探讨草地凋落物对草地水文功能的影响,在内蒙古典型草原对不同放牧强度的草地凋落物的持水能力进行了测定.结果表明:随着放牧强度的增加,草地凋落物的持水量呈现先增加后降低的趋势,重度放牧下草地凋落物的持水量仅为108g/kg,比中度放牧区的持水量1971.57g/kg降低了95%,这是凋落物组成成分差异的结果,凋落物的吸水速率和浸泡时间的回归分析表明,二者之间具有明显的相关性,回归方程分别为:对照区:Y=738.1X-0.656;轻度放牧区:Y=1569.3X-0.665;中度放牧区:Y=2650X-0.715;重度放牧区:Y=162.38X-0.563.

As a main linkage between material cycle and energy flow in ecosystem, the litter decomposition plays a very important role in soil organic matter formation and nutrient release rate. The research progress on litter decomposition in domestic and overseas were reviewed, and combining with its research trends in three different types of terrestrial ecosystems (forest, grassland and desert), the process of litter decomposition and its affecting effect were described, and the main factors which affect litter decomposition rate from different aspects including physical and chemical properties of litter, CO2 concentration, climatic factors and soil properties were analyzed as well. It could be concluded that the long term and fixed onsite research and the establishment of decomposition model would be the research hot pots in the future.

凋落物分解是生态系统物质循环和能量流动的主要环节，对土壤有机质的形成和养分释放速率有着重要意义。对国内外在凋落物分解方面的研究进行综述，并结合森林、草地、荒漠3种不同陆地生态系统类型中凋落物的研究动态，阐述了凋落物分解的过程、影响效应及从凋落物本身的理化性质和CO2浓度升高、气候因子、土壤特性等方面综合分析了影响凋落物分解的主要因子。在此基础上对凋落物分解的未来研究方向进行展望，得出长期定位研究、建立凋落物分解模型等方面将会成为今后研究的热点。

Litter decomposition is an important component of nutrient cycling and carbon decomposition in grassland ecosystems, and livestock grazing has been a major human intervention to these process. The effects of grazing on litter decomposition vary with climate environment conditions and grassland vegetation types. Alpine mesophytic meadow and alpine semi-hydric marsh meadow are the two rangeland ecosystems commonly seen on the eastern Qinghai-Tibet Plateau, which differentiate themselves by not only the physic/bio environments but also the plant species composition and therefore the litter qualities. In order to understand grazing effects on the litter decomposition of these two meadows, grazed and fenced plots were set respectively on the both meadows. The rates of decomposition and nutrient release were measured for the three littler samples (mesophytic meadow mixed litter, Deschampsia caespitos litter, and Potentilla anserine litter) in the alpine mesophytic meadow plots, and three litter samples (semi-hydric marsh mixed litter, Carex muliensis litter、 Kobresia tibetica litter) in the semi-hyddric marsh meadow plots. The four species generally also represented the dominant species showing respectively in the reverse succession series driven by grazing and climate warming. It was found that there were significant differences in litter decompositions for the dominant species. In alpine mesophytic meadow, Potentilla anserine decomposed faster than Deschampsia caespitos , while in alpine semi-hydric meadow Kobresia tibetica decomposed more quickly. Grazing accelerated the litter decomposition in general, but the responses varied with the species. On the other hand, Deschamp siacaespitos and Carex muliensis have lower decomposition rates in the grazed plots. Grazing has little effect on organic carbon decomposition and the release of C, but positively affected on the release of N and P from the litters. The patterns of litter decomposition and nutrient release of the dominant species suggested that there might exist a positive feedback effect in the alpine marsh meadow degradation due to the accelerating decomposition rate and C release along the reverse succession series. In addition, Potentilla anserine , a typical dominant species of in degraded meadow, was found to have higher litter quality and faster decomposition rate than the other species, reflecting that in the mesophytic community, the plant adopted 'evasion strategy’ rather than 'resistance strategy’ in response to heavy grazing.

