草地是世界上分布最广的植被类型之一,作为陆地生态系统的重要组成部分,参与了全球碳源/汇及碳循环过程,在全球气候变化中扮演着重要角色,并对其产生重大影响.以黄土高原草地植被为研究对象,结合国家退耕还林草与封山禁牧工程的实施,对封禁前后的天然草地和退化草地,采用样带多点调查与多年定位测定相结合的方法,分析了黄土高原不同类型草地植物活体、凋落物和根系碳密度分布格局与地带性规律,系统研究了黄土高原不同草地类型退化草地和封禁草地生物量与碳密度沿海拔及降水梯度的时空变异特征,阐述了影响草地碳密度分布的主要驱动因子及其作用机理.结果表明:4种草地类型3种处理的草地生物量和碳密度自西北向东南均与降雨量呈指数增长趋势,并随海拔降低而显著降低,且二者呈显著的线性回归关系;各草地类型地上/地下生物量与碳密度分布规律均为荒漠草原＜丘陵典型草原＜梁塬典型草原＜草甸草原;封禁11a草地活体植物、凋落物和根系碳密度总量:荒漠草原为7.066 t/hm2,丘陵典型草原为8.080 t/hm2,梁塬典型草原为15.319 t/hm2,草甸草原为20.982 t/hm2,分别是退化草地的14.8、8.33、6.5倍和15.88倍.充分表明,封禁不仅能使草地植被恢复和生物量提高,而且也是草地生产力和碳密度增加的一条重要途径.由此可见,气候干旱和草地退化是影响草地生物量和碳密度的关键因素,系统研究黄土高原封禁草地生物量增长与碳密度变化过程,将会对未来全球气候变化分析作出重要贡献.

Land use/cover change (LUCC) is one of the most concerned environmental problems by scientists, land managers and policy makers. LUCC can affect energy flow, biogeochemical and hydrological cycling in terrestrial ecosystems through altering land surface and species composition. Ecosystem carbon cycling responds differently to various LUCC types, showing a pattern of CO2 release into the atmosphere when LUCC from a high-biomass forest to low-biomass grassland, cropland or urban area. Previous reports indicated that global terrestrial ecosystem released 2.21 Pg C (1 Pg C=1015g C) per year induced by LUCC during the 1990s, which explain s about 25% of the global C emission per year in the same period; and in the last two centuries, the released C from LUCC accounts for 50% of the C emission from fossil fuel combustion. The LUCC patterns are totally diversified for regions around the world, which cause obviously different C fluxes among them. The reports showed that LUCC in the tropics is a C source, while it is a C sink in the middle and high latitude regions in the northern hemisphere, which possibly explain a large part of the “missing carbon sink" in the terrestrial ecosystems. Currently, modeling is the most popular way to simulate LUCC- induced changes in ecosystem C cycling. The quantitative relationship between LUCC patterns and their related processes and ecosystem carbon cycling remains uncertain. This uncertainty causes great discrepancies in the estimation of terrestrial ecosystem CO2 fluxes from land use/cover changes. In the near future, except for carrying on long-term experiments to determine these quantitative relationships, model development by integrating LUCC with vegetation dynamic model and ecosystem process model will be essential for making an accurate estimation of C fluxes induced by LUCC.Sound land management can greatly increase C storage in the terrestrial ecosystems during LUCC processes. However, the quantification of land management effects is not well-established yet and land management is thus not included in most simulation models of LUCC impacts, which needs more researches in the future.

土地利用/覆盖变化是学术界最为关注的环境变化问题之一，它能够影响陆地生态系统的 生物多样性、水、碳和养分循环、能量平衡，引起温室气体释放增加等其它环境问题。 不同类型的土地利用/覆盖变化对生态系统碳循环的作用不同，由高生物量的森林转化为 低生物量的草地、农田或城市后，大量的CO2将释放到大气中。全球土地利用/覆盖变化 具有很强的空间变异性，对生态系统碳循环的影响同样具有明显的空间差异：热带地区 的土地利用 /覆盖变化造成大量的碳释放，而中高纬度地区土地利用/覆盖变化则表现为 碳汇。目前，土地利用/覆盖变化引起的生态系统碳循环变化主要是通过模型模拟来估算 的。尽管土地利用/ 覆盖变化及其相关过程与生态系统碳循环的关系已经比较清楚，但 是，由于土地利用/覆盖变化过程复杂且影响广泛，对于如何量化两者之间的关系还存在 很多不确定性。目前的量化过程主要是利用经验数据来实现的，机理性不强，使得对土 地利用/覆盖变化造成的陆地生态系统CO2释放量的估测差异很大。除了进一步加强长期 定位研究以获得土地利用/覆盖变化与生态系统碳循环过程的定量关系外，土地利用/覆 盖变化模型与植被动态模型、生态系统过程模型的耦合也是今后模型发展的主要方向之 一。采用合理的管理措施能够大量增加土地利用/覆盖变化过程中的碳储存量，降低碳释 放量，因此在模型中耦合管理措施来研究土地利用/覆盖变化过程对生态系统碳循环的影 响是未来几年的工作重点。

