不同放牧管理模式对高寒草甸植被、土壤和碳氮储量特征的影响

发布时间：2018-09-04 20:40

【摘要】：青藏高原既是我国重要的特色畜牧业基地,同时也对北半球的气候有着重要影响,更是我国及周边国家多条母亲河的发源地,对我国东部及西南部生态环境和社会经济有巨大影响。青藏高原总面积的85%是高寒草地,是藏羊和牦牛放牧的主要草场,高寒草地在气候调节、多样性保护和水土保持等生态服务功能发挥着重要影响,也对区域生态系统碳库平衡具有十分重要的作用。然而,受全球性气候干旱、牧区人口增加、草原人为活动破坏和长期不合理的放牧利用模式等影响,青藏高原高寒草地退化严重。放牧是草地最主要的利用方式。目前,青藏高原高寒草地通常是整季,甚至全年连续放牧利用,过度放牧严重,这种不合理的利用方式对草地的破坏极大,尤其是在牧草返青期间,刚刚萌发返青的幼苗被采食后光合面积迅速减少,严重影响后期的生长和发育。合理放牧时期的确定,是草地实现休养生息,保持草地健康发展和可持续利用的重要手段。然而,不同放牧管理模式下,高寒草甸植被的结构和组成、土壤理化特征及碳氮储量特征的的变化尚不明确。因此,本研究以青藏高原东缘禁牧(NG)、全生长季休牧(RG)、传统放牧(TG)和连续放牧(CG)4种不同放牧管理模式高寒草甸为研究对象,以群落生态学原理为指导,通过野外调查与室内分析相结合,研究了不同放牧管理模式对高寒草甸植被、土壤理化特征和碳氮储量特征的影响,以阐明不同放牧管理对高寒草甸生态系统的作用,在此基础上,探寻适宜于该地区的最佳放牧管理模式,从而为高寒草地碳汇管理、天然草地退化及修复治理提供理论基础。本研究得出以下结果:1.与CG处理相比,NG和RG处理显著增加了垂穗披碱草(Elymus nutans)和冷地早熟禾(Poa crymophila)的重要值、各功能群(禾本科、莎草科、豆科和杂类草)植物的高度、禾本科植物密度和生物量以及总地上、地下生物量,其中以NG样地效果最为明显;降低杂类草植物的重要值、地下与地上生物量的比值、杂类草的生物量和密度;在4种放牧模式中,Shannon-Wiener指数(H)、Pielou均匀度指数(J)和丰富度指数(S)及群落总密度的排列顺序均为:CGNGTGRG。2.与CG处理相比,NG和RG改良了高寒草甸0~20 cm土壤物理结构,降低了土壤的紧实度,但对深层土壤影响较小;NG和RG不同程度地改善了高寒草甸土壤的持水能力。NG显著增加了0~30 cm土壤有机质含量,RG和TG显著增加了0~20 cm土壤有机质含量。NG,RG和TG显著提高了高寒草甸0~30 cm土壤全氮含量和20~30 cm土壤速效氮含量,而降低了0~10 cm土壤的速效氮含量。NG,RG和TG显著提高了高寒草甸0~30 cm土壤全磷和速效磷含量。不同模式放牧对高寒草甸土壤全钾含量无显著影响,但总体上,NG,RG和TG高于CG;NG,RG和TG降低了0~10 cm土层速效钾含量,而显著增加了10~30 cm土层速效钾含量。3.高寒草甸土壤呼吸速率月动态均表现出先增加后降低的变化态势,峰值出现在8月;在整个生长季,NG,RG和TG高寒草甸平均土壤呼吸值显著高于CG样地,其中,NG和RG间无显著差异,但显著高于TG;土壤含水量对土壤呼吸通量的影响存在一个阈值,30%左右为临界值,在此之前二者呈正相关,此后呈负相关。4.NG,RG和TG较CG显著提高了土壤、根系、植被和凋落物有机碳、氮储量。高寒草甸生态系统中,土壤中有机碳储量所占比例最大(88.8%-98.2%),其次为根系(1.6%-8.7%),再次为植被(0.17%-1.43%),最小为凋落物(0.022%-0.97%);氮储量占比例最大的是土壤(97.3%-99.6%),其次为根系(0.32%-2.07%),再次为植被(0.05%-0.44%),凋落物最小(0.003%-0.16%)。不同放牧管理模式下土壤有机碳、氮储量具有明显的垂直分布特征,随土壤深度的增加土壤有机碳、氮储量明显降低。短期不同放牧模式仅对0~40 cm土层土壤有机碳、氮储量有影响。土壤有机碳、氮储量主要分布在0~40 cm土层,同时,放牧有使有机碳、氮向深层转移的趋势。NG、RG和TG显著提高了高寒草甸生态系统总有机碳、氮储量,而CG显著降低了总有机碳、氮储量,导致有机碳、氮的流失。综上所述,禁牧和全生长季休牧均能有效恢复青藏高原东缘退化草地生态系统。考虑到草地资源的更新、均衡利用和牧民经济收入等,全生长季休牧既可充分利用牧草资源,有利于草地的生态恢复及可持续发展,是青藏高原高寒草甸类草地放牧管理的理想选择。同时,建议禁牧的同时,可采取其他一些人为干预措施(如非生长季放牧利用等)。
[Abstract]:The Qinghai-Tibet Plateau is not only an important characteristic animal husbandry base in China, but also has an important impact on the climate of the northern hemisphere. It is also the birthplace of many mother rivers in China and its surrounding countries. It has a great impact on the ecological environment and social economy in the eastern and southwestern parts of China. Major grasslands and alpine grasslands play an important role in climate regulation, diversity protection and soil and water conservation. They also play an important role in the balance of carbon pools in regional ecosystems. At present, Alpine Grassland in the Qinghai-Tibet Plateau is usually grazed continuously throughout the whole season, even throughout the year. Overgrazing is serious. This unreasonable use of alpine grassland has caused great damage to the grassland, especially during the period of grass turning green, the seedlings just germinating and turning green are picked. The photosynthetic area of alpine meadow decreased rapidly after grazing, which seriously affected the growth and development of grassland in the later period.The determination of reasonable grazing period is an important means to realize the recuperation, maintain the healthy development and sustainable utilization of grassland.However, under different grazing management modes, the structure and composition of alpine meadow vegetation, soil physicochemical characteristics and carbon and nitrogen storage characteristics. In this study, alpine meadows with four different grazing management modes (NG, RG, TG and CG) were selected as the research objects. Based on the principles of community ecology, different grazing management modes were studied through field investigation and indoor analysis. The effects of different grazing management on