bluuebunny/crossref_metadata_2025 huggingface dataset:
Net soil carbon input under ambient and elevated CO2 concentrations: isotopic evidence after 4 years
Authors: Van Kessel Chris , Horwath William R. , Hartwig Ueli , Harris David , LÜscher Andreas
Published: March 2003

Elevation of atmospheric CO2 concentration is predicted to increase net primary production, which could lead to additional C sequestration in terrestrial ecosystems. Soil C input was determined under ambient and Free Atmospheric Carbon dioxide Enrichment (FACE) conditions for Lolium perenne L. and Trifolium repens L. grown for four years in a sandy‐loam soil. The 13C content of the soil organic matter C had been increased by 5‰ compared to the native soil by prior cropping to corn (Zea mays) for > 20 years. Both species received low or high amounts of N fertilizer in separate plots. The total accumulated above‐ground biomass produced by L. perenne during the 4‐year period was strongly dependent on the amount of N fertilizer applied but did not respond to increased CO2. In contrast, the total accumulated above‐ground biomass of T. repens doubled under elevated CO2 but remained independent of N fertilizer rate. The C:N ratio of above‐ground biomass for both species increased under elevated CO2 whereas only the C:N ratio of L. perenne roots increased under elevated CO2. Root biomass of L. perenne doubled under elevated CO2 and again under high N fertilization. Total soil C was unaffected by CO2 treatment but dependent on species. After 4 years and for both crops, the fraction of new C (F‐value) under ambient conditions was higher (P= 0.076) than under FACE conditions: 0.43 vs. 0.38. Soil under L. perenne showed an increase in total soil organic matter whereas N fertilization or elevated CO2 had no effect on total soil organic matter content for both systems. The net amount of C sequestered in 4 years was unaffected by the CO2 concentration (overall average of 8.5 g C kg−1 soil). There was a significant species effect and more new C was sequestered under highly fertilized L. perenne. The amount of new C sequestered in the soil was primarily dependent on plant species and the response of root biomass to CO2 and N fertilization. Therefore, in this FACE study net soil C sequestration was largely depended on how the species responded to N rather than to elevated CO2.
Elevated atmospheric CO2 alters microbial population structure in a pasture ecosystem
Authors: Montealegre Constanza M. , Van Kessel Chris , Blumenthal Jürg M. , Hur Hor‐Gil , Hartwig Ueli A. , Sadowsky Michael J.
Published: March 2003

An increase in concentration of atmospheric CO2 is one major factor influencing global climate change. Among the consequences of such an increase is the stimulation of plant growth and productivity. Below‐ground microbial processes are also likely to be affected indirectly by rising atmospheric CO2 levels, through increased root growth and rhizodeposition rates. Because changes in microbial community composition might have an impact on symbiotic interactions with plants, the response of root nodule symbionts to elevated atmospheric CO2 was investigated. In this study we determined the genetic structure of 120 Rhizobium leguminosarum bv. trifolii isolates from white clover plants exposed to ambient (350 μmol mol−1) or elevated (600 μmol mol−1) atmospheric CO2 concentrations in the Swiss FACE (Free‐Air‐Carbon‐Dioxide‐Enrichment) facility. Polymerase Chain Reaction (PCR) fingerprinting of genomic DNA showed that the isolates from plants grown under elevated CO2 were genetically different from those isolates obtained from plants grown under ambient conditions. Moreover, there was a 17% increase in nodule occupancy under conditions of elevated atmospheric CO2 when strains of R. leguminosarum bv. trifolii isolated from plots exposed to CO2 enrichment were evaluated for their ability to compete for nodulation with those strains isolated from ambient conditions. These results indicate that a shift in the community composition of R. leguminosarum bv. trifolii occurred as a result of an increased atmospheric CO2 concentration, and that elevated atmospheric CO2 affects the competitive ability of root nodule symbionts, most likely leading to a selection of these particular strains to nodulate white clover.
Response of subarctic vegetation to transient climatic change on the Seward Peninsula in north‐west Alaska
Authors: Rupp T. Scott , Chapin F. Stuart , Starfield Anthony M.
Published: March 2003

Understanding the response of terrestrial ecosystems to climatic warming is a challenge because of the complex interactions of climate, disturbance, and recruitment across the landscape. We use a spatially explicit model (ALFRESCO) to simulate the transient response of subarctic vegetation to climatic warming on the Seward Peninsula (80 000 km2) in north‐west Alaska. Model calibration efforts showed that fire ignition was less sensitive than fire spread to regional climate (temperature and precipitation). In the model simulations a warming climate led to slightly more fires and much larger fires and expansion of forest into previously treeless tundra. Vegetation and fire regime continued to change for centuries after cessation of the simulated climate warming. Flammability increased rapidly in direct response to climate warming and more gradually in response to climate‐induced vegetation change. In the simulations warming caused as much as a 228% increase in the total area burned per decade, leading to an increasingly early successional and more homogenous deciduous forest‐dominated landscape. A single transient 40‐y drought led to the development of a novel grassland–steppe ecosystem that persisted indefinitely and caused permanent increases in fires in both the grassland and adjacent vegetation. These simulated changes in vegetation and disturbance dynamics under a warming climate have important implications for regional carbon budgets and biotic feedbacks to regional climate.
Growth and reproductive responses to elevated CO2 in wild cereals of the northern Negev of Israel
Authors: Grünzweig J. M. , Körner CH.
Published: March 2003

