【作者】 吕海波；

【导师】 梁宗锁；

【作者基本信息】 中国科学院研究生院(教育部水土保持与生态环境研究中心) ， 生态学， 2012， 博士

【摘要】 植被覆盖和土地利用方式的变化影响到土壤碳含量。大量研究发现农地转化为林地后土壤碳贮量也随之发生变化。然而，森林生长序列中土壤碳的变化并不保持一致的增长趋势。森林生态系统中土壤有机碳的动态变化机制的研究颇显重要。研究通过对纸坊沟流域四种年限刺槐林的土壤有机质各组分的调查，在总结其特点的基础上，分别设置野外培养试验和室内培养试验，旨在探索造成有机质变化的影响因素。主要结论如下：（1）对1975年柠条林N75、1974年耕地H74和1978年刺槐林C78土壤剖面有机碳、全N、土壤机械组成、碳酸钙、容重、pH值等指标进行分析，发现各样地土壤有机碳的积累与<0.02mm粒径的土壤颗粒有较高的相关；土壤剖面各指标在不同深度存在异常变化，<0.002mm粘粒物质大幅度增加，表现出古土壤层的特征；1m深度有机碳储量C78>N75>H74，但差异主要表现在30cm深度以上土层，特征层的存在可能导致H74剖面16.684g/m3的有机碳评价误差，以及C78剖面36.926g/m2的误差。（2）分析了类似立地条件下10年、25年、31年、35年四个刺槐林和一个对照农地土壤有机碳SOC各组分的变化。三深度平均SOC含量、活性有机碳AOC含量、水溶性有机碳DOC含量随刺槐林年限增加而增加；与农地相比，所有刺槐林样地AOC/SOC、惰性有机碳ROC/SOC呈高值表现，惰性有机碳LOC/SOC值较低，DOC/水溶性有机氮DON较低而280nm的UV吸收值较高；随退耕年限的增加，25年刺槐林表现出一个以深度分异为代表的退耕特殊阶段。在刺槐林生长过程中，（i）AOC和缓性有机碳ROC都出现累积趋势，刺槐林有助于土壤碳的储存；（ii）土壤碳的累积过程中有组分差异表现，DOC，DOC/DON以及UV吸收值出现与SOC不同的变化；（iii）各深度AOC及SOC并未表现出一致的增长趋势，有深度分异。刺槐林生长发育过程中SOC的积累有组分和深度的差异，其相关机理需进一步研究。（3）对1975年柠条林N75、1974年农地H74和1978年刺槐林C78在100cm深度土壤剖面有机碳、全N、土壤机械组成、碳酸钙进行差异度分析和线性相关性分析，发现退耕后两种林地SOC及全N含量虽然都有明显变化，但是C78的差异主要表现在0-20cm深度，而N75则主要表现在20-100cm。相关度分析表明，H74在20cm以下SOC、C/N值都与0.002-0.02mm粒径极显著相关，C78在40cm以下SOC含量与<0.002mm粒径含量显著相关，C/N值与<0.02mm粒径由0-100cm的负相关，变为正相关。结果证明柠条林和刺槐林对SOC和全N的影响存在深度的差异，分别表现在深层和浅层。农地和刺槐林土壤深层SOC与细颗粒土壤显著相关，性质稳定。（4）对C78样地均匀添加枯落物碎屑的土壤培养坑分3月、7月和11月进行一年期的培养和观测，发现SOC各组分有季节性变化，20cm和40cm深度在7月SOC，活性有机碳POC及总氮TN值最高，可溶性有机碳DOC和可溶性有机氮DON呈相反变化趋势；培养过程中各指标出现深度分异，与20cm不同，在60cm深度，SOC随培养过程而递减，POC及全氮递增，而DOC在7月出现高值。SOC在初始积累过程中先增后减，体现出自我调节。SOC各组分的深度分异，反映出培养坑60cm深度SOC来源出现多元化，枯落物腐解产物影响程度减弱。（5）采集安塞纸坊沟31年刺槐林土样及林下混合枯落物，通过碱液吸收法测定100%、20%和2%含水量条件下3深度土样20cm，40cm，60cm、去除DOC土样（仅100%含水量条件下）、三种处理枯落物混合土样（林下混合枯落物、刺槐枯落物和草本类枯落物）培养过程中CO₂的累计释放量。结果表明，100%和20%含水量条件下各深度土壤CO₂释放量为20cm>60cm>40cm；20cm土样去除DOC后CO₂释放量明显减少，40cm明显增加，60cm没有明显变化；混合枯落物土样在100%含水量条件下CO₂释放量最高；20%和2%含水量条件下刺槐枯落物CO₂释放量明显大于草类，而100%含水量条件下草类枯落物略大于刺槐枯落物。研究证明土壤含水量对SOC组分含量和枯落物种类不同的土壤层呼吸强度存在差异性影响，强降水对DOC的淋失可造成表层土壤呼吸的减弱。（6）设置野外培养坑，将混合枯落物的土样和未混合枯落物的土样用致密的尼龙布隔开，LDOM（难以自由迁移的那部分WEOM）的含量用两者同时培养后WEOM含量的差值来计算。野外培养两年并分段采样，在7月份，样坑表层被吸附的WEOC（LDOC）和WEOC比率较其他时段低，并随样坑深度增加，比率升高；UV280nm吸收值及LDON/WDON较高，LDOC/WDOC较低。7月20cm LDOC/LDON与WEOC/WEON相当，但3月和11月前者高于后者，说明7月份LDOC/LDON值与RDOC/RDON没有明显差异，但在其他时间前者呈高值表现。研究证明LDOM有季节性和深度分异，当比较WEOM和DOM的研究结果时，应当注意到这个问题。更多还原

【Abstract】 Soils have the potential for C release or sequestration，can be affected by vegetationcover and land management. Many studies found the transformation of cultivated soil toforest ecosystem can change soil carbon sequestering. However, soil carbon stock change inforest chronosequence is likely to appear different results. Hence, accurate estimate on themechanism of SOC dynamics in forest chronosequences is necessary. The study investigatedthe variation patterns of organic matter of four selected Robinia pseudoacacia forests aged10,25,31,35years, and explore the rules. On basias of the rules, we made field and labortaryincubational experimentes to explore the effected factors. The main conclusions were showedas follows:（1）The study gives a anlysis on indexes such as SOC、Tatol nitrogen、particle size、CaCO3、CECand pH,etc,in the soil profile of Caragana Korshinskii Kom planted in1975、plowland since1974and Robinia