【作者】 李英臣；

【导师】 宋长春；

【作者基本信息】 中国科学院研究生院(东北地理与农业生态研究所) ， 环境科学， 2012， 博士

【摘要】 氮素是大气圈中含量最丰富的元素，同时也是陆地生态系统植物进行光合作用不可或缺的元素之一。全球变暖已经成为一个不争的事实，而北方高纬度地区对气候变化的响应最为敏感。气候变暖将使北方多年冻土区冻土融化，活性层加深，将改变土壤氮可利用性及碳蓄积。因此本论文在我国东北不同类型冻土区选择典型性样地，运用空间代替时间的方法研究不同冻土区土壤氮可利用性变化特征，枯落物分解及元素释放特征，以及不同氮可利用性变化对有机碳矿化、枯落物分解和N₂O释放的影响，为预测全球变化背景下我国北方沼泽湿地土壤氮可利用性变化特征及其对土壤和枯落物碳氮活性的影响提供基础资料。主要得到以下研究结论：不同冻土区湿地土壤全氮含量从连续多年冻土区至季节性冻土区湿地呈明显的降低趋势，土壤氨氮含量、硝氮含量、土壤微生物量氮（MBN）含量都有明显的季节变化；不同冻土区湿地土壤剖面铵态氮，硝态氮，溶解性有机氮含量都有随剖面深度加深而降低，但是不同冻土区和不同形态氮变化趋势有所差异。连续多年冻土区湿地土壤各氮组分含量平均值均高于岛状多年冻土区湿地和季节性冻土区湿地。不同冻土区湿地土壤净矿化、净硝化速率均呈现明显的季节变化特征，净矿化速率都在生长季初期和中期出现正值，而在生长季末期出现负值，随着纬度的升高，净矿化速率出现负值的时间有所提前。总之，土壤氮可利用性在多年冻土区湿地较高，但是由于寒冷干燥的气候条件，使土壤氮的利用效率较低。在未来气候变暖的趋势下，温度升高对连续多年冻土区湿地作用更加剧烈。不同冻土区湿地土壤有机碳含量差异显著，连续多年冻土区泥炭沼泽高于岛状多年冻土区沼泽湿地和季节性冻土区冻土区沼泽湿地。土壤微生物量碳（MBC）含量的空间时间变异性比较大，与温度和湿地类型都有一定的相关性；各不同冻土区土壤微生物量碳含量都随剖面深度增加而逐渐降低。连续多年冻土区土壤剖面可溶性有机碳（DOC）含量高于岛状多年冻土区湿地和季节性冻土区小叶章湿地，随深度的增加差异逐渐减小。通过对不同冻土区湿地土壤氮输入研究表明，土壤有机碳矿化速率和累积矿化量与初始的土壤有机碳，全氮含量和微生物量碳含量呈显著相关关系，表明有机碳矿化受初始理化性质和微生物群落组成的影响；氮输入对不同冻土区土壤有机碳矿化产生抑制作用，随氮输入量的增大，对不同土壤抑制作用有所差异。培养结束后有机碳累积矿化量与MBN及MBC/MBN有明显的相关关系，表明氮输入可能通过改变土壤微生物群落的结构或组成对有机碳矿化产生影响。基于连续多年冻土区氮输入对不同深度土壤有机碳矿化实验，结果表明土壤有机碳矿化随土层深度增加而降低，原因可能与不同层次土壤质量有关。土壤含水量，pH值和全磷含量与土壤有机碳矿化有明显的相关性，但是土壤有机碳含量和全氮含量与土壤有机碳矿化的相关性不明显。研究结果表明，在北方泥炭地，土壤全碳或者全氮含量可能不是影响土壤有机碳矿化的主要原因，磷或许是影响有机碳矿化的关键因素。氮输入对表层（0-30cm）土壤无影响或有促进作用，对深层（30-100cm）土壤有抑制作用，随氮输入量增大作用增强。结果表明氮输入对有机碳矿化的促进和抑制作用可能同时存在，具体表现出促进或者抑制作用可能与碳基质质量有关。运用分解袋法研究不同冻土区枯落物分解，结果表明季节性冻土区地表残余物分解速率明显高于岛状多年冻土区和连续多年冻土区湿地地表残余物。培养结束后，季节性冻土区小叶章枯落物碳残留率明显低于其它几种枯落物，季节性冻土区毛苔草地表残余物和连续多年冻土区地表残余物净碳残留率差异不明显，但都低于岛状多年冻土区臌囊苔草湿地地表残余物；几种枯落物净氮残留率随分解时间变异很大，但总体几种枯落物之间差异不明显；枯落物磷残留率四种枯落物差异明显，试验结束后净磷残留率从低到高顺序为季节性冻土区毛苔草湿地，季节性冻土区小叶章湿地，连续多年冻土区湿地，岛状多年冻土区湿地。表明积水条件有利于湿地碳蓄积，但是加速磷释放；温度升高则会增加枯落物碳释放。在未来全球变暖背景下，冻土退化而导致的湿地变干将不利于碳蓄积。羊胡子草枯落物在不同冻土区分解实验表明，羊胡子草枯落物在不同冻土区分解速率差异达到极显著水平（p<0.001），表明环境条件对枯落物分解意义重大。羊胡子草枯落物净碳残留率和枯落物分解质量残留率的变化趋势基本一致，连续多年冻土区枯落物净碳残留率高于岛状多年冻土区和季节性冻土区；净氮残留率与枯落物分解在三个实验点呈现相反的趋势,季节性冻土区明显高于岛状多年冻土区和连续多年冻土区；羊胡子草枯落物磷残留率变化趋势基本一致，连续多年冻土区湿地，岛状多年冻土区湿地和季节性冻土区湿地羊胡子草枯落物磷残留率分别为89.8%，108.9%和124.2%。氮输入对不同冻土区残余物分解实验发现，氮输入对不同冻土区残余物分解都有一定程度的抑制作用，且随氮输入量的增加抑制作用有所增强，但是对不同冻土区地表残余物的抑制作用有所不同。培养结束后氮输入增加枯落物氮含量，且氮输入与不同残余物氮含量有很好的线性相关关系。磷含量对氮输入的响应不同的地表残余物有所不同，但是高氮处理都使地表残余物磷含量有降低的趋势。连续多年冻土区湿地土壤N₂O排放随土层深度增加而降低，至深层表现为N₂O的净吸收。氮输入对不同层次土壤都有明显的促进作用，尤其是在开始阶段，氮输入对N₂O排放产生激发效应，随氮输入量增大激发效应增强。在培养20天之后氮输入对不同层次土壤N₂O排放影响不显著。培养结束后，不同深度土壤N₂O累积排放量随氮输入量的增大而增加，底层土壤高氮处理高于表层土壤，表明底层土壤对氮输入的响应更敏感。室内培养实验结果表明，各枯落物在培养期内，氮输入都明显促进了枯落物N₂O排放，但是对不同枯落物有所差异。随氮输入量的增大，氮输入对枯落物影响持续的时间增加，低氮输入只在培养开始1-6d阶段比较明显，中氮在培养约一个月左右促进作用显著，高氮处理在整个培养期都存在明显的促进作用。培养结束后，不同枯落物低氮处理与对照处理的差异没有达到显著水平，中氮和高氮处理水平除季节性冻土区毛苔草枯落物外都明显促进了N₂O累积排放量。连续多年冻土区地表残余物中氮输入时N₂O累积排放量最大，表明连续多年冻土区地表残余物对N₂O排放的影响并不是随氮输入量的增大而增大。更多还原

【Abstract】 Nitrogen （N）, as the richest element in atmosphere, is one of limiting elementsfor plant photosynthesis and primary productivity in terrestrial ecosystem, especiallyin high latitudes area in Northern Hemisphere. Global warming is an irrefragable factand north high latitudes are sensitive to this change. With global warming, the northpermafrost will thaw, active layer will deepen, which would change soil nitrogenavailability and carbon （C） storage. So in the present study, we selected typicalwetlands in different frozen areas in Northeast China, used the method of spatial scalereplace temporal scale to research soil nitrogen availability, litter decomposition andN₂O emission. This thesis would offer some basic information for us to predict soilnitrogen