How might wild relatives of modern cereals have responded to past, and how might they respond to future, atmospheric CO2 enrichment under competitive situations in a dry, low‐nutrient environment? In order to test this, Aegilops and Hordeum species, common in semiarid annual grasslands of the Middle East, were grown in nine model ecosystems (400 kg each) with a natural matrix of highly diverse Negev vegetation established on native soil shipped to Basel, Switzerland. In a simulated, seasonally variable climate of the northern Negev, communities experienced a full life‐cycle in 280 (preindustrial), 440 (immediate future) and 600 ppm of CO2 (end of the next century). Neither Aegilops (A. kotschyi and A. peregrina), nor Hordeum spontaneum showed a significant biomass response to CO2 concentrations exceeding 280 ppm The reproductive output remained unaffected or even declined (A. peregrina) under elevated CO2. Non‐structural carbohydrates in leaf tissues increased and N concentration decreased with increasing CO2 concentration. N concentration, germination success and seedling development of newly formed grains were either unchanged or reduced in response to high CO2 treatment of parent plants. In a separate fertilizer × CO2 trial with A. kotschyi nested in smaller model communities, we found no effect of P addition, but a 2–3‐fold biomass increase by NPK addition compared to the unfertilized control. A significant stimulation of biomass by CO2 enrichment (+ 44% between 280 and 600 ppm) was obtained only in the NPK treatment. These data suggest that increased CO2 concentration had little direct effect on growth and reproduction in these ‘wild cereals’ in the recent past, and the same seems to hold for their future, except if N‐rich fertilizer is added.
Modelling carbon responses of tundra ecosystems to historical and projected climate: a comparison of a plot‐ and a global‐scale ecosystem model to identify process‐based uncertainties
Authors: Clein J. S. , Kwiatkowski B. L. , McGuire A. D. , Hobbie J. E. , Rastetter E. B. , Melillo J. M. , Kicklighter D. W.
Published: March 2003

We are developing a process‐based modelling approach to investigate how carbon (C) storage of tundra across the entire Arctic will respond to projected climate change. To implement the approach, the processes that are least understood, and thus have the most uncertainty, need to be identified and studied. In this paper, we identified a key uncertainty by comparing the responses of C storage in tussock tundra at one site between the simulations of two models – one a global‐scale ecosystem model (Terrestrial Ecosystem Model, TEM) and one a plot‐scale ecosystem model (General Ecosystem Model, GEM). The simulations spanned the historical period (1921–94) and the projected period (1995–2100). In the historical period, the model simulations of net primary production (NPP) differed in their sensitivity to variability in climate. However, the long‐term changes in C storage were similar in both simulations, because the dynamics of heterotrophic respiration (RH) were similar in both models. In contrast, the responses of C storage in the two model simulations diverged during the projected period. In the GEM simulation for this period, increases in RH tracked increases in NPP, whereas in the TEM simulation increases in RH lagged increases in NPP. We were able to make the long‐term C dynamics of the two simulations agree by parameterizing TEM to the fast soil C pools of GEM. We concluded that the differences between the long‐term C dynamics of the two simulations lay in modelling the role of the recalcitrant soil C. These differences, which reflect an incomplete understanding of soil processes, lead to quite different projections of the response of pan‐Arctic C storage to global change. For example, the reference parameterization of TEM resulted in an estimate of cumulative C storage of 2032 g C m−2 for moist tundra north of 50°N, which was substantially higher than the 463 g C m−2 estimated for a parameterization of fast soil C dynamics. This uncertainty in the depiction of the role of recalcitrant soil C in long‐term ecosystem C dynamics resulted from our incomplete understanding of controls over C and N transformations in Arctic soils. Mechanistic studies of these issues are needed to improve our ability to model the response of Arctic ecosystems to global change.
Land–atmosphere energy exchange in Arctic tundra and boreal forest: available data and feedbacks to climate
Authors: Eugster Werner , Rouse Wayne R , Pielke Sr Roger A. , Mcfadden Joseph P. , Baldocchi Dennis D , Kittel Timothy G. F , Chapin F. Stuart , Liston Glen E. , Vidale Pier Luigi , Vaganov Eugene , Chambers Scott
Published: March 2003

This paper summarizes and analyses available data on the surface energy balance of Arctic tundra and boreal forest. The complex interactions between ecosystems and their surface energy balance are also examined, including climatically induced shifts in ecosystem type that might amplify or reduce the effects of potential climatic change.

High latitudes are characterized by large annual changes in solar input. Albedo decreases strongly from winter, when the surface is snow‐covered, to summer, especially in nonforested regions such as Arctic tundra and boreal wetlands. Evapotranspiration (QE) of high‐latitude ecosystems is less than from a freely evaporating surface and decreases late in the season, when soil moisture declines, indicating stomatal control over QE, particularly in evergreen forests. Evergreen conifer forests have a canopy conductance half that of deciduous forests and consequently lower QE and higher sensible heat flux (QH). There is a broad overlap in energy partitioning between Arctic and boreal ecosystems, although Arctic ecosystems and light taiga generally have higher ground heat flux because there is less leaf and stem area to shade the ground surface, and the thermal gradient from the surface to permafrost is steeper.

