bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of seismic reflections from seismic attributes through fractal analysis
Authors: Nath Sankar Kumar , Dewangan Pawan
Published: March 2003

The concept of fractals is used here for the identification of seismic reflectors with special emphasis on thin‐bed delineation, which is generally overlooked during standard data processing. A new fractal analysis scheme is applied to both synthetic and real field seismic data. The fractal dimensions of the three seismic attributes – amplitude, phase, and instantaneous frequency – have been analysed and evaluated. A change in fractal dimension is found to occur whenever there is a reflection. However, the resolution in the delineation of reflectors varies, depending on the attribute under consideration and the method of fractal dimension estimation used. Fractal analysis is performed on both noise‐free and noisy synthetic data to establish the noise tolerance limit for both the ‘divider method’ and the ‘Hurst method’. It is then tested with different peak frequencies of the source wavelet to establish the criteria for using the divider method and the Hurst method. The divider method is found to be suitable for high peak frequency source wavelets (> 25 Hz), while the Hurst method is best suited for low peak frequency source wavelets (< 25 Hz). Finally, when applied to the digitally processed and migrated field seismic data, it could even delineate reflectors which otherwise went undetected on the migrated time section.
Effects of enhanced UVB on populations of the phloem feeding insectStrophingia ericae(Homoptera: Psylloidea) on heather (Calluna vulgaris)
Authors: Salt David T. , Moody Sandra A. , Whittaker JohN. B. , Paul Nigel D.
Published: March 2003

Heather plants (Calluna vulgaris(L.) Hull) were grown for two years (April 1994–October 1996) under ambient or enhanced ultraviolet‐B radiation (UVB: 280–315 nm), provided as a modulated treatment simulating a 15% ozone depletion (seasonally adjusted). Populations of the psyllid (Strophingia ericae(Curtis)) were measured before treatment and at yearly intervals thereafter. Before treatment there was no significant difference in the psyllid populations between treatments, or between the experimental and source populations. Enhanced UVB progressively produced a reduction inS. ericaepopulations compared with controls over 27 months. Analyses of C, N, total water soluble phenolics, total free amino acids and measurements of leaf angles and distances between leaflets demonstrated no effects of UVB treatment. However, concentrations of the amino acid isoleucine were lower (28%) inC. vulgarisexposed to the enhanced UVB treatment. Over the duration of the experiment the psyllid population structure at Lancaster changed from that typical of the upland site of origin (two‐year cycle with overlapping cohorts) to a one‐year life cycle typical of lowland sites, but this was independent of UVB treatments.

Reduced isoleucine might explain the negative effects of elevated UVB on psyllid population numbers, but the precise effects of UVB on host chemistry and morphology are unknown. The problem of interpreting herbivore responses to enhanced UVB treatments in the field is discussed.
Responses of multiple generations of Gastrophysa viridula, feeding on Rumex obtusifolius, to elevated CO2
Authors: Brooks G. L. , Whittaker J. B.
Published: March 2003

Rumex obtusifolius plants and three generations of the tri‐voltine leaf beetle Gastrophysa viridula were simultaneously exposed to elevated CO2 (600 ppm) to determine its effect on plant quality and insect performance. This exposure resulted in a reduction in leaf nitrogen, an increase in the C/N ratio and lower concentrations of oxalate in the leaves than in ambient air (350 ppm). Despite these changes in food quality, the effect of elevated CO2 on larvae of Gastrophysa viridula over three generations was minimal. However, the effect of CO2 did differ slightly between the generations of the insect. For the first generation, the results obtained were different from many of the published results in that elevated CO2 had no measurable effects on performance, except that third instar larvae showed compensatory feeding. Food quality, including leaf nitrogen content, declined over time in material grown in both ambient and elevated CO2. The results obtained for the second generation were similar to the first except that first instar larvae showed reduced relative growth rate in elevated CO2. Development time from hatching to pupation decreased over each generation, probably as a result of increasing temperatures. Measurements of adult performance showed that fecundity at the end of the second generation was reduced relative to the first, in line with the reduction in food quality. In addition at the end of the second generation, but not at the end of the first generation, adult females in elevated CO2 laid 30% fewer eggs per day and the eggs laid were 15% lighter than those in ambient conditions. These lighter eggs, coupled with no effect of elevated CO2 on growth during the third generation, meant that the larvae were consistently smaller in elevated CO2 during this generation. These results offer further insights into the effect that elevated CO2 will have on insect herbivores and provide a more detailed basis for population predictions.
A semi‐empirical model of methane emission from flooded rice paddy soils
Authors: Huang YaO. , Sass Ronald L. , Fisher, Jr Frank M.
Published: March 2003

