【作者】 罗达；

【导师】 史作民；

【作者基本信息】 中国林业科学研究院 ， 生态学， 2014， 博士

【摘要】 人工林正逐步成为世界森林资源的关键组分，并在整个森林可持续经营管理过程中发挥着重要作用。然而，长期以来为了片面追求经济效益，国内外人工林都存在诸如生物多样性丧失，土壤肥力退化，生态系统稳定性降低等问题。在我国亚热带，为减少低效人工林带来的负面影响，促进人工林的多目标经营，提高人工林的生态功能和经济价值，许多乡土珍贵阔叶树种(包括固氮树种)逐渐被用于亚热带人工林营建的生产实践中。有关该地区不同森林经营措施对人工林影响的研究主要集中在林分生产力的经济效益方面。然而，由于不同人工林的凋落叶、根系的数量和质量以及冠层结构等的差异都将导致土壤环境特征、理化性质，以及土壤生物化学过程的不同。因此，从生态功能的角度深入探索不同营林模式对人工林生态系统碳氮特征的影响变得十分必要。全球CO2浓度和温度升高、氮沉降、物候变化和干旱胁迫等都可能导致森林枯落物输入量发生变化，因此，在研究森林土壤碳氮动态变化过程中考虑枯落物输入改变的影响变得非常重要。为此，本研究在南亚热带的广西壮族自治区凭祥市中国林业科学研究院热带林业实验中心选取了林龄相同、立地条件相似、位置邻近的三种幼龄人工林类型[格木(Erythrophleumfordii)纯林、马尾松(Pinus massoniana)纯林、格木与马尾松混交林]为研究对象，同时结合凋落物输入的控制实验，主要采用常规理化分析法、气压过程分离技术(BaPS)和磷脂脂肪酸技术(PLFA)，研究了：1)不同树种人工林生态系统碳氮储量及其空间分布特征；2)不同树种人工林土壤呼吸和总硝化速率以及微生物群落结构的季节变异；3)人工林土壤呼吸和总硝化速率以及微生物群落结构对凋落物输入改变的响应；4)环境因子与土壤呼吸和总硝化速率之间的相关关系，以期为南亚热带人工林经营过程中的树种选择及合理的营林方式提供数据参考和科学依据。主要研究结果如下：(1)格木、马尾松幼龄纯林及马尾松与格木混交林生态系统碳氮储量存在差异。格木、混交林和马尾松人工林生态系统总碳储量分别为134.07t hm-2、137.75t hm-2和131.10thm-2，总氮储量则分别为10.19t hm-2、8.68t hm-2和7.01t hm-2。三种人工林生态系统碳氮库空间分布基本一致，绝大部分碳氮储存于0～100cm土壤层，平均分别占生态系统总碳和氮储量的81.49%和96.91%，其次为乔木层(分别占17.52%和2.69%)，林下植被和凋落物层所占比例最小。林地土壤碳主要集中于表土层，其中，0～30cm土层平均碳储量为52.52t hm-2，占土壤总碳储量(0～100cm)的47.99%，土壤氮的分布则无明显规律。相比于纯林，与固氮树种混交的营林方式表现出更大的碳储存能力。同时，三种幼龄人工林生态系统较低的地上与地下部分碳氮分配比，表明其仍具有较强的碳氮固持潜力。(2)三种人工林土壤呼吸和总硝化速率均呈现明显的季节变异(p<0.05)，具体表现为，土壤呼吸和总硝化速率从2012年9月到2013年1月的旱季下降至最低值(平均分别为2.63mg C kg-1SDW d-1和0.34mg N kg-1SDW d-1)，然后持续升高直到2013年7月的雨季(平均分别为22.44mg C kg-1SDW d-1和1.23mg N kg-1SDW d-1)。土壤呼吸和总硝化速率与土壤温度和湿度之间存在显著相关关系(p<0.05)，表明土壤温度和湿度是影响土壤呼吸和总硝化速率的关键环境因子。土壤全氮、铵态氮和硝态氮与土壤呼吸和总硝化速率也呈显著相关关系(p<0.05)，这表明土壤碳氮转化作用在受土壤微环境条件影响的同时，还受土壤其它环境因子的综合影响。不同人工林中，格木人工林土壤呼吸和总硝化速率显著高于混交林和马尾松林(p<0.05)，这主要归因于树种生物学特性的差异，阔叶固氮树种格木较高的凋落叶和细根生物量和质量以及较快的分解速率使得林地土壤养分和底物有效性高于其它两种人工林。与其它研究结果对比表明，土壤呼吸和总硝化速率，以及Q10值均可能因植被类型、立地质量、林龄或气候带的不同而有差异。(3)三种人工林旱季平均土壤微生物PLFAs总量、细菌PLFAs量、真菌PLFAs量、放线菌PLFAs量及丛枝菌根真菌PLFAs量分别比雨季高170.1%、182.1%、152.1%、232.5%和185.2%(p<0.05)。不同人工林中，马尾松林旱季土壤微生物的PLFAs总量、细菌PLFAs量、真菌PLFAs量、放线菌PLFAs量均最高，混交林次之，格木林最低；而雨季格木人工林土壤微生物的PLFAs总量、细菌PLFAs量、真菌PLFAs量、丛枝菌根真菌PLFAs量显著高于马尾松林(p<0.05)。主成分分析结果表明，土壤微生物群落结构组成受林分类型和季节的双重影响。冗余分析表明，土壤温湿度、pH值、全氮及铵态氮含量与单个特征磷脂脂肪酸之间呈显著相关关系(p<0.05)，这表明不同人工林营建改变了土壤微环境条件、凋落叶和根系基质数量和质量，以及土壤的理化性质，特别是土壤氮含量，从而进一步直接或间接驱动土壤微生物群落结构的改变。此外，全年(旱季和雨季)水平上，混交林土壤真菌/细菌比(分别为0.27和0.31)始终高于马尾松林(分别为0.26和0.28)和格木林(分别为0.22和0.26)(p<0.05)，表明格木与马尾松混交更有利于提高土壤生态系统的稳定性。(4)不同枯落物处理格木和马尾松土壤呼吸和总硝化速率均呈现明显的季节变异，雨季格木和马尾松土壤呼吸速率平均分别是旱季的7.12倍和6.07倍；雨季土壤总硝化速率则分别是旱季的3.37倍和3.89倍。枯落物处理实验前期(2012年9月和11月)，两种林分土壤呼吸和总硝化速率随枯落物的增厚而减小，主要因不同林地土壤温度而引起。随着枯落物处理时间延长至2013年，土壤呼吸和总硝化速率随枯落物增厚而增加，主要与土壤养分和可利用底物有效性有关。与对照相比，凋落物去除处理的格木和马尾松土壤呼吸分别平均降低3.59%和2.68%，凋落物添加处理则分别平均提高14.08%和26.54%；凋落物去除处理的格木和马尾松土壤总硝化分别平均降低11.52%和17.67%，凋落物添加处理则分别平均升高9.69%和2.22%。相关分析结果表明，两种林分土壤呼吸和总硝化速率均受土壤温度、湿度、全氮、铵态氮和硝态氮等多种环境因子的综合影响。不同枯落物输入在影响土壤微环境特征的同时，也驱动其微生物群落结构发生变异。冗余分析表明，格木土壤微生物群落结构主要受土壤温度和铵态氮含量的影响，而土壤温度和硝态氮含量则是影响马尾松土壤微生物群落结构最主要的环境因子，这表明不同人工林类型中影响土壤微生物群落结构的环境因子不同。微生物作为土壤养分循环的关键驱动者，其对枯落物输入改变的响应将影响土壤碳氮转化速率。相关分析表明，无论是枯落物去除或是添加处理，大部分微生物特征PLFAs对土壤碳氮转化作用有显著影响。更多还原

