bluuebunny/crossref_metadata_2025_split huggingface dataset:
The energy and water balance of high‐latitude wetlands: controls and extrapolation
Authors: Rouse Wayne R. 
Published: March 2003

SummaryThis paper examines, with examples, controls on the energy and water balance of northern wetlands. Most wetlands have organic soils and are thus peatlands. High‐latitude wetlands are underlain by ice‐rich permafrost, which helps maintain wetland systems and also imparts special characteristics to their energy and water balances. In North America, components of the radiation balance decrease linearly poleward, whereas the poleward rate of decrease of temperature and precipitation lessens. During the four‐month summer of a high subarctic wetland, net radiation is large and the latent heat flux dominates the energy cycle. The ground heat flux is substantial, especially in early summer, when the ice‐rich ground is rapidly thawing. Winter begins in October and heat loss from the ground approximately balances negative net radiation. The summer energy and water balance differs among terrain units. Large shallow lakes exhibit larger net radiation and potential evaporation rates than surrounding wetland surfaces which, in turn, exhibit substantially larger magnitudes than dryland terrain. There is a variable withdrawal rate of soil moisture depending on soil types and plant rooting characteristics, which influences the actual evaporation from the surface. Synoptic weather systems play a major role in day‐to‐day energy and water responses to climate forcing. Long‐term modelling of the water balance of a wetland shows year‐to‐year persistence in climatic patterns. Although net radiation, temperature and precipitation all influence the magnitudes of water deficit, the precipitation inputs are of paramount importance. Our ability to fully understand, model and extrapolate, in space and time, the major controls on the surface climate of wetlands, is evaluated. Spatial extrapolation is seen to be more readily achieved than temporal extrapolation.
Integrated models of livestock systems for climate change studies. 1. Grazing systems
Authors: Parsons D. J. , Armstrong A. C. , Turnpenny J. R. , Matthews A. M. , Cooper K. , Clark J. A. 
Published: March 2003

SummaryThe potential impact of climate change by the year 2050 on British grazing livestock systems is assessed through the use of simulation models of farming systems. The submodels, consisting of grass production, livestock feeding, livestock thermal balance, the thermal balance of naturally ventilated buildings and a stochastic weather generator, are described. These are integrated to form system models for sheep, beef calves and dairy cows. They are applied to scenarios representing eastern (dry) lowlands, western (wet) lowlands and uplands. The results show that such systems should be able to adapt to the expected climatic changes. There is likely to be a small increase in grass production, possibly allowing an increase in total productivity in some cases.
Modelling respiration of vegetation: evidence for a general temperature‐dependent Q10
Authors: Tjoelker Mark G. , Oleksyn Jacek , Reich Peter B. 
Published: March 2003

SummaryTemperature responses of rates of respiratory CO2 efflux from plants, soils, and ecosystems are frequently modelled using exponential functions with a constant Q10 near 2.0 (fractional change in rate with a 10 °C increase in temperature). However, we present evidence that Q10 declines with short‐term increases in temperature in a predictable manner across diverse plant taxa. Thus, models using a constant Q10 are biased, and use of a temperature‐corrected Q10 may improve the accuracy of modelled respiratory CO2 efflux in plants and ecosystems in response to temperature and predicted global climate changes.
Integrated models of livestock systems for climate change studies. 2. Intensive systems
Authors: Turnpenny J. R. , Parsons D. J. , Armstrong A. C. , Clark J. A. , Cooper K. , Matthews A. M. 
Published: March 2003

SummaryThe potential impact of climate change by the year 2050 on intensive livestock systems in Britain is assessed through the use of simulation models of farming systems. The submodels comprise livestock feeding, livestock thermal balance and the thermal balance of controlled environment buildings and a stochastic weather generator. These are integrated to form system models for growing pigs and broiler chickens. They are applied to scenarios typical of SE England, which is the warmest region of the country and represents the worst case. For both species the frequency of severe heat stress is substantially increased, with a consequent risk of mortality. To offset this, it would be necessary to reduce stocking densities considerably, or to invest in improved ventilation or cooling equipment. Other effects on production are likely to be small.
Elevated carbon dioxide and irrigation effects on water stable aggregates in a Sorghum field: a possible role for arbuscular mycorrhizal fungi
Authors: Rillig Matthias C. , Wright Sara F. , Kimball Bruce A. , Pinter Paul J. , Wall Gary W. , Ottman Michael J. , Leavitt Steve W. 
Published: March 2003