Permafrost creates a strong heat sink in summer that reduces surface temperature and therefore heat flux to the atmosphere. Loss of permafrost would therefore amplify climatic warming. If warming caused an increase in productivity and leaf area, or fire caused a shift from evergreen to deciduous forest, this would increase QE and reduce QH. Potential future shifts in vegetation would have varying climate feedbacks, with largest effects caused by shifts from boreal conifer to shrubland or deciduous forest (or vice versa) and from Arctic coastal to wet tundra. An increase of logging activity in the boreal forests appears to reduce QE by roughly 50% with little change in QH, while the ground heat flux is strongly enhanced.
Isopod effects on decomposition of litter produced under elevated CO2, N deposition and different soil types
Authors: HÄttenschwiler Stephan , Bretscher Daniel
Published: March 2003

The performance of Oniscus asellus (Isopoda) and its influence on litter mass loss and mineralization was assessed in a microcosm experiment, using beech (Fagus sylvatica) leaf litter that was produced on different soil types, contrasting atmospheric CO2 concentrations, and different nitrogen deposition rates. Litter quality was significantly altered by these treatments, and many of the CO2 and N effects differed between soil types. Litter quality affected subsequent litter mass loss rates, microbial respiration, and leaching of dissolved organic carbon (DOC) and nitrate. These effects were largely independent of the presence of isopods, even though isopods highly accelerated litter mass loss, stimulated microbial respiration by 37%, and increased nitrate leaching by 50%. Isopods did not change their relative rates of litter consumption and growth in response to litter quality. Isopod mortality, however, increased with increasing litter lignin/N ratios, and was significantly different between soil types, which may indicate long‐term effects on litter decomposition through altered isopod densities. Having the choice among the litter of three different species [maple (Acer pseudoplatanus), beech (Fagus sylvatica) and oak (Quercus robur)] grown at either ambient or elevated CO2, isopods preferred maple to beech when all the litter was produced under elevated CO2. This suggests that beyond changes in consumption, an altered food selection by isopods in a CO2‐enriched atmosphere may affect the temporal and spatial composition of the litter layer in temperate forests. In contrast to previous findings, we conclude that isopods do not always increase their consumption rates, and hence do not differentially affect microbial decomposition in litter of poorer quality. Nevertheless changes in animal densities and/or shifts in their food preferences, could result in altered decomposition and carbon and nutrient turnover rates.
Year‐round observations of the net ecosystem exchange of carbon dioxide in a native tallgrass prairie
Authors: Suyker Andrew E. , Verma Shashi B.
Published: March 2003

An Ameriflux site was established in mid 1996 to study the exchange of CO2 in a native tallgrass prairie of north‐central Oklahoma, USA. Approximately the first 20 months of measurements (using eddy covariance) are described here. This prairie, dominated by warm season C4 grasses, is typical of the central Kansas/northern Oklahoma region. During the first three weeks of the measurement period (mid‐July–early August 1996), moisture‐stress conditions prevailed. For the remainder of the period (until March 1998), however, soil moisture was nonlimiting. Mid‐day net ecosystem CO2 exchange (NEE), under well‐watered conditions, reached a maximum magnitude of 1.4 mg CO2 m−2 s−1 (flux toward the surface is positive) during peak growth (mid‐July 1997), with green leaf area index of 2.8. In contrast, under moisture‐stress conditions in the same growth stage in 1996, mid‐day NEE was reduced to near‐zero. Average night NEE ranged from near‐zero, during winter dormancy, to − 0.50 mg CO2 m−2 s−1, during peak growth. Most of the variance in average night NEE was explained by changes in soil temperature (0.1 m depth) and green leaf area. The daytime NEE measurements were examined in terms of a rectangular hyperbolic relationship with incident photosynthetically active radiation. The analysis showed that the quantum yield during peak growth was similar to those measured in other prairies and the y‐intercept, so obtained, can be potentially used as an estimate of night‐time CO2 emissions when eddy covariance data are unavailable. Daily integrated NEE reached its peak magnitude of 30.8 g CO2 m−2 d−1 (8.4 g C m−2 d−1) in mid‐July when the green LAI was the largest (about 2.8). In general, the seasonal trend of daily NEE (on relatively clear days) followed that of green LAI. Annually integrated carbon exchange, between prescribed burns in 1997 and 1998, was 268 g C m−2 y−1. After incorporating carbon loss during the prescribed burn , the net annual carbon exchange in this prairie was near‐zero in 1998.
Seasonal respiration of foliage, fine roots, and woody tissues in relation to growth, tissue N, and photosynthesis
Authors: Vose James M. , Ryan Michael G.
Published: March 2003

Autotrophic respiration may regulate how ecosystem productivity responds to changes in temperature, atmospheric [CO2] and N deposition. Estimates of autotrophic respiration are difficult for forest ecosystems, because of the large amount of biomass, different metabolic rates among tissues, and seasonal variation in respiration rates. We examined spatial and seasonal patterns in autotrophic respiration in a Pinus strobus ecosystem, and hypothesized that seasonal patterns in respiration rates at a common temperature would vary with [N] for fully expanded foliage and fine roots, with photosynthesis for foliage, and with growth for woody tissues (stems, branches, and coarse roots). We also hypothesized that differences in [N] would largely explain differences in maintenance or dormant‐season respiration among tissues.