Reliable regional or global estimates of methane emissions from flooded rice paddy soils depend on an examination of methodologies by which the current high variability in the estimates might be reduced. One potential way to do this is the development of predictive models. With an understanding of the processes of methane production, oxidation and emission, a semi‐empirical model, focused on the contributions of rice plants to the processes and also the influence of environmental factors, was developed to predict methane emission from flooded rice fields. A simplified version of the model was also derived to predict methane emission in a more practical manner. In this study, it was hypothesized that methanogenic substrates are primarily derived from rice plants and added organic matter. Rates of methane production in flooded rice soils are determined by the availability of methanogenic substrates and the influence of environmental factors. Rice growth and development control the fraction of methane emitted. The amount of methane transported from the soil to the atmosphere is determined by the rates of production and the emitted fraction. Model validation against observations from single rice growing seasons in Texas, USA demonstrated that the seasonal variation of methane emission is regulated by rice growth and development. A further validation of the model against measurements from irrigated rice paddy soils in various regions of the world, including Italy, China, Indonesia, Philippines and the United States, suggests that methane emission can be predicted from rice net productivity, cultivar character, soil texture and temperature, and organic matter amendments.
Effects of elevated CO2 and O3 on the rate and duration of grain growth and harvest index in spring wheat (Triticum aestivum L.)
Authors: MULHOLLAND B. J. , CRAIGON J. , BLACK C. R. , COLLS J. J. , ATHERTON J. , LANDON G.
Published: March 2003

Wheat (Triticum aestivum L.) cv. Minaret was grown in open‐top chambers (OTCs) in 1995 and 1996 under three carbon dioxide (CO2) and two ozone (O3) levels. Plants were harvested regularly between anthesis and maturity to examine the rate of grain growth (dG/dt; mg d–1) and the rate of increase in harvest index (dHI/dt;% d–1). The duration of grain filling was not affected by elevated CO2 or O3, but was 12 days shorter in 1995, when the daily mean temperature was over 3 °C higher than in 1996. Season‐long exposure to elevated CO2 (680 μmol mol–1) significantly increased the rate of grain growth in both years and mean grain weight at maturity (MGW) was up to 11% higher than in the chambered ambient air control (chAA; 383 μmol mol–1). However, the increase in final yield obtained under elevated CO2 relative to the chAA control in 1996 resulted primarily from a 27% increase in grain number per unit ground area. dG/dt was significantly reduced by elevated O3 under ambient CO2 conditions in 1995, but final grain yield was not affected because of a concurrent increase in grain number. Neither dG/dt nor dHI/dt were affected by the higher mean O3 concentrations applied in 1996 (77 vs. 66 nmol mol–1); the differing effects of O3 on grain growth in 1995 and 1996 observed in both the ambient and elevated CO2 treatments may reflect the contrasting temperature environments experienced. Grain yield was nevetheless reduced under elevated O3 in 1996, primarily because of a substantial decrease in grain number. The data obtained show that, although exposure to elevated CO2 and O3 individually or in combination may affect both dG/dt and dHI/dt, the presence of elevated CO2 does not protect against substantial O3‐induced yield losses resulting from its direct deleterious impact on reproductive processes. The implications of these results for food production under future climatic conditions are considered.
Long‐term growth at elevated carbon dioxide stimulates methane emission in tropical paddy rice
Authors: ZISKA L. H. , MOYA T. B. , WASSMANN R. , NAMUCO O. S. , LANTIN R. S. , ADUNA J. B. , ABAO E. , BRONSON K. F. , NEUE H. U. , OLSZYK D.
Published: March 2003

Recent anthropogenic emissions of key atmospheric trace gases (e.g. CO2 and CH4) which absorb infra‐red radiation may lead to an increase in mean surface temperatures and potential changes in climate. Although sources of each gas have been evaluated independently, little attention has focused on potential interactions between gases which could influence emission rates. In the current experiment, the effect of enhanced CO2 (300 μL L–1 above ambient) and/or air temperature (4 °C above ambient) on methane generation and emission were determined for the irrigated tropical paddy rice system over 3 consecutive field seasons (1995 wet and dry seasons 1996 dry season). For all three seasons, elevated CO2 concentration resulted in a significant increase in dissolved soil methane relative to the ambient control. Consistent with the observed increases in soil methane, measurements of methane flux per unit surface area during the 1995 wet and 1996 dry seasons also showed a significant increase at elevated carbon dioxide concentration relative to the ambient CO2 condition (+49 and 60% for each season, respectively). Growth of rice at both increasing CO2 concentration and air temperature did not result in additional stimulation of either dissolved or emitted methane compared to growth at elevated CO2 alone. The observed increase in methane emissions were associated with a large, consistent, CO2‐induced stimulation of root growth. Results from this experiment suggest that as atmospheric CO2 concentration increases, methane emissions from tropical paddy rice could increase above current projections.
Impacts of elevated atmospheric CO2 on litter quality, litter decomposability and nitrogen turnover rate of two oak species in a Mediterranean forest ecosystem
Authors: GAHROOEE FAYEZ RAIESI
Published: March 2003

