【作者】 邓钰；

【导师】 柳小妮； 辛晓平；

【作者基本信息】 甘肃农业大学 ， 草业科学， 2012， 硕士

【摘要】 家畜的采食减少了碳素由地上向地下的输入，使草地的固碳能力降低。光合作用和土壤呼吸是全球碳循环的重要组成部分。通过对呼伦贝尔草甸草原区域，不同放牧强度下天然草地优势种—羊草的光合生理指标以及草地土壤呼吸及其环境变化进行研究；进一步分析个体水平上羊草光合特性对放牧强度的适应机制和寻找合适放牧强度以降低放牧对草地土壤呼吸的不利影响。从而为放牧生态系统C循环模拟与监测提供基础数据。以不同放牧强度下（R0，R1，R2，R3，R4，R5）呼伦贝尔草甸草原未采食和采食羊草（Leymus chinensis）光合生理特征，天然草地土壤呼吸以及其环境因子为研究对象；采用红外线CO2气体分析仪（IRGA）、丙酮乙醇法、烘干法和环刀法分别进行系统研究。结果表明：1、在连续放牧方式下，羊草叶片的Pn、Tr、Gs对不同放牧强度响应日动态，既有“单峰”曲线也有“双峰”曲线，Ci呈“U”字型变化；不同放牧强度下未采食和采食羊草Pn、Tr季节变化均呈单峰型，而Tr变化较Pn剧烈。羊草叶片Pn、Tr、Gs日均值随着放牧强度的增大而下降；未采食和采食羊草季节变化，除R1外，随放牧强度增加而降低；Ci却相反。处于生长盛期羊草的光合指标值均优于生长晚期。采食羊草比未采食羊草Pn略低；Tr略高。大气温度、大气相对湿度、PAR综合作用于Pn和Tr。采食后，受损羊草Pn、Tr对环境水热因子的响应更为敏感；而R1较轻度放牧强度对羊草光合特性无显著影响，而R4和R5下均存在显著影响。除R1外，随R增大，羊草的最大净光合速率（Pmax）、表观量子效率（AQY）和暗呼吸速率（Rd）下降，而光补偿点（LCP）和光饱和点（LSP）增加。羊草对弱光吸收利用能力低，对强光敏感性弱。羊草采食后的叶绿素含量并未升高，随放牧强度增大，羊草光合色素变化激烈，并受季节影响。2、2011年测试期，SRR日变化与土壤温度（ST）和土壤含水量（SWC）及牧草生育期相关。SRR最大值出现在10:00～12:00；最小值分两个生长阶段，6月12日和7月10日（生长盛期）出现在16:00～18:00；8月12日和9月14日出现在6:00～8:00。SRR日变化呈单峰曲线，2010和2011年SRR季节变化趋势分别呈双峰形式和多峰波动形式；SRR日均值和各测试时间下SRR值，均随着放牧强度（除R1外）增大而下降，放牧强度间差距越大，SRR差异也越显著。在生长盛季，放牧强度越大，SRR日变化、季节变化浮动越剧烈，在生长后期变化减缓。放牧强度在一定程度上改变SRR的微环境，其中SWC、AB、RB和LA均随随放牧强度（除R1）增大而降低；放牧强度差异越大，影响因子之间差异越显著；ST的变化不具显著性，但R4和R5的值明显高于R0或R1。当温度低于生物最低生长温度时（如：2010年9月30日和2011年9月的3个测试日），各放牧强度之间SRR差异不显著；其它测试时间下，草地土壤呼吸随放牧强度（除R1外）增大而下降；其中，R4和R5显著低于R0和R1，而相邻放牧强度之间SRR不存在显著性差异。在时间序列上，ST是影响SRR的主要因子之一；而R4和R5放牧强度下，SWC与SRR的相关系数大于R0。SRR与生物因子（AB、RB和LA）和该环境下水热因子（大气温度、降水量、ST、SWC）呈正相关，与放牧强度干扰和壤容重呈负相关。综上可得， R1对羊草光合特性、SRR及其环境因子均无影响，而R4和R5对以上研究内容均有显著影响，R2和R3对它们的影响介于二者之间。因此，从生产的角度，R2和R3是合理的放牧强度；从生态的角度，R1是合理的放牧强度。更多还原

