Jürg Fuhrer

Critical levels for ozone effects on vegetation in Europe.

The evidence of detrimental effects of ozone on vegetation in Europe, and the need to develop international control policies to reduce ozone exposures which are based on the effects of the pollutant, has led to attempts to define so-called critical levels of ozone above which adverse effects on trees, crops and natural vegetation may occur. This review is a critical assessment of the scientific basis of the concepts used to define critical levels for ozone and identifies the key limitations and uncertainties involved. The review focuses on the Level I critical level approach, which provides an environmental standard or threshold to minimise the effects of ozone on sensitive receptors, but does not seek to quantify the impacts of exceeding the critical level under field conditions. The concept of using the AOT (accumulated exposure over a threshold) to define long-term ozone exposure is demonstrated to be appropriate for several economically important species. The use of 40 ppb (giving the AOT40 index) as a threshold concentration gives a good linear fit to experimental data from open-top chambers for arable crops, but it is less certain that it provides the best fit to data for trees or semi-natural communities. Major uncertainties in defining critical level values relate to the choice of response parameter and species; the absence of data for many receptors, especially those of Mediterranean areas; and extrapolation to field conditions from relatively short-term open-top chamber experiments. The derivation of critical levels for long-lived organisms, such as forest trees, may require the use of modelling techniques based on physiological data from experimental studies. The exposure-response data which have been applied to derive critical levels should not be used to estimate the impacts of ozone over large areas, because of the uncertainties associated with extrapolation from the open-top chamber method, especially for forest trees, and because of spatial variation in atmospheric and environmental conditions, which may alter ozone uptake.

Agroecosystem responses to combinations of elevated CO2, ozone, and global climate change

Abstract Global climate change, caused by increased emissions of greenhouse gases, is likely to affect agroecosystems in many ways, but the outcome, for instance, as a shift in productivity, depends on the combined effects of climate (temperature, precipitation) and other global change components. The focus of this review is on temperature, soil moisture, atmospheric CO2 and tropospheric ozone (O3). Changes in agricultural productivity can be the result of direct effects of these factors at the plant level, or indirect effects at the system level, for instance, through shifts in nutrient cycling, crop–weed interactions, insect pest occurrence, and plant diseases. Based on results of factorial experiments under a range of experimental conditions, it is difficult to draw generalized conclusions. With respect to C3 crops, the data suggest that elevated CO2 may have many positive effects, including yield stimulation, improved resource-use efficiency, more successful competition with C4 weeds, reduced O3 toxicity, and in some cases better pest and disease resistance. However, many of these beneficial effects may be lost—at least to some extent—in a warmer climate. Warming accelerates plant development and reduces grain-fill, reduces nutrient-use efficiency, increases crop water consumption, and favors C4 weeds over C3 crops. Also, the rate of development of insects may be increased. In grasslands, elevated CO2 stimulates dry matter production, in particular, in N-fixing legumes, but warming again reduces the positive CO2 effect. A major effect of climate warming in the temperate zone could be a change in winter survival of insect pests, whereas at more northern latitudes shifts in phenology in terms of growth and reproduction, may be of special importance. However, climate warming disturbs the synchrony between temperature and photoperiod; because insect and host plant species show individualistic responses to temperature, CO2 and photoperiod, it is expected that climate change will affect the temporal and spatial association between species interacting at different trophic levels. Although predictions are difficult, it seems reasonable to assume that agroecosystem responses will be dominated by those caused directly or indirectly by shifts in climate, associated with altered weather patterns, and not by elevated CO2 per se. Overall, intensive agriculture may have the potential to adapt to changing conditions, in contrast to extensive agricultural systems or low-input systems which may be affected more seriously.

Diastolic dysfunction precedes myocardial hypertrophy in the development of hypertension

