Species-specific responses to ozone and drought in six deciduous trees

Saplings of alder (Alnus glutinosa), birch (Betula pendula), hazel (Corylus avellana), beech (Fagus sylvatica), ash (Fraxinus excelsior) and oak (Quercus robur) were exposed to five episodic ozone regimes in solardomes, with treatment means between 16 and 72 ppb. All trees were kept fully watered for the first five weeks of exposure, after which half the trees continued to be well-watered, whereas the other half were subjected to a moderate drought and received approximately 45% of the amount of water. Species-specific reductions in growth in response to both ozone and drought were found, which could result in reduced potential carbon sequestration in future ozone climates. In well watered conditions the ozone treatments resulted in total biomass reductions for oak (18%), alder (16%), beech (15%), ash (14%), birch (14%) and hazel (7%) in the 72 ppb compared to the 32 ppb treatment. For beech there was a reduction in growth in response to ozone in the well watered treatment, but an increase in growth in response to ozone in the drought treatment, assumed to result from changes in hormonal signalling. For alder, in addition to a decrease in root biomass there was reduced biomass of root nodules with high compared to low ozone for both drought treated and well-watered trees. There was also a large reduction in the biomass of nodules from drought trees compared to well-watered. It is therefore possible that changes in the nitrogen dynamics of alder could occur due to reduced nodulation in both drought and elevated ozone conditions

Ozone pollution affects flower numbers and timing in a simulated BAP priority calcareous grassland community

Mesocosms representing the BAP Priority habitat ‘Calcareous Grassland’ were exposed to eight ozone profiles for twelve-weeks in two consecutive years. Half of the mesocosms received a reduced watering regime during the exposure periods. Numbers and timing of flowering in the second exposure period were related to ozone concentration and phytotoxic ozone dose (accumulated stomatal flux). For Lotus corniculatus, ozone accelerated the timing of the maximum number of flowers. An increase in mean ozone concentration from 30 ppb to 70 ppb corresponded with an advance in the timing of maximum flowering by six days. A significant reduction in flower numbers with increasing ozone was found for Campanula rotundifolia and Scabiosa columbaria and the relationship with ozone was stronger for those that were well-watered than for those with reduced watering. These changes in flowering timing and numbers could have large ecological impacts, affecting plant pollination and the food supply of nectar feeding insects

Ozone Tolerance Found in Aegilops tauschii and Primary Synthetic Hexaploid Wheat

Modern wheat cultivars are increasingly sensitive to ground level ozone, with 7–10% mean yield reductions in the northern hemisphere. In this study, three of the genome donors of bread wheat, Triticum urartu (AA), T. dicoccoides (AABB), and Aegilops tauschii (DD) along with a modern wheat cultivar (T. aestivum ‘Skyfall’), a 1970s cultivar (T. aestivum ‘Maris Dove’), and a line of primary Synthetic Hexaploid Wheat were grown in 6 L pots of sandy loam soil in solardomes (Bangor, North Wales) and exposed to low (30 ppb), medium (55 ppb), and high (110 ppb) levels of ozone over 3 months. Measurements were made at harvest of shoot biomass and grain yield. Ae. tauschii appeared ozone tolerant with no significant effects of ozone on shoot biomass, seed head biomass, or 1000 grain + husk weight even under high ozone levels. In comparison, T. urartu had a significant reduction in 1000 grain + husk weight, especially under high ozone (−26%). The older cultivar, ‘Maris Dove’, had a significant reduction in seed head biomass (−9%) and 1000 grain weight (−11%) but was less sensitive than the more recent cultivar ‘Skyfall’, which had a highly significant reduction in its seed head biomass (−21%) and 1000 grain weight (−27%) under high ozone. Notably, the line of primary Synthetic Hexaploid Wheat was ozone tolerant, with no effect on total seed head biomass (−1%) and only a 5% reduction in 1000 grain weight under high ozone levels. The potential use of synthetic wheat in breeding ozone tolerant wheat is discussed

Ozone dose-response relationships for tropical crops reveal potential threat to legume and wheat production, but not to millets

The tropical-grown crops common bean (Phaseolus vulgaris), mung bean (Vigna radiate), cowpea (Vigna unguiculata), pearl millet (Pennisetum glaucum), finger millet (Eleusine coracana), amaranth (Amaranthus hypochonriacus), sorghum (Sorghum bicolour) and wheat (Triticum aestivum) were exposed to different concentrations of the air pollutant ozone in experimental Solardome facilities. The plants were exposed to ozone treatments for between one and four months, depending on the species. There was a large decrease in yield of protein-rich beans and cowpeas with increasing ozone exposure, partly attributable to a reduction in individual bean/pea weight. Size of individual grains was also reduced with increasing ozone for African varieties of wheat. In contrast, the yield of amaranth, pearl millet and finger millet (all C4 species) was not sensitive to increasing ozone concentrations and there was some evidence of an increase in weight of individual seedheads with increasing ozone for finger millet. Sorghum did not reach yield, but was not sensitive to ozone based on changes in biomass. Dose-response relationships for these crop species demonstrate that tropospheric ozone pollution could reduce yield of important crops, particularly legumes, in tropical regions such as sub-Saharan Africa

How do increasing background concentrations of tropospheric ozone affect peatland plant growth and carbon gas exchange?

