The long-term variability of plant species, functional groups and compensatory effects between functional groups within a Leymus chinensis community were studied during 1980-1999 in the Xilin River Basin of Inner Mongolia. The results showed that long-term variability of aboveground biomass decreased from the plant species level to the functional group and community levels. Plant species and functional composition were the principal factors explaining the long-term variation in production of the community. There were obvious compensatory effects in the dynamics of biomass between perennial bunch grasses and perennial rhizome grasses and forbs, between xerads and intermediate xerads, and between intermediate mesophytes and mesophytes. Longterm variability in the biomass of populations seems to depend on the sensitivity of species to environmental fluctuations and amplification of environmental fluctuations by interactions among species. Biodiversity may increase community stability by promoting diversity among species due to their differentiated responses to environmental fluctuations, and by compensatory effects among plant functional groups.

分析了内蒙古锡林河流域羊草(Leymus chinensis)草原群落植物种群、功能群和群落生物量的长期变异性，以及植物功能群间的补偿作用对群落稳定性的影响，结果表明：从种群水平到功能群和群落水平，地上生物量的年度间变异性逐渐降低，而稳定性则逐渐增加。植物功能群组成对群落稳定性具有更强烈的影响，在植物生活型功能群组成中多年生根茎禾草与多年生丛生禾草和多年生杂类草功能群，在生物量的年度变化上具有补偿作用，在生态类群组成中，旱生植物与中旱生植物也具有补偿作用。植物种群多度的长期变异性可能依赖于物种对环境波动的敏感性和种间相互作用对环境波动的放大效应，生物多样性使物种对环境波动响应的多样性增加，并通过不同响应类型(功能群)间的补偿作用使群落稳定性增加。

Ranging from 83 o 41' to 95 o 11'E and from 30 o 27' to 35 o 39'N, northern Tibet in the highest of Tibet is known as the ridge of the roof of world with a mean elevation of 4500 m. Northern Tibet is the headstream of the Yangtze River, Nujiang River and Lancang River. It is both the "sensitive area" of climate system and the "water tower" of China. The environmental condition of this area has significant effect on the main rivers, climate and eco-environment of Tibet and the whole country, even on the globe for its rigorous natural condition and fragile ecosystem. This study selected vegetation cover as the main evaluation index, calculated the grassland degradation index (GDI) and established the remote sense monitoring and evaluation system for grassland degradation in northern Tibet, according to the national standard (GB19377-2003), based on the remote sensing data such as NDVI data derived from NOAA/AVHRR with a spatial resolution of 8 km of 1981-2000 and from SPOT/VGT with a spatial resolution of 1 km of 2001 and from MODIS with a spatial resolution of 0.25 km of 2002-2004 respectively in this area, in combination with the actual condition of grassland degradation. The grassland degradation processes and their response to climate change during 1981-2004 were discussed and analyzed systematically in the study. The result indicated that grassland degradation in northern Tibet is very severe, and mean value of the GDI in recent 20 years is 2.54 which belongs to the severe degradation grade. From 1981 to 2004, the grassland degradation fluctuated evidently with great interannual variations in proportion of degradation degree and GDI but the total tendency turned to severe during this period with the grassland degradation grade changed from light to severe in northern Tibet. The extremely seriously degraded and seriously degraded respectively occupied 1.7% and 8.0% of the study area, the moderately and lightly degraded grassland accounted for 13.2% and 27.9% respectively and un-degraded grassland occupied 49.2% of the total grassland area in 2004. The grassland degradation was severe especially in the conjunctive area of Naqu, Biru and Jiali counties, the headstream of the Yangtze River that is Galadandong snow mountain, the areas along the Qinghai-Tibet railway and highway, and areas around the Tanggula and Nyainqentanglha snow mountains and glaciers. So the snow mountains and glaciers as well as their adjacent areas in northern Tibet which were sensitive to climate change and the areas along the vital communication line with frequent human activities experienced relatively severe grassland degradation.

