bluuebunny/crossref_metadata_2025_split huggingface dataset:
Marine eutrophication and benthos: the need for new approaches and concepts
Authors: Grall Jacques , Chauvaud Laurent 
Published: March 2003

AbstractIn this review, using examples drawn from field observations or experimental studies, our goals are (i) to briefly summarize the major changes, in terms of species composition and functional structure, occurring in phyto and zoobenthic communities in relation to nutrient enrichment of the ecosystems; particular interest is given to the major abiotic and biotic factors occurring during the eutrophication process, (ii) to discuss the direct and indirect influences of benthic organisms on eutrophication and whether the latter can be controlled or favoured by benthos; most benthic species play a major role in the process of benthic nutrient regeneration, affecting primary production by supplying nutrients directly and enhancing rates of pelagic recycling; experimental studies have shown that the impact of benthic fauna on benthic–pelagic coupling and nutrient release is considerable. Thus, once the eutrophication process is engaged—that is, high organic matter sedimentation—it may be indirectly favoured by benthic organisms; benthos should always be considered in eutrophication studies, (iii) to evaluate the limits of our observations and data, highlighting the strong need for integrated studies leading to new concepts. Coastal ecosystems and benthic communities are potentially impacted by numerous human activities (demersal fishing, toxic contaminants, aquaculture…); in order to design strategies of ecosystem restoration or rehabilitation, we have to better understand coastal eutrophication and develop tools for quantifying the impacts; in order to achieve this goal, some possible directions proposed are: integrated studies leading to new concepts, model development based on these concepts and finally comparison of various ecosystems on a global scale.
Spatio‐temporal variability and environmental controls of methane fluxes at the forest–tundra ecotone in the Fennoscandian mountains
Authors: Sjögersten Sofie , Wookey Philip A. 
Published: March 2003

AbstractWe report on temporal and spatial variability in net methane (CH4) fluxes measured during the thaw period of 1999 and 2000 at three study sites along a c. 8° latitudinal gradient in the Fennoscandian mountain range and across the mountain birch‐tundra ecotone. All of the sites studied here were underlain by well‐drained mesic soils. In addition, we conducted warming experiments in the field to simulate future climate change. Our results show significant CH4 uptake at mesic sites spanning the forest‐tundra ecotone: on average 0.031 and 0.0065 mg CH4 m−2 h−1 during the 1999 and 2000 thaw periods, respectively, in Abisko (Sweden), and 0.019 and 0.032 mg CH4 m−2 h−1 during 2000 in Dovrefjell and Joatka (Norway), respectively. These values were both temporally and spatially highly variable, and multiple regression analysis of data from Abisko showed no consistent relationship with soil‐moisture status and temperature. Also, there was no consistent difference in CH4 fluxes between forest and tundra plots; our data, therefore, provide no support for the hypothesis that conversion of tundra to mountain birch forest, or vice versa, would result in a systematic change in the magnitude or direction of net CH4 fluxes in this region. Experimental warming treatments were associated with a 2.4 °C increase in soil temperatures (5 cm depth) in 1999 in Abisko, but no consistent soil warming was noted at any of the three field locations during 2000. In spite of this, there were significant treatment effects, principally early during the thaw period, with increased CH4 uptake compared with control (ambient) plots. These results suggest that direct effects of air warming on vegetation processes (e.g. transpiration, root exudation and nutrient assimilation) can influence CH4 fluxes even in predominantly methanotrophic environments. We conclude that net CH4 oxidation is significant in these cold, mesic soils and could be strengthened in an environmental change scenario involving a combination of (i) an increase in the length of the thaw period and (ii) increased mean temperatures during this period in combination with decreased soil‐moisture content.
Seasonal variability in the effect of elevated CO2 on ecosystem leaf area index in a scrub‐oak ecosystem
Authors: Hymus Graham J. , Pontailler Jean‐Yves , Li Jiahong , Stiling Peter , Hinkle C. Ross , Drake Bert G. 
Published: March 2003

