bluuebunny/crossref_metadata_2025 huggingface dataset:
A note on the computation of the offset distance XY in the generalized reciprocal method of seismic refraction interpretation1
Authors: Wright C.
Published: April 2006

A simple numerical procedure is described for measuring the distance XY in the generalized reciprocal method when there are significant measurement errors in the refracted arrival times. It is applicable when the XY value is of similar magnitude to or less than the receiver spacing. Such conditions frequently occur in using the reciprocal or generalized reciprocal methods to estimate static corrections from first‐break times measured in multifold seismic reflection profiling. The use of the method is illustrated with data from both deep and high‐resolution seismic reflection profiles.
Rapid least‐squares inversion of apparent resistivity pseudosections by a quasi‐Newton method1
Authors: Loke M.H. , Barker R.D.
Published: April 2006

A fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer. This technique is based on the smoothness‐constrained least‐squares method and it produces a two‐dimensional subsurface model from the apparent resistivity pseudosection. In the first iteration, a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically. For subsequent iterations, a quasi‐Newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times, respectively, compared to the conventional least‐squares method. Tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly. This technique takes about one minute to invert a single data set on an 80486DX microcomputer.
Evaluation of transport and storage properties in the soil and groundwater zone from induced polarization measurements1
Authors: Börner F.D. , Schopper J.R. , Weller A.
Published: April 2006

Spectral induced polarization as well as complex electrical measurements are used to estimate, on a non‐invasive basis, hydraulic permeability in aquifers. Basic laboratory measurements on a variety of shaly sands, silts and clays showed that the main feature of their conductivity spectra in the frequency range from 10‐3 to 103 Hertz is a nearly constant phase angle. Thus, a constant‐phase‐angle model of electrical conductivity is applied to interpret quantitatively surface and borehole spectral induced polarization measurements. The model allows for the calculation of two independent electrical parameters from only one frequency scan and a simple separation of electrical volume and interface effects. The proposed interpretation algorithm yields the true formation factor, the cation exchange capacity and the surface‐area‐to‐porosity ratio, which corresponds to the inverse hydraulic radius. Using a Kozeny–Carman‐like equation, the estimation of hydraulic permeability is possible.
A physical model for shear‐wave velocity prediction1
Authors: Xu Shiyu , White Roy E.
Published: April 2006

The clay‐sand mixture model of Xu and White is shown to simulate observed relationships between S‐wave velocity (or transit time), porosity and clay content. In general, neither S‐wave velocity nor S‐wave transit time is a linear function of porosity and clay content. For practical purposes, clay content is approximated by shale volume in well‐log applications. In principle, the model can predict S‐wave velocity from lithology and any pair of P‐wave velocity, porosity and shale volume. Although the predictions should be the same if all measurements are error free, comparison of predictions with laboratory and logging measurements show that predictions using P‐wave velocity are the most reliable. The robust relationship between S‐ and P‐wave velocities is due to the fact that both are similarly affected by porosity, clay content and lithology. Moreover, errors in the measured P‐wave velocity are normally smaller than those in porosity and shale volume, both of which are subject to errors introduced by imperfect models and imperfect parameters when estimated from logs.

Because the model evaluates the bulk and shear moduli of the dry rock frame by a combination of Kuster and Toksöz’ theory and differential effective medium theory, using pore aspect ratios to characterize the compliances of the sand and clay components, the relationship between P‐ and S‐wave velocities is explicit and consistent. Consequently the model sidesteps problems and assumptions that arise from the lack of knowledge of these moduli when applying Gassmann's theory to this relationship, making it a very flexible tool for investigating how the vP‐vs relationship is affected by lithology, porosity, clay content and water saturation. Numerical results from the model are confirmed by laboratory and logging data and demonstrate, for example, how the presence of gas has a more pronounced effect on P‐wave velocity in shaly sands than in less compliant cleaner sandstones.
Variability in temperature regulation of CO2 fluxes and N mineralization from five Hawaiian soils: implications for a changing climate
Authors: HOLLAND ELISABETH A. , TOWNSEND ALAN R. , VITOUSEK PETER M.
Published: April 2006

We examined the possibility that microbial adaptation to temperature could affect rates of CO2, N2O and CH4 release from soils. Laboratory incubations were used to determine the functional relationship between temperature and CO2, N2O and CH4 fluxes for five soils collected across an elevational range in Hawaii. Initial rates of CO2 production and net N mineralization increased exponentially from 15 °C to 55 °C; initial rates of CH4 and N2O release were more complex. No optimum temperature (in which rates decline at higher and lower temperatures) was apparent for any of the gases, but respiration declined with time at higher temperatures, suggesting rapid depletion of readily available substrate. Mean Q10S for respiration varied from 1.4 to 2.0, a typical range for tropical soils. The functional relationship between CO2 production and temperature was consistent among all five soils, despite the substantial differences in mean annual temperature, soils, and land‐use among the sites. Temperature responses of N2O and CH4 fluxes did not follow simple Q10 relationships suggesting that temperature functions developed for CO2 release from heterotrophic respiration cannot be simply extrapolated. Expanding this study to tropical heterotrophic respiration, the flux is more sensitive to changes in Q10 than to changes in temperature on a per unit basis: the partial derivative with respect to temperature is 2.4 Gt C ·° C−1 with respect to Q10, it is 3.5 Gt C · Q10 unit−1. Therefore, what appears to be minor variability might still produce substantial uncertainty in regional estimates of gas exchange.
Elevated concentrations of CO2 may double methane emissions from mires
Authors: HUTCHIN PAUL R. , PRESS MALCOLM C. , LEE JOHN A. , ASHENDEN TREVOR W.
Published: April 2006

