【作者】 徐嘉；

【导师】 刘世荣；

【作者基本信息】 中国林业科学研究院 ， 生态学， 2014， 博士

【摘要】 近两百年来，人类活动导致的以全球变暖为主要特征的气候变化，正在改变全球降水格局和水循环，极端降水事件频发，全球总体上呈干旱化的趋势，对陆地生态系统碳循环过程产生重大影响。森林生态系统是陆地生态系统的主体，在调节全球陆地生态系统碳平衡和减缓气候变化方面发挥着不可替代的重要作用，探讨降雨格局变化对森林生态系统碳库/源汇效应的影响正逐步成为当前国际全球变化生态学研究的前沿和热点问题。我国南方人工林分布面积大，人工造林增加碳汇已成为积极应对全球气候变化的主要手段。降雨格局变化对人工林生态系统碳固持和土壤碳的稳定性影响存在相当的不确定性。因此，研究气候变化背景下我国人工林生态系统碳循环关键过程的响应规律及其内在机理，有助于科学评价我国人工林生态系统在全球气候变化影响下碳循环变化及其碳汇发展潜力。本研究在中国林科院热带林业实验中心选取具有相同林龄及相似立地条件的红锥(Castanopsis hystrix)和马尾松(Pinus massoniana)人工林为研究对象，开展原位林下穿透雨减水的控制试验，采用常规理化分析法、土钻法、氯仿熏蒸法、土壤CO2通量红外气体分析法、磷脂脂肪酸法等多种方法，研究了(1)控制减水试验对两种人工林土壤碳储量和土壤理化性质的影响；(2)两种人工林土壤呼吸对降雨减少的响应方式及其影响因子；(3)降雨减少影响下土壤微生物群落变化规律。主要研究结果如下：(1)减雨装置有效截留了林下穿透雨，显著改变了土壤湿度。红锥林下的减雨装置年总截留穿透雨量为655.36mm，分别为年总降雨量和穿透雨量的36.84%和49.82%。而马尾松林下的减雨装置总截留量为733.51mm，占年总降雨量和穿透雨量的41.24%和50.06%。减雨装置截留率全年变化范围在44.92%～54.68%之间，表现出较好的稳定性。减雨处理显著改变了土壤湿度，造成红锥和马尾松人工林年均土壤湿度分别降低了37.73%和31.53%。(2)降雨减少通过影响红锥人工林土壤容重和有机碳密度，导致其土壤表层(0～10cm)有机碳库明显减少。降雨减少显著提高了雨季红锥人工林表层土壤(0～10cm)pH值和和NH4+-N含量，降低了土壤微生物碳(MBC)含量，减少了旱季马尾松人工林土壤微生物氮(MBN)含量。红锥人工林和马尾松人工林细根生物量对降雨减少响应方式不同，红锥人工林表层土壤(0～10cm)细根生物量显著降低，而马尾松细根生物量则显著增加。上述结果意味着，降雨减少导致红锥人工林表层细根生物量降低，是导致红锥人工林土壤碳储量降低的主要原因之一，而马尾松人工林土壤碳储量可能会因细根碳输入增加而提高。(3)减雨处理并未改变红锥人工林和马尾松人工林土壤呼吸的季节动态节律，但两种人工林土壤呼吸速率对降雨减少的响应并不相同。减雨处理显著抑制了红锥人工林呼吸速率，导致年累计呼吸通量降低了9.70%。相反，减雨处理提高了马尾松人工林的呼吸速率，导致其年均土壤表层呼吸通量显著提高了6.55%。减雨处理并未影响土壤温湿度与土壤呼吸之间的相关关系。两种人工林土壤呼吸速率均与土壤温度和湿度呈显著相关关系。土壤表层5cm温度能解释红锥人工林和马尾松人工林70%以上的土壤呼变异，但土壤水分解释量不到30%。红锥人工林对照样地土壤呼吸的年均温度敏感性(Q10)为1.98±0.16，显著高于减雨处理样地土壤呼吸雨季Q10值(1.46±0.19)(P<0.05)。而减雨处理提高了马尾松人工林土壤呼吸的Q10值。本研究发现红锥人工林土壤呼吸通量与细根生物量、微生物碳、土壤有机碳和土壤碳氮比等多个因子呈显著线性相关关系。减雨处理对不同林分细根生产力、土壤有机质含量的影响产生的差异，从而造成红锥和马尾松人工林土壤呼吸对减雨处理的响应不同。(4)减雨处理对土壤微生物PLFAs量存在明显影响，但其影响程度在不同季节、不同人工林中存在差异。减雨处理对红锥人工林土壤微生物群落PLFAs量的影响表现为雨季增加而旱季减少。而减雨处理对马尾松人工林土壤微生物群落PLFAs量总体表现为雨季减少，而在旱季影响不明显。在雨季，减雨处理只对少数菌群的相对丰度产生显著影响，而在旱季对大部分菌群的相对丰度均产生明显影响。总体上，减雨处理显著降低了丛枝菌根菌的相对丰度以及真菌细菌比，而提高了细菌、革兰氏阳性菌的相对丰度以及革兰氏菌阳性阴性比。本研究中，土壤pH值、土壤温度、湿度和土壤NH4+-N与土壤微生物群落结构变化显著相关。同时，微生物胁迫指数与上述指标存在明显线性相关关系。减雨处理造成的土壤水热状况、pH值、以及氮素(全氮、铵态氮和硝态氮)等因子的变异，对土壤微生物群落产生选择压力是造成土壤微生物变化的重要原因之一。更多还原

【Abstract】 In recent two hundred years, the climate change caused by anthropogenic activities withthe main characteristics of global warming has been changing the global precipitation patternand water cycling. Extreme precipitation events ocurred frequently, and there exsits a trend ofglobal drought events, which has a significant impact on the carbon cycle process of terrestrialecosystems. Being the main component of terrestrial ecosystems, forest ecosystems are playingan important role in regulating terrestrial carbon cycle by which to mitigte climate change.However, the effects of rainfall pattern changes on forest ecosystem carbon sink/source isincreasingly concerned, and thus has become an important research topic in the field of globalchange ecology. There are wide range distribution of planted forests in southern China, andafforestation/reforestation have become the effective measures to cope with global climatechange by sequestering more CO2from the atmosphere. Globle and regional rainfall patternchange will be likely to have a great impact on carbon sequestration of plantations and wouldjeopardize its carbon sink capacity, while there is still considerably uncertain about its impacts.Therefore, there is a clear need