For April–November, mean respiration at 15 °C varied from 1.5 to 2.8 μmol kg−1 s−1 for fully expanded foliage, 1.7–3.0 for growing foliage, 0.8–1.6 for fine roots, 0.6–1.1 (sapwood) for stems, 0.5–1.8 (sapwood) for branches, and 0.2–1.5 (sapwood) for coarse roots. Growing season variation in respiration for foliage produced the prior year was strongly related to [N] (r2 = 0.94), but fine root respiration was not related to [N]. For current‐year needles, respiration did not covary with [N]. Night‐time foliar respiration did not vary in concert with previous‐day photosynthesis for either growing or fully expanded needles. Stem growth explained about one‐third of the seasonal variation in stem respiration (r2 = 0.38), and also variation among trees (r2 = 0.43). We did not determine the cause of seasonal variation in branch and coarse root respiration, but it is unlikely to be directly related to growth, as the pattern of respiration in coarse roots and branches was not synchronized with stem growth. Seasonal variations in temperature‐corrected respiration rates were not synchronized among tissues, except foliage and branches. Spatial variability in dormant‐season respiration rates was significantly related to tissue N content in foliage (r2 = 0.67), stems (r2 = 0.45), coarse roots (r2 = 0.36), and all tissues combined (r2 = 0.83), but not for fine roots and branches. Per unit N, rates for P. strobus varied from 0.22 to 3.4 μmol molN−1 s−1 at 15 °C, comparable to those found for other conifers. Accurate estimates of annual autotrophic respiration should reflect seasonal and spatial variation in respiration rates of individual tissues.
Seasonal and interannual variation in carbon dioxide exchange and carbon balance in a northern temperate grassland
Authors: Flanagan Lawrence B. , Wever Linda A. , Carlson Peter J.
Published: March 2003

Net ecosystem carbon dioxide (CO2) exchange (NEE) was measured in a northern temperate grassland near Lethbridge, Alberta, Canada for three growing seasons using the eddy covariance technique. The study objectives were to document how NEE and its major component processes—gross photosynthesis (GPP) and total ecosystem respiration (TER)—vary seasonally and interannually, and to examine how environmental and physiological factors influence the annual C budget. The greatest difference among the three study years was the amount of precipitation received. The annual precipitation for 1998 (481.7 mm) was significantly above the 1971–2000 mean (± SD, 377.9 ± 97.0 mm) for Lethbridge, whereas 1999 (341.3 mm) was close to average, and 2000 (275.5 mm) was significantly below average. The high precipitation and soil moisture in 1998 allowed a much higher GPP and an extended period of net carbon gain relative to 1999 and 2000. In 1998, the peak NEE was a gain of 5 g C m−2 d−1 (day 173). Peak NEE was lower and also occurred earlier in the year on days 161 (3.2 g C m−2 d−1) and 141 (2.4 g C m−2 d−1) in 1999 and 2000, respectively. Change in soil moisture was the most important ecological factor controlling C gain in this grassland ecosystem. Soil moisture content was positively correlated with leaf area index (LAI). Gross photosynthesis was strongly correlated with changes in both LAI and canopy nitrogen (N) content. Maximum GPP (Amax: value calculated from a rectangular hyperbola fitted to the relationship between GPP and incident photosynthetic photon flux density (PPFD)) was 27.5, 12.9 and 8.6 µmol m−2 s−1 during 1998, 1999 and 2000, respectively. The apparent quantum yield also differed among years at the time of peak photosynthetic activity, with calculated values of 0.0254, 0.018 and 0.018 during 1998, 1999 and 2000, respectively. The ecosystem accumulated a total of 111.9 g C m−2 from the time the eddy covariance measurements were initiated in June 1998 until the end of December 2000, with most of that C gained during 1998. There was a net uptake of almost 21 g C m−2 in 1999, whereas a net loss of 18 g C m−2 was observed in 2000. The net uptake of C during 1999 was the combined result of slightly higher GPP (287.2 vs. 272.3 g C m−2 year−1) and lower TER (266.6 vs. 290.4 g C m−2 year−1) than occurred in 2000.
Simulating fire regimes in human‐dominated ecosystems: Iberian Peninsula case study
Authors: Venevsky Sergey , Thonicke Kirsten , Sitch Stephen , Cramer Wolfgang
Published: March 2003

A new fire model is proposed which estimates areas burnt on a macro‐scale (10–100 km). It consists of three parts: evaluation of fire danger due to climatic conditions, estimation of the number of fires and the extent of the area burnt. The model can operate on three time steps, daily, monthly and yearly, and interacts with a Dynamic Global Vegetation Model (DGVM), thereby providing an important forcing for natural competition. Fire danger is related to number of dry days and amplitude of daily temperature during these days. The number of fires during fire days varies with human population density. Areas burnt are calculated based on average wind speed, available fuel and fire duration. The model has been incorporated into the Lund‐Potsdam‐Jena Dynamic Global Vegetation Model (LPJ‐DGVM) and has been tested for peninsular Spain. LPJ‐DGVM was modified to allow bi‐directional feedback between fire disturbance and vegetation dynamics. The number of fires and areas burnt were simulated for the period 1974–94 and compared against observations. The model produced realistic results, which are well correlated, both spatially and temporally, with the fire statistics. Therefore, a relatively simple mechanistic fire model can be used to reproduce fire regime patterns in human‐ dominated ecosystems over a large region and a long time period.
Effects of elevated CO2 on development and larval food‐plant preference in the butterfly Coenonympha pamphilus (Lepidoptera, Satyridae)
Authors: Goverde Marcel , Erhardt Andreas
Published: March 2003

