| In recent years, increasing tropospheric ozone concentration changes living environment of crops, such as rice, and has already posed a threat to food security. Rice is considered as one of moderate sensitive crops to ozone stress. What are the distinguishing features in growth, yield and lodging resistance of rice with different ozone sensitivity? And which indexes are most suitable for evaluating rice sensitivity to ozone stress? With the intention to answer these questions, we conducted a solar-illuminated gas fumigation platform,23 rice cultivars or lines were grown at two ozone treatments:indoor control (C-O3, about 10 nL·L-1) and elevated O3 (E-O3,100 nL·L1). Based on the decrease in above-ground biomass under high ozone concentration, these rice varieties were first clustered into 3 types (in low to high order A, B and C) by the MinSSw (dynamic clustering method-minimum sum of squares with in groups) method. Then the responses of rice types with different ozone sensitivity were investigated, in particular rice growth and development, yield formation, dry matter production, nutrient uptake and lodging resistance, and the relationship between these indexes and above-ground biomass was also studied. Results showed as follows:1. Compared to the control, ozone stress decreased above-ground biomass of three rice types A, B and C at grain maturity by 9%,38% and 52%, respectively, but significant treatment effects were only observed on B and C. A week interaction (p=0.07) was detected between ozone and rice types.2. Ozone stress had no significant effect on plant height at 16 days after treatment (DAT), but significantly reduced plant height at 30,44,58 DAT. The ozone-induced reduction in plant height was increased gradually with time, and different rice types showed the same trend.3. The tiller number per hill appeared a downward trend under ozone stress at 16,30,44,58 DAT. Ozone stress decreased tiller number of rice types A, B and C by 3%～11%,14%～25% and 11%～14% on an average of different growth periods, respectively. Ozone stress had no significant effect on tiller number of rice type A at all growth periods, but significantly reduced those of B and C. Weak interactions were detected between ozone and rice types for tiller number at all growth periods.4. Ozone stress decreased the SPAD value of the first leaf from the top of rice at each measurement point during the whole growth period, and the decline was increased gradually with time. The SPAD values of the second and third leaves from the top showed a similar trend, but the ozone-induced reduction was significantly increased with the decline of leaf position. Ozone stress significantly reduced the SPAD value of the first, second and third leaf from the top by 10%,19% and 32%, respectively, on an average of all measurement points during the whole growth period. There was no interaction between ozone and rice types for the SPAD value of leaf at different leaf position or growth period.5. Compared to the control, ozone stress slightly increased leaf dry weight of rice type A, but decreased leaf dry matter of rice types B and C by 11% and 25%. Ozone stress decreased stem dry weight of rice types A, B and C by 26%,41% and 57%; and decreased panicle weight of A, B and C by 34%,59% and 62%, respectively. Ozone stress changed the matter distribution within rice plants, the ratio of leaf to above-ground dry weight of rice types A, B and C were increased by 40%,46% and 56%, but the ratio of stem to above-ground dry weight were decreased by 8%,4% and 12%, respectively. Ozone stress also decreased the ratio of panicle to above-ground dry weight of rice types A, B and C by 19%,33% and 19%, respectively. Significant ozone effects were detected on the dry weight of each organ and its proportion to total above-ground dry weight of rice types B and C. There were significant interactions between ozone and rice types for the dry matter of different organs.6. Compared to the control, ozone stress significantly decreased grain yield of rice types A, B, and C by 77%,86% and 85%, spikelets per panicle by 16%,19% and 27%, filled grain percentage by 72%,80% and 75%, and filled grain weight by 6%,3% and 3%, respectively. In addition, ozone stress had no significant effect on panicle numbers per unit area and total spikelet numbers of rice type A, but significantly decreased panicle numbers per unit area of B and C by 16% and 26%, total spikelet numbers by 31% and 68%, respectively. There were significant or close to significant interactions between ozone and rice types for grain yield and its components.7. Compared to the control, ozone stress significantly increased N, P, K, Mg, Mn, Fe, Cu and Zn concentrations of rice straw by 24%,5%,22%,33%,42%,13%,20% and 25%, respectively, but had no effect on Ca concentration. The ozone-induced enhancement of elements concentration (except Fe) in stems was greater than those in leaves. The accumulation of N, P, K, Ca, Mg, Mn, Fe, Cu and Zn in rice straw were lower under high ozone concentration by 16%, 29%,18%,34%,11%,5%,21%,20% and 17%, respectively. Except for Mn accumulation, ozone effects had reached significant level for all other measured elements. The ozone-induced elements accumulation was greater in stems than the leaves. Ozone stress significantly increased the ratio of elements accumulation in leaves to those in stems (except Cu). There was barely interaction between ozone and rice types for elements concentration and allocation in straw or its components, but significant interactions were detected between ozone and rice types for elements accumulation.8. Compared to the control, ozone stress significantly decreased breaking-resistant strength of the third internode from the top of rice types A, B and C by 20%,19% and 19%, and the forth internode from the top by 28%,36% and 44% respectively. For breaking-resistant strength of the forth internode from the top, the ozone by rice types interaction reached p<0.1. Ozone stress significantly decreased the length, dry weight, dry weight per unit length, cross-sectional area, long diameter, short diameter, wall thickness of the third and forth internodes from the top. There were significant interactions between ozone and rice types for cross-sectional area, long diameter, short diameter, wall thickness of the third and forth internodes from the top.Correlation analysis showed that, there were significant positive correlation between the ozone-induced changes in above-ground biomass and tillers (r=0.74**, n=23), panicles per unit area (r=0.84**), spikelet per panicle (r=0.59**), spikelets per unit area (r=0.91**), sink capacity per unit area (r=0.76**), leaf biomass (r=0.88**), stem biomass (r=0.95**), straw biomass (r=0.67**) and elements accumulation of straw or its components (r=0.63**-0.91**), and there was significant negative correlation between ozone-induced changes in above-ground biomass and the ratio of leaf dry weight to above-ground dry weight (r=-0.55**). These results provide important information for selecting or breeding ozone-resistant rice cultivars to cope with high ozone concentration. |
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