Elevated CO2 may affect litter quality of plants, and subsequently C and N cycling in terrestrial ecosystems, but changes in litter quality associated with elevated CO2 are poorly known. Abscised leaf litter of two oak species (Quercus cerris L. and Q. pubescens Willd.) exposed to long‐term elevated CO2 around a natural CO2 spring in Tuscany (Italy) was used to study the impact of increasing concentration of atmospheric CO2 on litter quality and C and N turnover rates in a Mediterranean‐type ecosystem. Litter samples were collected in an area with elevated CO2 (>500 ppm) and in an area with ambient CO2 concentration (360 ppm). Leaf samples were analysed for concentrations of total C, N, lignin, cellulose, acid detergent residue (ADR) and polyphenol. The decomposition rate of litter was studied using a litter bag experiment (12 months) and laboratory incubations (3 months). In the laboratory incubations, N mineralization in litter samples was measured as well (125 days). Litter quality was expressed in terms of chemical composition and element ratios. None of the litter quality parameters was affected by elevated CO2 for the two Quercus species. Remaining mass in Q. cerris and Q. pubescens litter from elevated CO2 was similar to that from ambient conditions. C mineralization in Q. pubescens litter from elevated CO2 was lower than that from ambient CO2, but the difference was insignificant. This effect was not observed for Q. cerris. N mineralization was higher from litter grown at elevated CO2, but this difference disappeared at the end of the incubation. Litter of Q. pubescens had a higher quality than Q. cerris, and indeed mineralized more rapidly in the laboratory, but not under field conditions.
Diurnal and seasonal variation of carbon dioxide exchange from a former true raised bog
Authors: NIEVEEN JOOST P. , JACOBS COR. M. J. , JACOBS ADRIE F. G.
Published: March 2003

Carbon dioxide exchange was measured, using the eddy covariance technique, during a one and a half year period in 1994 and 1995. The measurements took place over a former true raised bog, characterized by a shallow peat layer and a vegetation dominated by Molinia caerulea. The growing season extended from May until late October, with a maximum LAI in August of 1.7.

The carbon balance shows a net release of 97 g C m–2 y–1 (265 kg C ha–1 y–1) from the peat bog ecosystem to the atmosphere. During June, July and August there is net consumption of CO2, while during the rest of the year there is net production of CO2. The average daytime assimilation rates ranged between – 0.2 and – 0.5 mg CO2 m–2 s–1 (– 45 and –11.3 μmol CO2 m–2 s–1), in a period where the LAI ranged between 1 and 1.7. A high vapour pressure deficit (> 15 hPa) corresponding with high temperatures was found to reduce the assimilation rate by on average 50%. Apart from these factors, LAI and the soil temperature codetermine the net exchange of CO2.

The total nocturnal respiration during the growing season lies within the same order as the average daytime net assimilation rate. Temperature was found to be the main factor controlling soil respiration, with a Q10 of 4.8.
The interaction of soil biota and soil structure under global change
Authors: YOUNG IAIN. M. , BLANCHART ERIC. , CHENU CLAIRE , DANGERFIELD MARK. , FRAGOSO CARLOS , GRIMALDI MICHEL , INGRAM JOHN. , MONROZIER LUCILE JOCTEUR
Published: March 2003

The structural framework of soil mediates all soil processes, at all relevant scales. The spatio‐temporal heterogeneity prevalent in most soils underpins the majority of biological diversity in soil, providing refuge sites for prey against predator, flow paths for biota to move, or be moved, and localized pools of substrate for biota to multiply. Just as importantly, soil biota play a crucial role in mediating soil structure: bacteria and fungi aggregate and stabilize structure at small scales (μm–cm) and earthworms and termites stabilize and create larger‐scale structures (mm–m). The stability of this two‐way interaction of structure and biota relations is crucial to the sustainability of the ecosystem.

Soil is constantly reacting to changes in microclimates, and many of the soil–plant–microbe processes rely on the functioning of subtle chemical and physical gradients. The effect of global change on soil structure–biota interactions may be significant, through alterations in precipitation, temperature events, or land‐use. Nonetheless, because of the complexity and the ubiquitous heterogeneity of these interactions, it is difficult to extrapolate from general qualitative predictions of the effects of perturbations to specific reactions. This paper reviews some of the main soil structure–biota interactions, particularly focusing on soil stability, and the role of biota mediating soil structures. The effect of alterations in climate and land‐use on these interactions is investigated. Several case studies of the effect of land‐use change are presented.
Non‐climatic variations in the oxygen isotopic compositions of plants
Authors: WANG XUE‐FENG. , YAKIR DAN. , AVISHAI MICHAEL
Published: March 2003

The 18O content of leaf water strongly influences the 18O contents of atmospheric CO2 and O2. The 18O signatures of these atmospheric gases, in turn, emerge as important indicators of large‐scale gas exchange processes. Better understanding of the factors that influence the isotopic composition of leaf water is still required, however, for the quantitative utilization of these tracers. The 18O enrichment of leaf water relative to local meteoric water, is known to reflect climatic conditions. Less is known about the extent variations in the 18O content of leaf water are influenced by nonclimatic, species‐specific characteristics. In a collection of 90 plant species from all continents grown under the same climatic conditions in the Jerusalem Botanical Garden we observed variations of about 9‰ in the δ18O values of stem water, δs, and of about 14‰ in the mid‐day δ18O enrichment of bulk leaf water, δLW–δs. Differences between δ18O values predicted by a conventional evaporation model, δM, and δLW ranged between – 3.3‰ and + 11.8‰. The δ18O values of water in the chloroplasts (δch) in leaves of 10 selected plants were estimated from on‐line CO2 discrimination measurements. Although much uncertainty is still involved in these estimates, the results indicated that δch can significantly deviate from δM in species with high leaf peclet number. The δ18O values of bulk leaf water significantly correlated with δ18O values of leaf cellulose (directly) and with instantaneous water use efficiency (A/E, inversely). Differences in isotopic characteristics among conventionally defined vegetation types were not significant, except for conifers that significantly differed from shrubs in δ18O and δ13C values of cellulose and in their peclet numbers, and from deciduous woodland species in their δ18O and δ13C values of cellulose. The results indicated that predictions of the δ18O values of leaf water (δLW, δM and δch) could be improved by considering plant species‐specific characteristics.
The δ13C of tree rings in full‐bark and strip‐bark bristlecone pine trees in the White Mountains of California
Authors: Tang Kuilian , Feng Xiahong , Funkhouser GarY.
Published: March 2003

