【作者】 赵宇航；

【导师】 解文艳；

【作者基本信息】 山西农业大学 ， 农业资源与环境， 2024， 硕士

【摘要】 土壤碳循环是土壤有机质周转的核心,也是影响土壤肥力的关键因素。秸秆还田作为提高土壤有机质的方法之一,既能减少秸秆焚烧给大气带来的污染,又有利于土壤有机质的提升。长期不同秸秆还田模式下土壤固碳速率、有机碳在不同组分之间的转化及其固定机制均有所不同。目前有关不同秸秆还田模式对黄土旱塬土壤有机碳固定的微生物作用机制的研究也较薄弱。本研究基于山西寿阳褐土农田长期定位试验,对秸秆覆盖还田(SM)、秸秆粉碎直接还田(SC)和秸秆过腹还田(CM)3种不同秸秆还田模式以及秸秆不还田(CK)的土壤有机碳、碳组分、与碳转化相关的酶活性、微生物量、微生物群落进行分析,揭示长期不同秸秆还田模式下土壤有机碳固定特征和微生物生态功能,并利用土壤稳定性标志物(氨基糖和木质素)对不同秸秆还田模式下土壤有机碳的来源进行辨析,试图阐明长期不同秸秆还田模式下土壤碳截获过程及其微生物作用机制,为理解旱作农田土壤有机碳固定过程提供科学依据,为秸秆还田模式的进一步实践提供理论参考。主要研究结果如下:(1)长期不同秸秆还田模式可显著提高耕层土壤有机碳及其组分含量、有机碳储量和作物产量。不同秸秆还田处理土壤总有机碳(SOC)、轻组有机碳(LFOC)、微生物量碳(MBC)、水溶性有机碳(DOC)、颗粒有机碳(POC)和易氧化有机碳(ROC)含量变化的趋势一致,均表现为CM>SC>SM>CK。各活性有机碳组分与土壤有机碳的比值表现为LFOC>ROC>POC>MBC>DOC;CM和SC处理下敏感指数最高的是DOC,DOC可作为CM和SC处理早期有机物变化的指示物;SM处理下敏感指数最高的是LFOC,LFOC可作为SM处理早期有机物变化的指示物。不同秸秆还田处理耕层土壤有机碳储量以0.55～0.89 t/(hm~2·a)的速率增加,总有机碳增加速率为0.26～0.60 t/(hm~2·a)。SOC与土壤p H呈现显著负相关关系,与其他因子呈现显著正相关关系。SOC的主要影响因子为TK、DOC和LFOC。与CK处理相比,SM、SC和CM处理累计产量分别增加了6.38%、7.82%和23.00%。20-40cm土层三种不同秸秆还田方式有机碳及其组分含量、有机碳储量也均有所增加,但是与耕层相比,增加幅度较小。(2)长期不同秸秆还田模式均提高了耕层土壤酶活性、细菌和真菌活体含量,提升效果均表现为CM>SC>SM>CK。与CK处理相比,长期不同秸秆还田模式下β-GC、CBH、POD、SC和DHA含量提升幅度分别介于10.12%～207.63%、46.61%～145.47%、5.44%～11.97%、41.57%～72.26%和60.38%～412.82%;土壤细菌和真菌活体含量分别增加了1.13～9.40 nmol/g和0.12～0.77 nmol/g。(3)长期不同秸秆还田模式提高了土壤细菌群落α-多样性,但真菌群落α-多样性没有显著差异。不同秸秆还田模式提高了拟杆菌门、变形菌门、厚壁菌门和放线菌门等细菌的相对丰度,分别提升了0.10%～7.66%、1.91%～5.82%、0.60%～1.10%和0.13%～1.31%,绿弯菌门和奇古菌门等细菌的相对丰度分别降低了1.39%～2.66%和4.85%～8.16%;真菌中被孢霉菌门降低了29.05%～31.12%,担子菌门提升了481.10%～24.76%。土壤p H是影响细菌和真菌群落组成的重要影响因素。网络分析结果表明,长期不同秸秆还田处理指示种归属于不同模块,其中CM处理中富集的Chryseolinea、Conocybe和Phaeoacremonium通过强烈共生关系形成特定功能微生物集群。基于FAPROTAX的功能预测发现:长期不同秸秆还田提高了土壤细菌对有机物质的分解潜力和氮组分转化潜力。FUNGuild分析结果表明,秸秆还田后提高了病理营养型真菌和腐生营养型真菌的相对丰度。结构方程模型结果表明玉米产量主要受SOC直接正向调控,而细菌模块4物种和真菌模块1物种可通过正向调节DHA和β-GC,间接影响SOC和玉米产量。(4)长期不同秸秆还田模式均可显著提高氨基糖和木质素含量,CM处理含量最高,显著高于其他处理,SC处理和SM处理间差异较小,但均高于CK处理。与CK相比,不同秸秆还田模式下氨基糖和木质素含量分别增加了33.82～144.92 mg/kg和78.97～827.24 mg/kg;细菌残体碳含量和真菌残体碳分别提高了10.93%～32.85%和24.26%～158.15%。SM、SC、CM和CK处理中微生物残体碳以真菌残体碳为主,细菌残体碳和真菌残体碳对SOC的贡献率分别在5.36%～5.66%和10.99%～19.86%之间,植物源碳对SOC的贡献率在1.48%～4.30%之间。不同秸秆还田模式提高了真菌残体碳和植物源碳的贡献率,但是细菌残体碳的贡献率却有所降低。20-40cm土层三种不同秸秆还田处理氨基糖和木质素均有所提高,但是与0-20cm土层相比,提升幅度较小。(5)还田秸秆为土壤补充大量养分,促进了微生物的移动与传播,真菌分解玉米秸秆的能力高于细菌,玉米秸秆投入后可以更大程度地刺激真菌增殖,从而更有利于真菌残体碳的积累。同时充分降解秸秆需要微生物种内和种间复杂的合作关系,在强烈的种间互作关系下,形成了特定的微生物集群(细菌模块1和真菌模块4),这些微生物集群通过促进胞外酶活性(β-GC和DHA),从而充分分解秸秆,增加活性有机碳组分,提高有机碳储量,从而促进土壤有机碳的累积与固定。综上,长期不同秸秆还田可以增加氨基糖和木质素含量,提高真菌残体碳和木质素在有机碳中的占比,增加了细菌、真菌活体含量和酶活性,改变了微生物群落结构和组成,提升土壤质量,改变各活性有机碳组分含量,增加机碳储量,提高作物产量。三种秸秆还田方式中秸秆过腹还田效果最好,可作为褐土的最佳培肥施肥选择。更多还原

【Abstract】 Soil carbon cycle is the core of soil organic matter turnover and the key factor affecting soil fertility.As one of the methods to improve soil organic matter,straw returning can not only reduce the pollution caused by straw burning to the atmosphere,but also help to improve soil organic matter.The soil carbon sequestration rate,the transformation of organic carbon among different components and its fixation mechanism are different under different long-term straw returning modes.At present,the research on the microbial mechanism of different straw returning modes on soil organic carbon fixation in the Loess Plateau is also weak.Based on the long-term positioning experiment of cinnamon soil farmland in Shouyang,Shanxi Province,we analyzed the soil organic carbon,carbon components,enzyme activities related to carbon conversion,microbial biomass,and microbial community under four different straw returning methods:no straw returning(CK),straw mulching(SM),straw crushing and