根据草地退化国家标准和藏北地区草地退化实际情况以及遥感数据特征,选择草地植被盖度为草地退化的遥感监测指标,建立藏北地区草地退化遥感监测和评价指标体系,并对藏北地区近24年的草地退化进行遥感监测和评价。结果表明：藏北地区草地退化现状 (2004年) 十分严重,重度和极重度退化草地面积分别占草地总面积的8.0%和1.7%,区域草地退化指数 (GDI) 为1.86,接近中度退化等级;其中藏北地区冰川与雪山及其周围等气候变化较为敏感区域和交通要道沿线等人类活动较为频繁区域的草地退化相对严重;从1981年到2004年的近24年以来,藏北地区及其各个区域草地退化较为严重,其草地退化等级分布比例和草地退化指数年际波动较大,草地退化等级在轻度退化至重度退化等级之间波动;近几年藏北全地区总体草地退化情况及中部、东部和北部地区的草地退化具有更加严重的趋势,而西部地区草地退化状况则略有减缓趋势。

Normalized difference vegetation index (NDVI), which is closely related to plant absorbability of photosynthetically active radiation (PAR), is generally taken to be a good indicator of terrestrial vegetation. We used time series (1982-2003) NDVI from the Global Inventory Modeling and Mapping Studies (GIMMS) in combination with climatic data from eight meteorological stations to examine the relationships between climatic factors and NDVI for grasslands of different types across the Northern Tibetan Plateau. Also, we discussed contributors affecting the correlation between NDVI and climatic factors. A bivariate correlation analysis was performed to examine the linear correlations and lag-linear correlations between monthly maximized NDVI and 6 monthly climatic factors, including mean monthly air temperature, mean minimum air temperature, mean maximum air temperature, relative humidity, mean wind velocity and cumulative precipitation. The partial correlations between temperature/precipitation, temperature/precipitation/wind velocity and NDVI were investigated by a partial correlation analysis in order to remove errors resulting from interactions among these climatic factors. Except the Gerze and Gaer stations, there were significant positive linear correlations between NDVI and temperature, precipitation and air moisture of the current month (P<0.001) in other six stations. The climatic factor having the highest correlation with NDVI was mean monthly minimum temperature. Correlation coefficients between NDVI and mean monthly minimum air temperature for the Suoxian, Nagqu, Amdo, Damxung, Baingion and Xainza stations decreased in sequence. Alpine meadow showed the highest positive correlation with monthly cumulative precipitation than did grasslands of other types. Mean monthly wind velocity was negatively correlated to NDVI (i.e. Damxung, P<0.05；other stations, P<0.001). NDVI of the Gerze station showed the highest correlation with wind velocity compared with other climatic factors of the current month. Regarding grasslands of all types across the Northern Tibetan Plateau, the response of NDVI to temperature and precipitation showed a time lag effect. Except the Gaer station, the time lag as to responses of NDVI to precipitation and temperature for grasslands of different types was around one month and one to two months or so, respectively. The accumulated time lag periods of NDVI and corresponding precipitation was two months for the Suoxian and DamXung stations, four months for the Gerze and Gaer stations, and one month for the other four stations. The results of partial correlation analysis showed that temperature was the most important factor affecting NDVI of grasslands, and wind was another key factor affecting NDVI of grasslands. In general, changes in NDVI for the Suoxian, Nagqu, Baingion and Xainza stations were primarily driven by temperature-wind velocity-precipitation, but for the Amdo and Damxung stations, that relation was changed to temperature-precipitation-wind velocity. It was concluded that vegetation type, altitude, mean annual wind velocity and mean annual precipitation have significant influences on the correlation between NDVI and climatic factors.

本文利用1982年~2003年GIMMS 每15d合成的归一化植被指数（Normalized Difference Vegetation Index，NDVI）数据集和藏北高原8个气象站1981年~2003年逐月气象资料，用相关分析研究了NDVI 与6个气候因子的相关性及其对气候因子的时滞响应情况，同时计算了气温、降水和风速3个气候因子与NDVI的偏相关系数。结果表明：①除噶尔和改则之外，6个站的 NDVI与同期月均气温、月均最高气温、月均最低气温、月均相对湿度和月降水量都呈高度正相关（P<0.001），其中与月均最低气温的相关性最好，NDVI与当月降水量的相关系数为那曲＞索县＞安多＞当雄＞班戈＞申扎；月均风速与藏北高原草地NDVI呈高度负相关（P<0.001；当雄除外，为P<0.05）；②NDVI对气温和降水的响应有滞后效应：改则和噶尔NDVI对气温滞后3个月，其它6个站滞后1个月；噶尔NDVI对降水的滞后期为2个月，其它7个站均滞后1个月；申扎和改则（噶尔）NDVI对空气湿度分别滞后1和2个月，其它5个站无滞后；那曲、安多、班戈和申扎NDVI对降水的累积滞后期为1个月，当雄和索县为2个月，改则和噶尔为4个月，NDVI对降水响应的累积滞后相关系数从东到西呈降低趋势；③除改则和噶尔之外的6个站NDVI变化受气温的影响大于降水；在气温-降水-风速组合下，除改则和噶尔之外的6个站NDVI第一相关因子仍是气温，但索县、那曲、班戈和申扎属于气温-风速-降水驱动型，安多和当雄属于气温-降水-风速驱动型。藏北草地NDVI与气候因子的相关性受植被类型、海拔、年降水量和年平均风速的影响。

