| 1. |
- Broberg, Malin, 1989, et al.
(author)
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Effects of elevated CO2 on wheat yield: Non-linear response and relation to site productivity
- 2019
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In: Agronomy. - : MDPI AG. - 2073-4395. ; 9:5
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Journal article (peer-reviewed)abstract
- © 2019 by the authors. Elevated carbon dioxide (eCO 2 ) is well known to stimulate plant photosynthesis and growth. Elevated carbon dioxide’s effects on crop yields are of particular interest due to concerns for future food security. We compiled experimental data where field-grown wheat (Triticum aestivum Linnaeus) was exposed to different CO 2 concentrations. Yield and yield components were analyzed by meta-analysis to estimate average effects, and response functions derived to assess effect size in relation to CO 2 concentration. Grain yield increased by 26% under eCO 2 (average ambient concentration of 372 ppm and elevated 605 ppm), mainly due to the increase in grain number. The response function for grain yield with CO 2 concentration strongly suggests a non-linear response, where yield stimulation levels off at ~600 ppm. This was supported by the meta-analysis, which did not indicate any significant difference in yield stimulation in wheat grown at 456–600 ppm compared to 601–750 ppm. Yield response to eCO 2 was independent of fumigation technique and rooting environment, but clearly related to site productivity, where relative CO 2 yield stimulation was stronger in low productive systems. The non-linear yield response, saturating at a relatively modest elevation of CO 2 , was of large importance for crop modelling and assessments of future food production under rising CO 2
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| 2. |
- Broberg, Malin, 1989, et al.
(author)
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Harvest index and remobilization of 13 elements during wheat grain filling: Experiences from ozone experiments in China and Sweden
- 2021
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In: Field Crops Research. - : Elsevier BV. - 0378-4290. ; 271:15 September 2021
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Journal article (peer-reviewed)abstract
- Wheat efficiently remobilize and allocate a large fraction of aboveground biomass and nutrients into their grains during maturation. This senescence process has been streamlined through crop breeding, which lead to increasing harvest index (HI) for biomass. With field data from two ozone exposure experiments, we derived HI for 13 elements, both nutrients and non-essential, to determine how efficiently they are allocated into the wheat grain in two different agro-ecological environments (Sweden and China) and under different ozone exposure regimes. Element HI ranged from 10 to 90 %, with highest rates for P, N and Zn (90 %, 80 % and 70 %, respectively), while HI was low for the non-mobile elements Ba, Sr and Ca (<10 %). HI for biomass was about 50 %, and the non-essential and toxic element Cd was in the same range (∼40 %). Overall element HI was very similar in Chinese and Swedish wheat cultivars. This was also the case when comparing the two Chinese genotypes. We conclude that element HI for wheat crops are highly element specific and not strongly dependent on site or cultivar. Ozone exposure significantly reduced HI for both macronutrients (Ca, K, Mg, N, P) and micronutrients (Cu, Mn, Mo, Zn), but also for Cd, while there was no ozone effect on the total aboveground pool for any element except P and Ba. Consequently, the reduction in grain element yield induced by elevated ozone, observed in previous studies, can be explained by lower remobilization rates rather than reduced total uptake. Our results provide new insights of nutrient use efficiency in wheat crops in general and under ozone exposure, which can be implemented in crop modelling and also useful for breeding strategies aiming to improve the nutritional value of food crops.
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| 3. |
- Broberg, Malin, 1989, et al.
(author)
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Ozone effects on wheat grain quality - A summary
- 2015
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In: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 197, s. 203-213
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Büker, P, et al.
(author)
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New flux based doseeresponse relationships for ozone for European forest tree species
- 2015
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In: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 206, s. 163-174
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Journal article (peer-reviewed)abstract
- To derive O3 doseeresponse relationships (DRR) for five European forest trees species and broadleaf deciduous and needleleaf tree plant functional types (PFTs), phytotoxic O3 doses (PODy) were related to biomass reductions. PODy was calculated using a stomatal flux model with a range of cut-off thresholds (y) indicative of varying detoxification capacities. Linear regression analysis showed that DRR for PFT and individual tree species differed in their robustness. A simplified parameterisation of the flux model was tested and showed that for most non-Mediterranean tree species, this simplified model led to similarly robust DRR as compared to a species- and climate region-specific parameterisation. Experimentally induced soil water stress was not found to substantially reduce PODy, mainly due to the short duration of soil water stress periods. This study validates the stomatal O3 flux concept and represents a step forward in predicting O3 damage to forests in a spatially and temporally varying climate.
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| 5. |
- Feng, Zhaozhong, et al.
