evaluation or an experimental characterization, it can then be simulated by a composite‐source concept. This effective source is implemented in the modelling algorithm by means of a perturbation technique, which first computes the intensity and directional spectra of the single electromagnetic sources. Their location is optimized to obtain the best fit with a minimum number of sources. The approach is, in principle, valid for the far‐field radiation pattern of the antenna.
A multichannel approach to long‐period multiple prediction and attenuation
Authors: Rosenberger  , Meyer  , Buttkus
Published: March 2003

A method is presented for the prediction and attenuation of long‐period water‐layer multiples based on an adaptive multichannel lattice algorithm. The multichannel approach can be viewed as a generalization of two‐dimensional linear prediction. The multichannel linear least‐squares prediction problem is reviewed briefly and the performance and limitations of the algorithm are demonstrated on two different marine data sets with different properties of the simple and peg‐leg multiple system. The algorithm works well even on problematic data sets and is very easy to apply.
Marine seismic wavefield measurement to remove sea‐surface multiples
Authors: Ziolkowski  , Taylor  , Johnston
Published: March 2003

We propose a new method for removing sea‐surface multiples from marine seismic reflection data in which, in essence, the reflection response of the earth, referred to a plane just above the sea‐floor, is computed as the ratio of the plane‐wave components of the upgoing wave and the downgoing wave. Using source measurements of the wavefield made during data acquisition, three problems associated with earlier work are solved: (i) the method accommodates source arrays, rather than point sources; (ii) the incident field is removed without simultaneously removing part of the scattered field; and (iii) the minimum‐energy criterion to find a wavelet is eliminated.

Pressure measurements are made in a horizontal plane in the water. The source can be a conventional array of airguns, but must have both in‐line and cross‐line symmetry, and its wavefield must be measured and be repeatable from shot to shot. The problem is formulated for multiple shots in a two‐dimensional configuration for each receiver, and for multiple receivers in a two‐dimensional configuration for each shot. The scattered field is obtained from the measurements by subtracting the incident field, known from measurements at the source. The scattered field response to a single incident plane wave at a single receiver is obtained by transforming the common‐receiver gather to the frequency–wavenumber domain, and a single component of this response is obtained by Fourier transforming over all receiver coordinates. Each scattered field component is separated into an upgoing wave and a downgoing wave using the zero‐pressure condition at the water‐surface. The upgoing wave may then be expressed as a reflection coefficient multiplied by the incident downgoing wave plus a sum of scattered downgoing plane waves, each multiplied by the corresponding reflection coefficient. Keeping the upgoing scattered wave fixed, and using all possible incident plane waves for a given frequency, yields a set of linear simultaneous equations for the reflection coefficients which are solved for each plane wave and for each frequency. To create the shot records that would have been measured if the sea‐surface had been absent, each reflection coefficient is multiplied by complex amplitude and phase factors, for source and receiver terms, before the five‐dimensional Fourier transformation back to the space–time domain.
Difficulties in determining electrical anisotropy in subsurface investigations
Authors: Christensen Niels B.
Published: March 2003

Surface electrical and electromagnetic methods have a limited resolution capability for determining the conductivity structure of the earth. In one‐dimensional modelling a collection of many thin layers is frequently considered as one composite layer, which is then macro‐anisotropic. Neither galvanic methods nor inductive methods alone can resolve the anisotropy of the ground, but a joint inversion of galvanic and inductive data may do so. The necessity of including the coefficient of anisotropy in the joint inversion of galvanic and inductive sounding data is demonstrated. An analysis is made of the combined use of geoelectrical and transient soundings to resolve the coefficient of anisotropy of a subsurface layer for varying thickness, resistivity and coefficient of anisotropy. It is found that the coefficient of anisotropy is well resolved only for layers that are many times thicker than the overburden and for coefficients of anisotropy that are not too small. The ability of the joint inversion of geoelectrical and transient sounding data to resolve macro‐anisotropic layers is tested using realistic earth models determined from electrical logs.
Controlled sources for shear‐wave surveys in mines
Authors: Holmes Gordon M. , Crampin Stuart , Young R. Paul
Published: March 2003