Dendrochronological work at Sheep Mountain in the White Mountains, CA has demonstrated that bristlecone pine trees in two forms, full‐bark and strip‐bark, have experienced different cambial growth rates over the past century or longer. The strip‐bark trees showed a greater growth increase than the full‐bark ones. A calculation of the plant water‐use efficiency (W) in response to anthropogenic CO2released into the atmosphere shows that W of trees in both forms has increased for the past 200 years. However, there is no significant difference between the two tree forms in the rate of increase in W. This implies at least two possibilities with respect to the CO2fertilization effect. First, the biomass in both tree forms might have increased, but carbon distribution among different parts of a tree was different. Second, the biomass may increase without causing any corresponding change in the plant water‐use efficiency.
Trophic relationships in the soil microfood‐web: predicting the responses to a changing global environment
Authors: WARDLE DAVID A. , VERHOEF HERMAN A. , CLARHOLM MARIANNE
Published: March 2003

In this article, we evaluate how global environmental change may affect microfood‐webs and trophic interactions in the soil, and the implications of this at the ecosystem level. First we outline how bottom‐up (resource control) and top‐down (predation‐control) forces regulate food‐web components. Food‐web components can respond either positively or negatively to shifts in NPP resulting from global change, thus creating difficulties in developing general principles about the response of soil biota to global change phenomena. We also demonstrate that top‐down effects can be important in soil food‐webs, creating negative feed‐backs which may partially counter bottom‐up effects. Secondly, we determine how soil food‐webs and the processes they regulate respond to various global change phenomena. Enhanced atmospheric CO2levels can have two main effects on plants which are relevant for the soil food‐web, i.e. enhanced NPP (often positive) and diminished organic matter quality (with negative effects, at least in the short term). Climate change effects resulting from elevated CO2levels may be mainly secondary through alteration of vegetation, as shown by examples. Intensification of land management is usually associated with greater disturbance, which alters soil food‐web composition and key processes; this is particularly apparent in comparisons of conventionally tilled and nontilled agroecosystems. Global change involves shifts in plant species composition and diversity, possibly affecting soil food‐webs; we interpret this in terms of theories relating biodiversity to ecosystem function. We conclude that a more detailed understanding of interactions between NPP, soil organic matter and components of the soil food‐web, as well as their regulation of biogeochemical processes and ultimately ecosystem‐level properties, is essential in better understanding long‐term aspects of global change phenomena.
Long‐term responses of boreal vegetation to global change: an experimental and modelling investigation
Authors: Beerling D. J.
Published: March 2003

The response of boreal ecosystems to future global change is an uncertain but potentially critical component of the feedback between the terrestrial biosphere and the atmosphere. To reduce some of the uncertainties in predicting the responses of this key ecosystem, the climate change experiment (CLIMEX) exposed an entire undisturbed catchment of boreal vegetation to CO2 enrichment (560 ppmv) and climate change (+ 5 °C in winter, + 3 °C in summer) for three years (1994–96). This paper describes the leaf metabolic responses of the vegetation to the experimental treatment and model simulations of possible future changes in the hydrological and carbon balance of the site. Randomized intervention analysis of the leaf gas exchange measurements for the dominant species indicated Pinus sylvestris had significantly (P < 0.01) higher photosynthetic rates and Betula pubescens and Vaccinium myrtillus had significantly (P < 0.01) lower stomatal conductances after three years treatment compared to the controls. These responses led to sustained increases in leaf water‐use efficiency of all species of trees and ground shrubs, as determined from carbon isotope analyses. Photosynthesis (A) vs. intercellular CO2 (ci) response curves (A/ci responses), RuBisCo analysis and leaf nitrogen data together suggested none of the species investigated exhibited down‐regulation in photosynthetic capacity. At the whole ecosystem level, the improved water economy of the plants did not translate into increased catchment runoff. Modelling simulations for the site indicate this was most likely brought about by a compensatory increase in evapotranspiration. In terms of the carbon budget of the site, the ecosystem model indicates that increased CO2 and temperature would lead to boreal ecosystems of the type used in CLIMEX, and typical of much of southern Norway, acting as moderate net sinks for CO2.
Monoterpene emission from coniferous trees in response to elevated CO2 concentration and climate warming
Authors: Constable JohN. V. H. , Litvak Marcy E. , Greenberg James P. , Monson Russell K.
Published: March 2003

