【作者】 黄雪蔓；

【导师】 刘世荣；

【作者基本信息】 中国林业科学研究院 ， 生态学， 2013， 博士

【摘要】 桉属是中国南方大面积种植的一类人工林，伴随着桉树人工林迅速发展给社会带来巨大经济效益的同时，由于不合理的经营管理也带来一系列的生态问题。土壤呼吸即土壤表面CO2的排放，其排放量在决定生态系统作为碳源或碳汇方面起着重要作用。揭示土壤有机碳的输入和释放动态变化及其调控机制对全球碳收支的描述和估算都具有重要意义，然而，目前有关人工林的经营管理对土壤碳固持的影响存在相当的不确定性。本研究在广西壮族自治区中国林科院热林中心选取了位置相邻，具有相似的立地条件的南亚热带四种桉树人工林类型：桉树一代纯林(PP1)、桉树一代/马占相思混交林(MP1)、桉树二代纯林(PP2)、桉树二代/降香黄檀混交林(MP2)。主要采用常规理化实验分析方法、Li-Cor-8100土壤碳通量测量系统红外气体分析仪法、磷脂脂肪酸(PLFA)法和酶底物法，研究了(1)不同连栽的桉树纯林及其与混交林不同土壤呼吸组分季节变化及其影响因子；(2)不同连栽的桉树纯林及其混交林土壤年累积呼吸的差异及其相关因子；(3)不同连栽的桉树纯林及其混交林土壤微生物群落结构的季节变化及其影响的生物和非生物因子；(4)不同连栽的桉树纯林及其混交林土壤酶活性的季节变化及其环境因子。本研究的目的是揭示固氮树种对南亚热带桉树人工林土壤碳固持潜力的影响及其微生物机制，为我国高碳汇桉树人工林的经营提供科学依据。主要研究结果如下：(1)桉树4种人工林土壤总呼吸速率及各呼吸组分速率季节变化均与5cm处土壤温度(T5)变化基本相似，季节变异很大程度上依赖于5cm处土壤温度。峰值出现在6-8月，谷值出现在12月底至1月初。土壤含水量(SWC)仅与MP2林土壤呼吸在时间上存在弱的负相关，与其他三个林分土壤呼吸均无相关关系。(2)通过壕沟法对桉树不同人工林各呼吸组分自养呼吸(RR)和异养呼吸(RH)进行分离，研究发现，自养呼吸和异养呼吸的时间上的变异可以由5cm处土壤温度通过指数模型解释。PP1和MP1、PP2和MP2之间总呼吸全年累积量(RS)、自养呼吸累积量(RR)和异养呼吸累积量(RH)都有显著性差异。PP1的全年累积土壤总呼吸通量为(1106.47g C m-2)，比MP1(968.66g C m-2)增加了12.45%；PP2的全年累积土壤总呼吸通量为1147.41g Cm-2，比MP2(844.08g C m-2)增加了26.44%。MP1的自养呼吸累积量(403.99g C m-2)比PP1(693.13g C m-2)减少了41.71%，但其异养呼吸累积量(564.66g C m-2)却比PP1增加了36.61%；MP2的自养呼吸累积量(506.72g C m-2)比PP2的降低了MP2(136.87g C m-2)降低72.99%，而其异养呼吸累积量(707.21g C m-2)比PP2(640.69g C m-2)增加了10.38%。异养呼吸贡献率由PP1的37.54%增加到MP1的58.25%，从PP2的56.03%增加到MP2的83.94%。纯林和混交林的细跟生物量差异以及土壤有机质含量、凋落物有机质含量、土壤C/N比率、凋落物量和凋落物C:N的不同而造成土壤微生物生物量差异是导致自养呼吸异养呼吸产生差异的主要原因。RS、RR与土壤碳储量(0-10cm)凋落物量显著负相关，而与细根生物量和凋落物C/N显著正相关；而RH仅与凋落物C/N显著负相关。PP1和MP1自养呼吸和异养呼吸温度敏感性(Q10)没有差异。然而，在PP2和MP2之间，异养呼吸温度敏感性(Q10)没有差异，MP2自养呼吸温度敏感性(Q10)显著高于PP1。(3)PP1和MP1土壤微生物量和群落结构均存在显著差异，具体表现为总的磷脂脂肪酸量(Total PLFAs)(作为评估微生物量的指标)。在干季和湿季，MP1的微生物量比PP1分别高出27.56%和21.86%，均显著高于PP1。MP1和MP2混交林的细菌、放线菌、丛枝菌根真菌都显著高于对应的PP1和PP2纯林，而真菌刚好相反，混交林的真菌生物量均低于相对应纯林，MP1的总土壤微生物量显著高于PP1，但MP2的土壤总微生物量没有显著提高。马占相思与桉树一代混交8年后，显著提高了总细菌、革兰氏阴性细菌、丛枝杆菌的相对丰富度和显著降低真菌的相对丰富度；而降香黄檀与桉树二代混交4年后，显著提高细菌相对丰富度和显著降低真菌的相对丰富度。通过冗余度分析(RDA)，得出造成微生物群落结构变化的原因可能是固氮树种引入后，改变了凋落物的数量和质量，影响土壤理化性质，特别是增加土壤氮含量及其有效性，是驱动桉树人工林土壤微生物生物量和群落结构的主要因素。固氮树种通过驱动微生物生物量和群落结构的变化将可能增加桉树人工林土壤有机碳储量和提高有机碳的稳定性。(4)固氮树种(马占相思)和桉树混交8年后，对土壤酶活性也产生了一定影响。在干季(2月)，固氮树种和桉树一代混交能显著提高土壤水解酶活性(β-葡萄糖苷酶)，对其它土壤酶活性影响较小；在湿季(8月)，和纯林相比，混交林土壤的β-葡萄糖苷酶活性有了显著的提高，但过氧化物酶活性却显著减少。固氮树种(降香黄檀)和桉树二代林混交4年后，对土壤酶活性也产生了一定影响。在干季(2月)，固氮树种(降香黄檀)和桉树二代混交能显著提高土壤水解酶活性(β-葡萄糖苷酶)，对其它土壤酶活性影响较小，均无显著差异；在湿季(8月)，和纯林相比，混交林土壤的β-葡萄糖苷酶活性有了显著的提高，但过氧化物酶活性却显著减少。本研究结果表明，固氮树种与林桉混交后，能明显改变桉树人工林土壤酶活性。造成这种变化的原因可能是固氮树种引入后，显著增加土壤有机碳含量，提高氮的有效性和可利用性，显著改变土壤微生物群落生物量和结构，显著增加了细菌的生物量和丰富度，但显著减少了腐生真菌的生物量和丰富度，从而造成了跟这些微生物紧密相关的土壤水解酶活性显著增加和氧化酶活性的显著减少，在一定程度上阐明了影响桉树人工林土壤有机碳输入和稳定的酶动力学机制。更多还原

【Abstract】 Eucalyptus have been large-scale cultivated in the south of China. With the rapidlydevelopment of eucalyptus plantation, a great of economic benefits have been brought to thesocial, however, lots of ecological problems have been emerged because of irrationallymanagement practices. Soil respiration is the CO2efflux from the surface of soil, which playsan important role in determining whether an ecosystem is a carbon sink or source to theatmosphere. A good understanding of the dynamic changes and mechanisms underlying soilcarbon inputs or outputs will help us to