【Objective】The distribution characteristics of soil organic carbon (SOC) storage were studied for the purpose to determine the reasonable grazing management way and provide a basis for the regional carbon estimation in grassland ecosystem. 【Method】The SOC storage of 0-100 cm soil depth was measured by using field method of stratified sampling in the typical steppe.【Result】The SOC storage was between 9.72-14.84 kg•m-2 in the three study plots. No significant difference was found in SOC storage in three study plots of spatial distance. The significant difference of SOC storage was found between four different grazing managements treatments in study area, and the order was moderate grazing (MG)＞light grazing (LG)＞heavy grazing (HG)＞control area (CK). The SOC storage decreased with the increasing of soil depth, and a significant difference was detected between SOC among different soil layers. A positive significant relationship was found between SOC storage and soil layer (P＜0.01), and the relationship could be described by using logarithmic and linear equations.【Conclusion】The SOC storage was relatively stable in the typical steppe, and presented a vertical descending characteristics. The effect of different grazing managements on SOC storage in the same vegetation type was significantly higher than the effect of spatial distance. Moderate grazing is benefit for carbon fixation of grassland ecosystem.

【目的】从草地生态系统土壤有机碳（soil organic carbon，SOC）储量分布特征来确定合理的放牧管理方式并为区域SOC储量估算提供依据。【方法】采用野外调查法分层测定典型草原0—100 cm SOC储量。【结果】①3个研究样地SOC储量为9.72—14.84 kg•m-2；②具有空间距离的3个研究样地土壤碳储量差异无统计学意义，样地内4种处理之间SOC储量差异显著，且均表现为中度放牧处理（moderate grazing，MG）＞轻度放牧处理（light grazing，LG）＞重度放牧处理（heavy grazing，HG）＞对照（control area，CK）；③随土层深度的增加SOC储量呈递减趋势，且不同土层之间SOC均有显著性差异。SOC储量与土层深度呈极显著相关关系（P＜0.01），这种关系可以用对数和线性方程描述。【结论】典型草原亚带草地生态系统SOC储量具有相对稳定性，且呈现明显的垂直递减特征；同一植被亚带不同处理对SOC储量的影响显著高于空间差异；适度放牧利用有利于草地生态系统SOC固持。

摘　要： 草地生态系统在全球碳循环中起着极为重要的作用。但是实测数据十分匮乏,文中利用2008年全国草原地面监测数据,以及卫星遥感数据,对2008年中国草地的碳储量进行了估算。主要结论如下：中国草地总面积约为341.7×104km2,2008年中国草地总有机碳为35.96Pg,其中地上生物量有机碳为0.1613Pg,地下生物量碳为0.7395Pg,地下根系储存的碳是地上碳储量的5倍左右,中国草地土壤有机碳为35.06Pg。

介绍了草地土壤有机碳的测定方 法、评价指标以及草地土壤碳储量的估算方法,从碳的输入、输出和碳素的转化方面阐述了草地土壤碳素转化与积累的特征,总结了国内外关于草地土壤有机碳的研 究结果,并对研究结果进行了对比与评价,指出了当前研究中存在的问题和今后工作的努力方向,为草地生态系统土壤有机碳储量的研究提供参考。

The Hulunber grasslands in Inner Mongolia cover an area of up to 9.97×10 6 km 2 . Within this area, the Hulunber Leymus chinensis meadow steppe is located in the eastern part of the Eurasian continent grassland region. It is a very important example of a temperate grassland ecosystem. Grazing is the most common land use in the Hulunber meadow grasslands, therefore, understanding the changes of soil carbon, soil nitrogen and carbon sequestration under different grazing gradients will provide an important scientific basis for grassland carbon sink management in Inner Mongolia. Six stocking rate treatments (0, 0.23, 0.34, 0.46, 0.69 and 0.92 Au/hm 2 ) repeated three times for each treatment, were established, with soil samples collected in early August 2011. The experimental results showed that the grazing gradient has a distinct effect on the change of soil carbon and nitrogen content and soil carbon and nitrogen storage. Soil carbon and nitrogen storage and carbon sequestration potential in the top 0-30 cm soil layers had a significant linear downward trend as the grazing gradient increased. Compared with non-grazed grassland G0.00 (107.1 t/hm 2 ), the soil carbon sequestration potentials are 108.61-109.67 t/hm 2 , 107.06 t/hm 2 , 95.13-100.14 t/hm 2 in light grazing, moderate grazing and heavy grazing grassland, respectively. For the soil nitrogen, compared with non-grazed grassland G0.00 (9.22 t/hm 2 ), soil nitrogen sequestration potentials were 8.37-8.65 t/hm 2 , 8.20 t/hm 2 , 6.74-7.35 t/hm 2 in light grazing, moderate grazing and heavy grazing grassland, respectively. Light grazing improved the soil carbon storage and carbon sequestration potential. With an extension of the grazing time, the soil carbon and nitrogen content, carbon and nitrogen storage, and carbon and nitrogen sequestration potential in soils of heavily grazed grasslands decreased significantly. There were obvious vertical distributions in the soil carbon and nitrogen content and carbon and nitrogen storage under different grazing gradients. The change of soil carbon and nitrogen was higher in the 0-10 cm soil layer under different grazing gradients while soil carbon and nitrogen content and carbon and nitrogen storage significantly decreased with the increase in soil depths in different grazing gradients. About 42.26% of the soil organic carbon was distributed in the top 0-10 cm soil layer, 30.67% in the 10-20 cm layer, and 27.07% in the 20-30 cm layer. For the 0-10 cm, 10-20 cm and 20-30 cm soil layers, the total soil contents were 44.39%、30.13% and 25.48%, respectively; the soil carbon storage were 39.60%, 31.26% and 29.14%, respectively; the soil nitrogen storage were 41.57%, 30.97% and 27.46%, respectively. The soil carbon and nitrogen content and soil carbon and nitrogen storage for the 0-10 cm soil layer were significantly higher than those for the 10-20 cm and 20-30 cm soil layer. We found that there was an underlying transformation from soil carbon sequestration under light grazing gradient to soil carbon loss under a heavy grazing gradient, and this transformation threshold was found to be 0.46 Au/hm 2 . In short, the Hulunber meadow steppe of Inner Mongolia has a good capacity to sequester carbon in soil, and that can increase the soil carbon sequestration potential through rational control of grazing gradients to achieve carbon sinks. We can increase the soil carbon sequestration potential to achieve carbon sinks through controlling grazing gradients.