【Abstract】 Plantation is becoming a key component of the world’s forest resources and playing animportant role in the context of sustainable forest management. For a long time, however, inorder to pursuit one-side of economic efficiency, there were many problems existing inplantations at home and abroad, such as the loss of biodiversity, degradation of soil fertility,reduction of ecosystem stability. In subtropical area of China, many indigenous valuablebroadleaf tree species (include nitrogen-fixing tree species) are being developed for theconstruction of plantations in production practice so as to decrease the negative effects whichinduced by inefficient plantations, promoting the multi-purpose management and improvingthe ecological function and economic value of plantations. The research about the impact ofdifferent forest management measures on plantations were mainly concentrated in theeconomic benefit of stand productivity in this region. However, the soil microclimatecharacteristics, physical and chemical properties, as well as soil biochemical process would bedifferent result from the differences of quality and quantity of leaf litter and root, and canopystructure of different plantations. Therefore, exploring the effects of different forestmanagement mode on the characteristics of carbon and nitrogen of plantation ecosystem fromthe ecological function perspective has become extremely necessary. Additionally, Theincrease of CO2concentration and temperature, nitrogen deposition, as well as the phenologicalchange and drought stress could cause the change of forest litter input, therefore, it is soimportant to consider the influence of litter input change in the research of forest soil carbonand nitrogen dynamics.In this study, the experimental site is located at the Experimental Center of TropicalForestry, the Chinese Academy of Forestry, Pingxiang City, Guangxi Zhuang AutonomousRegion, PR. China. Based on the same stand age, similar site conditions and adjacent position,three young experimental stands (a monoculture Erythrophleum fordii, a monoculture Pinus massoniana and a mixed stand of the two species) were selected, and combined with leaf litterinput controlled experiment, by using elemental anaysis, barometric process separation (BaPS)and phospholipid fatty acid (PLFA) methods, to1) examine the carbon and nitrogen storageand spatial distribution of different tree species plantation ecosystems;2) examine the seasonalvariation of soil respiration, gross nitrification and microbial community structure in differenttree species plantations;3) explore the response of soil respiration and gross nitrification rates,as well as soil microbial community structure in different tree species plantations to litter inputchange;4) understand the relationship between environmental factors and soil respiration andgross nitrification rates. So as to provide data references and scientific basis for the tree speciesselection and rational management measures in the plantation management in southernsubtropical China. The main results are as follows:(1) There were differences in the carbon and nitrogen storage among E. fordii, P.massoniana and their mixed plantation stands. The total carbon storage of ecosystems of the E.fordii, mixed plantation stand and P. massoniana stand were134.07t hm-2,137.75t hm-2and131.10t hm-2, respectively. While the total nitrogen storage of ecosystems were10.19t hm-2,8.68t hm-2and7.01t hm-2, respectively. The spatial distribution of carbon and nitrogen poolswere identical across the three plantation stands, with the majority of carbon and nitrogenfound in the upper0-100cm of soil, occupying by an average of81.49%and96.91%of thetotal carbon and nitrogen storage, respectively, followed by above ground biomass representedby the trees, occupying by an average