It was hypothesized that high CO2 availability would increase monoterpene emission to the atmosphere. This hypothesis was based on resource allocation theory which predicts increased production of plant secondary compounds when carbon is in excess of that required for growth. Monoterpene emission rates were measured from needles of (a) Ponderosa pine grown at different CO2 concentrations and soil nitrogen levels, and (b) Douglas fir grown at different CO2 concentrations. Ponderosa pine grown at 700 μmol mol–1 CO2 exhibited increased photosynthetic rates and needle starch to nitrogen (N) ratios when compared to trees grown at 350 μmol mol–1 CO2. Nitrogen availability had no consistent effect on photosynthesis. Douglas fir grown at 550 μmol mol–1 CO2 exhibited increased photosynthetic rates as compared to growth at 350 μmol mol–1 CO2 in old, but not young needles, and there was no influence on the starch/N ratio. In neither species was there a significant effect of elevated growth CO2 on needle monoterpene concentration or emission rate. The influence of climate warming and leaf area index (LAI) on monoterpene emission were also investigated. Douglas fir grown at elevated CO2 plus a 4 °C increase in growth temperature exhibited no change in needle monoterpene concentration, despite a predicted 50% increase in emission rate. At elevated CO2 concentration the LAI increased in Ponderosa pine, but not Douglas fir. The combination of increased LAI and climate warming are predicted to cause an 80% increase in monoterpene emissions from Ponderosa pine forests and a 50% increase in emissions from Douglas fir forests. This study demonstrates that although growth at elevated CO2 may not affect the rate of monoterpene emission per unit biomass, the effect of elevated CO2 on LAI, and the effect of climate warming on monoterpene biosynthesis and volatilization, could increase canopy monoterpene emission rate.
A search for predictive understanding of plant responses to elevated [CO2]
Authors: Luo YiqI. , Reynolds James , Wang Yingping , Wolfe David
Published: March 2003

This paper reviews two decades of effort by the scientific community in a search for predictive understanding of plant responses to elevated [CO2]. To evaluate the progress of research in leaf photosynthesis, plant respiration, root nutrient uptake, and carbon partitioning, we divided scientific activities into four phases: (I) initial assessments derived from our existing knowledge base to provide frameworks for experimental studies; (II) experimental tests of the initial assessments; (III) in cases where assessments were invalidated, synthesis of experimental results to stimulate alternative hypotheses and further experimentation; and (IV) formation of new knowledge. This paper suggests that photosynthetic research may have gone through all four phases, considering that (a) variable responses of photosynthesis to [CO2] are generally explainable, (b) extrapolation of leaf‐level studies to the global scale has been examined, and (c) molecular studies are under way. Investigation of plant respiratory responses to [CO2] has reached the third phase: experimental results have been accumulated, and mechanistic approaches are being developed to examine alternative hypotheses in search for new concepts and/or new quantitative frameworks to understand respiratory responses to elevated [CO2]. The study of nutrient uptake kinetics is still in the second phase: experimental evidence has contradicted some of the initial assessments, and more experimental studies need to be designed before generalizations can be made. It is quite unfortunate that we have not made much progress in understanding mechanisms of carbon partitioning during the past two decades. This is due in part to the fact that some of the holistic theories, such as functional balance and optimality, have not evolved into testable hypotheses to guide experimental studies. This paper urges modelers to play an increasing role in plant–CO2research by disassembling these existing theories into hypotheses and urges experimentalists to design experiments to examine these holistic concepts.
Solar ultraviolet‐B radiation influence on Sphagnum bog and Carex fen ecosystems: first field season findings in Tierra del Fuego, Argentina
Authors: Searles Peter S. , Flint Stephan D. , Díaz Susana B. , Rousseaux M. Cecilia , Ballaré Carlos L. , Caldwell Martyn M.
Published: March 2003

Stratospheric ozone depletion occurs over Tierra del Fuego, southern Argentina and Chile, in the austral spring and summer due to the precession of the Antarctic ‘ozone hole’ and the general erosion of the ozone layer. Plots receiving either near‐ambient or reduced UV‐B radiation were established using different louvered plastic film filters over Sphagnum bog and Carex fen ecosystems in October 1996. In the Sphagnum bog system, growth measurements during the late spring and summer showed no significant differences in the moss Sphagnum magellanicum, or the vascular plants (Empetrum rubrum, Nothofagus antarctica, and Tetroncium magellanicum) between near‐ambient and attenuated UV‐B radiation treatments. In the Carex fen system, leaf length and spike height did not differ in the two dominant species, Carex decidua and C. curta, between UV‐B radiation treatments. The length of individual spikelets of C. curta under near‐ambient UV‐B radiation was less than under the reduced UV‐B radiation treatment, but this was not evident in C. decidua. No differences in seed number, seed mass, or viability were seen in either Carex species between the UV‐B treatments. Two important constituents of the microfauna that inhabit the Sphagnum bog are testate amoebae and rotifers. These both appeared to be more numerous under near‐ambient UV‐B radiation than under reduced UV‐B radiation. The subtle responses of the Sphagnum and Carex ecosystems may become more apparent in subsequent years as the treatments are continued. Trophic‐level changes, such as the differences in number of amoebae and rotifers, may be more sensitive to solar UV‐B radiation than growth and productivity of the vegetation.
Biomass production and species composition change in a tallgrass prairie ecosystem after long‐term exposure to elevated atmospheric CO2
Authors: Owensby Clenton E. , Ham Jay. M. , Knapp Alan. K. , Auen Lisa. M.
Published: March 2003