为认识放牧对青藏高原东部中生性的高寒草甸草地和半湿生的沼泽草地凋落物分解的影响,在这两种草地上分别设置了围栏和放牧样地,研究了其各自的混合凋落物样品和4个优势物种(发草 Deschampsiacaespitos 、鹅绒委陵菜 Potentilla anserine 、木里苔草 Carexmuliensis 、藏嵩草 Kobresiatibetica )凋落物的分解和养分释放动态,这4个优势物种也大致代表了当地沼泽草地生态系统在放牧和气候变暖驱动下逆行演替不同阶段的优势物种类群。结果表明,各优势物种凋落物的分解速率有显著差异;放牧在总体上促进了凋落物的分解,但不同物种的响应有所不同;放牧对凋落物C的释放影响不显著或有抑制作用,但对N、P的释放具有一定促进作用。对各优势物种凋落物分解和养分释放模式的分析表明,群落逆行演替过程中,凋落物分解和C释放加速,可能促进沼泽湿地退化的正反馈效应。草甸草地的退化标志物种鹅绒委陵菜具有较高的凋落物质量和分解速度,反映了中生条件下植物应对牲畜啃食采用"逃避"而非"抵抗"策略的趋向。

Trampling is one of three ways for livestock to impact on grazing land is recognized to have longer active time and more permanent effect than intaking and excrement. It is therefore important to study the mechanism of trampling on grazing land in order to discover the mechanism of grassland degeneration and properly manage grazing ecosystems.(1) Trampling on vegetationWhile the trampling of livestock physically damaged aboveground herbage and buried the seeds, it was determined to be beneficial to the germ...

放牧家畜的践踏作用是家畜作用于草地的 3个途径之一 ,相对于采食和排泄物的作用具有作用时间长、直接作用的草地组分多和效果持久的特点。家畜践踏损伤牧草、埋实种子、促进萌发 ,减少凋落物的现存量 ,增加土壤的紧实度、容重 ,降低土壤孔隙度、水稳性团聚体、透水性和透气性 ,导致雨后水涝和植物根区缺氧 ,引发水土流失。国内外使用的 4种践踏强度指标分别存在不确定性大、忽视践踏强度的时间依赖性和畜种间差异、没有考虑放牧行为及其时间分配模式等问题 ,分析认为践踏强度应为家畜放牧行为、不同行为的持续时间、家畜体重、放牧地面积和坡度的函数。家畜的践踏作用因草地的健康状况差异而与之存在正或负的反馈机制以及践踏强度阈值 ,可能在草地退化和健康维护中起主导作用。今后需建立严格的研究方法和科学的践踏强度指标 ,重视草地植被对践踏的耐受阈限、践踏对牧草更新的调控机理及其对凋落物产生和分解的影响 ,以及土壤水分与践踏作用的关系 ,确定放牧系统的践踏强度阈值。

摘　要： 枯枝落叶积累可改变原生态环境，地表温度、土壤ＰＨ值积累量呈线性负相关，蒸发量、土壤容重 与积累量呈指数负相关，土壤水分、土壤孔隙度与积累量呈线性正相关，枯枝落叶积累可为植物生长创造良好的生境。土壤中主要营养物质随着枯枝落叶积累均有明 显提高当积累量达６００ｇ／ｍ＾２时，有机质、Ｎ、Ｐ、Ｋ含量分别比无枯枝落叶层提高１．８倍、８８．２％、２．１５倍和３７％。枯枝落叶积累对草原生产 力有促进作用，在一定范围内

In order to identify the features of plant seeds in dung of yak and Tibetan sheep grazing at different grazing stages of winter pasture (alpine meadow) on Eastern Qilian Mountain, the number of species, the seed diversity index, the seed number and density were studied. The results showed that in the same grazing stage, the number of seed species in yak dung was higher than in Tibetan sheep dung. The seed density in yak dung was lower than in the Tibetan sheep dung, but the difference was significant only at the middle grazing stage. At the initial and final grazing stages, the seed diversity index in yak dung was significantly higher than that in Tibetan sheep dung. The seed species number and seed density (grains·kg -1 ) in yak dung at the different grazing stages were both in order of final grazing stage > initial grazing stage > middle grazing stage, and those in Tibetan sheep dung were in order of initial grazing stage > final grazing stage > middle grazing stage and of middle grazing stage > final grazing stage > initial grazing stage, respectively. The seed number of sedge was the highest in yak dung, while the seed number of forbs was the highest in Tibetan sheep dung. The different conditions of winter pasture at the different grazing stages made the seed distribution different in each synusia of plant community, together with the differences in grazing habit, forage intake per bite and digestibility of yak and Tibetan sheep, causing the differences in seed density, seed species and seed diversity of their dung.