AbstractWe report effects of elevated atmospheric CO2 concentration (Ca) on leaf area index (LAI) of a Florida scrub‐oak ecosystem, which had regenerated after fire for between three and five years in open‐top chambers (OTCs) and was yet to reach canopy closure. LAI was measured using four nondestructive methods, calibrated and tested in experiments performed in calibration plots near the OTCs. The four methods were: PAR transmission through the canopy, normalized difference vegetation index (NDVI), hemispherical photography, and allometric relationships between plant stem diameter and plant leaf area. Calibration experiments showed: (1) Leaf area index could be accurately determined from either PAR transmission through the canopy or hemispherical photography. For LAI determined from PAR transmission through the canopy, ecosystem light extinction coefficient (k) varied with season and was best described as a function of PAR transmission through the canopy. (2) A negative exponential function described the relationship between NDVI and LAI; (3) Allometric relationships overestimated LAI. Throughout the two years of this study, LAI was always higher in elevated Ca, rising from, 20% during winter, to 55% during summer. This seasonality was driven by a more rapid development of leaf area during the spring and a relatively greater loss of leaf area during the winter, in elevated Ca. For this scrub‐oak ecosystem prior to canopy closure, increased leaf area was an indirect mechanism by which ecosystem C uptake and canopy N content were increased in elevated Ca. In addition, increased LAI decreased potential reductions in canopy transpiration from decreases in stomatal conductance in elevated Ca. These findings have important implications for biogeochemical cycles of C, N and H2O in woody ecosystems regenerating from disturbance in elevated Ca.
Decomposition of secondary compounds from needle litter of Scots pine grown under elevated CO2and O3
Authors: Kainulainen Pirjo , Holopainen Toini , Holopainen Jarmo K. 
Published: March 2003

AbstractElevated atmospheric carbon dioxide (CO2) and ozone (O3) concentrations have both been shown to affect plant tissue quality, which in turn could affect litter decomposition and carbon (C) and nutrient cycling. In order to evaluate effects of climate change on litter chemistry, needle litter was collected from Scots pine (Pinus sylvestrisL.) saplings exposed to elevated CO2or O3concentration and their combination over three growing seasons in open‐top chambers. The decomposition of needle litter was followed for 19 months in a pine forest. During decomposition, needle samples for secondary compound analysis were collected and the mass loss of needles was followed. Main nutrients and total phenolics were analysed from litter in the beginning and at the end of the experiment. After 19‐month decomposition, the accumulated mass loss was about 34%; however, no significant differences were found in decomposition rates of needle litter between various treatments. Concentrations of total monoterpenes were about 4%, total resin acids 21% and total phenolics 14% of the initial concentrations in litter after 19‐month decomposition. In the beginning of litter decomposition, concentrations of individual monoterpenes –α‐pinene and β‐pinene – were significantly higher in needle litter grown under elevated CO2. However, concentrations of total monoterpenes during the whole decomposition period were not significantly affected by CO2or O3treatments. Concentrations of some individual and total resin acids were higher in needle litter grown under elevated CO2or O3than under ambient air. There were no significant differences in concentrations of total phenolics as well as nitrogen (N) and the main nutrient concentrations between treatments during decomposition. High concentrations of monoterpenes and resin acids in needles might slightly delay C recycling in forest soils. It is concluded that elevated CO2and O3concentrations do not have remarkable impacts on litter decomposition processes in Scots pine forests.
Direct and indirect effects of elevated CO2 on transpiration from Quercus myrtifolia in a scrub‐oak ecosystem
Authors: Li J.‐H. , Dugas W. A. , Hymus G. J. , Johnson D. P. , Hinkle C. R. , Drake B. G. , Hungate B. A. 
Published: March 2003