To determine the long‐term impact of elevated CO2 on primary production of native tallgrass prairie, we compared the responses of tallgrass prairie at ambient and twice‐ambient atmospheric CO2 levels over an 8‐year period. Plots in open‐top chambers (4.5 m diameter) were exposed continuously (24 h) to ambient and elevated CO2 from early April to late October each year. Unchambered plots were monitored also. Above‐ground peak biomass was determined by clipping each year in early August, and root growth was estimated by harvesting roots from root ingrowth bags. Plant community composition was censused each year in early June. In the last 2 years of the study, subplots were clipped on 1 June or 1 July, and regrowth was harvested on 1 October. Volumetric soil water content of the 0–100 cm soil layer was determined using neutron scattering, and was generally higher in elevated CO2 plots than ambient. Peak above‐ground biomass was greater on elevated CO2 plots than ambient CO2 plots with or without chambers during years with significant plant water stress. Above‐ground regrowth biomass was greater under elevated CO2 than under ambient CO2 in a year with late‐season water stress, but did not differ in a wetter year. Root ingrowth biomass was also greater in elevated CO2 plots than ambient CO2 plots when water stress occurred during the growing season. The basal cover and relative amount of warm‐season perennial grasses (C4) in the stand changed little during the 8‐year period, but basal cover and relative amount of cool‐season perennial grasses (C3) in the stand declined in the elevated CO2 plots and in ambient CO2 plots with chambers. Forbs (C3) and members of the Cyperaceae (C3) increased in basal cover and relative amount in the stand at elevated compared to ambient CO2. Greater biomass production under elevated CO2 in C4‐dominated grasslands may lead to a greater carbon sequestration by those ecosystems and reduce peak atmospheric CO2 concentrations in the future.
Nitrogen accumulation and distribution in Danthonia richardsonii swards in response to CO2 and nitrogen supply over four years of growth
Authors: Lutze Jason L. , Gifford Roger M.
Published: March 2003

Nitrogen‐stressed microcosms of the C3 grass Danthonia richardsonii gained nitrogen from the environment when grown under ambient or enriched (359, ‘amb’ or 719 μL L− 1‘enr’, respectively) atmospheric CO2 concentrations over a 4‐y period. This gain was apparent at all rates of supplied mineral N (2.2, 6.7 or 19.8 g N m− 2 y− 1– low‐N, mid‐N or high‐N), although it was small at high‐N. Small losses of N occurred from the microcosm as leachate, while gaseous losses of N were estimated to be between 10% and 25% of applied mineral N. Losses of applied mineral N were slightly lower under CO2 enrichment only at the highest rate of mineral N supply. Levels of 15N natural abundance in green leaf (δ15Ν) of − 2‰ (amb low‐N) and of below − 4‰ (enr low‐ & mid‐N) suggest that absorption of atmospheric NH3 may have been a source of some of the extra N in the low and mid‐N treatments. Biological N2 fixation, of up to 2 g m− 2 y− 1 was hypothesized to form the remainder of the environmental N source. Microcosm C:N ratio was higher under CO2 enrichment. Nitrogen productivity of microcosm carbon gain (g C accumulated g− 1 leaf N day− 1) was increased (up to 100%) by CO2 enrichment at all rates of mineral N supply. Green leaf %N was reduced by CO2 enrichment, and there was less nitrogen in the green leaf pool under CO2 enrichment. Less, or the same amount of nitrogen was present in senesced leaf, surface litter and root under CO2 enrichment while more nitrogen was present in the soil in organic forms, and as NH4 +  at the highest rate of mineral N supply.
Carbon budgeting in plant–soil mesocosms under elevated CO2: locally missing carbon?
Authors: Cheng Weixin , Sims Daniel A. , Luo Yiqi , Johnson Dale W. , Ball J. Timothy , Coleman James S.
Published: March 2003

Studies have suggested that more carbon is fixed due to a large increase in photosynthesis in plant–soil systems exposed to elevated CO2 than could subsequently be found in plant biomass and soils –‐ the locally missing carbon phenomenon. To further understand this phenomenon, an experiment was carried out using EcoCELLs which are open‐flow, mass‐balance systems at the mesocosm scale. Naturally occurring 13C tracers were also used to separately measure plant‐derived carbon and soil‐derived carbon. The experiment included two EcoCELLs, one under ambient atmospheric CO2 and the other under elevated CO2 (ambient plus 350 μL L− 1). By matching carbon fluxes with carbon pools, the issue of locally missing carbon was investigated. Flux‐based net primary production (NPPf) was similar to pool‐based primary production (NPPp) under ambient CO2, and the discrepancy between the two carbon budgets (12 g C m− 2, or 4% of NPPf) was less than measurement errors. Therefore, virtually all carbon entering the system under ambient CO2 was accounted for at the end of the experiment. Under elevated CO2, however, the amount of NPPf was much higher than NPPp, resulting in missing carbon of approximately 80 g C m− 2 or 19% of NPPf which was much higher than measurement errors. This was additional to the 96% increase in rhizosphere respiration and the 50% increase in root growth, two important components of locally missing carbon. The mystery of locally missing carbon under elevated CO2 remains to be further investigated. Volatile organic carbon, carbon loss due to root washing, and measurement errors are discussed as some of the potential contributing factors.
Carbon‐13 input and turn‐over in a pasture soil exposed to long‐term elevated atmospheric CO2
Authors: Van Kessel Chris , Nitschelm Jennifer , Horwath William R. , Harris David , Walley Frances , Lüscher Andreas , Hartwig Ueli
Published: March 2003