The potential impact of an increase in methane emissions from natural wetlands on climate change models could be very large. We report a profound increase in methane emissions from cores of mire peat and vegetation as a direct result of increasing the CO2 concentration from 355 to 550 μol mol−1 (a 60% increase). Increased CH4 fluxes were observed throughout the four month period of study. Seasonal variation in CH4 flux, consistent with that seen in the field, was observed under both ambient and elevated CO2. Under ambient CO2, methane fluxes rose from 0.02 μol m‐2 s−1 in May to 0.11 μol m−2 s−3 in July before declining again in August. Under elevated CO2 methane fluxes were at least 100% greater throughout the experiment, rising from 0.05 μol m‐2 s−1 in May to a peak of 0.27 μol m−2 s−1 in July. The stimulation of CO4 emissions was accompanied by a 100% increase in rates of photosynthesis from 4.6 (± 0.3) under ambient CO2 to 9.3 (± 0.7) μol m−2 s−1. Root and shoot biomass were unaffected.
Effects of elevated CO2 and/or O3 on growth, development and physiology of wheat (Triticum aestivum L.)
Authors: BARNES JEREMY D. , OLLERENSHAW JOHN H. , WHITFIELD CLARE P.
Published: April 2006

Two cultivars of spring wheat (Triticum aestivum L. cvs. Alexandria and Hanno) and three cultivars of winter wheat (cvs. Riband, Mercia and Haven) were grown at two concentrations of CO2 [ambient (355 pmol mol−1) and elevated (708 μmol mol−1)] under two O3 regimes [clean air (< 5 nmol mol−1 O3) and polluted air (15 nmol mol−1 O3 at night rising to a midday maximum of 75 nmol mol−1)] in a phytotron at the University of Newcastle‐upon‐Tyne. Between the two‐leaf stage and anthesis, measurements of leaf gas‐exchange, non‐structural carbohydrate content, visible O3 damage, growth, dry matter partitioning, yield components and root development were made in order to examine responses to elevated CO2 and/or O3.

Growth at elevated CO2 resulted in a sustained increase in the rate of CO2 assimilation, but after roughly 6 weeks' exposure there was evidence of a slight decline in the photosynthetic rate (c.‐15%) measured under growth conditions which was most pronounced in the winter cultivars. Enhanced rates of CO2 assimilation were accompanied by a decrease in stomatal conductance which improved the instantaneous water use efficiency of individual leaves. CO2 enrichment stimulated shoot and root growth to an equivalent extent, and increased tillering and yield components, however, non‐structural carbohydrates still accumulated in source leaves. In contrast, long‐term exposure to O3 resulted in a decreased CO2 assimilation rate (c. ‐13%), partial stomatal closure, and the accumulation of fructan and starch in leaves in the light. These effects were manifested in decreased rates of shoot and root growth, with root growth more severely affected than shoot growth.

In the combined treatment growth of O3‐treated plants was enhanced by elevated CO2, but there was little evidence that CO2 enrichment afforded additional protection against O3 damage. The reduction in growth induced by O3 at elevated CO2 was similar to that induced by O3 at ambient CO2 despite additive effects of the individual gases on stomatal conductance that would be expected to reduce the O3 flux by 20%, and also CO2‐induced increases in the provision of substrates for detoxification and repair processes. These observations suggest that CO2 enrichment may render plants more susceptible to O3 damage at the cellular level. Possible mechanisms are discussed.
Elevated atmospheric CO2: effects on phytochemistry, insect performance and insect‐parasitoid interactions
Authors: ROTH SHERRY K. , LINDROTH RICHARD L.
Published: April 2006

This study was conducted to examine the effects of CO2‐mediated changes in tree chemistry on the performance of the gypsy moth ((Lymantria dispar L.) and the parasitold Cotesia melanoscela (Ratz.). We used carbon‐nutrient balance theory to develop hypotheses regarding changes in tree chemistry and the performance of both insects under elevated CO2. As predicted, levels of foliar nitrogen declined and concentrations of carbon‐based compounds (e.g. starch and phenolics) increased under elevated CO2. Gypsy moth performance (e.g. growth, development) was altered by CO2‐mediated changes in foliar chemistry, but the magnitude was small and varied across tree species. Larvae feeding on high CO2 aspen exhibited the largest reduction in performance, relative to larvae feeding on birch, oak, or maple. Parasitism by C. melanoscela significantly prolonged gypsy moth development and reduced growth rates. Overall, the effect of parasitism on gypsy moth performance did not differ between CO2 treatments. Altered gypsy moth performance on high CO2 foliage in turn affected parasitoid performance, but the response was variable: parasitoid mortality increased and adult female size declined slightly under high CO2, while development time and adult male size were unaffected. Our results suggest that CO2‐induced changes in plant chemistry were buffered to the extent that effects on third trophic level interactions were weak to non‐existent for the system examined in this study.
Effect of land‐use change and methane mixing ratio on methane uptake from United Kingdom soil
Authors: WILLISON T.W. , GOULDING K.W.T. , POWLSON D.S.
Published: April 2006

