bluuebunny/crossref_metadata_2025 huggingface dataset:
Rice responses to drought under carbon dioxide enrichment. 2. Photosynthesis and evapotranspiration
Authors: BAKER JEFFREY , HARTWELL ALLEN L. , BOOTE KENNETH , PICKERING NIGEL
Published: November 2003

Future climate change is projected to include a strong likelihood of continued increases in atmospheric carbon dioxide concentration ([CO2]) and possible shifts in precipitation patterns. Due mainly to uncertainties in the timing and amounts of monsoonal rainfall, drought is common in rainfed rice production systems. The objectives of this study were to quantify the effects and possible interactions of [CO2] and drought stress on rice (Oryza sativa, L.) photosynthesis, evapotranspiration and water‐use efficiency. Rice (cv. IR‐72) was grown to maturity in eight naturally sunlit, plant growth chambers in atmospheric carbon dioxide concentrations [CO2] of 350 and 700 μmol CO2 mol–1 air. In both [CO2], water management treatments included continuously flooded controls, flood water removed and drought stress imposed at panicle initiation, anthesis, and both panicle initiation and anthesis. Potential acclimation of rice photosynthesis to long‐term [CO2] growth treatments of 350 and 700 μmol mol–1 was tested by comparing canopy photosynthesis rates across short‐term [CO2] ranging from 160 to 1000 μmol mol–1. These tests showed essentially no acclimation response with photosynthetic rate being a function of current short‐term [CO2] rather than long‐term [CO2] growth treatment. In both long‐term [CO2] treatments, photosynthetic rate saturated with respect to [CO2] near 510 μmol mol–1. Carbon dioxide enrichment significantly increased both canopy net photosynthetic rate (21–27%) and water‐use efficiency while reducing evapotranspiration by about 10%. This water saving under [CO2] enrichment allowed photosynthesis to continue for about one to two days longer during drought in the enriched compared with the ambient [CO2] control treatments.
Possibilities for carbon sequestration in tropical and subtropical soils
Authors: BATJES N.H. , SOMBROEK W.G.
Published: November 2003

Soil organic matter is a key component of all terrestrial ecosystems, and any variation in its composition and abundance has important effects on many of the processes that occur within the system. The role of soil organic matter in soil nutrient cycling and soil gaseous emissions is discussed in the context of agricultural sustainability and global environmental change. Recent data on organic carbon and nitrogen reserves in the soils of the world are presented, with special reference to the subtropical and tropical regions. Possibilities for long‐lasting, enhanced sequestration of carbon in the soil through management of the land and water resources are reviewed. Finally, the need is stressed for an up‐to‐date database on soil resources and for a global monitoring system in order to permit the study of changes in soil organic matter quantity and quality over time, as determined by changes in land‐use and climate.
Temperature‐controlled open‐top chambers for global change research
Authors: NORBY RICHARD , EDWARDS NELSON , RIGGS JEFFERY , ABNER CHARLES , WULLSCHLEGER STAN , GUNDERSON CARLA
Published: November 2003

To enable experiments on the interactive effects of elevated atmospheric CO2 and increased air temperature on physiological processes in trees to be carried out, we altered the standard design of open‐top chambers by replacing blowers with evaporative coolers and in‐line heaters, with a feedback control system to maintain ambient or elevated air temperatures within the chambers. Ambient and elevated (+ 4 °C) temperature regimes were attained consistently and reliably throughout the growing season, with high reproducibility between chambers. From May through December the average of nearly 300,000 temperature measurements was 18.5 °C in ambient air, 18.9 ± 0.6 °C in six ambient chambers, and 22.4 ± 0.9 °C in six elevated temperature chambers. The difference in soil temperature between ambient and elevated chambers was 1.2 °C. Absolute humidity (vapour pressure) in the chambers was higher than that of ambient air, but it was generally similar between temperature treatments. Vapour pressure deficit therefore was higher in elevated temperature chambers than in ambient chambers, and this difference is considered an inseparable part of the temperature treatment. The addition of a temperature control system to open‐top chambers removes what has been an important flaw in this important tool for global change research.
Growth response of Trifolium repens L. and Lolium perenne L. as monocultures and bi‐species mixture to free air CO2 enrichment and management
Authors: HEBEISEN THOMAS , LÜSCHER ANDREAS , ZANETTI SILVIA , FISCHER BERNT , HARTWIG UELI , FREHNER MARCO , HENDREY GEORGE , BLUM HERBERT , NÖSBERGER* JOSEF
Published: November 2003

Trifolium repens L. and Lolium perenne L. were grown in monocultures and bi‐species mixture in a Free Air Carbon Dioxide Enrichment (FACE) experiment at elevated (60 Pa) and ambient (35 Pa) CO2 partial pressure (pCO2) for three years. The effects of defoliation frequencies (4 and 7 cuts in 1993; 4 and 8 cuts in 1994/95) and nitrogen fertilization (10 and 42 g m–2 y–1 N in 1993; 14 and 56 g m–2 y–1 N in 1994/95) on the growth response to pCO2 were investigated.