放牧是内蒙古呼伦贝尔草甸草原主要的利用方式，弄清放牧情况下草地土壤碳氮变化和固碳效应，将为我国内蒙古地区草地碳汇管理提供重要的科学依据。通过小区控制放牧实验(放牧梯度0.00，0.23，0.34，0.46，0.69，0.92Au/hm 2 )，探讨了不同放牧梯度下土壤碳氮变化及固碳效应，实验结果表明：放牧梯度对土壤碳氮含量、土壤碳氮贮量的变化有明显的影响，0-30 cm土层碳氮贮量随着放牧梯度增加呈显著的线性下降趋势。随着放牧时间的延续，轻度放牧利于提高草地的土壤有机碳密度和碳固持潜力，重度放牧显著降低了土壤碳氮含量、碳氮贮量和碳氮固持潜力。不同放牧梯度下土壤碳氮含量和碳氮贮量具有明显的垂直分布特征，随着土壤深度的增加土壤碳氮含量、碳氮贮量均呈明显的下降趋势。轻度放牧草地表现为碳固持，重度放草地表现为碳流失，对呼伦贝尔羊草草甸草原而言，土壤碳固持/碳流失的转化阈值为0.46Au/hm 2 ，通过合理控制放牧梯度能够达到增加草地土壤固碳潜力，实现碳增汇的目的。

研究地形和土地利用对深层土壤有机碳(soil organic carbon,SOC)的影响,对准确评估土壤固碳潜力和土壤碳循环具有重要意义.以3种地形(峁顶、峁坡、沟底)和7种土地利用类型(农田、果园、天然草地、人工与天然灌木林、人工与天然乔木林)为对象,在黄土丘陵沟壑区燕沟流域采集53个0～1 m土壤剖面中6个层次,898个土壤样品,研究了地形和土地利用方式对黄土丘陵沟壑区小流域深层SOC含量和分布影响.结果表明,地形、土地利用方式、土层深度及其两两交互作用对流域深层SOC空间分布有极显著影响(p<0.01).深层(10～100 cm)与表层(0～10 cm)SOC在3种地形的分布不同.对于表层土壤(0～10 cm),峁坡SOC含量(10.7 g·kg-1)最高,其次是沟底(8.9 g·kg-1),峁顶最低(4.4 g·kg-1);对深层土壤有机碳,沟底最高(5.6 g·kg-1),峁坡次之(4.5 g·kg-1),峁顶最低(3.2 g·kg-1).深层SOC空间分布因土地利用方式存在显著差异.与农田相比,果园0～40 cm土层SOC含量降低21%,但80～100 cm土层SOC含量提高13%;天然灌木林40～100 cm平均含量(5.3 g·kg-1)较农田高66%(p<0.05);但天然乔木林40～100 cm与其它土地利用方式差异较小.沟底深层(20～100 cm)SOC储量(5.04 kg·m-2)最大,占1 m剖面SOC储量的71.4%;峁坡占63.6%;峁顶占72.3%.深层(20～100 cm)SOC储量天然灌木林最高,为6.01 kg·m-2,占1 m剖面SOC储量的64.7%,天然乔木林深层相对储量最小,仅占49.7%;农田和果园深层相对储量均达到70%以上.

In order to determine the effects of land use changes on the storage of soil organic carbon (SOC) in deep soil layers (100~200 cm), SOC content and the distribution characteristics of five typical land use types in Ziwuling forest zone on the hilly Loess Plateau were studied in the paper. Response of SOC storage in deep soil to the land use changes was analyzed under four kinds of land use changes, including from natural woodland to artificial woodland, from natural woodland to cropland, from natural shrubland to cropland and from natural shrubland to revegetated grassland. The results showed that SOC content of natural woodland, natural shrubland, artificial woodland, revegetated grassland and cropland was 5.85, 3.96, 4.98, 3.09 and 3.20 g · kg -1 , respectively. SOC content of natural woodland and artificial woodland was significantly higher than those of natural shrubland, revegetated grassland and cropland ( p -2 under the four aforementioned types of land use changes.SOC storages in 0~100cm profile decreased by 2%~48% while the deep layer decreased by 12%~22%.Compared with conversion from woodland to cropland, SOC recovered slowly when land use changed from cropland to woodland. The results suggested different sensitivity of SOC to land use changes in the upper (0~100 cm) and deep (100~200 cm) soil, and SOC in deep soil layers were more stable than that in upper soil layers.