为明确高寒草甸冷季牧场牦牛粪和藏羊粪中种子含量，研究了天祝东祁连山高寒草甸冷季牧场不同放牧时期牦牛粪和藏羊粪中可萌发植物种子的密度数量和多样性。结果表明，高寒草甸冷季牧场的同一放牧时期，牦牛粪中种子的物种数高于藏羊粪；种子密度牦牛粪低于藏羊粪，放牧初期和末期差异不显著，放牧中期差异显著。放牧初期和末期牦牛粪中种子的Shannon指数显著高于藏羊粪，放牧中期差异不显著。牦牛粪中的种子物种数为：末期>初期>中期；藏羊粪为：初期>末期>中期。单位重量牦牛粪中的种子数量变化规律是：末期>初期>中期，藏羊粪为：中期>末期>初期。牦牛粪中所含莎草科的植物种子最多，而藏羊粪中则以杂类草为主。高寒草甸冷季牧场不同放牧时期草地状况的不同，使得草地贮草量和种子在草层内的分布不同，加之牦牛和藏羊各自采食习性、单口采食量的差异，以及牦牛和藏羊消化道对种子的消化率不同，最终导致牦牛和藏羊粪便中的种子密度、种类和多样性存在差异。  

Taking the litters of  species  Hippophae rhamnoides ,  Medicago sativa ,  Populus simonii ,  Robinia pseudoacaci ,  Salix psammophila , and  Stipa bungeana  in the Loess Plateau of Northeast China as test objects, and by using mesh bags, this paper studied the dynamic changes of the litters mass, carbon, and nitrogen during decomposition after buried in the field in semiarid region. The litters buried were from one, two, or three of the plant species, and mixed thoroughly with equal proportion of masses. During decomposition, the mass loss rate, total carbon and nitrogen release rates, and total soluble carbon and nitrogen contents of different litters were higher at the early than at the later decomposition stage. After 412 d decomposition, the average mass loss rate of the litters was in the order of mixed litters of three plant species > mixed litters of two plant species > one plant species litter. By the end of this experiment, the average release rates of the litter total carbon and nitrogen ranked as one plant species litter > mixed litters of two plant species > mixed litters of three plant species, the litter soluble organic carbon content was mixed litters of two plant species > mixed litters of three plant species > one plant species litter, while the litter soluble total nitrogen content was mixed litters of three plant species > mixed litters of two plant species > one plant species litter. Correlation analysis showed that the litter mass loss rate had definite correlation with the litter soluble organic matter, especially soluble organic carbon. From the viewpoint of mass loss rate, the mixture of the litters of  P. simonii ,  H. rhamnoide , and  M. sativa  was the optimum. It was suggested that in the process of returning farmland into forestland and grassland in the gully and valley region of Loess Plateau, it would be required to rationally increase plant species diversity to improve soil fertility.

以黄土高原区典型植物刺槐、小叶杨、沙棘、沙柳、苜蓿和长芒草的凋落物为对象,采用网袋法研究了半干旱区(神木)分解过程中,单种、两种及3种凋落物等质量配比混合后其质量、碳和氮的动态变化.结果表明： 在整个分解过程中,不同处理凋落物的质量损失率,全碳、全氮的释放速率以及可溶性有机碳和可溶性总氮的含量均表现为前期大于后期.经过412 d的分解,3种凋落物混合后的平均质量损失率高于两种混合凋落物,单种凋落物最低.到分解试验结束时,不同处理凋落物的全碳、全氮平均释放率均表现为单种＞两种混合＞3种混合;而不同处理的可溶性有机碳平均含量表现为两种混合＞单种＞3种混合,但未达到显著水平;可溶性总氮含量则为3种混合＞两种混合＞单种,达到显著水平.凋落物的质量损失率与可溶性有机物,特别是可溶性有机碳具有一定的相关性.从质量损失率来看,小叶杨、沙棘与苜蓿凋落物的组合为最佳组合.建议在黄土高原区退耕还林还草工程建设中,合理增加植物种类多样性,促进土壤改善养分状况.