The ability to analyse shear‐wave anisotropy in a mine environment is greatly aided by using multiple source orientations of a reproducible, impulsive shear‐wave source. The analysis of what is probably the first controlled source shear‐wave experiment in a mine environment demonstrates clearly that shear‐wave polarizations and time delays between split shear‐wave arrivals are reliably measured because of the use of multiple source orientations rather than a single shear‐wave source. Reliability is further aided by modelling the shear‐wave source radiation pattern, which allows for the unequivocal discrimination between seismic raypaths where shear‐wave splitting did and did not occur. The analysis also demonstrates the great importance of high reproducibility of the seismic source for the use of shear waves in time‐lapse surveys to monitor changes in a rockmass.
Seismic anisotropy in granite at the Underground Research Laboratory, Manitoba
Authors: Holmes Gordon M. , Crampin Stuart , Young R. Paul
Published: March 2003

The Shear‐Wave Experiment at Atomic Energy of Canada Limited's Underground Research Laboratory was probably the first controlled‐source shear‐wave survey in a mine environment. Taking place in conjunction with the excavation of the Mine‐by test tunnel at 420 m depth, the shear‐wave experiment was designed to measure the in situ anisotropy of the rockmass and to use shear waves to observe excavation effects using the greatest variety of raypath directions of any in situ shear‐wave survey to date. Inversion of the shear‐wave polarizations shows that the anisotropy of the in situ rockmass is consistent with hexagonal symmetry with an approximate fabric orientation of strike 023° and dip 35°. The in situ anisotropy is probably due to microcracks with orientations governed by the in situ stress field and to mineral alignment within the weak gneissic layering. However, there is no unique interpretation as to the cause of the in situ anisotropy as the fabric orientation agrees approximately with both the orientation expected from extensive‐dilatancy anisotropy and that of the gneissic layering. Eight raypaths with shear waves propagating wholly or almost wholly through granodiorite, rather than granite, do not show the expected shear‐wave splitting and indicate a lower in situ anisotropy, which may be due to the finer grain size and/or the absence of gneissic layering within the granodiorite. These results suggest that shear waves may be used to determine crack and mineral orientations and for remote monitoring of a rockmass. This has potential applications in mining and waste monitoring.
Detecting small‐scale targets by the 2D inversion of two‐sided three‐electrode data: application to an archaeological survey
Authors: Candansayar M. Emin , Başokur Ahmet T.
Published: March 2003

The detecting capabilities of some electrical arrays for the estimation of position, size and depth of small‐scale targets were examined in view of the results obtained from 2D inversions of apparent‐resistivity data. The two‐sided three‐electrode apparent‐resistivity data are obtained by the application of left‐ and right‐hand pole–dipole arrays that also permit the computation of four‐electrode and dipole–dipole apparent‐resistivity values without actually measuring them. Synthetic apparent‐resistivity data sets of the dipole–dipole, four‐electrode and two‐sided three‐electrode arrays are calculated for models that simulate buried tombs. The results of two‐dimensional inversions are compared with regard to the resolution in detecting the exact location, size and depth of the target, showing some advantage for the two‐sided three‐electrode array. A field application was carried out in the archaeological site known as Alaca Hoyuk, a religious temple area of the Hittite period. The two‐dimensional inversion of the two‐sided three‐electrode apparent‐resistivity data has led to locating a part of the city wall and a buried small room. The validity of the interpretation has been checked against the results of subsequent archaeological excavations.
Successive cracking steps of a limestone highlighted by ultrasonic wave propagation
Authors: Couvreur J.F. , Vervoort A. , King M.S. , Lousberg E. , Thimus J.F.
Published: March 2003

A number of laboratory tests (uniaxial, triaxial and hydrostatic) have been conducted on a dry porous limestone. A conceptual model is proposed to correlate deformation and damage fields (including acoustic emission activity) with the variation of ultrasonic velocities, quality factors and energies as measures of attenuation. This correlation is presented in a stress deviator versus confining pressure diagram. In this way, the successive steps occurring in the damage process of this rock are well described. In particular, the quality factor of S‐waves distinguishes clearly the onset of the initially stable cracking, while the velocity of S‐waves and strain measurements are sensitive to dilatancy which appears later in the damage process of the limestone studied.
Pulled array continuous electrical sounding with an additional inductive source: an experimental design study
Authors: Christensen Niels B. , Sørensen Kurt
Published: March 2003

Electrical and electromagnetic profiling methods are used extensively in environmental geophysical investigations for many different purposes. The pulled array continuous electrical sounding (PACES) method, where a tail of electrodes is towed behind a small vehicle while continuously and simultaneously measuring several electrode configurations, has been used extensively for mapping the vulnerability of aquifers in Denmark. Measurements are taken every 1 m, and 10–15 km of profile can be achieved in one day.

