Helena Danielsson

Grain protein accumulation in relation to grain yield of spring wheat (Triticum aestivum L.) grown in open-top chambers with different concentrations of ozone, carbon dioxide and water availability

The present investigation was undertaken in order to study the influence of ozone, carbon dioxide and water availability on the relationship between grain protein and grain yield in wheat (Triticum aestivum L.). Results were combined from spring wheat, field grown in 16 different open-top chamber experiments, from four different countries. Protein concentration of the grain was negatively (linear) associated with grain yield. This relationship was symmetrical for yield reductions and yield stimulations, despite the fact that the major cause for increases in yield (elevated carbon dioxide concentrations) was different from that causing crop loss (elevated ozone concentrations). The relationship between off-take (the amount of protein taken away from the farmland per unit area) of grain protein and grain yield was clear and highly consistent, but not linear. Yield loss in relation to the reference used (open-top chamber with non-filtered air) was associated with a larger negative change in protein off-take than the positive change in protein off-take corresponding to a yield increase of the same size. The water treatments used in some of the experiments influenced yield and protein content to a very limited extent. It is concluded from the present study that the change of the grain protein from factors such as ozone and carbon dioxide can be explained largely by a simple relationship between grain protein and grain yield at a certain level of nitrogen availability to the plants.

An ozone flux-response relationship for wheat

Six open-top chamber experiments with field-grown wheat Triticum aestivum L. (five with spring wheat and one with winter wheat) were combined to test which of the two ozone exposure indices, AOT40 and CFO(3), that provided the most consistent relationship between relative yield loss and ozone exposure. AOT40 is the accumulated exposure over a threshold ozone concentration of 40 nl l(-1), while CFO(3) is the cumulative flux of ozone (uptake) to the flag leaves. The ozone uptake of the flag leaves was estimated using a stomatal conductance model, sensitive to phenology, light, vapour pressure deficit (VPD) and temperature in combination with measurements of the boundary layer conductance in the open-top chambers. Both indices were calculated for the grain-filling period, defined as the time from anthesis until 2 weeks before harvest. The duration of the grain-filling period was shown to be closely related to the rate of accumulation of thermal time above a base temperature of 0 degrees C. The CFO(3) index provided a much more consistent pattern in terms of ozone effects compared to the AOT40 index. This was especially the case for spring wheat, for which a linear regression between relative yield and CFO(3) using all five data sets is presented. According to the stomatal conductance model, VPD limited daytime stomatal conductance in warm and dry years, while temperature was the most important limiting factor during daytime in cool and humid years. The effect of light was mainly to delimit the time period of the day during which substantial uptake of ozone took place. It is concluded that, compared to the AOT40 index, the more mechanistically relevant flux-based index CFO(3) will estimate larger yield loss in the relatively humid parts of western and northern Europe, while smaller yield loss will be estimated for the dry summer climates in south and central Europe. The use of an ozone flux threshold, similar to the cut-off concentration 40 nl l(-1) in AOT40, did not improve the performance of the CFO(3) index.

Surface wetness enhances ozone deposition to a pasture canopy

A mass balance approach was used to estimate the deposition of ozone to a grass-clover canopy enclosed in open-top chambers. Three different concentrations of ozone were used. Deposition measurements were made before and after spraying the canopy with water. It was found that the wet canopy absorbed more ozone than the dry canopy. After spraying, the vapour pressure deficit (VPD) decreased in the chambers. Thus, an increase in stomatal conductance was expected, which would lead to an increase in ozone uptake by the plants. The change in VPD was, however, of a magnitude which is unlikely to account for more than part of the change in deposition velocity for ozone. It is concluded that the surface wetness as such accounted for a substantial part of the increase in ozone deposition after spraying.

Updated stomatal flux and flux-effect models for wheat for quantifying effects of ozone on grain yield, grain mass and protein yield

Field measurements and open-top chamber experiments using nine current European winter wheat cultivars provided a data set that was used to revise and improve the parameterisation of a stomatal conductance model for wheat, including a revised value for maximum stomatal conductance and new functions for phenology and soil moisture. For the calculation of stomatal conductance for ozone a diffusivity ratio between O(3) and H(2)O in air of 0.663 was applied, based on a critical review of the literature. By applying the improved parameterisation for stomatal conductance, new flux-effect relationships for grain yield, grain mass and protein yield were developed for use in ozone risk assessments including effects on food security. An example of application of the flux model at the local scale in Germany shows that negative effects of ozone on wheat grain yield were likely each year and on protein yield in most years since the mid 1980s.