【Abstract】 The input of carbon has decreased from the aboveground to the underground, toreduce the carbon sequestration capacity of grassland. Photosynthesis and soilrespiration are the elementary component of global carbon cycle. The photosyntheticand physiological indexes of dominant species-Leymus chinensis, soil respiration andits controlled factors were measured in Hulunber meadow steppe. It can be analyzedby the photosynthesis of L. chinensis for the adaptation to grazing intensities on theindividual level, looking for suitable grazing intensity to reduce the adverse effects,providing basic data for the simulation and monitoring of carbon cycle.The photosynthetic characteristics of ungrazed and grazed Leymus chinensis andsoil respiration were studied by the method of infrared radiation gas analyzer underthe treatments of six different grazing intensities （R0, R1, R2, R3, R4and R5） among allexperimental plots in Hulunber meadow steppe. The photosynthetic pigments andbiomass （including aboveground and root） were studied by Acetone ethanol methodand drying method.The results have showed as follow.（1） Results show that daily variation of net photosynthetic rate （Pn）, transpiration rate （Tr）,stomatal conductance （Gs） appears single peak curve and double peak curve, but intercellular CO2concentration （Ci） demonstrates shape of U. Which responsed to different grazing intensitiesunder condition of continuous grazing. Pn, Tr of ungrazed and grazed L. chinensis have showedsingle peak curve during the period of experiment under different grazing intensities. Tr is moresensitive to different grazing intensities and seasonal change than Pn. In addition, Pn, Tr, Gs of L.chinensis shows the decrease with the increase of grazing intensities, but Ci presents the increase.Pn, Tr of ungrazed and grazed L. chinensis has presented the decline with the increase of grazingintensities, Ci reverses （except R1） in the period of growing season2011year. The photosyntheticvalues of early growth stage are better than late. The Pnof grazed L. chinensis were lower thanungrazed L. chinensis, while Tr higher. Air temperature （Ta）, relative humidity （RH）,photosynthetically active radiation （PAR） were combined the effects of each other rather thanoperated by a single factor. After grazing, Pn, Tr of damaged L. chinensis are severely sensitive toresponse to hydrothermic factors. R1has no significance with photosynthesis of L. chinensis, while R4and R5achieve the significant level. The maximum of net photosynthetic rate （Pmax）, apparentquantum yield （AQY）, and apparent dark respiration rate （R_d） of L. chinensis with the increase ofgrazing intensities （except R1） have decreased. It showed that the absorption and utilization abilityof L. chinensis was low of weak light, and was weak sensitivity of strong light. The content ofchlorophyll of grazed L. chinensis were not rising. With the increase of grazing intensities, thecontent of chlorophyll L. chinensis has changed dramatically, influencing on seasonal condition.（2） The diurnal variation of soil respiration rate （SRR） has correlated with soil temperature（ST）, soil water content （SWC） and the growing period of herbage. The maximum has appearedbetween10and12o’clock. But the time of appearing minimum was inconsistent. The minimumappeared in the period of16to18o’clock on12June and10July, while it showed in the period of6to8o’clock on12August and14September. The diurnal variation trend of SRR has presented asingle peak trait curve, the seasonal change trend of SRR among experimental period haspresented a double peak trait curve under different grazing intensities in2010year, while hasexpressed the form of multi-peak fluctuations in2011year. The mean value of SRR decreased withthe increase of grazing intensities. The difference of SRR was more obvious with the increase ofgrazing intensity gap. In the peak of growing season, the diurnal changes of SRR fluctuatedfiercely with the increase of grazing intensities, then, the extent of fluctuation slowed down in thelate stage of growing season. Grazing intensity has altered the micro-enviroment of SRR in thesome extent. Such as, SWC, above ground biomass （AB）, root biomass （RB） and litteraccumulation （LA） have declined with the increase of grazing intensities （except R₁）. The gap ofgrazing intensities was larger, the difference of controlled factors being more sharply. ST has noregular changes under different grazing intensities, while the ST of R4and R5are distinctly higherthan R0or R1. When the temperature is lower than the minimum of growth （such as, on30thSeptember in2010year, on three experimental days September in2011year）, the difference ofSRR has had no significance among different grazing intensities. SRR has decreased with theincrease of grazing intensities （except R1） on the rest of experimental days, therein, R4and R5aresignificantly lower than R0and R1. SRR of the adjacent grazing intensities did not exist significantdifference. In the series of time, ST has been the main controlled factor of SRR. The correlationcoefficient between SWC and SRR under R4and R5, has been extremely higher than R0. SRR waspositive correlation with biotic factors （including AB, RB and LA） and the hydrothermic factor （main including SWC, ST） in these experimental surroundings, negative correlation with grazingintensity and soil bulk density.In a word, R1has had no significance with the photosynthetic characteristics of L.chinensis, SRR and its controlled factors. While R4and R5have expressed appreciableimpact on above studies. R2and R3have influenced on them between R1and R4, R5.Hence, R2and R3are the reasonable grazing intensities from the viewpoint of yield.But R1could be suitable choice, from the perspective of ecology.更多还原