There were significant interspecific differences in the CO2 responses during the first two years, while in the third growing season, these interspecific differences disappeared. Yield of T. repens in monocultures increased in the first two years by 20% when grown at elevated pCO2. This CO2 response was independent of defoliation frequency and nitrogen fertilization. In the third year, the CO2 response of T. repens declined to 11%. In contrast, yield of L. perenne monocultures increased by only 7% on average over three years at elevated pCO2. The yield response of L. perenne to CO2 changed according to defoliation frequency and nitrogen fertilization, mainly in the second and third year. The ratio of root/yield of L. perenne increased under elevated pCO2, low N fertilizer rate, and frequent defoliation, but it remained unchanged in T. repens. We suggest that the more abundant root growth of L. perenne was related to increased N limitation under elevated pCO2.

The consequence of these interspecific differences in the CO2 response was a higher proportion of T. repens in the mixed swards at elevated pCO2. This was evident in all combinations of defoliation and nitrogen treatments. However, the proportion of the species was more strongly affected by N fertilization and defoliation frequency than by elevated pCO2. Based on these results, we conclude that the species proportion in managed grassland may change as the CO2 concentration increases. However, an adapted management could, at least partially, counteract such CO2 induced changes in the proportion of the species. Since the availability of mineral N in the soil may be important for the species’ responses to elevated pCO2, more long‐term studies, particularly of processes in the soil, are required to predict the entire ecosystem response.
Yield of wheat across a subambient carbon dioxide gradient
Authors: MAYEUX HERMAN , JOHNSON HYRUM , POLLEY WAYNE , MALONE STEPHEN
Published: November 2003

Yields and yield components of two cultivars of day‐neutral spring wheat (Triticum aestivum L.) were assessed along a gradient of daytime carbon dioxide (CO2) concentrations from about 200 to near 350 μmol CO2 (mol air)–1 in a 38 m‐long controlled environment chamber. The range in CO2 concentration studied approximates that of Earth’s atmosphere since the last ice age. This 75% rise in CO2 concentration increased grain yields more than 200% under well‐watered conditions and by 80–150% when wheat was grown without additions of water during the last half of the 100‐day growing season. The 27% increase in CO2 from the pre‐industrial level of 150 years ago (275 μmol mol–1) to near the current concentration (350 μmol mol–1) increased grain yields of ‘Yaqui 54’ and ‘Seri M82’ spring wheats by 55% and 53%, respectively, under well‐watered conditions. Yield increased because of greater numbers of grains per spike, rather than heavier grains or numbers of spikes per plant. Water use increased little with CO2 concentration, resulting in improved water use efficiency as CO2 rose. Data suggest that rising CO2 concentration contributed to the substantial increase in average wheat yields in the U.S. during recent decades.
Soil microbial responses to increased concentrations of atmospheric CO2
Authors: SADOWSKY MICHAEL , SCHORTEMEYER MARCUS
Published: November 2003

Terrestrial ecosystems respond to an increased concentration of atmospheric CO2. While elevated atmospheric CO2 has been shown to alter plant growth and productivity, it also affects ecosystem structure and function by changing below‐ground processes. Knowledge of how soil microbiota respond to elevated atmospheric CO2 is of paramount importance for understanding global carbon and nutrient cycling and for predicting changes at the ecosystem‐level. An increase in the atmospheric CO2 concentration not only alters the weight, length, and architecture of plant roots, but also affects the biotic and abiotic environment of the root system. Since the concentration of CO2 in soil is already 10–50 times higher than that in the atmosphere, it is unlikely that increasing atmospheric CO2 will directly influence the rhizosphere. Rather, it is more likely that elevated atmospheric CO2 will affect the microbe–soil–plant root system indirectly by increasing root growth and rhizodeposition rates, and decreasing soil water deficit. Consequently, the increased amounts and altered composition of rhizosphere‐released materials will have the potential to alter both population and community structure, and activity of soil‐ and rhizosphere‐associated microorganisms. This occurrence could in turn affect plant health and productivity and plant community structure. This review covers current knowledge about the response of soil microbes to elevated concentrations of atmospheric CO2.
Effects of temperature elevation on the population dynamics of the upland heather psyllid Strophingia ericae (Curtis) (Homoptera: Psylloidea)
Authors: MILES J.E. , BALE J.S. , HODKINSON I.D.
Published: November 2003

1 Cloches permeable to gas and water were used to simulate the effect of climate warming on upland populations of the heather psyllid Strophingia ericae at Moor House National Nature Reserve in the North Pennines, UK.

2 The cloches produced an average warming of about 1 °C in the heather canopy over a period of one year.

3 The density of S. ericae increased markedly in cloches within a few months of erection.

4 Species composition and numbers of potential predators were similar inside cloches and in control plots.

5 In the two year life‐cycle of S. ericae, the warming effect advanced the phenology from the second to third instar in the first winter, but in the second winter, fifth instar nymphs did not moult prematurely to adult.