The objective of this study was to determine how increasing atmospheric CO2 change plant tissue quality in four native grassland grass species (Agrostis stolonifera, Anthoxanthum odoratum, Festuca rubra, Poa pratensis) which are all larval food‐plants of Coenonympha pamphilus (Lepidoptera, Satyridae). We assessed the effect of these changes on the performance and larval food‐plant preference of C. pamphilus in a greenhouse experiment. Furthermore, we tested the interactive effects of elevated CO2 and soil nutritional availability in F. rubra and its effect an larval development of C. pamphilus. In general, elevated CO2 decreased leaf water concentration, nitrogen concentration and specific leaf area (SLA), while leaf starch concentration was increased in all grass species. A species‐specific reaction to elevated CO2 was only found for foliar starch concentration. P. pratensis did not increase its starch concentration under elevated CO2 conditions, whereas the other three species did. Fertilisation, investigated only for F. rubra, increased leaf nitrogen concentration and amplified the CO2‐induced decrease in leaf nitrogen. Development time of C. pamphilus was on the average prolonged by two days under elevated CO2 and the prolongation differed from 0.7 to 5.3 days among food‐plant species. Pupal fresh weight differed marginally between CO2 treatments. Fertilisation of the larval food‐plant F. rubra shortened development time by one day and significantly increased pupal and adult fresh weights. C. pamphilus larvae showed a clear food‐plant preference among grass species at the age of 36 h or older. Additionally, a change of food‐plant preference under elevated CO2 was found. Larvae at ambient CO2 preferred Agrostis stolonifera and F. rubra, while under elevated CO2Anthoxanthum odoratum and P. pratensis were preferred. The present study demonstrates that larval development of C. pamphilus is affected by food‐plant species and CO2 induced changes in foliar chemistry. Although we found some species‐specific reactions to elevated CO2 for foliar chemistry, no such CO2 by species interaction was found for insect development. The change in food‐plant preference of larvae under elevated CO2 implies potential changes in selection pressure for grass species and might therefore affect evolutionary processes.
Soil compaction effects on utilization of nitrogen from livestock slurry applied to grassland
Authors: Douglas J. T. , Crawford C. E.
Published: March 2003

In order to determine whether wheel‐induced soil damage affected the subsequent utilization of livestock slurry by grass managed for silage production, dry‐matter yield and nitrogen offtake were compared in a replicated field experiment over three years in the presence or absence of soil compaction. Typical and zero compaction were compared in each year, and nominal controlled compaction was included in the two later years. Soil structure, as characterized by porosity and hydraulic conductivity measurements, was of poorest quality in the typical compaction treatment. Averaged over 3 years, typical compaction resulted in an annual yield reduction, relative to non‐compaction, of 2·14 t has−1 (20%) and 1·66 t ha−1 (13%) when 198 and 285 kg N ha−1 respectively were provided as ammonium nitrate fertilizer plus slurry‐derived ammonium‐N. The largest and most consistent yield reductions as a result of compaction occurred at first harvest each year following slower growth on the most compacted soil of the typical treatment. In general, compaction‐induced yield penalties increased with increased soil wetness. Offtake of nitrogen from both fertilizer alone and slurry and fertilizer combined was significantly reduced by soil compaction. First‐harvest yield response to increasing N rate was larger in the zero compaction treatment than in the typical treatment. Averaged over 3 years, the total annual apparent recovery of applied nitrogen was 55% after typical compaction and 71% after zero compaction. It was likely that the larger proportion of non‐recovered N in the former was lost as a consequence of greater surface run‐off, denitrification and ammonia volatilization. Over 2 years, the yield and nitrogen offtake trends in the controlled compaction treatment were intermediate between those of the zero and typical treatments, and in general more similar to the former than to the latter.

The results indicated that when livestock slurry is recycled as a source of nitrogen, prevention of soil compaction is an important component of efficient and environmentally protective grassland management.
Effect of time of day on grazing behaviour by lactating dairy cows
Authors: Gibb M. J. , Huckle C. A. , Nuthall R.
Published: March 2003

An experiment was conducted to examine the effect of time of day on the rate of intake of herbage by grazing dairy cows. Eight unsupplemented Holstein Friesian cows in their fourth month of lactation grazed grass swards maintained at a sward surface height of 6·5 cm. Commencing at 07.00, 11.30, 16.00 and 19.00 h, intake rates were estimated by measuring the liveweight change, corrected for insensible weight loss, over a period of 1 h while grazing. During the period of grazing, recordings of jaw movement activity were made to determine total eating time, number of grazing jaw movements (GJMs) and bites. Total eating time over 24 h was measured: once before and once after determination of intake rate.

Although time of day did not affect GJM rate, it had a quadratic effect on the proportion of GJMs represented by biting and non‐biting jaw movements, resulting in a significant effect on bite rate. Bite rate showed a quadratic effect of time, decreasing between 07.00 and 11.30 h, and then increasing by 16.00 h to reach a maximum at 19.00 h (52·6, 47·5, 51·6 and 59·4 bites min−1 respectively). Bite mass (mg fresh matter bite−1) was greatest at 07.00 h because of the lower dry‐matter (DM) content of the herbage and the presence of surface moisture at that time, but the effect of time of day was not significant. Mean bite mass measured as DM or organic matter (OM) differed significantly between the different times of day (332, 384, 481 and 402 mg DM and 302, 348, 438 and 367 mg OM bite−1 respectively). The net result of these differences in bite rate and bite mass was a linear increase in DM and OM intake rate over the day. The magnitude of such differences will have profound effects on mean daily intakes when calculated as the product of total eating time and intake rate.
Sheep grazing and defoliation of contrasting varieties of organically grown winter wheat with and without undersowing
Authors: Gooding M. J. , Cosser N. D. , Thompson A. J. , Davies W. P.
Published: March 2003