Vegetation phenology is closely related to seasonal dynamics of the lower atmosphere and, therefore, is thus considered as an important indicator that influences the feedback mechanisms of global climate variation to the terrestrial ecosystem. Detecting vegetation phenological metrics using time series remote sensing dataset at the regional or global scale has become an active research topic in geography and ecology. This paper presents a dynamic thresholding method to extract the vegetation phenological metrics (greenup date, growing season length, maximum EVI and wilting date) of typical grassland, including alpine shrub meadow in the eastern region, alpine meadow in the central region, alpine steppe and alpine desert steppe in the western region of northern Tibetan Plateau, using a time-series TERRA/MODIS EVI dataset from 2001 to 2010 which was reconstructed using the asymmetric Guassian function fitting method. Furthermore, the relationship between inter-annual variation of phenological metrics and climatic factors was analyzed based on the measured data of weather stations close to the sampling areas, the results showed that:(1) The ordinal relationship of these typical vegetation samples in phenological metrics was in the sequence of alpine shrub meadow, alpine meadow, alpine steppe, and alpine desert steppe (for greenup date and the wilting date, the sequence respectively referred to be earlier and later). (2) The annual, spring, summer and winter average temperature of northern Tibetan Plateau all showed significant ascending trend, the increased rate was between 0.8℃/10a and 3.9℃/10a. While the decreased trend of precipitation was not apparent. Due to the warming and drier climate, the greenup date of four types of typical vegetation was advanced (approximately 7.2-15.5d/10a earlier) and the growing season length became longer (approximately 8.4-19.2d/10a), whereas the wilting date of four types of vegetation cover did not show apparent advanced or lingering trend; (3) The maximum EVI of different typical vegetation cover types was affected by different climatic factors. As follows, alpine shrub meadow was mainly affected by spring average temperature and spring precipitation, and precipitation had more important influence on phenological variation than temperature; Alpine meadow was affected by both spring and summer average temperature and precipitation; Alpine steppe and alpine desert steppe were primarily influenced by summer average temperature and precipitation, while for alpine steppe vegetation the inhibition of summer average temperature was more intense than the promotion effect of summer precipitation, among four types of vegetation cover, alpine desert steppe had the closest relationship with summer precipitation (the correlation coefficient, -0.752); (4) As for greenup date, alpine shrub meadow was mainly affected by autumn precipitation of the previous year, the correlation coefficient was closed to -0.579; however, other three types of vegetation cover were mainly influenced by spring average temperature, and the character was the most obvious for desert steppe (the correlation coefficient, -0.559). That was due to that high temperature in spring expedited snow melting and tundra soil thawing which are indispensable for vegetation greenup, especially for high-altitude regions in northern and western Tibet. In addition, the autumn precipitation and winter average temperature in the previous year also had some impact on the vegetation greenup of alpine steppe and alpine desert steppe.

