【作者】 侯颖；

【导师】 王开运；

【作者基本信息】 华东师范大学 ， 生态学， 2010， 博士

【摘要】 自工业革命以来,全球范围内大气CO2浓度及其他温室气体浓度逐渐升高,并引发温室效应,导致全球温度上升。CO2浓度和温度升高及由此引起的其他环境问题对自然生态系统及人类社会的影响已成为全球变化研究中的焦点。而高山树线区的复合群落,因其生长在环境异质性高、生长条件相对苛刻的环境中而对外界干扰异常敏感,这使其成为气候变化对植物影响研究的一个理想平台。川西亚高山林草交错区是青藏高原东缘亚高山针叶林和亚高山草甸交错地带,微生境梯度变化剧烈,环境异质性高,是全球变化的敏感地带之一。该地区气候变化对植物生长影响的信息有助于理解北半球中纬度地区植物群落结构和组成在未来气候条件下的变化。本文通过人工控制环境生长室系统,模拟未来变化的气候条件,分别研究CO2浓度升高、温度升高及二者同时升高对林线建群种的生长、生理和形态结构的影响,并从生理和形态结构的角度探讨植物生长对气候变化的响应机理。以期通过对川西亚高山林线区主要木本和草本植物的研究,明确气候变化对不同物种影响的差异,为预测未来气候变化条件下群落的动态提供理论依据,也为C循环模型的运行提供基础数据。主要研究结果和结论如下：1) CO2浓度和温度升高对群落生物量的影响CO2浓度升高、温度升高及二者同时升高3种处理下群落的生物量均比对照降低,分别为645.95g/m2、515.83g/m2和584.19g/m2,而对照处理下群落的生物量为769.48g/m2；进一步的研究表明,群落生物量的减少是由群落中不同物种对CO2浓度和温度升高响应的不同、及由此导致的各组分所占群落比例的变化造成的。糙野青茅和甘肃苔草生物量占群落生物量的比例较大,因此,其生物量的大幅降低抵消了冷杉、东方草莓和紫花碎米荠生物量的增加,引起群落生物量的降低。群落中不同组分生物量变化的不同、甚至相反,可能导致群落组成和结构的变化。2)乔木和草本植物生长、生理和形态结构对CO2浓度和温度升高的响应CO2浓度和温度升高均使乔木物种冷杉幼苗生物量的积累增加,对其生长产生正效应。而且,温度升高促进了CO2浓度对冷杉幼苗的这种正效应。草本植物中,除CO2浓度升高条件下糙野青茅生物量没有显著变化外,CO2浓度升高、温度升高及二者同时升高均使糙野青茅和甘肃苔草的生物量降低。相反,3种处理下,东方草莓和紫花碎米荠的生物量均增加(除东方草莓在温度升高下降低外)。这表明,CO2浓度和温度升高有利于冷杉和非优势草本物种(东方草莓和紫花碎米荠)的生长,而优势草本植物(糙野青茅和甘肃苔草)的生长被抑制。因此,气候变化条件下,优势草本植物和非优势草本植物可能会互相转换。CO2浓度升高与CO2浓度和温度同时升高条件下,由于CO2对Rubisco结合位点竞争的增强或叶片中光合系统结构的改变,冷杉和草本植物的光合速率均比对照增加,而水分利用效率的提高则与光合速率和蒸腾速率的变化有关；温度升高使乔木和草本植物的气孔导度和蒸腾速率均增加,但由于冷杉、糙野青茅和甘肃苔草的光合速率没有变化,导致其水分利用效率降低；而东方草莓和紫花碎米荠因光合速率提高而使水分利用效率增加。气候变化下,物种水分利用效率的提高有助于缓解由温度升高或降雨分配变化引起的干旱胁迫,增加其在群落中的竞争力。乔木和4种草本植物在CO2浓度升高、温度升高及二者同时升高环境下生长2个生长季后,均出现光合速率下调现象。但是,综合来看,冷杉的光合参数下降幅度小于4种草本植物。通过对Pn-PAR和Pn-Ci响应曲线的模拟计算可知,乔木和草本植物的表观量子产量、羧化速率均降低,这意味着植物在高CO2浓度和温度条件下转化光能的能力和Rubisco酶含量或活性降低；CO2补偿点和光补偿点的升高则意味植物利用CO2和光能的范围缩小。乔木和草本植物的N养分吸收和利用效率对C02浓度和温度升高的响应差别较大。CO2浓度升高、温度升高及二者同时升高均增加冷杉的养分吸收量,但养分利用效率在单独CO2浓度升高和单独温度升高情况下均无显著变化；相反,草本植物的N吸收总量在3种处理下降低或不变,但其养分利用效率提高,这可能会部分缓解因N吸收不足导致的生长限制。这表明不同功能类型植物的养分吸收和利用策略对气候变化的响应不同。CO2浓度升高、温度升高及二者同时升高均影响冷杉的树冠结构：树冠体积和总叶面积增加、树冠内枝的角度、长度和分布发生改变,使其更有利于接受光能；CO2浓度升高和温度升高使冷杉的根冠比增加。这些变化有利于其对地上和地下资源的获取。相反,糙野青茅和甘肃苔草根冠比和总叶面积在3种处理下均降低,这降低了其获取资源的可能性。因此,植物能够通过结构的改变而影响对资源的获取或利用效率。CO2浓度升高使乔木和草本植物的比根长均增加,而根长N吸收率降低,表明植物对地下资源的获取是通过增加资源的投入而扩大占据的空间,从而增加对资源的获得。这可能与CO2浓度升高使土壤中可利用的N减少有关；温度升高及CO2浓度和温度同时升高条件下,冷杉比叶面积增大,而根长N吸收率降低,草本植物的变化与冷杉相反。这表明温度升高对不同植物地上-地下资源投入与获取效率影响具有差异性。3)植物生长对CO2浓度和温度升高响应的机理因不同物种而异乔木和草本植物的生长对CO2浓度和温度升高的响应机理不同。CO2浓度升高条件下冷杉生物量的增加主要与占有的总空间、总资源吸收、光合和水分利用效率的增加有关,而与N有关的生理特征和形态特征对冷杉的生长不利；CO2浓度和温度同时升高条件下,总资源的增加和单位资源利用效率的提高共同促进冷杉生物量的增加,这使得二者同时升高条件下冷杉幼苗的生物量增加幅度大于单独升高条件下生物量增加的幅度。CO2浓度升高及CO2浓度和温度同时升高条件下,东方草莓和紫花碎米荠的生长被促进,糙野青茅和甘肃苔草的生长因受形态结构的不利影响而受到限制。温度升高通过扩大总的占有空间、增加对资源的吸收,而不是通过提高光合速率及资源的利用效率来促进冷杉的生长。温度升高条件下草本植物(除东方草莓外)则因资源吸收和形态上的不利其生长受到限制。这种生长变化机理上的差异表明,运用碳循环模型对未来气候条件下C循环进行预测时,在不同的模拟情景下、对不同的群落及物种,植物的生理和形态结构指标应加以修正。更多还原

【Abstract】 The atmosphere CO2 concentration and other greenhouse gas have steadily risen globally after the industrial revolution, and result in the increased temperature due to the global greenhouse effects. The influences of these changes and other environmental problems on natural ecosystem and human society have become a major topic of discussion in global climate change studies. Ecotone at subalpine treeline is highly sensitive to disturbance and environmental change due to high environmental heterogeneity and harsh condition. Many species are at the limits of their distributional ranges at ecotone. So, ecotone can be a suitable platform for climate change research. Subalpine transition zone of forest and grass at Western Sichuan Province is in eastern edge of Qinghai-Tibetan Plateau. It is one of the major concerns in global climate change studies, with sharp environment gradient. The study on effects of climate change on plant growth would be helpful for understanding the change