AbstractElevated atmospheric carbon dioxide (Ca) usually reduces stomatal conductance, but the effects on plant transpiration in the field are not well understood. Using constant‐power sap flow gauges, we measured transpiration from Quercus myrtifolia Willd., the dominant species of the Florida scrub‐oak ecosystem, which had been exposed in situ to elevated Ca (350 µmol mol−1 above ambient) in open‐top chambers since May 1996. Elevated Ca reduced average transpiration per unit leaf area by 37%, 48% and 49% in March, May and October 2000, respectively. Temporarily reversing the Ca treatments showed that at least part of the reduction in transpiration was an immediate, reversible response to elevated Ca. However, there was also an apparent indirect effect of Ca on transpiration: when transpiration in all plants was measured under common Ca, transpiration in elevated Ca‐grown plants was lower than that in plants grown in normal ambient Ca. Results from measurements of stomatal conductance (gs), leaf area index (LAI), canopy light interception and correlation between light and gs indicated that the direct, reversible Ca effect on transpiration was due to changes in gs caused by Ca, and the indirect effect was caused mainly by greater self‐shading resulting from enhanced LAI, not from stomatal acclimation. By reducing light penetration through the canopy, the enhanced self‐shading at elevated Ca decreased stomatal conductance and transpiration of leaves at the middle and bottom of canopy. This self‐shading mechanism is likely to be important in ecosystems where LAI increases in response to elevated Ca.
Cross validation of open‐top chamber and eddy covariance measurements of ecosystem CO2 exchange in a Florida scrub‐oak ecosystem
Authors: Dore Sabina , Hymus Graham J. , Johnson David P. , Hinkle C. R. , Valentini Riccardo , Drake Bert G. 
Published: March 2003

AbstractSimultaneous measurements of net ecosystem CO2 exchange (NEE) were made in a Florida scrub‐oak ecosystem in August 1997 and then every month between April 2000 to July 2001, using open top chambers (NEEO) and eddy covariance (NEEE). This study provided a cross validation of these two different techniques for measuring NEE. Unique characteristics of the comparison were that the measurements were made simultaneously, in the same stand, with large replicated chambers enclosing a representative portion of the ecosystem (75 m2, compared to approximately 1–2 ha measured by the eddy covariance system). The value of the comparison was greatest at night, when the microclimate was minimally affected by the chambers. For six of the 12 measurement periods, night NEEO was not significantly different to night NEEE, and for the other periods the maximum difference was 1.1 µmol m−2s−1, with an average of 0.72 ± 0.09 µmol m−2s−1. The comparison was more difficult during the photoperiod, because of differences between the microclimate inside and outside the chambers. During the photoperiod, air temperature (Tair) and air vapour pressure deficits (VPD) became progressively higher inside the chambers until mid‐afternoon. In the morning NEEO was higher than NEEE by about 26%, consistent with increased temperature inside the chambers. Over the mid‐day period and the afternoon, NEEO was 8% higher that NEEE, regardless of the large differences in microclimate. This study demonstrates both the uses and difficulties associated with attempting to cross validate NEE measurements made in chambers and using eddy covariance. The exercise was most useful at night when the chamber had a minimal effect on microclimate, and when the measurement of NEE is most difficult.
Photosynthetic responses of Mojave Desert shrubs to free air CO2 enrichment are greatest during wet years
Authors: Naumburg Elke , Housman David C. , Huxman Travis E. , Charlet Therese N. , Loik Michael E. , Smith Stanley D. 
Published: March 2003

AbstractIt has been suggested that desert vegetation will show the strongest response to rising atmospheric carbon dioxide due to strong water limitations in these systems that may be ameliorated by both photosynthetic enhancements and reductions in stomatal conductance. Here, we report the long‐term effect of 55 Pa atmospheric CO2 on photosynthesis and stomatal conductance for three Mojave Desert shrubs of differing leaf phenology (Ambrosia dumosa—drought‐deciduous, Krameria erecta—winter‐deciduous, Larrea tridentata—evergreen). The shrubs were growing in an undisturbed ecosystem fumigated using FACE technology and were measured over a four‐year period that included both above and below‐average precipitation. Daily integrated photosynthesis (Aday) was significantly enhanced by elevated CO2 for all three species, although Krameria erecta showed the greatest enhancements (63% vs. 32% for the other species) enhancements were constant throughout the entire measurement period. Only one species, Larrea tridentata, decreased stomatal conductance by 25–50% in response to elevated CO2, and then only at the onset of the summer dry season and following late summer convective precipitation. Similarly, reductions in the maximum carboxylation rate of Rubisco were limited to Larrea during spring. These results suggest that the elevated CO2 response of desert vegetation is a function of complex interactions between species functional types and prevailing environmental conditions. Elevated CO2 did not extend the active growing season into the summer dry season because of overall negligible stomatal conductance responses that did not result in significant water conservation. Overall, we expect the greatest response of desert vegetation during years with above‐average precipitation when the active growing season is not limited to ∼2 months and, consequently, the effects of increased photosynthesis can accumulate over a biologically significant time period.
Soil carbon stores in Nordic well‐drained forest soils—relationships with climate and texture class
Authors: CALLESEN I. , LISKI J. , RAULUND‐RASMUSSEN K. , OLSSON M. T. , TAU‐STRAND L. , VESTERDAL L. , WESTMAN C. J. 
Published: March 2003