通过研究黄土丘陵子午岭林区5种典型土地利用类型土壤剖面有机碳分布特征,分析了天然乔木林转变为人工乔木林、天然乔木林转变为农田、天然灌木林转变为农田及撂荒后土壤有机碳变化特征.同时,以浅层(0~100 cm)土壤为对照,探讨了土地利用变化对深层(100~200 cm)土壤有机碳储量的影响.结果表明,在0~200 cm剖面上,天然乔木林、天然灌木林、人工乔木林、撂荒地、农田土壤有机碳含量分别为5.85、3.96、4.98、3.09、3.20 g · kg -1 ,天然乔木林、人工乔木林土壤有机碳含量显著高于天然灌木林、撂荒地和农田( p -2 ,减幅为7%、39%、21%、13%,其中,浅层土壤减少了2%~48%,深层土壤减少了12%~22%.相对于林地开垦为农田而言,农田退耕还林后土壤有机碳的恢复要慢得多.研究结果揭示了浅层和深层土壤有机碳对土地利用变化的敏感性,反映了深层土壤有机碳具有较大的稳定性.

Taking the  Robinia pseudoacacia  woodlands,  Caragana korshinskii  shrublands, and abandoned croplands with different years of revegetation in the hilly Loess Plateau region of Northwest China as test objects, this paper studied the profile distribution and accumulation dynamics of organic carbon storage in deep soil (100-400 cm), with those in 0-100 cm soil profile as the control. In 0-100 cm soil profile, the organic carbon storage decreased significantly with the increase of soil depth; while in deep soil, the organic carbon storage had a slight fluctuation. The total organic carbon storage in 100-400 cm soil profile was considerably high, accounting for approximately 60% of that in 0-400 cm soil profile. The organic carbon storage in 80-100 cm soil layer had a significant linear correlation with that in 100-200 and 200-400 cm soil layers, and among the organic carbon storages in the five layers in 0-100 cm soil profile, the organic carbon storage in 80-100 cm soil layer had the strongest correlation with that in 100-400 cm soil profile, being able to be used to estimate the organic carbon storage in deep soil in this region. The organic carbon storage in 0-20 cm soil layer in the three types of revegetation lands was significantly higher than that in slope croplands, but the organic carbon storage in deep soil had no significant difference among the land use types. The orga〖JP2〗nic carbon storage in deep soil  increased with the increasing years of revegetation. In R. pseudoacacia woodlands and  C. korshinskii  shrub lands, the average increasing rate of the organic carbon storage in 100-400 cm soil layer was 0.14 and 0.19 t·hm -2 ·a -1 , respectively, which was comparable to that in the 0-100 cm soil layer in  C. korshinskii shrublands. It was suggested that in the estimation of the soil carbon sequestration effect of revegetation in hilly Loess Plateau region, the organic carbon accumulation in deep soil should be taken into consideration. Otherwise, the effect of revegetation on soil carbon sequestration would be significantly underestimated.

以黄土丘陵区不同恢复年限的人工刺槐林、人工柠条林和自然撂荒地为对象,以0～100 cm(浅层)土壤为对照,研究了不同植被类型下100～400 cm(深层)土壤有机碳(SOC)储量的剖面分布特征和累积动态.结果表明: 随土壤深度增加,浅层SOC储量显著降低,深层SOC变化趋势不明显,但储量很高,约占0～400 cm 剖面SOC的60%.80～100 cm土层的SOC储量与深层100～200和200～400 cm的SOC储量呈显著线性相关,是0～100 cm 5个土层中与深层SOC储量变化相关性最强的一层,可用以估算深层SOC储量.人工刺槐林、柠条林、撂荒地表层(0～20 cm)SOC储量显著高于坡耕地,而深层SOC储量在不同利用类型间差异不显著.随植被恢复年限的增加,深层SOC储量呈上升趋势,人工刺槐林和人工柠条林100～400 cm SOC平均累积速率分别为0.14和0.19 t·hm -2 ·a -1 ,人工柠条林与浅层SOC累积速率相当.在估算黄土丘陵区植被恢复的土壤固碳效应时,应考虑深层土壤有机碳累积量,否则会严重低估植被恢复的土壤固碳效应.