of community structure and components in the future climate.In this study, fir(Abies faxoniana) and four herbs with native soil from subalpine tree line ecotone were transferred into enclosed-top chambers for elevated CO2 and temperature treatments. The objective of this study was to determine the effects of CO2 and temperature on growth, physiology and morphology under competitive condition. At the same time, the possible mechanism of growth is discussed in terms of physiology and morphology. With research on fir and 4 herbs under elevated CO2 and temperature, we hope to detect the difference in effects of elevated CO2 and temperature on different species. Therefore, our results intent to provide theoretical evidence for predicting developments of community and basic data for carbon cycle model in future climate.The results and conclusions are as follows:1) Effects of elevated CO2 aud temperature on biomass of community Biomass of community was 645.95g/m2,515.83g/m2 and 584.19g/m2 respectively under elevated CO2, elevated temperature and the combination of elevated CO2 and temperature, which decreased significantly compared to the control (769.48g/m2). Further analysis showed that the different responses of species to elevated CO2 and temperature resulted in change of community components. Decreases in biomass of Deyeuxia scabrescen and Carex kansuensis, which contributed larger proportion to community biomass, offset increases in biomass of fir, Fragaria orientali and Cardamine tangutorum. The difference in biomass response of species to elevated CO2 and temperature, even reverse, resulted in change of community components and structure.2) Responses of Arbor and 4 herbs to elevated CO2 and temperature in growth, physiology and morphologyElevated CO2, elevated temperature and the combination of elevated CO2 and temperature stimulated the growth of fir. Furthermore, high temperature accelerated the stimulation of elevated CO2 on growth. Except for Deyeuxia scabrescen under elevated CO2, elevated CO2, elevated temperature and the combination decreased the biomass of Deyeuxia scabrescen and Carex kansuensis. On the contrary, biomass of Fragaria orientali and Cardamine tangutorum increased under elevated CO2, elevated temperature and the combination, except for Fragaria orientali under elevated temperature. The above meant that elevated CO2 and temperature was favorable for the growth of fir and some of herbs, but disadvantageous to the other herbs, which suggested that in low temperature ecotone, dominant and subordinate herbs in subalpine ecotone might shift relative to each other in the climate change.Elevated CO2 and the combination of elevated CO2 and temperature increased the photosynthesis and water use efficiency of arbor and 4 herbs. Elevated temperature increased stomata conductance and transpiration of arbor and 4 herbs. So, water use efficiency of fir, Deyeuxia scabrescen and Carex kansuensis decreased due to no change in photosynthesis, while increased for Fragaria orientali and Cardamine tangutorum due to increased photosynthesis. Increased water use efficiency of some species under the changed climate would alleviate dry stress caused by elevated temperature or changed precipitation, which might improve the competitive ability. Photosynthetic acclimation was observed in arbor and 4 herbs under elevated CO2, elevated temperature and the combination of elevated CO2 and temperature. In addition, the magnitude of reduction in photosynthetic parameter of fir was smaller than that of 4 herbs. Analysis on Pn-PAR and Pn-Ci curve showed that apparent quantum