Fluxes of CO2,CH4 and N2O from alpine grassland in the Tibetan Plateau

Using static chamber technique,fluxes of CO2,CH4 and N2O were measured in the alpine grassland area from July 2000 to July 2001,determinations of mean fluxes showed that CO2 and N2O were generally released from the soil,while the alpine grassland accounted for a weak CH4 sink.Fluxes of CO2,CH4 and N2O ranged widely.The highest CO2 emission occurred in August,whereas almost 90?of the whole year emission occurred in the growing season.But the variations of CH4 and N2O fluxes did not show any clear patterns over the one-year-experiment.During a daily variation,the maximum CO2 emission occurred at 16:00,and then decreased to the minimum emission in the early morning.Daily pattern analyses indicated that the variation in CO2 fluxes was positively related to air temperatures(R^2=0.73)and soil temperatures at a depth of 5 cm(R^2=0.86),whereas daily variations in CH4 and N2O fluxes were poorly explained by soil temperatures and climatic variables.CO2 emissions in this area were much lower than other grasslands in plain areas.

Precipitation-use efficiency along a 4500-km grassland transect

National Natural Science Foundation of China [30590381, 40971027]; State Key Technologies RD Program [2006BAC08]; Chinese Academy of Sciences ; National Key Research and Development Program [2010CB833501]

Grassland degradation in the

Supported by MSS images in the mid and late 1970s, TM images in the early 1990s and TM/ETM images in 2004, grassland degradation in the "Three-River Headwaters" region (TRH region) was interpreted through analysis on IRS images in two time series, then the spatial and temporal characteristics of grassland degradation in the TRH region were analyzed since the 1970s. The results showed that grassland degradation in the TRH region was a continuous change process which had large affected area and long time scale, and rapidly strengthen phenomenon did not exist in the 1990s as a whole. Grassland degradation pattern in the TRH region took shape initially in the mid and late 1970s. Since the 1970s, this degradation process has taken place continuously, obviously characterizing different rules in different regions. In humid and semi-humid meadow region, grassland firstly fragmentized, then vegetation coverage decreased continuously, and finally "black-soil-patch" degraded grassland was formed. But in semi-arid and and steppe region, the vegetation coverage decreased continuously, and finally desertification was formed. Because grassland degradation had obviously regional differences in the TRH region, it could be regionalized into 7 zones, and each zone had different characteristics in type, grade, scale and time process of grassland degradation.

Effects of nitrogen fertilization on soil respiration in temperate grassland in Inner Mongolia, China

Nitrogen addition to soil can play a vital role in influencing the losses of soil carbon by respiration in N-deficient terrestrial ecosystems. The aim of this study was to clarify the effects of different levels of nitrogen fertilization (HN, 200 kg N ha(-1) year(-1); MN, 100 kg N ha(-1) year(-1); LN, 50 kg N ha(-1) year(-1)) on soil respiration compared with non-fertilization (CK, 0 kg N ha(-1) year(-1)), from July 2007 to September 2008, in temperate grassland in Inner Mongolia, China. Results showed that N fertilization did not change the seasonal patterns of soil respiration, which were mainly controlled by soil heat-water conditions. However, N fertilization could change the relationships between soil respiration and soil temperature, and water regimes. Soil respiration dependence on soil moisture was increased by N fertilization, and the soil temperature sensitivity was similar in the treatments of HN, LN, and CK treatments (Q (10) varied within 1.70-1.74) but was slightly reduced in MN treatment (Q (10) = 1.63). N fertilization increased soil CO2 emission in the order MN > HN > LN compared with the CK treatment. The positive effects reached a significant level for HN and MN (P < 0.05) and reached a marginally significant level for LN (P = 0.059 < 0.1) based on the cumulative soil respiration during the 2007 growing season after fertilization (July-September 2007). Furthermore, the differences between the three fertilization treatments and CK reached the very significant level of 0.01 on the basis of the data during the first entire year after fertilization (July 2007-June 2008). The annual total soil respiration was 53, 57, and 24% higher than in the CK plots (465 g m(-2) year(-1)). However, the positive effects did not reach the significant level for any treatment in the 2008 growing season after the second year fertilization (July-September 2008, P > 0.05). The pairwise differences between the three N-level treatments were not significant in either year (P > 0.05).

Vegetation Responses to A Long-term Grazing Intensity Experiment in Alpine Shrub Grassland on Qinghai-Tibet Plateau

在青藏高原中国科学院海北高寒草甸生态系统定位研究站对金露梅高寒灌丛草场植被开展了长期不同放 牧强度试验,分别在短期(4 年) 、中期(11 年) 和长期(18 年) 放牧阶段研究不同放牧干扰强度对草地植物物种多样 性、群落结构、地上生物量和草场质量的影响。研究表明,在不同放牧阶段,随着放牧强度增加植物群落的高度和 盖度都降低。在中期放牧干扰阶段,物种多样性指数和均匀度指数随着放牧强度增加呈现典型的单峰曲线模式; 在长期放牧干扰阶段,随着放牧强度增加,占优势地位的灌木和禾草被典型杂类草替代,其中的重度放牧干扰简化 了高寒灌丛植被群落结构,减少了地上现存生物量,特别是可食优良牧草生物量。植被对放牧的响应除了与放牧 强度和放牧时间阶段密切相关外,还与该地区水热条件的变化有一定的相关性。针对长期放牧干扰的反应特性可 将金露梅灌丛草场中植物划分为增加型、敏感型、忍耐型和无反应型4 种类型。除了丰富度指数、多样性指数和均 匀度指数外,其它一些特征参数并不支持著名的中度干扰假说。本研究发现,长期重度放牧促进了青藏高原高寒 草地退化,适度放牧有利于高寒灌丛草场的生物多样性保护和牧草利用;“取半留半”的放牧原则在青藏高原草场 放牧管理实践中值得推荐,它将有利于防止草场退化,提高牧草利用率和维持较高的生物多样性。