【作者】 吴敏；

【导师】 张文辉；

【作者基本信息】 西北农林科技大学 ， 森林培育， 2013， 博士

【摘要】 为了阐明栓皮栎种群实生苗定居生态学过程及其耐旱特性，本研究以陕西不同分布区域(黄土高原、秦岭北坡、秦岭南坡)、不同生境(坡向)的栓皮栎种群为研究对象，通过野外固定样地观测与室内控制试验，幵展种群及生理生态调查、测定，研究了栓皮栎种群从结实、种子扩散、幼苗定居的过程；以及栓皮栎实生苗对干旱环境的适应机制，分析了栓皮栎种子萌发与幼苗定居适宜的土壤水分条件，为栓皮栎次生林恢复或人工丰产林栽培提供了依据。研究结论如下：1、黄土高原、秦岭北坡、秦岭南坡栓皮栎个体结实数量、种子形态、质量(千粒重和生活力)均为阳坡大于阴坡；结实数量、种子形态和质量均为秦岭南坡〉秦岭北坡>黄土高原。栓皮栎坚果主要分布于树冠上层和树冠阳面。对林内17个环境因子多元回归分析表明：影响其结实、种子形态与质量的重要因子为母树冠幅面积、冠幅体积、以及林内的温度、光照条件、土壤速效氮和速效钾含量；其中林内温度、光照条件作用最大。2、不同分布区栓皮栎种子雨观测表明：黄土高原种子雨降落开始时间最晚，结束最早，持续时间约76天，其中高峰期约14天；而秦岭南坡种子雨开始最早，结束最晚，持续时间最长91天，高峰期长达33天。同一分布区，阳坡落种早于阴坡，而阴坡落种高峰期较集中。种子雨和种子库总密度均为秦岭南坡〉秦岭北坡〉黄土高原，且阳坡大于阴坡。种子雨降落均以成熟种子为主，主要集中在高峰期降落，成熟饱满种子比例最高为黄土高原阴坡(56.60%);败育、虫蛀和被动物哨食种子主要集中在种子雨起始期和末期，虫蛀和被啃食种子比例以秦岭南坡最高；败育种子比例以秦岭北坡的阴坡最高，达到33.34%。各分布区种子库数量组成随时间发展呈动态变化，阳坡成熟种子消失速度快于阴坡，动物取食和霉烂是导致栓皮栎土壤种子库种子减少的主要因素。3、三个分布区固定样地检测表明：实生苗随年龄增长密度下降；黄土高原实生苗通过降低茎叶生长，增加根系的生长适应不良生境；秦岭北坡实生苗随着年龄的增长，适应能力增强，逐渐将更多干物质累积在茎叶器官；秦岭南坡阳坡实生苗生长发育最好，主要通过提高叶面积指数，提高光竞争能力，促进其生长。通径分析表明，改善光照条件、土壤含水率、土壤速效氮的含量和枯落物层厚度，同时降低灌木层盖度和林分密度有利于栓皮栎林实生苗定居。4、PEG模拟干旱胁迫试验表明：干旱胁迫使栓皮栎种子萌发时间延缓，萌发活力指数(VI)下降；但轻度胁迫(-O.lMPa)使种子的萌发率(GP)和日平均萌发速度均提高9.81%,萌发势(GRI)提高4.58%，并促进种子胚根增长；在中、重度胁迫(-0.3?-1.5MPa)下，抑制种子萌发，且胚根和胚芽生长缓慢。种苗通过提高根芽比(R/P)适应环境水势的降低(-0.1～-1.2MPa)，但重度胁迫(-1.5MPa)下，种子不能产生胚芽。随胁迫强度的增加，种子群体萌动、萌发和出苗达50%概率时间延长，各阶段环境临界水势依次为：-0.12MPa、-0.08MPa和-0.06MPa，说明种子出苗过程对环境水分胁迫较为敏感，耐旱能力最弱。当水势低于-0.6MPa时，种子的渗透调节物质(游离脯氨酸、可溶性糖和可溶性蛋白)积累降低、抗氧化保护酶(SOD、POD、CAT、APX)活性和抗氧化剂(ASA)含量显著下降，导致MDA大量积累，抑制种子萌发。5、长期干旱胁迫导致栓皮栎幼苗株高、基茎、健康叶片数量、叶面积和干物质累积减少；轻度干旱可增加幼苗不同直径等级根系数量、长度、表面积、体积。尽管栓皮栎幼苗通过增加叶面积比和比叶面积抵御干旱环境，但其作用效果并不显著；当胁迫程度超过中度时，幼苗长期水分利用效率下降。此外，栓皮栎幼苗可通过在叶片、小直径细根(0＜D≤0.5mm)和大直径细根(0.5＜D≤2mm)大量积累渗透调节物质、迅速降低渗透势、启动抗氧化保护系统抵御长期轻度干旱胁迫。而中度胁迫下，叶片和细根部分抗氧化保护酶活性和抗氧化剂含量均已发生下降，导致幼苗耐旱能力下降且生长缓慢。重度胁迫导致幼苗各器官可溶性蛋白含量、CAT、POD和APX的活性，以及ASA含量均迅速降低，而MDA含量迅速增加，细根活力下降，幼苗生长停滞。6、在轻度和中度胁迫下，幼苗叶片相对含水率(RWC)均保持在60%以上，在重度胁迫下，叶片RWC仅为42%，暗示叶片吸水保水能力下降。幼苗通过大幅度的降低饱和渗透势(Ψ100s)和初始质壁分离渗透势(Ψ0s)，保持更多的非渗透水含量(RWCa)和更低的组织细胞弹性模量()适应轻度胁迫。然而在长期重度胁迫导致Ψ100s和Ψ0s升高，渗透调节作用受阻。栓皮栎幼苗日光合进程呈双峰型曲线，两次高峰分别出现在10：00～11：00和15：00～16：00之间；在中午13：00发生“午休”现象。干旱胁迫导致净光合速率(Pn)降低，其原因包括气孔因素和非气孔因素。轻度胁迫可以提高叶片瞬时水分利用效率；而重度导致其显著降低。干旱胁迫会引发叶片的光合色素含量降低，但Chla/Chlb和Car/Chla+b为升高趋势。7、栓皮栎次生林中应加强实生苗保护，使其顺利渡过不良环境；未来栓皮栎资源培育中，丰产林培育应该在种子雨高峰期时采种；培育丰产林地点应该选择在秦岭林区；在对次生林改造与丰产林培育中，应及时抚育间伐，控制林分郁闭度，保证林地充足的光照，土壤水分维持在21.1±0.6%～14.6±1.2%之间，促进种子萌发及实生苗生长发育。更多还原

【Abstract】 In order to explain ecological processes of seedlings settlement of Quercus variabilis Blpopulation and their drought tolerance, different distribution regions(including Loess Plateau,Qinling north slope and Qinling south slope), and different slope aspect were taken as theobject of our study in Shaanxi province. By field investigation and controlled experiment inthe laboratory, methods of population and physiological ecology were applied to exploresystematically process from seed and to seedling establishment; meanwhile avoidance or/andtolerance mechanisms of Q. variabilis Bl was clarified in drought environment, and we foundsuitable soil moisture conditions for seed germination and seedling establishment.The resultsof the present study provide information for vegetation restoration with this species in aridand semi-arid regions of northwestern China. The main results were as follows:1.The sunny slope showed greater fruiting number, seed morphology and quality(including1000-seed mass and seed vitality) in parent tree individual of Q. variabilis Bl thanshady slope in Loess Plateau, Qinling north slope and Qinling south slope. The fruitingnumber from high to low was Qinling South Slope, Qinling North Slope and Loess Plateau,and the sunny side and upper canopy of parent tree produced relatively more fruits. Fruitingnumber maintained significant difference among different distribution, aspect and canopyposition. Stepwise multiple regression analysis for fruiting number, seed morphology andquality related17environmental