of17.52%and2.69%of the total carbon and nitrogenstorage, respectively, and the understory vegetation and litterfall. Average organic carbonstorage in the top0-30cm soil was52.52t hm-2(occupied47.99%of the total0-100cm),acting as the primary service to the ecosystem. While nitrogen was irregularly distributed insoil. The results showed that mixed plantation stands with a nitrogen-fixing tree speciesshowed a greater capacity for carbon storage in comparison to monoculture stands insubtropical China. The lower above-/underground ratio of carbon and nitrogen suggests thatthese three young plantation stands have a high potential for carbon and nitrogen sequestration. (2) There were significant seasonal variation in the soil respiration and gross nitrificationrates in these three plantation stands (p<0.05). From September2012to January2013(dryseason), soil respiration and gross nitrification rates decreased to the lowest (the averages were2.63mg C kg-1SDW d-1and0.34mg N kg-1SDW d-1, respectively), and then increasedcontinuously until July2013(rainy season)(the averages22.44mg C kg-1SDW d-1and1.23mg N kg-1SDW d-1, respectively). There were significant correlation between soil respirationand gross nitrification rates and soil temperature and humidity (p<0.05), which showed thatsoil temperature and humidity were the key environmental factors in affecting soil respirationand total nitrification rates. Soil total nitrogen, ammonium nitrogen and nitrate nitrogen weresignificantly correlated with soil respiration and gross nitrification rates (p<0.05), whichindicated that soil carbon and nitrogen transformation were influenced by soil microclimateconditions while synthetically affected by other soil environmental factors. In differentplantation stands, soil respiration and gross nitrification rates in the E. fordii were significantlyhigher than those in the mixed plantation and P. massoniana stand significantly (p<0.05),which were mainly attributed to the biological characteristic differences of tree species. Therewere higher quantity and quality of litter and root, and faster decomposition in the E. fordii,which resulted in soil nutrient and substrate availability higher than the other two plantationstands. Compared with other study results, we found that the soil respiration and grossnitrification rates, as well as the Q10might be varied under different forest type, site condition,stand age and climate zone.(3) The amounts of microbial total PLFAs and PLFAs of each microbial group (bacteriaPLFAs、fungal PLFAs、actinomycetes PLFAs and arbuscular mycorrhizal fungal (AMF) PLFAs)in these three plantation stand soils were significant higher by an average of170.1%、182.1%、152.1%、232.5%and185.2%in dry season than those in rainy season, respectively (p<0.05). Indry season, the amounts of microbial total PLFAs, bacterial PLFAs, fungal PLFAs, andactinomycetes PLFAs were the highest in the P. massoniana soil, then in the mixed plantationsoil, and the lowest in the E. fordii soil. But the amounts of microbial total PLFAs, bacterial PLFAs, fungal PLFAs, and AMF PLFAs in the E. fordii soil were higher than those in the P.massoniana soil significantly in rainy season (p<0.05). Principal component analysis (PCA)indicated that the variations in soil microbial community structure composition were affectedby both plantation types and seasons. Redundancy analysis (RDA) of