G. Selldén

Yield and grain quality of spring wheat (Triticum aestivum L., cv. Drabant) exposed to different concentrations of ozone in open-top chambers

Spring wheat (Triticum aestivum L., cv. Drabant) was exposed to different concentrations of ozone in open-top chambers for two growing seasons, 1987 and 1988, at a site located in south-west Sweden. The chambers were placed in a field of commercially grown spring wheat. The treatments were charcoal-filtered air (CF), non-filtered air (NF) and non-filtered air plus extra ozone (NF(+)). In 1988, one additional ozone concentration (NF(++)) was used. Grain yield was affected by the ozone concentration of the air. Air filtration resulted in an increase in grain yield of about 7% in both years, compared to NF. The addition of ozone (NF(+), NF(++)) reduced grain yield and increased the content of crude protein of the grain in both years. Filtration of the air had no significant effect on the content of crude protein, compared to NF. The results showed a strong positive chamber effect on grain yield in the cold and wet summer of 1987. In 1988, there was no net chamber effect on grain yield. The relative differences between the CF, NF and NF(+) treatments with respect to grain yield were of the same magnitude in the two years, despite the very different weather conditions.

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.

Chlorophyll concentration of potatoes grown under elevated carbon dioxide and/or ozone concentrations

Abstract Potato cv. Bintje was grown in open-top-chambers and free-air-CO2-enrichment systems at 7 sites across Europe for 2 years (1998–99). The effect of different treatments (CO2 enrichment and O3 fumigation) on the chlorophyll content of fully expanded upper and lower canopy leaves was investigated collecting Minolta SPAD-502 meter readings. In both CO2 treated and O3 fumigated plants, leaves had lower chlorophyll content than those in ambient air controls; season-long chlorophyll averages were 9.3% lower in the ‘CO2’ treatments, 9.1% lower in ‘O3’ treatments and 12.3% lower in ‘CO2+O3’ treatments. The analysis of chlorophyll content in three different growth phases (Emergence–Tuber Initiation; Tuber Initiation–Maximum Leaf Area; Maximum Leaf Area–Harvest) showed that in the early growth period, i.e. before tuber initiation there was a slight indication for an higher chlorophyll content at elevated CO2 (+3.8%) or O3 (+1.7%). However, from tuber initiation onwards the leaves of plants grown under elevated CO2 or O3 showed a progressively lower chlorophyll content (−4.8% for CO2 treatments and −2.6% for O3 treatments) indicating a faster senescence of leaves that increased during the late growth period (−12.8% for CO2 treatments and −12.7% for O3 treatments) and that was enhanced by CO2–O3 interaction (−17.8%).

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.

Effects of ozone on biomass, non-structural carbohydrates and nitrogen in spring wheat with artificially manipulated source/sink ratio

Abstract Field grown spring wheat ( Triticum aestivum ) cv. Dragon, with artificially altered source/sink ratios, was exposed to ozone in open-top chambers in order to test whether the ozone sensitivity was affected by a shift in the source/sink relationship. The source and sink were manipulated by removing the flag leaf or the upper part of the ear, respectively. In 1995, three different chamber treatments were used: non-filtered air without extra ozone (NF), with ozone added before anthesis (NF+pre) or with ozone added during and after anthesis (NF+post). The ozone exposure during the treatment periods was 2417 and 2508 nmol mol −1 hours (AOT40) in NF+pre and NF+post, respectively. In 1997, the plants were exposed to filtered air (F) or to non-filtered air without extra ozone (NF) or with three different levels of ozone added (NF1+, NF2+ and NF3+). The ozone exposure expressed as AOT40 was 0, 13, 1924, 5881 and 10 375 nmol mol −1 hours in F, NF, NF1+, NF2+ and NF3+, respectively. The dry weight per grain and the amount of total non-structural carbohydrates and nitrogen per grain were reduced by ozone exposure in 1997. In 1995, the dry weight per grain in the source-manipulated shoots was reduced by ozone, especially when the exposure was conducted during and after anthesis. The ozone effect in 1997 was smaller in sink-manipulated shoots than in source-manipulated and non-manipulated shoots. It is concluded that the ozone sensitivity of wheat is higher when the grain growth is source-limited. It is also concluded that the ozone sensitivity of wheat is higher during and after anthesis than before anthesis, although source-limited wheat plants may be sensitive also to early ozone exposure.

Impact of ozone on the growth of birch (Betula pendula) saplings.