植被物候作为陆地生态系统对气候变化的响应和反馈的重要指示,已成为区域或全球生态环境领域研究的热点。基于非对称高斯拟合方法重建了2001-2010年MODIS EVI时间序列影像,利用动态阈值法提取藏北高原植被覆盖2001-2010年每年关键物候参数。选取研究区内东部高寒灌丛草甸、中部高寒草甸及西部高寒草原和高寒荒漠4种典型植被类型,并结合附近的4个气象台站气候资料,分析典型植被物候在近10a对关键气候因子的响应特征。研究结果表明:(1) 4种不同典型植被的物候特征(EVI max 降低、返青期延后和生长季长度缩短)均表现出高寒灌丛草甸→高寒草甸→高寒草原→高寒荒漠草原的过渡;(2) 藏北高原近10a的年平均气温及春、夏、冬三个季度的平均气温均呈显著升高的趋势,升温幅度在0.8-3.9℃/10a,降水减少趋势不显著,在这种水热条件下典型植被均表现出返青提前(7.2-15.5d/10a)、生长季延长(8.4-19.2d/10a)的趋势,而枯黄出现时间为年际间自然波动;(3) 高寒灌丛草甸EVI max 主要受春季降水量和气温影响,且降水的影响程度大于气温;对高寒草甸植被而言,春、夏季的气温和降水均有较大的影响;而高寒草原和高寒荒漠草原主要受夏季平均气温和降水量影响;(4) 高寒灌丛草甸的返青时间主要受前一年秋季降水量的影响,相关系数达-0.579;而高寒草甸、高寒草原和高寒荒漠草原主要受春季平均气温影响,高寒荒漠草原的特征最为明显 ( r =-0.559)。

Alpine rangeland in the Northern Tibetan region of China plays important role not only in yak and Tibetan sheep production, but also in the ecological safety shelter zone for China, even Southeast Asia region. However, the alpine rangeland degradation in this area has caused the water erosion, low economic development, and poor living of herders, which create a dilemma of sustainable development of the northern Tibetan region. Thus alpine rangeland degradation not only threatens the local ecological safety and life of the local residents, but also threatens further ecological security of the down-streams of the rivers and the Southeast Asia rivers. Ecological compensation is seen as an innovative approach to controlling degradation of rangeland by making compensation to rangeland users in return for adopting practices that secure rangeland ecosystem conservation and restoration of degradation alpine rangeland. Therefore, on the basis of closely combining the problems in natural science and economical development policy in social science, establishing effectively ecological compensation mechanism of rangeland by evaluating ecological services value of rangeland and is urgent to maintain ecological services function of rangeland and coordinate the relationships among population, resource environment and economic development, which will provide useful information for protecting rangelands from the further degradation and achieving sustainable development of ecological, economic and social. The aim of this study was to design the efficient mechanism and implementation scheme of ecological compensation for rangeland ecosystem in the northern Tibet regions. As a case of the study, four indicators, including productivity, importance of seasonal grazing, ecological services value, and ecological environmental sensitivity of each alpine rangeland subtype were applied to design the functional sectors model for rangeland management in this study for determining ecological compensation regions in the Naqu region of northern Tibet. This study classified alpine rangelands of the Naqu region in northern Tibet into the production sector with moderate grazing, restoration sector with reducing livestock number, and conservation sector by anti-grazing. In function sectors, the grades of ecological compensation were designed for alpine rangeland. On the basis of grading results, this study proposed the organization management system and its process, the profit and loss evaluation mechanism and constraint the mechanism of rewards and the punishments of ecological compensation. The corresponding ecological compensation plan was made in the Naqu region of northern Tibet. Based on the results of functional sectors and their grades, content and target of the ecological compensation for different functional area of alpine rangeland in the Naqu region of northern Tibet were established and presented, in which the ecological compensation period was considered as 5 yeares and the total ecological compensation fund for alpine rangeland of the Naqu region was 35.77 billion RMB, which was allocated 19.4 billion RMB for the moderate production sector, 15.77 billion RMB for restoration sector, and 0.6 billion RMB for conservation sector. The mechanism of ecological compensation for rangelange, based on the functional sectors and grading compensation, has important significance in theory and practice, which would provide the valuable information for alpine rangeland ecological protection, increase in economic income of herdsman and the sustainable development of alpine rangeland ecosystem.