This study examined the litter of degraded desert steppe among different years of enclosure and the unenclosed grassland in Yanchi. It showed that the litter accumulation reached a maximum in September and October then declined with the time increasing. The litter decomposition rate was gradually decreased with the time. The litter decomposition rates of the enclosed grassland were higher than that of the unenclosed. With time increasing, natural water holding rates of litter reached a maximum and then declined gradually. Both the total nitrogen content of litter and the total phosphor content of litter of the enclosed grassland were lower than that of the unenclosed. The total kalium content of litter reached a minimum at the 5th year.

以盐池县退化荒漠草地为对象,对未围封和不同围封年限的草地凋落物进行研究。结果表明,草地凋落物的积累量随时间的延长而增加,达到增长峰期(9-10月)后逐渐降低;草地凋落物的分解速率随分解时间的延长逐渐降低,围封草地凋落物分解速率高于未围封草地;草地凋落物的自然持水率随着分解时间推移,不断升高达到一个峰值后逐渐降低;凋落物的全氮、全磷含量随围封时间延长而降低,全钾含量在围封5年时含量最低。

 Litter decomposition is ecosystem material circulation and the main part of energy flow. The protection of soil and water has an irreplaceable role of litter decomposition. This paper analyzes the impacts of nonbiological factors (precipitation, temperature), biological factors (animals, microbes, species) and objective factors on grass litter decomposition. The results showed that these factors could affect litter decomposition process directly and indirectly. The direct effects mainly changed the litter size and vegetation composition, thus changed the decomposition rate eventually. On the other hand, the indirect effects included changing the litter substrate C/N ratio and contents of litter lignin and nitrogen.

分析了主要的非生物因素（降水、温度、地形）、生物因素（动物、微生物、植物）和管理因素（放牧、灌溉、刈割）对草地凋落物分解的作用机理和途径。在一定范围内，凋落物分解速率分别随降水和积温的升高而增加；土壤养分高有利于凋落物分解；凋落物分解，土壤微生物的作用在前期至关重要，中期则土壤动物起决定性作用，后期以两者共同作用为主；适度放牧、灌溉和刈割促进凋落物分解。这些因素通过改变凋落物的基质质量、生境，或直接改变（物理作用）凋落物的量，以调控凋落物的分解。从定量研究和前沿问题的角度，提出草地凋落物管理今后值得研究的几个方面。

Grazing degradation trajectories of the main steppe rangelands in Inner Mongolia were studied by combining the experiments in the typical steppe area and the investigation in a large region. 1. The positive and negative,qualitative and quantitative grazing indicator species were distinguished; Species with preference to moderate grazing pressure were also recognized.2. Restoration of the degraded steppe rangeland demonstrated that the rhizomatic grass rehabilitated more quickly than tossuck grass; the restoration process was of monostable state; and the restoration dynamics corresponded generally to its spatial changes along a grazing gradient.3. The main steppe rangeland communities dominated by Stipa gobica, S. breviflora, S. krylovii, S. grandis, S. baicalensis and Aneurolepidium chinense will converge into Artemisia frigida community under sustaining grazing influence. A. frigida is the most effective quantitative indicator species of grazing pressure. It is also a fine forage species and an important species for resisting steppe degradation.4. The concept of steppe degradation was discussed. The difference and relations between steppe retrogression and rangeland degradation were analyzed. The grazing retrogression of steppes was divided into two successive stages, that is, rangeland utilization (improvement) and degradation. The quantitative critaria of rangeland degradation were established.5. A computerized monitoring and decision-making system of steppe rangelands was preliminarily discussed, including the three steps of monitoring, assessment and decision-making.

本文将定位研究与路线考察相结合，将放牧影响下草原的动态演替及其在牧压梯度上的空间变化相对比，研究了内蒙古主要草原草场的放牧退化模式，并在此基础上初步探讨了判别草场退化的数量指标和退化监测专家系统。1)植物种与牧压关系的分析，区别出放牧的定性和定量指示植物及宜中牧植物，并划分植物为不同的放牧生态种组。2)退化草原恢复过程的研究表明，根茎禾草的恢复快于丛生禾草；群落恢复过程是单稳态的，且恢复演替动态与其牧压梯度上的空间变化相对应。3)内蒙古高原主要草原草场在持续放牧影响下均趋同于冷蒿(Artemisia frigida)草原。冷蒿是最可靠的正定量放牧指示植物，但同时又是优良牧草和草原退化的阻击者。4)讨论了草原草场退化的概念，论述了草原逆向演替与草场退化的区别和联系，提出了区分草原的逆向演替为草场熟化和退化两个过程，并依草场群落与牧压的关系建立了判定草场是否退化及退化程度的数量指标。5)初步设计了草原草场退化监测—决策专家系统，包括监测、判别和决策三个步骤。