6 The density of S. ericae was higher on Calluna vulgaris at its boundary with Juncus squarrosus than in the pure C. vulgaris sward (in both cloched and control plots).
Interannual variability of seasonal succession events in a temperate lake and its relation to temperature variability
Authors: MÜLLER‐NAVARRA DÖRTHE , GÜSS STEFAN , VON STORCH HANS
Published: November 2003

The assessment of possible implications of anthropogenic climate change requires the evaluation of results obtained with complex climate models. Here we considered the problem of assessing the impact of climate variability on successional events in a lake (Plußsee) of the temperate region between January and May. We first established a statistical link between large‐scale air temperature, at about 1500 m height, and the local temperature, in order to bridge the spatial gap of information obtained from global climate models and local climate which forces processes in the lake. Secondly, the local temperatures were statistically related to biologically induced dynamic features in the lake, derived from Secchi depths readings (as integrated measures). The observed relationships were compared with results from a phyto‐ and zooplankton population‐dynamic model run under different temperature regimes. The local temperatures approximated closely the large‐scale temperature. The timing of phyto‐ and zooplankton maxima (clearwater phase) were negatively related to the temperature. Thus, with a temperature increase both occurred earlier. The intensity of the spring algal maximum was negatively related to its timing, whereas no clear relation between the timing and intensity of the clearwater phase (zooplankton maximum) could be obtained.
Contribution of transpiration to forest ambient vapour based on isotopic measurements
Authors: MOREIRA MARCELO , STERNBERG LEONEL , MARTINELLI LUIZ , VICTORIA REYNALDO , BARBOSA EDELCILIO , BONATES LUIZ , NEPSTAD DANIEL
Published: November 2003

Using a simple isotope mixing model, we evaluated the relative proportion of water vapour generated by plant transpiration and by soil evaporation at two sites in the Amazon basin. Sampling was carried out at two different soil covers (forest and pasture), in a seasonal tropical rainforest at eastern Amazon where major deforestation is the result of land‐use change, and compared to a less seasonal central Amazon forest. In both forests, vapour from transpiration was responsible for most, if not all, of the water vapour generated in the forest, while it could not be detected above the grassy pastures. Thus the canopy transpiration may be a major source of water vapour to the forest and perhaps to the atmosphere during the dry season. The results are discussed in relation to predictive models based on net radiation that usually are not able to distinguish between transpiration and evaporation.
Methane emission from Texas rice paddy soils. 1. Quantitative multi‐year dependence of CH4 emission on soil, cultivar and grain yield
Authors: HUANG YAO , SASS RONALD , FISHER FRANK
Published: November 2003

Methane emissions at different rice productivity levels were observed from Texas rice paddy soils during the years 1991–95. Analysis of field measurements showed that seasonal methane emission (E) was strongly dependent on soil, cultivar, and rice grain yield. The relationship can be quantitatively described by E (g m–2) = 0.048 × SI × VI × GY. SI is a soil index to characterize the relative effect of soil texture on emission and is linked with soil sand percentage. VI is a variety index to identify the intervarietal difference in methane emission and is related to the amount of methane emission per unit grain yield. GY is grain yield (g m–2). Constant 0.048 was derived from the measurements of 10 cultivars planted in 1993. Computed emission applying the relationship is well matched with measured data. The comparison of computed with measured seasonal methane emission over an 80‐day period using a total of 32 data sets yields a correlation coefficientr2 of 0.800. In addition, the ratio of seasonal methane emission to net primary productivity was calculated on a carbon to carbon basis, which produces an average value of 2.8%, ranging from 1.2% to 5.4%. A further investigation indicated that the ratio is soil and variety dependent and can be quantitatively explained by C[CH4]/C[NPP] (%) = 3.21 × SI × VI + 0.12 (r2 = 0.738, n = 32). Under the condition of 30% soil sand, this ratio is ≈ 3% for the majority of cultivars.
Soil fungal‐arthropod responses to Populus tremuloides grown under enriched atmospheric CO2 under field conditions
Authors: KLIRONOMOS JOHN , RILLIG MATTHIAS , ALLEN MICHAEL , ZAK DONALD , KUBISKE MARK , PREGITZER KURT
Published: November 2003

We investigated the influence of elevated CO2 and soil N availability on the growth of arbuscular mycorrhizal and non‐mycorrhizal fungi, and on the number of mycophagous soil microarthropods associated with the roots of Populus tremuloides. CO2 concentration did not significantly affect percentage infection of Populus roots by mycorrhizal or non‐mycorrhizal fungi. However, the extra‐radical hyphal network was altered both qualitatively and quantitatively, and there was a strong interaction between CO2 and soil N availability. Under N‐poor soil conditions, elevated CO2 stimulated hyphal length by arbuscular mycorrhizal fungi, but depressed growth by non‐mycorrhizal fungi. There was no CO2 effect at high N availability. High N availability stimulated growth by opportunistic saprobic/pathogenic fungi. Soil mites were not affected by any treatment, but collembolan numbers were positively correlated with the increase in non‐mycorrhizal fungi. Results indicate a strong interaction between CO2 concentration and soil N availability on mycorrhizal functioning and on fungal‐based soil food webs.
Effects of elevated CO2‐grown loblolly pine needles on the growth, consumption, development, and pupal weight of red‐headed pine sawfly larvae reared within open‐topped chambers
Authors: WILLIAMS RAY , LINCOLN DAVID , THOMAS RICHARD
Published: November 2003