根据藏北那曲高寒草地的生产力、季节放牧重要性、生态服务价值、生态环境敏感性,构建了基于草地亚类的功能分区模型,从空间上将高寒草地划分为适度生产功能区、减畜恢复功能区和禁牧封育功能区,据此构建了基于高寒草地功能分区的分级生态补偿模式,设计了高寒草地生态补偿的组织管理体系及流程、生态补偿的损益评估机制和约束奖惩机制; 提出了针对不同功能区的生态补偿方案。根据藏北那曲高寒草地功能分区结果和不同功能区生态补偿内容和目标,确定生态补偿周期为5a,核算出适度生产功能区、减畜恢复功能区和禁牧封育保护功能区分别需要补偿资金19.4亿元、15.77亿元和0.6亿元,每年分别需补偿资金3.88亿元、3.16亿元和0.12亿元,5a全区共需补偿资金35.77亿元,年需7.16亿元。通过对高寒草地的功能分区分级生态补偿,对提高高寒草地的生态保护能力,增加牧民的经济收入,促进藏北高寒草地生态系统的可持续发展具有重要的理论和实践意义。

Agpoyron trachyeaulun L., Elymus nutans Griseb, Bromus inermis Layss and Poa crymophila Keng were reseeded in fenced areas using no-tillage. Vegetation height, coverage and grass yield were studied in order to reveal the effects of different restoration measures for vegetation characters, underground biomass, seed bank and diversity of Amdo in a typical degraded meadow in Tibet. Results showed that vegetation height, coverage and grass yield improved after no-tillage reseeded and fenced. Plant diversities increased slightly while there were significant differences among dominant species. Further, changes were seen in underground biomass of plant communities. Biomass of 0~10 cm soil layer ascended dramatically after fenced and reseeded. Additionally, the numbers of seeds in both fenced and reseeded plots were greater outside the fence and distributed mainly within 0~5 cm soil layer.

为探讨不同恢复措施条件对草地植被特征、地下生物量、地下种子库以及多样性等方面的影响,在西藏安多典型退化草地进行围栏,并选用细茎冰草( Agpoyron trachyeaulun L.)、垂穗披碱草( Elymus nutans Griseb)、无芒雀麦( Bromus inermis Layss)和冷地早熟禾( Poa crymophila Keng)4种牧草,在围栏内进行免耕补播的试验研究。结果表明:经过免耕补播和围栏封育后,草地植物高度、盖度、产量均有不同程度的提高;植物多样性有少量增加,植被优势种差异较显著;植物群落地下生物量变化幅度较大,特别是经过围栏和补播的草地,其0~10 cm地下生物量增加明显;此外,土壤种子库测定表明,围栏和补播试验地种子总数明显高于围栏外,增加的种子数主要分布在0~5 cm的土层中。

Using the methods of comparative analysis and substituting temporal serial with spatial serial, the changing characteristics of plant communities biomass and soil nutrient in the process of plant restoration were studied based on the survey data of abandoned lands in the Loess Hilly Region with the five different ecological restoration periods (0-5,6-10,11-15,16-20,and 21-25 years). The results showed that the main dominant species in the Loess Hilly Region with these five plant restoration periods were Leymus scalinus , Artemisia scoparia , Lespedeza davurica , Stipa bungeana and Bothriochloa ischaemun , respectively. Generally, Simpson index, Shannon-Wiener index, Pielou index and Margalef index increased firstly and then decreased which suggested that the ecological system in the Loess Hilly Region can gradually improved by both natural and artificial restoration modes. With the increase of restoration period, the aboveground biomass, soil organic matter, total nitrogen and available nitrogen content decreased firstly and then increased, however, the total phosphorus content changed in opposite way. The soil nutrient contents in different layer decreased with soil depth (0-20 cm, 20-40 cm, 40-60 cm) increased. Soil organic matter and total nitrogen reached the peak in area with the 21-25 years restoration period and total phosphorus content reached the peak in area with the 16-20 years restoration period which indicated that the content of soil nutrient in the Loess Hilly Region can be gradually improved with low speed.

采用对比分析以及空间代替时间的方法,根据黄土丘陵区5个恢复年限(0-5,6-10,11-15,16-20和21-25年)弃耕地的调查数据,研究其在植被恢复过程中随着弃耕年限的增加植物群落生物量及其土壤养分的变化特征.结果表明,在5个恢复阶段内黄土丘陵区主要的优势物种依次为赖草( Leymus scalinus ),猪毛蒿( Artemisia scoparia ),达乌里胡枝子( Lespedeza davurica ),长芒草( Stipa bungeana ),白羊草( Bothriochloa ischaemun ).期间,Simpson多样性指数(D),Shannon-Wiener多样性指数(H),Pielou均匀度指数(Jsw),Margalef丰富度指数(Dma)总体上均呈先增大后减小的趋势,其植被覆盖度呈逐渐增加的趋势,这表明黄土丘陵区的植被生物量在自然和人工恢复方式下可以逐渐增加.随着植被恢复年限的增加,黄土丘陵区地上生物量总体上呈现先减少后增加的趋势.土壤养分含量随土层深度(0-20,20-40,40-60 cm)的增加而下降,随植被恢复年限的增加土壤有机质,全N和速效K含量呈先减少后增大的趋势,土壤全P含量呈先增大后减小的趋势.植被恢复过程中,21-25年的土壤有机质和全N含量达到峰值,16-20年的土壤全P含量达到峰值,这表明在植被恢复过程中黄土丘陵区土壤养分含量能够得到一定改善,但改善速度缓慢.

