【作者】 张红；

【导师】 吕家珑；

【作者基本信息】 西北农林科技大学 ， 土壤学， 2017， 博士

【摘要】 农作物秸秆是一种生物质能资源,它含有大量有机质及植物生长所必需的氮、磷、钾和其它中微量元素。陆地生态系统中,秸秆腐解是土壤有机质的重要来源。秸秆在土壤中的转化速率不仅与秸秆本身的物质构成有关,还与温度、水分、土壤性状等环境条件有关。微生物是地球化学循环中的重要组成部分,在秸秆腐解过程中发挥着很重要的作用,而秸秆性质和环境因素也会导致微生物群落结构和功能多样性的差异。本试验利用陕西关中的3个长期试验地(农田、桃园和葡萄园),采用尼龙网袋法进行秸秆腐解试验,结合土壤性质、Biolog和土壤酶的分析,对比研究了不同秸秆在不同利用方式下的土壤和秸秆腐解微生物群落结构组成特征和演替规律,分析了环境条件、土壤类型和秸秆性质对腐解微生物种群演变的综合影响,探寻秸秆结构组成与分解秸秆的微生物群落演替的相关性,为秸秆生物质能源发挥最大效益研究奠定基础,并为长期试验条件下土壤有机碳转化研究和科学养地用地研究提供科学依据。所取得的结论如下:1.随着腐解时间的增加,新鲜秸秆的残留率波动不大,3个试验地的变化基本一致,主要趋势为FB(新鲜大豆秸秆)>FCN(新鲜玉米秸秆+氮)>FC(新鲜玉米秸秆),整个腐解过程分为2个阶段:0-10d迅速下降,10-360d缓慢下降,腐解结束后,各处理的腐解残留率基本下降到原来质量的17.61~30.43%。烘干粉碎过的秸秆腐解残留率变化较大,主要趋势为DB(烘干大豆秸秆)>DC(烘干玉米秸秆)>DCN(烘干玉米秸秆+氮),整个腐解过程分为3个阶段:0-10d迅速降低,10-270d缓慢降低,270-360d保持稳定,腐解结束后,各处理的腐解残留率基本下降到原来质量的36.11~47.24%。随着腐解时间的增加,残留率的变化趋势为烘干秸秆>新鲜秸秆,无论秸秆的新鲜与否、体积大小以及C/N如何,秸秆残体腐解的速度均为玉米秸秆>大豆秸秆。土壤温度明显影响了秸秆在试验地的腐解残留率,土壤平均温度表现为农田14.7℃>葡萄园14.0℃>桃园13.6℃,土壤温差的大小影响了土壤中微生物活性的稳定程度,进而影响不同秸秆在不同试验地腐解残留率的差异。土壤含水量对秸秆的腐解速度影响不大,而秸秆本身的含水量在一定程度上影响秸秆的腐解残留率。2.对3个长期试验地秸秆腐解过程中土壤微生物群落多样性动态的研究结果表明,随着秸秆腐解时间的延长,土壤微生物群落的稳定性的趋势为农田>葡萄园>桃园。随着秸秆腐解时间的延长,3个试验地土壤微生物碳代谢群落比较相似,其优势种群基本上均为糖类代谢群,其次为多聚物类。土壤微生物的物种丰富度有所降低而常见种群的优势度略有增加,且均匀度也有所降低,这期间可能出现一些分解秸秆的优势种群。3个试验地土壤微生物的优势种群中最弱碳代谢群落均为芳香化合物代谢群。3.随着腐解时间的增加,农田土壤中秸秆FB微生物群落的物种丰富度降低而最常见种群的优势度变化不明显,说明可能出现一些分解秸秆的优势种群,导致农田土壤中不同秸秆处理的腐解残留率变化比较明显。果园土壤中秸秆FB微生物群落丰富度不断增加,且其优势度保持不变或降低。整体秸秆微生物群落功能多样性呈现一定演替规律并有趋同的趋势。3个不同试验地秸秆腐解微生物群落结构对6类碳源利用的顺序不太一致,但是它们在腐解过程中的优势种群主要以糖类和多聚物为主,且伴随着芳香化合物在腐解中后期的逐渐累积,表明对芳香化合物的利用最弱。4.本研究发现,3个试验地土壤的过氧化氢酶活性明显影响了不同秸秆在不同土壤之间的腐解残留率,且土壤温度对土壤过氧化氢酶活性的影响较明显。随着秸秆腐解时间的延长,果园土壤牧草覆盖可以维持或提高土壤脲酶和蔗糖酶的活性,而农田土壤中脲酶以及蔗糖酶活性却降低;不同利用方式下土壤过氧化氢酶活性均随腐解时间的延长而有所降低,且3个试验地土壤之间的过氧化氢酶活性差异不显著(P>0.05)。在不同环境条件下,所有秸秆处理与秸秆微生物群落的优势度、对糖类和芳香化合物的利用无显著相关关系。土壤pH与土壤脲酶和蔗糖酶呈极显著负相关关系,土壤有机质与土壤过氧化氢酶呈极显著正相关,土壤速效钾与土壤过氧化氢酶呈极显著正相关关系,表明土壤pH、有机质和速效钾显著影响了土壤酶活性。5.选取南方红壤(典型酸性土)和北方塿土(石灰性土壤)2种土壤、5种重金属(Cd、Cr、Pb、Hg、As)和2种秸秆(小麦秸秆和玉米秸秆),采用室内培养试验,定期取样,研究了在秸秆不同腐解阶段,不同重金属对土壤酶的影响。结果发现,各处理的土壤过氧化氢酶、脲酶和蔗糖酶活性基本趋势都是塿土>红壤,且塿土过氧化氢酶活性对Pb和Cr相对敏感;红壤过氧化氢酶活性对Cr更敏感;土壤脲酶活性对重金属Hg胁迫影响更大;添加重金属Pb明显激活土壤蔗糖酶活性。土壤总体酶活性中Cr对红壤不同处理土壤总体酶活性敏感度最高,而Hg在塿土中变化比较剧烈。更多还原

【Abstract】 Crop straw is one kind of biomass resource that contains large amounts of organic matter,nitrogen,phosphorus,potassium,and other trace elements necessary for plant growth.In the terrestrial ecosystem,straw decomposition is an important source of soil organic matter.The rate of straw decomposition in the soil is not only related to the material composition of the straws itself,but also to the environmental conditions such as temperature,moisture,and soil properties.Microorganisms are an important part of the geochemical cycle and play a very important role in the straw decomposition process.Various straws characteristics and environmental factors could lead to distinct microbial community structures and functional diversities.In this work,the mesh bag method was used to explore howplant straws decompose in fields with three long-term field experiments(Farmland,Peach orchard and Vineyards)in Guanzhong of Shann’xi Province.Combining with soil properties,Biolog,and soil enzymes analysis,soil microbial community diversities were investigated under various straws decomposings in different land uses.The effect of environmental factors,soil types,and straws properties was explored to find out the relationships between straw properties and microbial communities decomposing