Effects Of Sulfur-containing Industrial By-products On Microbial Diversity From Yellow Paddy Fields

Desulfurized gypsum is a by-product of flue gas desulfurization in coal-fired power plants.Its main component is calcium sulfate dihydrate?CaSO₄·2H₂O?,which is rich in elements such as sulfur,calcium,silicon,iron and boron.It has effects on plant growth,soil physical and chemical properties which gives it potential for application in agriculture.The State Council explicitly proposed to promote the application of desulphurized gypsum in agricultural field as of 31^st May 2016.Application of desulfurized gypsum into the soil specifically improves the soil porosity and nutrient content which in turn enhances soil fertility and water holding capacity.These changes in soil physical and chemical properties result in an alteration of the living environment of microorganism,consequently impacting the microbial community structure.At the same time,desulfurized gypsum brings in a large amount of SO₄^2-,which enhances the competition between sulfate-reducing bacteria and methanogens for sediment?acetic acid/H₂?,thus suppressing the CH₄ emission in rice fields.However,the current research on the application of desulfurized gypsum in agriculture mainly focuses on the improvement of saline-alkali land and the growth of dry land plants.There are few concerns about changes in abundance of functional bacteria?methane-producing bacteria and methane-oxidizing bacteria?related to soil bacteria,archaeal community structure and methane emissions in paddy fields,and these are key biological factors regulating methane flux in paddy soils.Therefore,in this study,we selected the yellow paddy rice fields in Qitang town,Bishan as the research object,and set up five desulfurization gypsum treatments,namely CK(0t·ha^-1),T1(2t·ha^-1),T2(4t·ha^-1),T3(8t·ha^-1),and T4(16t·ha^-1).Using high-throughput sequencing?Illumina MiSeq?,fluorescence quantitative PCR static chamber-gas chromatography technique to analyze the effects of the bacterial and archaeal community structure and diversity,methane emissions and the abundance of functional genes of methanogens and methane oxidizing bacteria.This was done by different desulfurized gypsum-treatments in paddy soils to provide theoretical basis for the application of desulfurized gypsum in paddy fields.The main findings are as follows:1.Diversity of bacterial community in paddy soilIn the initial stage of growth,the Chao1 index and Shannon index of soil bacteria which treated with T1 and T2 increased compared with CK,while T3 and T4 treatment decreased.During the mature period,the Chao1 index and Shannon index of soil bacteria in the desulfurization gypsum treatment group had no significant changes compared with CK.Compared with the initial stage of growth,the Chao1 index and Shannon index of soil bacteria in various treatments at different stages of maturity were reduced.It showed that desulfurized gypsum increased the bacterial richness and diversity in the initial stage of growth,but after a certain amount(8 t·ha^-1),the soil bacteria richness and diversity decreased,and the desulfurization gypsum had richness and diversity of bacteria in mature soil.The impact of sexuality was less,the bacterial richness and diversity of soil in mature period was lower than the initial stage of growth.2.Changes of bacterial community structure in paddy soilThe dominant bacteria in rice soil were Proteobacteria,Chloroflexi,Acidobacteria,Bacteroidetes,etc.In the early stage of growth,desulfurization gypsum was treated as compared with CK.The relative abundances of the soil proteobacteria,acidobacteria and Bacteroidetes decreased by 9.5%-19.63%,1.04%-30.26%,59.99%-85.92%.Respectively,while the relative abundance of the green beetle bacteria increased by 37.68%-90.64%.During the mature period,the relative abundance of bacterial gates in the desulfurized gypsum-treated group was not significantly different from that of CK treatment.Based on genus level cluster analysis,there was a large difference in bacterial community structure between CK treatment and T1,T2,T3 treatment in the initial stage of growth.But there was little difference in bacterial community structure between CK and desulfurization gypsum treatment in mature stage.After the application of desulfurized gypsum,the bacterial community structure in the initial stage of growth has a greater impact.3.Changes of soil bacterial community diversity in paddy soilsThere was no significant change in the Chao1 index and Shannon index of soil archaea in the initial stage of growth and maturity of the desulfurization gypsum group compared with CK.Compared with the initial stage of growth,the Chao1 index and the Shannon index of the soil bacteria in the rice fields treated at various stages of maturity were reduced to different degrees.It showed that the effect of desulfurized gypsum on the abundance and diversity of archaea in soil is small,and the diversity and richness of soil archaea in each treatment period during mature period are lower than that in the early growth stage.4.Changes of soil bacterial community structure in paddy fieldThe dominant archaea in the paddy soils were Euryarchaeota,Thaumarchaeota and Miscellaneous Crenarchaeotic Group.At the beginning of growth,the relative abundance of bacterial phylum level between treatments was small.At maturity,the relative abundance of Euryarchaeota treated soil was lower by 41.30%than that of CK treatment,the relative abundance of Miscellaneous Crenarchaeotic Group was increased by 35.53%compared with CK,and the relative abundance of Thaumarchaeota was 70.20%lower than that of CK.There was no significant change in the gypsum treatment group.Compared with the growth period,the relative abundances of Miscellaneous Crenarchaeotic Group and Thaumarchaeota in mature soils increased,but the relative abundance of Euryarchaeota decreased.Based on the analysis of genus level,the main dominance of archaea relative to the desulfurization gypsum treatment group in the early growth stage and mature stage was relatively.Abundance had no significant change compared to CK.Cluster analysis showed that the community structure of soil archaea was similar between CK treatment and T1,T2,T4 treatment at the initial stage of growth,while the soil archaeal community structure was similar between CK and T1,T3,T4 treatments.5.Methane emissions from rice fields and their associated functional microbial population changesThe average emission flux of CH₄ in the rice field was 25.72 mgC·m^-2·h^-1,and the average flux of CH₄ in the gypsum-treated gypsum group was 4.56-18.00 mgC·m^-2·h^-1,which was lower than that of CK by 30.00%,36.66%,59.05%,82.28%.In the initial stage of growth,the relative abundance of sulfate-reducing bacteria in the desulfurized gypsum-treated soil group was increased by 13.56%-6.98%compared with that of CK,and increased with the increase in the amount of desulfurized gypsum.The relative abundances of Nitrospira,Clostridium,Rhodobacter rhizobacteria varied in different degrees,and the mcrA gene abundance of rice methanogens decreased by 4.7%-15.8%?P<0.05?.The abundance of mcrA genes in methanogens increased by2.1%⁶.2%.During mature period,the relative abundance of sulphate reducing bacteria in the desulfurized gypsum treatment group was 6.60%-30.50%higher than that of CK.And the relative abundances of nitrosobacilli,Clostridium,and Rhodobacter were different.The degree changes.The mcrA gene abundance of rice methanogens decreased by 15.1%-31.27%in paddy soils,and the abundance of pmoA gene of methane oxidizing bacteria varied in different degrees.Compared with the growth phase,the relative abundances of the sulphate reducing bacteria and nitrosospira in the soils at the ripening stage were all decreased,and the other genus did not change significantly.Both the mcrA gene and the pmoA gene abundance of the soil methanogen bacterium were both abundant.The overall pmoA/mcrA ratio increased over the two periods.In addition,the results of correlation analysis showed that the average flux of CH₄ in rice fields was positively correlated with the abundance of methanogens?P<0.05?,compared with the abundance of methane oxidizing bacteria,relative abundance of sulfate reducing bacteria,and pmoA/mcrA ratio.Negative correlation.This showed that desulphurized gypsum can suppress CH₄ emissions by reducing soil methanogenic abundance and increasing the abundance of methane oxidizing bacteria.