bluuebunny/crossref_metadata_2025_split huggingface dataset:
Elevated atmospheric CO2: effects on phytochemistry, insect performance and insect‐parasitoid interactions
Authors: ROTH SHERRY K. , LINDROTH RICHARD L. 
Published: April 2006

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

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

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

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

AbstractIn 1993 a project was set up at Upper Teesdale to investigate some of the effects of predicted increased temperatures and increased nutrient availability resulting from increased litter decomposition rates, and atmospheric deposition of nitrogen, on the interaction between bracken and heather, two species which cover large areas globally. 32 2 × 2 m plots were laid out on a hillside on, and just below, the interface between the two species. Half of the plots were placed on pure bracken, and the other half on the boundary. Within each vegetation type half of the plots were covered with open‐topped polythene tents to simulate climate warming, while the other plots remained open. The second treatment consisted of additional fertilizer at 50 kg N ha−1 y−1 simulating increased decomposition rates at higher temperatures and increased atmospheric nitrogen deposition. The two treatments and their controls were combined in a 2 × 2 factorial design, with two replicates in each of two blocks.Results obtained in the first two summers indicated that fronds emerged earlier in spring and senesced later in autumn inside the tents, effectively lengthening the growing season. Fronds were taller when growing in warmer conditions, and carried more pinnae. In addition, the frond density was higher inside the tents, and together these effects contributed to greatly enhanced vigour of bracken in some of the conditions predicted by General Circulation Models. It seems likely that bracken will be more competitive, and have the potential to further encroach into heather dominated areas under these conditions.
Growth and photosynthesis of two eucalypt species during high temperature stress under ambient and elevated [CO2]
Authors: RODEN JOHN S. , BALL MARILYN C. 
Published: April 2006

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

AbstractThe turbulent exchanges of CO2 and water vapour between an aggrading deciduous forest in the north‐eastern United States (Harvard Forest) and the atmosphere were measured from 1990 to 1994 using the eddy covariance technique. We present a detailed description of the methods used and a rigorous evaluation of the precision and accuracy of these measurements. We partition the sources of error into three categories: (1) uniform systematic errors are constant and independent of measurement conditions (2) selective systematic errors result when the accuracy of the exchange measurement varies as a function of the physical environment, and (3) sampling uncertainty results when summing an incomplete data set to calculate long‐term exchange.Analysis of the surface energy budget indicates a uniform systematic error in the turbulent exchange measurements of ‐20 to 0%. A comparison of nocturnal eddy flux with chamber measurements indicates a selective systematic underestimation during calm (friction velocity < 0.17 m s−1) nocturnal periods. We describe an approach to correct for this error. The integrated carbon sequestration in 1994 was 2.1 t C ha−1 y−1 with a 90% confidence interval due to sampling uncertainty of ±0.3 t C ha−1 y−1 determined by Monte Carlo simulation. Sampling uncertainty may be reduced by estimating the flux as a function of the physical environment during periods when direct observations are unavailable, and by minimizing the length of intervals without flux data. These analyses lead us to place an overall uncertainty on the annual carbon sequestration in 1994 of ‐0.3 to +0.8 t C ha−1 y−1.
Seasonal variations of CO2 and water vapour exchange rates over a temperate deciduous forest
Authors: GRECO SUSANNA , BALDOCCHI DENNIS D. 
Published: April 2006

AbstractLong‐term and direct measurements of CO2 and water vapour exchange are needed over forested ecosystems to determine their net annual fluxes of carbon dioxide and water. Such measurements are also needed to parameterize and test biogeochemical, ecological and hydrological assessment models. Responding to this need, eddy covariance measurements of CO2 and water vapour were made ever a deciduous forest growing near Oak Ridge, TN, between April 1993 and April 1994. Periodic measurements were made of leaf area index, stomatal resistance, soil moisture and pre‐dawn leaf water potential to characterize the gas exchange capacity of the canopy.Four factors had a disproportionate influence on the seasonal variation of CO2 flux densities. These factors were photon flux densities (during the growing season), temperature (during the dormant season), leaf area index and the occurrence of drought The drought period occurred during the peak of the growing season and caused a significant decline in daily and hourly CO2 flux densities, relative to observations over the stand when soil moisture was plentiful.The annual net uptake of carbon was calculated by integrating flux measurements and filling missing and spurious data with the relations obtained between measured CO2 fluxes and environmental forcing variables. The net flux of carbon for the period between April 1993 and April 1994 was ‐525 g C m−2 y−1. This value represents a net flux of carbon from the atmosphere and into the forest. The net annual carbon exchange of this southern temperate broadleaved forest exceeded values measured over a northern temperate forest (which experiences a shorter growing season and has less leaf area) by 200 g C m−2 y−1 (cf. Wofsy et al 1993).The seasonal variation of canopy evaporation (latent heat flux) was controlled mostly by changes in leaf area and net radiation. A strong depression in evaporation rates was not observed during the drought Over a broadleaved forest large vapour pressure deficits promote evaporation and trees in a mixed stand are able to tap a variety of deep and shallow water sources.
The relative merits of open‐ and closed‐path analysers for measurement of eddy fluxes
Authors: LEUNING RAY , JUDD MURRAY J. 
Published: April 2006

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

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

AbstractWe present a simple theoretical analysis of the long term response of forest growth and carbon allocation to increased atmospheric [CO2] and N deposition. Our analysis is based on a recent model which predicts that plant light‐use efficiency increases with [CO2] but is independent of plant N supply. We combine that model with simple assumptions for nitrogen fluxes in the soil. A quasi‐equilibrium analysis of the short term tree and soil pools is then used to develop a simple graphical depiction of the long term carbon and nitrogen supply constraints on total growth, stem growth and foliar allocation.Our results suggest that long‐term growth responses to [CO2] and N deposition depend strongly on the extent to which stem allocation and foliage allocation are coupled. At one extreme (‘no coupling’), when stem allocation is fixed and independent of foliage allocation, there is no response of total growth or stem growth to increased [CO2] unless N deposition increases. At the other extreme (‘linear coupling’), when stem allocation is proportional to foliage allocation, there is a significant long‐term increase in total growth following a doubling of [CO2], even when N deposition is unchanged, but stem growth decreases because of a long‐term decrease in foliage allocation. For both types of coupling, total growth and stem growth increase with increasing N deposition. In the case of linear coupling, however, the N deposition response of stem growth is significantly larger than that of total growth, because of a long‐term increase in foliage allocation. We compare our results with those obtained previously from an alternative model of canopy light‐use efficiency involving a dependence on the foliar N:C ratio in addition to [CO2].Our results highlight the need for more experimental information on (i) the extent to which canopy light‐use efficiency is independent of N supply, and (ii) the relationship between foliage allocation and stem allocation.
System‐level adjustments to elevated CO2 in model spruce ecosystems
Authors: HÄTTENSCHWILER STEPHAN , KÖRNER CHRISTIAN 
Published: April 2006

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

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