pseudoacadia planted in1978. Soil organic carbonaccumulation in each site has a high correlation with the percent of <0.02mm diameter; somefactors in soil profiles exist unnormal changes in different depths, the <0.002mm clay matrialhas a substantial increase, represents the charactors of illuvial horizon; In the depth of100cm,it is C78>N75>H74on SOC content, however, the main difference was reflected in theupper30cm depth. The presence of ancient soil lead to16.684g/m3error on H74SOCassessment, as well as36.926g/m2Error on C78SOC assessment.（2）We investigated the variation patterns of organic carbon of four selected Robiniapseudoacacia forests aged10,25,31,35years, and a contrastive tillage site in similartopography condition. On average of20cm,40cm,60cm depth, SOC, active organic carbon（AOC）, DOC gradually increase with the forest growth. Compared with tillage sites,AOC/SOC ratio, ROC （resistant organic carbon）/SOC ratio show a higher value, and LOC（slow organic carbon）/SOC ratio shows a lower value. DOC/DON is lower and UV absorptionat280nm shows a higher value in all forest sites. During forest restoration,25-year-oldRobinia pseudoacacia forest shows a special phase in four forest sites represented by depthdistribution. During forest restoration （i） not only AOC, but ROC take an accumulationprocess, Robinia pseudoacacia forest restoration contributes to SOC accumulation.（ii） DOC,DOC/DON, UV-absorbance appear changes but not obviously accordant to SOC, suggestingdifferent changes during SOC accumulation.（iii） SOC, AOC don’t show a persistent increase in each depth of soil profile and which indicate a depth distribution. Our study found SOChad compounds-distribution and depth-distribution, but the relative machisms need to beexplore.（3）Analyzed the quantity of SOC, total nitrogen, particle size, CaCO3for the diversityanalysis and the correlation ratio in100cm soil profiles respectly in Caragana KorshinskiiKom forest planted in1975（N75）、tillage since1974（H74） and Robinia pseudoacadia forestplanted in1978（N78）. The results suggest that compared with tillage site, though SOC andtotal of nitrogen in two restored forest sites show obvious changes, the distinct diversity inC78appears mainly in the depth of0-20cm, and the same state appears at20-100cm for N75.At20-100cm in H74site, SOC, C/N show remarkable correlations with percent of0.002-0.02mm particle size. Below40cm in C78site, SOC are remarkable correlation with<0.002mm particle size, the correlation rate between C/N and <0.02mm changes from minusvalue for0-100cm depth to positive value for40-100cm. Our study indicate that after forestrestoration, changes of SOC and total of nitrogen mainly represent a obvious diversity at40cm and60cm soil layer for Caragana Korshinskii Kom forest, but diversity appearsat20cmfor Robinia pseudoacadia forest. SOC in deep soil layer of tillage and Robinia pseudoacadiaforest is closely adsorbed by fine particle size soil, with a steady quality.