Soil organic carbon (SOC) is an important component of the global carbon cycle. Uncertainties remain about the estimation of SOC storage because of a lack of information about temporal SOC accumulation in deep soil layers. Four ages of a Black locust (Robinia pseudoacacia) revegetation chronosequence including 9 (ch9), 15 (ch15), 24 (ch24) and 34 years (ch34) in the hilly Loess Plateau region was selected for this study. Vegetation characteristics and SOC dynamics down to a depth of 2m were investigated along the revegetation chronosequence to determine the accumulation of SOC in the deep soil layer and its response to revegetation. The results showed that the deep soil layer of the hilly Loess Plateau conserved a large amount of soil organic carbon. Deep layer (50-200cm) SOC content (1.35-2.39 g?kg-1) was equivalent to approximately 25% of that found in the shallow layer (0-50cm). Deep layer SOC storage (26.28-46.50 t?hm-2) accounted for more than 50% of total SOC storage (0-200cm), and deep layer SOC storage was significantly higher than that found in the shallow layer. The results demonstrated that total SOC storage will be underestimated by approximately 1/3 in this region if SOC was only measured to a depth of 1m. When compared to ch9，SOC storage and SOC content in deep soil layer increased significantly after more than 20 years revegetation. Average SOC content for 10cm increments down to a depth of 2m for ch9, ch15, ch24 and ch34 were (1.65±0.05） g?kg-1, (1.70±0.06) g?kg-1, (3.10±0.12) g? kg-1, and (3.35±0.16) g?kg-1 respectively. As a vigorous accumulation exhibited in the mature phase (15-24a) of Black Locust, average SOC content of 2m was doubled after 20 years revegetation (ch24, ch34) compared to that of 9ch. And for the entire revegetation chronosequence (9-34a) the increase in SOC storage down to a depth of 2m (43.02 t?hm-2) was distinctly higher than that in 1m (34.65 t?hm-2). Unlike the shallow soil layer had significant differences in SOC content in adjacent increments (0-30cm), in the deep soil layer the differences were only 0.12-0.42 g?kg-1. Black Locust growing conditions (coverage, basal diameter and height) showed significant correlation with both deep and shallow SOC content, demonstrating the significant influence of deep-rooting vegetation to deep layer SOC and the integrity of the whole soil organic carbon pool. Our results indicated that SOC storage in the deep soil layer should be considered when estimating the effects of soil carbon sequestration of revegetation in the hilly Loess Plateau region.

以恢复9、15、24a和34a的刺槐林为研究对象，探究黄土丘陵区深层土壤有机碳（SOC）积累以及对植被恢复的响应。区域深层土壤（50-200cm）SOC含量高达1.35-2.39 g? kg-1，约为浅层土壤（0-50cm）SOC含量的25%；深层土壤SOC储量高达26.28-46.50 t?hm-2，占2m土层SOC储量的50%以上，显著高于浅层SOC储量；植被恢复20多年后与恢复9a相比，深层SOC含量和储量都有极显著提高。2m土层SOC含量随植被恢复20多年后较9a提高1倍左右；2m土层SOC储量增幅为4302 t? hm-2（9-34a），明显高于1m土层SOC储量增幅34.65 t? hm-2 (9-34a）。浅层土壤中的0-30cm相邻土层间SOC含量差异显著，而深层SOC含量较稳定。深层SOC含量与刺槐盖度、基径、高度呈极显著正相关。在评价黄土丘陵区植被恢复的土壤固碳效应时应充分考虑深层土壤有机碳储量和变化。

Temperate grasslands in the northern China account for approximately 110 million hectares, and grazing is common in the grasslands of Inner Mongolia. Therefore, understanding soil carbon (C) sequestration and its mechanism in these grazing grasslands is very important for the regional carbon budget. However, how and to what extent is soil C sequestration affected by increasing grazing intensities have not been well documented. To date, it is still uncertain whether changes in topography have modified soil C sequestration in these grazing grasslands; this is a crucial issue for the decision makers of grassland management. On the basis of previous grazing experiments with 7 stocking rates (i.e., 0 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep/hm 2 ) in the plat and slope grasslands, respectively, and by selecting free-grazing grasslands as control (CK), we specifically investigated soil C sequestration and the effects of increasing stocking rates on this sequestration and quantified the influence of topography on soil C sequestration in temperate grasslands of northern China. The experimental results showed that C storage in the 0-30 cm and 0-100 cm soil layers increased to a certain extent when the grazing intensity was light, and increases in soils N were relatively lower. In addition, the C and N storage in soils of heavy-grazing grasslands decreased slightly. Our findings prove the existence of an underlying transformation from soil C sequestration under low-grazing pressure to soil C loss under heavy-grazing pressure, and this transforming threshold was found to be 4.5 sheep/hm 2 in flat grasslands and 3.0 sheep/hm 2 in slope grasslands. Furthermore, the effect of increasing stocking rates on soil C sequestration was modified by topography, and slope grasslands were found to be stronger than flat grasslands. Our results showed that soil C sequestration rates in the grazing grasslands of Inner Mongolia are modified by topography; therefore, we need to focus more on identifying the potential impact of topography in future studies in order to accurately evaluate soil C sequestration in these grazing grasslands. Although this topic has limited scope, we attempted to experimentally demonstrate the presence of an underlying transforming threshold of soil C sequestration that changes with increasing stocking rates and the changes in topography; this study was essential for not only assessing the regional C budget but also optimizing grassland management to improve soil organic matter. Altogether, our findings suggest that grazing grasslands in northern China have a good capacity to sequester C in soil with rational grazing and that the different effects in flat and slope grasslands due to increasing grazing intensities should be taken into account for grassland management.