Seedlings of loblolly pine, Pinus taeda, were grown in open‐topped chambers under four levels of CO2: two ambient and two elevated. Larvae of the red‐headed pine sawfly, Neodiprion lecontei, were reared from early instar to pupation, primarily on branches within chambers. Larval growth and mortality were assessed and leaf phytochemistry samples of immature and mature leaves collected weekly. Mature leaves grown under elevated CO2 had significant reductions in leaf nitrogen and increases in non‐structural carbohydrate contents, resulting in foliage being a poorer food source for larvae, i.e. higher carbohydrate:nitrogen ratio. Nutritional constituents of immature needles were unaffected by seedling CO2 treatment. Volatile mono‐ and sesquiterpenes were unrelated to plant CO2 treatments for either leaf age class. Larval consumption of immature needles significantly increased on seedlings grown under CO2 enrichment, while mature needle consumption was not different between the treatments. The average weight gain per larva significantly declined in late instar larvae consuming elevated CO2‐grown needles. In spite of this reduced growth, neither the days to pupation nor pupal weights were different among the CO2 treatments. This study suggests that enriched CO2‐induced alterations in pine needle phytochemistry can affect red‐headed pine sawfly performance. However, compensatory measures by larvae, such as choosing to consume more nutritious immature needles, apparently helps offset enriched CO2‐induced reductions in the leaf quality of mature needles.
Short‐term decomposition of litter produced by plants grown in ambient and elevated atmospheric CO2 concentrations
Authors: BALL S. , DRAKE BERT
Published: November 2003

The effects of elevated atmospheric CO2 (ambient + 340 μmol mol–1) on above‐ground litter decomposition were investigated over a 6‐week period using a field‐based mesocosm system. Soil respiratory activity in mesocosms incubated in ambient and elevated atmospheric CO2 concentrations were not significantly different (t‐test, P > 0.05) indicating that there were no direct effects of elevated atmospheric CO2 on litter decomposition.

A study of the indirect effects of CO2 on soil respiration showed that soil mesocosms to which naturally senescent plant litter had been added (0.5% w/w) from the C3 sedge Scirpus olneyi grown in elevated atmospheric CO2 was reduced by an average of 17% throughout the study when compared to soil mesocosms to which litter from Scirpus olneyi grown in ambient conditions had been added. In contrast, similar experiments using senescent material from the C4 grass Spartina patens showed no difference in soil respiration rates between mesocosms to which litter from plants grown in elevated or ambient CO2 conditions had been added.

Analysis of the C:N ratio and lignin content of the senescent material showed that, while the C:N ratio and lignin content of the Spartina patens litter did not vary with atmospheric CO2 conditions, the C:N ratio (but not the lignin content) of the litter from Scirpus olneyi was significantly greater (t‐test;P < 0.05) when derived from plants grown under elevated CO2 (105:1 compared to 86:1 for litter derived from Scirpus olneyi grown under ambient conditions). The results suggest that the increased C:N ratio of the litter from the C3 plant Scirpus olneyi grown under elevated CO2 led to the lower rates of biodegradation observed as reduced soil respiration in the mesocosms. Further long‐term experiments are now required to determine the effects of elevated CO2 on C partitioning in terrestrial ecosystems.
Elevated CO 2and water supply interactions in grasslands: a pastures and rangelands management perspective
Authors: CAMPBELL B.D. , STAFFORD SMITH D.M. , MCKEON G.M.
Published: November 2003

Water is a key variable driving the composition and productivity of pastures and rangelands, and many of the ecosystems in these grasslands are highly sensitive to changes in water supply. The possibility that elevated CO2 concentrations may alter plant water relations is therefore particularly relevant to pastures and rangelands, and may have important consequences for grassland ecosystem function, water use, carbon storage and nutrient cycling. The planning of effective research to better understand these changes requires attention to both: (i) gaps in knowledge about CO2 and water interactions, and (ii) knowledge of how precisely the effects of CO2 must be understood in relation to other factors, in order to predict changes in grassland structure and production. A recent microcosm experiment illustrates that non‐linear effects of CO2 and water stress could perturb primary production by triggering changes in grassland community composition. The magnitudes of the effects of CO2 on key grassland ecosystems remain to be precisely determined through ecosystem‐level experiments. A simplified simulation of the impact of different levels of productivity change in a water‐limited Australian rangeland system was conducted by varying effects of CO2 on radiation and water use efficiency. The results indicate that direct effects of CO2 may be moderated at the enterprise scale by accompanying changes in adaptive management by farmers. We conclude that future research should aim to construct quantitative relationships and identify thresholds of response for different grassland systems. The sensitivity of these systems to management (such as grazing pressure) should also be considered when developing integrated predictions of future effects of CO2 on water supply to grassland ecosystems.
Carbon balance and water use efficiency of frequently cut Lolium perenne L. swards at elevated carbon dioxide
Authors: SCHAPENDONK A.H.C.M. , DIJKSTRA P. , GROENWOLD J. , POT C.S. , VAN DE GEIJN S.C.
Published: November 2003

The impact of doubled atmospheric [CO2] on the carbon balance of regularly cut Lolium perenne L. swards was studied for two years under semi‐field conditions in the Wageningen Rhizolab. CO2 and H2O vapour exchange rates of the swards were measured continuously for two years in transparent enclosures. The light utilization efficiencies of the swards ranged between 1.5 g CO2 MJ–1 global radiation (high light, ambient [CO2]) and 2.8 g CO2 MJ–1 (low light, doubled [CO2]). The above‐ground net primary productivity (NPP) in the enclosures was greater by 29% in 1994 and 43% in 1995 in the doubled [CO2] treatments, but only 20% and 25% more carbon was recovered in the periodical cuts. Thus, NPP increased significantly more than did the harvested above‐ground biomass. The positive [CO2] effect on net carbon assimilation is therefore associated with a preferential allocation of extra carbon to the roots and soil.