factors, which showed that crown width area and volume ofparent tree individual, the temperature, light conditions, soil available nitrogen and potassiumin Q. variabilis Bl. forest were key factors, whereas the temperature and light conditionsalways play the greatest role in enhancement of fruiting number, seed morphology andquality.2. There were differences in the dissemination process, occurrence time, and composition ofseed rain among the three distribution regions. The lastest landing time and earliest endingtime were observed in Loess Plateau; seed rain lasted about76days, while peak time lastedabout14days. In contrast, the earliest landing time and lastest ending time was found inQinling South Slope. The whole seed rain lasted91days and the peak time lasted about33days. Seed rain in sunny slope started earlier than that in the shady slope in same distribution region, while apparent peak time was presented in shady slope. Total intensities of seed rainand soil seed bank was Qinling South Slope＞Qinling North Slope＞Loess Plateau, which insunny slope were greater than in shady slope in same distribution region. The process ofseed rain was dominated by mature seeds, and mature seeds mainly concentrated in the peakof the landing. The largest proportion of mature seeds was found in Loess Plateau, accountingfor56.60%. Immature, seeds eaten by insect pests and animals mainly landed in the startingand final phase of seed rain, the largest proportions of seeds eaten by insect pests and animalswere found in Qinling South Slope, while the largest proportion of immature seeds reaching33.34%, was observed in Qinling North Slope. The number of seed development changeddynamically in soil seed bank by time, and the speed of the disappearance of mature seeds insunny slope was faster than that in shady slope. The seed descreased by seeds eaten byanimals and moldy resulted in soil seed bank.3. The densities of seedlings decreased with age increasing in three distribution regions.In order to adapt to the Loess Plateau habitat, the seedlings increase root growth and decreasethe growth of leaves and stem. Northern slope of seedlings enhanced ability to adapt in theQinling North Slope with age increasing, more dry mass was gradually accumulated in leavesand stem. Seedling growth in sunny slope of Qinling South Slope was better than that inshady slope, and improvement of leaf area index and light competitiveness was adopted topromote seedling regeneration. Path analysis showed that improving lighting conditions, soilmoisture, soil available nitrogen content and the thickness of the litter layer, and reducing theshrub layer cover and forest stand density are conducive to the seedlings settement. Moreover,the best seedling growth was found in the sunny slope of Qinling South Slope, but the worstone was displayed in sunny slope of Loess Plateau.4. With decreasing water potential caused by increasing concentrations of PEG tosimulate different drought stress intensities, germination time delayed and germination vitalityindex(VI) decreased gradually. When compared to controlled treatment(0MPa), seedgermination percentage (GP) and daily average germination rate under light drought stress(-0.1MPa) both increased by9.81%, germination vigor (GRI) increased by4.58%, as well asthe growth of seed radicle promoted. The moderate and severe drought stress treatmentsinhibited seed germination, as well as slowed growth of the seed radicle and plumule.Germchit adapted to the decreasing environmental water potential (from-0.1to-1.2MPa) byincreasing the radicle to plumule ratio (R/P), whereas seed could not produce plumule undersevere drought treatment (-1.5MPa). It must take more time to finish50%seeds radicalemergence, plumule emergence and seedling establishment than that of controls underdrought stress. Critical