【作者】 王卫霞；

【导师】 史作民；

【作者基本信息】 中国林业科学研究院 ， 生态学， 2013， 博士

【摘要】 20世纪80年代，在我国热带和亚热带地区发起了大规模的造林运动，对退化荒坡进行生态恢复。然而在我国热带和亚热带林区造林恢复过程中，普遍存在着人工针叶纯林所占比重较大，由此引起生态稳定性较差、生态服务功能低、易受病虫害的攻击等一系列的问题。为了减少这些针叶人工纯林所带来的不利影响，许多不同功能型的阔叶树种（如速生树种和乡土珍贵树种，固氮树种和非固氮树种等）用于改造人工林经营模式已成为我国该地区人工林经营的发展趋势。关于不同功能型乡土珍贵阔叶树种，人们更多的是关注其木材收益，缺乏对其人工林生态系统碳氮特征的研究。本研究以中国林业科学研究院热带林业实验中心为研究地点，选取立地条件、林龄和经营历史相似的南亚热带不同树种人工林：格木（Erythrophleum fordii）人工林、红椎（Castanopsis hystrix）人工林和马尾松（Pinus massoniana）人工林，主要运用常规理化实验分析方法、气压过程分离技术（BaPS）、磷脂脂肪酸法（PLFA）和凋落物分解袋法，研究了：（1）不同树种人工林生态系统不同组分碳氮储量及其分配格局；（2）不同树种人工林土壤碳、氮元素转化的基本规律及其环境响应；（3）不同树种人工林土壤微生物群落结构组成及其对土壤碳氮转化的影响；（4）不同树种凋落物叶和细根分解特征及其相关关系。主要目的是通过对南亚热带不同树种人工林生态系统碳氮特征的比较研究，以期能为该区人工林营建中的树种选择以及人工碳汇林的经营管理提供科学参考。主要研究结果如下：（1）不同树种人工林乔木层各器官碳的分布与器官年龄的关系不明显，而氮的分布与器官年龄的关系则较为密切，表现为幼嫩器官中的氮含量大于老化器官，而老化器官的C/N比值大于幼嫩器官。说明碳具有相对稳定性，而氮具有流动性，并且氮素对幼嫩器官的生长具有重要作用。由于树种不同，其土壤有机碳和全氮含量具有显著差异，表土层有机碳和全氮含量均是乡土固氮树种格木林表现为最高，其次是红椎林，说明在本研究区乡土阔叶树种是最具有潜力的土壤改良树种。格木、红椎和马尾松人工林生态系统碳储量分别为236.22t·hm^-2、267.84t·hm^-2和200.57t·hm^-2，氮储量分别为17.91t·hm^-2、12.38t·hm^-2和10.59t·hm^-2。乔木层碳储量分别占42.57%、36.31%和40.28%，0^-100cm土壤碳储量分别占55.77%、62.52%和57.83%；氮储量则是土壤占绝对优势，分别为92.00%、93.72%和95.53%。以上结果表明，在本研究区乡土阔叶树种人工林具有较高的碳氮储存量。（2）不同树种人工林土壤呼吸及土壤总硝化表现出明显的季节变化，且雨季碳、氮转化速率显著高于干季。所有林分土壤呼吸及土壤总硝化的季节动态变化很大程度上依赖于土壤温度和土壤水分含量，土壤温度分别解释了土壤呼吸和土壤总硝化变异的76-86%和54-79%；土壤水分含量分别解释了土壤呼吸和土壤总硝化变异的31-56%和14-32%。由于不同树种对土壤环境的影响不同，不同林分间土壤呼吸速率及土壤总硝化速率存在显著差异。与其他两种林分相比，固氮树种格木林林下土壤具有较低的C/N比值和较高的有机碳含量、全氮含量及有效氮含量，因此，格木林土壤呼吸速率及总硝化速率显著高于红椎林和马尾松林。（3）不同树种人工林林分间土壤微生物生物量和土壤碳氮转化存在显著差异，土壤有机碳、全氮含量较高的乡土阔叶树种红椎林和格木林下土壤微生物生物量和总PLFAs量也较高，固氮树种格木林下土壤碳氮转化速率表现为最高，且由于格木林下土壤较低的C/N比和pH值，导致格木林下土壤真菌生物量显著低于其它两种林分。产生这种差异的主要原因是不同树种由于自身凋落物组分和质量的差异而改变土壤的化学性质、土壤微生物特征，从而影响土壤碳氮转化速率。从季节变化来看，不同林分下土壤微生物生物量均表现为干季大于雨季，而土壤碳氮转化速率却表现为雨季最大，造成这种格局的主要原因是雨季（植物生长的旺盛期）植物对土壤养分的大量需求限制了土壤微生物对养分的可利用性，因此减少了微生物生物量的固持。这也暗示了植物生长对养分的吸收与土壤微生物对体内养分的保持具有同步性。（4）格木、红椎和马尾松凋落物叶分解系数分别为0.98a^-1、0.88a^-1和0.62a^-1，而细根分解系数则分别为0.65a^-1、0.59a^-1和0.47a^-1。不同树种对凋落物分解的影响不仅受凋落物自身化学性质的影响，还受不同树种林分内环境条件的影响，不同树种凋落物分解速率均与凋落物中氮含量呈正比，与C/N比、木质素/N比呈反比，与土壤水分含量的关系也较密切。不同树种凋落叶分解速率和细根分解速率表现出明显的正相关性，这归因于土壤水分含量和凋落叶、细根基质质量对凋落叶分解速率和细根分解速率的影响具有明显的相似性。更多还原