In addition to higher canopy photosynthesis and leaf elongation rates, a small part of the positive [CO2] effects on NPP could be attributed to a decrease of the specific respiration of the shoots. On a canopy basis however, respiration was equal or slightly higher at doubled [CO2] due to the higher amount of standing biomass.

Comparison of NPP and carbon recovered in different harvests showed that allocation to roots and soil was highest in spring, it was low in early summer and increased again in late summer and autumn.

The total gross amount of carbon partitioned to the roots and soil during the two year period was 57% more at doubled [CO2]. The total amount of carbon that was sequestered in the soil after subtraction of the respiratory losses was 458 g m–2 and 779 g m–2 in the ambient and doubled [CO2] treatments, respectively.

The average water use efficiency (WUE) of the swards was increased by a factor 1.5 at doubled [CO2]. Both WUE and its positive interaction with [CO2] varied between years and were positively correlated with global irradiance. At doubled [CO2], the higher WUE was fully compensated for by a higher leaf area index. Therefore, total transpiration on a canopy basis was equal for the ambient and the doubled [CO2] concentrations in both years.
The potential for feedback effects induced by global warming on emissions of nitrous oxide by soils
Authors: SMITH KEITH
Published: November 2003

About 65% of all emissions of nitrous oxide, N2O, are from soils, and are caused by aerobic nitrification and anaerobic denitrification. Tropical forest soils are probably the most important single source, followed by cultivated soils. Emission rates in natural systems are related to the rate of N mineralization from organic matter, and N deposition; in agricultural systems they are related to the quantities of N used as fertilizers and, where relevant, to recent land use change. The global budget for N2O is not well balanced, and sources may still be underestimated. Direct evidence of a positive feedback of global warming on N2O emissions comes from studies of air in ice cores. One of the projected effects of future global warming is a lowering of water tables in northern peatlands; experiments suggest that this would lead to increased emissions, but that the effect on total emissions would be small. The results of many experiments with non‐peatland soils indicate that the effect of temperature on soil emissions is generally positive, and that the rate of increase may be very steep when denitrification is the principal process involved. Process‐level modelling suggests that the reason is increased soil respiration, which causes an increase in anaerobic volume in which denitrification can take place, in addition to the increased denitrification rate per unit anaerobic volume brought about directly by the rise in temperature. These results imply that generally a positive feedback on emissions from soils is likely. However, in some environments, a large proportion of total annual emissions can occur during freeze–thaw cycles; such cycles may become more or less frequent, depending on the climatic zone, and this may result in either a positive or negative feedback effect due to global warming. Models of global and regional trends give very conflicting predictions of the direction and the magnitude of climatic impacts on fluxes, but the prediction of a positive feedback seems to be the more soundly based.
Thirty years of in situ tree growth under elevated CO2: a model for future forest responses?
Authors: HÄTTENSCHWILER STEPHAN , MIGLIETTA FRANCO , RASCHI ANTONIO , KÖRNER CHRISTIAN
Published: November 2003

Rising concentrations of atmospheric carbon dioxide have been predicted to stimulate the growth of forest trees. However, long‐term effects on trees growing to maturity and to canopy closure while exposed to elevated CO2 have never been examined. We compared tree ring chronologies of Mediterranean Quercus ilex which have been continuously exposed to elevated CO2 (around 650 μmol mol–1) since they were seedlings, near two separate natural CO2 springs with those from trees at nearby ambient‐CO2‘control’ sites. Trees grown under high CO2 for 30 years (1964–93) showed a 12% greater final radial stem width than those growing at the ambient‐CO2 control sites. However, this stimulation was largely due to responses when trees were young. By the time trees were 25–30 y old the annual difference in tree ring width between low and high CO2 grown trees had disappeared. At any given tree age, elevated CO2 had a relatively greater positive effect on tree ring width in years with a dry spring compared to years with more rainfall between April and May. This indicates a beneficial effect of elevated CO2 on tree water relations under drought stress. Our data suggest that the early regeneration phase of forest stands can be accelerated in CO2‐enriched atmospheres and that maximum biomass per land area may be reached sooner than under lower CO2 concentrations. In our study, high CO2 grown Q. ilex trees reached the same stem basal area at the age of 26 y as control trees at 29 y, i.e. three years earlier (faster turnover of carbon?). Reliable predictions of the future development of forests need to account for the variable responses of trees over their entire lifetime. Such responses to elevated CO2 can presently only be assessed at such unique field sites.
The biogeochemistry of nitrous oxide in permanently ice‐covered lakes of the McMurdo Dry Valleys, Antarctica
Authors: PRISCU
Published: November 2003