availability and the effects of nitrogen availability on carbon storage inwetland ecosystems in Northeast China under global warming conditions. The resultsare as follows:The total N contents were significantly different in various wetland types; soilmicrobial biomass carbon （MBC） contents had an obvious tendency of seasonalchange. The soil NH₄⁺-N, NO₃--N, dissolved organic nitrogen （DON） contents indepths were decreased as the depth increasing, but the decreased tendency wasvarious in different frozen areas. The average content of all N components fromhighest to lowest was continuous permafrost, island permafrost and seasonally frozenground. The net soil mineralization and nitrification in different wetland ecosystemhad evidently seasonal change, net mineralization rates were positive in the beginningof growing season, and negative in the end of growing season. In a word, Navailability was higher in continuous permafrost, but the N efficiency was low due tolow temperature. In the tendency of global warming, temperature increasing will hadmore intensive effect in continuous permafrost.The difference of total organic C was significant in three wetland ecosystems, continuous permafrost soil> island permafrost soil>seasonally frozen ground soil.MBC content had various temporal and spatial changes and had obvious correlationwith temperature and wetland types. The MBC content at depth was decreased. Thesoil dissolved organic carbon （DOC） content was decreased with decreased latitudes,continuous permafrost soil> island permafrost soil>seasonally frozen ground soil,and the difference was gradually reduced as soil depth increasing.The soil was collected in three frozen areas and investigated effects of exogenousnitrogen availability on carbon mineralization. The results showed that the cumulativeC mineralization of three types of soil under control treatment existed positivecorrelation with initial amount of soil organic C, total N and MBC in the end ofincubation, which indicated that C mineralization was effected by initial characteristicproperty and microbial communities. N input suppressed C mineralization and thesuppression increased as the amount of N increasing, but the suppression under Ninput was different in three soils. After incubation, cumulative mineralizationpositively related with MBN and negatively related with MBC/MBN, which indicatedthat N availability may affect the carbon mineralization by changing microbialstructure and composition.Through laboratory experiment to investigate the effects of N availability oncontinuous permafrost soil organic mineralization （SOC） in different depths, resultsindicated the SOC mineralization in boreal peatlands soil decreased with depth, whichmay be caused by soil initial characteristics in different soil layers. Water content, pHand total P content had evident correlation with SOC mineralization, while total SOCand total N had no or slight effect on SOC mineralization. Our results indicated that inboreal peatlands, SOC mineralization may not be limited by C or N energy, pavailability may be the mainly factor affecting SOC mineralization.A litter decomposition experiment was set in different wetland ecosystems. Theresults showed that the surface residues biomass from biggest to smallest wasseasonally frozen ground （SJ）, island permafrost （YH） and continuous permafrost（TQ）. The decomposition rates of SJM and SJX were evidently higher