本研究采用样线法对天然草原自由放牧方式下家庭牧场形成的放牧梯度进行了定量划分,定量确定了不同放牧梯度的界限。在此基础上,对草地生态系统的结构和功能进行了年度、季节和放牧强度干扰的响应机制分析。通过对草地生态系统健康评价的理论和研究方法的探讨,对其评价方法进行了一些新的探索,并且对此进行了理论论述。应用模糊数学法和CVOR方法对草地生态系统健康评价进行了评价。在草地健康评价研究的基础上对不同放牧强度的草地生态系统服务价值进行了评估,并且对整个区域的生态系统服务价值进行了评价,研究结果对草地生态系统管理和放牧影响机制的研究具有一定的理论和实践价值。主要的研究结果如下: (1)应用草地植被采食率确定了不同放牧强度的含义,即不放牧的为对照、草地植被采食率为18.66%的为轻度放牧、草地植被采食率为36.27%的为中度放牧和草地植被采食率为53.72%的为重度放牧。 (2)草地普遍存在空间异质性,随着放牧强度的增大草地空间异质性变小。草地基况评价结果为:轻度、中度和重度放牧草地的草地基况分别为44.18、38.03、25.75。建立了可用于草地监测的模型,即VOM读数与草地植被现存量的回归模型:Y=20.13x+35.55,相关系数为R=0.80。 (3)放牧强度和气候对草地净初级生产力都有较大的影响。总的枯落物在各放牧梯度之间的变化显著:CK﹥LG﹥MG﹥HG,并且10月份的量要高于5月份的量,放牧强度的增加可能会促进草地植物的繁殖,是草地植物种群繁衍与放牧的协同适应结果。重度放牧使草地植物发生了小型化现象。 (4)植物功能群中禾草植物功能群的生态作用较大,主要是本样地主要以禾草(包括类禾草)占优势。α多样性指数随放牧强度的增加都表现为先增加后降低的趋势,其值都在LG的草地中最大,支持了“中度干扰理论”,β多样性指数随放牧强度的增加而变大,不同放牧强度的草地植物种类相似性变差。 (5)随放牧强度的增加土壤容重变大,但放牧对土壤容重没有累积效果;年度气候和放牧强度对土壤含水量都有影响,随放牧强度的增加土壤含水量呈现下降的趋势;随放牧强度的增加砂粒含量增加、粉粒含量降低,粘粒变化不显著;随土壤深度的增加砂粒含量增加、粉粒含量降低,粘粒含量变化不明显;随放牧强度的增加土壤pH值升高;随放牧强度的增加土壤有机质降低、土壤全氮有升高的趋势、土壤全磷、全钾变化不显著。土壤速效氮、磷、钾变化更多受其他因素的影响,与放牧强度的关系不明显。 (6)随放牧强度的增加,土壤微生物数量降低,主要是占微生物总数89.19%的细菌降低的结果。土壤微生物生物量随放牧强度的增加呈下降的趋势,土壤脲酶、过氧化氢酶、蔗糖酶、蛋白酶都随放牧强度的增加而呈现降低的趋势。 (7)根据草地生态系统中各指标的稳定性和对放牧的敏感性,共找出了11个“草”系统指标和12个“土”系统指标,应用模糊数学方法与CVOR评价方法得到的不同放牧强度草地生态系统健康指数较为一致。将两种方法评价结果中CK草地生态系统的健康指数化为1,则模糊数学法评价结果为:CK草地为1、LG草地为0.97、MG草地为0.78、HG草地为0.65;CVOR评价法的评价结果为:CK草地为1、LG草地为0.88、MG草地为0.73、HG草地为0.59。草地生态系统健康状况可划分为健康阈(0.65～1)、不健康阈(0.30～0.65)和崩溃阈(0～0.30)3个健康阈水平。 (8)不同放牧强度的草地生态系统服务单位面积的价值分别是:CK草地为376.59 US$/hm~2·a;LG草地为330.10 US$/hm~2·a;MG草地为274.31 US$/hm~2·a;HG草地为223.16 US$/hm~2·a,总样地的生态系统服务价值为1.13×10~4 US$/a。西乌旗所有草地类型的生态系统服务价值总和为4.66×10~8 US$/a,是财政总收入的15.84倍。