(author)
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A stomatal ozone flux–response relationship to assess ozone-induced yield loss of winter wheat in subtropical China
- 2012
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In: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 164, s. 16-23
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Journal article (peer-reviewed)abstract
- Stomatal ozone flux and flux–response relationships were derived for winter wheat (Triticum aestivum L.) grown under fully open-air ozone fumigation. A stomatal conductance (gsto) model developed for wheat in Europe was re-parameterized. Compared to European model parameterizations, the main changes were that the VPD and radiation response functions were made less and more restrictive, respectively, and that the temperature function was omitted. The re-parameterized gsto model performed well with an r2 value of 0.76. The slope and intercept of the regression between observed and predicted gsto were not significantly different from 1 to 0, respectively. An ozone uptake threshold of 12 nmol m−2 s−1 was judged most reasonable for the wheat flux–response relationship in subtropical China. Judging from both flux- and concentration-based relationships, the cultivars investigated seem to be more sensitive to ozone than European cultivars. The new flux–response relationship can be applied to ozone risk assessment in subtropical regions.
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| 6. |
- Feng, Zhaozhong, et al.
(author)
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A unifying explanation for variation in ozone sensitivity among woody plants
- 2018
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:1, s. 78-84
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Journal article (peer-reviewed)abstract
- Tropospheric ozone is considered the most detrimental air pollutant for vegetation at the global scale, with negative consequences for both provisioning and climate regulating ecosystem services. In spite of recent developments in ozone exposure metrics, from a concentration-based to a more physiologically relevant stomatal flux-based index, large-scale ozone risk assessment is still complicated by a large and unexplained variation in ozone sensitivity among tree species. Here, we explored whether the variation in ozone sensitivity among woody species can be linked to interspecific variation in leaf morphology. We found that ozone tolerance at the leaf level was closely linked to leaf dry mass per unit leaf area (LMA) and that whole-tree biomass reductions were more strongly related to stomatal flux per unit leaf mass (r 2 =0.56) than to stomatal flux per unit leaf area (r 2 =0.42). Furthermore, the interspecific variation in slopes of ozone flux–response relationships was considerably lower when expressed on a leaf mass basis (coefficient of variation, CV=36%) than when expressed on a leaf area basis (CV=66%), and relationships for broadleaf and needle-leaf species converged when using the mass-based index. These results show that much of the variation in ozone sensitivity among woody plants can be explained by interspecific variation in LMA and that large-scale ozone impact assessment could be greatly improved by considering this well-known and easily measured leaf trait.
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| 7. |
- Feng, Zhaozhong, et al.
(author)
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Constraints to nitrogen acquisition of terrestrial plants under elevated CO2
- 2015
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 21:8, s. 3152-3168
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Journal article (peer-reviewed)abstract
- A key part of the uncertainty in terrestrial feedbacks on climate change is related to how and to what extent nitrogen (N) availability constrains the stimulation of terrestrial productivity by elevated CO2 (eCO2), and whether or not this constraint will become stronger over time. We explored the ecosystem-scale relationship between responses of plant productivity and N acquisition to eCO2 in Free-Air CO2 Enrichment (FACE) experiments in grassland, cropland and forest ecosystems and found that: (i) In all three ecosystem types, this relationship was positive, linear, and strong (r2 = 0.68), but exhibited a negative intercept such that plant N acquisition was decreased by 10% when eCO2 caused neutral or modest changes in productivity. Since the ecosystems were markedly N limited, plants with minimal productivity responses to eCO2 likely acquired less N than ambient CO2-grown counterparts because access was decreased, and not because demand was lower. (ii) Plant N concentration was lower under eCO2, and this decrease was independent of the presence or magnitude of eCO2-induced productivity enhancement, refuting the long-held hypothesis that this effect results from growth dilution. (iii) Effects of eCO2 on productivity and N acquisition did not diminish over time, while the typical eCO2-induced decrease in plant N concentration did. Our results suggest that, at the decennial time scale covered by FACE studies, N limitation of eCO2-induced terrestrial productivity enhancement is associated with negative effects of eCO2 on plant N acquisition rather than with growth dilution of plant N or processes leading to progressive N limitation.
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| 8. |
- Fleming, Zoe L., et al.