Methane (CH4) is a trace gas 30 times more radiatively active than carbon dioxide and, apart from a recent decrease, its atmospheric concentration has been increasing at a rate of ∼ 1%per annum since 1945. The increase results from an imbalance between CH4 production and consumption. Here we assess the impact that changes in land use and increasing atmospheric CH4 mixing ratios have had on CH4 uptake rates by soil in the UK since before the Iron age. This has been achieved by making retrospective analyses of CH4 uptake in UK soils under four different conditions of land use and CH4 mixing ratio. The calculations indicate that 54% of the current CH4 uptake by UK soils is the result of increased CH4 mixing ratio but that land‐use change has caused a reduction of ∼ 37 kt CH4 y−1 in the potential sink strength of UK soils for CH4. The results are discussed with respect to the compilation of greenhouse gas inventories.
The effects on Arbutus unedo L. of long‐term exposure to elevated CO2
Authors: JONES M.B. , BROWN J. CLIFTON , RASCHI A. , MIGLIETTA F.
Published: April 2006

Arbutus unedo is a sclerophyllous evergreen, characteristic of Mediterranean coastal scrub vegetation. In Italy, trees of A. unedo have been found close to natural CO2 vents where the mean atmospheric carbon dioxide concentration is about 2200 μmol mol−1. Comparisons were made between trees growing in elevated and ambient CO2 concentrations to test for evidence of adaptation to long‐term exposure to elevated CO2. Leaves formed at elevated CO2 have a lower stomatal density and stomatal index and higher specific leaf area than those formed at ambient CO2, but there was no change in carbon to nitrogen ratios of the leaf tissue. Stomatal conductance was lower at elevated CO2 during rapid growth in the spring. In mid‐summer, under drought stress, stomatal closure of all leaves occurred and in the autumn, when stress was relieved, the conductance of leaves at both elevated and ambient CO2 increased. In the spring, the stomatal conductance of the new flush of leaves at ambient CO2 was higher than the leaves at elevated CO2, increasing instantaneous water use efficiency at elevated CO2. Chlorophyll fluorescence measurements suggested that elevated CO2 provided some protection against photoinhibition in mid‐summer. Analysis of A/Ci curves showed that there was no evidence of either upward or downward regulation of photosynthesis at elevated CO2. It is therefore anticipated that A. unedo will have higher growth rates as the ambient CO2 concentrations increase.
Effects of climate change on productivity of cereals and legumes; model evaluation of observed year‐to‐year variability of the CO2 response
Authors: GRASHOFF CEES , DIJKSTRA PAUL , NONHEBEL SANDERINE , SCHAPENDONK AD H.C.M. , VAN DE GEIJN SIEBE C.
Published: April 2006

The effect of elevated [CO2] on the productivity of spring wheat, winter wheat and faba bean was studied in experiments in climatized crop enclosures in the Wageningen Rhizolab in 1991–93. Simulation models for crop growth were used to explore possible causes for the observed differences in the CO2 response. Measurements of the canopy gas exchange (CO2 and water vapour) were made continuously from emergence until harvest. At an external [CO2] of 700 μmol mol−1 Maximum Canopy CO2 Exchange Rate (CCERmax) at canopy closure was stimulated by 51% for spring wheat and by 71% for faba bean. At the end of the growing season, above ground biomass increase at 700 μmol mol−1 was 58% (faba bean), 35% (spring wheat) and 19% (winter wheat) and the harvest index did not change. For model exploration, weather data sets for the period 1975‐88 and 1991–93 were used, assuming adequate water supply and [CO2] at 350 and 700 μmol mol−1. For spring wheat the simulated responses (35–50%) were at the upper end of the experimental results. In agreement with experiments, simulations showed smaller responses for winter wheat and larger responses for faba bean. Further model explorations showed that this differential effect in the CO2 response may not be primarily due to fundamental physiological differences between the crops, but may be at least partly due to differences in the daily air temperatures during comparable stages of growth of these crops. Simulations also showed that variations between years in CO2 response can be largely explained by differences in weather conditions (especially temperature) between growing seasons.
Responses of bracken to increased temperature and nitrogen availability
Authors: WERKMAN B. R. , CALLAGHAN T. V. , WELKER J. M.
Published: April 2006

In 1993 a project was set up at Upper Teesdale to investigate some of the effects of predicted increased temperatures and increased nutrient availability resulting from increased litter decomposition rates, and atmospheric deposition of nitrogen, on the interaction between bracken and heather, two species which cover large areas globally. 32 2 × 2 m plots were laid out on a hillside on, and just below, the interface between the two species. Half of the plots were placed on pure bracken, and the other half on the boundary. Within each vegetation type half of the plots were covered with open‐topped polythene tents to simulate climate warming, while the other plots remained open. The second treatment consisted of additional fertilizer at 50 kg N ha−1 y−1 simulating increased decomposition rates at higher temperatures and increased atmospheric nitrogen deposition. The two treatments and their controls were combined in a 2 × 2 factorial design, with two replicates in each of two blocks.

