Nitrogen application is required to realize wheat yield stimulation by elevated CO2 but will not remove the CO2 -induced reduction in grain protein concentration.

Elevated CO2 (eCO2 ) generally promotes increased grain yield (GY) and decreased grain protein concentration (GPC), but the extent to which these effects depend on the magnitude of fertilization remains unclear. We collected data on the eCO2 responses of GY, GPC and grain protein yield and their relationships with nitrogen (N) application rates across experimental data covering 11 field grown wheat (Triticum aestivum) cultivars studied in eight countries on four continents. The eCO2 -induced stimulation of GY increased with N application rates up to ~200 kg/ha. At higher N application, stimulation of GY by eCO2 stagnated or even declined. This was valid both when the yield stimulation was expressed as the total effect and using per ppm CO2 scaling. GPC was decreased by on average 7% under eCO2 and the magnitude of this effect did not depend on N application rate. The net effect of responses on GY and protein concentration was that eCO2 typically increased and decreased grain protein yield at N application rates below and above ~100 kg/ha respectively. We conclude that a negative effect on wheat GPC seems inevitable under eCO2 and that substantial N application rates may be required to sustain wheat protein yields in a world with rising CO2 .

Ozone impact on wheat in Europe, Asia and North America - A comparison.

Data from experiments where field-grown wheat was exposed to ozone were collated in order to compare the effects in Europe, Asia and North America using dose-response regression. In addition to grain yield, average grain mass and harvest index were included to reflect the influence of ozone on the crop growth pattern. In order to include as many experiments as possible, daytime average ozone concentration was used as the ozone exposure index, but AOT40, estimated from average ozone concentrations, was also used to compare the performance of the two exposure metrics. The response to ozone differed significantly between the continents only for grain yield when using AOT40 as the exposure index. North American wheat was less sensitive than European and Asian that responded similarly. The variation in responses across all three continents was smallest for harvest index, followed by grain mass and grain yield. The highly consistent effect on harvest index shows that not only effects on biomass accumulation, but also on the partitioning of biomass, are important for the ozone-induced grain yield loss in wheat. The average duration of daily ozone exposure was longer in European experiments compared to North American and Asian. It cannot be excluded that this contributed to the indicated higher ozone sensitivity in European wheat in relation to North American. The main conclusions from this study are that on the average the response of wheat to ozone was lower for the older North American experiments and that the ozone response of the growth pattern reflected by grain mass and harvest index did not differ between continents.

Crop quality under rising atmospheric CO2.

Crops grown under elevated CO2 (eCO2) typically exhibit enhanced yields but at the same time decreased nutritional quality. The latter effect has often been explained as a growth dilution phenomenon, but this cannot be the only process involved since crop nutrient concentrations are decreased also when production is unaffected by eCO2. We review the current knowledge on eCO2 effects on crop nutritional quality with focus on the current understanding of the possible mechanisms and processes causing these effects. Emphasis is on crop nitrogen (N) and protein concentrations but effects on other nutrients and how they compare with those on N are also covered.

Current surface ozone concentrations significantly decrease wheat growth, yield and quality.

Tropospheric ozone is known to adversely affect crops and other vegetation. Most studies have focussed on the effects of elevated ozone levels vs. present ambient. We investigated the effect of present ambient surface ozone (O3) concentrations vs. preindustrial on a range of agronomically important response variables in field-grown wheat, using results from 33 experiments (representing 9 countries, 3 continents, 17 cultivars plus one set of 4 cultivars) having both charcoal filtered (CF) and non-filtered (NF) air treatments. Average filtration efficiency was 62%, reducing the O3 concentration from 35.6±10.6SDppb in NF to 13.7±8.8SDppb in CF. Average CF concentrations were in the range of levels believed to represent pre-industrial conditions, while NF concentrations were 7% lower than in the ambient air at plant height on the experimental sites. NF had significant (p<0.05) negative effects compared to CF on grain yield (-8.4%), grain mass (-3.7%), harvest index (-2.4%), total above-ground biomass (-5.4%), starch concentration (-3.0%), starch yield (-10.9%), and protein yield (-6.2%). No significant effect was found for grain number and protein concentration. There was a significant relationship between the effect of filtration on grain yield and the difference in O3 concentration between NF and CF treatments. The average yield loss per ppb O3 removed was 0.38% and did not systematically vary with year of experiment (ranging from 1982 to 2010) or with the average O3 level in the experiments. Although there are many differences among the field experiments included in this meta-analysis (e.g. genotype, degree of O3 pollution of the site and year, nutrient and soil condition, filtration efficiency), our study clearly shows that there is a consistent and significant effect of present ambient O3 exposure on a range of important response variables in wheat, the most strongly affected being starch yield.

Fertilizer efficiency in wheat is reduced by ozone pollution.

Inefficient use of fertilizers by crops increases the risk of nutrient leaching from agro-ecosystems, resulting in economic loss and environmental contamination. We investigated how ground-level ozone affects the efficiency by which wheat used applied nitrogen (N) fertilizer to produce grain protein (NEP, N efficiency with respect to protein yield) and grain yield (NEY, N efficiency with respect to grain yield) across a large number of open-top chamber field experiments. Our results show significant negative ozone effects on NEP and NEY, both for a larger data set obtained from data mining (21 experiments, 70 treatments), and a subset of data for which stomatal ozone flux estimates were available (7 experiments, 22 treatments). For one experiment, we report new data on N content of different above-ground plant fractions as well as grain K and P content. Our analysis of the combined dataset demonstrates that the grain yield return for a certain investment in N fertilizer is reduced by ozone. Results from the experiment with more detailed data further show that translocation of accumulated N from straw and leaves to grains is significantly and negatively affected by ozone, and that ozone decreases fertilizer efficiency also for K and P. As a result of lower N fertilization efficiency, ozone causes a risk of increased N losses from agroecosystems, e.g. through nitrate leaching and nitrous oxide emissions, a hitherto neglected negative effect of ozone. This impact of ozone on the N cycle implies that society is facing a dilemma where it either (i) accepts increased N pollution and counteracts ozone-induced yield reductions by increasing fertilization or (ii) counteracts N pollution under elevated ozone by reducing fertilization, accepting further yield loss adding to the direct effect of ozone on yield.

Ozone effects on wheat grain quality - a summary.

We synthesized the effects of ozone on wheat quality based on 42 experiments performed in Asia, Europe and North America. Data were analysed using meta-analysis and by deriving response functions between observed effects and daytime ozone concentration. There was a strong negative effect on 1000-grain weight and weaker but significant negative effects on starch concentration and volume weight. For protein and several nutritionally important minerals (K, Mg, Ca, P, Zn, Mn, Cu) concentration was significantly increased, but yields were significantly decreased by ozone. For other minerals (Fe, S, Na) effects were not significant or results inconclusive. The concentration and yield of potentially toxic Cd were negatively affected by ozone. Some baking properties (Zeleny value, Hagberg falling number) were positively influenced by ozone. Effects were similar in different exposure systems and for spring and winter wheat. Ozone effects on quality should be considered in future assessments of food security/safety.