CO2 and ozone effects on canopy development of potato crops across Europe

This paper describes the effects of elevated CO2 (550 and 680 μl l−1) and O3 (60 nl l−1 O3 as an 8 h mean), alone or in combination, on canopy development and senescence in potato (Solanum tuberosum L. cv Bintje) across a range of European agro-climatic conditions. The assessments were made within the European CHIP project (CHanging climate and potential Impacts on Potato yield and quality) that was conducted for two growing seasons (1998 and 1999) in free air CO2 enrichment systems (FACE) and open-top chamber facilities (OTCs) at seven European sites. A comparison of chambered and unchambered experimental plots was included to examine the effects of chamber enclosure. Phenological growth stages, plant height, leaf area index (LAI) and the number of green and yellow leaves were recorded non-destructively throughout the growing season and by a destructive intermediate harvest at maximum leaf area (MLA). In the dynamic growth analysis CO2 and O3 effects were studied over three developmental stages: canopy expansion, full canopy and canopy senescence. Chamber enclosures promoted potato crop development (taller plants, more leaves) during the initial growth stages and led to a faster decline of LAI and a higher number of yellow leaves. The growth in ambient plots varied between sites and seasons, as did the scale of the treatment responses. Despite the large background variation, some overall treatment effects could be detected across all sites. Both levels of increased CO2 reduced final plant height in comparison to ambient concentrations, which indicates a premature ending of the active plant growth. At the stage of full canopy and crop senescence the average number of green leaves was significantly (P<0.05) decreased by 680 μl l−1 CO2 (OTC experiments) and LAI showed the same tendency (P=0.07). As there was however no indication of a decreased leaf formation during initial growth and at full canopy, this must have been due to an earlier leaf fall. In the FACE experiments LAI had already began to decline at the stage of full canopy at 550 μl l−1 CO2 but not in ambient CO2 (DAE×CO2, P<0.05). These observations strongly indicated that elevated CO2 induced a premature senescence during full canopy. O3 did not have an overall detrimental effect on crop development during initial growth nor at full canopy, but did induce a faster reduction of LAI during crop senescence (DAE×O3, P<0.05). Final plant height was not affected by O3. There were few CO2×O3 interactions detected. There was a suggestion (P=0.06) that O3 counteracted the CO2-induced decrease of green leaves at full canopy, but on the other hand during crop senescence the decline of LAI due to elevated O3 was faster at ambient compared to elevated CO2 (P<0.05). These responses of canopy development to elevated CO2 and O3 help to explain the treatment responses of potato yield within the CHIP project at sites across Europe.

Clover Sweden — A national three-year study of the effects of tropospheric ozone on Trifolium subterraneum, L.

In 1992 a cooperative project, Clover Sweden, was initiated. The aim was to study if subterranean clover could be used as a bioindicator in the different climate zones in Sweden by studying the impact of ambient ozone concentrations on this species in different parts of the country during three consecutive summer seasons. Plants of subterranean clover, Trifolium subterraneum, L., were exposed to ambient air at 24 sites from north to south Sweden. The project was designed to be compatible with the international programme, ICP Crops within the UNECE and the Convention on Long Range Transboundary Air Pollution. The results showed that subterranean clover is a useful bioindicator of ozone in all agricultural areas of Sweden, with the exception for very cool and rainy summers resulting in poor growth of the plants. In 1992, and especially in 1994, ozone injury was detected at almost all sites in Sweden, reflecting the higher ozone levels of those summers as compared to 1993, when ozone concentrations were generally low and not much injury was detected. Typical injury was chlorotic and bifacial necrotic lesions on parts of the leaf surface. It is concluded that at mean ozone concentrations of 25 ppb (24 h mean) and 30 ppb (7 h mean) there is a potential risk for injury on 10% of the leaves. When % injured leaves was plotted against AOT (Accumulated exposure Over a Threshold) using different thresholds, it became obvious that a threshold of 20 ppb ozone should be used in order to fully protect from leaf injury under Swedish conditions.

Clover as a tool for bioindication of phytotoxic ozone--5 years of experience from southern Sweden--consequences for the short-term critical levels.