This paper presents a theoretical study of the resolution capabilities of PACES measurements as they are now performed, and an experimental design study for including an inductive source in the measuring equipment. The joint interpretation of the galvanic data set of ordinary PACES measurements with inductive data from a horizontal magnetic dipole source will enhance the resolution capabilities of the data set significantly. The study is carried out as an analysis of the uncertainty of the model parameters of one‐dimensional three‐layer models using the estimation error variances of the inversion problem.

The results indicate that the addition of only two frequency data from a magnetic dipole source will substantially improve the resolution of the subsurface resistivity structure. The improvement is model dependent, but reduction in the relative error of model parameters by an order of magnitude is observed.
The use of instantaneous velocity in uplift investigations
Authors: Al‐Chalabi M.
Published: March 2003

Uplift and the accompanying reduction in overburden result in anomalously high velocity in the uplifted rock unit relative to its current depth. The present work utilizes the non‐uniqueness of the parameters of instantaneous velocity versus depth functions as an effective tool for uplift studies. The linear function with its two parameters, V0 and k, is a very simple function and is used as the illustrative vehicle. In the parameter space, i.e. in a plot where one axis represents V0 and the other axis represents k, non‐uniqueness can be represented by contours of equal goodness‐of‐fit values between the observed data and the fitted function. The contour delimiting a region of equivalent solutions in the parameter space is called a ‘solution trough’. Uplift corresponds to a rotation of the solution trough in the parameter space. It is shown that, in terms of relative depth changes, there are five possible configurations (five cases) of uplift in a given area (the mobile location) relative to another area (the reference location). The cases depend on whether the uplifted location had attained a (pre‐uplift) maximum depth of burial that was greater than, similar to, or smaller than the maximum depth of burial at the reference location. Interpretation of the relationships between the solution troughs corresponding to the different locations makes it possible to establish which of the five cases applies to the uplifted location and to estimate the amount of uplift that the unit had undergone at that location. The difficulty in determining the reduction in velocity due to decompaction resulting from uplift is a main source of uncertainty in the estimate of the amount of uplift. This is a common problem with all velocity‐based methods of uplift estimation. To help around this difficulty, the present work proposes a first‐order approximation method for estimating the effect of decompaction on velocity in an uplifted area.
Vibroseis deconvolution: a comparison of cross‐correlation and frequency‐domain sweep deconvolution
Authors: Brittle K.F. , Lines L.R. , Dey A.K.
Published: March 2003

Ideally, traditional vibroseis processing produces a band‐limited zero‐phase Klauder wavelet through cross‐correlation of the sweep with the recorded signal. An alternative wavelet processing method involves deconvolving the sweep from the recorded vibroseis trace. This deconvolution can be achieved through frequency‐domain division. We compare and contrast the advantages and disadvantages of sweep deconvolution versus cross‐correlation on synthetic and real data.
Common‐reflection‐surface (CRS) stack for common offset
Authors: Zhang Yonghai , Bergler Steffen , Hubral Peter
Published: March 2003

We provide a data‐driven macro‐model‐independent stacking technique that migrates 2D prestack multicoverage data into a common‐offset (CO) section. We call this new process the CO common‐reflection‐surface (CRS) stack. It can be viewed as the generalization of the zero‐offset (ZO) CRS stack, by which 2D multicoverage data are stacked into a well‐simulated ZO section. The CO CRS stack formula can be tailored to stack P‐P, S‐S reflections as well as P‐S or S‐P converted reflections. We point out some potential applications of the five kinematic data‐derived attributes obtained by the CO CRS stack for each stack value. These include (i) the determination of the geometrical spreading factor for reflections, which plays an important role in the construction of the true‐amplitude CO section, and (ii) the separation of the diffractions from reflection events. As a by‐product of formulating the CO CRS stack formula, we have also derived a formula to perform a data‐driven prestack time migration.
Series approximation of the Kirchhoff method for wavefield computation on a rough subsurface
Authors: Kadioğlu Selma , Kayiran Turan
Published: March 2003