The present study analyzed the plant biomass, soil physical and chemical properties and soil microbial quantities of different community composition using quadrat sampling method. The results showed the aboveground biomass of Salix paraqplesia alpine shrubs meadow was significantly higher (P

利用样方法，分析了青藏高原不同植被类型生物量、土壤理化性状及土壤微生物数量。结果表明，高山柳（Salix paraqplesia）灌丛草甸的地上生物量显著高于圆穗蓼（Polygonum macrophyllum）草甸、藏嵩草（Kobresia tibetica）草甸和小嵩草（K. pygmaea）草甸（P≤0.05），而藏嵩草草甸的地下生物量显著高于小嵩草草甸、高山柳灌丛草甸和圆穗蓼草甸（P≤0.05）。藏嵩草草甸的土壤有机质、土壤全氮依次高于圆穗蓼草甸、高山柳灌丛草甸和小嵩草草甸。相反，土壤养分居于中间水平，土壤含水量较低的圆穗蓼草甸土壤微生物数量则最多。

This study analyzed soil organic carbon content (SOC) in major types of grassland along the middle range of Helan mountain in Alex,Inner Mongolia. Factors affecting carbon distribution such as annual precipitation, temperature, plant cover and productivity, soil water content, mountainous desert steppe>steppe desert>G...

以阿拉善左旗境内贺兰山中段 (西坡 )及其山前地带主要草地类型为研究对象 ,分析了不同草地类型土壤有机碳 (SOC)的分布特征及其与气候因子、植被特征和土壤特性的关系。结果表明 :土壤有机碳含量随海拔高度的降低而逐渐降低 ,其垂直分异规律是 :山地荒漠草原沿土壤剖面依次降低 ,高山草甸、草原化荒漠和沙砾质草原化荒漠 0～ 2 0 cm与 2 0～ 40 cm土层差异不显著 ,但高于 40～ 60 cm土层。 0～ 2 0 cm和 2 0～ 40 cm土层土壤有机碳含量与年降水量、植被盖度、草地生产力、土壤含水量和<0 .0 5mm颗粒含量呈极显著正相关 ,与年均温、土壤 p H值呈极显著负相关 (P<0 .0 0 1)。偏相关分析显示 ,影响 0～ 2 0 cm土层有机碳含量最主要的因素是植被盖度、草地生产力和年降水量 ,而影响 2 0～ 40 cm土层有机碳含量的最主要因素是草地生产力和植被盖度。放牧与围封对荒漠草地土壤有机碳含量有显著影响 ,在重度放牧下 0～ 2 0 cm土壤有机碳含量明显低于轻、中度放牧处理 (P<0 .0 5) ;重度退化草地围封 3 a后土壤有机碳含量比自由放牧草地显著增加。研究区沙砾草原化荒漠区0~20cm土层土壤有机碳含量在15a持续过度放牧后下降了25.2%。

A study on the community structure and productivity, and plant composition and diversity of alpine meadow under different degrees of degradation, including nondegradation, lightdegradation, moderatedegradation, heavydegradation and overdegradation in the upper area of Daitong river. Results indicated that there were more than 60 plant species, which are belong to 24 families and 51 genus, in study ared. The dominant species in was conduced nondegradation and overdegradation grasslands were Kobresia pygmaea and Saussurea pulchra, respectively. The ShannonWiener index and Simpson index in moderatedegradation (P