soil microbialcommunity structure and environmental factors showed that soil temperature, soil moisture, pH,total nitrogen content, and ammonium nitrogen content had significant correlations withindividual PLFA signatures (p<0.05), which indicates that the changes of soil microbialcommunity structure were attributed to the changes of the soil microclimate conditions, thequantity and quality of litter and root, and the physical and chemical properties of soil,especially for soil nitrogen content, caused by constructing of different plantation stands. Inaddition, the ratio of fungal PLFAs to bacterial PLFAs within the whole year (dry and rainyseason) in the mixed plantation soil (0.27and0.31respectively) was significant higher thanthat in the P. massoniana (0.26and0.28respectively) soil and E. fordii soil (0.22and0.26respectively)(p<0.05), indicating that mixed plantation stands could facilitate more improvingthe stability of the soil ecosystem.(4) There were significant seasonal variation in the soil respiration and gross nitrificationrates in different leaf litter treatments in E. fordii and P. massoniana, and soil respiration in theE. fordii and P. massoniana was7.12and6.07times in the rainy season as much as those inthe dry season, respectively, while gross nitrification was3.37and3.89times in the rainyseason as much as those in the dry season, respectively. Early in the leaf litter treatments(September and November2012), the soil respiration and gross nitrification rates decreasedwith the thickening of leaf litter in these two plantation stands, which mainly attributed todifferent soil temperature. With the leaf litter treatments extended to2013, the soil respirationand gross nitrification rates increased with the thickening of leaf litter, which mainly related tosoil nutrient and substrate availability. Litter leaf removal in the E. fordii and P. massonianadecreased the soil respiration by an average of3.59%and2.68%, whereas litter leaf additionincreased it by14.08%and26.54%compared with the control, respectively. Soil gross nitrification in the E. fordii and P. massoniana were lower by an average of11.52%and17.67%in litter leaf removal, whereas it higher by9.69%and2.22%in litter leaf addition thanthat in control, respectively. Correlation analysis revealed that the soil respiration and grossnitrification rates were combinedly affected by environmental factors of soil temperature,moisture, total nitrogen, ammonium nitrogen and nitrate nitrogen. Different leaf litter inputwould affect soil microclimate characteristics and drove the variation of microbial communitystructure. The RDA showed that soil microbial community structure in E. fordii mainlyinfluenced by soil temperature and ammonium nitrogen content, while soil temperature andnitrate nitrogen content were the major environmental factors regulating soil microbialcommunity structure in P. massoniana, these suggests that there were different environmentalfactors in different plantation stands that affected the soil microbial community structure.Microorganisms as a key driver of soil nutrient cycling, its response to the change of leaf litterinput would affect the soil carbon and nitrogen transformation. Whether leaf litter was removedor added, the correlation analysis suggested that most of signature PLFAs had a significantimpact on soil carbon and nitrogen transformation.更多还原