Field experiments in Gloucestershire, UK, in the 1990–91, 1991–92, 1993–94 and 1994–95 growing seasons explored the merits of grazing in spring a traditional tall wheat (Triticum aestivum) variety, Maris Widgeon, with more modern shorter varieties. In the first 2 years, defoliation was achieved by mowing at 7 cm in March and/or April. In the second 2 years, varieties sown at two sowing dates were grazed by sheep at a stocking rate of 42 × 50 kg sheep ha−1 for 3 or 4 days in March. Defoliation reduced crop height and interception of photosynthetically active radiation (PAR). In 1991–92, mowing significantly reduced grain yield of some of the shorter varieties but not of Maris Widgeon. This interaction was related to the amount of PAR intercepted. In this year, mowing improved the establishment of undersown white clover (Trifolium repens) and perennial ryegrass (Lolium perenne), but in subsequent years the conditions were much drier and undersowing failed. In the last two experiments, grazing in March did not significantly reduce grain yield of any variety. The quality of the forage eaten by the sheep had a modified acid‐detergent fibre (MADF) content of less than 300 g kg−1 dry matter (DM) and a crude protein (CP) content of more than 200 g kg−1 DM in both seasons. Yield of DM and calculated metabolizable energy (ME) of different varieties removed by the sheep interacted strongly with sowing date. September‐sown Maris Widgeon provided ≈ 0·7 and 0·3 t DM ha−1 (or 7·8 and 3·4 GJ ME ha−1) in March 1994 and March 1995 respectively. However, the shorter wheat varieties, Hereward and Genesis, only provided 0·3 and 0·1 t DM ha−1 when sown at the same time in the 2 years. At later sowing dates all of the varieties only provided about 0·1 t DM ha−1 when sown in October 1993, or 0·01 t DM ha−1 when sown in November 1994. Sheep grazing reduced total weed biomass in June, and reduced the emergence of weed seedlings from soil samples collected after the wheat harvest. Effects of defoliation on foliar infection by Septoria tritici were inconsistent.
Priority for allocation of water‐soluble carbohydrate reserves during regrowth of Lolium perenne
Authors: Donaghy  , Fulkerson
Published: March 2003

A glasshouse study was undertaken to determine the priority within the perennial ryegrass (Lolium perenne L.) plant for leaf and root growth and daughter tiller initiation after defoliation, in relation to various levels of water‐soluble carbohydrate (WSC) reserves at defoliation. Individual plants were arranged in mini‐swards, and underwent varying defoliation frequencies and ambient temperatures before defoliation, and harvest heights at defoliation, to obtain a gradient of WSC content at H1, the date when all plants were defoliated. Defoliation interval consisted of defoliating either three times at the one new leaf tiller–1 stage (1‐leaf stage) of regrowth, or once only at the 3‐leaf stage, up to H1, while night temperature in the week prior to H1 was altered from 15°C to either 8 or 20°C. At H1, plants were defoliated to a stubble height of either 20 or 50 mm. Plants were subsequently destructively harvested at days 4, 6, 8, 12, 18 and 27. Leaf and root extension and tiller dynamics were also measured.

On a regrowth timescale, tiller initiation was most sensitive, root regrowth moderately sensitive, and leaf regrowth relatively insensitive to a decrease in WSC. The time of daughter tiller initiation also coincided with replenishment of stubble WSC levels.

In contrast to this sequence of regrowth events following defoliation, the quantitative effects on growth were different, with elongation and survival of roots most affected by reduced WSC levels. A 30‐fold difference in stubble WSC at H1 between high and low WSC plants (1·52 vs. 0·05 mg tiller–1) produced only a 4‐fold increase in leaf dry matter (DM) after 27 d (2·2 vs. 0·6 g plant−1), while tiller number plant−1 increased 6‐fold (138 vs. 23% increase in tiller number from H1). Root elongation rate was 59 times higher in the high than in the low WSC plants (1·18 vs. 0·02 mm d−1).

From a pasture management perspective, the study confirms that defoliation, coinciding with the 3‐leaf stage of regrowth and around a stubble height of 50 mm, optimizes persistence and productivity of perennial ryegrass. By allowing more rapid replenishment of WSC reserves, this optimal defoliation strategy enables a greater proportion of WSC to be allocated to maintain a more active root system, and promotes tillering, compared with more frequent and close defoliation.
Annual cool‐season legumes for forage production in mild winter areas
Authors: Iglesias  , Lloveras
Published: March 2003

The forage potential of several annual winter legumes – crimson clover (Trifolium incarnatum L.), faba beans (Vicia faba L.), forage peas (Pisum sativum L.), serradella (Ornithopus sativus Brot.) and vetches (Vicia sativa L. and Vicia villosa Roth.) – was evaluated over two growing seasons in the wet and mild winter areas of Galicia (north‐west Spain) with a moderately acid soil, at the two normal harvesting dates in the region, April and May.