放牧是典型草地最重要的利用方式,弄清放牧对草地碳固速率的影响,将为我国内蒙古地区草地碳汇管理提供重要的科学依据。通过在平坦草地和斜坡草地设置相同的放牧梯度实验 (放牧强度0、1.5、3.0、4.5、6.0、7.5、9.0 羊/hm 2 ),探讨了放牧和地形对草地土壤碳固持速率的影响。实验结果表明:轻度放牧草地表现为碳固持,重度放草地表现为碳流失;对放牧草地而言,存在碳源/碳汇的转化阈值(或放牧强度),且坡地阈值低于平地。为了实现草地碳增汇目的,平坦草地的放牧强度应低于 4.5羊/hm 2 (放牧期6-9月),斜坡草地应低于3 羊/hm 2 。地形因素(平地 VS 斜坡)使准确评估放牧草地土壤的碳固持速率变得更加复杂。总之,内蒙古地区放牧草地具有较大的碳固持潜力,通过控制放牧强度是实现其碳固持潜力的重要途径之一。

In recent decades, the carbon (C) cycle and soil respiration of terrestrial ecosystems have been become hot topics for the global climate change, and research focused on the temperature sensitivity and priming effects of soil microbial respiration (or soil C mineralization) has increased rapidly since 2000. In this study, we focused on long-term fenced Stipa grandis grassland (FG) and grazing Stipa grandis grassland (GG) in Inner Mongolia, China, investigating the impact of land-use change on the temperature sensitivity and the priming effects of soil microbial respiration by incubating soils in the laboratory under a temperature gradient (5, 10, 15, 20, 25 and 30℃) and with substrate addition (mixed litter). The incubation experiment was continued for 6 weeks, and the rates of soil C mineralization were measured throughout using our newly developed equipment. The results showed that the amount of soil C mineralization was higher in GG than that in FG duration the 6-weeks incubation. The rates of soil C mineralization increased significantly with increasing incubation temperature for both GG and FG (temperature coefficient ( Q 10 ) values ranged from 1.1 to 1.9), however, the Q 10 values for GG and FG were not significantly different. After mixed-litter addition, the rates of soil C mineralization not only in GG but also in FG increased significantly, and showed the apparent "priming effects" of C mineralization. Compared with long-term fenced grassland (FG), grazing grassland (GG) had higher priming effects, which even after only 7 d were 6.38 times higher. Moreover, the priming effects increased with increasing incubation temperature in the first week, although these effects were the highest at 15℃ duration the 42 d of incubation. These findings suggest that, on a longer time scale, medium temperatures should promote soil C mineralization. On the whole, long-term grazing exclusion depressed the priming effect of soil microbial respiration and resulted in less C emission under the same mixed litter input. This is probably one of the mechanisms underlying the capacity of long-term fenced grasslands to sequester CO 2 in Inner Mongolia.

土壤呼吸及其控制机理是全球变化研究的重点之一,其中土壤呼吸的温度敏感性和激发效应是近年来的研究热点。以长期围封的大针茅草地(Fenced grassland, FG)和自由放牧草地(Grazing grassland, GG)为对象,通过不同温度(5、10、15、20、25℃和30℃)和添加混合凋落物的室内培养途径,探讨了长期围封对草地碳矿化(或土壤微生物呼吸)的温度敏感性和激发效应的影响。实验结果表明:在培养42 d内,长期围封的大针茅草地的土壤碳矿化累积量高于自由放牧草地;土壤碳矿化量随温度的升高而升高,围封对大针茅草地土壤碳矿化的温度敏感性的影响不显著, Q 10 值介于1.1-1.9之间。添加混合凋落物使土壤碳矿化表现出了明显的激发效应,且自由放牧草地的激发效应高于长期封育草地;在培养的前7 d,土壤激发效应随着培养温度升高而增强,激发效应最高值达6.38;但在整个培养期(42 d)土壤激发效应15℃为最大。从长远角度看,中间温度更有利于土壤激发效应以及土壤碳矿化。在相同的有机物质输入状况下,长期围封大针茅草地的激发效应更低,可能是大针茅草地在长期围封状况下仍然具有碳固持效应的重要机制之一。

Soil carbon sequestration and potential has been a focal issue in global carbon research. Under the background of global change, the estimation of the extent well as its change of soil organic carbon (SOC) storage is of great importance. Based on soil data from the second soil survey of China and field survey during 2011-2012, this paper studied spatial distribution and changes of topsoil (0-20 cm) organic carbon storage in Inner Mongolia grassland between the 1980s and 2010s, by using the regression relation between soil data and remote sensing data. The results showed that (1) the SOC storage values in Inner Mongolia grassland in the 1980s and 2010s were estimated to be 2.05 and 2.17 Pg C, with an average density of 3.48 and 3.69 kg C · m -2 , respectively. The SOC storage was mainly distributed in the typical steppe and meadow steppe, which accounted for over 98% of the total. The spatial distribution showed a decrease trend from the meadow steppe, typical steppe to the desert steppe, corresponding to the temperature and precipitation gradient. (2) SOC variations during 1982-2012 were estimated to be 0.12 Pg C, at 7.00 g C· m -2 · yr -1 , which did not show a significant change. This indicates that SOC storage in grassland ecosystem of Inner Mongolia remained relatively stable over this period. However, topsoil organic carbon of different grassland ecosystems showed different trends of carbon source/sink during the past three decades. Meadow steppe and typical steppe, as a carbon sink, had sequestered at 0.15 and 0.03 Pg C, respectively, while desert steppe, as a carbon source, had lost 0.06 Pg C. It is concluded that SOC storage in grassland ecosystem may respond differently to climate change, which is related to vegetation type, regional climate type and grazing intensity. These results will provide references for decision makers to find proper resolutions to protect grassland soil resource.