to investigate the ecosystem carbon cycle and its underlyingmechanism of planted forests China, which helps evaluate the future role of planted forests inglobal carbon cycle and its carbon sink capacity under the global climate change. In thisstudy, two types of planted forests, including Castanopsis hystrix (CH) and Pinus massoniana(PM) plantaitons with the same age and similar site conditions in Experimental center oftropical forestry (Chinese Academy of Forestry) in Pingxiang city, Guangxi Autonomousregion were selected to explore impacts of the in situ experimental drought treatment throughthroughfall exclusion on ecosystem carbon cycle and soil microbial community by combiningsoil conventional physical and chemical analysis, soil drilling method, chloroform fumigationmethod, with soil CO2flux infrared gas analysis and phospholipid fatty acid analysis (PLFA).The objectives of the study are to explore:(1) the effects of thgouhfall exclusion on soil carbon stock and soil physical and chemical properties,(2) the responses of soil respiration tothroughfall exclusion and its controlling factors,(3) the impacts of throughfall exclusion onsoil microbial community and the underlying mechanism.The main reults are as follows:(1) The manipulation experiment of throughfall exclusionhas been successfully implemented and performed, with the expected outcome of effectivelyintercepted throughfall under the canopy and consequently significant changes in soil moisture.The annual total amont of intercepted throughfall by the manipulation treatment in CHplanation was655.36mm, taking up36.84%and49.82%of the annual total precipitation andthroughfall, respectively. While in PM plantion, the total annual amount of throughfallinterception was733.51mm, taking up41.24%and50.06%of the annual total precipitationand throughfall, respectively. The rate of throughfall interception to the total throughfallannually range between44.92%～54.68%, showing a better consistency throughout theexperiment. Furthermore, throughfall exclusion significantly changed the soil moisture, theannual average soil moisture in CH and PM plantations were significantly reduced by37.73%and37.73%, respectively, relative to the controls.(2) throughfall exclusion led a significant decline in soil organic carbon at surface soillayer (0～10cm) by altering soil bulk density and organic carbon density in CH plantation. Inaddition, throughfall exclusion significantly increased soil pH and NH4+-N content at surfacesoil layer (0～10cm), but sinificantly decreased soil microbial biomass carbon (MBC) contentin CH plantation at rainy season and sinificantly decreased soil microbial biomass nitrogen(MBN) content in PM plantation at dry season. The responses of fine root biomass in twoplantaitons to throughfall exclusion were different, with the significant decrease in fine rootcarbon biomass at surface layer (0～10cm) in CH plantation, but the significant increase infine root biomass in PM plantation. The results indicated that throughfall exclusion caused adecline in SOM and fine root biomass at surface layer (0～10cm) in CH plantation, resultingin a reduction in soil organic carbon stock, while in PM plantation, soil organic carbon stockmight be increased with the