bluuebunny/crossref_metadata_2025_split huggingface dataset:
Feedback significantly influences the simulated effect of CO2 on seasonal evapotranspiration from two agricultural species
Authors: Wilson KelL. B. , Carlson TobY. N. , Bunce James A. 
Published: March 2003

SummaryThe direct effect of elevated carbon dioxide on evapotranspiration over a growing season was investigated by scaling up single‐leaf gas exchange measurements on soybean and corn plants grown and measured at three carbon dioxide concentrations. Stomatal conductance decreased markedly with increasing carbon dioxide in these species under most conditions. Coupled soil–vegetation–atmosphere models were used to scale up these single‐leaf level measurements to simulate evapotranspiration at the regional scale from planting to harvest. The coupled modelling system introduced feedbacks over the season that are not present at the measurement level, which decreased the effect of carbon dioxide on evapotranspiration. Four sets of simulations were performed to evaluate specifically the magnitude of four feedbacks; two resulting from scale, surface layer and mixed layer feedback, one resulting from soil evaporation and one resulting from the interactions of stomatal conductance and the simulated canopy microclimate (physiological feedback). The feedbacks occurring from scale were consistent with previous analytical work indicating that transpiration becomes less dependent on stomatal conductance at larger scales. Evaporation from the soil has been generally neglected in past studies on carbon dioxide effects, but was especially important in decreasing the effects of carbon dioxide on evapotranspiration and showed a seasonal dynamic. The feedback resulting from physiological responses has also received less attention than the feedbacks from scale, but was only moderately important in these simulations. We also investigated the seasonal dynamics of how the observed increase in leaf area at elevated carbon dioxide affects evapotranspiration. Considering all the feedbacks and the observed increase in leaf area at elevated carbon dioxide, the simulated decrease in evapotranspiration was not negligible but was much less than the decrease in stomatal conductance. At the regional scale and maximum complexity in our model, the simulated decrease in seasonal evapotranspiration at doubled carbon dioxide (700 μmol mol–1) was 5.4% for soybeans and 8.6% for corn.
Climate change effects on net carbon exchange of a boreal aspen–hazelnut forest: estimates from the ecosystem model ecosys
Authors: Grant R. F. , Nalder I. A. 
Published: March 2003

SummaryAlthough boreal forests are currently sinks for atmospheric C, there is some concern that they may not remain so under hypothesized warming of the boreal climate. The ecosystem model ecosys was used to evaluate possible changes in ecosystem C exchange and accumulation under changes in atmospheric CO2 concentration (Ca) proposed in emissions scenario IS92a, and accompanying changes in air temperature and precipitation proposed by general circulation models running under IS92a. Ecosys was first tested under current climate by comparing modelled rates of C exchange and accumulation with those measured in a mixed aspen–hazelnut stand in central Saskatchewan. The model was then run with daily increments of Ca, temperature and precipitation, and differences in C exchange and accumulation between current and changing climates were evaluated. Model results indicated that over a 120‐y period, a mixed aspen–hazelnut stand currently accumulates about 14 kg C m−2. Under the hypothesized changes in climate this stand would accumulate an additional 8.5 kg C m−2, largely through higher rates of CO2 fixation and longer growing seasons under higher Ca and temperature. This additional accumulation would be entirely as aspen wood, while soil organic matter would change little. This accumulation would therefore be vulnerable to losses from fire and insects.
Seasonal soil‐surface carbon fluxes from the root systems of young Pinus radiata trees growing at ambient and elevated CO2 concentration
Authors: Thomas Stephen M. , Cook Freeman J. , Whitehead David , Adams John A. 
Published: March 2003

