The Effects Of Coexistence Of Straw And Plastic Film With Different Degradation On Soil Organic Carbon Mineralization And Aggregates Formation

Soil organic carbon（SOC）sequestration is of great significance for sustainable agricultural development and mitigation of climate warming.The coexistence of crop residues and residual plastic film has been widespread in farmland soil in arid regions,but the effect and mechanism of their coexistence on SOC turnover process are still unclear.On the basis of traditional application of straw decomposition agents to accelerate straw decomposition,further research is needed to determine whether the coexistence of plastic film and straw will promote SOC turnover and soil aggregation.Therefore,this study took Loess soil in rain-fed agricultural area as the research object,with straw,film with different degradation and straw decomposition agents as the research factors,and carried out indoor constant temperature incubation experiments.During the incubation period,indexes such as SOC mineralization,soil aggregates fractions and their organic carbon components,microbial activity,soil enzyme activity and kinetic parameters were determined,effective measures aimed at alleviating the impact of residual plastic film on organic carbon sequestration in farmland soil.The results are as follows:1.In order to reveal the influence of coexistence of film and straw on SOC mineralization in farmland,straw（without adding or adding）and film with different degradation（without adding,polyethylene film fragments,polylactic acid composite biodegradable film fragments,and bast fiber biodegradable film fragments）were used as research factors to form a complete experiment design.After 60 days of incubation,the results showed that the cumulative CO₂ release of straw treatment was significantly increased by 550.99%compared with that without straw.The contents of SOC,microbial biomass carbon（MBC）,microbial biomass nitrogen（MBN）and dissolved carbon（DOC）were significantly increased by 5.99%,91.00%,111.84%and 30.47%,respectively,while the ratio of MBN:MBC was significantly decreased.Compared with the control,the addition of film only promoted the increase of microbial biomass,MBC and MBN both showed an increasing trend,and DOC showed a decreasing trend.Compared with the addition of only straw,the combined addition of polyethylene film and straw significantly increased the DOC by 11.36%,he MBC of polyethylene film or hemp fiber film combined with straw was significantly decreased by 10.25%and 10.77%,respectively.The addition of bast fiber biodegradable film in biodegradable plastic film significantly increased the total accumulated mineralization of soil organic carbon,and further increased it when coexisting with straw.Both types of polymer plastic film,whether added alone or together with straw,had little effect on organic carbon mineralization.2.Different effects of coexistence of plastic film and straw on soil aggregation and organic carbon composition were observed,in terms of main effect,straw addition significantly increased the mass proportion of soil macro-aggregates,mean weight diameter（MWD）and geometric mean weight diameter（GMD）,the increases were 147.68%,76.43%and 127.12%,respectively.The content of particulate organic carbon（POC）in macro-aggregates and micro-aggregates decreased significantly by 24.47%and 8.27%,respectively,while the proportion of mineral association organic carbon（MAOC）increased.In addition,the content and proportion of high labile organic carbon in MAOC of macro-aggregate were significantly decreased by 6.4%and 7.95%respectively,while the content of labile organic carbon in MAOC of micro-aggregate were significantly increased by 8.85%,and the content and proportion of labile organic carbon in MAOC of silt+clay particle were significantly increased by 12.95%and 11.22%,respectively.Compared with the control,the MWD,GMD and mass proportion of macro-aggregates were significantly decreased by 26.96%,11.33%and 57.59%,respectively,under the addition of film only,and the contents of SOC and no-labile MAOC in micro-aggregates were significantly increased,which did not occur after straw was added.However,the addition of straw and polylactic acid film showed a trend of increasing the labile organic carbon in the silt and clay,the polylactic acid composite film reduced the formation of large aggregates,while the polyethylene film only showed an inhibitory trend in the formation of aggregates.3.To reveal the effects of different biodegradable films on soil aggregation and related enzyme activities in accelerating straw decomposition,the experimental design consisted of straw compost（added and not added）and different biodegradable films（no film added,polyethylene film fragments,and polylactic acid biodegradable film fragments）.The results showed that compared with only adding straw compost,the addition of polyethylene and polylactic acid films with straw compost significantly increased MBC by 44.78%and81.84%,respectively,while the addition of only polyethylene film significantly increased MBN by 15.83%.The addition of straw compost significantly decreased the mass proportion of large aggregates after 60 days of cultivation compared to the control group without compost and film.The addition of polylactic acid film complemented with straw compost significantly increased the SOC content of large aggregates.The activity ofβ-1-4glucosidase（BG）significantly increased by 12.49%with the addition of straw compost,and the activity ofβ-N-acetylglucosaminidase（NAG）decreased significantly with the addition of straw compost or film.The addition of polyethylene film significantly increased BG catalytic efficiency of large aggregates,NAG catalytic efficiency of micro-aggregates,and NAG catalytic efficiency of glue spheres after the addition of straw compost.The addition of polylactic acid biodegradable film significantly increased NAG catalytic efficiency of large aggregates,while the catalytic efficiency of the two enzymes in micro-aggregates decreased in combination with straw compost.In summary,the addition of straw compost can promote SOC mineralization,accelerate straw decomposition,and increase microbial activity,resulting in the breakdown of aggregates.The use of film can aggravate this process.Combining compost and film can increase the microbial enzyme catalytic efficiency of micro-aggregates and glue spheres,leading to the potential for mineralization of stable organic carbon.Therefore,efforts must be made to reduce the amount of residual film in soil for long-term development.