Results obtained in the first two summers indicated that fronds emerged earlier in spring and senesced later in autumn inside the tents, effectively lengthening the growing season. Fronds were taller when growing in warmer conditions, and carried more pinnae. In addition, the frond density was higher inside the tents, and together these effects contributed to greatly enhanced vigour of bracken in some of the conditions predicted by General Circulation Models. It seems likely that bracken will be more competitive, and have the potential to further encroach into heather dominated areas under these conditions.
Growth and photosynthesis of two eucalypt species during high temperature stress under ambient and elevated [CO2]
Authors: RODEN JOHN S. , BALL MARILYN C.
Published: April 2006

Two species of eucalypt (Eucalyptus macrorhyncha and E. rossii) were grown under conditions of high temperatures (45 °C, maximum) and high light (1500 μmol m−2 s−1, maximum) at either ambient (350 μL L−1) or elevated (700 μL L−1) CO2 concentrations for 8 weeks. The growth enhancement, in terms of total dry weight, was 41% and 103% for E. macrorhyncha and E. rossii, respectively, when grown in elevated [CO2]. A reduction in specific leaf area and increased concentrations of non‐structural carbohydrates were observed for leaves grown in elevated [CO2]. Plants grown in elevated [CO2] had an overall increase in photosynthetic CO2 assimilation rate of 27%; however, when measured at the same CO2 concentration a down‐regulation of photosynthesis was evident especially for E. macrorhyncha. During the midday period when temperatures and irradiances were maximal, photosynthetic efficiency as measured by chlorophyll fluorescence (Fv/Fm) was lower in E. macrorhyncha than in E. rossii. Furthermore, Fv/Fm was lower in leaves of E. macrorhyncha grown under elevated than under ambient [CO2]. These reductions in Fv/Fm were accompanied by increases in both photochemical (qP) and nonphotochemical quenching (qN and NPQ), and by increases in the concentrations of xanthophyll cycle pigments with an increased proportion of the total xanthophyll cycle pool comprising of antheraxanthin and zeaxanthin. Thus, increased atmospheric [CO2] may enhance photoinhibition when environmental stresses such as high temperatures limit the capacity of a plant to respond with growth to elevated [CO2].
Measurements of carbon sequestration by long‐term eddy covariance: methods and a critical evaluation of accuracy
Authors: GOULDEN MICHAEL L. , MUNGER J. WILLIAM , FAN SONG‐MIAO , DAUBE BRUCE C. , WOFSY STEVEN C.
Published: April 2006

The turbulent exchanges of CO2 and water vapour between an aggrading deciduous forest in the north‐eastern United States (Harvard Forest) and the atmosphere were measured from 1990 to 1994 using the eddy covariance technique. We present a detailed description of the methods used and a rigorous evaluation of the precision and accuracy of these measurements. We partition the sources of error into three categories: (1) uniform systematic errors are constant and independent of measurement conditions (2) selective systematic errors result when the accuracy of the exchange measurement varies as a function of the physical environment, and (3) sampling uncertainty results when summing an incomplete data set to calculate long‐term exchange.

Analysis of the surface energy budget indicates a uniform systematic error in the turbulent exchange measurements of ‐20 to 0%. A comparison of nocturnal eddy flux with chamber measurements indicates a selective systematic underestimation during calm (friction velocity < 0.17 m s−1) nocturnal periods. We describe an approach to correct for this error. The integrated carbon sequestration in 1994 was 2.1 t C ha−1 y−1 with a 90% confidence interval due to sampling uncertainty of ±0.3 t C ha−1 y−1 determined by Monte Carlo simulation. Sampling uncertainty may be reduced by estimating the flux as a function of the physical environment during periods when direct observations are unavailable, and by minimizing the length of intervals without flux data. These analyses lead us to place an overall uncertainty on the annual carbon sequestration in 1994 of ‐0.3 to +0.8 t C ha−1 y−1.
Seasonal variations of CO2 and water vapour exchange rates over a temperate deciduous forest
Authors: GRECO SUSANNA , BALDOCCHI DENNIS D.
Published: April 2006

Long‐term and direct measurements of CO2 and water vapour exchange are needed over forested ecosystems to determine their net annual fluxes of carbon dioxide and water. Such measurements are also needed to parameterize and test biogeochemical, ecological and hydrological assessment models. Responding to this need, eddy covariance measurements of CO2 and water vapour were made ever a deciduous forest growing near Oak Ridge, TN, between April 1993 and April 1994. Periodic measurements were made of leaf area index, stomatal resistance, soil moisture and pre‐dawn leaf water potential to characterize the gas exchange capacity of the canopy.

Four factors had a disproportionate influence on the seasonal variation of CO2 flux densities. These factors were photon flux densities (during the growing season), temperature (during the dormant season), leaf area index and the occurrence of drought The drought period occurred during the peak of the growing season and caused a significant decline in daily and hourly CO2 flux densities, relative to observations over the stand when soil moisture was plentiful.

The annual net uptake of carbon was calculated by integrating flux measurements and filling missing and spurious data with the relations obtained between measured CO2 fluxes and environmental forcing variables. The net flux of carbon for the period between April 1993 and April 1994 was ‐525 g C m−2 y−1. This value represents a net flux of carbon from the atmosphere and into the forest. The net annual carbon exchange of this southern temperate broadleaved forest exceeded values measured over a northern temperate forest (which experiences a shorter growing season and has less leaf area) by 200 g C m−2 y−1 (cf. Wofsy et al 1993).