Alpine grassland is widely distributed in Northern Tibet. Stipa purpurea alpine grassland is one of the most important and representative meadow types in this area. In recent years, due to global warming and human activities such as overgrazing or excessive reclamation, the alpine grassland in Northern Tibet has undergone an accelerated and large-scale degradation. The grassland′s productivity and biological diversity have decreased significantly and locally, this has also become a great obstacle to sustainable social, economic and ecological development. To investigate community characteristics and α diversity of Stipa purpurea alpine grassland under different grazing intensity in Northern Tibet is critical not only to the understanding of local degradation mechanisms, but also to the establishment of rational grassland management procedures, as required for continued healthy and sustainable development of alpine grassland.In our study, based on a grazing experiment in Northern Tibet grassland ecosystem, the community characteristics of Stipa purpurea alpine grassland under different grazing intensity were investigated. The research was conducted at the grazing experimental site of Anduo County, Naqu, Tibet Autonomous Region, at an average elevation over 4,500 m above sea level. The experiment included four different stocking rates: no grazing (0 head/hm2, CK), light grazing (2.395 head/hm2, LG), moderate grazing (3.593 head/hm2, MG) and heavy grazing (5.988 head/hm2, HG). Based on the method of community investigation, community structure characteristics, such as species height, coverage and density were recorded. Aboveground biomass within areas of 0.5 m×0.5 m quadrat was also measured during the grass vigorous growth period. The species important value and summed dominance ratio were calculated by combining relative coverage, relative frequency and relative height. The species important value and summed dominance ratio were selected as comprehensive evaluation index of the importance of the species. The species diversity was measured using the Shannon-Wiener index and Pielou evenness index.The results showed that, with increasing grazing intensity, the above-ground biomass and the total coverage of plant communities followed a decreasing trend. Compared with the no grazing and light grazing treatments, the above-ground biomass and total coverage in the heavy grazing treatment were significantly lower. The important value of Stipa purpurea and other species was reduced gradually with increasing grazing intensity. Sedges such as Carex moorcroftii and other forbs, which the local livestock was rather avoiding, and also poisonous grasses were observed increased. The Shannon-Wiener index and Pielou evenness index changed according to the same pattern: MG﹥LG﹥HG﹥CK. The species diversity index of alpine grassland in this area reached the highest level under moderate grazing intensity. However, when the grazing intensity continued to increase beyond that level, the indices would decline rapidly.Comprehensive analysis indicated that the grassland had not only the highest diversity index under moderate grazing intensity, but could also resist a certain carrying capacity and prevent grassland degradation. Moderate grazing should be the most reasonable management strategy in Stipa purpurea alpine grassland. However, if grazing intensity continues to increase, the Stipa purpurea grassland type in this area would be transformed into a Carex moorcroftii, Herbarum variorum grassland community, which was clearly found to be of lesser economic and ecological value under the observed conditions.

基于放牧试验，研究了不同放牧强度下藏北地区紫花针茅(Stipa purpurea)高寒草原植物群落特征的变化规律。结果表明，随着放牧强度的增强，植物群落盖度、地上生物量均呈现显著降低的趋势；紫花针茅等禾草类植物的重要值逐渐降低，莎草类中青藏苔草(Carex moorcroftii)、牲畜不喜食的杂类草及有毒有害植物均有增加的趋势；如果持续过度放牧，植物群落表现出由紫花针茅等禾草为建群种的草地型向青藏苔草(Carex moorcroftii)、杂类草(Herbarum variarum)草地型过度的趋势；在中度放牧强度下，紫花针茅高寒草原α物种多样性达到最高水平，而继续增强放牧强度，则造成各项指标的迅速降低。

本研究针对川西北高山草甸缺乏科学管理，过度放牧导致草场退化，并由此引发的一系列生态环境问题，选取红原县瓦切乡1996年草地承包后形成的四个放牧强度草场，即不放牧、轻度(1.2头牦牛hm-1)、中度(2.0头牦牛hm-1)和重度放牧(2.9头牦牛hm-1)，作为研究对象，研究了不同放牧强度对草地植物-土壤系统中碳、氮这两个最基本物质的分布格局和循环过程的影响，并探讨了放牧干扰下高山草甸生态系统的管理。　　 1.放牧对草地植物群落物种组成，尤其是优势种，产生了明显的影响。不放牧、轻度、中度和重度放牧草地群落物种数分别为22，23，26，20种，群落盖度分别是不...

