Responses Of Soil Bacterial Communities In Different Rice Varieties Under Elevated CO₂ Concentrations

Elevated atmospheric[CO₂]can affect crop growth and soil nutrient cycling,thus changing the structure and function of agroecosystem.Rice is an important food crop.The response level of different rice varieties to the increase of[CO₂]is different,and the soil microbial community also responds to it.In this study,four rice varieties,WYJ27,HD5,YY1540 and LLY1988 with different response levels to[CO₂]elevation were selected as test materials,and two[CO₂]levels were set respectively:normal concentration(a CO₂)and[CO₂]elevation(e CO₂),the latter being200%higher than the former?mol·mol^-1.The response of soil bacterial community structure and diversity to elevated[CO₂]and different rice varieties was studied by measuring soil physical and chemical properties at different growth stages of rice and using the second generation high-throughput sequencing technology.The main conclusions are as follows:(1)The paddy soil TC increased with the increase of[CO₂],while the soil TN of high response cultivar LLY1988 at tillering stage was significantly higher than that of the control(P<0.05).The content of TN at early tillering stage was also significantly higher than that of high response cultivar YY1540(P<0.05);(2)In the both CO₂environments,Acidobacteria,Planctomycetes,Proteobacteria,Actinobacteria and Chloroflexi were the main soil bacterial groups.When[CO₂]increased,there was a significant difference in soil bacterial community composition between HD5 and YY1540(P<0.01).In each growth period,the increase of[CO₂]and varieties had no significant effect on soil microbial diversity.The most abundant response group of soil bacteria was at grain filling stage,followed by heading stage.The relative abundances of Cyanophyta and cyanobacteria in the soil of low response varieties WYJ27 and HD5 were significantly lower than those of the control at heading and filling stages(P<0.05),and the abundances of Rice Cluster I,a class of methanogens in the soil of WYJ27,were also significantly lower at heading stage.At heading stage and grain filling stage,elevated[CO₂]also made low response varieties and high response varieties appear more indicator species;(3)With the increase of atmospheric[CO₂],soil doc was the most important environmental factor affecting soil bacterial community structure of different rice varieties,followed by soil NO₃^--N and NO₂^--N.both of them had extremely significant effects on species relative abundance(P<0.01),and had significant correlation with some groups of bacteria(P<0.05).Soil doc had a direct and significant negative effect on bacterial community richness(P<0.05);(4)After the increase of[CO₂],there is no significant response relationship between the overall diversity of the bacterial community in paddy soil and the yield.Under high[CO₂]conditions,the relationship between soil Proteobacteria and yield may be closer than that of the bacterial group of Actinomycetes.In high-response varieties,the two were significantly negatively correlated(P<0.05).As the abundance of Proteobacteria increased,high-response rice tended to decrease yield.In summary,the soil bacterial communities of low-response varieties at the heading and filling stages of rice had the most prominent response to the increase in[CO₂],and under the conditions of elevated[CO₂],the soil bacterial communities of low-response varieties also had higher response varieties.There are more indicator species.With the increase of[CO₂],the increase of DOC content in paddy soil has a tendency to increase the abundance of some bacteria in the soil bacterial community and reduce the diversity of the community.In the future,high-response hybrid rice planting may require the growth of some bacteria in the soil Proteobacteria.Reproduction is suppressed to maintain high yields.