（4）We have observed the dynamics of SOC and it’s relative factors of three depths（20cm,40cm,60cm） incubation holes, which were backfilled soils mixed with litter rags inadvance, in C78Robinia pseudoacacia forest, and took samples in March, July and November,2010. The results represent reasonal changes, at20cm and40cm, SOC, POC, TN in July arehighest, but decrease in November, and reverse states represent for DOC. Different with thoseat20cm, SOC at60cm decreases gradually in the process of incubation and TN and POChave increase trend, DOC in July appears a high value. During C accumulation, SOCincreases but decrease later, represents self-modulation function. DOC has different sourcesfor deeper soil layer with those at20cm, SOC suggests complex sources at60cm, theproduction of litters decomposition have limited effect.（5）Took soil and mixed litter samples in31year old Robinia Pseudoacacia forest anddetermined the accumulative CO₂-release of soil samples and DOC-removal soil samples（100%water content only） at three soil layers （20cm，40cm，60cm）, three controlledlitter-mixed soil samples （mixed by complex litters, included Robinia Pseudoacacia littersand herbage litters）, in laboratory under the different soil moisture levels of100%,20%,2%water content respectively. The results showed that the CO₂-release levels in different depthswere suggested by20cm>60cm>40cm in controlled100%and20%water content; In the condition of100%water content, when DOC were removed, the accumulative CO₂-releasequantity of20cm soil samples decreased, but obviously increase for samples at40cm andhad no marked change at60cm; The accumulative CO₂-release of complex litter-mixed soilsamples had highest value in the condition of100%water content, those of simply RobiniaPseudoacacia litter-mixed samples was obvious higher than that of herbage litter-mixedsamples in20%and2%water content, but slightly lower in100%water content. Theasynchronous effect of water content levels is suggested on the respiratory intensity of the soillayers with different SOC compositions and litter kinds, heavy precipitation removes DOCfrom soil subsurface layers, can weaken the soil respiratory intensity.（6）In two-year incubation experiment, litter-mixture soil （outside bags） and nolitter-mixture soil （inside bags） were insulated by nylon cloth in incubation holes, changes inthe LDOM portion of the soil were then monitored by comparing the WEOM levels outsidethe bags with inside the bags., In July, the ratio of locked WEOC （LDOC） to WEOC outsidebags （LDOC/WEOC） was low in the topsoil, and increased gradually with depth while thelocked WEON （LDON） to WEON ratio outside bags （LDON/WEON） suggested no obviousrule. At20cm In July, LDOC/WEOC were lower and LDON/WEON were higher than thosein March and November, solutions of the soil samples had highest UV-absorbance at280nm,The LDOC:LDON ratio at20cm was comparable in July with, but higher in March andNovember than WEOC:WEON ratio of samples outside bags, which implied thatLDOC:LDON has little difference compared to that of RDOM in July, but represents highervalue at other times of the year. The study proves that LDOM has seasonal variability anddepth distribution, which brings a difficult to distinguish the difference between WEOM andDOM （RDOM）.更多还原