SummaryElevated atmospheric CO2 concentration may result in increased below‐ground carbon allocation by trees, thereby altering soil carbon cycling. Seasonal estimates of soil surface carbon flux were made to determine whether carbon losses from Pinus radiata trees growing at elevated CO2 concentration were higher than those at ambient CO2 concentration, and whether this was related to increased fine root growth.Monthly soil surface carbon flux density (f) measurements were made on plots with trees growing at ambient (350) and elevated (650 μmol mol−1) CO2 concentration in large open‐top chambers. Prior to planting the soil carbon concentration (0.1%) and f (0.28 μmol m−2 s−1 at 15 °C) were low. A function describing the radial pattern of f with distance from tree stems was used to estimate the annual carbon flux from tree plots. Seasonal estimates of fine root production were made from minirhizotrons and the radial distribution of roots compared with radial measurements of f. A one‐dimensional gas diffusion model was used to estimate f from soil CO2 concentrations at four depths.For the second year of growth, the annual carbon flux from the plots was 1671 g y−1 and 1895 g y−1 at ambient and elevated CO2 concentrations, respectively, although this was not a significant difference. Higher f at elevated CO2 concentration was largely explained by increased fine root biomass. Fine root biomass and stem production were both positively related to f. Both root length density and f declined exponentially with distance from the stem, and had similar length scales. Diurnal changes in f were largely explained by changes in soil temperature at a depth of 0.05 m.Ignoring the change of f with increasing distance from tree stems when scaling to a unit ground area basis from measurements with individual trees could result in under‐ or overestimates of soil‐surface carbon fluxes, especially in young stands when fine roots are unevenly distributed.
Temperature responses of carbon mineralization in conifer forest soils from different regional climates incubated under standard laboratory conditions
Authors: Dalias Panagiotis , Anderson Jonathan M. , Bottner Pierre , Coûteaux Marie‐Madeleine 
Published: March 2003

Summary 14C‐labelled straw was mixed with soils collected from seven coniferous forests located on a climatic gradient in Western Europe ranging from boreal to Mediterranean conditions. The soils were incubated in the laboratory at 4°, 10°, 16°, 23° and 30 °C with constant moisture over 550 days. The temperature coefficient (Q10) for straw carbon mineralization decreased with increasing incubation temperatures. This was a characteristic of all the soils with a difference of two Q10 units between the 4–10° and the 23− 30 °C temperature ranges. It was also found that the magnitude of the temperature response function was related to the period of soil incubation. Initial temperature responses of microbial communities were different to those shown after a long period of laboratory incubation and may have reflected shifts in microbial species composition in response to changes in the temperature regime. The rapid exhaustion of the labile fractions of the decomposing material at higher temperatures could also lead to underestimation of the temperature sensitivity of soils unless estimated for carbon pools of similar qualities. Finally, the thermal optima for the organic soil horizons (Of and Oh) were lower than 30 °C even after 550 days of incubation. It was concluded that these responses could not be attributed to microbial physiological adaptations, but rather to the rates at which recalcitrant microbial secondary products were formed at higher temperatures. The implication of these variable temperature responses of soil materials is discussed in relation to modelling potential effects of global warming.
Organic carbon cycling in Taylor Valley, Antarctica: quantifying soil reservoirs and soil respiration
Authors: Burkins Melody B. , Virginia Ross A. , Wall Diana H. 
Published: March 2003

SummaryOrganic carbon reservoirs and respiration rates in soils have been calculated for most major biomes on Earth revealing patterns related to temperature, precipitation, and location. Yet data from one of the Earth's coldest, driest, and most southerly soil ecosystems, that of the McMurdo Dry Valleys of Antarctica, are currently not a part of this global database. In this paper, we present the first regional calculations of the soil organic carbon reservoirs in a dry valley ecosystem (Taylor Valley) and report measurements of CO2 efflux from Antarctic soils. Our analyses indicate that, despite the absence of visible accumulations of organic matter in most of Taylor Valley's arid soils, this soil environment contained a significant percentage (up to 72%) of the seasonally unfrozen organic carbon reservoir in the terrestrial ecosystem. Field measurements of soil CO2‐efflux in Taylor Valley soils were used to evaluate biotic respiration and averaged 0.10 ± 0.08 μmol CO2 m−2 s−1. Laboratory soil microcosms suggested that this respiration rate was sensitive to increases in temperature, moisture, and carbon addition. Finally, a steady‐state calculation of the mean residence time for organic carbon in Taylor Valley soils was 23 years. Because this value contradicts all that is currently known about carbon cycling rates in the dry valleys, we suggest that the dry valley soil carbon dynamics is not steady state. Instead, we suggest that the dynamic is complex, with at least two (short‐ and long‐term) organic carbon reservoirs. We also suggest that organic carbon in the dry valley soil environment may be more important, and play a more active role in long‐term ecosystem processes, than previously believed.
Interannual variability in global soil respiration, 1980–94
Authors: Raich James W. , Potter Christopher S. , Bhagawati Dwipen 
Published: March 2003