Saplings of one half-sib family of birch, Betula pendula, were exposed to three levels of ozone in open-top chambers (OTCs) during two growing seasons 1997-1998. The ozone treatments were non-filtered air (NF, accumulated daylight AOT40 over the two growing seasons of 3.0 l l-1 h), non-filtered air with extra ozone (NF+, accumulated daylight AOT40 of 27.3 l l-1 h) and non-filtered air with additional extra ozone (NF++, accumulated daylight AOT40 of 120 l l-1 h). The birch saplings, including the roots, were harvested after the first and second growing seasons. After the first growing season, the NF++ treatment reduced the total wood biomass by 22%, relative to the NF treatment. There was no further reduction of the total wood biomass in the NF++ treatment after the second growing season. The root biomass was reduced by 30% after the first growing season. The shoot/root ratio, as well as the proportional biomass of leaves, were increased by ozone during both years. The ozone impact on the relative growth rate was estimated to -2% per 10 l l-1 h daylight AOT40 per growing season.

Peroxisome proliferation in Norway spruce induced by ozone

SummaryCatalase (EC 1.11.1.6) activity (both total and specific activity) of particulate fractions of needles of Norway spruce [Picea abies (L.) Karst.] was elevated approximately 2-fold following exposure of trees to 60–70 μg/m3 of ozone during the growing season compared to trees receiving charcoal filtered air (about 15 μg/m3 ozone). Measurements were from homogenates fractionated into particulate and soluble (supernatent) activities. In contrast, the catalase activity of the supernatant was unchanged in response to ozone treatment. Catalase activity declined as the needles aged comparing current, 1-, and 2-year needles but the ozone-induced increment remained constant. Electron microscope cytochemistry using peroxidatic coupling with 3,3′-diaminobenzidine carried out in parallel, revealed catalase-containing peroxisomes both in situ and in the particulate fractions analyzed for catalase activity. The tissue volume occupied by peroxisomes in response to needle age and ozone appeared to vary approximately in proportion to the measured catalase activity. Overall cytochemical reactivity for catalase declined with needle age, but, for all years, was greater in needles of trees receiving air supplemented with ozone compared to those of trees receiving charcoal filtered air.

Ozone deposition to an oat crop (Avena sativa L.) grown in open-top chambers and in the ambient air

Abstract Fluxes and deposition velocities for ozone were determined for open-top chambers with and without an oat crop, and for the adjacent field, using a resistance analogue model and the aerodynamic wind-profile method, respectively. During a period when the canopy was green and the ambient wind speeds modest, the fluxes and deposition velocities were higher in the chamber with plants than in the field crop. The deposition to chamber walls and soil in the chamber only accounted for part of that difference. The deposition velocity for ozone to the crop was light-dependent both in the chamber with plants and in the ambient air. With increasing plant senescence, the deposition velocity declined and the light dependence disappeared. Fluctuations in deposition velocity superimposed on the overall declining trend followed the same temporal pattern in the chambers with and without plants. These fluctuations in deposition velocity may partly be explained by variations in surface wetness. Differences in boundary layer conductance between chamber and ambient, which under certain conditions may significantly influence the validity of the chamber as a test system, were observed.

Impact of ozone and reduced water supply on the biomass accumulation of Norway spruce saplings

Norway spruce saplings [Picea abies (L.) Karst.] were exposed during four growing seasons to two different ozone treatments in open-top chambers: charcoal filtered air (CF), and non-filtered air with extra ozone (NF+, 1.4xambient concentrations). Within each ozone treatment the saplings were either kept well watered or treated with a 7-8 week period with reduced water supply each growing season. The total biomass of the trees was measured in April and September during each of the last three growing seasons. NF+ significantly reduced the total biomass accumulation of Norway spruce saplings during the fourth growing season. No interaction between ozone and reduced water supply could be detected. The magnitude of the ozone impact after 4 years of exposure was an 8% reduction of the total plant biomass and a 1.5% reduction of the RGR. The reduced water supply reduced the total biomass 29% and the RGR 12%.

Yield and quality of spring barley, Hordeum vulgare L., exposed to different concentrations of ozone in open-top chambers

Abstract Spring barley ( Hordeum vulgare L., cv. ‘Lina’) was exposed to different concentrations of ozone in open-top chambers (OTCs) for 6 weeks following anthesis at a site located in south-west Sweden during the summer of 1989. The chambers were placed in a field of commercially grown barley. The treatments were charcoal-filtered air (CF), non-filtered air (NF) and non-filtered air plus extra ozone (NF +). Presence of the OTCs reduced grain yield, number of ears per unit area, and 1000-grain weight, probably due to increased drought during the warm and dry weather in the summer of 1989. The chamber also increased the crude protein content of grain. These effects were, however, not statistically significant. Grain yield was not affected by 7 h day −1 seasonal mean ozone concentrations up to 45 nl l −1 (24 h seasonal mean = 22 nl l −1 ) compared to charcoal-filtered air. It is concluded that barley is likely to be less sensitive to ozone than wheat. The possible role of differences in the process of grain filling between the two species for the differences in ozone sensitivity is discussed.