The seasonal variation of canopy evaporation (latent heat flux) was controlled mostly by changes in leaf area and net radiation. A strong depression in evaporation rates was not observed during the drought Over a broadleaved forest large vapour pressure deficits promote evaporation and trees in a mixed stand are able to tap a variety of deep and shallow water sources.
The relative merits of open‐ and closed‐path analysers for measurement of eddy fluxes
Authors: LEUNING RAY , JUDD MURRAY J.
Published: April 2006

Theoretical and practical aspects of measuring eddy fluxes of trace gases using open‐and closed‐path analysers are presented. Trace gas fluxes measured with an open‐path analyser require the concurrent measurement of sensible and latent heat fluxes to correct for density fluctuations in trace gas concentration caused by these fluxes. A closed‐path analyser eliminates the corrections due to sensible heat flux, but not for water vapour, provided temperature fluctuations are completely removed without significantly reducing fluctuations in the trace gas mixing ratio. Theory for the design of heat exchangers and for the attenuation of concentration fluctuations during air flow through tubes is used to provide design criteria for closed‐path systems. Spectral transfer functions are used to estimate flux losses caused by flow through the sampling tube and gas analyser. Other factors considered include cross‐sensitivity of infrared CO2 analysers to water vapour, and deterioration of system performance caused by contaminants on the walls of sampling tubes. Of two open‐path, infrared CO2 analysers tested, one showed a strong interaction between CO2 and water vapour, while the other showed little sensitivity to the presence of water vapour, other than caused by dilution. A commercial closed‐path CO2 analyser also showed little cross‐sensitivity to water vapour. Compared to results for a clean sampling tube, the spectral bandwidth for water vapour fluctuations decreased significantly after several weeks of sampling. No such deterioration in bandwidth was observed for CO2. These findings are attributed to differential adsorption/desorption of water vapour by dust or salt on the tubing walls. Rain and dust must be removed from open‐path analysers to obtain satisfactory measurements. Careful system design and maintenance is required for both open‐ and closed‐path systems to ensure satisfactory long‐term measurement of trace gas fluxes. With these precautions, both approaches will provide satisfactory flux measurements.
Air‐surface exchange measurement in heterogeneous regions: extending tower observations with spatial structure observed from small aircraft
Authors: CRAWFORD TIMOTHY L. , DOBOSY RONALD J. , McMILLEN ROBERT T. , VOGEL CHRISTOPH A. , HICKS BRUCE B.
Published: April 2006

Strategies to assess long‐term atmosphere‐ecosystem exchange of CO2 and H2O must deal not only with time trends but also with spatial variability. Flux towers efficiently measure time trends, but only at discrete sites, always limited in number. Representativeness of these sites and the causes of spatial variation between sites are difficult to investigate from tower data alone. Such issues are better addressed with flux measurements from moving vehicles, particularly aircraft. Recent technological advancements in aircraft and instrumentation now allow mobile flux measurement with enhanced precision, greater ease, and lower cost. Results are presented which illustrate the importance of spatial variability, and some suggestions are given for assessment of flux‐tower representativeness. Unfortunately, airborne observations of the kind presented here are practical only during a part of the daylight hours in brief intensive field campaigns. Extrapolation of spatial‐structure information derived from these measurements to night‐time or to long‐term averages thus remains problematic. For the foreseeable future this extrapolation will require models that faithfully simulate both space and time characteristics of H2O and CO2 exchange. The development and validation of such models will be greatly enhanced by the increased availability of measurements from moving vehicles, which record spatial as well as temporal structure.
A model of the long‐term response of carbon allocation and productivity of forests to increased CO2concentration and nitrogen deposition
Authors: MEDLYN BELINDA E. , DEWAR RODERICK C.
Published: April 2006

We present a simple theoretical analysis of the long term response of forest growth and carbon allocation to increased atmospheric [CO2] and N deposition. Our analysis is based on a recent model which predicts that plant light‐use efficiency increases with [CO2] but is independent of plant N supply. We combine that model with simple assumptions for nitrogen fluxes in the soil. A quasi‐equilibrium analysis of the short term tree and soil pools is then used to develop a simple graphical depiction of the long term carbon and nitrogen supply constraints on total growth, stem growth and foliar allocation.

Our results suggest that long‐term growth responses to [CO2] and N deposition depend strongly on the extent to which stem allocation and foliage allocation are coupled. At one extreme (‘no coupling’), when stem allocation is fixed and independent of foliage allocation, there is no response of total growth or stem growth to increased [CO2] unless N deposition increases. At the other extreme (‘linear coupling’), when stem allocation is proportional to foliage allocation, there is a significant long‐term increase in total growth following a doubling of [CO2], even when N deposition is unchanged, but stem growth decreases because of a long‐term decrease in foliage allocation. For both types of coupling, total growth and stem growth increase with increasing N deposition. In the case of linear coupling, however, the N deposition response of stem growth is significantly larger than that of total growth, because of a long‐term increase in foliage allocation. We compare our results with those obtained previously from an alternative model of canopy light‐use efficiency involving a dependence on the foliar N:C ratio in addition to [CO2].