water potential of50%seeds radical emergence, plumule emergence and seedling establishment was-0.12,-0.08and0.06MPa, respectively, which indicated thatseedling establishment was most sensitive to external water potential. When soilenvironmental water potential was below-0.6MPa, the contents of three osmoregulationsubstances (free proline, soluble sugar and protein), the activities of four protective enzymes[(superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbateperoxidase(APX)], and antioxidant content [ascorbic acid (ASA)] were significantlydecreased, and malondialdehyde (MDA) significantly increased, resulting in lipidperoxidation. Therefore seed germination was inhibited.5. The seedlings had optimal height, basal diameter, and healthy number of leaves, leafarea under controlled treatment. Afterwards, these parameters significantly decreased asdrought intensity increased. The number, length, surface area, volume of different diameterclass root under light drought treatment significantly increased compared with those atcontrolled treatment, whereas these parameters decreased at moderate and severe droughtstress. Leaf area ratio (LAR) and specific leaf area (SLA) increased to withstand progressivedrought stress, but their effects were not significant. The long-term water-use efficiency(WUEL) started to decline at moderate drought stress, resulting seedling slow growth.Increasing accumulation of osmoregulation substances, decreasing osmotic potential anddeveloping antioxidant defense system of leaf, thin fine root (0<D≤0.5mm) and thick fineroots (0.5<D≤2mm) withstood light drought stress. Part of the protective antioxidant enzymeactivity and antioxidant content have declined, leading to decreasing ability of droughtresistance under moderate drought stress. However, prolonged severe drought stresssuppressed to increase in soluble protein, activities of CAT, POD and APX, as well as ASAcontent, leading to a rapid increase in MDA and decline in fine root vitality. Therefore,seedling growth was almost stagnant at severe drought stress.6. Q. variabilis Bl seedlings still were able to maintain an adequate leaf water status(RWC>60%) at light and moderate drought treatment. The deficient leaf water status (RWC<42%) was observed at severe drought resulting in serious leaf wilting. Exposure to lightdrought resulted in quickly significant reductions in the saturated osmotic potential (Ψ100s) andinitial plasmolysis osmotic potential (Ψ0s), meanwhile seedling maintained a relatively highernon-permeate water content (RWCa) and lower bulk modulus of elasticity (). However, Ψ100sand Ψ0swere improved at prolonged severe drought stress, leading to an inhibitedosmoregulation. The photosynthesis diurnal courses of Q. variabilis Bl seedlings werebimodal curve during clear days of the growing season. Peak value appeared at10:00to11:00and15:00to16:00, having a significant photosynthetic midday depression phenomenon at13:00. Drought stress induced significant decline in net photosynthetic rate (Pn), and the main reason for this depression of seedling included stomatal factor and non-stomatal factor.Leaves instantaneous water use efficiency (WUEI) was improved at light drought, butsignificantly decrease at severe drought. Drought stress led to a reduced photosyntheticpigment content, while Chla/Chlband Car/Chla+benhanced.7. Seedlings should be protected in Q. variabilis Bl secondary forests to adapt adverseenvironmental. Cultivation of high-yield Q. variabilis Bl forest should collectes in peak timeof seed rain, and the location should be selected at Qinling forest area. In addtion, thinningwas suitable for cultivation and management to provide the favorable light conditions and soilwater contents keep being between21.1±0.6%to14.6±1.2%for Q. variabilis Bl seedgermination and seedlings growth.更多还原