| In recent years,cadmium pollution in paddy fields is becoming more and more serious.Agronomic measures have been widely used in the management of heavy metal contaminated farmland due to their low cost,easy operation and wide spread.In this study,12 production sample areas of subtropical double-cropping rice area located in Zhuzhou of eastern Hunan province with traditional high yield were selected as research objects.Each paddy field was divided into two parts,one half as control,and the other half was treated with lime,commercial organic fertilizer and soil conditioner.According to rice growth stage?Green stage,tillering stage,booting stage,full heading stage and yellow ripening stage?,0-15cm topsoil samples were collected by self-made soil drill,and the effects of lime,commercial organic fertilizer and soil conditioner on cadmium content,soil physical and chemical properties of rice,soil were studied by indoor analysis technology.The effects of lime,commercial organic fertilizer and soil conditioner on soil microbial community and bacterial abundance in paddy fields were studied by phospholipid fatty acid analysis?PLFA?and 16sRNA gene sequencing.The purpose of this study was to provide basic data and scientific basis for cadmium reduction and fertilization effect in subtropical paddy fields.The results showed that:?1?Continuous 3a?2015-2017?.Compared with the control group,lime,organic fertilizer and soil conditioner had a significant impact on the cadmium content in the paddy field ecosystem.Cadmium content in brown rice of early rice was significantly reduced by57%-67%,16%-45%and 37%-72%,respectively.Cadmium content in late rice decreased by54%-68%,18%-53%and 40%-80%,respectively.The effective cadmium content in early rice soil was reduced by 5%-17%,3%-12%and 7%-11%by applying lime,organic fertilizer and soil conditioner for 3a consecutive years.Late rice was reduced by 2%-15%,4%-14%and 0.3%-15%,respectively.The content of soil available Cd decreased significantly in both tillering and panicle stages of rice,especially in the panicle stage of rice,when the decrease of soil available Cd content was the highest?2%-17%?.?2?Physical properties:when lime,organic fertilizer and conditioner were applied,soil bulk density decreased by 0.03,0.01 and 0.16 g/cm3,while total porosity increased by1.17%,0.40%and 5.81%,respectively.The maximum water holding capacity of soil increased by 4.03mm,1.71mm and 12.52mm,respectively.Soil capillary water holding capacity increased by 5.74mm,1.18mm and 12.29mm,respectively.In addition,the aggregate content of the treated lime increased significantly?>2 mm?by 21.64%,and decreased significantly?0.053-0.25mm,<0.053mm?by 7.29%and 12.44%.The content of the aggregate increased significantly?0.053-0.25mm,<0.053mm?with the application of the conditioner,while the content of the aggregate decreased significantly?>2mm?by 21.62%.Chemical properties:for consecutive 3a years,compared with the control,the pH of soil increased by 3%-29%,1%-8%and 1%-17%when lime,organic fertilizer and conditioner were applied.The content of exchangeable calcium in soil increased by 13%with lime and conditioner.The soil exchangeable magnesium increased by 17%.At the same time,the application of lime,organic fertilizer and soil conditioner had a certain increase in the content of active organic matter components in the soil.The organic carbon content of fine particles increased by 22%,44%and 41%respectively.The increase was 57%,52%and36%,respectively.?3?The absolute contents of total PLFA in soil increased by 14.51 nmol·g-1 and 34.40nmol·g-1,respectively.The absolute PLFA content of g-bacteria increased by 10.71 nmol·g-1and 11.51 nmol·g-1,respectively.The absolute PLFA content was increased by 4.55 nmol·g-1and 6.03 nmol·g-1,respectively.The absolute content of PLFA increased by 0.99 nmol·g-1and 1.91 nmol·g-1,respectively.Absolute PLFA content of methane-oxidizing bacteria increased by 3.20 nmol·g-1 and 3.26 nmol·g-1,respectively.Compared with the control soil,the soil microbial community diversity indexes of lime,organic fertilizer and conditioner increased as a whole.The shannon-wiener index was highest with lime treatment?2.553?.The richness index was highest with organic fertilizer and conditioner?both reached 25?.The evenness index was highest when lime was applied?0.809?.The OTU abundance of surface soil samples treated was expressed as SH3>CK3>SY7>CK7.The Alpha diversity analysis results showed that the Ace index and Chao index values of each treatment were CK7>SH3>SY7>CK3,and the Shanno index values of each treatment were SH3>CK7>CK3>SY7.The results showed that application of lime and organic fertilizer could obviously improve the richness and diversity of bacterial community in paddy soil.A total of 3,245 bacterial OTUs were obtained from soil samples in each surface layer,and the total number of OTUs among the four was 1,739,accounting for 53.6%of the total number of OTUs,indicating that the application of lime and commercial organic fertilizer had a significant impact on the bacteria OUT abundance in surface soil.At the same time,the results of the multi-species difference analysis of bacteria in topsoil at the genus level showed that the species abundance of soil Xanthobacteraceae,Bradyrhizobium,and No rank CSBR2076 were significantly increased after the application of lime compared with the control?P<0.1?.Compared with the control,Pseudarthrobacter,Massilia and Sphingomonas significantly increased after organic fertilizer application?P<0.1?. |
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