ABSTRACT Computation of the wavefield due to reflection from an irregular surface is carried out for subsurfaces with large radii of curvature. The Kirchhoff approximation is proved to be sufficiently accurate provided that the acoustic wavelength is sufficiently small with respect to the asperities of the rough surface. For cases where the irregular surface does not fulfil this condition, a series solution is proposed. The first term of this series appears to be the result obtained by conventional Kirchhoff approximation. The series, initially developed in the space–wavenumber domain by Meecham, is transformed into the space–time domain, and the general expression for the series is obtained by calculation of the normal derivative of the field function. The series solution, restricted to the first two terms, is illustrated by application to three synthetic examples. Applications show that the series approximation obtained by the Kirchhoff method contributes significantly to the modelling of narrow, steep and deep structures and consequently it appears that the second term in the series cannot be ignored in the computation of the wavefields arising from a rough surface.
Effects of climate change on nitrogen dynamics in upland soils. 1. A transplant approach
Authors: Ineson Philip , Taylor Kenneth , Harrison Anthony F. , Poskitt Janet , Benham David G. , Tipping Edward , Woof Colin
Published: March 2003

The impact of climate change on N leaching from hill land plant/soil systems was investigated using a transplant technique involving the movement of intact lysimeter cores of three contrasting soil types down an altitudinal gradient at Great Dun Fell, Cumbria. Air and soil temperatures and precipitation were monitored at four elevations down an altitudinal transect using automatic weather stations for a period of two years. The altitudinal sequence of air temperature followed the anticipated pattern, providing mean annual temperatures at the four locations of 3.4, 5.0, 6.3 and 8.1 °C. Lapse rates of both mean air and soil temperatures over the altitudinal range 171–845 m were 6.6 (1993) and 7.0 °C km–1 (1994). Soil monthly temperature gradients for a particular soil type for each of the two years showed a seasonal range of 6.0 and 7.4 °C km–1, respectively, and for air temperature of 4.3 and 3.1 °C km–1. Precipitation gradients showed the expected general increase with altitude, but were less predictable. Inorganic nitrogen leaching was studied in lysimeter leachates with climatic amelioration resulting in dramatic reductions in leachate nitrate concentrations and associated total concentrations of inorganic nitrogen. Decreases in leachate nitrate concentrations were observed for all three soil types studied. Soils receiving supplemented rainfall also showed decreased N concentrations, suggesting that temperature was the main controlling factor responsible for the observed reductions. Increased N uptake by the vegetation, in response to the increases in temperature, is considered to be critical in controlling soil solution chemistry at these sites.
Integration of photosynthetic acclimation to CO2at the whole‐plant level
Authors: WOLFE DAVID W. , GIFFORD ROGER M. , HILBERT DAVID , LUO YIQI.
Published: March 2003

Primary events in photosynthetic (PS) acclimation to elevated CO2concentration ([CO2]) occur at the molecular level in leaf mesophyll cells, but final growth response to [CO2] involves acclimation responses associated with photosynthate partitioning among plant organs in relation to resources limiting growth. Source–sink interactions, particularly with regard to carbon (C) and nitrogen (N), are key determinants of PS acclimation to elevated [CO2] at the whole‐plant level. In the long term, PS and growth response to [CO2] are dependent on genotypic and environmental factors affecting the plant's ability to develop new sinks for C, and acquire adequate N and other resources to support an enhanced growth potential. Growth at elevated [CO2] usually increases N use efficiency because PS rates can be maintained at levels comparable to those observed at ambient [CO2] with less N investment in PS enzymes. A frequent acclimation response, particularly under N‐limited conditions, is for the accumulation of leaf carbohydrates at elevated [CO2] to lead to repression of genes associated with the production of PS enzymes. The hypothesis that this is an adaptive response, leading to a diversion of N to plant organs where it is of greatest benefit in terms of competitive ability and reproductive fitness, needs to be more rigorously tested.

