| In recent years,the impact of increasing ozone concentration on plants has attracted widespread attention at home and abroad.Based on the advantages of modern sustainable agriculture-straw return to the field,this study carried out the response of soybean photosynthetic characteristics,yield,soil enzyme activity and soil nutrient content under the two-factor condition of ozone and straw return to the field.The purpose is to explore whether returning straw to the field can alleviate the effect of high concentrationozoneonsoybean.In this study,open-top air chamber methods(OTCs)were used to study the two methods of returning fields(full straw return and non-return straw)to different ozone concentrations(CK:ozone setting environmental concentration,T1:ozone concentration setting(80±10)nmol·mol-1,T2:ozone concentration setting(110±10)nmol·mol-1)of soybean photosynthetic fluorescence characteristics,soil enzyme activity,nutrient content and yield.The results show that:(1)With the increase of ozoneconcentration for two consecutive years,the net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),and water use efficiency(WUE)of soybeans decreased,and intercellular carbon dioxide concentration(Ci)was the first downward trend and an upward trend;In 2018,Pn was significantly reduced by 48.59%compared with S1 under T1 treatment during the pod-setting period(p<0.05);Tr and Gs significantly increased by 51.26%and 50.41%compared with SO under the T2 treatment at the branching stage(p<0.05);The original photochemical efficiency of PS Ⅱ(Fv/Fm),the potential activity of PSⅡ(Fv/Fo),and the actual photochemical efficiency of PSⅡ(ΦPSⅡ)showed a trend of rising first and then decreasing.The photochemical quenching coefficient(qP)and the photosynthetic electron transfer rate(ETR)are reduced instead of the photochemical quenching coefficient(NPQ)being increased.Under the T1 treatment of Fv/Fo,S1 was significantly reduced by 30.13%compared with SO(p<0.05).As ozone concentration increases,the main limiting factors of photosynthesis in soybean leaves are converted from stomatal factors to non-stomatal factors,which reduces the rate of electron transfer,increases heat dissipation and consumes excess light energy to adapt to the ozone stress environment.The net photosynthetic rate and transpiration rate in 2018 were higher and significantly different from 2017,and all photosynthetic indicators in 2018 decreased significantly only during the pod-forming period T1.In 2018,cpPS Ⅱ、Fv/Fm、and Fv/Fowere lower than in 2017 and the differences were significant.(2)The ozone concentration increased,the activity of polyphenol oxidase increased,the activities of invertase and catalase did not change significantly,and the activities of amylase and urease decreased.Phosphatase showed a tendency to increase first and then decrease.Except for polyphenol oxidase and urease,the enzyme activity under straw returning treatment was significantly higher than that under non-returning treatment.The activity of polyphenol oxidase has not changed significantly for two consecutive years.In 2018,the activities of invertase,amylase,catalase,and urease were significantly lower than in 2017,while phosphatase was significantly increased in 2018.(3)Increased ozone concentration can directly affect soil nutrients.,soilorganiccarbon and total nitrogen increase first and then decrease,and total phosphorus and total potassium content decrease first and then increase,soil nutrient content under strawturning treatment is higher than that without returning treatment.There was no significant difference in the contents of organic carbon,total nitrogen,total phosphorus and total potassium for two consecutive years.(4)For two consecutive years 100-grain weight was not significantly changed by increasing ozone concentration,while the number of pods per plant,number of grains per plant,and grain weight per plant significantly decreased,and the yield was significantly positively correlated with Pn and ETR,indicating a high concentrationozonereduces soybean yield by inhibiting photosynthesis of soybean plants and reducing the rate of electron transfer.The photosynthetic fluorescence characteristics,soil enzyme activity,nutrient content and yield of soybean plants under straw return treatment were higher than those without return,and the yield was significantly positive with Pn,ETR,total nitrogen,organic carbon,invertase,catalase,this indicates that the increase in ozone concentration caused changes in the distribution of photosynthetic products by inhibiting photosynthesis of soybeans,which indirectly affected the changes in soil nutrients and soil enzyme activities,and ultimately reduced soybean yield.Returning straw to the field reduced the effect of ozone on photosynthetic fluorescence characteristics,soil enzyme activity,nutrient content and yield of soybean to a certain extent,but failed to fundamentally eliminate the negative effects of ozone stress.Based on the research results of the above treatments,increased ozone concentration reduces soybean photosynthesis and leads to a reduction in soybean yield,and straw returning to the field can partially alleviate the stress caused by the increase in ozone concentration.In the future,in order to deal with the problem of decreasing soybean production caused by the increase of ozone concentration,we can consider taking measures to return straw to the field under elevated ozone concentration in agricultural production. |
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