better describe and estimate the global land carbonbudget. However, the effects of forest management on stocking and stability of soil carbon areuncertainty.The experimental site is located at the Experimental Center of Tropical Forestry, theChinese Academy of Forestry, Pingxiang City, Guangxi Zhuang Autonomous Region, PR.China. Based on the similar topography, soil texture, and stand management history, thefollowing four experimental stands were selected, i.e., the first pure rotation ofEucalyptusplantation(PP1), the mixed plantation of the first pure rotation of Eucalyptus andAcacia mangium(MP1), the second pure rotation of Eucalyptus plantation (PP2) and the mixedplantation of the second pure rotation of Eucalyptus and Dalbergia odorifera(MP2). Usingelemental anaysis, Li-COR infrared gas analysis, PLFA and substrate method, The fouradjacent plantations were selected to (1) examine the seasonal dynamics and the effect fators ofthe differrent rotations of pure eucalyptus plantations and the eucalyptus mixed with N-fixingspecies;(2) determine the differences and the effect factors of annually cumulative respirationcomponents between pure and mixed plantations;(3) explore the effects of N-fixing treespecies on microbial biomass C and microbial community composition and key soil biotic andabiotic properties influencing the microbial community composition;(4) understand the enzyme activity and the effect factors under different eucalyptus plantations. The main resultsare as follows:(1) Temporal variations of RSand the different components of soil respiration rate of thefour forests largely depended on soil temperature at5cm depth (T5). The maxium value ofrespiration rate appears between June and August, and the minimum value of respiration rateappears between December and January. In MP2forest, soil water content (SWC) had a weaknegative effect on the temporal variation of RS, while there is no correlation between SWC andthe other three forests.(2) Plot trenching experiments were conducted to partion soil respiration components inthe different eucalyptus plantations (PP1and MP1, PP2and MP2) in Subtropical of China.Total soil CO2efflux (RS) was partitioned into rhizospheric (RR) and heterotrophic respiration(RH)across2012. It was found that the temperal that the temporal variations of RRand RHcouldbe well explained by soil temperature at5cm depth (T5) using exponential aquation. Therewere significant differences in the RS, RRand RHduring annual gross among the fourplantations. The estimated RS, RRand RHvalues for PP1averaged1106.47g C m-2,693.13g Cm-2and413.34g C m-2respectively, and the estimated RS, RRand RHvalues for MP1averaged968.66g C m-2,403.99g C m-2and564.66g C m-2respectively. While their correspondingestimated RS, RRand RHvalues for PP2averaged1147.41g C m-2,506.72g C m-2and640.69g C m-2respectively, and the estimated RS, RRand RHvalues for MP2averaged844.08g C m-2,136.87g C m-2and707.21g C m-2. The estimated RCincreased from37.54%in the PP1to58.25%in the MP1, and increased from56.03%in the PP2to83.94%in the MP2. There wassignificant correlation between total