SummaryWhile soil biota and processes are becoming increasingly appreciated as important parameters for consideration in global change studies, the fundamental characteristic of soil structure is a neglected area of research. In a sorghum [Sorghum bicolor (L.) Moench] field experiment in which CO2[supplied using free‐air CO2 enrichment (FACE) technology] was crossed factorially with an irrigation treatment, soil aggregate (1–2 mm) water stability increased in response to elevated CO2. Aggregate water stability was increased by 40% and 20% in response to CO2, at ample and limited water supply treatments, respectively. Soil hyphal lengths of arbuscular mycorrhizal fungi (AMF) increased strongly (with a threefold increase in the dry treatment) in response to CO2, and the concentrations of one fraction (easily extractable glomalin, EEG) of the AMF‐produced protein glomalin were also increased. Two fractions of glomalin, and AMF hyphal lengths were all positively correlated with soil aggregate water stability. The present results further support the hypothesis that AMF can become important in global change scenarios. Although in this field study a causal relationship between hyphal length, glomalin and aggregate stability cannot be demonstrated, the present data do suggest that AMF could mediate changes in soil structure under elevated CO2. This could be of great importance in agricultural systems threatened by erosional soil loss.
Species‐specific responses of plant communities to altered carbon and nutrient availability
Authors: Joel Geeske , Chapin F. Stuart , Chiariello Nona R. , Thayer Susan S. , Field Christopher B. 
Published: March 2003

SummaryIn a field microcosm experiment, species‐specific responses of aboveground biomass of two California annual grassland communities to elevated CO2 and nutrient availability were investigated. One community grows on shallow, nutrient‐poor serpentine‐derived soil whereas the other occurs on deeper, modestly fertile sandstone/greenstone‐derived substrate. In most species, CO2 effects did not appear until late in the growing season, probably because the elevated CO2 increased water‐use‐efficiency easing, the onset of the summer drought. Responses of aboveground biomass to elevated CO2 differed depending on nutrient availability. Similarly, biomass responses to nutrient treatments differed depending on the CO2 status. For the majority of the species, production increased most under elevated CO2 with added nutrients (N,P,K, and micro nutrients). Some species were losers under conditions that increased overall community production, including Bromus hordeaceus in the serpentine community (negative biomass response under elevated CO2) and Lotus wrangelianus in both communities (negative biomass response with added nitrogen). Treatment and competitive effects on species‐specific biomass varied in both magnitude and direction, especially in the serpentine community, significantly affecting community structure. Individual resource environments are likely to be affected by neighbouring plants, and these competitive interactions complicate predictions of species' responses to elevated CO2.
Seasonal variation in pathways of CH4 production and in CH4 oxidation in rice fields determined by stable carbon isotopes and specific inhibitors
Authors: Krüger Martin , Eller Gundula , Conrad Ralf , Frenzel Peter 
Published: March 2003

