230 000 ha grassland accounted for 58.76% of the total grassland area have degraded at Tianzhu County in 2010. At present, the county’s natural grassland is still degrading by a rate of 13 300 ha per year. The grassland degradation was caused by both natural factors and human activities. However, overgrazing was a main reason for natural grassland degradation from light to heavy. Therefore, comprehensive countermeasures based on controlling grazing capacity and resolving conflicts between grass and livestock were put forward for natural grassland in the paper, which can help sustainable development of Tianzhu natural grassland and offer technical references for areas of Qilian Mountains on rational utilization of grassland resources and control of degradation.

2010年天祝县天然草地退化面积为23.00万hm2，占草地面积的58.76%，目前仍以每年1.33万hm2的速度退化。草地退化是自然因素和人为因素共同作用的结果，但超载过牧是主要原因，它引起天然草地由轻度退化向中度和重度退化演变。因此，本研究以控制载畜量、解决草畜矛盾为核心措施，提出天然草地综合治理对策，以促进天祝县天然草地走上可持续发展的道路，为祁连山草地资源合理利用和草地退化防治提供技术参考。

Sustained overgrazing and rodent’s destruction are responsible for the degradation of more than 50% of grassland in north-western China. In fact these persistent adverse effects caused a reduction in the number of high quality forage species and grassland productivity, accompanied with an increase in the incidence of weed and poisonous plants. The degradation of the grassland ecosystem causes serious social and economical problems in the region. To prevent and control grassland degradation, intensive multidisciplinary research projects have been performed in this area. However information on the microbial population changes in the grassland is scarce. Soil microbial activity plays an important and vital role in grassland ecosystem because it affect soil physical properties like the stability of aggregates, soil aeration and water holding capacity, and it is responsible of the mineralization and recycling of several important nutrients like carbon, nitrogen and phosphorus. Soil organic matter is also significantly affected by microbial activity. Thus, grassland soil microbial importance and diversity can be used as an index of grassland health and soil fertility. The present work was performed in the alpine region of Tianzhu, eastern part of the Qinghai-Tibetan Plateau, which is characterized by high altitude, important daily temperature variations with sparse air, strong radiation and low temperature. We studied the temporal changes in vegetation and soil properties, the different physiological groups of soil microorganisms and the effect of the degree of grassland deterioration on soil microbes, by comparing measurements made in 1982 with those made in 2003. In general, the vegetation condition as well as soil physical and chemical characteristics were obviously in better condition in 1982 as compared to 2003. In 2003, the parameters showing important decreases as compared to 1982, included: the dominant plant species of the vegetation coverage, forage yield, soil water content, soil organic matter, N and P content. On the contrary an increase in soil pH was observed. The total microbial population in 1982 was higher than in 2003. Soil bacterial population decreased from log 8.97 cfu g-1 of dry soil in 1982 to log 6.79 in 2003. Similarly from 1982 to 2003, the observed population decreases in cfu g-1 of dry soil were as follows: actinomycetes from log 6.91 to log 6.17; fungi from log 3.89 to log 3.28; nitrifiers from log 4.29 to log 3.54; aerobic nitrogen fixing bacteria from log 5.54 to log 3.90 and cellulose degraders from log 5.65 to log 3.68.The number of physiological groups was also from 1.5 to 4.5 times higher in the moderately deteriorated grassland (fenced) than in the severely deteriorated grassland (unfenced and rodents hill). The results clearly illustrate the important decline of the soil microbial population associated with the deterioration of the grassland.

对天祝高寒草地21a前（1982年）、后（2003年）植被状况、土壤理化性质、土壤三大类微生物（细菌、放线菌和真菌）和各生理群微生物（硝化细菌、好气性固氮菌和好气性纤维素分解菌）及不同退化程度（围栏内、围栏外和鼠丘地）草地土壤微生物数量变化特点进行了对比研究。结果表明：(1）与1982年相比，目前该区天然草地植被总盖度、主要优良牧草种类、产草量等显著下降，草地植被退化明显；(2）草地土壤pH升高，土壤含水量、有机质、氮、磷含量均下降，草地土壤理化性质劣于1982年；(3）目前该区天然草地土壤三大类微生物数量及各生理群微生物数量变化十分明显，1982年土壤细菌、放线菌和真菌及微生物总数分别是2003年的153.6、5.5、4.1倍和151.2倍；土壤硝化细菌、好气性固氮菌和好气性纤维素分解菌数量分别是2003年的5.7、43.3倍和94.4倍；(4）轻度退化草地（围栏内）土壤各类微生物数量明显高于严重退化草地（围栏外、鼠丘地），其数量前者一般为后者的1.5～4.5倍

A reseeding study was carried out on the Tianzhu degraded grassland from 2007 to 2009 to explore the effects of reseeding on species richness and aboveground biomass. The results showed that: After reseeding, the species richness increased in 2007, but decreased after 2007; It was increased that the vegetation height, coverage and aboveground biomass, and more, there was especially significance about the aboveground biomass of grass. Therefore, according to comprehensive evaluation based on vegetation height, coverage species richness and biomass, it was more efficient to recover degraded grassland reseeding with Elymus nutans+Bromus inermis+Festuca sinensis, and this method should be used in recovering alpine degraded grassland in Tianzhu county.

为了探究补播对高寒退化草地物种丰富度和生产力的影响，于2007―2009年在甘肃天祝县开展了利用不同禾草混播改良治理退化草地的试验。结果表明，补播当年物种丰富度增加，补播第2年后物种丰富度整体下降。补播明显提高了草群高度、植被盖度和地上生物量，且禾草类生物量一直都占据主要部分，草地的经济价值得以提高。综合补播后退化草地的草群高度、盖度、物种丰富度以及各经济类群的生物量和总生物量进行评价，垂穗披碱草（Elymus nutans）+无芒雀麦(Bromus inermis)+中华羊茅(Festuca sinensis)组合补播治理天祝县高寒草地的效果最佳，可以作为高寒退化草地恢复治理措施推广应用。

The contents of soil nutrients of different types and planting times of perennial sown pasture established in “grain for green” project were measured. The result showed that the contents of soil organic matter, total N, total P, available N and available P decreased with the soil depth, in which, the variation range of total P was small. Compared to the control, the contents of soil nutrients of pasture were significantly increased within 0 to 10 cm and 10 to 20 cm soil layers (P

分析了不同类型退耕还（林）草多年生栽培草地的土壤养分，结果表明：退耕还（林）草不同类型栽培草地的土壤有机质、全氮、全磷、速效氮、速效磷随着土层的加深，均呈现下降的趋势，但土壤全磷的变化幅度较小。退耕还（林）草不同类型栽培草地与其各自对照区的土壤有机质、全氮、全磷、速效氮、速效磷在010、1020 cm土层上多呈现显著差异（P