BACKGROUND Left ventricular (LV) hypertrophy and impaired diastolic function may occur early in systemic hypertension, but longitudinal studies are missing. METHODS We performed an echocardiographic follow-up study in young initially normotensive male offspring of hypertensive (OHyp) (n = 25) and normotensive (ONorm) (n = 17) parents. Blood pressure (BP), LV mass, and mitral inflow were determined at baseline and after 5 years. Pulmonary vein flow pattern assessment and septal myocardial Doppler imaging were additionally performed at follow-up. RESULTS At follow-up, BP was not significantly different between the two groups (128 +/- 11/84 +/- 10 v 123 +/- 11/81 +/- 5 mm Hg, OHyp v ONorm) but five OHyp had developed mild hypertension. LV mass index remained unchanged and was not different between the two groups at follow-up (92 +/- 17 v 92 +/- 14 g/m2). Diastolic echocardiographic properties were similar at baseline, but, at follow-up, the following differences were found: mitral E deceleration time (209 +/- 32 v 185 +/- 36 msec, P < .05) and pulmonary vein reverse A wave duration (121 +/- 15 v 107 +/- 12 msec, P < .05) were prolonged in the OHyp as compared to the ONorm. Compared to the normotensive subjects, the five OHyp who developed hypertension had more pronounced alterations of LV diastolic function, that is, significantly higher mitral A (54 +/- 7 v 44 +/- 9 cm/sec, hypertensives v normotensives, P < .05), lower E/A ratio (1.31 +/- 0.14 v 1.82 +/- 0.48, P < .05), increased systolic-to-diastolic pulmonary vein flow ratio (1.11 +/- 0.3 v 0.81 +/- 0.16, P < .005), longer myocardial isovolumic relaxation time (57 +/- 7 v 46 +/- 12 msec, P < .05) as well as smaller myocardial E (10 +/- 1 v 13 +/- 2 cm/sec, P < .05) and E/A ratio (1.29 +/- 0.25 v 1.78 +/- 0.43, P < .05), despite similar LV mass (91 +/- 16 v 93 +/- 18 g/m2). CONCLUSIONS Over a 5-year follow-up, initially lean, normotensive, young men with a moderate genetic risk for hypertension, developed Doppler echocardiographic alterations of LV diastolic function compared to matched offspring of normotensive parents. These alterations were more pronounced in the OHyp who developed mild hypertension and occurred without a distinct rise in LV mass.

An international cooperative programme indicates the widespread occurrence of ozone injury on crops

The UN/ECE ICP-Vegetation 1 routinely investigates the effects of ambient ozone pollution on crops throughout Europe. Each year, a series of co-ordinated ambient air experiments are conducted over a large area of Europe and a range of crop species are observed for the occurrence of injury following ozone episodes. In 1995 and 1996, ozone injury was observed at sites throughout Europe from United Kingdom (Nottingham) to the Russian Federation (Moscow) and from Sweden (Ostad) to Italy (Naples). The only site participating in the ICP-Vegetation where it was not observed was that at Finland (Jokioinen). Injury was identified on subterranean and white clover, French bean, soybean, tomato, and watermelon at one or more sites. Injury was also detected in gardens and on crops growing in commercial fields. Two short-term critical levels which incorporate ozone dose and air saturation vapour pressure deficit (VPD) were derived from the 1995 data. These were (i) an AOT40 2 of 200 ppb.h over 5 days when mean VPD (0930‐1630 h) is below 1.5 kPa and (ii) an AOT40 of 500 ppb.h over 5 days when mean VPD (0930‐1630 h) is above 1.5 kPa. In general, the 1996 data supported these critical levels although injury did occur on two occasions when the AOT40 was less than 50 ppb.h, and the VPD was less than 0.6 kPa. Thus, ICP-Vegetation experiments have shown that ozone injury can occur over much of Europe and that plants are most at risk in conditions of high atmospheric humidity. ©2000 Elsevier Science B.V. All rights reserved.

The relationship between the stable carbon isotope composition of needle bulk material, starch, and tree rings in Picea abies

We investigated the relationship between the δ13C signal in current-year and 1-year-old needle bulk material, starch extracts, and early- or late-wood in mature spruce trees (Picea abies) to identify the modifying influence of climatic conditions on the different δ13C signals. Seasonal patterns of δ13C were determined in total bulk needle material from 1998 to 2000, and in acid soluble starch extracts in 1999 and 2000, and δ13C values of early- and late-wood were measured for the years 1991–2000. δ13C of bulk needle material was most enriched in spring with a trend towards depletion in the course of the season. Current-year needles showed a more distinct seasonal pattern in δ13C compared to 1-year-old needles. Seasonal trends in bulk material and starch were similar, but the highly enriched signal in spring could not be fully explained by the influence of the δ13C values of starch (weighted with the corresponding starch amounts). δ13C of starch in 1-year-old needles, and to a lesser extent of current-year needles, correlated with δ13C of early-wood, indicating a transfer of the isotopic signal. In addition, early-wood δ13C corresponded weakly to winter precipitation. In the summer, δ13C of total bulk needle material and starch showed no relation to the late-wood δ13C signature. Late-wood δ13C, however, related to global radiation, relative humidity and temperature, with more enriched values corresponding to warmer and drier conditions. We conclude that the signature of early-wood is determined more by biochemical fractionation, e.g. during starch formation, than by climatic conditions, which exert only a minor influence and are reflected in the isotopic signal of late-wood.