increase in fine roots carbon inputs. (3) Throughfall exclusion did not change seasonal dynamics of soil respiration in eitherCH or PM plantations, but with the different responses of soil respiration rate. In addition,throughfall exclusion significantly inhibited soil respiration rate, leading a decline by9.70%inannual accumulative total respiration flux in CH plantation. However, Throughfall exclusionsignificantly increased soil respiration rate in PM plantation, leading a increase by6.55%inaverage annual soil respiration flux. Furthermore, throughfall exclusion did not affect therelationship between soil temperature and humidity, and soil respiration. Soil respiration rateswere significantly corelated with soil temperature and humidity in two plantations. Moreover,soil temperature at5cm depth can explain more than70%of the total variation of soilrespiration, while soil moisture can explain less than30%.In CH plantations, the throughfall exclusion caused a significant decline in the annualaverage temperature sensitivity (Q10)(1.46±0.19)(P<0.05) compared to that in control plots(1.98±0.16). However, throughfall exclusion significantly increased Q10in PM plantation.Furthermore, This study also found that soil respiration flux showed significant linearcorrelations with the multiple factors such as fine root biomass, MBC, soil organic carbon andC/N. The results showed that different effects of throughfall exclusion on fine root productivity,soil organic matter content in different plantations can account for the different responses ofsoil respiration in CH and PM plantations.(4) Throughfall exclusion significantly influenced soil microbial PLFAs, but its influencedegree variated with season and plantation type. In CH plantation, throughfall exclusiontreatment increased soil microbial PLFAs biomass in rainy season, but decreased in dry season.In PM plantation, throughfall exclusion treatment decreased soil microbial PLFAs biomass inrainy season, but there was no significant effects at dry season. During rainy season,throughfall exclusion only significantly influenced the relative abundance of few mcirobialcommunies, but the relative abundances of most mcirobial communies were impacted in thedry season. Generally, throughfall exclusion significantly reduced the relative abundance ofarbuscular mycorrhizal fungi as well as the ratio of the relative abundance of fungal PLFAs to bacterial PLFAs, but significantly incresed the relative abundance of bacterial PLFAs andgram-positive bacterial PLFAs and the ratio of the relative abundance of gram-positivebacterial PLFAs to gram-negative bacterial PLFAs. In the present study, soil microbialcommunity structure was significantly correlated with NH4+-N, soil pH, soil temperature, soilwater content. Meanwhile, the stress index of soil microbial communites showed linearrelationship with the above mcirobial variables. The results showed that the alterations of soilhydrothermal condition, pH, and nitrogen (total nitrogen, ammonium nitrogen and nitratenitrogen) as well as other factors caused by experimental throughfall exclusion producedselection pressure on soil microorganisms, which was one of the important reasons accountingfor the altered soil microbial community.更多还原