than YHM andTH, the difference between YHM and TH was not significant. Net C remaining of SJX residues was significant lower than other residues, net C remaining between SJMand TH was similar, but all lower than YHM residues. Net N remaining of all residueswas various in different experimental stages, but the difference among residues wassmall. In the end of experiment, the N remaining from highest to lowest was TH, SJM,SJX and YHM. The residues P remaining was evidently different after one yearexperiment, from highest to lowest was SJM, SJX, TH and YHM. These resultsindicated that inundated condition was favorable for carbon storage, but accelerated Prelease; increased temperature would improve C release.Eriophorum vaginatum litter decomposition was investigated in various wetlandecosystems. The results showed that decomposition rates were significant different indifferent wetland ecosystems （p<0.001）, indicated environmental condition plays animportant role in litter decomposition. The tendency of C remaining was similar withlitter decomposition, in the end of one year decomposition, litter C remaining fromhighest to lowest was TQ, YH, SJ, however, the amount of N remaining was oppositewith litter decomposition, from highest to lowest was SJ, YH, TQ; P remaining in TQ,YH and SJ was similar, the amount of P remaining was89.8%,108.9%and124.2%,respectively.N addition suppressed residue decomposition, the inhibition enhanced as theamount of N addition increasing, but the response of different residue to four levels ofN addition was various. In the end of incubation, N addition increased residue Ncontent; a significant linear correlation existed between the amount of nitrogenaddition and N content of SJX, SJM and TH residue. P content of residues haddifferent effects on N addition, but high N addition decreased the P content of allresidues in different wetland ecosystems.Soil N₂O emission rates decreased at depths, and became a sink of N₂O in deepsoil. N addition evidently improved N₂O emission rates under different soil depth,especially in the initial stage of N addition. N addition had a priming effect on N₂Oemission, and the effect increased as N amount increasing. N addition had small effecton soil N₂O emission after20d incubation. In the end of incubation, cumulative N₂Oemission at depths was increased as N amount increasing, which of soil in deep depth was higher than in surface soil under high N treatment. These results indicated thatdeep soil was more sensitive to N addition than surface soil on N addition.Through laboratory experiment during134d, N addition enhanced N₂O emission,but the response of different residues to four levels of N addition was various. Theeffect of N addition on residues decomposition lasted longer period as the amount ofexogenous N increasing. The low N treatment impacted on N₂O emission only at first6-10days; the medium N treatment affected the N₂O emission at about the first month;while the high N treatment affected the N₂O emission in all incubated period. In theend of incubation, Low N treatment did not affect cumulated N₂O emissionsignificantly, while medium N and high N treatment evidently enhanced N₂Oemission （p<0.05）, except the SJM residue under medium N treatment. CumulativeN₂O emission of TH residues was biggest under medium N addition treatment; thisresult indicated that the effect of N addition on TH residues was not linear.更多还原