本研究以青藏高原地区的西藏自治区工布江达县境内的高寒嵩草草甸草原和青海省湟源县的夏、冬季放牧草场为研究对象，利用“二值出现次数”法和地上生物量测定法对草地群落进行实地调查，并运用γ分布模型、幂乘方法则和β-二项分布模型分析数据，从空间异质性的角度来定量探究放牧对青藏高原草地植被群落的物种组成、物种多样性、地上生物量及其空间分布格局的影响，以期为高寒牧区退化草地的恢复及生产力的提高提供理论依据，并为我国草原物种多样性的维持与草地生态系统的可持续利用提出有效对策。 取得的主要结论如下： （1）γ分布模型、幂乘方法则和β-二项分布模型对于研究青藏高原草地植被群落空间分布规律具有很好的吻合性，这些数理统计模型可继续应用于今后草地群落空间异质性的定量研究中。 （2）对不同放牧压下西藏工布江达县的高寒嵩草草甸草原地上生物量的调查研究，可知：总物种数、物种多样性指数、L-样方内的平均物种数、平均物种多样性指数、平均生物量均表现为：未放牧草地（N）适度放牧草地（M）重度放牧草地（H）。群落整体的空间异质性表现为：未放牧草地（N）重度放牧草地（H）适度放牧草地（M）。由此可知，未放牧草地的空间异质性高于放牧草地；且在受到放牧干扰的草地中，随着牧压强度的增大，草地植物群落的生物量与其空间异质性呈负相关性；L-样方内的物种数与生物量之间存在正相关关系；草地植被群落组成发生了很大变化，如针茅（Stipa capillata）等适口性好的禾本科牧草大量减少，而以甘肃马先蒿（Pediculariskansuensis）为代表的毒杂草开始大面积入侵，表明此高寒草甸草原生态系统退化严重，而未放牧草地中，植被的地上生物量、物种数和物种多样性指数均是最高的，说明围栏封育对于青藏高原地区退化高寒草甸草原的恢复起到了非常有效的作用。 （3）不同放牧强度下，西藏工布江达县境内的高寒嵩草草甸草原植被群落整体上均具有比随机分布强的空间异质性，且3种样地植被群落的空间异质性表现为：未放牧草地（N）重度放牧草地（H）适度放牧草地（M）。不同放牧压下草地的共同优势种有3种，分别为高山嵩草（Kobresia pygmaea）、针茅、西藏粉报春（Primula tibetica），在适度放牧草地，它们的异质性指数值都极低（δi=0），而在未放牧草地和重度放牧草地，仅高山嵩草的异质性指数值低，从而导致适度放牧草地异质性程度最低。草地群落的物种多样性指数、均匀度指数、L-样方内的平均物种数、平均物种多样性指数和平均生物量，这些指标均表现为：N M H。 （4）青海省湟源县冬季放牧草场的总物种数、物种多样性指数、群落整体的空间异质性指数、L-样方内的平均物种数和平均物种多样性指数均大于夏季放牧草场；两种放牧草场的植被群落组成发生了很大变化，其中，在夏季实施围栏封育而冬季进行放牧利用的草地中，草地早熟禾（Poa pratensis）、垂穗披碱草（Elymus nutans）、小嵩草（Kobresia pygmaea）等优质牧草增加，而在夏季放牧场中，草地退化的标志性植物鹅绒萎陵菜（Potentilla anserina）和车前（Plantago asiatica）占据优势地位。夏季和冬季放牧草场中，除均匀分布的物种外，植物种群的空间异质性指数均随着其出现频率的增大而增大，说明物种空间分布的异质性程度与其出现频率二者之间呈现显著正相关，且冬季放牧场植被群落整体的空间异质性程度高于夏季放牧场。所以，在草地的实际管理与利用中，应尽量避开牧草的生长季节，实行冬季放牧更加有利于草地的可持续发展。