The biological control mechanisms which plants have evolved to acclimate to shifts in source–sink balance caused by elevated [CO2] are complex, and will only be fully elucidated by probing at all scales along the hierarchy from molecular to ecosystem. Use of environmental manipulations and genotypic comparisons will facilitate the testing of specific hypotheses. Improving our ability to predict PS acclimation to [CO2] will require the integration of results from laboratory studies using simple model systems with results from whole‐plant studies that include measurements of processes operating at several scales.

Abbreviations:CAM, crassulacean acid metabolism; FACE, Free‐Air CO2Enrichment; Pi, inorganic phosphate; LAR, leaf area ratio (m2g‐1); LWR, leaf weight ratio (g g‐1); NAR, net assimilation rate (g m‐2d‐ 1); PS, photosynthetic; RGR, relative growth rate (g g‐1d‐1); R:S, root/shoot ratio; rubisco, ribulose bisphosphate carboxylase/oxygenase; RuBP, ribulose bisphosphate; SLA, specific leaf area (m2g‐1); SPS, sucrose phosphate synthase; WUE, water use efficiency (g biomass g H2O‐1).
Ameliorating effect of UV‐B radiation on the response of Norway spruce and Scots pine to ambient ozone concentrations
Authors: Schnitzler Jörg‐Peter , Langebartels Christian , Heller Werner , Liu Jinchen , Lippert Michael , Döhring Thorsten , Bahnweg Günther , Sandermann Heinrich
Published: March 2003

Elevated levels of both ozone and UV‐B radiation are typical for high‐altitude sites. Few studies have investigated their possible interaction on plants. This study reports interactive effects of O3 and UV‐B radiation in four‐year‐old Norway spruce and Scots pine trees. The trees were cultivated in controlled environmental facilities under simulated climatic conditions recorded on Mt Wank, an Alpine mountain in Bavaria, and were exposed for one growing season to simulated ambient or twice‐ambient ozone regimes at either near ambient or near zero UV‐B radiation levels. Chlorotic mottling and yellowing of current year needles became obvious under twice‐ambient O3 in both species at the onset of a high ozone episode in July. Development of chlorotic mottling in relation to accumulated ozone concentrations over a threshold of 40 nL L–1 was more pronounced with near zero rather than ambient UV‐B radiation levels. In Norway spruce, photosynthetic parameters at ambient CO2 concentration, measured at the end of the experiment, were reduced in trees cultivated under twice‐ambient O3, irrespective of the UV‐B treatment. Effects on photosynthetic capacity and carboxylation efficiency were restricted to trees exposed to near zero levels of UV‐B radiation, and twice‐ambient O3. The data indicate that UV‐B radiation, applied together with O3, ameliorates the detrimental effects of O3. The data also demonstrate that foliar symptoms develop more rapidly in Scots pine than in Norway spruce at higher accumulated ozone concentrations.

Symbols and abbreviations: LSD, least significant difference; PAS300, UV‐B irradiance weighted according to the plant action spectrum of
Green et al. (1974)
normalized at 300 (nm); AOT40, (AOT = accumulated over threshold) reflects the sum of hourly ozone concentrations above 40 nL L–1 during daylight hours (> 50 Wm–2) (
Kärenlampi & Skärby 1996); A350, net photosynthesis at ambient CO2; G350, stomatal conductance for water vapour at ambient CO2; A2500, net photosynthesis at saturating CO2 (maximal potential photosynthetic activity); CE, carboxylation efficiency; ROS, reactive oxygen species; RuBP, ribulose 1,5‐bisphosphate; Rubisco, ribulose 1,5‐bisphosphate carboxylase/oxygenase; GLM, general linear model.
Soil carbon dynamics in regrowing forest of eastern Amazonia
Authors: De Camargo Plínio B. , Trumbore Susan E. , Martinelli LuiZ. A. , Davidson EriC. A. , Nepstad Daniel C. , Victoria Reynaldo L.
Published: March 2003

