高寒嵩草草甸退化分异过程及发生机理初步研究

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	高寒嵩草草甸退化分异过程及发生机理初步研究
其他题名	Preliminary Study on the Process and Mechanism of the Degradation grassland in Alpine Kobresia Meadow
	杜岩功
学位类型	硕士
导师	曹广民
	2008-06-04
学位授予单位	中国科学院西北高原生物研究所
学位授予地点	西北高原生物研究所
关键词	高寒草甸被动和主动退化草毡表层营养供求阈值
摘要	高寒嵩草草甸是广布于青藏高原的地带性植被之一，自20世纪80年代以来发生退化，形成大面积的“黑土型”次生裸地。有关高寒草甸的退化原因，现有研究报道普遍认为高寒草甸的退化归咎于过度放牧引起的植被演替和鼠类活动的破坏。草地生态系统是由家畜-牧草-土壤-环境构成的一个连续体，任何一个环节的改变，必然会导致各层次的适应与反馈，该理论注重了草地退化的表观现象（放牧作用、植被演替、鼠类活动和黑土型草地发生）之间的关联，而无法反应高寒草地退化过程中草地的内在本质变化。本文在对“三江源”和中国科学院海北高寒草甸生态系统研究站地区退化草地长期观测的基础上，提出了高寒嵩草草甸的被动和主动退化假说，并在海北站地区选择了四种典型退化阶段的高寒嵩草草甸为研究对象，对该假说进行了初步的验证，其研究内容包括如下： 1、提出高寒嵩草草甸被动和主动退化假说：放牧高寒嵩草草甸退化分为“四个时期、三个阶段、两种动力”。四个时期：异针茅+羊茅—矮嵩草群落、矮嵩草群落、小嵩草群落、杂类草黑土型次生裸地。三个阶段：被动退化阶段（异针茅+羊茅-矮嵩草群落向矮嵩草群落的演替）、主动退化阶段（矮嵩草群落经小嵩草群落到杂类草黑土型次生裸地的演替）和过渡阶段（矮嵩草群落）。两种动力：在被动退化阶段，家畜的选择性采食和践踏造成的禾本科牧草生长、繁殖受阻，而引起草地植被群落的被动演替是该阶段发生的主要动力。在主动退化阶段，其退化动力主要是小嵩草植物特殊的生物学特性（高地下/地上比）。 2、被动和主动退化假说的佐证在高寒嵩草草甸四个演替时期：植物功能群及生物量变化：地上生物量和禾本科的比例逐渐减小，在杂类草黑土型次生裸地稍有增加，禾本科比例依次为30.75%、29.28%、15.41%、19.79%，莎草科、杂类草的比例逐渐增加，在杂类草和黑土型次生裸地稍有降低，分别为12.53%、14.73%、19.65%、8.17%和27.48%、35.83%、45.64%、43.47%。草毡表层变化：草毡表层为高寒草甸所特有，是草地承载外界干扰，抵抗家畜践踏的屏障。草毡表层从异针茅+羊茅-矮嵩草草甸群落的4.03±0.49cm可以发育到小嵩草群落的10.1±0.38cm，在“三江源”地区甚至可以达到40cm，地下根系系统极度发育。统计分析表明,草皮层厚度达到极显著差异水平（p＜ 0.01）。土壤湿度和渗透速率变化：土壤湿度和水分渗透速率都逐渐降低，降幅分别为81.48%和83.03%，土壤湿度和水分渗透速率组间差异达到极显著水平（p＜0.01）。营养供求变化：牧草地上部生长需氮和需磷量（用于牧业生产）逐渐减少，需氮量从8.22降到4.17 g/m2，需磷量从0.59下降到0.30 g/m2，其中2/3用于地下生长需要，滞留于土壤，在高寒环境下，根系的更新与死亡根系的分解极为缓慢，使得速效养分本就贫乏的高寒草地养分流通数量更为馈乏。 3、被动和主动退化假说的指导意义高寒草甸具有较高的维持系统稳定性的能力，但系统遭到破坏后的恢复能力极差。其维持系统稳定性的机制主要有牧草的低矮化、细绒化、草毡化。今日高寒草甸的大面积退化，是人类所赋加于草地的承载力远超过其承载力阈值，而导致系统稳定性的崩溃。高寒草甸退化过程有不同的分异阈值。对处于主动退化阶段之前的高寒嵩草草甸，通过降低\解除的牧压，通过补播和耙松等措施，就可以使草地得到休养生息。而一旦进入主动退化阶段，草皮的塌陷、班驳，最终形成“黑土滩”型退化草地，这是不可避免的也是不可逆转的。保持草毡表层在一定限度，既可以使草地保持较高生产力又可以缓解草地的退化。关键词：高寒草甸；被动和主动退化；草毡表层；营养供求；阈值
其他摘要	Alpine Kobresia Meadow is one of the main vegetation types wide spreading in Qinghai-Tibet Plateau. The degradation of alpine Kobresia meadow was more and more seriously from 1980s and excessive grazing intensity was the essential reason which leaded to the pasture ecosystem degradation. Generally，it was thought that vegetation degradation succession was caused by excessive grazing and the rodent leaded to the degradation in alpine Kobresia meadow. But a few works on the grassland degradation were done by considering the conflict about the livestock, pasture, soil and the environment. Grassland ecosystem was a continuum of the livestock, pasture, the soil and the environment. Any changes of above factors would inevitably lead to all levels of adaptation and feedback. This theory of the grassland degradation was focus on the apparent phenomenon (grazing, vegetation succession, rodents and “black-soil-type”) and the association. It could not respond the inherent nature of grass changes. Therefore, we put forward that passive-active degradation process and its mechanism in Alpine Kobresia meadow after consideration. Our hypothesis was focused on the incrassation process of mattic epipedon. Four kinds of alpine meadow under different grazing intensity were selected as research plot for studying disturbance of grazing to alpine meadow vegetation succession rule and soil response process to grazing intensity at Haibei ecosystem research station, Chinese Academy of Sciences. The pasture maintained relatively stably grazing intensity and formed obvious grazing grads on surface character and species component. The time of the experiment was from July, 2005 to September, 2008. The grazing intensity was obtained by investigating livestock quantity and field acreage. Three questions were answered in this research. 