AbstractSoil organic carbon (SOC) pools in forest floors and mineral soil to a depth of 100 cm were determined in 234 well‐drained Nordic forest soils from latitude 55–68???°‐N, and longitude 6–28???°‐E. The data were compiled in a database of Nordic forest soils, from literature, and sources of validated data the authors had access to. The SOC pool increased with both mean annual temperature (MAT) and mean annual precipitation (MAP), and the increase with MAT was more pronounced for coarse‐textured soils than for medium‐textured soils. Soil organic carbon in fine‐textured soils was not correlated with MAT and MAP. Differences between texture classes were mainly due to different carbon stores in the upper 40 cm of the mineral soil and in the forest floor. The emphasis on well‐drained soils eliminated the impact of hampered decomposition in hydromorphic soils. Large carbon accumulation in such soils probably explains the negative relationship between SOC and temperature reported in other studies. The increase in SOC with temperature and precipitation is interpreted as an indirect effect of higher net primary production.
Net changes in regional woody vegetation cover and carbon storage in Texas Drylands, 1937–1999
Authors: ASNER GREGORY P. , ARCHER STEVE , HUGHES R. FLINT , ANSLEY R. JAMES , WESSMAN CAROL A. 
Published: March 2003

AbstractAlthough local increases in woody plant cover have been documented in arid and semiarid ecosystems worldwide, there have been few long‐term, large‐scale analyses of changes in woody plant cover and aboveground carbon (C) stocks. We used historical aerial photography, contemporary Landsat satellite data, field observations, and image analysis techniques to assess spatially specific changes in woody vegetation cover and aboveground C stocks between 1937 and 1999 in a 400‐km2 region of northern Texas, USA. Changes in land cover were then related to topo‐edaphic setting and historical land‐use practices. Mechanical or chemical brush management occurred over much of the region in the 1940–1950s. Rangelands not targeted for brush management experienced woody cover increases of up to 500% in 63 years. Areas managed with herbicides, mechanical treatments or fire exhibited a wide range of woody cover changes relative to 1937 (−75% to + 280%), depending on soil type and time since last management action. At the integrated regional scale, there was a net 30% increase in woody plant cover over the 63‐year period. Regional increases were greatest in riparian corridors (33%) and shallow clay uplands (26%) and least on upland clay loams (15%). Allometric relationships between canopy cover and aboveground biomass were used to estimate net aboveground C storage changes in upland (nonriparian) portions of regional landscapes. Carbon stocks increased from 380 g C m−2 in 1937 to 500 g C m−2 in 1999, a 32% net increase across the 400 km2 region over the 63‐year period. These plant C storage change estimates are highly conservative in that they did not include the substantial increases in woody plant cover observed within riparian landscape elements. Results are discussed in terms of implications for ‘carbon accounting’ and the global C cycle.
Analysis of the nutritive value of timothy grown with varying N nutrition
Authors: Bélanger G. , McQueen R.E. 
Published: March 2003

AbstractNitrogen fertilization affect growth and yield of timothy (Phleum Pratense L.), but there are conflicting report on its effect on nutritive value. Two experiments were conducted to describe changes in nutritive value of field‐grown timothy fertilized with four rates of N fertilizer during spring and summer growth cycles, and to analyse relationships between parameters of nutritive value and the leaf to weight ratio (LWR). Early in the regrowth cycles when the harvestabe shoot biomass was approximately 200 g dry matter (DM) m−2 and under non‐limiting N and water conditions, the in vitro true digestibility (IVTD) of DM was greater in spring than in summer because the concentration of neutral‐detergent fibre (NDF) was lower and its in vitro cell wall digestibility (IVCWD) was greater. However, the rates of decline in IVTD and IVCWD and the rate of increase in NDF were greater in spring than in summer. Nitrogen deficiency decresed IVTD and IVCWD, and increased NDF concentration early in the regrowth cycles. Nitrogen deficiency, however, reduced the rate of change in the three parameters of nutritive value. By the end of growth cycles, IVTD was 59 and 42 g kg−1 DM greater when no N was applied than with non‐limiting N conditions in spring and summer respectively. When no N was applied, the IVCWD was 76 and 52 g kg−1 NDF greater, whereas the NDF concentration was 35 and 42 g kg−1 DM less than under non‐limiting N conditions in spring and summer respectively. The N deficiency increased the proportion of leaves in the biomass, which can explain for the most part the positve effect of the N deficiency on the nutritive value of timothy. This positive effect of the N deficiency on nutritive value though the proportion of leaves in the biomass, however, was reduced by the negative effect of N deficiency on the nutritive value of leaves or stems or both.
The effects of the inclusion of either maize silage, fermented whole crop wheat or ure‐treated whole crop wheat in a diet based on a high‐quality grass silage on the performance of dairy cows
Authors: Hameleers A. 
Published: March 2003