This manuscript presents an overview of published work on nitrous oxide in the permanently ice‐covered lakes of the McMurdo Dry Valleys, Antarctica. One of these lakes contains the highest concentration of nitrous oxide reported for natural aquatic systems (??bg 500 000% with respect to the global average mixing ratio in air). Recent data on nitrous oxide from the major lakes in this region of Antarctica are used to draw general conclusions regarding sources and sinks for this gas within the liquid water column, and to estimate exchanges with the atmosphere. Nitrous oxide maxima are usually found in regions where oxygen concentrations and redox potentials are decreasing (i.e. where high gradients exist); nitrous oxide is virtually absent in anoxic, and very low redox zones. These trends, together with positive relationships between apparent oxygen utilization (AOU) and apparent nitrous oxide production (ANP) indicate that nitrous oxide is primarily a product of nitrification; experiments showed that denitrification is a sink for this gas in anoxic water. ANP/AOU ratios are several orders of magnitude higher than that for the ocean. Yield ratios for nitrous oxide [ANP/(NO2–+NO3–)] averaged 4.2% (i.e. 1 atom of N appears in nitrous oxide for every 24 atoms appearing in oxidized N), greatly exceeding existing reports for pelagic systems, being similar to that from reduced sediments. Production and consumption rates, computed with a one‐dimensional diffusion model, ranged from 0 to 5.3 nM‐N d–1 and 0–2.7 nM‐N d–1, respectively. Rates were usually greatest in the region of largest oxygen and inorganic nitrogen gradients. Turnover times averaged 2917 and 1277 years for production and consumption which is in the range of the mixing times for the lakes. Areal flux from the lakes to the atmosphere (6.17 gN m–2 y–1) is several hundred times greater than areal fluxes reported for oceanic systems. Owing to the relatively small combined surface area of these lakes, absolute atmospheric transfer (1.2 × 105 gN y–1) is only a small fraction of annual global emission.
The effect of doubled CO2 on water use by alfalfa and orchard grass: simulating evapotranspiration using canopy conductance measurements
Authors: BUNCE .A. , WILSON KELLY , CARLSON TOBY
Published: November 2003

Alfalfa and orchard grass crops were grown at ambient and twice ambient carbon dioxide concentrations in field plots for several years in Beltsville, MD, using semi‐open chambers. Canopy conductances throughout many days were determined from water vapour exchange measurements, and indicated significant reductions in canopy conductance to water vapour at elevated carbon dioxide in both species. However, recognizing that the artificial ventilation in the chambers made direct comparisons of evapotranspiration rates questionable, we used a soil–vegetation–atmosphere model to determine what field‐scale evapotranspiration rates would have been with natural ventilation. Unlike the ‘omega’ approach, the model used allowed feedbacks between the canopy and the atmosphere, such that, for example, canopy conductance responses affected profiles of temperature and water vapour. Simulations indicated that although canopy conductances were lower at elevated carbon dioxide by as much as 20% in alfalfa and 60% in orchard grass, evapotranspiration rates never differed by more than 3% in alfalfa or 8% in orchard grass. Daily totals of evapotranspiration were only 1–2% lower at elevated carbon dioxide in alfalfa, and 2–5% lower in orchard grass. The results are partly explained by the fact that aerodynamic conductances to water vapour were generally smaller than the stomatal conductance, and also by canopy–atmosphere feedback processes which largely compensated for the lower conductance at elevated carbon dioxide by increasing the gradient for evaporation.
Apex marine predator declines ninety percent in association with changing oceanic climate
Authors: VEIT RICHARD , MCGOWAN JOHN , AINLEY DAVID , WAHL TERENCE , PYLE PETER
Published: November 2003

Three time series of pelagic bird abundance collected in disparate portions of the California Current reveal a 90% decline in Sooty Shearwater (Puffinus griseus) abundance between 1987 and 1994. This decline is negatively correlated with a concurrent rise in sea‐surface temperatures; Sooty Shearwaters have declined while sea temperatures have risen. There is a nine‐month lag in the response by shearwaters to changing temperatures. The geographical scale of our study demonstrates that the decline of Sooty Shearwaters is not a localized phenomenon, nor can it be ascribed to a short‐term distributional shift. The Sooty Shearwater is the numerically dominant species of the California Current System (CCS) in summer (austral winter), with an estimated population in the late 1970s of 5 million individuals. If the observed warming of the waters of the California Current System is an irreversible manifestation of a changing global climate, then the impact upon Sooty Shearwater populations seems likely to be profound.
Herbage yield, tiller number and root system activity after defoliation of prairie grass (Bromus catharticus Vahl)
Authors: Jatimliansky J. R. , Gimenez D. O. , Bujan A.
Published: November 2003

The effects of defoliation upon root and shoot systems of prairie grass (Bromus catharticus Vahl) were examined in both field and pot studies. The varieties used were 78–32 (HY), a high‐yielding variety; 79–42 (LY), a low‐yielding variety; and the commercial variety Grasslands Matua. In the field, the presence of roots in early and late spring was estimated by measuring uptake of [32P]phosphate by roots; herbage yields and tiller numbers were recorded. In a pot study, root and shoot dry‐matter (DM) yields were analysed. In the field, roots were detected to a depth of 1·2 m. After defoliation to a height of 0·1 m, root presence decreased more than 50% at depths of 0·6 m for LY and 1·0 m for Matua in early spring and at several depths for each variety in late spring. After a second defoliation, the apparent growth rate of shoots decreased by 35% in relation to the first regrowth period. In pots, shoot DM and root DM of control plants (undefoliated) had the following allometric relationship of the form: In (shoot DM) = 0·61 + 1·14 ln (root DM) (r2= 0·81). After defoliation, compared with undefoliated controls, the relative growth rate of shoots and total herbage yields were higher, but root and stubble DM were lower in all three varieties. Pooled root DM means were 10·3 and 6·8 g plant−1 and pooled stubble DM means were 12·7 and 7·6 g plant−1 for control and defoliated plants respectively. HY produced heavier tillers than LY, pooled means being 0·94 and 0·53 g DM tiller−1 (field study) and 3·44 and 2·05 g DM tiller−1 (pot study) for HY and LY respectively. HY had 5–6 green leaves per tiller, whereas LY had 3–4. Developed green leaves were heavier in HY (58 g m−2) than in LY (48 g m−2). It is suggested that differences in both leaf parameters may be related to higher herbage yields for HY than LY.
Influence of maceration at cutting on lactic acid bacteria populations, silage fermentation and voluntary intake and digestibility of precision‐chopped lucerne silage
Authors: Charmley E. , Savoie P. , McQueen R. E.
Published: November 2003