The results indicate that, in April, serradella and crimson clover (in the warmer location), can produce dry‐matter (DM) yields of 4–5 t ha−1, which is similar to other winter forages in the same area, with an average growing season of 212–237 d, corresponding to about 339–420 accumulated degree–days above 10°C (GDD10). In May, mainly in the warmer location, fava beans, peas and vetches yielded on average 4·7–8·5 t ha−1 DM, with an average growing season of 166–206 d but with only 233–278 GDD10 units. Faba bean, with an average of 8·5 t ha−1 DM in the May harvest, was the highest producing forage legume. The results also suggest that some cool‐season legumes could fit into double‐cropping systems based on summer crops, such as maize, because of their forage yields and nutritive value. However, in order to produce consistent DM yields, the date of sowing is crucial; they must either be sown much earlier than the dates in this study or the harvests must be delayed until the end of April.
Prediction of the clover content of red clover‐ and white clover‐grass mixtures by near‐infrared reflectance spectroscopy
Authors: Wachendorf  , Ingwersen  , Taube
Published: March 2003

This study assesses near‐infrared reflectance spectroscopy (NIRS) as a rapid and reliable method for estimating the clover content of clover/grass mixtures. NIRS calibrations were derived both for red clover (Trifolium pratense) and white clover (T. repens) mixtures. To maximize variability, the set of samples for analysis was selected from field plots receiving a wide range of nitrogen fertilizer application and harvested over 2 years at weekly intervals throughout the growing season. The samples were scanned using a NIR‐Systems model 5000 monochromator. A total of 183 white clover/grass and 282 red clover/grass samples were used to calibrate and cross‐validate the equations derived. The NIRS calibrations obtained from this study have the potential to be used in research on clover/grass mixtures as well as for advisory work.
Concentration of ergot alkaloids in Czech ecotypes of Lolium perenne and Festuca pratensis
Authors: Cagaš  , Flieger  , Olšovská
Published: March 2003

The content of ergot alkaloids (ergovaline and chanoclavine), and their production in October 1996 and during the period May–September 1997, were investigated in seventeen ecotypes of perennial ryegrass (Lolium perenne L.) and in nineteen ecotypes of meadow fescue (Festuca pratensis Huds.), naturally infected with Neotyphodium spp. The ecotypes were collected in the north‐eastern part of the Czech Republic. In 1996 the content of ergovaline in the ecotypes of perennial ryegrass ranged from 0·00 to 2·73 μg g–1 dry matter (DM) (one cut), and in 1997 from 0·00 to 4·65 μg g–1 DM (five cuts). In meadow fescue the content of ergovaline varied from 0·00 to 0·61 μg g–1 DM (one cut) in 1996, and in 1997 from 0·00 to 2·31 μg g–1 DM (five cuts). The content of chanoclavine (investigated in 1997 in four cuts only) in perennial ryegrass ranged between 0·00 and 3·39 μg g–1 DM, and in meadow fescue between 0·00 and 2·26 μg g–1 DM. Most ecotypes of L. perenne reacted to the high temperature and heavy rainfall in June and July of 1997 with an enhanced production of ergovaline, whereas the content of chanoclavine was not changed. Such reaction to stress conditions was not observed in the ecotypes of F. pratensis. Large differences in the production of both ergot alkaloids between different ecotypes of both plant species were observed.
Endophyte effects on reproduction of a root‐knot nematode (Meloidogyne marylandi) and osmotic adjustment in tall fescue
Authors: Elmi  , West  , Robbins  , Kirkpatrick
Published: March 2003

In a 2 × 2 × 2 factorial experiment, plants of one genotype of tall fescue (Festuca arundinacea) were grown in soil in pots in a glasshouse on two occasions. The treatments were either with (E+) or without (E–) infection by the fungal endophyte Neotyphodium coenophialum; with (N+) or without (N–) inoculation by the root‐knot nematode Meloidogyne marylandi; and with or without water deficit stress. In the first experiment, nematode numbers after 5 weeks had increased 10 times in the E–/N– watered pots and 22 times in the E–/N+ stressed plants. Root dry weight was decreased in all E–/N+ pots, compared with E–/N–. In contrast, nematode numbers in all E+/N+ pots decreased to nearly zero and root dry weight was unaffected. Osmotic adjustment in the growing zone of stressed plants was –0·35 MPa in E–/N– pots, but only –0·10 MPa in E–/N+ pots. Osmotic adjustment was greatest (–0·64 MPa) in E+ pots of both nematode treatments and almost no nematodes survived in the N+ pots. In the second experiment, there was complete nematode mortality in the E+ pots. Plant water relations were unaffected by treatments, however. It is concluded that endophyte‐enhanced persistence of tall fescue in M. marylandi‐infested soils that are prone to drought may be explained at least partly by endophyte protection of roots from nematode damage. Nematode inhibition by the endophyte may operate in addition to direct influences of the endophyte on enhancing drought tolerance of the host.
The influence of defoliation height on dry‐matter partitioning and CO2 exchange of perennial ryegrass miniature swards
Authors: Hernández Garay A. , Matthew C. , Hodgson J.
Published: March 2003

This study investigated the effects of defoliation intensity on the above‐ and below‐ground plant mass, rates of CO2 exchange and leaf appearance rate of ryegrass miniature swards maintained at constant cutting height ranging from 20 mm to 160 mm for 5 months. Total plant mass, above‐ground herbage mass and root mass increased as cutting height increased from 20 to 120 mm. Further increase in cutting height did not increase total plant mass or its components. Leaf appearance rate and photosynthesis per unit of leaf dry matter (DM) decreased as defoliation height increased from 20 to 160 mm. Gross and net CO2 uptake per unit soil surface area increased with cutting height to 120 mm. Further increase in cutting height to 160 mm decreased gross and net CO2 uptake and herbage harvested. A multivariate canonical discriminant analysis indicated different responses of root and shoot mass to cutting height and a reduction in CO2 uptake rate at the 160 mm cutting height. The implications of those responses to defoliation management of forage plants are discussed.
Successive annual applications of organic manures for cut grass: short‐term observations on utilization of manure nitrogen
Authors: Beckwith C. P. , Lewis P. J. , Chalmers A. G. , Froment M. A. , Smith K. A.
Published: March 2003