AbstractWe used a climate‐driven regression model to develop spatially resolved estimates of soil‐CO2emissions from the terrestrial land surface for each month from January 1980 to December 1994, to evaluate the effects of interannual variations in climate on global soil‐to‐atmosphere CO2fluxes. The mean annual global soil‐CO2flux over this 15‐y period was estimated to be 80.4 (range 79.3–81.8) Pg C. Monthly variations in global soil‐CO2emissions followed closely the mean temperature cycle of the Northern Hemisphere. Globally, soil‐CO2emissions reached their minima in February and peaked in July and August. Tropical and subtropical evergreen broad‐leaved forests contributed more soil‐derived CO2to the atmosphere than did any other vegetation type (∼30% of the total) and exhibited a biannual cycle in their emissions. Soil‐CO2emissions in other biomes exhibited a single annual cycle that paralleled the seasonal temperature cycle. Interannual variability in estimated global soil‐CO2production is substantially less than is variability in net carbon uptake by plants (i.e., net primary productivity). Thus, soils appear to buffer atmospheric CO2concentrations against far more dramatic seasonal and interannual differences in plant growth. Within seasonally dry biomes (savannas, bushlands and deserts), interannual variability in soil‐CO2emissions correlated significantly with interannual differences in precipitation. At the global scale, however, annual soil‐CO2fluxes correlated with mean annual temperature, with a slope of 3.3 Pg C y−1per °C. Although the distribution of precipitation influences seasonal and spatial patterns of soil‐CO2emissions, global warming is likely to stimulate CO2emissions from soils.
Estimation of the carbon sequestration by a heterogeneous forest: night flux corrections, heterogeneity of the site and inter‐annual variability
Authors: AUBINET MARC , HEINESCH BERNAD , LONGDOZ BERNAD 
Published: March 2003

AbstractContinuous measurements of the net CO2 flux exchanged in a mixed forest with the atmosphere were performed over 5 years at the Vielsalm experimental site. The carbon sequestration at the site was deduced by a summation of the measurements. Problems associated with this summation procedure were discussed. The carbon sequestration in the ecosystem was presented and its interannual variability was discussed.An estimation of the night flux correction was given. The correction was applied by replacing measurements made during quiet nights by a parameterization. The impact of the correction was shown to vary between 10 and 20% of the uncorrected flux, according to the year. The need to include the storage flux during turbulent periods was emphasized: its neglect leads to an error which will be greater than the one it tries to correct.It was also shown that the heterogeneity of the site made it necessary to split the data into separate series corresponding to the different vegetation patches and to fill the data gaps by using an algorithm that takes account of the weather conditions. Two series were defined, one corresponding to a beech subplot, the other to a conifer subplot. The uncertainty owing to the data split and the data gap‐filling was about 15–20% annually.The carbon sequestration was then analysed in both the subplots. The length of the growing season was about 210 days in the beech and 240 days in the conifer. The carbon sequestration over 5 years was 2.28 kg C m2−2 in the beech and 3.58 kg C m2−2 in the conifer. The main difference between the species appeared in spring, between March and May, when the beeches were leafless.Significant interannual variations were observed in both the subplots. They appeared mainly in summer and were primarily because of the variations in the radiation and air humidity regimes. In addition, an impact of the interannual variation of the vegetation area index (VAI) and of the leaf initiation date was observed in the beech. Finally, a decline of the carbon sequestration efficiency of the ecosystem during the season was observed in both the subplots. It was because of neither the variation in any climatic variables nor VAI variation.
Does elevated atmospheric carbon dioxide affect internal nitrogen allocation in the temperate trees Alnus glutinosa and Pinus sylvestris?
Authors: Temperton Victoria M. , Millard Peter , Jarvis Paul G. 
Published: March 2003