Laboratory experiments with lucerne (Medicago sativa) have shown that maceration at cutting improves silage fermentation. Samples taken during wilting and after various ensiling periods were analysed for lactic acid bacteria (LAB) numbers and indices of silage fermentation. In Experiment 1, in which maceration was tested in unwilted and wilted lucerne, there was an additive effect of maceration and wilting on LAB numbers at ensiling, thus LAB numbers were approximately 108 colony‐forming units (cfu) g−1 fresh crop for wilted, macerated forage compared with 103 cfu g−1 fresh crop for unwilted, unmacerated forage at ensiling. Initially, maceration reduced pH (P < 0·001) and increased lactic acid (unwilted comparison only; P < 0·001) and insoluble N (wilted comparison only; P < 0·001) concentrations. After 70 d ensiling, beneficial effects of maceration were associated only with the wilted silage. In Experiment 2, macerated lucerne was compared with unmacerated material, which was either ensiled after a wilting period of similar length or after wilting had proceeded to the same DM concentration as in the macerated forage. During wilting, LAB numbers were significantly higher in macerated than unmacerated forage (P < 0·05). This was also the case during the first 16 h of ensiling (P < 0·01). A decline in pH was observed earlier in macerated silage. Two days after ensiling, lactic acid concentration was higher in macerated silage (P < 0·05), but insoluble N concentration was not different. In a third experiment, unconditioned forage was compared with forages ensiled after regular conditioning or maceration. Although drying rate over 30 h was not influenced by degree of conditioning, LAB numbers during wilting increased with the degree of conditioning. In silages made from these treatments after 6 h wilting, there were no major effects on fermentation characteristics. In a fourth experiment, digestibility and voluntary intake of precision‐chopped silage were measured in sheep and found not to be increased by maceration. It was concluded that maceration per se resulted in marginal improvements in fermentation; however, when maceration also increased DM concentration, fermentation was markedly improved. In these precision‐chopped silages, maceration had no effect on intake or digestibility.
Microlaparoscopy: diagnostic and sterilization without general anaesthesia: a safe, practical and cost‐effective technique
Authors: Phipps J.H. , Hassanien M. , Miller R.
Published: November 2003

The aim of the study was to assess the technique of ‘microlaparoscopy’, i.e. the use of a small diameter (2.2 mm outer diameter or less) rigid laparoscope for outpatient diagnostic and sterilization purposes without general anaesthesia. Volunteer patients were offered and underwent either diagnostic laparoscopy using local anaesthesia alone, or laparoscopic sterilization using both local anaesthesia and intravenous sedation. There were no control groups. The setting was a purpose‐built private outpatient facility, 3 miles from a district general hospital, and the subjects included 52 volunteer patients (10 for sterilization and 42 for diagnostic laparoscopy). All operations were carried out successfully without complication and with good patient acceptability. Microlaparoscopy is a useful tool for performing both diagnostic and sterilization laparoscopy in an outpatient setting, and avoids the need for general anaesthesia. The procedures are safe and cost effective, provided adequate facilities are properly designed and utilized.
Laparosopic sacrocolpopexy in the management of vaginal vault prolapse
Authors: Mahendran D. , Prashar S. , Smith A.R.B. , Murphy S.
Published: November 2003

There are many procedures described for the treatment of vaginal vault prolapse. This paper describes the use of minimal access surgical techniques, in the form of laparoscopic sacrocolpopexy, for the treatment of this condition. The outcomes for the first 29 women to have undergone this procedure are described. Of the operations, 26 were completed without any intra‐operative problems. On two occasions the bladder was perforated during the procedure, and in one case the inferior epigastric artery was injured. One patient had a urinary tract infection postoperatively. The remaining patients had uneventful postoperative courses. Most patients were discharged home on the 2nd postoperative day. All patients were reviewed at 2 weeks and at 6 weeks, and 28 have been reviewed at 3 months and at 6 months, and 14 for greater than 6 months, following surgery. All patients have been able to return to their normal lifestyle very rapidly and there were no reports of dyspareunia. There were eight cases of rectocoele at the 6‐month review, and one patient had a recurrence of vault prolapse. Four patients have required a further surgical procedure, namely posterior repair. All except one patient had good support of the vaginal vault.
Cervical conservation: the future of hysterectomy?
Authors: Brown R. , Erian J.
Published: November 2003

Objective There has been much debate about the place of subtotal hysterectomy in gynaecological practice. With the more widespread introduction of the laparoscopic approach to cervical conservation, this issue has once again been brought into prime focus. We have reviewed the currently available literature in an attempt to present a balanced summary of the evidence encompassing both laparoscopic and conventional subtotal hysterectomy.