Net primary production and carbon stocks in differently managed grasslands: simulation of site-specific sensitivity to an increase in atmospheric CO2 and to climate change

Elevated atmospheric CO2 and climate changes are expected to influence managed grassland ecosystems. The mechanistic pasture simulation model (PaSim) was used to quantify effects on net primary productivity (NPP) and carbon (C) stocks at three locations differing in climate and soil type. An earlier model version was modified to enable long-term simulations at different altitudes, and to consider management in the form of either cutting or grazing by lactating cows. Results from simulations under current conditions agreed favourably with measured data for yield and C stocks, and model behaviour appeared to be plausible. Elevated CO2 alone or in combination with increased temperature stimulated NPP at all sites. The stimulation was positively related to increasing precipitation at dry sites, but negatively at cool sites. Climate change scenarios in combination with elevated CO2 led to increase C stocks. The sensitivity of C stocks to changes in temperature and precipitation was similar, and much larger than to management. Grazing led to higher C stocks compared with cutting, depending mainly on the difference in NPP between the management options. Grazing had a positive effect on C stocks under cool conditions, but the effect tended to become negative with increasing temperature. Comparing different sites revealed that local conditions affect system behaviour qualitatively. In quantitative terms, the results confirm that the combination of elevated CO2 and climate change affects NPP and C stocks, and that the influence of management is site-specific.

Organic Farming and Soil Carbon Sequestration: What Do We Really Know About the Benefits?

Organic farming is believed to improve soil fertility by enhancing soil organic matter (SOM) contents. An important co-benefit would be the sequestration of carbon from atmospheric CO2. Such a positive effect has been suggested based on data from field experiments though many studies were not designed to address the issue of carbon sequestration. The aim of our study was to examine published data in order to identify possible flaws such as missing a proper baseline, carbon mass measurements, or lack of a clear distinction between conventional and organic farming practices, thereby attributing effects of specific practices to organic farming, which are not uniquely organic. A total of 68 data sets were analyzed from 32 peer-reviewed publications aiming to compare conventional with organic farming. The analysis revealed that after conversion, soil C content (SOC) in organic systems increased annually by 2.2% on average, whereas in conventional systems SOC did not change significantly. The majority of publications reported SOC concentrations rather than amounts thus neglecting possible changes in soil bulk density. 34 out of 68 data sets missed a true control with well-defined starting conditions. In 37 out of 50 cases, the amount of organic fertilizer in the organic system exceeded that applied in the compared conventional system, and in half of the cases crop rotations differed between systems. In the few studies where crop rotation and organic fertilization were comparable in both systems no consistent difference in SOC was found. From this data analysis, we conclude that the claim for beneficial effects of organic farming on SOC is premature and that reported advantages of organic farming for SOC are largely determined by higher and often disproportionate application of organic fertilizer compared to conventional farming.

Ozone exposure-response relationships for mixtures of perennial ryegrass and white clover depend on ozone exposure patterns

Abstract The effect of different ozone (O3) exposure regimes on yield and species composition of frequently cut mixtures of ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) was studied in order to assess the importance of intermittent periods with low O3 and to evaluate the need to use an exposure index that emphasizes peak concentrations. Exposure-response relationships were used to test the performance of different indices characterising the accumulated exposure. Potted plant mixtures were exposed in open-top chambers and cut repeatedly after four-week growth periods (GP). Yield data were related to O3 exposure expressed as AOT40 (accumulated exposure above 40 ppb during daylight hours) for the GP immediately preceding the harvest, or for all GPs combined. Data for relative clover yield showed that the effect determined after several GPs represented the combined effect of all preceding GPs, and significant correlations were found between clover yield and AOT40 calculated over all GPs. During GPs with low O3, clover recovered to some extent from injury produced during previous exposures to high O3. By comparing the effects of treatments with similar AOT40 values but different peak concentrations, i.e. a treatment with a more constant O3 exposure vs a treatment with episodic O3 stress, no difference in the effect on clover yield was found, but a stronger effect on total forage yield by the episodic treatment. The strength of the correlation between total yield and AOT increased with increasing threshold concentration suggesting that peak concentrations are more effective in eliciting the yield response than are lower concentrations. It is concluded that AOT40 calculated over all GPs is a suitable exposure index to describe the effect of O3 on the species composition of this type of mixture, but to describe the effect on total forage yield, peak concentrations of > 110 ppb must be emphasized by using an AOT with higher threshold concentrations. A comparison with Swiss O3 monitoring data revealed, however, that in ambient air such high concentrations rarely occur.