direct returning(SC),and cattle manure(CM).The characteristics of soil organic carbon fixation and microbial ecological function under different straw returning modes were revealed,and the sources of soil organic carbon under different straw returning modes were analyzed by using soil stability markers(amino sugar and lignin).We attempts to clarify the process of soil carbon sequestration and its microbial mechanism under different long-term straw returning modes,provide a scientific basis for understanding the process of soil organic carbon sequestration in dry farmland,and provide a theoretical reference for the further practice of straw returning mode by this study.The main results were as follows:(1)Long-term different straw returning modes can significantly increase the content of soil organic carbon and its components,organic carbon storage and crop yield.The contents of soil total organic carbon(SOC),light fraction organic carbon(LFOC),microbial biomass carbon(MBC),water-soluble organic carbon(DOC),particulate organic carbon(POC)and readily oxidizable organic carbon(ROC)in different straw returning treatments showed the same trend,which was CM>SC>SM>CK.The ratio of each active organic carbon component to soil organic carbon was LFOC>ROC>POC>MBC>DOC.The highest sensitivity index under CM and SC treatments was DOC,which could be used as an indicator of early organic matter changes under CM and SC treatments.LFOC had the highest sensitivity index under SM treatment,and LFOC could be used as an indicator of early organic matter changes under SM treatment.The soil organic carbon storage of different straw returning treatments increased at a rate of 0.55~0.89 t/(hm2·a),and the total organic carbon increased at a rate of 0.26~0.60 t/(hm2·a).SOC showed a significant negative correlation with soil p H and a significant positive correlation with other factors.The main influencing factors of SOC were TK,DOC and LFOC.Compared with CK treatment,the cumulative yield of SM,SC and CM treatments increased by 6.38%,7.82%and 23.00%,respectively.The content of organic carbon and its components and the storage of organic carbon in the three different straw returning methods in the 20-40cm soil layer also increased,but the increase was smaller than that in the plough layer.(2)Long-term different straw returning modes all increased the soil enzyme activity,bacterial and fungal content in the plough layer,and the improvement effect was CM>SC>SM>CK.Compared with CK treatment,the contents ofβ-GC,CBH,POD,SC and DHA increased by 10.12%-207.63%,46.61%-145.47%,5.44%-11.97%,41.57%-72.26%and 60.38%-412.82%respectively under different straw returning modes.The content of soil bacteria and fungi increased by 1.13-9.40 nmol/g and 0.12-0.77 nmol/g,respectively.(3)Long-term different straw returning patterns increased theα-diversity of soil bacterial community,but there was no significant difference in theα-diversity of fungal community.The relative abundance of bacteria such as Bacteroidetes,Proteobacteria,Firmicutes and Actinobacteria increased by 0.10%-7.66%,1.91%-5.82%,0.60%-1.10%and 0.13%-1.31%,respectively,and the relative abundance of bacteria such as Chloroflexi and Thaumarchaeota decreased by 1.39%-2.66%and 4.85%-8.16%,respectively.Mortierella in fungi decreased by 29.05%-31.12%,and Basidiomycetes increased by 481.10%-24.76%.Soil p H is an important factor affecting the composition of bacterial and fungal communities.The results of network analysis showed