The impact of elevated CO2 and N‐fertilization on soil C‐cycling in Lolium perenne and Trifolium repens pastures were investigated under Free Air Carbon dioxide Enrichment (FACE) conditions. For six years, swards were exposed to ambient or elevated CO2 (35 and 60 Pa pCO2) and received a low and high rate of N fertilizer. The CO2 added in the FACE plots was depleted in 13C compared to ambient (Δ−  40‰) thus the C inputs could be quantified.

On average, 57% of the C associated with the sand fraction of the soil was ‘new’ C. Smaller proportions of the C associated with the silt (18%) and clay fractions (14%) were derived from FACE. Only a small fraction of the total C pool below 10 cm depth was sequestered during the FACE experiment.

The annual net input of C in the FACE soil (0–10 cm) was estimated at 4.6 ± 2.2 and 6.3 ± 3.6 (95% confidence interval) Mg ha− 1 for T. repens and L. perenne, respectively. The maximum amount of labile C in the T. repens sward was estimated at 8.3 ± 1.6 Mg ha− 1 and 7.1 ± 1.0 Mg ha− 1 in the L. perenne sward. Mean residence time (MRT) for newly sequestered soil C was estimated at 1.8 years in the T. repens plots and 1.1 years for L. perenne. An average of 18% of total soil C in the 0–10 cm depth in the T. repens sward and 24% in the L. perenne sward was derived from FACE after 6 years exposure. The majority of the change in soil δ13C occurred in the first three years of the experiment. No treatment effects on total soil C were detected.

The fraction of FACE‐derived C in the L. perenne sward was larger than in the T. repens sward. This suggests a priming effect in the L. perenne sward which led to increased losses of the old C. Although the rate of C cycling was affected by species and elevated CO2, the soil in this intensively managed grassland ecosystem did not become a sink for additional new C.
The role of low‐level ozone exposure and mycorrhizas in chemical quality and insect herbivore performance on Scots pine seedlings
Authors: Manninen Anne‐Marja , Holopainen Toini , Lyytikäinen‐Saarenmaa Päivi , Holopainen Jarmo K.
Published: March 2003

The effects of low‐level ozone exposure and suppression of natural mycorrhizas on the above‐ground chemical quality of Scots pine (Pinus sylvestrisL.) needles and insect herbivore performance were studied in a two‐year field experiment. Seedlings were fumigated with the ozone doses 1.5–1.7 times the ambient, and natural mycorrhizal infection level was about 35% reduced in roots with fungicide propiconazole. On ozone‐exposed seedlings the mean relative growth rate (MRGR) ofLygus rugulipennisPopp. nymphs was lower than on ambient ozone seedlings, butGilpinia pallidaKlug sawfly larvae grew better on elevated ozone seedlings than on ambient ozone seedlings. MRGR ofSchizolachnus pinetiFabr. andCinara pineaL. aphid nymphs orNeodiprion sertiferGeoffr. sawfly larvae or the oviposition ofL. rugulipennisandN. sertiferwere not affected by ozone exposure. Although ozone exposure did not affect total phenolics, total terpene, total or individual resin acid, total free amino acid, nutrient or sugar concentrations in needles, MRGR ofL. rugulipennispositively correlated with total terpenes and MRGR ofG. pallidapositively with total amino acids. In addition, ozone exposure increased serine and proline concentration and marginally also starch concentration in needles. When mycorrhizas were reduced with fungicide, only MRGR ofL. rugulipennisnymphs increased, but performance of other insect herbivores studied was not changed. However, number ofL. rugulipenniseggs correlated positively with mycorrhizal infection level and also with total sugars. Reduction of mycorrhizas did not strongly affect the concentrations of analysed compounds in needles, because only phosphorus and potassium and some individual resin acids were reduced by fungicide treatment. These results suggest that low‐level ozone exposure and moderately declined mycorrhizal infection do not drastically affect either the above‐ground chemical quality of Scots pine seedlings or performance of studied insect herbivores.
Genetic variation and spatial structure in sugar maple (Acer saccharum Marsh.) and implications for predicted global‐scale environmental change
Authors: Gunter L.E.E. E. , Tuskan Gerald A. , Gunderson Carla A. , Norby R.I.chard J.
Published: March 2003