AbstractSixteen multiparous Holstein/Friesian cows were used to examine the effect on food intake and milk production of replacing 40% of the dry matter (DM) of first cut perennial ryegrass silage (G) with either maize silage (M), fermented (F) or urea‐treated (U) wheat whole crop silage. In addition to the forage mixtures, the animals received 5.25 kg DM d −1 of a standard concentrate and 1.75 kg DM d −1 of soya bean meal. The experiment consisted of four periods, each of 4 weeks duration, in a Latin square design. The grass silage used was of high quality with an estimated metabolizable energy (ME) content of 11.4 MJ kg −1 DM and in vitro digestibility of 748 g kg −1 DM. DM intake was significantly increased (s.e.d. = 0.364, P < 0.01) with the inclusion of M, F and U. The resulting total DM intakes were 17.6, 18.4, 19.2 and 20.1 kg d −1 for treatments G, M, F and U respectively. None of the animal production variables was significantly affected by the treatments. Milk yield was 27.4, 26.4, 27.1 and 26.9 kg d −1 for treatments G, M, F and U respectively. Milk fat content was 48.9, 46.9, 49.0 and 48.1 g kg −1, and milk protein content was 34.1, 33.6, 34.0 and 34.3 g kg −1 for treatments G, M, F and U respectively. The results show that partly (40%) replacing a high‐quality grass silage with forage maize, fermented whole crop wheat or urea‐treated whole crop wheat will increase DM intake in dairy cows but is not accompanied by an increase in animal performance and therefore will result in decreased efficiency of forage DM utilization.
Effects of crop properties, weather conditions and mechanical treatments on the wilting rate of dipliod and tetraploid Italian ryegrass for silage
Authors: Borreani G. , Tabacco E. 
Published: March 2003

AbstractThe relationship between rate of water loss of Italian ryegrass (Lolium multiflorum) and crop properties, weather conditions and mechanical treatments were studied on a field scale, as was the importance of the variables and their combined effects on influencing the wilting process.Eleven forage‐drying experiments were performed between 1992 and 1994 on diploid and tetraploid cultivars cut at different growth stages, ranging from early elongation to flowering, under environmentally variable conditions. The rate of drying was measured until a moisture content of 1 g water g−1 dry matter (DM) (500 g kg−1) was reached, or for a maximum of 2 days by calculating the rate of water loss from two consecutive hourly weights of swath portions placed on trays. Multiple regression analysis was used to correlate the drying rate (k) with crop properties and with meteorological and mechanical treatment variables.The interaction between potential evapotranspiration (ET0) and the moisture content of grass at cutting (Mgrass appeared to be the most important variable, from the twenty‐one tested, in influencing K. This variable shows that the same quantity of energy available for evaportaion acts in different ways when the water content of the crop at cutting differs. The rate of water loss is also influenced by the Mgrass itself, surgacae density of the swath, tedding and the weather conditions on the first day of drying.The value of Mgrass at cutting is greatly greatly dependent on crop maturity and ploidy. The tetraploid cultivars, with a higher inital moisture content, lost water more slowly than diploid cultivars did. Because the date of cutting cannot be delayed, owing to the decline in nutrive value, it is helpful to select for cultivars with low moisture contents at cutting, as well as applying mechanical treatment (spreading and tedding), in order to keep the wilting period as short as possible.A validated drying model can be useful for operational purposes to understand the drying process and to assess technological choices for forage drying.