采用样方法对祁连山区大通河上游不同退化程度高寒草甸植物群落进行调查，分析了该草地群落结构、物种多样性和草地生产力。结果表明，该类草地由24科51属60多种植物组成；随着草地退化程度的加重，草地优势种由高山嵩草（Kobresia pygmaea）向细叶亚菊（Ajania tenuifolia）过渡；中度退化草地的ShannonWiener指数和Simpson指数均最高（P

Phosphorus (P) is a key element of all life and the limiting nutrient in many ecosystems of the world. P biogeochemistry partly controls ecosystem structure and function. Over the past couple of decades, the importance of P biogeochemistry in controlling terrestrial ecosystem processes has received increasing attention. Advances in P cycling in terrestrial ecosystems were reviewed in this paper. Characteristics of P cycling in ecosystem were attributed to factors such as the source of P, the chemical form, traits in soils and the complexity of its controlling factors. P in terrestrial ecosystems is derived mainly from weathering of apatite, and biological and chemical processes, such as microbial absorption, precipitation and adsorption by Fe and Al oxides and CaCO3, easily immobilize P in soil.Transformations of P between different chemical forms in the ecosystem, especially in the soil, and its controlling factors were discussed in detail. P cycling in terrestrial ecosystems is mainly intra-ecosystem cycling which is controlled mainly by the genotype of plant and soil properties, especially pH and ion concentration. The relative importance of different controlling factors differs among ecosystems and across temporal and spatial scales. Also, methods for studying P cycling in terrestrial ecosystems were reviewed. Pot experiments, fertilization trials and sequential extraction procedures were commonly used to test for the bioavailability of different forms of soil P; however, in situ field experiments that used resin bags, litter bags, new isotope tracer methods using 32P and 33P, and NMR spectroscopy to study P dynamics and the chemical structure of soil P were more useful for understanding P cycling and plant availability. Additionally, the significance of P cycling in arid regions was analyzed. P cycling in arid regions, where vegetation is sparse and soil is infertile, are very different from humid regions, and ecosystems there are more easily limited by P. Finally, the trends and hotspots of P cycling in terrestrial ecosystems are summarized for different temporal and spatial scales, different study areas and contents.

磷是生命系统的重要组成成分，其在生态系统内的迁移转化是生态系统结构和功能的决定性因素之一。近20年来，磷在陆地生态系统内的重要性受到越来越多的关注。该文总结了国内外磷循环研究的成果，从磷的来源、在土壤中的存在形态和固定特性、影响因素的复杂性等方面分析了磷素循环的特点；系统阐述了磷在陆地生态系统各库之间及其内部，主要是植被-土壤亚系统内的迁移转化规律及影响因素。陆地生态系统磷素循环主要是系统内部的生物化学循环，由植物自身的遗传特性和土壤的生物、理化性质共同控制，不同控制因素的相对重要性因生态系统类型、时间和空间尺度而异。文章简述了磷循环研究方法的发展及存在的局限性；另外，分析了干旱、半干旱地区磷循环研究的重要性和意义；干旱区生态系统的脆弱性及其植被、土壤特性决定了其磷素循环有其自身的特点及研究的必要性。最后指出了当前陆地生态系统磷循环研究的发展趋势。

The present study was to investigate the effects of grazing intensity on soil organic matter, pH, total nitrogen, available nitrogen, total phosphorus, available phosphorus, total potassium, and available potassium in soil of Kobresia pygmaea meadow community of Tibet plateau. The results showed that the contents of soil total nitrogen, available nitrogen and available potassium decreased, while the contents of total potassium increased firstly and then decreased with the increasing of grazing intensity. Heavy grazing intensity significantly reduced the contents of total nitrogen, available nitrogen, available potassium and available phosphorus(P 0.05). The results suggested that delayed grazing with moderate grazing intensity could protect grassland from degeneration.

以西藏高山嵩草(Kobuesia tygmaea)草甸土壤为研究对象，分析不同放牧强度下土壤中全氮、全磷、全钾，速效氮、速效磷、速效钾，有机质及pH值的变化。结果表明，随着放牧强度的增加，在不同土层中，全氮、速效氮和速效钾含量减少；而全钾含量随着放牧强度的增加呈现先增加后减小的趋势；重度放牧显著降低了土壤中全氮、速效氮和速效钾的含量（P 0.05）。因此，延迟+适度放牧和适度放牧可以有效地保护草地，防止高山嵩草草甸进一步退化。