organic carbon(TOC) of litterfall, fine root biomass(FR),C:N ratio of litterfall and RSand RR. However, there was just significant relationship betweenRHand the C:N ration of litterfall.The apparent temperature sensitivity (Q10) of RRand RHwere not different between PP1and MP1. However, the Q10of RRwas significantly higher inMP2than PP2. (3) The microbial biomass and communitycomposition were significantly differentbetween PP1and MP1. The total PLFAs in MP1, which was described as the microbialbiomass, was27.56%higher in the dry season and21.86%higher in the wet season than PP1.Thebiomass of bacterial, actinomycetes and arbuscular mycorrhizal fungi(AM) weresignificantly higer in MP1and MP2than the corresponding pure plantations PP1and PP2.However, the biomass of fungi in the mixed plantations were significantly lower than the pureplantations. The microbial biomass was significantly higer in the MP1than PP1, however therewas higher but not sinificant microbial biomass in MP2than PP2. After eight years of mixingwith N-fixing species (Acacia mangium), MP1significant increase the relative abundance ofbacteria, Gram-negative bacteria and arbuscular mycorrhizal fungi but decrease the relativeabundance of fungi. And after four years of mixing with N-fixing species (Dalbergiaodorifera), MP2significant increase the relative abundance of bacteria, but decrease therelative abundance of fungi. Redundancy analysis (RDA) indicated that the changes of themicrobial biomass and community composition were attributed to the changes of the quantityand quality of litterfall, the physical and chemical properties of soil especially for Navailabilitycaused by introduce the mixing N-fixing tree species. Mixing with N-fixing speciescould increased C accumulation and enhance the C stability though changing the microbialbiomass and community composition in the soil.(4) After eight years of mixing with N-fixing species (Acacia mangium)(MP1), there wassome influence on the enzymes activity of soil. Mixing with N-fixing (MP1) species canmarkedly increase the hydrolytic enzyme (β-glucosidase) but no difference for other threeenzyme activity at the dry season. At the wet season, hydrolytic enzyme (β-glucosidase)activity was significant increase but the oxidase enzymes (phenol oxidase and peroxidase)activity were significant decrease in MP1. After four years of mixing with N-fixing species(Dalbergia odorifera)(MP2), the trend of the effects on enzymes activity of soil was similarwith MP1. It was found that mixing with N-fixing species can markedly influence on theenzymes activity of soil. Which may because of the increase the soil carbon content and the available of nitrogen and then changing the microbial biomass and community composition inthe soil by the N-fixing species. Mixing with N-fixing species(MP1and MP2) can significantincrease the biomass and relative abundance of bacteria but markedly decrease the biomass andrelative abundance of fungi meanwhile markedly influence the related enzymes activity. It waspartly explain the enzymes activity mechanism about soil carbon accumulation and stability in.更多还原