AbstractNitrogen‐fixing plant species growing in elevated atmospheric carbon dioxide concentration ([CO2]) should be able to maintain a high nutrient supply and thus grow better than other species. This could in turn engender changes in internal storage of nitrogen (N) and remobilisation during periods of growth. In order to investigate this one‐year‐old‐seedlings of Alnus glutinosa (L.) Gaertn and Pinus sylvestris (L.) were exposed to ambient [CO2] (350 µmol mol−1) and elevated [CO2] (700 µmol mol−1) in open top chambers (OTCs). This constituted a main comparison between a nitrogen‐fixing tree and a nonfixer, but also between an evergreen and a deciduous species. The trees were supplied with a full nutrient solution and in July 1994, the trees were given a pulse of 15N‐labelled fertiliser. The allocation of labelled N to different tissues (root, leaves, shoots) was followed from September 1994 to June 1995. While N allocation in P. sylvestris (Scots pine) showed no response to elevated [CO2], A. glutinosa (common alder) responded in several ways. During the main nutrient uptake period of June–August, trees grown in elevated [CO2] had a higher percentage of N derived from labelled fertiliser than trees grown in ambient [CO2]. Remobilisation of labelled N for spring growth was significantly higher in A. glutinosa grown in elevated [CO2] (9.09% contribution in ambient vs. 29.93% in elevated [CO2] leaves). Exposure to elevated [CO2] increased N allocation to shoots in the winter of 1994–1995 (12.66 mg in ambient vs. 43.42 mg in elevated 1993 shoots; 4.81 mg in ambient vs. 40.00 mg in elevated 1994 shoots). Subsequently significantly more labelled N was found in new leaves in April 1995. These significant increases in movement of labelled N between tissues could not be explained by associated increases in tissue biomass, and there was a significant shift in C‐biomass allocation away from the leaves towards the shoots (all above‐ground material except leaves) in A. glutinosa. This experiment provides the first evidence that not only are shifts in C allocation affected by elevated [CO2], but also internal N resource utilisation in an N2‐fixing tree.
The use of n‐alkanes to estimate herbage intake and diet composition by dairy cows offered a perennial ryegrass/white clover mixture
Authors: Hameleers A. , Mayes R. W. 
Published: March 2003

AbstractThe n‐alkane technique for estimating herbage intake and diet selection in dairy cows fed perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) herbages was evaluated. Pairs of animals were offered either 8, 10, 12 or 14 kg dry matter (DM) d−1 of herbage alone or with 2 kg DM d−1 of barley. Fresh herbage was cut daily from a perennial ryegrass/white clover sward and the appropriate amount was fed in four feeds during the day. Individual intakes and the white clover proportion of the diet were estimated during a 12‐d period using the n‐alkane technique. Animals were dosed twice daily with paper pellets containing dotriacontane (C32‐alkane). Faecal grab samples were collected after the morning and afternoon milking. Three least‐squares optimization methods were compared in calculating the white clover proportion in the diet; then, total DM intake was calculated. The different least‐squares optimization methods gave similar predictions of the white clover content of the forage consumed. No significant (P < 0.05) effects of sampling routine, concentrate (barley) fed or interactions between the two were detected with respect to the difference between calculated and actual intake, the difference as a proportion of the total intake and estimated white clover content of the diet. The difference between the calculated and actual intake ranged from 139 to 366 g DM d −1, which resulted in a proportional difference ranging from 0.004 to 0.02 depending on sampling routine. The actual white clover content of the herbage mixture fed was 0.42 ± 0.008, whereas the estimated white clover content ranged from 0.41 ± 0.006 to 0.43 ± 0.008. The results suggest that accurate herbage intake estimates can be achieved in dairy cows grazing perennial ryegrass/white clover swards if representative samples from herbage consumed can be collected.
The establishment of alfalfa into different maize residues by conservation‐tillage and its effect on insect infestation
Authors: Byers  , Bahler  , Stout  , Leath  , Hoffman  
Published: March 2003

