Study On The Straw Degradation And Microbial Process Of Different Aggregates Soil

China's crop straw resources are abundant every year,accounting for more than a quarter of the world's total straw.Straw is rich in various nutrients and has a wide range of uses.At present,straw returning to field is a common,convenient and efficient way to utilize straw.Reasonable straw returning to the field can not only promote the use of renewable resources in the farmland,increase the yield and quality of crops and the income of growers;it can also improve the physical structure of the soil,increase soil fertility and nutrients,and promote the activity of microorganisms in the soil and it will promote the sustainable development of agriculture.Studies have shown that long-term straw returning to the soil causes changes in soil structure,especially the formation of big aggregates in the soil.However,the effect of differences in soil structure on the straw degradation process is currently unclear.In this experiment,the wet sieve method was used to divide the soil into big aggregates?BA,>2 mm?,small aggregates?SA,2-0.25 mm?,and micro-aggregates?MA,<0.25 mm?and set the original soil?OS?component that is not sieved.The incubation experiment was carried out by adding ¹³C stable isotope-labeled straw,combined with CT scanning technology,gas chromatography,high-throughput sequencing technology and other methods.The physical and chemical indexes and microbial community changes of the soil with aggregates of particle size during straw degradation were analyzed.The results are as follows:1. The CT scanning technology was used to visually and quantitatively analyze the pore structure of aggregates with different particle sizes before and after incubation.The analysis results show that the pore structures of four aggregates are very different.OS aggregates have the largest porosity,large pore size,and complicated pore structure;the porosity of MA aggregates are second only to OS,but have the smallest pore size and a single pore structure;BA and SA aggregates have smaller porosity,but the pore size is higher than that of MA aggregates,and the pore complexity is also higher.After 60 days of straw incubation,the pores of aggregates of various sizes became dense,the porosity and pore size also increased,and the complexity of the pore structure of four aggregates tended to be consistent.2. During straw incubation,collect gas and soil samples at 0,8 h,16 h,1 d,3 d,10 d,30 d,and 60 d to determine the respiration strength and physical and chemical properties of each aggregate at each incubation time.The results show that the order of total carbon,total nitrogen and soil organic carbon content in the process of straw degradation are MA>SA>BA.The microbial biomass carbon of the BA and OS aggregates increased significantly within a short period of incubation.As the particle size of the aggregates decreases,both the CO₂ emission rate and the emission amount decrease,and the contribution of exogenous straw carbon to SOC decreases.The physical and chemical indexes of OS aggregates are between BA,SA and MA.3. The soil samples incubated at 0,1 d,10 d,30 d,and 60 d were subjected to DNA extraction,and the microbial community changes of different aggregates in each incubation period were analyzed by sequencing.The study found that the degradation of straw has a staged characteristic.The bacterial and fungal alpha diversity of each aggregates in the control group without straws did not change much with the incubation time.The addition of straw made the fungus alpha diversity is significantly reduced in the middle and late stages of incubation,and it has a significant impact on the bacterial and fungal community composition in the middle and late incubation.After straw was added,the abundance of Firmicutes in each aggregates increased,the abundance of Chloroflexi decreased,and Ascomycota was significantly enriched in the middle and late stages of degradation.The MA aggregates were significantly enriched in Actinobacteria and Basidiomycota in the early and middle incubation.In summary,the effect of aggregates of different particle sizes on straw degradation is inconsistent.The aggregates with large particle size have small porosity,large pore size,high microbial activity in the early stage of straw degradation,and strong ability to convert straw carbon into SOC,but the emission rate and amount of CO₂ are high.The aggregates with small particle size have large porosity and small pore size,and the soil respiration after straw addition is weak,but the SOC content is high,and Basidiomycota is significantly enriched during the micro-aggregate incubation period,which is conducive to the decomposition of refractory lignin.Generally speaking,in the process of straw degradation,aggregates of different particle sizes play different roles.Bigger aggregates may be beneficial for SOC retention and function in the early stage of straw degradation.The smaller aggregates may be beneficial to the decomposition of refractory organic matter in the middle and late stages of straw degradation.The results of this study can provide a theoretical basis for formulating relevant straw return measures from the perspective of soil structure,so as to achieve a better return effect.