1.The content of the passive-active degradation process and its mechanism was studied. The degradation process of alpine meadow can be divided into four stages, three phases and two driving power. Four stages were Stipa sliena +Festuca ovina+ Kobresia humilis, Kobresia humilis, Kobresia parva and herb－“black-soil-type”. It was passive phase from Stipa sliena +Festuca ovina+ Kobresia humilis to Kobresia humilis, and it was active phase from Kobresia parva to herb－“black-soil-type”, and it was the transition phase in Kobresia humilis. There were two drives on the grassland degradation. The degradation mechanism should be deepened to excessive grazing and its eating (the livestock) in passive stage. The degradation driving power was the special biological characters of the Kobresia in active stage. The roots were increased sharply in this stage, so it leaded to much nutrient fixed into the soil. Furthermore the nutrient supply-demand maladjustment and drought intimidation caused by the mattic epipedon increasing maybe was one inherent reason of the degradation in alpine Kobresia meadow. The degenerated pasture could be recoverd by reducing grazing intensity, killing rodent and setting up enclosure in passive stage, however once into active stage it was inevitable and unreversed, and it formed finally “black-soil-type” meadow. 2.The evidence of the passive and active degradation process was studied. The change of biomass and function group was as follow: The aboveground biomass and the ratio of the gramineae were decreased ,and it was 30.75%、29.28%、15.41%、19.79%,but the ratio of cyperaceae and leguminosae, and the forbs biomass were increased gradually it was 27.48%、35.83%、45.64%、43.47% in four stages. The mattic epipedon was exited only in alpine meadow, and it was important to the pasture for reducing the degradation. The depth of mattic epipedon was increased from 4.03±0.49cm in Stipa sliena +Festuca ovina+ Kobresia humilis to 10.1±0.38cm,even to 30-40cm in Kobresia parva. It was showed that they were significantly different （p<0.01）. The soil moisture and saturation ratio decreased gradually, and the range reached to 81.48% and 83.03%, during the pasture degradation. There were significant differences on soil moisture between four stages（p<0.01）. Both the requisite nitrogen and phosphorus diminished, and it became from 8.22 to 4.17 g/m2 by 97.1% on nitrogen, on the other hand it was from 0.59 to 0.30 g/m2 by 96.7%. Especially, it increased one times on nitrogen and phosphorus; inside more than 2/3 were spent on underground pasture growth, which turned into biology fixation and cumulated into soil. It leaded to the nutrient pinch and accelerated the pasture degradation in alpine meadow. 3.The significance and guide to the degradation was studied. Alpine Kobresia Meadow had performed special mechanism to maintain its stability in the long-term evolving process though it’s simple in structure. So it could bear the anthropic disturbance and climate fluctuation, meanwhile it had higher ability of controlling and resuming system in a certain degree. Alpine Kobresia Meadow maintaining its systematic stability mechanism was by lowed, villiform and mattic growth. People usually think that alpine meadow function fragile should be interpreted as its ability was poor at recovering from destroyed system, not as poor at counteracting outside disturbance. Nowadays it had degenerated in large areas in alpine meadow. The fact was that the carrying capacity appended by human had exceeded the capture threshold then made the system stability lose, not as that the system was fragile. It was important on the choice of major guiding for a restoration of degraded grassland management measures by a correct understanding of the degradation process and the mechanism. We can get the grass to recuperate, by reducing and lifting the existing grazing pressure, through the rake-and-sowing and other measures in a passive stage. Once entered the active stage of degradation, the collapse of the turf, denudation and eventually a “black-soil-type” degradation of the grassland, it is inevitable and irreversible. Key words: alpine meadow; passive and active degradation; mattic epipedon; nutrient supply and demand; threshold
页数	46
语种	中文
文献类型	学位论文
条目标识符	http://210.75.249.4/handle/363003/3200
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	杜岩功. 高寒嵩草草甸退化分异过程及发生机理初步研究[D]. 西北高原生物研究所. 中国科学院西北高原生物研究所,2008.

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