Our results highlight the need for more experimental information on (i) the extent to which canopy light‐use efficiency is independent of N supply, and (ii) the relationship between foliage allocation and stem allocation.
System‐level adjustments to elevated CO2 in model spruce ecosystems
Authors: HÄTTENSCHWILER STEPHAN , KÖRNER CHRISTIAN
Published: April 2006

Atmospheric carbon dioxide enrichment and increasing nitrogen deposition are often predicted to increase forest productivity based on currently available data for isolated forest tree seedlings or their leaves. However, it is highly uncertain whether such seedling responses will scale to the stand level. Therefore, we studied the effects of increasing CO2 (280, 420 and 560 μL L‐1) and increasing rates of wet N deposition (0, 30 and 90 kg ha‐1 y‐1) on whole stands of 4‐year‐old spruce trees (Picea abies). One tree from each of six clones, together with two herbaceous understory species, were established in each of nine 0.7 m2 model ecosystems in nutrient poor forest soil and grown in a simulated montane climate for two years. Shoot level light‐saturated net photosynthesis measured at growth CO2 concentrations increased with increasing CO2, as well as with increasing N deposition. However, predawn shoot respiration was unaffected by treatments. When measured at a common CO2 concentration of 420 μL L‐1 37% down‐regulation of photosynthesis was observed in plants grown at 560 μL CO2 L‐1. Length growth of shoots and stem diameter were not affected by CO2 or N deposition. Bud burst was delayed, leaf area index (LAI) was lower, needle litter fall increased and soil CO2 efflux increased with increasing CO2. N deposition had no effect on these traits. At the ecosystem level the rate of net CO2 exchange was not significantly different between CO2 and N treatments. Most of the responses to CO2 studied here were nonlinear with the most significant differences between 280 and 420 μL CO2 L‐1 and relatively small changes between 420 and 560 μL CO2 L‐1. Our results suggest that the lack of above‐ground growth responses to elevated CO2 is due to the combined effects of physiological down‐regulation of photosynthesis at the leaf level, allometric adjustment at the canopy level (reduced LAI), and increasing strength of below‐ground carbon sinks. The non‐linearity of treatment effects further suggests that major responses of coniferous forests to atmospheric CO2 enrichment might already be under way and that future responses may be comparatively smaller.
Climate‐lake interactions recorded in varved sediments from a Swedish boreal forest lake
Authors: ANDERSON* N. J. , ODGAARD B. V. , SEGERSTRÖM U. , RENBERG I.
Published: April 2006

A 1100‐year long record of lake ecosystem response to climate and catchment change with precise chronological control is reported. Diatom and pollen assemblages of an annually laminated (varved) sediment from a northern Swedish lake (Kassjön, Våsterbotten) were used as records of lake diatom communities and catchment vegetation. These data were compared with summer temperature estimates based on tree‐ring records of the same geographical area to identify the effects of climate change and catchment disturbance on diatom assemblages in the lake. In a canonical ordination, 23% of the variability in the total diatom assemblages for the period AD1040–1804 was accounted for by changes in pollen data which reflect agricultural development in the catchment. Diatom species richness, however, exhibited a stronger relationship with summer temperature and, significantly, declined with the lower temperatures associated with the Little Ice Age minimum (early 17th century). Summer temperature accounted for 23% of the variability in diatom species richness 20 years later. The mechanism behind this time‐lag is unclear, but may be related to catchment‐mediated effects, given recent evidence for lags in the response of boreal‐forest vegetation regeneration cycles to climatic variability. These results suggest that climate‐related effects on lakes occurring over medium timescales can be resolved in lake sediments. Moreover, it is possible to identify these effects despite cultural‐related signals, but as the latter become more extreme in the late 20th century the climate signal is obscured.
THE ESTIMATION OF FEED INTAKE BY SHEEP ON A SILAGE DIET
Authors: McDonald P. , Purves D.
Published: April 2006

The results of nineteen digestibility trials with sheep on different silages have been reported. From these data and from the results of forty trials with sheep carried out by Watson (15) it has been shown that Lancaster's method of calculating feed intake (9) can be applied to silages when the crude protein content is within the range studied (9–24% of the dry matter). For silages in this category, no advantage has been found in taking the nitrogen content of the silage dry matter into account in calculating feed intake.

The digestibility of crude protein and Lancaster's‘constant’have both been correlated with the crude protein content of the silage dry matter for the fifty‐nine trials considered (r = 0.767 and r = 0.452 respectively). Although it has been found unnecessary to take the protein content of silage into account in calculating dry matter intake when feeds containing 9.24% crude protein in the dry matter are used, evidence is presented which indicates that this factor is of considerable importance when herbage of low protein content is fed. The equation,
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which has been derived from the silage data considered, has been found to be valid when compared with the results of trials with fresh herbage and well preserved hays of low protein content.

The results of this work indicate that Lancaster's method is a suitable one for estimating the feed intake of animals engaged in self feeding of silage, provided the silage has been well preserved.
THE EFFECT OF TEMPERATURE AND PHOTOPERIOD ON INFLORESCENCE DEVELOPMENT IN STRAINS OF TIMOTHY (PHLEUM SPP.)
Authors: Cooper J. P.
Published: April 2006

A study has been made of the flowering requirements, for temperature and photoperiod, of a range of timothy strains, including American, British and Scandinavian material.

