| Since the beginning of the Industrial Revolution,the emissions of ozone(O3)precursors have been continuously increasing,leading to a continuous increase in the concentration of O3 in the troposphere.Rice is one of the most important food crops in the world,and lodging is a common problem in current rice production.High O3 concentration inhibits rice growth,reduces grain yield,and deteriorates quality.However,there are few reports on the impact and interspecific differences on rice lodging resistance.At the same time,in the context of global climate change,the increase in atmospheric temperature and O3 concentration occurs simultaneously,but whether there is an interaction effect between the two on rice lodging resistance has not been reported.Exogenous application of silicon can enhance antioxidant defense ability,alleviate damage caused by stress,and on the other hand,facilitate the deposition of silicon in plant tissues,enhance cell wall strength and rigidity,thereby improving lodging resistance.However,it remains to be determined whether foliar silicon application can alleviate the adverse effects of O3 stress on rice lodging resistance.The unique spatial advantages of the large FACE(Free air gas concentration enrichment)platform provide a good means for studying the changes in rice lodging resistance in high O3 concentration environments.Based on the FACE platform located in a large rice field,this experiment conducted an interaction experiment between high O3 concentration(1.5 times the environmental O3)and varieties(japonica rice,indica rice,and hybrid rice),high temperature(2℃ temperature increase at night and 2℃ temperature increase throughout the day),and foliar silicon application(spraying 300 ppm chelated silicon solution*6 times)to study the changes and influencing factors of the main lodging traits of rice under high O3 concentration environment.The main results are as follows:(1)Variety experiments showed that high O3 concentration significantly reduced the plant height and effective tiller number of all rice varieties during the mature stage,with Yongyou 2640(-13%,-32%)showing the largest decrease.All rice varieties with high O3 concentration showed a 44%**and 29%**decrease in single plant and single stem resistance in the field,respectively.Among them,the decrease in hybrid rice was greater than that in japonica and indica rice.High O3 concentration significantly reduced the bending resistance of rice basal internodes,with Yuan Liangyou 1000 and Nanjing 5718 showing the greatest decrease.High O3 concentration significantly reduced the bending moment of different internodes in rice,with Yongyou 2640 showing the largest decrease.High O3 concentration significantly increased the lodging index between the 3rd and 4th internodes of different rice varieties,with Jiuyou Yuehe Silk Seedling showing the largest increase,and the lodging index between the 5th internode showing an increasing trend.Among them,Yangdao 6 showed the largest increase.High O3 concentration significantly reduced the length,dry weight,long diameter,short diameter,cross-sectional area,and wall thickness of internodes between the top 1 and bottom 2 of different rice varieties.Analysis of variance showed that O3 treatment had significant interaction effects with rice varieties in terms of plant height,single plant resistance,single stem resistance,bending moment,top 5 internode resistance,top 4 and bottom 5 internode dry weight,top 1 and bottom 2 internode length,top 3 internode short diameter,and top 4 internode stem wall thickness.(2)The high temperature experiment showed that under high O3 concentration environment,the plant height(-4%)and effective tiller number(-17%)of Nanjing 9108 significantly decreased.The decrease in plant height was greater under high temperature,but the decrease in effective tiller number was greatest under environmental temperature.The high concentration of O3 significantly reduced the single plant resistance(-32%)and single stem resistance(-18%)of Nanjing 9108,with a decrease in environmental temperature greater than nighttime warming and an increase in temperature throughout the day.High O3 concentration reduces the bending resistance of rice basal internodes under ambient temperature,but there is no significant change under nighttime and all day warming conditions.High O3 concentration significantly reduced the bending moment between different nodes(-11%～12%),and the trend was consistent at different temperatures.Unlike this,ozone stress has no significant effect on lodging index under different temperature conditions.High O3 concentration leads to a decrease in the length,dry weight,long diameter,short diameter,cross-sectional area,and wall thickness of different internodes at ambient temperature,but the decrease decreases or even slightly increases under high temperature conditions.High temperature significantly reduced plant height(-12%),but slightly increased the effective tillering number.High temperature significantly increased the resistance to thrust per plant(+31%)and the resistance to thrust per stem(+23%).High temperature significantly increased the bending resistance of the basal internodes of rice,but significantly decreased the bending moment of the internodes,resulting in a significant decrease in the lodging index of rice under high temperature treatment.From the perspective of internode morphology,high temperature significantly reduced the length of different internodes,but significantly increased the dry weight,long diameter,short diameter,cross-sectional area,and wall thickness of internodes.(3)The experiment of foliar silicon application showed that high O3 concentration had no significant effect on the plant height of Nanjing 9108 and Yangdao 6,resulting in a significant decrease in tiller number of 14%and 9%,respectively,and a significant reduction in the reduction of silicon application in rice.High O3 concentration significantly reduced the average resistance to thrust per plant and stem of the tested varieties by 31%and 22%,with a decrease of no silicon application>silicon application treatment.Under high O3 concentration environment,the bending resistance and bending moment of rice basal internodes significantly decreased,but the lodging index significantly increased.The response of the above lodging resistance traits to high O3 concentration was higher in Yangdao 6 than in Nanjing 9108.From the perspective of stem morphology traits,high O3 concentration led to a downward trend in both rice varieties,with a significant decrease of over 0.1 in internode length,dry weight,dry weight per unit length,long diameter,short diameter,cross-sectional area,and stem wall thickness of the top 5 and bottom 3,respectively.The response of the above internode morphological traits to high O3 concentration was higher in Yangdao 6 than in Nanjing 9108.Under different O3 concentrations,foliar silicon application had no effect on the plant height of both rice varieties,but significantly increased the tiller number(+10%)of both varieties.The application of silicon on the leaves significantly increased the resistance to thrust per plant(19%)and the resistance to thrust per stem(+10%)of rice.Leaf silicon application significantly increased the bending resistance of rice at the 3rd and 4th internodes,but had no significant effect on the bending moment and lodging index at the basal internodes.From the perspective of internode morphology,foliar silicon application showed an increasing trend in internode length,dry weight per unit length,long diameter,short diameter,and stem wall thickness,with significant increases in long diameter,short diameter,and stem wall thickness.In summary,high O3 concentration significantly reduces the lodging resistance of rice,but there are significant differences among varieties.Among them,the resistance of japonica rice varieties is greater than that of indica and hybrid rice,while the lodging resistance of Huaidao 5 and Nanjing 9108 is more prominent.Under high temperature treatment,the effect of O3 on rice decreases.High temperature reduces the load on the center of gravity and the basal internodes of the rice plant.This change in plant structure is beneficial for reducing bending moment and thus reducing the risk of lodging.The application of silicon on the leaf surface increases the roughness,thickness,and plumpness of the basal internodes in rice,thus reducing to some extent the negative effects of the increased O3 concentration environment on the lodging resistance of rice stems. |
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