Method Papers were identified using Current Contents (clinical medicine) and the Index Medicus (Medline). Various outcomes were examined, in particular cervical stump carcinoma, sexual function, urinary function, psychic health and operative complications.

Conclusion The risk of carcinoma of the stump is very low and techniques to remove the transformation zone may all but eliminate this risk. There appears not to be any long‐term statistically significant difference between total and subtotal hysterectomy with respect to sexual function, urinary function or psychic health. Comparisons between different operative techniques are lacking; however operative complications involving the urinary tract and postoperative sepsis are less common with cervical conservation. With improvements in laparoscopic technique, this modality of surgery appears to be as safe as conventional surgery with particular benefits evident for the supracervical approach.
Successful delivery after laparoscopic treatment of combined intra‐abdominal and intra‐uterine pregnancy in spontaneous conception cycles
Authors: Inoue H. , Yoshioka H. , Nabuchi K. , Ishihara Y. , Kobayashi M.
Published: November 2003

Objective We report a case of combined intra‐abdominal and intra‐uterine pregnancy from spontaneous conception, diagnosed and treated with laparoscopy in the first trimester. A revision of Studdiford criteria for diagnosis of an intra‐abdominal pregnancy in heterotopic pregnancy is proposed for laparoscopic procedures. Case A 20‐year‐old woman conceived spontaneously and experienced an episode of abdominal pain at 5 weeks of gestation. Combined intra‐abdominal and intra‐uterine pregnancies were diagnosed and the intra‐abdominal pregnancy was treated using a laparoscopic technique, in the first trimester. There were good fetal and maternal outcomes. Conclusion Less invasive diagnostic and therapeutic management of intra‐abdominal pregnancy in early pregnancy should be employed to save the intra‐uterine gestation of the heterotopic pregnancy. We propose modified Studdiford criteria for probable and definite laparoscopic diagnosis of primary abdominal pregnancy.
Myometrial leiomyosarcoma following transcervical resection of the endometrium
Authors: Reed H. , Callen P.J.
Published: November 2003

A case is presented in which endometrial resection was performed to treat menorrhagia in the presence of a fibroid. The patient’s symptoms remained unchanged and a total abdominal hysterectomy was performed. Histological investigation of the fibroid showed it to be a leiomyosarcoma. This is a rare complication which should be considered in any patient being treated by conservative measures.
A review of the use of minimally invasive surgery in the management of ectopic pregnancy in a district general hospital
Authors: Tozer A.J. , Shaxted E.J.
Published: November 2003

The objective of this study was to review the management of ectopic pregnancy with the introduction of laparoscopic surgery over a 5‐year period, 1990–1994. This was a retrospective review, looking particularly at those women treated during 1994. The findings showed that a minimal access approach has been used with increasing frequency over the 5‐year period, with an increase in the number of women treated conservatively by salpingotomy. In 1990, all women underwent a laparotomy for an ectopic pregnancy with only 2% of women (1 out of 48) having a salpingotomy, compared to 1994 when 73.8% of women (45 out of 61) had a laparoscopic approach, with 47.5% of women (29 out of 61) having their fallopian tube conserved. The duration of postoperative hospital stay was significantly shorter in the 45 women treated laparoscopically than in the 16 women treated via a laparotomy (1.5 vs. 4.1 days). It can be concluded that the laparoscopic management of women with an ectopic pregnancy results in the increased frequency of a conservative approach, with a significantly shorter hospital stay.
Review of major complications of laparoscopy in a free‐standing gynaecological day case hospital
Authors: Tsaltas J. , Healy D. L. , Lloyd D.
Published: November 2003

Objectives Our purpose was to review all the major complications of laparoscopy in 6500 consecutive laparoscopies from one centre. We also felt it was important to conduct this study because of the current debate on the use of the Veress needle or the Hasson cannula. Design All the major complications from laparoscopies performed from June 1 1991 to March 31 1995 were documented. This is the largest series from one centre. Each laparoscopy was registered on computer. A distinction between operative and diagnostic laparoscopies was not made by the computer. Results A major complication was defined as one that required laparotomy. In this series eight major complications were recorded. The incidence of major complications was 1.23 per 1000. No vascular injury occurred as a result of using a Veress needle or closed trocar entry. Conclusion Despite advances in operative and diagnostic laparoscopy, complications still occur. From this study there is currently no evidence to suggest that the Veress needle should be banned in favour of the open Hasson technique. The gynaecologist, anaesthetist and consumer need to be aware of the complication rates for gynaecological day surgery laparoscopy.
Gasless laparoscopy with conventional surgical instruments
Authors: Kruczynski D. , Schäffer U. , Knapstein P.G.
Published: November 2003

The main advantages of gasless laparoscopy arise from the use of conventional laparotomy instruments (clamps, scissors and needle pushers). The operative time, for example, for hysterectomy procedures decreases to about 60% of the time taken hysterectomy for using conventional gas techniques. During cauterization, smoke escapes immediately through the open trocars and may even be suctioned using a conventional suction tube. As far as the nursing team is concerned, the equipment is familiar as they use the same instruments and the same sutures as in laparotomy. High respiration pressure, caused by the elevated abdominal pressure, as well as hypercapnia, are avoided. Therefore this procedure may also be performed on higher risk patients. The advantages for the patients are the shorter operative time, pain reduction and fewer complications, while retaining all the benefits of minimally invasive surgery.