The future flora of Amazonia will include significant areas of secondary forest as degraded pastures are abandoned and secondary succession proceeds. The rate at which secondary forests regain carbon (C) stocks and re‐establish biogeochemical cycles that resemble those of primary forests will influence the biogeochemistry of the region. Most studies have focused on the effects of deforestation on biogeochemical cycles. In this study, we present data on the recuperation of carbon stocks and carbon fluxes within a secondary forest of the eastern Amazon, and we compare these measurements to those for primary forest, degraded pasture, and productive pasture. Along a transect from a 23‐y‐old degraded pasture, through a 7‐y‐old secondary forest, through a 16‐year‐old secondary forest, and to a primary forest, the δ13C values of soil organic matter (SOM) in the top 10 cm of soil were – 21.0, – 26.5, – 27.4, and – 27.9‰, respectively, indicating that the isotopic signature of SOM from C3 forest plants was rapidly re‐established. The degraded pasture also had significant inputs of C from C3 plants. Radiocarbon data indicated that most of the C in the top 10 cm of soil had been fixed by plants during the last 30 years. Differences in soil C inventory among land use types were small compared to uncertainties in their measurement. Root inputs were nearly identical in primary and secondary forests, and litterfall in the secondary forest was 88% of the litterfall rate of the primary forest. In contrast, the secondary forest had only 17% of the above ground biomass. Because of rapid cycling rates of soil C and rapid recovery of C fluxes to and from the soil, the below ground C cycle in this secondary forest was nearly identical with those of the unaltered primary forest.
Comparative responses of model C3 and C4 plants to drought in low and elevated CO2
Authors: Ward JoY. K. , Tissue David T. , Thomas Richard B. , And . , Strain BoyD. R.
Published: March 2003

Interactive effects of CO2 and water availability have been predicted to alter the competitive relationships between C3 and C4 species over geological and contemporary time scales. We tested the effects of drought and CO2 partial pressures (pCO2) ranging from values of the Pleistocene to those predicted for the future on the physiology and growth of model C3 and C4 species. We grew co‐occurring Abutilon theophrasti (C3) and Amaranthus retroflexus (C4) in monoculture at 18 (Pleistocene), 27 (preindustrial), 35 (current), and 70 (future) Pa CO2 under conditions of high light and nutrient availability. After 27 days of growth, water was withheld from randomly chosen plants of each species until visible wilting occurred. Under well‐watered conditions, low pCO2 that occurred during the Pleistocene was highly limiting to C3 photosynthesis and growth, and C3 plants showed increased photosynthesis and growth with increasing pCO2 between the Pleistocene and future CO2 values. Well‐watered C4 plants exhibited increased photosynthesis in response to increasing pCO2, but total mass and leaf area were unaffected by pCO2. In response to drought, C3 plants dropped a large amount of leaf area and maintained relatively high leaf water potential in remaining leaves, whereas C4 plants retained greater leaf area, but at a lower leaf water potential. Furthermore, drought‐treated C3 plants grown at 18 Pa CO2 retained relatively greater leaf area than C3 plants grown at higher pCO2 and exhibited a delay in the reduction of stomatal conductance that may have occurred in response to severe carbon limitations. The C4 plants grown at 70 Pa CO2 showed lower relative reductions in net photosynthesis by the end of the drought compared to plants at lower pCO2, indicating that CO2 enrichment may alleviate drought effects in C4 plants. At the Pleistocene pCO2, C3 and C4 plants showed similar relative recovery from drought for leaf area and biomass production, whereas C4 plants showed higher recovery than C3 plants at current and elevated pCO2. Based on these model systems, we conclude that C3 species may not have been at a disadvantage relative to C4 species in response to low CO2 and severe drought during the Pleistocene. Furthermore, C4 species may have an advantage over C3 species in response to increasing atmospheric CO2 and more frequent and severe droughts.
Current and elevated levels of UV‐B radiation have few impacts on yields of perennial forage crops
Authors: Papadopoulos Yousef A. , Gordon Robert J. , Mcrae Kenneth B. , Bush RoY. S. , Bélanger Gilles , Butler E. AnnE. , Fillmore Sherry A. E. , Morrison Malcolm
Published: March 2003