【Abstract】 In the1980s, China’s tropical and subtropical regions launched a massive afforestationcampaign for ecological restoration of degraded slopes. In tropical and subtropical area ofChina, most of the plantations are composed of pure coniferous species. These pure coniferousspecies caused a series of problems, such as low ecosystem service and ecological instability,susceptible to pests and diseases attack.Many different functional hardwood species （such as fast-growing tree species and nativevaluable tree species, nitrogen-fixing and non-fixing tree species） are being advocated as aprospective silvicultural management to substitute large coniferous plantations in subtropicalChina. However, to different functional native hardwood species, people often pay moreattention to their timber income, little information is known about characteristics of ecosystemcarbon and nitrogen.In Tropical Forestry Experimental Center of Chinese Academy of Forestry Science, thethree adjacent monospecific plantations were selected to examine carbon and nitrogen storageunder different plantations, the effects of environmental factors on the transformation of carbonand nitrogen, the effects of soil microbial biomass and community composition on thetransformation of carbon and nitrogen, and the decomposition of leaf litter and fine root ofdifferent functional species, by using elemental analysis, barometric process separation （BaPS）,phospholipid fatty acid （PLFA）, and litter/root decomposition bags methods. One coniferousplantation was composed of Pinus massoniana, and the other broadleaf plantations wereErythrophleum fordii and Castanopsis hystrix. The main results are as follows:（1） The allocation of carbon in the organs of the different tree species had no significantcorrelation with their age, while that of nitrogen had closer relationship with the age. Thenitrogen concentration in young organs was higher than that in aged ones and the C/N ratio was higher in aged organs than that in young ones. It means that carbon is relatively stable, andnitrogen has an important role in the growth of young organs. Variations in soil organic carbonand total nitrogen among tree species could be primarily explained by the differentcharacteristics of tree species. The soil organic carbon and total nitrogen concentration werethe highest under the nitrogen-fixing species （E. fordii plantation）, followed by C. hystrixplantations, suggesting that indigenous broadleaf tree species in this study area are the mostpotential species for soil amelioration. The total ecosystem carbon storage of E. fordii, C.hystrix and P. massoniana plantations was236.22t·hm^-2,267.84t·hm^-2and200.57t·hm^-2andnitrogen storage was17.91t·hm^-2,12.38t·hm^-2and10.59t·hm^-2respectively. Carbon storageof tree layer occupied42.57%,36.31%and40.28%while0^-100cm soil occupied55.77%,62.52%and57.83%, respectively. Nitrogen storage of soil occupied92.00%,93.72%and95.53%. Our study indicated that the higher carbon and nitrogen sequestration ability in thenative broadleaf plantations.（2） Soil respiration and gross nitrification at all three plantations showed a pronouncedseasonal pattern with significantly higher rates during the wet versus dry season. Seasonalvariations of soil respiration and gross nitrification of the three plantations largely depended onsoil temperature and water content. Regression analysis showed that soil temperature explained76-86and54-79percent of the observed variance of soil respiration and gross nitrification,respectively, and soil water content explained31-56and14-32percent of the observedvariance of soil respiration and gross nitrification, respectively. The significant differences insoil respiration and gross nitrification rates between the three plantations could also beattributed to the influences of the tree species on the soil environment. Soil respiration andgross nitrification rates of the E. fordii plantation were much higher than those of the other twoplantations. These differences probably reflect the narrower C/N ratio and higher organic Ccontents in the soils of the E. fordii plantation.（3） The soil microbial community composition and the effects of soil microbialcommunity composition on the transformation of carbon and nitrogen were investigated in south subtropical plantations, in China. The results showed that the soil microbial biomass andsoil microbial community composition and C, N turnover rates were significantly influencedby plantation type. The soil organic carbon, total nitrogen, microbial biomass and total PLFAswere higher under the native broadleaf plantations, the highest turnover rates of C and N werefound under the soil of E. fordii plantation. Moreover, we found that the highest C and Nturnover rates coincided with the lowest fungal biomass could be primarily explained by thelower C/N ratio and pH value in E. fordii plantation. We also found the lowest microbialbiomass during the wet season, during the period of the lowest microbial biomass, however, weobserved the highest soil respiration and gross nitrification rates. These differences could bemostly attributed to the relatively greater nutrient demand by plants during the wet season （thepeak vegetative growth period） limited the availability of nutrients to soil microbes and therebyreduced their immobilization in microbial biomass. This also implies that the plant absorbnutrients for growth and soil microorganisms immobilize nutrients for microbial biomasswhich the two processes occur concurrently.（4） Decomposition parameter of leaf litter of E. fordii, C. hystrix and P. massoniana was0.98year^-1,0.88year^-1and0.62year^-1and decomposition parameter of fine root was0.65year^-1,0.59year^-1and0.47year^-1, respectively. Decomposition rates of leaf litter and fine root wereinfluenced not only by the chemical properties of the litter, but also by the environmentalfactors in different plantations. The leaf litter and fine root decomposition rates showedsignificant similarity among tree species. Leaf litter and fine root decomposition rates in threestands were positively correlated with nitrogen content and soil water content, negativelycorrelated with C/N ratio, lignin/N ratio. The significant correlation between leaf litter and fineroot decomposition rates could also be attributed to soil water content and chemical propertiesof the litter on decomposition rates of leaf litter and fine root were very similar.更多还原