【作者】 孙英；

【导师】 张德罡；

【作者基本信息】 甘肃农业大学 ， 草业科学， 2012， 硕士

【摘要】 为了研究放牧对高寒草甸优势植物不同季节光合特性的影响，在东祁连山天祝县南泥沟河谷地的披碱草-嵩草型草地设置禁牧（Non-grazing grassland，NG）和放牧（Grazinggrassland，G）两块样地，选取垂穗披碱草（Elymus nutans）、矮嵩草（Kobresia humilis）、黄花棘豆（Oxytropis ochrocephala）、扁蓿豆（Melissitus rutenica）4种优势植物，采用GFS-3000便携式光合仪和Imaging-PAM便携式叶绿素荧光仪，分别测定了4种植物在7、8、9这3个月中放牧和禁牧两种草地中的光合—光响应曲线（Pn-PAR curves）和叶绿素荧光参数。主要研究结果如下：1)禁牧草地中，2种豆科植物（黄花棘豆，扁蓿豆）的光合能力要强于莎草（矮嵩草）和禾草（垂穗披碱草），而且扁蓿豆要强于黄花棘豆。而在放牧草地中，7月和8月时黄花棘豆的光合能力最强，9月时扁蓿豆的光合能力最强。虽然在7、9月，黄花棘豆的光合潜力和热耗散能力都降低，但是由于垂穗披碱草、矮嵩草、扁蓿豆作为家畜喜食的牧草，地上部分大部分被采食，整个植株的生长受到影响，导致光合能力下降；而且放牧导致禾草和嵩草等的比例减少，最终使得黄花棘豆作为一种典型的毒草，获得了一定的滋生空间，叶片的接受光面积增大，光合能力增强。2)7月是当地草地植物旺盛生长的前期，此时4种植物都有较高的光合速率。在禁牧和放牧两种草地中，综合来看，垂穗披碱草对强光的适应能力最弱，但能有效利用弱光；而扁蓿豆在较强的光辐射下才能发挥出光合潜力，且具有较强的光合能力。放牧提高了4种植物对强光的适应能力，同时提高了垂穗披碱草、黄花棘豆、扁蓿豆对弱光的利用能力。3)8月，试验地较干旱，不论是在禁牧草地还是在放牧草地中，4种草的P_max、Fv/Fm、qP都处于最低值，远低于7月和9月，说明它们的光合能力受到严重影响。且对弱光的利用能力和对强光的适应能力都降低。所以8月是本地区草地的敏感时期，该时期应该适当减少放牧家畜的数量、减少放牧时间，使草地能在生长后期尽快恢复。扁蓿豆和矮嵩草对干旱不敏感，其LCP、LSP、Fv/Fm、NPQ等都没有因为放牧而降低。放牧使得黄花棘豆的Fv/Fm和qP升高了，且放牧草地中的P_max显著高于其他3种草的，它的竞争力得到了提升。4)9月（干旱过后），4种植物的光合能力得到了不同程度的恢复。垂穗披碱草、矮嵩草的光合能力虽然得到了一定程度的恢复，但仍然达不到7月的水平。而黄花棘豆、扁蓿豆的光合能力不但得到了恢复，还高于7月。9月放牧增强了垂穗披碱草、黄花棘豆、扁蓿豆这3种草的光合能力，提高了4种草的光合活性和光呼吸水平，也降低了4种草的光合潜力（扁蓿豆的没有受到显著影响）。而相比较来看，扁蓿豆的光合潜力和光呼吸速率最大，但光合活性和热耗散能力小；黄花棘豆的光合活性最高，垂穗披碱草的热耗散能力最强。更多还原

【Abstract】 In order to study the influence of grazing on photosynthetic characteristics of dominantplants in alpine meadow, two plots, including non-grazing （NG） and grazing grassland （G）, weredesigned in Nanni Valley of Tianzhu County in the eastern Qilian Mountains. Four dominantplants in the plots, including, Kobresia humilis, Elymus nutans, Melissitus rutenica, Oxytropisochrocephala, were selected to study their photosynthesis-light response and measure theirchlorophyll fluorescence characteristics in July, August, and September respectively using theGFS-3000portable photosynthesis system and Imaging-PAM portable chlorophyll fluorescenceanalyzer. The main results are as follows:1) The photosynthetic capacity of two legumes （O. ochrocephala, M. rutenica） was strongerthan sedge （K. humilis） and grasses （E. nutans） in non-grazing grassland. While the capacity ofM. rutenica was stronger than O. ochrocephala. On the contrary, the photosynthetic capacity ofO. ochrocephala was the strongest in July and August, and M. rutenica in September. Althoughthe photosynthetic potential and heat dissipation capacity of O. ochrocephala （as a typicalpoisonous weed） decreased in July and September under grazing treatment, it still occupied acertain amount of room for growth because of the defoliation of E. nutans, K. humilis and M.rutenica （favorable forages for livestock） through grazing resulted in lower compitation causedby the decrease of photosynthetic capacity. And finally, its light-receiving area of leaf increasedand then the photosynthetic capacity was increased.2) July was the early period of vigorous growth of the native grasses. During this period, thephotosynthetic rates of these four plants were very high. In non-grazing and grazing grasslands,the adaptability of E. nutans to strong light was the lowest, but it could effectively utilize weaklight. On the contrary, the photosynthetic potential of M. rutenica could be fully exploited onlyin stronger light radiation with higher photosynthetic capacity. Grazing could increase theadaptability of the four plants to strong light, meanwhile, increase the ability of E. nutans, O.ochrocephala and M. rutenica to weak light utilization. 3) The weather was drought in research site in August. The P_max, Fv/Fm, qP of the fourplants were at the minimum value in three months, and much lower than those in July andSeptember in both non-grazing and grazing plots. This indicated that their photosyntheticcapacities were seriously affected. Their ability of weak light utilization and the adaptability tostrong light decreased. Therefore, August was a sensitive period of local grassland plants. In thisperiod, the grazing intensity and time should be reduced so that the grassland could recovere inthe later stage of growth as soon as possible. LSP, Rd, P_maxand a of E. nutans and O.ochrocephala decreased significantly in grazing grassland. LCP, LSP, Fv/Fm and NPQ of K.humilis and M. rutenica, however, did not decrease significantly. It indicated that these twoplants were not sensitive to drought. The photosynthetic potential and photosynthetic activity ofO. ochrocephala were improved, and its P_maxwas significantly higher than the rest three plantsin grazing grassland and its competitiveness was improved.4) In September （after the drought）, the photosynthetic capacity of the four plants recoveredin a certain degree. E. nutans and K. humilis performed not as good as O. ochrocephala and M.rutenica. Grazing in September enhanced the photosynthetic capacity of E. nutans, O.ochrocephala and M. rutenica, the photosynthetic activity and the photorespiration level of fourplants. However, it reduce the photosynthetic potential of the four grasses （M. rutenica was notsignificantly affected）. In comparison, photosynthetic potential and photorespiration rate of M.rutenica were the highest, but the photosynthetic activity and heat dissipation capacity were thelowest. The photosynthetic activity of O. ochrocephala was the the highest, and heat dissipationcapability of E. nutans was the highest.更多还原