alpine meadow ecosystem were clarified. On this basis, the best grazing management model suitable for the region was explored, which provided theoretical basis for carbon sink management of alpine meadow, degradation and restoration of natural grassland. Compared with CG treatment, NG and RG treatment significantly increased the important values of Elymus nutans and Poa crymophila, the plant height of functional groups (Gramineae, Cyperaceae, Leguminosae and Weeds), the density and biomass of Gramineae plants, and the total aboveground and underground biomass, of which NG was the most effective. In order to reduce the important value of weeds, the ratio of underground and aboveground biomass, the biomass and density of weeds, the order of Shannon-Wiener index (H), Pielou evenness index (J), richness index (S) and total community density in four grazing patterns were: CGNGTGRG.2. Compared with CG treatment, NG and RG improved alpine meadow 0. The physical structure of ~20 cm soil decreased soil compactness, but had little effect on deep soil; NG and RG improved water holding capacity of alpine meadow soil to some extent. NG significantly increased soil organic matter content of 0~30 cm, RG and TG significantly increased soil organic matter content of 0~20 cm. NG, RG and TG significantly increased total soil organic matter content of 0~30 cm in alpine meadow soil. NG, RG and TG significantly increased soil total phosphorus and available phosphorus content in 0-30 cm alpine meadow. Different grazing patterns had no significant effect on total potassium content in alpine meadow soil, but in general, NG, RG and TG were higher than CG, RG and TG were lower than CG, RG and TG in 0-10 cm soil layer. The monthly dynamics of soil respiration rate in alpine meadow showed a trend of increasing first and then decreasing, and the peak value appeared in August. In the whole growing season, the average soil respiration value of NG, RG and TG in alpine meadow was significantly higher than that of CG plot, and there was no significant difference between NG and RG, but significantly higher than that of TG. There was a threshold value of soil water content on soil respiration flux, about 30% was the critical value, before which there was a positive correlation between them, and after that there was a negative correlation between them.4.NG, RG and TG significantly increased soil, root, vegetation and litter organic carbon, nitrogen storage than CG. In alpine meadow ecosystem, soil organic carbon storage accounted for the largest proportion (88.8% - 98%). 2%, followed by root system (1.6% - 8.7%), vegetation (0.17% - 1.43%) and litter (0.022% - 0.97%); soil organic carbon (97.3% - 99.6%) accounted for the largest proportion of nitrogen storage, followed by root system (0.32% - 2.07%), vegetation (0.05% - 0.44%) and litter (0.003% - 0.16%). Soil organic carbon and nitrogen storage were mainly distributed in 0-40 cm soil layer. At the same time, grazing tended to make organic carbon and nitrogen transfer to deeper layer. NG, RG and TG increased significantly. The total organic carbon and nitrogen reserves of the cold meadow ecosystem were significantly reduced by CG, which led to the loss of organic carbon and nitrogen. In conclusion, grazing prohibition and rest in the whole growing season could effectively restore the degraded grassland ecosystem in the eastern margin of the Qinghai-Tibet Plateau. Rest grazing can make full use of grassland resources, which is conducive to ecological restoration and sustainable development of grassland. It is an ideal choice for grazing management of alpine meadow grassland in Qinghai-Tibet Plateau.
【学位授予单位】：甘肃农业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：S812.8

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