放牧强度对环青海湖高寒草地生态系统碳固持的影响

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	放牧强度对环青海湖高寒草地生态系统碳固持的影响
	李冰
学位类型	硕士
导师	徐世晓
	2014-05
学位授予单位	中国科学院研究生院
学位授予地点	北京
学位专业	生态学
关键词	高寒草地青海湖放牧净生态系统交换量生态系统呼吸生态系统总初级生产力土壤呼吸
摘要	在高寒草地生态系统中,放牧是最重要利用方式之一,显著影响草地植物群落地上、地下生物量和生物多样性等，长期的放牧活动势必对高寒草地碳收支产生影响。草地生态系统碳循环研究中应包含草地-草食动物-土壤界面系统下的碳循环，而当前对草地这一重要陆地生态系统碳循环的研究主要聚焦于植物的光合、呼吸作用及土壤微生物分解等方面，对其碳储量的估算几乎都是在草地－土壤界面上开展的，忽略了放牧家畜这一重要组成部分在草地生态系统碳循环中的作用。试验于青海省青海湖北岸刚察县的高寒草地试验区进行，试验动物为当地绵羊，设置六个放牧梯度，分别为围封禁牧（CK）、牧草利用率30%（G1）、牧草利用率40%（G2）、牧草利用率50%（G3）、牧草利用率60%（G4）、牧草利用率70%（G5）。对净生态系统碳交换(NEE)、生态系统呼吸(R_eco)、土壤呼吸(R_s)、土壤有机碳(SOC)等指标进行了系统的测定，以量化放牧活动对生长季高寒草地生态系统碳收支的影响。主要取得以下的主要结论：（1）随着放牧强度的增加，群落地上生物量呈现降低的变化趋势，莎草科地上生物量差异不显著，禾本科和豆科生产力降低，杂草类生物量有增加趋势，禾草、豆科比例减小，莎草和杂类草比例增加；（2）与不放牧处理相比，随着放牧强度的增加，地上净初级生产量呈现先增加后减少的趋势，在放牧处理为50%的G3组，达到最大值。放牧处理为G1、G2、G3显著大于对照组，说明高寒草地在适度放牧处理条件下存在“超补偿性”生长。0-30cm地下生物量总体上随放牧率的增加而降低，草地植被地下生物量主要分布在0-10cm土层；（3）高寒草地生态系统NEE、R_eco和GPP均表现明显的季节变化，NEE在整个生长季的变化趋势呈“U”型，R_eco和GPP为单峰型变化趋势。随着放牧强度增大，NEE呈先增加后降低的趋势，R_eco和Rs总体上呈降低趋势；（4）不同放牧处理样地相比于对照组，NEE和GPP更早达到生长季最大值，说明放牧能够促进最大净初级生产力出现的时间提前。放牧可以增加生态系统碳吸收和总初级生产力，降低生态系统呼吸。在中度放牧处理下，高寒草地NEE和GPP具有最大值；（5）随着放牧强度的增加，土壤容重呈增大趋势，土壤含水量逐渐变小；生长季放牧活动对土壤表层有机碳有一定的影响，重度处理使土壤有机碳减少幅度最大。同一放牧区土壤容重、土壤含水量和有机碳的含量随土壤深度的增加而呈下降趋势, 不同层次间均呈现出显著差异。
其他摘要	In the alpine grassland ecosystem, grazing is one of the most important disturbances, which influences the species composition and biodiversity, and long-term grazing must affect carbon circle of the alpine meadow ecosystem. Meadow-grass-eating animals-soil surface is a system which alpine grassland ecosystem carbon circle must contain. Present research are focused on photosynthesis、respiration of plants and soil microbial decomposition, etc. Most estimation of carbon storage of alpine ecosystem were set up and develop on the grass-soil system. Grazing livestock, the important part in carbon circle of alpine ecosystem, was neglected. The research was a grazing trial on alpine grassland in Gangcha county on the north of Qinghai Lake of Qinghai Province, and take the local Tibetan sheep as the test animal, six grazing gradient were designed to explore the response of carbon budget to grazing activities，which were no grzaing(CK)、grass usage 30%(G1)、grass usage 40%(G2)、grass usage 50%(G3)、grass usage 60%(G4)、grass usage 70%(G5). Measurements of net ecosystem CO2 exchange、respiration of ecosystem、soil respiration rate and soil organic carbon were carried in the experiment to quantize the impact of grazing. Results as following are achieved in this research in 2013： (1) With the increase in grazing intensity, aboveground biomass showed decreasing trends, aboveground biomass of Cyperaceae was not significant, the productivity of Poaceae and Leguminosae sp. was in decline, the biomass of weed had an increasing trend, the proportion of Poaceae and Leguminosae sp. increased and the proportion of Cyperaceae and weed reduced. (2) Compared with no grazing treatment,aboveground net primary productivity showed a decreasing trend after the first increase with increasing grazing intensity.When the grazing intensity was 50%, ANPP of G3 reaches a maximum. The value of G1, G2, G3 was significantly higher than that of CK, which indicated that the presence of alpine meadow "overcompensating" grown under moderate grazing treatment conditions. 0-30cm below-ground biomass in general with increasing grazing intensity, grassland underground biomass was mainly in the 0-10cm soil. (3) NEE, Reco and GPP of alpine grassland ecosystem showed obvious seasonal variation, NEE trend in the growing season was "U" shape, the shape of Reco and GPP as a single peak trends. As grazing intensity increases, NEE first increased and then decreased, Reco and Rs were decreasing overall. (4) Compared with no grazing treatment, NEE and GPP of different grazing treatment plots earlier reached the maximum in growing season, indicating that grazing treatment can promote maximum of net primary productivity occurs in advance. Grazing can improve ecosystem carbon sink and gross primary productivity, reduce ecosystem respiration. Under moderate grazing treatment, NEE and GPP of alpine meadows had a maximum value. (5) With increaseing grazing intensity, soil bulk density was in increase and soil moisture becomes smaller. Grazing activities had an impact on the soil surface organic carbon in growing season, the soil organic carbon was the largest drop under heavy grazing treatment. soil bulk density, soil moisture and organic carbon on the same grazing area, they were in a downward trend with the increase of soil depth and showed significant variations between different soil levels.
文献类型	学位论文
条目标识符	http://210.75.249.4/handle/363003/4009
专题	中国科学院西北高原生物研究所
推荐引用方式 GB/T 7714	李冰. 放牧强度对环青海湖高寒草地生态系统碳固持的影响[D]. 北京. 中国科学院研究生院,2014.

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