Critical levels (CLs) for ozone effects on plants in Europe have been defined within the UN-ECE Convention on Long-Range Transboundary Air Pollution, CLRTAP. The purpose of the short-term CLs is to ensure protection of all crops to acute ozone injury. The currently used CLs are based on the ozone exposure of the plants during daylight hours expressed as AOT40 (Accumulated exposure Over the Threshold 40 nmol mol(-1) ozone). The aims of this study were: to test the performance of the current short-term CLs, to test alternative ozone exposure indices and to test if changes in the ozone cut-off concentration, the inclusion of a lag-period (LP) between exposure and identification of visible ozone injury or the duration of the ozone integration period improved the performance of the exposure index. The analysis was based on 38 different datasets from experiments with subterranean clover, Trifolium subterraneum in southern Sweden. AOT indices generally performed better than averaged ozone concentrations or SUM (Sum of ozone concentrations when a threshold is exceeded) indices. Regression analysis showed that the current short-term CL, AOT40 with a VPD (water vapour pressure deficit) threshold of 1.5 kPa, explained 56% of the variation in visible injury. A longer exposure period and the introduction of a LP, admitting visible ozone injury time to develop after exposure, improved the performance of the exposure index. AOT30 accumulated over 10 days before harvest, excluding a LP of 3 days before injury observation, performed best and explained 88% of the variation in visible injury. AOT40 indices left a rather large amount of visible injury unexplained indicating that a lower cut-off concentration for ozone is preferable. The results of the investigation indicated that a visible injury threshold of 10% improved the distinction between harmful and less harmful exposure.

Ozone sensitivity, growth and flower development in Phleum genotypes of different geographic origin in the Nordic countries

Abstract Nine genotypes of Phleum pratense, with origins ranging from the southernmost part of Denmark to the Scandian mountains and the coast of the Barents sea, and three genotypes of Phleum alpinum, all from the boreal region of north Sweden, were exposed to four treatments: charcoal and purafil filtered air with or without an addition of 140 g m−3 ozone, and non-filtered air with or without an addition of 100 g m−3 ozone, in open-top chambers. Plants were also grown in the ambient air to be able to control the influence of the chamber climate. Filtration of the air did not significantly affect plant growth or flowering. In terms of growth reduction, P. alpinum was more sensitive to the elevated ozone concentration than P. pratense, but the effects of elevated ozone on P. pratense were also large and significant. The ozone sensitivity of P. pratense genotypes did not vary systematically with the geographical origin but covaried with the growth rate. The higher temperature in the open-top chambers had a positive effect on biomass production of genotypes from the sites with the highest summer temperatures, while it affected negatively growth and flowering in most of the genotypes from the sites with the lowest summer temperature. On average, the higher temperatures in the open-top chambers affected positively the average aboveground biomass production of the P. pratense genotypes, while the development of flowers was slightly negatively affected.

Exposure of a grass-clover mixture to ozone in open-top chambers : effects on yield, quality and botanical composition

Abstract A field-grown grass-clover mixture was exposed to four different levels of ozone in open-top chambers: filtered air, non-filtered air and non-filtered air with two different levels of ozone added. There was also an ambient air treatment with no chambers. The same pasture was exposed to ozone for two consecutive growing seasons. Three cuts per season were made. There was a negative relationship between yield and ozone concentration, and a significant regression was obtained between total dry weight yield for all six harvests and the Accumulated exposure Over Threshold 40 nl l−1 (AOT40) for the whole exposure period. Analysis of variance did not reveal significant ozone effects on quality parameters (fibre content, energy content, protein, Ca, Fe, Mo). Fibre content and botanical composition were, however, influenced by enclosure of the plants in the open-top chambers. The importance of the ozone concentration gradient above a field crop for the estimation of yield loss is discussed. It is hypothesised that the lower ozone sensitivity in pasture compared with wheat is due to the fact that pasture is harvested before natural senescence, while wheat is exposed during this ozone sensitive phase of plant development.

Economic Assessment of the Negative Impacts of Ozone on Crop Yields and Forest Production. A Case Study of the Estate Östads Säteri in Southwestern Sweden

Abstract Ground level ozone concentrations, in combination with the prevailing climate, at the estate Östads Säteri in southwestern Sweden were estimated to reduce the yield of wheat and potato ranging between 5% and 10%. Occasionally, in years with the highest ozone concentrations and/or climatic conditions favoring high rates of ozone uptake to the leaves, yield loss levels above 10% may occur. Based on simple extrapolation, these ozone-induced reductions of crop yields at Östads Säteri represent a potential total annual yield loss in Sweden in the range of 24.5 million Euro for wheat and 7.3 million Euro for potato, respectively. A simulation of forest growth at Östad Säteri predicted that prevailing mean ozone exposure during 1993–2003 had the potential to reduce forest growth by 2.2% and the economic return of forest production by 2.6%. Using this value for extrapolation to the national level, the potential annual economic loss for Sweden due to negative impacts of ozone on forest production would be in the range of 56 million Euro (2004 prices).