以我国内蒙古草原为研究区域,结合1982-1988 年第二次土壤普查资料以及2011-2012年实地考察数据,构建了基于遥感数据和土壤数据的区域表层土壤有机碳储量估算方法,对研究区1980s 和2010s 表层土壤有机碳储量、空间分布特征及其变化进行研究,结果表明:(1)1980s、2010s 内蒙古草地表层土壤(0~20 cm) 有机碳储量分别为2.05 Pg C、2.17 Pg C,土壤有机碳密度约为3.48 kg C·m -2 、3.69 kg C·m -2 ,其空间分布上呈现从草甸草原、典型草原、荒漠草原逐渐降低的特征;(2) 1982-2012 年间,内蒙古草地表层土壤有机碳储量略有增加,但增加幅度较小,其中草甸草原和典型草原表层土壤有机碳储量增加,荒漠草原则表现为减少。研究结果将为研究区因地制宜地采取固碳措施,实现草地可持续管理提供科学参考。

Soil organic carbon(SOC),organic carbon density and organic carbon storage in four different natural grassland types(forest steppe,typical grassland,alpine meadow steppe and desert steppe) in the Loess Plateau were analyzed.Results indicate that the content of soil organic carbon decreases with soil depth and a diversity in different grassland types.The variation of soil organic carbon content with soil depth in alpine meadow grassland has the biggest amplitude,while the variation has the smallest one in desert grassland.Organic carbon density of four different grassland types are ranked as Alpine meadow grassland > typical steppe > forest steppe > desert steppe.In the whole soil layer of 0～100 cm,the coefficients of variation of soil organic carbon density are different in four grassland types.The coefficient of variation of typical grassland is the largest while the Alpine meadow grassland is the minimum.In the horizontal direction,organic carbon density is unevenly distributed in the natural grassland of central Loess Plateau.The total area of natural grassland in the region is 2.02 × 10 7 hm 2 ,and the soil carbon storage is 1.06 Pg C in 1 m depth.

对黄土高原水平方向的4种主要草地类型(森林草原、典型草原、高寒草甸草原、荒漠草原),分析其土壤有机碳含量、有机碳密度及其碳储量,以期揭示黄土高原中部不同草地类型土壤有机碳分布特征,初步估算黄土高原中部天然草地土壤有机碳储量。结果表明:各草地类型土壤有机碳含量和土壤碳密度均随深度增加而减少,但类型不同其减少程度不同。高寒草甸草原的土壤有机碳含量减少幅度最大,荒漠草原减幅最小;4种类型草地的土壤有机碳密度排序为:高寒草甸草原>典型草原>森林草原>荒漠草原,对于整个土层而言,草地类型间的土壤有机碳密度变异程度不同,典型草原变异系数最大,高寒草甸草原最小;在水平方向上,黄土高原中部有机碳密度分布很不均匀。黄土高原中部天然草地总面积2.02×10 7 hm 2 ,其1 m深度土壤碳储量为1.06 Pg C。

The warm steppe, alpine steppe, alpine meadow steppe and alpine meadow are the main grassland types which widely distribute in Qinghai-Tibetan plateau. It's widely distribution and diverse development environments make it play an important role in the ecosystem: supporting regional economic development, guaranteeing water conservation of the plateau, maintaining biodiversity, fixation of carbon, etc. A quantitative survey of the variation feature of soil inorganic carbon(SIC)stored in warm steppe, alpine steppe, alpine meadow steppe and alpine meadow were carried out in Qinghai province. Results showed that the total storage of SIC in the four types grassland appeared to be warm steppe> alpine steppe> meadow steppe> alpine meadow, and the values were 16.51kgC/m 2 ,16.48 kgC/m 2 ,3.37 kgC/m 2 and 0.12 kgC/m 2 , respectively. One-Way ANOVA analysis indicated that warm steppe、alpine steppe had a significant difference with alpine meadow steppe and alpine meadow( P P > 0.05). The warm steppe and alpine steppe grassland are the main reserve pool of SIC in alpine grassland. The SIC stored in 50-100cm accounted separately for 60.2% and 51.8% of the total storage in 0-100cm profile of the warm steppe and alpine steppe, while in alpine meadow steppe and alpine meadow, it occupied 50.1% and 55.8% respectively of the 30-50cm in 0-50cm. Deep soil layer is the main place of SIC storing in alpine grassland. Soil depth has an important effect on SIC storage in alpine grassland. In 0-50cm depth of the soil, SIC storing in the four types grassland were 6.57 kgC/m 2 ,7.95 kgC/m 2 ,3.37 kgC/m 2 and 0.12 kgC/m 2 , respectively. The change of SIC content with soil depth were different in the four types grassland. It increased with soil depth in warm steppe and alpine meadow steppe, but increased at first then decreased in alpine meadow steppe and alpine meadow. The calcium carbonate enrichment layer in the soil tallied with the foam examination by hydrochloric acid in the soil profile investigation. The calcium carbonate accumulate in the deep soil of steppe, but enrich rather shallow in meadow. SIC storage in the four types of grassland had a significantly positive correlation with soil bulk density and pH value but a significantly negative correlation with underground biomass. The SIC storage increased from south to north in the grassland of Qinghai province and the total SIC storage of the four types grassland reached 1.34 Pg in the profile. The SIC storage in the alpine meadow is very small and it mainly distributed in the south of Qinghai province. Warm steppe which has the largest SIC storage mainly distributed nearby the Qinghai Lake. Climate change and human activity may affect the capacity and distribution of the carbon storage which would bring the ecological risk to the inorganic carbon fixation.

