| In this experiment,based on the method of soil chemical analysis combined with molecular ecology research,based on the field experiment,four representative rice varieties were selected to study the effects of different nitrogen application on inorganic nitrogen content and soil microbial community structure in paddy soil.The soil microbiology basis for the continuous increase of hybrid rice provides a theoretical basis for large-area balanced high-yield cultivation and super rice breeding practice.The project was carried out in the rice production base of Henan Agricultural University,Xinyang City,Henan Province in 2016-2017.The representative varieties Liangyoupei 9,Y Liangyou 1,Y Liangyou 2 and Y Liangyou 900,which have achieved the yield target of Chinese fourth super rice,were used as the experimental materials,and a total of 4 different nitrogen treatments are set:control,no nitrogen fertilizer(N0);low nitrogen treatment,nitrogen application is 210kg/hm2(N210);medium nitrogen treatment,nitrogen application is 300kg/hm2(N300);high nitrogen treatment,nitrogen application is 390kg/hm2(N390).Nitrogen application significantly increased the content of ammonium nitrogen and nitrate nitrogen in the paddy soil and increased the content of inorganic nitrogen in the soil profile.The high yield of Y Liangyou 2 had higher ammonium nitrogen content at heading stage.The content of ammonium nitrogen and inorganic nitrogen varied greatly during the whole growth period,and the whole showed a trend of decreasing first,then increasing and then decreasing,and peaked at the seedling stage and heading-filling stage.The nitrate nitrogen content showed the opposite trend during the whole growth period,with peaks in the tillering stage,heading stage and maturity stage.With the increase of nitrogen application,the content of ammonium nitrogen and nitrate nitrogen in the soil increased gradually.The inorganic nitrogen was mainly composed of ammonium nitrogen and nitrate nitrogen,so the inorganic nitrogen content also increased with the increase of nitrogen application.With the increase of yield potential,Y Liangyou 2 and Y Liangyou 900 have higher ammonium nitrogen content,while Liangyoupei 9 and Y Liangyou 1 have higher nitrate nitrogen content.The content of ammonium nitrogen,nitrate nitrogen and inorganic nitrogen in the depth of 0~15cm soil layer is higher than the depth of 15~30cm soil layer.The strong nitrogen cycle occurs in shallow soil mainly because the roots of super rice are mostly distributed in0~20cm.Nitrogen application significantly increased the soil enzyme activity in the paddy soil and promoted the nitrification of paddy soil.The higher yield of Y Liangyou 2 soil enzyme activity was higher.With the increase of nitrogen application,the activities of urease,sucrase and acid phosphatase in paddy soil increased first and then decreased.The activity of soil enzyme was the highest in N300 treatment,and the excessive nitrogen application inhibited soil enzyme activity.Among the four super rice varieties,Y Liangyou 2 had the highest soil enzyme activity.Nitrogen application significantly increased the ammoxidation potential and nitrification intensity of paddy soils,especially the nitrification of shallow soils(0~15 cm).The nitrification of soil profiles at different depths increased with the increase of nitrogen application..Among the four super rice varieties,Y Liangyou 1 has the largest nitrification effect.The higher nitrification of the first two varieties is also one of the main causes of the increase in nitrate nitrogen content.Variety is the largest source of variation in soil-related bacterial community structure,and nitrogen application has a certain impact.The diversity of bacterial communities decreased with increasing nitrogen application and yield potential.In the fourth stage super rice,the species observation number,Chao1 index and Shannon index decreased with the increase of nitrogen application,while the Simpson index increased with the increase of nitrogen application.Nitrogen application significantly reduced the soil microbial diversity in super rice fields.In the analysis of the differences between communities,it was found that when the nitrogen application rate was 210kg/hm2 and 300kg/hm2,the difference between microbial communities was small,and there were significant differences between the microbial communities treated with N0 and N390.In addition,the number of species observations,Chao1 index and Shannon index decreased with the increase of yield potential,and the Simpson index increased with the increase of yield potential.The soil microbial community diversity of the four super rice varieties also showed Gradually decreasing trend.There were significant differences among the soil microbial communities in the fourstage super hybrid rice.The differences in microbial communities between Liangyoupei 9 and Y Liangyou 1 were small,and there were significant differences between the microbial communities with Y Liangyou 2 and Y Liangyou 900.The levels of the phylum are mainly Acidobacteria,Bacteroidetes,Chloroflexi,Firmicutes,Nitrospirae and Proteobacteria which accounted for 73.80% or more.With the increase of nitrogen application,the Acidobacteria and the Chloroflexi decreased with the increase of nitrogen application,and other dominant bacteria phylum increased with the increase of nitrogen application.Compared with the previous two varieties,the Chloroflexi and Firmicutes increased in the latter two varieties,while the proteobacteria decreased.The levels of the class are mainly Anaerolineae,Nitrospira,Betaproteobacteria,Gammaproteobacteria,Deltapodeobacteria and Bacteroides which accounting for 55.84% or more.Among them,the relative abundances of ?-proteobacteria,?-proteobacteria,Nitrospira and Bacteroides increased with the increase of nitrogen application,and other phylum decreased with the increase of nitrogen application.Compared with the previous two varieties,the Clostridia and Anaerolineae of the latter two varieties increased,while the Nitrospira and?-Proteobacteria decreased.Nitrogen application and variety stimulate soil nitrification in super rice fields,and change soil nitrate nitrogen content,which in turn causes changes in soil-related bacterial community structure and relative abundance.With the increase of nitrogen application,the soil urease activity increased,and the large amount of ammonium nitrogen produced by the violent decomposition of urea,in addition to the absorption of the plant itself,promoted the nitrification to a large extent,and the nitrate nitrogen content increased.With the increase of yield potential,the photosynthetic potential accumulation and root-shoot ratio at heading stage increased,and the carbon source of microorganisms in the soil could be changed by rhizosphere sedimentation,which affected the distribution of soil microbial community.Redundancy analysis and correlation analysis showed that the Acidobacteria,Chloroflexi,Acidobacteria-6,Anaerolineae,Phycisphaerae and Solibacteres were significantly negative correlation with ammonia oxidation potential,nitrification intensity and nitrate nitrogen content.?-proteobacteria,?-proteobacteria,Nitrospira and Bacteroides were significantly positive correlated with ammonia oxidation potential,nitrification intensity and nitrate nitrogen content.In summary,with the increase of nitrogen application,the soil enzyme activity in super rice paddy is increased,the nitrogen fertilizer is decomposed by a large amount,and the inorganic nitrogen content in the soil is greatly increased,resulting in higher ammonium nitrogen to promote soil nitrification,resulting in the accumulation of nitrate nitrogen in the soil profile;nitrogen application decreased soil microbial diversity,and the difference of super rice varieties was the largest source of variation of soil microbial community structure.Redundancy analysis and correlation analysis showed that the differences in soil nitrification and nitrate nitrogen content caused by variety and nitrogen application may be the main soil factors for soil microbial community structure change in super rice fields. |
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