AbstractFlooded rice fields, which are an important source of the atmospheric methane, have become a model system for the study of interactions between various microbial processes. We used a combination of stable carbon isotope measurements and application of specific inhibitors in order to investigate the importance of various methanogenic pathways and of CH4 oxidation for controlling CH4 emission. The fraction of CH4 produced from acetate and H2/CO2 was calculated from the isotopic signatures of acetate, carbon dioxide (CO2) and methane (CH4) measured in porewater, gas bubbles, in the aerenchyma of the plants and/or in incubation experiments. The calculated ratio between both pathways reflected well the ratio determined by application of methyl fluoride (CH3F) as specific inhibitor of acetate‐dependent methanogenesis. Only at the end of the season, the theoretical ratio of acetate: H2 = 2 : 1 was reached, whereas at the beginning H2/CO2‐dependent methanogenesis dominated. The isotope discrimination was different between rooted surface soil and unrooted deep soil. Root‐associated CH4 production was mainly driven by H2/CO2. Porewater CH4 was found to be a poor proxy for produced CH4.The fraction of CH4 oxidised was calculated from the isotopic signature of CH4 produced in vitro compared to CH4 emitted in situ, corrected for the fractionation during the passage from the aerenchyma to the atmosphere. Isotope mass balances and in situ inhibition experiments with difluoromethane (CH2F2) as specific inhibitor of methanotrophic bacteria agreed that CH4 oxidation was quantitatively important at the beginning of the season, but decreased later. The seasonal pattern was consistent with the change of potential CH4 oxidation rates measured in vitro. At the end of the season, isotope techniques detected an increase of oxidation activity that was too small to be measured with the flux‐based inhibitor technique. If porewater CH4 was used as a proxy of produced CH4, neither magnitude nor seasonal pattern of in situ CH4 oxidation could be reproduced. An oxidation signal was also found in the isotopic signature of CH4 from gas bubbles that were released by natural ebullition. In contrast, bubbles stirred up from the bulk soil had preserved the isotopic signature of the originally produced CH4.
Interactive effects of nitrogen deposition, tropospheric ozone, elevated CO2 and land use history on the carbon dynamics of northern hardwood forests
Authors: Ollinger Scott V. , Aber John D. , Reich Peter B. , Freuder Rita J. 
Published: March 2003

AbstractTemperate forests are affected by a wide variety of environmental factors that stem from human industrial and agricultural activities. In the north‐eastern US, important change agents include tropospheric ozone, atmospheric nitrogen deposition, elevated CO2, and historical human land use. Although each of these has received attention for its effects on forest carbon dynamics, integrated analyses that examine their combined effects are rare. To examine the relative importance of all of these factors on current forest growth and carbon balances, we included them individually and in combination in a forest ecosystem model that was applied over the period of 1700–2000 under different scenarios of air pollution and land use history.Results suggest that historical increases in CO2 and N deposition have stimulated forest growth and carbon uptake, but to different degrees following agriculture and timber harvesting. These differences resulted from the effects of each land use scenario on soil C and N pools and on the resulting degree of growth limitations by carbon vs. nitrogen. Including tropospheric ozone in the simulations offset a substantial portion of the increases caused by CO2 and N deposition. This result is particularly relevant given that ozone pollution is widespread across much of the world and because broad‐scale spatial patterns of ozone are coupled with patterns of nitrogen oxide emissions. This was demonstrated across the study region by a significant correlation between ozone exposure and rates of N deposition and suggests that the reduction of N‐induced carbon sinks by ozone may be a common phenomenon in other regions.Collectively, the combined effects of all physical and chemical factors we addressed produced growth estimates that were surprisingly similar to estimates obtained in the absence of any form of disturbance. The implication of this result is that intact forests may show relatively little evidence of altered growth since preindustrial times despite substantial changes in their physical and chemical environment.
Estimating the beginning day of Japanese cedar pollen release under global climate change
Authors: INOUE SATOSHI , KAWASHIMA SHIGETO , TAKAHASHI YUICHI 
Published: March 2003

AbstractThis study examined the effects of snowfall on the beginning day of Cryptomeria japonica pollen release and predicted it under global climate change. We used a statistical method in order to investigate when the pollen release would start and how much sooner it would be, by using data on predicted meteorological conditions under global warming in Yamagata City, Japan. Estimation accuracy was improved by multiple regression by using the mean air temperature from January to February and snowfall depth in February. Adding snowfall depth yielded more accurate estimates of the beginning day of pollen release than using air temperature alone. It is possible that the effects of heat insulation and cooling by snow delay the flowering day. Under the predicted global climate change, we expect the beginning day of pollen release to become earlier in Yamagata City. The date would be 8 February in approximately 100 years, compared with 20 February at the earliest now. Eighty years from now the date could be earlier than any date recorded so far.
In deep shade, elevated CO2 increases the vigor of tropical climbing plants
Authors: GRANADOS JULIÁN , KÖRNER CHRISTIAN 
Published: March 2003