yield and carboxylated efficiency of arbor and 4 herbs decreased under elevated CO2, elevated temperature and the combination. This meant a decline in electron transport, Rubisco content and activity of fir and herbs grown at elevated CO2 and temperature. Increased CO2 compensated point and light compensated point meant that plant decreased their capacity to use the low CO2 concentration and light.Elevated CO2, elevated temperature and the combination of elevated CO2 and temperature increased N absorption of fir, but decreased or had no influence on herbs. N use efficiency of fir was not influenced by elevated CO2 and elevated temperature, but enhanced for herbs under elevated CO2, elevated temperature and the combination of elevated CO2 and temperature. High N use efficiency of herbs might alleviate N insufficiency. The above suggested that strategy in absorption and use of nutrient among species was different under elevated CO2 and temperature.Crown morphology of fir was influenced by elevated CO2, elevated temperature and the combination of elevated CO2 and temperature, with larger crown volume and leaf area, changed branch angle, length and distribution. Elevated CO2 and elevated temperature both increased root to shoot ratio (RSR). The above changes in morphology were favorable for fir to intercept light and absorb belowground resources. On the contrary, RSR and total leaf area of Deyeuxia scabrescen and Carex kansuensis decreased at elevated CO2, elevated temperature and the combination of elevated CO2 and temperature, which was disadvantageous for capturing resources. So, morphology of plants could regulate the potential to exploit resources.Specific root length of arbor and herbs increased at elevated CO2, while N absorption per root length decreased, which suggested that in order to exploit more resources, plants used more investment to occupy larger space. This might be related to less N availability of soil at elevated CO2. Elevated temperature and the combination of elevated CO2 and temperature increased specific leaf area of fir, but decreased N absorption per root length. The reverse was true for herbs. The above showed that elevated temperature had different effects on efficiency of investment and acquisition between fir and herbs.3) The mechanism of growth response to elevated CO2 and temperature was different among speciesThe mechanism of growth response in arbor and herbs to elevated CO2 and temperature was different. The stimulated growth of fir at elevated CO2 was resulted from larger occupied space, increased total absorbed resources, photosynthesis and water use efficiency, but the physiological and morphological traits related to N were disadvantageous to the growth of fir. The combination of elevated CO2 and temperature stimulated the growth of fir through increased total resources and high use efficiency of resources. Growth of Deyeuxia scabrescen and Carex kansuensis was constrained at elevated CO2 and the combination of elevated CO2 and temperature due to morphology. The increased growth of fir at elevated temperature was resulted from larger occupied space and increased total absorbed resources, but not from increasing use efficiency of resources. Except for Fragaria orientali, herbs growth were constrained at elevated temperature due to the low use efficiency of resources and morphology. The above differences in mechanism of growth response between fir and herbs suggested that the physiological and morphological parameter used in carbon cycle model should be adjusted when predicting the global carbon balance at the different conditions.更多还原