Two experiments assessed the effect of current and elevated levels of ultravioletB (UV‐B) radiation on forage crop production. The effect of current levels of UV‐B radiation was assessed by comparing the growth of eight cultivars of four legume and four grass species for three growing seasons (1994–96) under simulated sward conditions in the field. An exclusion system using cellulose diacetate or polyester covers provided comparable growing conditions for the plants, except for the presence or absence of ambient UV‐B radiation, respectively. The second experiment studied the effect of elevated levels of UV‐B on eight cultivars of two legume and two grass species in the greenhouse under simulated sward conditions. Natural lighting with sufficient supplemental light was used to provide ideal growing conditions for a 16‐h day length. Separate sets of UV lights were installed to provide UV‐B levels at approximately the same intensity as would be found in mid summer, and 33% and 66% more than this value. A fourth treatment consisted of removing UV‐B radiation by using a polyester filter. Plant production was measured in both experiments. In 1994, field herbage yields from all young grass and legume seedlings were not significantly affected by the exclusion of ambient UV‐B radiation, with the exception of alfalfa. Intra‐specific variations with alfalfa yields were found for reduced levels of UV‐B radiation. In general, these trends persisted as stands matured during two post seeding years. In the second experiment, no significant differences were observed for all tested species with increasing levels of UV‐B radiation, except with some alfalfa cultivars and one birdsfoot trefoil cultivar. Collectively, these results demonstrate that in the northern latitudes young and mature plants of the studied species are resistant to current and potentially higher levels of solar UV‐B radiation, with the exception of some alfalfa cultivars. The yield of these cultivars increased under enhanced levels of UV‐B radiation in the greenhouse and decreased when UV‐B was excluded in the field.
The influence of elevated CO2 and O3 on fine roots and mycorrhizas of naturally growing young Scots pine trees during three exposure years
Authors: Kasurinen AnnE. , Helmisaari Heljä‐Sisko , Holopainen Toini
Published: March 2003

Young Scots pine trees naturally established at a pine heath were exposed to two concentrations of CO2 (ambient and doubled ambient) and two O3 regimes (ambient and doubled ambient) and their combination in open‐top field chambers during growing seasons 1994, 1995 and 1996 (late May to 15 September). Filtered ozone treatment and chamberless control trees were also included in the treatment comparisons. Root ingrowth cores were inserted to the undisturbed soil below the branch projection of each tree at the beginning of the fumigation period in 1994 and were harvested at the end of the fumigation periods in 1995 and 1996. Root biomasses were determined from different soil layers in the ingrowth cores, and the infection levels of different mycorrhizal types were calculated. Elevated O3 and CO2 did not have significant effects on the biomass production of Scots pine coarse (Ø > 2 mm) or fine roots (Ø < 2 mm) and roots of grasses and dwarf shrubs. Elevated O3 caused a transient stimulation, observable in 1995, in the proportion of tuber‐like mycorrhizas, total mycorrhizas and total short roots but this stimulation disappeared during the last study year. Elevated CO2 did not enhance carbon allocation to root growth or mycorrhiza formation, although a diminishing trend in the mycorrhiza formation was observed. In the combination treatment increased CO2 inhibited the transient stimulating effect of ozone, and a significant increase of old mycorrhizas was observed. Our conclusion is that doubled CO2 is not able to increase carbon allocation to growth of fine roots or mycorrhizas in nutrient poor forest sites and realistically elevated ozone does not cause a measurable limitation to roots within a period of three exposure years.
Ocean annual phytoplankton carbon and new production, and annual export production estimated with empirical equations and CZCS data
Authors: Iverson Richard L. , Esaias Wayne E. , Turpie Kevin
Published: March 2003

Empirical equations are parameterized for use with chlorophyll a, derived from satellite ocean colour data, to calculate phytoplankton carbon production, phytoplankton new production, and export production. For environments in a high variance (HV) pigment statistical class, annual phytoplankton particulate organic carbon production (AIP) is linearly related to annual average in situ chlorophyll a within the near‐surface layer. Linear relations were also obtained between AIP and annual new nitrogen production, and between AIP and particulate organic carbon annually exported from the euphotic zone for environments in that class. We found no relation between AIP and CSFC, or between the annual production variables, for oceanic environments characterized by low pigment variance (LV). Ratios of export production to AIP, called e, and new production to nitrogen annually used in phytoplankton production, called f, are widely used to express marine food web processes. The trends of these ratios with AIP differ between HV and LV environments. This is a result of differences in the coupling between nitrogen and carbon transfer in pelagic food webs, which contain different organism size classes in HV compared to LV environments. We applied the empirical equations to CZCS data to estimate global new and export production. The HV environments are responsible for about 40% of global ocean annual phytoplankton carbon production and 70% of global ocean annual new and export production.