All the strains tested are long‐day in their photoperiodic responses, and there is no “winter requirement” for low temperature (0–5°C.) or short days before flowering. There is, however, an inhibitory effect of high temperature in the greenhouse on flower formation, lf the temperature is too high, no heads are produced, although photoperiod may be adequate. Instead elongated indeterminate shoots are formed which often become stoloniferous.

The effect of high temperature varies with the strain, and appears to be related to the May temperature of the region of origin. Under greenhouse temperatures of 55–65°F. American and Canadian commercial strains show little inhibition of flowering, but many plants of the Scandinavian strains fail to produce heads. The British hay strains show intermediate heading behaviour, but only an occasional plant of the diploid S.50 formed heads under these conditions.
STUDIES ON THE MAGNESIUM STATUS OF GRASSLAND HERBAGE AND ITS POSSIBLE SIGNIFICANCE IN ANIMAL HEALTH
Authors: Griffiths T. W.
Published: April 2006

Various forms of magnesium compounds were applied to grassland managed under modern intensive conditions and the effects on yield and composition of the herbage were measured. Magnesium limestone increased both yield and magnesium content. Commercial magnesite (MgO) increased the magnesium content rapidly and also gave a small increase in yield. An annual dressing of magnesium sulphate had little effect on magnesium content and tended to depress yield after two years.

A marked seasonal effect exists in pasture magnesium content. Increasing the magnesium content had little effect on its distribution within the plant, but it tended to depress calcium and potash.

The results are discussed with special reference to recent research on the magnesium metabolism in dairy cattle.
SOME ESTIMATES OF THE AREAS OF PASTURE FOULED BY THE EXCRETA OF DAIRY COWS
Authors: MacLusky D. S.
Published: April 2006

Observations were made of the areas of herbage receiving the faeces of grazing dairy cattle and of the areas and relative palatability of herbage whose growth was affected by faeces and urine. The average area covered by faeces was 7·3 sq. ft./cow/day. Faeces dropped during grazing had a negligible affect on the utilization of herbage at that grazing, but each dung‐pat probably affected the growth and palatability of an area of herbage about six times as great at the next grazing. The area of herbage whose growth was affected by urine was equal to that affected by faeces, but unlike faeces, urine improved the palatability of the herbage to dairy cows. The data were used to calculate approximate areas of herbage likely to be affected by excreta at different levels of stocking, and it appeared that excreta return plant nutrients to a given pasture acreage more quickly than some other estimates suggest.
THE PRODUCTION AND UTILIZATION OF WINTER GRASS AT VARIOUS CENTRES IN ENGLAND AND WALES, 1954–60
Authors: Baker H. K. , Chard J. R. A. , Hughes G. Pearson
Published: April 2006

The effects of management on the production of winter grass wen studied of 47 site England and Wales from 1954 to 1958.

Cocksfoot swards provided better grazing during December and January than perennial ryegrass. The best treatment for winter‐grass production from cockfoot swards was to rest from mid‐August, giving un application of 52 lb of nitrogen per acre at this time.

Perennial ryegrass produced relatively high yields if rested from early September, but the herbage should be grazed before the end of November because of the risk of it rotting.

Cocksfoot herbage in normal swards lost more weight from December to January than cocksfoot sown in wide drills.

Local Factors, such as aspect, altitude and sward vigour, were generally more important than latitude in determining level of yield in December. but there were greater lovsess of dry matter from December to January in the north than in the south.
ADVANCE NOTES ON RESEARCH
Authors: Alexander R. H. , McGowan Mary
Published: April 2006

Tilley et al. (1) have clearly demonstrated that their rumen liquor and pepsin procedure for the determination of digestibility of herbage is useful and precise. The method has, however, the disadvantage that the equipment required for the centrifugation stages is relatively expensive and, moreover, when using one centrifuge only the procedure is somewhat tedious. The method outlined below completely eliminates centrifugation; the rumen‐liquor stage is terminated by acidification and the residues from the pepsin stage is recovered by filtration, using a filter aid. Digestible dry matter or digestible organic matter may be determined; results for the former estimation on thirteen samples already examined at Hurley have given satisfactory results.
A TWO‐STAGE TECHNIQUE FOR THE IN VITRO DIGESTION OF FORAGE CROPS
Authors: Tilley J. M. A. , Terry R. A.
Published: April 2006

A simple technique for the determination in vitro of the dry‐ or organic‐matter digestibility of small (0·5 g) samples of dried forages is described. It involves incubation first with rumen liquor and then with acid pepsin. Using 146 samples of grass, clover and lucerne of known in vivo digestibility (Y), the regression equation Y= 0·99 X– 1·01 (S.E. ± 2·31) has been calculated, where X=in vitro dry‐matter digestibility. This technique has been used for the study of the digestibilities of plant breeder's material, of the leaf and stem fractions of herbage and of herbage consumed by animals.
THE INDUCTIVE REQUIREMENTS FOR FLOWERING OF SOME TEMPERATE GRASSES
Authors: Cooper J. P. , Calder D. M.
Published: April 2006

A survey was made of the flowering responses of 47 annual, biennial and perennial grasses, to measure the extent of any winter requirement for floral induction, and to see how far this could be provided by controlled cold or short‐day treatment.

