| At present, the ground-level ozone (O3) concentration exceeds the damage threshold (40 nL L-1) of the sensitive crops in many parts of the world and causes visible damage to the plants. Wheat is considered as one of the crops showing moderate sensitivity to ozone stress. Ozone stress significantly decreased grain yield in wheat, but the grain quality and plant lodging resistance in response to ozone stress was rarely reported, and whether ozone impacts vary within different cultivars is unclear. This study was conducted in 2014 and 2015 by using a solar-illuminated gas fumigation platform. Four wheat cultivars (Chokwang, Clark, Ning 7840, Qingzi 1 hao) were grown at two ozone levels:control (CK, about 10 nL L-1) and elevated O3 concentration (O3,100 nL L-1). The responses of different wheat cultivars to ozone stress were assessed by yield formation, dry matter production and distribution, leaf physiological indexes, nutrient uptake, grain quality and lodging resistance. The objective of this study was to provide scientific evidence for minimizing the ozone damage to wheat in the future high ozone conditions. Results showed as follows:1. Average across all tested cultivars, ozone stress reduced grain yield by 58%, and the grain yield of Chokwang, Clark, Ning 7840 and Qingzi 1 hao was decreased by 49%,51%,66% and 65%, respectively. The yield loss caused by ozone stress was mainly related to the reduction in grain number per panicle (-38%) and 1000-grain weight (-47%), while no significantiy change was observed in panicle numble per unit area. The ozone by cultivar interaction on the final yield, grain number per panicle and 1000-grain weight reached 0.05,0.1 and 0.01 level, respectively.2. Compared to the control, ozone stress significantly decreased above-ground biomass of four wheat cultivars at grain maturity by 28% in average, and above-ground biomass of Chokwang, Clark, Ning 7840 and Qingzi 1 hao was decreased by 18%,24%,38% and 34%, respectively. Ozone stress significantly increased leaf biomass (+22%) but decreased panicle biomass sharply (-50%), and had little effect on the stem biomass. From the aspect of material distribution, the ratio of leaf and stem to above-ground dry weight were significantly increased by 71% and 46%, respectively, but the ratio of panicle to above-ground dry weight were significantly decreased by 44%. In most cases, significant interactions between ozone and wheat cultivars were detected for above-mentioned parameters.3. The physiological characteristics of top three leaves of Chokwang, Clark and Ning 7840 in different growth periods showed that, leaf bronning score (LBS) of the first, second and third leaf from the top under ozone stress was 4.2,7.0 and 7.9, respectively. Ning 7840 showed highest LBS in all top three leaves among all tested cultivars. The SPAD value and the total chlorophyll content of the top three leaves of wheat were decreased by 38-80% and 22-77% under the ozone stress, and the decreasement increased gradually with leaf position. In contrast, the MDA and AsA content of the top three leaves of wheat were increased by 25-78% and 20-27% under the ozone stress. Except LBS, significant ozone by cultivar interactions were detected on most leaf traits of the top three leaves of wheat.4. The concentrations of N, P, K, Ca, Mg, Cu, Fe, Mn and Zn in different organs of the tested varieties were measured. Ozone stress increased mineral element concentrations in leaf, stem and grain by 3-103% ,3-68% and 9-33%, respectively. Ozone stress decreased mineral element accumulation in grains by 51-60% in average, but increased that in leaves and stems by 28-145% and 7-74%, respectively. The proportion of element accumulation in different organs relative to the total accumulation of plants showed that, ozone stress reduced the percentage of elements distributed in grains by 41-70%, but the distribution ratio of leaves (except Ca) and the stem (except Mg) increased by 24-226% and 5-127%, respectively. There were significant interactions between ozone and wheat cultivars for most of the above-mentioned parameters.5. Ozone stress reduced the grain volume of four wheat cultivars (-30%), which was mainly related to the reduction of grain width (-16%) and the thickness (-17%), while the decrease of grain length was relatively small (-8%). Ozone stress increased grain protein concentration by 21%, which was associated with a substantial increase in the concentration of globulin (+35%) and prolamin (+41%), while the albumin and globulin concentration did not change significantly. Under the ozone stress, total amino acids, essential amino acids and non essential amino acids increased by an average of 25-27%.The decrease in starch content (-9%) was mainly associated the strong decrease in amylopectin (-12%) but the increase in amylase content (+6%). Significant ozone by cultivar interactions were observed for the length, width, and thickness of grain, content of protein and amino acids.6. Ozone stress significantiy decreased the hardness and flour extractiom rate by 18% and 10% in average, but the wet gluten content and sedimentation value significantiy increased by 18% and 17%, respectively.Under the ozone stress, the peak viscosity, cold viscosity, final viscosity and setback in the RVA profile were significantiy increased by 10%,18%,17% and 13%, but the breakdown value was significantiy reduced by 9%. There were significant interactions between ozone and wheat cultivars for flour extractiom rate, wet gluten content, sedimentation value and peak time.7. The impacts of ozone stress on lodging index of basal internodes (the fifith, forth and third internodes form the top) varied with different cultivars:Chokwang and Clark were increased by 23-55% and 11-26%, respectively; while Ning 7840 and Qingzi 1 hao showed the opposite trend, with the largest decline reached 22%. Under the ozone stress, breaking-resistant strength, bending moment, cross-sectional area, fresh weight, dry weight and dry weight per unit length decreased on average by 47%,47%,12%,44%,29% and 30%, respectively, but there was no significant effect on the length of the internode. In most cases, there were significant interactions between ozone and wheat cultivars on the lodging related traits of basal internodes. |
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