The effect of management of maize residues on the population of insects inimical to the establishment of alfalfa, Medicago sativa L., was examined 1 month after sowing. Alfalfa was sown in early and late April, and late May for 3 consecutive years in Centre County, Pennsylvania, USA. The sowings were made by conservation tillage (direct drilled into maize residue with minimal disturbance of soil) into three different maize residues after (1) silage, (2) silage‐plus‐winter rye cover and (3) grain. A fourth sowing was by conventional tillage (spring ploughing and harrowing maize residue) after grain. A pesticide, carbofuran (granular formulation) was applied at sowing to half of the plots. Methiocarb bait, a molluscicide, was applied as a split application to the same plots, one‐half at sowing and the remainder 2 weeks later. Alfalfa plots in the silage‐plus‐rye maize residues were colonized with fewer insects than the other residue treatments. Excessive growth of rye in early spring that was not successfully suppressed by herbicide treatment produced vigorous rye plants and fewer alfalfa seedlings. Consequently, silage plus rye had the lowest yield of alfalfa in early April sowings in 2 out of 3 years. Insects known to feed on alfalfa, such as tarnished plant bugs, Lygus lineolaris (Palsot de Beauvois), the plant bug, Plagiognathus politus Uhler, pea aphids, Acyrthosiphon pisum (Harris), and meadow spittlebugs, Philaenus leucophthalmus spumarius (L.), were collected by sweep net 1 month after sowing and less often in the silage‐plus‐rye treatment. These species were present in greater numbers in the other maize residues that had significantly more alfalfa forage.The insidious flower bug, Orius insidious (Say), and a damsel bug, Nabis americoferus Carayon, were collected in significantly greater numbers in the early April sowings, which corresponded with the peak populations of pea aphid. The potato leafhopper, Empoasca fabae (Harris), was most abundant in plots sowed in late April or late May.Pesticide treatment applied at the time of sowing had very little effect on numbers of insects collected by sweep net 1 month later in 1986 and 1988. However, pesticide treatment significantly increased yield by 280 kg ha−1 in 1987, even though sweep net collections of insects were not reduced by the pesticide treatment. Therefore, the beneficial effect of the pesticide could not be explained on the basis of the insects collected.The highest yields of alfalfa were obtained from the early April sowing into maize residues. This coincided with the time when the majority of alfalfa pests were less abundant than in later sowings; fewer pests were found on the sowings into silage‐plus‐rye residue. Also, when the rye forage yield was combined with the alfalfa yield, this became the most productive system.
Laparoscopic salpingectomy: electrosurgery or sutures?
Authors: Sherif Lotfy S. , Foda Ahmed I. , El Zayat Moustafa M. , Badawy Ahmed M. , Magos Adam L. 
Published: March 2003

ObjectiveTo determine the optimal haemostatic method during laparoscopic salpingectomy.DesignObservational study.SettingThe Royal Free Hospital, London and Mansoura University Hospital, Egypt.Subjects72 patients undergoing laparoscopic salpingectomy for various indications.DesignThe patients were randomly allocated to one of two groups in which bipolar electrosurgery or pre‐tied sutures were used as the primary method of haemostasis. The two groups were compared with regard to several intraoperative and postoperative variables.ResultsThe times required for securing and cutting the fallopian tube and for completing the procedures were shorter in the bipolar electrosurgery group than in the suture group, but the differences were not statistically significant. There were no significant differences between the groups with regard to any of the intraoperative or postoperative follow‐up variables.ConclusionBipolar electrosurgery and suturing are equally effective for laparoscopic salpingectomy. Although many prefer to use bipolar electrosurgery for this procedure, the choice between different modalities will still depend upon the surgeon's preference and the circumstances obtaining during the procedure.
Endometrial carcinoma in postmenopausal patients using hormone replacement therapy: a report on four cases
Authors: Maia Hugo , Maltez Amelia , Calmon Luis C. , Moreira Katarina , Coutinho Elsimar M. 
Published: March 2003

ObjectiveTo report the occurrence of endometrial carcinoma in polyps in postmenopausal patients using hormone replacement therapy (HRT).SettingA private hospital with facilities for carrying out hysteroscopy.SubjectsFour postmenopausal patients who developed endometrial carcinoma while using HRT.InterventionsHysteroscopy with biopsy, immunohistochemical investigation for oestradiol, progesterone receptors and p53 overexpression.ResultsAll four cases of carcinoma were associated with endometrial polyps. The cancerous cells were positive for oestrogen receptors, negative for progesterone receptors and showed p53 overexpression in all cases.ConclusionsThe lack of detectable progesterone receptors in endometrial carcinomas arising in polyps in HRT patients indicates an unopposed action of oestrogens, which may accelerate the carcinomatous changes in polyps through a p53 pathway.