that the indicator species of long-term different straw returning treatments belonged to different modules,among which Chryseolinea,Conocybe and Phaeoacremonium enriched in CM treatment formed specific functional microbial clusters through strong symbiotic relationship.Based on the functional prediction of FAPROTAX,it was found that long-term different straw returning increased the potential of soil bacteria to decompose organic matter and transform nitrogen components.The results of FUNGuild analysis showed that straw returning increased the relative abundance of pathotrophic fungi and saprophytic fungi.The results of the structural equation model showed that maize yield was mainly directly and positively regulated by SOC,while 4 species of bacterial module and 1 species of fungal module could indirectly affect SOC and maize yield by positively regulating DHA andβ-GC.(4)Long-term different straw returning modes can significantly increase the content of amino sugar and lignin.The content of amino sugar and lignin in CM treatment is the highest,which was significantly higher than other treatments.The difference between SC treatment and SM treatment was small,but both are higher than that in CK treatment.Compared with CK,the contents of amino sugar and lignin in different straw returning modes increased by 33.82-144.92 mg/kg and 78.97-827.24 mg/kg,respectively.The carbon content of bacterial residues and fungal residues increased by 10.93%-32.85%and 24.26%-158.15%,respectively.In SM,SC,CM and CK treatments,the microbial residue carbon was mainly fungal residue carbon.The contribution rates of bacterial residue carbon and fungal residue carbon to SOC were 5.36%-5.66%and10.99%-19.86%,respectively.The contribution rate of plant-derived carbon to SOC was between 1.48%and4.30%.SM,SC and CM increased the contribution rate of fungal residue carbon and plant-derived carbon,but the contribution rate of bacterial residue carbon decreased.In the 20-40 cm soil layer,the amino sugar and lignin of the three different straw returning treatments were increased,but the increase was smaller than that of the 0-20 cm soil layer.(5)The ability of fungi to decompose corn straw is higher than that of bacteria.The input of corn straw can stimulate the proliferation of fungi to a greater extent,which is more conducive to the accumulation of carbon in fungal residues.At the same time,the full degradation of straw requires complex intraspecific and interspecific cooperation of microorganisms.Under the strong interspecific interaction,specific microbial clusters(bacterial module 1 and fungal module 4)are formed.These microbial clusters promote extracellular enzyme activity(β-GC and DHA),thereby fully decomposing straw,increasing active organic carbon components,increasing organic carbon storage,and thus promoting the accumulation and fixation of soil organic carbon.In summary,long-term different straw returning can increase the content of amino sugar and lignin,increase the proportion of fungal residue carbon and lignin in organic carbon,increase the content of bacteria and fungi in vivo and enzyme activity,change the structure and composition of microbial community,improve soil quality,change the content of active organic carbon components,increase the storage of organic carbon,and increase crop yield.Among the three straw returning methods,straw over-abdomen returning has the best effect,which can be used as the best fertilization choice for cinnamon soil.更多还原