AbstractClimbing plants have profound influences on tropical forest dynamics and may take particular advantage from atmospheric CO2 enrichment, thus potentially enhancing tree turnover. Here we test the effect of a four‐step CO2‐enrichment on growth of three typical Yucatan (Mexico) climbers, across two low photon flux densities, representing typical understory situations. In pairs of two, species of Gonolobus (Asclepiadaceae), Ceratophytum (Bignoniaceae) and Thinouia (Sapindaceae) were grown on Yucatan forest soil in growth cabinets, which simulated the diurnal climate variation. Biomass increased non‐linearly in response to CO2 enrichment from 280 (preindustrial) to 420 ppm and 560 ppm, but then (700 ppm) leveled off. The relative effect of CO2‐enrichment between the two lower (280–420 ppm) CO2 concentrations was 63% at low light (LL == 42 µmol m2−2 s2−1), compared to 37% at high light (HL = 87 µmol m2−2 s2−1). This overall response of species pairs was the combined effect of linear and non‐linear responses of the individual species across CO2 treatments. Plant biomass was 61% larger in HL compared to LL. The species‐specific response depended on the neighbor, a species grew with h, irrespective of plant size. Stem length increased, but not consistently across species and light conditions. Specific stem length (SSL, length per dry mass) declined non‐linearly in all three species as CO2 concentration increased (more pronounced at LL than at HL). SLA (leaf area per unit leaf dry mass) became lower as CO2 concentration increased (more pronounced in HL). Enhanced vigor of climbers under elevated CO2 as documented here may accelerate tropical forest dynamics and lead to greater abundance of early succesional tree species. This could reduce forest carbon stocking in the long run.
Competition in perennial ryegrass–white clover mixtures under cutting. 1. Dry‐matter yield, species composition and nitrogen fixation
Authors: Elgersma  , Nassiri  , Schlepers  
Published: March 2003

Persistence of white clover (Trifolium repens) in mixtures was studied in a long‐term experiment. Mixtures of two cultivars of perennial ryegrass (Lolium perenne) with contrasting growth habits and three white clover cultivars differing in leaf size were sown in 1991 and evaluated at two cutting frequencies. During 1995 and 1996 mixtures with large‐leaved white clover cv. Alice had the highest dry‐matter (DM) content, clover and N yield, and the highest white clover content, and mixtures with medium‐leaved Retor the lowest, whereas mixtures with small‐leaved Gwenda yielded most grass DM. In 1995 averaged over cutting treatments and mixtures, the mixtures yielded 11·8 t DM ha−1 with a white clover content of 0·6; the apparent N fixation was 393 kg N ha−1. In 1996 these values declined to 8·5 t DM ha−1, 0·48 white clover and 236 kg N ha−1. There was no significant effect of cutting frequency on DM yield or white clover content, whereas the effects of grass cultivar were not consistent.In spring there was a peak in the DM production of the mixtures, coinciding with a peak in production of the grass component. However, in summer and autumn the seasonal pattern of DM production of the mixtures was similar to that of the white clover component. Both cultivars of perennial ryegrass showed the same seasonal response, but the seasonal growth pattern of white clover differed slightly between clover cultivars and cutting treatments. In later years only one cutting frequency was imposed, and no yield measurements were taken. White clover was judged to have performed well during 1997; the clover content in September was very high (0·76), whereas in October 1998 it was 0·45. Mixtures with Alice contained most white clover. Despite fluctuations in white clover content during 1991–98, all clover cultivars had persisted 7 years after sowing, irrespective of companion grass cultivar, at both cutting treatments.
Effect of annual stocking rates in grass and maize+rye system on production by dairy cows
Authors: Mosquera‐Losada R. , González‐Rodríguez A. 
Published: March 2003

