Response Of Soil Carbon Cycle Microecology To Long-term Different Soil Tillage Measures In The Double-cropping Rice Paddy Field

Unreasonable soil tillage measures usually lead to a sharp decline in soil carbon（C）storage capacity in paddy field,reduce soil fertility,and result in the safety of rice production.Based on long-term field experiment,this paper systematically studied the long-term different tillage measures（CT:conventional tillage with crop residues removed as control;CTS:conventional tillage with crop residues incorporation;NTS:no-tillage straw returning to paddy field）.In order to clarify the effects of different long-term tillage measures on soil C cycle microecology in the double-cropping rice field,the effects of soil phychemical properties and soil organic carbon（SOC）accumulation characteristics,soil microbial community structure,number of soil microorganisms related to C cycle and soil enzyme activities,characteristics of microbial carbon source utilization efficiency（CUE）in paddy fields and rice yield.There results were provided theoretical basis for SOC sequestration and sustainable utilization in paddy soil.The main results were as follows:1.Compared with CT treatment,CTS,RTS and NTS treatments were beneficial to increasing soil water content and decreasing soil impermeability in paddy field.Soil impermeability of early rice and late rice treated with CTS,RTS and NTS decreased by6.34%,32.09%and 13.06%,30.29%and 12.77%compared with CT treatment,respectively.Straw returning and no-tillage increased soil SOC content in paddy field.Rhizosphere SOC with CTS,RTS and NTS treatments were 15.3%,23.3%and 19.7%higher than that of CT treatment,respectively.In non-rhizosphere soil,SOC with CTS,RTS and NTS treatment were 18.5%,26.1%and 22.8%higher than that of CT treatment,respectively.30.7%-40.7%of the SOC stored in paddy fields was residual carbon derived from microorganisms,and 45.7%-54.2%of the SOC accumulated in carbon derived from plant residues.Straw returning significantly increased the content of soil lignin and phenol and promoted the accumulation of plant-derived SOC.The content of soil lignin and phenol with RTS treatment were significantly higher than that of CTS treatment.The content of amino sugar in rhizosphere soil were higher than that of non-rhizosphere soil,and the measure of returning straw to field increased the content of amino sugar.Plant-derived C were greater than microbial residue C in the double-cropping rice field in southern of China.2.Long-term different tillage treatments significantly changed soil bacterial and fungal diversity and community composition.Diversity index of Richness,Shannon and Mc Intosh in rhizosphere soil were higher than that of non-rhizosphere soil,and increased due to straw returning to the field.In the composition of soil bacterial community structure,at the phylum level,Proteobacteria and Bacteroidota the sum of their relative abundance was more than 40%.At class level,Gammaproteobacteria were the first dominant class,Burkholderiales was the first dominant order,and NTS treatment has the highest relative abundance of Burkholderiales（15.4%）.The composition of soil fungal community structure,at the phylum level,the ascomyceteswas the absolutely dominant phylum,and the relative abundance range was46.4%,61.5%.At the class level,Sordariomycetes was the first dominant class,and CT treatment has the highest relative abundance of Sordariomycetes（44.6%）.At the order level,Sordariales were the first dominant order.The relative abundance of Burkholderiales in rhizosphere treated with CT were the highest（41.1%）.In a word,the measures of no-tillage or rotary tillage combined with straw returning are beneficial to improve the soil microbial community structure of double-cropping paddy field and establish a stable and functional soil environment.3.The number of main microorganisms in rhizosphere and non-rhizosphere soil treated with NTS and RTS were higher than that of CTS and CT.No-tillage and rotary tillage combined with straw returning can effectively increase the number of soil C cycle microorganisms（photosynthetic bacteria,methane bacteria,rhizobia,methane oxidizing bacteria）in paddy soil.The main enzyme activities of C cycle in rhizosphere and non-rhizosphere soil with all treatments increased with the advance of rice growth process,and reached the maximum at tillering stage or booting stage.The variation range of dehydrogenase activity in rhizosphere soil of early rice and late rice was26.47-75.18μg（g·h）^-1and 27.89-74.15μg（g·h）^-1,respectively.Tillage combined with straw returning was beneficial to improve the activities of C cycle enzymes（dehydrogenase and sucrase）in rhizosphere and non-rhizosphere soil of early and late rice.Straw returning can effectively improve the activity of C cycling enzymes in paddy soil in southern double-cropping rice area.4.Utilization efficiency of microbial carbon sources,the utilization characteristics of microbial carbon sources under different long-term tillage measures by using the method of mixing ¹⁸O labeled water with microbial genomic DNA to determine the were studied.The results found that ranges of rhizosphere and non-rhizosphere microbial biomass carbon（SMBC）,basic soil respiration rate,C_Growthand CUE of different tillage treatments were 682.6-814.5mg kg^-1,252.6-378.7ng（g·h）^-1,216.7-237.4ng（g·h）^-1and 0.38-0.47,respectively.The utilization efficiency of microbial carbon in rhizosphere soil and non-rhizosphere soil were increased with removal of straw residues,and SMBC content and C_Growthincreased with addition of straw residues into paddy field.The metabolic ability of rhizosphere soil microorganisms to exogenous C sources was lower than that of non-rhizosphere soil.Straw returning can improve the utilization rate of carboxylic acids,amino acids and carbohydrates by soil microorganisms.5.Based on the analysis of the long-term yield data from 2005 to 2019,it was found that full straw returning was beneficial to increase rice yield,but the effect of increasing rice yield varied with tillage methods.Compared with ploughing combined with straw returning treatment,no-tillage straw returning or rotary tillage straw returning in double-cropping paddy soil in the south was beneficial to increase the annual rice yield and had higher carbon sequestration effect.As a result,no-tillage/rotary tillage and straw returning can significantly improve the microbial community structure of carbon cycle in rhizosphere and non-rhizosphere soil of paddy field,improve the utilization efficiency of soil microbial carbon and SOC sequestration,which is beneficial to ensure the yield of double-cropping rice and is of great significance to achieve"carbon neutralization"and alleviate the pressure of food security.