Prevalence of asymptomatic and electrically undetectable intracardiac inside-out abrasion in silicon-coated Riata® and Riata® ST implantable cardioverter-defibrillator leads

BACKGROUND Recently, several cases of symptomatic and/or electrically detectable intracardiac inside-out abrasions in silicon-coated Riata® and Riata® ST leads have been described. However, the prevalence in asymptomatic patients with unremarkable implantable cardioverter defibrillator (ICD) interrogation is unknown. The aim of this study was to determine the prevalence of asymptomatic and electrically undetectable intracardiac inside-out abrasion in silicon-coated Riata® and Riata® ST leads. METHODS All 52 patients with an active silicone-coated Riata® and Riata® ST lead followed up in our outpatient clinic were scheduled for a premature ICD interrogation and a biplane chest radiograph. When an intracardiac inside-out abrasion was suspected, this finding was confirmed by fluoroscopy. RESULTS Mean time since implantation was 71 ± 18 months. An intracardiac inside-out abrasion was confirmed by fluoroscopy in 6 patients (11.5%). Mean time from lead implantation to detection of intracardiac inside-out abrasion was 79 ± 14 months. In all patients with an intracardiac inside-out abrasion, ICD interrogation showed normal and stable electrical parameters. Retrospectively, in 4 of these 6 patients, a coronary angiography performed 25 ± 18 months before diagnosis of intracardiac inside-out abrasion already showed the defect. Despite undetected intracardiac inside-out abrasion, 2 of these 4 patients experienced adequate antitachycardia pacing and ICD-shocks. ICD leads were replaced in all 6 patients. CONCLUSIONS The prevalence of asymptomatic intracardiac inside-out abrasion in silicon-coated Riata® and Riata® ST leads is higher than 10% when assessed by fluoroscopy, and most intracardiac inside-out abrasions are not detectable by ICD interrogation.

Video-assisted thoracoscopic pericardial fenestration for loculated or recurrent effusions

OBJECTIVE The validity of video-assisted thoracoscopic pericardial fenestration was prospectively assessed for loculated effusions. effusions previously treated by percutaneous catheter manoeuvres and those with concurrent pleural diseases. METHODS Inclusion criteria consisted of echocardiographically documented pericardial effusions requiring diagnosis or relief of symptoms and recurrent effusions after failed percutaneous drainage and balloon pericardiotomy. Pre-operative CT-scan was used to delineate additional pleural pathology and to determine the side of intervention. All patients were followed clinically and by echocardiographic examination 3 months post-operatively. RESULTS Twenty-four patients underwent thoracoscopic pericardial fenestration with 11 patients (54%) being previously treated by percutaneous catheter drainage, balloon pericardiotomy or subxyphoidal fenestration. Pre-operative echocardiography revealed septation and loculation in 18 patients (72%). Additional pleural pathology was identified on CT scan in 12 patients (50%) and talc pleurodesis was performed in six patients, all suffering from malignant pleural effusion. The mean operation time was 45 min (range 30-60 min) with no complications being observed. All patients were followed 3 months post-operatively by clinical and echocardiographic examination; relief of symptoms was achieved in all patients but echocardiography showed a recurrence in one patient (4%). Another recurrence was found by echocardiography after a mean follow-up time of 33 months in the 12 patients suffering from a non-malignant pericardial effusion. No recurrence of pleural or pericardial effusion was observed in the subset of patients with talc pleurodesis. CONCLUSION Video-assisted thoracoscopic pericardial fenestration is safe and effective for loculated pericardial effusions previously treated by percutaneous drainage manoeuvres and those with concomitant pleural disease.