AbstractThe effects on the production from dairy cows of two annual stocking rates (2.5 and 3.0 cows ha−1) and two systems (grass and maize+rye) were examined. The experiement included three treatments: Treatment A was a grass system with an annual stocking rate of 2.5 cows ha−1 and Treatments B and C were maize+rye systems with a stocking rate of 2.5 and 3.0 cows ha−1 respectively. There were twenty cows per treatment and the total area of the system was 22 ha. Treatment A had 4.05 ha of grass silage area, Treatment B had 0.8 ha of grass silage area and 3.2 ha designated to silage crops (maize+rye), whereas Treatment C had 0.4 ha of grass silage area and 2.7 ha of silage crops. Maize silage had a higher nutritive value that the rye or grass silage. The greter production from the maize+rye crops allowed the silage needs of the cows to be met in systems with a seasonal herbage production when stocking rates are higher than for grass‐only systems. Rye plus maize system allowed higher stocking rates (2.7 cows per ha) than grass‐only system (2.1 cows per ha) because of more efficident use of land resources. Lower stocking rates and grass‐only systems increased milk production per cow but not per hectare in comparison with rye plus maize systems.
Hay production from lowland semi‐natural grasslands: a review of implications for ruminant livestock systems
Authors: Tallowin  , Jefferson  
Published: March 2003

Data on total, seasonal and between‐year variability in the productivity and nutritional quality of cut forages obtained from a range of lowland semi‐natural grasslands are reviewed.Dry‐matter production, as hay, from unfertilized species‐rich semi‐natural grasslands ranged from less than 20% to about 80% of the production that might be expected from agriculturally improved and intensively managed grasslands. Unfertilized species‐rich grasslands had lower growth rates, reflecting low nutrient availability in spring and early summer. Low soil phosphorus availability appears to be a key factor allowing high species‐richness to be maintained.The in vitro digestibilities of herbage cut for hay from semi‐natural grasslands were 20%, or more, below values for conserved forages from intensively managed grassland. When losses incurred during the hay‐making process were taken into account, then the nitrogen content of hays from many semi‐natural grasslands appear to be sub‐optimal for productive livestock. Metabolizable energy values of herbage cut for hay were 10–40% below values for intensively managed conserved grass. Phosphorus content of forages from most species‐rich grasslands was either below the metabolic requirement of livestock or inadequate to sustain high individual animal performance. Potential problems associated with supplementation of the diet with phosphorus, and with high calcium‐to‐phosphorus ratios, are discussed. Although potassium content of most of the herbage cut for hay was adequate for productive ruminant livestock, exceptions arise with hay cut after July. The magnesium content of cut herbage from some semi‐natural grasslands was below an adequate level for productive livestock. Most cut herbage appeared to contain adequate amounts of sodium. Inadequacy of the mineral content of hays from semi‐natural grasslands for ruminant livestock will be exacerbated by nutrient losses incurred during the hay‐making process and particularly so when hay‐ making is prolonged by wet weather.Few feeding studies using hays from semi‐natural grasslands of high nature conservation interest have been conducted. Lack of such data makes it difficult to plan any integrated use of these hays in ruminant feed budgets for livestock systems.
Control of Molinia caerulea on moorland
Authors: Todd  , Phillips  , Putwain  , Marrs  
Published: March 2003

Burning, grazing and herbicide (glyphosate) treatments were applied in factorial combination to Molinia‐dominated moorland in three regions of England: Exmoor, North Peak and Yorkshire Dales. In each region, agri‐environment schemes are in place in an attempt to reduce Molinia and encourage the development of dwarf shrub vegetation. Within each region, the same experiment was carried out on two types of vegetation (Molinia‐dominated ‘white’ moorland and a mixture of Molinia and Calluna‘grey’ moorland).Of the treatments applied, glyphosate had the most significant effect on Molinia at all study sites. There was little difference between the use of low and high application rates, 0·27 and 0·54 kg ai ha–1 respectively. The cover of dwarf shrubs, including Calluna in the ‘grey’ sites, was affected by the herbicide treatment in two regions, but there was no significant reduction in the North Peak. Some Calluna plants were killed or damaged by glyphosate.Two techniques for the re‐establishment of Calluna were also investigated in the Molinia‐dominated ‘white’ moorland: the two treatments applied in factorial combination were (1) removal of Molinia leaf litter by raking; and (2) application of Calluna seed. Greater Calluna seedling densities were found in the plots in which herbicide was applied, the Molinia litter was removed and seed added.