Abstract The recovery of nitrogen (N) from, and the fertilizer‐N value of, low dry‐matter (DM) cattle slurry and farm yard manure (FYM), applied annually to perennial ryegrass swards grown at two sites, on sandy loam and shallow calcareous silty clay loam soils, were studied over a 4‐year period. Slurry or FYM, applied at target rates of either 150 kg N ha−1 or 300 kg N ha−1 in either October, February or May/June, in combination with 150 kg N ha−1 inorganic fertilizer‐N (applied as split dressings before the first and second grass cut), were compared with a set of inorganic fertilizer‐N response treatments. DM yield, N offtake, apparent manure‐N recovery (in herbage) and manure‐N efficiency (compared with inorganic fertilizer‐N) were determined at two silage cuts each summer. Soil mineral nitrogen (SMN) measurements in autumn and spring were used to assess potential N leaching loss over winter and to quantify available N residues in the soil in spring. Apparent manure‐N recovery and manure‐N efficiency were usually greater from slurry applications in February than from those in October, but the timing of the application of FYM had a much smaller effect, compared with the timings of the application of slurry, on the utilization of N from manure by grass. Spring assessment of SMN was useful in quantifying available N residues from October slurry applications. Manure‐N recovery for all application timings was, on average, higher from the sandy loam than the shallow calcareous clay loam. The application of slurry to grass in early spring, at a rate of 150 kg total N ha−1, with the addition of a supplementary 50 kg inorganic fertilizer‐N ha−1, was the most suitable strategy for utilizing slurry‐N effectively and for supplying the N requirement for first‐cut silage.
Laparoscopic myomectomy during pregnancy
Authors: Luxman Dov , Cohen Jacob R. , David Menachem P.
Published: March 2003

Objective

To describe a unique case of laparoscopic myomectomy during pregnancy.

Setting

A university‐affiliated maternity hospital.

Subject

A 27‐year‐old primigravida presenting with acute abdominal pain at 15 weeks of gestation. A diagnosis of torsion of a subserous myoma was made following failure of conservative treatment.

Intervention

On laparoscopy, a 7‐cm subserous pedunculated myoma was demonstrated. Laparoscopic myomectomy was successfully accomplished.

Results

No intra‐ or postoperative complications were recorded. The woman delivered vaginally a healthy baby at 39 weeks' gestation.

Conclusions

Laparoscopic myomectomy during pregnancy is feasible. This procedure cannot be generally recommended since data concerning the safety of laparoscopic operation in general and myomectomy in particular, are limited. The patients should be carefully selected, and the operation should be performed by an experienced surgeon to guarantee a favourable outcome.
Two cases of Fitz‐Hugh–Curtis syndrome
Authors: Servaes Sophie , Lewis B. Victor
Published: March 2003

We present two cases of young patients with vague abdominal pain. During laparoscopy, multiple violin string‐like adhesions in the upper abdomen were seen. This appearance is thought to be caused by Chlamydia infection and this perihepatitis is called the Fitz‐Hugh–Curtis syndrome. Laparoscopic intervention using endoscissors to cut the adhesions was performed. Both patients made an uneventful recovery. A 14‐day course of doxycycline for the patients and their partner is the optimal medical treatment.
Regression of residual tissue after incomplete resection of submucous myomas
Authors: Dueholm Margit , Forman Axel , Ingerslev Jakob
Published: March 2003

Objective

Assessment of regression of residual tissue after incomplete transcervical resection of myomas (TCRM), by transvaginal ultrasound examination with the use of saline infusion into the cavity (hysterosonographic examination; HSE).

Settings

A university teaching department.

Subjects

45 patients with menometrorrhagia.

Interventions

The patients were followed up with HSE for 6 months after TCRM. The mean diameter of the myomas as assessed by preoperative HSE was 3.2 cm (range 1.5–5). According to the European Society of Gynaeological Endoscopy (ESGE) standards the myomas were classified as 11 type II, 28 type I and 6 type 0 myomas. TCRM was performed until the incision was level with the myometrium. Resection was complete in seven patients, who mainly had pedunculated tumours.

Results

At 2 weeks after the operation 33 of the 38 patients who had undergone incomplete resection still had residual tissue demonstrated at HSE, and all the patients had endometrial defects. During the following 2 months, re‐resection was performed in three patients because of persistent heavy bleeding. At 3 months after the operation, total regression of residual tissue was found in a further 16 patients. Thus, at 3 months, out of 35 of the patients with an initially incomplete resection, 21 patients showed spontaneous regression. Re‐resection was subsequently performed in four patients and hysterectomy in one patient. During observation for a further 3 months or more, total regression was seen in one patient. Accordingly spontaneous regression was observed in a total of 22 of 35 patients with an incomplete primary resection.

Conclusions

The results indicate that spontaneous regression of residual tissue left behind after incomplete resection of partially intramural submucous myomas is seen in more than half of patients with incomplete primary resection, mainly during the first 3 months.