straws.The results will apply the basic research data for maximally benefiting from straw biomass energy and provide the scientific basis for soil organic carbon conversion and reasonable use of long-term experimental fields.The main results are listed as follows:Results showed that with the decomposition time increasing,the residue rate of fresh plant straws did not varied much.The three long-term field experiments showed the similar trend,with an order of FB(Fresh bean stalk)> FCN(Fresh corn stalk + nitrogen fertilizer)> FC(Fresh corn stalk).The decomposition process was divided into two stages: 0-10d(decreased rapidly)and 10-360d(slow decline).The residue rate of straws in all treatments decreased to 17.61-30.43%,when decomposition completed.The residue rate of dried milled straw varied among different treatments,with the order of DB(Dry bean stalk)> DC(Dry corn stalk)> DCN(Dry corn stalk + nitrogen fertilizer).The whole decomposition process was divided into three phases: 0-10d(decreased rapidly),10-270d(slow decreases),and 270-360d(stable).When decomposition completed,the residue rate of straws in all treatments decreased to 36.11-47.24%.With the increase of decomposition time,the residue rate of drying straws was higher than fresh straws.Regardless of fresh or dry straws,the volume size,and C / N how,the stalk straws showed the more rapid decomposition rate compared with the soybean straws.Soil temperature significantly affected the residue rate of straw decomposition in different experimental fields.Soil temperature deviation affected the stability of soil microbial activity and thereby resulted in distinct decomposing residue rate in different experimental fields.Soil water content did not significantly affect the straws decomposition rate.When the hard decomposing component accumulated gradually,slowing greatly the rate of straw decomposition in experimental fields.The water content of straws affected the straw decomposition residue,especially for the high-quality of plant residues was more obvious.By comparing with dry straw decomposing residue rate,we founded that high water content of straws did not necessarily speed up the decomposition rate,which need more complex chemical reaction to complete the straw decomposition process.In terms of soil microbial community activity(average well color development,AWCD),the microbial community stability of three long-term experiments followed an order of Vineyard > Peach orchard > Farmland.With the extension of the time of the straw decomposition,the soil microbial carbon metabolism of the three experimental soil was similar,and the dominant population was basically shown as the carbohydrate metabolism group,and the second was polymer.The diversity index results showed that with the increase of decay time,the species richness of microorganisms in three land uses soil decreased and the dominance of common species increased slightly.Meanwhile,the evenness also decreased,indicating the possible occur of some dominant population decomposition of straw.The aromatic compound metabolism group was the weakest carbon metabolism group in all tested soils.The diversity index analysis indicated that with the increase of decomposition time,the microbial species richness in straw FB treatment in farmland soil reduced,while the dominance species were stable.It was indicated