Current ecosystem model predictions concerning the effects of global temperature increase on forest responses do not account for factors influencing long‐term evolutionary dynamics of natural populations. Population structure and genetic variability may represent important factors in a species' ability to adapt to global‐scale environmental change without experiencing major alterations in current range limits. Genetic variation and structure in sugar maple (Acer saccharum Marsh.) were examined across three regions, between two stands within regions, and among four to five open‐pollinated families within stands (total N = 547 genotypes) using 58 randomly amplified polymorphic DNA (RAPD) markers. Differences within open‐pollinated families account for the largest portion of the total variation (29%), while differences among regions represent less than 2% of the total variation. Genetic diversity, as indicated by estimates of percent polymorphic loci, expected heterozygosity, fixation coefficients, and genetic distance, is greatest in the southern region, which consists of populations with the maximum potential risk due to climate change effects. The high level of genetic similarity (greater than 90%) among some genotypes suggests that gene flow is occurring among regions, stands, and families. High levels of genetic variation among families indicate that vegetational models designed to predict species' response to global‐scale environmental change may need to consider the degree and hierarchical structure of genetic variation when making large‐scale inferences.
Phenology of British butterflies and climate change
Authors: Roy D. B. , Sparks T. H.
Published: March 2003

Data from a national butterfly monitoring scheme were analysed to test for relationships between temperature and three phenological measures, duration of flight period and timing of both first and peak appearance. First appearances of most British butterflies has advanced in the last two decades and is strongly related to earlier peak appearance and, for multibrooded species, longer flight period. Mean dates of first and peak appearance are examined in relation to Manley's central England temperatures, using regression techniques. We predict that, in the absence of confounding factors, such as interactions with other organisms and land‐use change, climate warming of the order of 1 °C could advance first and peak appearance of most butterflies by 2–10 days.
A global distribution of biodiversity inferred from climatic constraints: results from a process‐based modelling study
Authors: Kleidon Axel , Mooney Harold A.
Published: March 2003

We investigated the connection between plant species diversity and climate by using a process‐based, generic plant model. Different ‘species' were simulated by different values for certain growth‐related model parameters. Subsequently, a wide range of values were tested in the framework of a ‘Monte Carlo' simulation for success; that is, the capability of each plant with these parameter combinations to reproduce itself during its lifetime. The range of successful parameter combinations approximated species diversity. This method was applied to a global grid, using daily atmospheric forcing from a climate model simulation. The computed distribution of plant ‘species' diversity compares very well with the observed, global‐scale distribution of species diversity, reproducing the majority of ‘hot spot' areas of biodiversity. A sensitivity analysis revealed that the predicted pattern is very robust against changes of fixed model parameters. Analysis of the climatic forcing and of two additional sensitivity simulations demonstrated that the crucial factor leading to this distribution of diversity is the early stage of a plant's life when water availability is highly coupled to the variability in precipitation because in this stage root‐zone storage of water is small. We used cluster analysis in order to extract common sets of species parameters, mean plant properties and biogeographic regions (biomes) from the model output. The successful ‘species' cannot be grouped into typical parameter combinations, which define the plant's functioning. However, the mean simulated plant properties, such as lifetime and growth, can be grouped into a few characteristic plant ‘prototypes', ranging from short‐lived, fast growing plants, similar to grasses, to long‐lived, slow growing plants, similar to trees. The classification of regions with respect to similar combinations of successful ‘species' yields a distribution of biomes similar to the observed distribution. Each biome has typical levels of climatic constraints, expressed for instance by the number of ‘rainy days' and ‘warm days'. The less the number of days favourable for growth, the greater the level of constraints and the less the ‘species' diversity. These results suggest that climate as a fundamental constraint can explain much of the global scale, observed distribution of plant species diversity.
Modelling the recent historical impacts of atmospheric CO2 and climate change on Mediterranean vegetation
Authors: Osborne C. P. , Mitchell P. L. , Sheehy J. E. , Woodward F. I.
Published: March 2003

During the past century, annual mean temperature has increased by 0.75°C and precipitation has shown marked variation throughout the Mediterranean basin. These historical climate changes may have had significant, but presently undefined, impacts on the productivity and structure of sclerophyllous shrubland, an important vegetation type in the region. We used a vegetation model for this functional type to examine climate change impacts, and their interaction with the concurrent historical rise in atmospheric CO2. Using only climate and soil texture as data inputs, model predictions showed good agreement with observations of seasonal and regional variation in leaf and canopy physiology, net primary productivity (NPP), leaf area index (LAI) and soil water. Model simulations for shrubland sites indicated that potential NPP has risen by 25% and LAI by 7% during the past century, although the absolute increase in LAI was small. Sensitivity analysis suggested that the increase in atmospheric CO2 since 1900 was the primary cause of these changes, and that simulated climate change alone had negative impacts on both NPP and LAI. Effects of rising CO2 were mediated by significant increases in the efficiency of water‐use in NPP throughout the region, as a consequence of the direct effect of CO2 on leaf gas exchange. This increase in efficiency compensated for limitation of NPP by drought, except in areas where drought was most severe. However, while water was used more efficiently, total canopy water loss rose slightly or remained unaffected in model simulations, because increases in LAI with CO2 counteracted the effects of reduced stomatal conductance on transpiration. Model simulations for the Mediterranean region indicate that the recent rise in atmospheric CO2 may already have had significant impacts on productivity, structure and water relations of sclerophyllous shrub vegetation, which tended to offset the detrimental effects of climate change in the region.