In this study we have demonstrated that plants originating from upland peat bogs are sensitive to increasing background concentrations of ozone. Peatland mesocosms from an upland peat bog in North Wales, UK were exposed to eight levels of elevated background ozone in solardomes for 4 months from May to August, with 24 h mean ozone concentrations ranging from 16 to 94 ppb and cumulative AOT024hr ranging from 45.98 ppm h to 259.63 ppm h. Our results show that plant senescence increased with increasing exposure to ozone, although there was no significant effect of increasing ozone on plant biomass. Assessments of carbon dioxide and methane fluxes from the mesocosms suggests that there was no change in carbon dioxide fluxes over the 4 month exposure period but that methane fluxes increased as cumulative ozone exposure increased to a maximum AOT 024hr of approximately 120 ppm h and then decreased as cumulative ozone exposure increased further

Substantial yield reduction in sweet potato due to tropospheric ozone, the dose-response function

Impacts of tropospheric ozone on sweet potato (Ipomoea batatas) are poorly understood despite being a staple food grown in locations deemed at risk from ozone pollution. Three varieties of sweet potato were exposed to ozone treatments (peaks of: 30 (Low), 80 (Medium), and 110 (High) ppb) using heated solardomes. Weekly measurements of stomatal conductance (gs) and chlorophyll content (CI) were used to determine physiological responses, along with final yield. gs and CI were reduced with increasing ozone exposure, but effects were partially masked due to elevated leaf senescence and turnover. Yield for the Erato orange and Murasaki varieties was reduced by ∼40% and ∼50% (Medium and High ozone treatments, respectively, vs Low) whereas Beauregard yield was reduced by 58% in both. The DO3SE (Deposition of Ozone for Stomatal Exchange) model was parameterized for gs in response to light, temperature, vapour pressure deficit and soil water potential. Clear responses of gs to the environmental parameters were found. Yield reductions were correlated with both concentration based AOT40 (accumulated ozone above a threshold of 40 ppb) and flux based POD6 (accumulated stomatal flux of ozone above a threshold of 6 nmol m− 2 s− 1) metrics (R2 0.66 p = 0.01; and R2 0.44 p = 0.05, respectively). A critical level estimate of a POD6 of 3 (mmol m−2 Projected Leaf Area−1) was obtained using the relationship. This study showed that sweet potato yield was reduced by ozone pollution, and that stomatal conductance and chlorophyll content were also affected. Results from this study can improve model predictions of ozone impacts on sweet potato together with associated ozone risk assessments for tropical countries

Chronic ozone exposure affects nitrogen remobilization in wheat at key growth stages

The interaction between nitrogen storage and translocation, senescence, and late phase photosynthesis is critical to the post-anthesis grain fill period in wheat, but ozone's effect on nitrogen dynamics within the wheat plant is not well understood. This study used solardomes to expose a widely grown elite spring wheat cultivar, cv. Skyfall, to four levels of ozone (30 ppb, 45 ppb, 70 ppb, 85 ppb) for 11 weeks, with two levels of nitrogen fertilization, 140 kg ha−1 and 160 kg ha−1, the higher rate including an additional 20 kg N ha−1 at anthesis. Chronic ozone exposure triggered earlier senescence in the 4th, 3rd and 2nd leaves but not the flag leaf, with a similar pattern of reduced chlorophyll content in the lower, older leaf cohorts, which started before senescence became visible. At anthesis there was no evidence of any effect of ozone on nitrogen storage in upper plant parts. However, high ozone increased levels of residual nitrogen found within plant parts at harvest, with concomitant reductions in C:N ratios and Nitrogen Remobilization Efficiency. Extra nitrogen fertilization applied at anthesis appeared to ameliorate the effect of ozone on nitrogen content and nitrogen translocation. The application of 15N ammonium nitrate at anthesis confirmed that the majority of post-anthesis nitrogen uptake had been translocated to the ear/grain by harvest, with no effect of ozone on the translocation of nitrogen around the plant. These data can inform future modelling of ozone's effect on nitrogen dynamics and global wheat yields