The annual species showed little or no inductive requirement, nor did the perennials Arrheuatherum elatius, Ceratochloa unioloides, Phleum pratense and Poa nemoralis. Most perennials possessed a definite inductive requircinent. A few species, such as Lolium perenne, responded to both cold and short‐day given to the young seedling, while others, such as Phleum nodosum, Agrostis alba, A. canina, A. stolonifera and A. tenuis, responded to short‐day induction but not to cold.

Many temperate perennials, however, including Cynosurus cn'status, Dactylis glomerata, Festuca pratensis, F. rubra, Poa pratensis and P. trivialis did not respond to seedling induction and possibly have a juvenile stage before they are able to respond to inductive conditions.

The sequence of flowering responses in the temperate perennial grasses is evidently more complex than was previously thought, and the perennial habit can be achieved by many different developmental pathways.
A COMPARISON OF LEAF AND TILLER GROWTH IN SEVEN PERENNIAL GRASSES AS INFLUENCED BY NITROGEN AND TEMPERATURE
Authors: Ryle G. J. A.
Published: April 2006

Leaf and tiller development along the main shoot of cocksfoot, ryegrass, timothy, Hordeum bulbosum, meadow fescue, S170 tall fescue and an Algerian tall fescue are described. Comparisons between plants grown at two levels of applied nitrogen, and in a heated and an unheated glasshouse, from January to April, 1961, showed that timothy, cocksfoot and, to a lesser extent, H. bulbosum and ryegrass, generally developed leaves faster than the fescues. Numbers of live leaves per shoot, and numbers of actively‐elongating leaves per shoot declined in a similar varietal order. Despite this, the large leaves of the fescues resulted in their having a leaf area per main shoot equal to, or exceeding that of, the other grasses for most of the experiment. In general, rate of leaf appearance, number of live leaves, number of actively‐elongating leaves and leaf length were increased by a high level of N and high temperature, but high tesnperature reduced leaf width and, in some instances, tiller numbers.
PLANT JUICES IN RELATION TO SILAGE FERMENTATION III. Effect of water activity of juice
Authors: Greenhill W. L.
Published: April 2006

The water activity of juice available for fermentation, after breakdown of the cell walls during the ensiling of plant material, depends largely on the moisture content of the sample. Water activity increases with moisture content, but probably never becomes so high as seriously to limit lactic‐acid fermentation, although high moisture contents have other detrimental effects. With low moisture contents, the limited availability of the juice rather than its lowered water activity is most probably the factor primarily responsible for poor lactic‐acid production.
A MODIFIED METHOD FOR THE IN VITRO DETERMINATION OF HERBAGE DIGESTIBILITY IN PLANT‐BREEDING STUDIES
Authors: Rogers H. H. , Whitmore E. T.
Published: April 2006

In plant–breeding studies large numbers of samples, often taken from single plants, are assessed for digestibility. A modified in vitro method for such estimations, which has proved accurate and less time‐consuming than other methods, is described and results obtained for some grasses are presented.
THE FREQUENCY OF DEFOLIATION OF INDIVIDUAL TILLERS IN A SET‐STOCKED SWARD
Authors: Hodgson J.
Published: April 2006

A method designed to study the defoliation of individual tillers in a set‐stocked sward is described. This was used on S23 ryegrass swards carrying 19 (medium‐stocked) and 30 (heavily‐stocked) sheep/ac.

The tillers in the heavily‐stocked sward were defoliated, on average, every 7–8 days, and those in the medium‐stocked sward every 11–14 days. The total green leaf length (GLL) of tillers grazed by the sheep was generally greater than that of tillers not grazed. On average 27 and 40% of the GLL of tillers in the medium‐ and heavily‐stocked swards respectively was removed at each grazing. Older leaves on the grazed tillers were defoliated much less frequently than were younger leaves.

It is suggested that a rational analysis of the relationship between the grazing animal and the grazed sward cannot be made without more work of this nature.
SOME FACTORS CAUSING DIFFERENCES IN DIGESTIBILITY OF GRASSES MEASURED BY AN IN VITRO METHOD
Authors: Walters R. J. K. , ap Griffith G. , Hughes Roy , Jones D. I. H.
Published: April 2006

Stage of growth, leafiness and the accumulation of dead material were evaluated as factors causing differences in digestibility between varieties of perennial ryegrass, cocksfoot and timothy. In first growth these factors only partly accounted for the variation in digestibility between species but almost entirely accounted for the variation between varieties within each species. In the regrowths, heading behavior and leafiness were not closely associated with digestibility, which indicated that the variation between grasses following first growth may be a result of inherent differences.
SEASONAL VARIATION IN APPEARANCE AND GROWTH OF GRASS ROOTS
Authors: Garwood E. A.
Published: April 2006

Data from two field experiments, and from a root observation trench, suggest an annual cycle of root growth by grass swards. The production of adventitious roots from the tillers of four grass species, and from perennial ryegrass in a grass/clover sward varied greatly during the year. They were produced in increasing numbers through late winter to early spring; this rate fell sharply in April or May, and was low in summer. The differences in this annual cycle between grass species were small. Examination of roots of perennial ryegrass in a glass‐sided trench showed that root elongation was most rapid in summer and was largely confined to the lower soil horizons. Rather more roots were produced in early autumn than during summer, but the rate of elongation was slow from October until spring.

Individual roots of grasses appeared to survive for limited periods. Their longevity depended upon the time of year in which they were first formed; those produced in autumn or winter lived longer than those produced in spring or summer.