(author)
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Tropospheric Ozone Assessment Report: Present-day ozone distribution and trends relevant to human health
- 2018
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In: Elementa. - : University of California Press. - 2325-1026. ; 6
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Journal article (peer-reviewed)abstract
- This study quantifies the present-day global and regional distributions (2010-2014) and trends (2000-2014) for five ozone metrics relevant for short-term and long-term human exposure. These metrics, calculated by the Tropospheric Ozone Assessment Report, are: 4th highest daily maximum 8-hour ozone (4MDA8); number of days with MDA8 > 70 ppb (NDGT70), SOMO35 (annual Sum of Ozone Means Over 35 ppb) and two seasonally averaged metrics (3MMDA1; AVGMDA8). These metrics were explored at ozone monitoring sites worldwide, which were classified as urban or non-urban based on population and nighttime lights data. Present-day distributions of 4MDA8 and NDGT70, determined predominantly by peak values, are similar with highest levels in western North America, southern Europe and East Asia. For the other three metrics, distributions are similar with North-South gradients more prominent across Europe and Japan. Between 2000 and 2014, significant negative trends in 4MDA8 and NDGT70 occur at most US and some European sites. In contrast, significant positive trends are found at many sites in South Korea and Hong Kong, with mixed trends across Japan. The other three metrics have similar, negative trends for many non-urban North American and some European and Japanese sites, and positive trends across much of East Asia. Globally, metrics at many sites exhibit non-significant trends. At 59% of all sites there is a common direction and significance in the trend across all five metrics, whilst 4MDA8 and NDGT70 have a common trend at similar to 80% of all sites. Sensitivity analysis shows AVGMDA8 trends differ with averaging period (warm season or annual). Trends are unchanged at many sites when a 1995-2014 period is used; although fewer sites exhibit non-significant trends. Over the longer period 1970-2014, most Japanese sites exhibit positive 4MDA8/SOMO35 trends. Insufficient data exist to characterize ozone trends for the rest of Asia and other world regions.
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| 9. |
- Li, Pin, et al.
(author)
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Combining carbon and oxygen isotopic signatures to identify ozone-induced declines in tree water use efficiency
- 2021
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In: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 41:12, s. 2234-2244
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Journal article (peer-reviewed)abstract
- Ground-level ozone (O3) pollution affects the plant carbon and water balance, but the relative contributions of impaired photosynthesis and the loss of stomatal functioning to the O3-induced reductions in water use efficiency (WUE) remain unclear. We combined the leaf stable dual isotopic signatures of carbon (δ13C) and oxygen (δ18O) with related instantaneous gas exchange performance to determine the effects of O3 dose on the net photosynthetic rate (An), stomatal conductance (gs) and intrinsic WUE (iWUE = An/gs) in four tree species (one being a hybrid) exposed to five O3 levels. The iWUE declined for each step increase in O3 level, reflecting progressive loss of the coupling between leaf carbon gain and water loss. In ambient compared to charcoal-filtered air, the decreased iWUE was associated with reductions in both An and gs (i.e., decreased δ13C and increased δ18O). In elevated O3 treatments, however, the iWUE declines were caused by reduced An at constant or increased gs. The results show that the dual isotope approach provides a robust way to gather time-integrated information on how O3 pollution affects leaf gas exchange. Our study highlights that O3-induced decoupling between photosynthesis and stomatal regulation causes large and progressive declines in the WUE of forest trees, demonstrating the need for incorporating this, hitherto unaccounted, effect into vegetation models.
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| 10. |
- Mills, Gina, 1959, et al.
(author)
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Closing the global ozone yield gap: Quantification and cobenefits for multistress tolerance
- 2018
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:10, s. 4869-4893
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Journal article (peer-reviewed)abstract
- Increasing both crop productivity and the tolerance of crops to abiotic and biotic stresses is a major challenge for global food security in our rapidly changing climate. For the first time, we show how the spatial variation and severity of tropospheric ozone effects on yield compare with effects of other stresses on a global scale, and discuss mitigating actions against the negative effects of ozone. We show that the sensitivity to ozone declines in the order soybean>wheat>maize>rice, with genotypic variation in response being most pronounced for soybean and rice. Based on stomatal uptake, we estimate that ozone (mean of 2010–2012) reduces global yield annually by 12.4%, 7.1%, 4.4% and 6.1% for soybean, wheat, rice and maize, respectively (the “ozone yield gaps”), adding up to 227Tg of lost yield. Our modelling shows that the highest ozone-induced production losses for soybean are in North and South America whilst for wheat they are in India and China, for rice in parts of India, Bangladesh, China and Indonesia, and for maize in China and the United States. Crucially, we also show that the same areas are often also at risk of high losses from pests and diseases, heat stress and to a lesser extent aridity and nutrient stress. In a solution-focussed analysis of these results, we provide a crop ideotype with tolerance of multiple stresses (including ozone) and describe how ozone effects could be included in crop breeding programmes. We also discuss altered crop management approaches that could be applied to reduce ozone impacts in the shorter term. Given the severity of ozone effects on staple food crops in areas of the world that are also challenged by other stresses, we recommend increased attention to the benefits that could be gained from addressing the ozone yield gap.
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