that some decomposition straw dominant population occur,resulting in the decomposing rate significantly changed among different straw treatment in farmland soil.For the straw FB treatment in orchard soil,microbial community richness increased with the decomposing time and the dominance remained the same or lower,which need to be studied further to find out which microorganism affecting decomposing.With the increase of decomposing time,the microbial community function showed some regularity and the convergence trend.The utilization orders of the 6 kinds of carbon sources by microbial community in different land uses soils were not consistent.However,the dominant species were mainly composed of sugars and polymers with the aromatic compounds accumulation gradually in the middle of decomposing process,which indicating the weakest use of aromatic compounds.The results showed that the soil catalase activity significantly affected residual rate of straw decomposing in different experimental fields.Soil temperature also influenced the soil catalase activities.With the extension of the straw decomposition time,orchard soil with grass coverage would maintain and improve the activities of soil urease and invertase,while reduced the activities of soil urease and invertase in farmland.The soil catalase activity decreased with the decomposition time increased and showed the similar valuesin all soils with different land uses(P>0.05).Due to the different management practices and fertilization methods in different experimental fields,the activities of soil enzyme had changed with different trends,particularly between soil urease and invertase in the orchard.The pasture cover did not show the advantages of nitrogen fixation and affected the rate of decomposition straws.Different straw treatments had different sensitivities to environmental factors,which affecting the growth environment of microorganisms and resulting in different diversity of microbial communities in the process of straw decomposition.The results showed that there was no significant correlation among the dominance of straw microbe,the utilization of sugars,and aromatic compounds.Soil pH had extremely significant negative correlation with the soil urease and sucrose.Soil organic matter was significant positive correlated with soil catalase.Soil available phosphorus and potassium were very significant positive correlated with soil catalase,indicating that the soil pH,organic matter,and available potassium significantly affected the soil enzyme activity.We selected southern red soil(typical acidic soil)and the north Lou soil(calcareous soil)to explore the affect of 5 kinds of heavy metal(Cd,Cr,Pb,Hg,As)on soil enzymes at the different stages of two straw decomposition(wheat straw and corn straw)by indoor cultivation experiments.The results showed that compared with red soils,the catalase,urease,and sucrose enzyme activities were higher than Lou soils.The catalase activity in Lou soils was more sensitive to Pb and Cr than in red soils.The catalase activity in red soil was more sensitive to Cr.The soil urease activity showed sensitive change on heavy metal Hg stress.The addition of Pb obviously increased on the soil sucrose enzyme activity.The total enzyme activity of red soil was the most sensitive to Cr,while for Lou soil,it was most sensitive to Hg.更多还原