以青海省主要高寒草地类型即温性草原、高寒草原、草甸草原以及高寒草甸为研究对象，进行其土壤无机碳（SIC）储量分异特征研究。结果表明，在取样剖面内四类草地SIC储量依次为温性草原 >高寒草原 >草甸草原 >高寒草甸，其值分别为16.51、16.48 、3.37 kgC/m 2 和0.12 kgC/m 2 ，温性草原与高寒草原土壤是高寒草地无机碳的主要储蓄库。温性草原与高寒草原50-100cm SIC储量分别占0-100cm总储量的60.2%和 51.8%，而草甸草原与高寒草甸30-50cmSIC储量分别占0-50cm总储量的50.1%和55.8%，说明土体下部是高寒草地无机碳储蓄的主要场所。四类草地SIC含量随土层深度的变化过程各异，其碳酸钙富集层与野外剖面调查所得碳酸钙盐酸泡沫检验结果相吻合。SIC储量与土壤容重和土壤pH均呈显著正相关关系，与地下生物量呈显著负相关关系。

The relationships between grazing managements and soil carbon, nitrogen, phosphorus storage and their variations were studied in the degraded alkali-saline grassland by comparative study between fencing and grazing on time series. The results showed that aboveground biomass of degraded grassland decreased by 10.3%, 52.6% and 80.7% after 5, 6 and 8-years continuous grazing, respectively, however, the aboveground biomass of degraded grassland increased by 33.9%, 72.4% and 92.2% after 5, 6 and 8-years fencing, respectively. The underground biomass had similar response with aboveground biomass to grazing managements. Continuous grazing increased the soil pH and bulk density and reduced soil nutrient concentration whereas fencing reduced soil pH and bulk density and increased soil nutrient concentrations. With fencing, organic carbon and total phosphorus storage in surface layer soil gradually increased, however, total nitrogen storage firstly decrease and then increased. With grazing, soil carbon, nitrogen and phosphorus storage in surface layer soil all firstly increased and then decreased. After 5 years for fencing, the soil carbon, nitrogen and phosphorus storage was lower than grazing due to decreasing soil bulk density. The soil organic carbon significantly responded to aboveground biomass which suggested that the aboveground vegetation can be used as an effective indicator for soil carbon storage.

通过时间序列上围封和放牧的对比,研究了退化盐碱草地土壤碳、氮、磷储量及其变化与放牧管理的关系。结果表明,持续放牧5、6、8年后退化草地地上生物量分别降低了10.3%、52.6%和80.7%;而围封5、6、8年后地上退化草地地上生物量分别增加了33.9%、72.4%和92.2%;地下生物量对放牧管理的响应趋势与地上生物量相同。持续放牧增加了土壤pH和容重,降低了土壤养分浓度;围封对土壤pH、容重和土壤养分浓度的作用与放牧相反。围封后,表层土壤有机碳和总磷储量逐渐增加,总氮储量先降低后增加。然而放牧下,表层土壤碳、氮、磷储量均表现为先增加后降低。由于土壤容重的降低,封育5年后,围封地土壤碳、氮、磷储量要低于放牧地。土壤碳储量的变化对地上生物量的变化响应显著,因此,地上植被的变化能作为土壤碳储量有效的指示因子。

In order to evaluate the carbon source/carbon sink function of grassland and explore the sustainable grassland management measures, the combined methods of field sampling and laboratory analysis were employed to analyze the variation of soil organic carbon (SOC) and soil microbial biomass carbon (SMBC) in Xilingol typical grassland in Inner Mongolia. The effects of different management and grazing measures on the distribution and carbon reserves of SOC and SMBC were discussed. The studied measures included fenced enclosure for 29 years (WF29), fenced enclosure for 8 years (WF8), filling-up Medicago sativa (RA), filling-up Leymus chinensis (RC), and three grazing measures . The surface soil layer was higher carbon pool because the SOC and SMBC in the soil profile decreased with soil depth increasing. The SOC and SMBC of WF8 and WF29 were higher than that of HG in root system soil layer (0-30 cm). There were significantly positive effects of WF8 management on SMBC and SOC. There was significantly positive correlation ( P <0.05) between SOC and SMBC. The variations of SMBC not only reflect the changes of SOC, but aslo reflect the changes of soil organic carbon pool. The total SOC and SMBC carbon reserves were 788.84 Gg C and 9.47 Gg C in Xilinhot, respectively. The SOC and SMBC carbon reserves were highest under fenced enclosure for 8 years (661.76 Gg C, 6.76 Gg C), and lowest under the artificial filling-up measures (0.61 Gg C, 5.73 t C). SOC and SMBC were the indicators of soil fertility and soil quality and important evaluation index of grassland carbon sink.

为评估草地的碳源/汇功能, 探索可持续发展的草地管理措施, 以内蒙古锡林郭勒典型草原为研究区域, 采用野外调查取样结合室内分析的方法, 分析了土壤有机碳(Soil Organic Carbon, SOC)和土壤微生物量碳(Soil Microbial Biomass Carbon, SMBC)的变化规律, 探讨了围栏封育29年(WF29)、围栏封育8年(WF8)、补播苜蓿( Medicago sativa )(RA)、补播羊草( Leymus chinensis )(RC)、以及轻度放牧(LG)、中度放牧(MG)和重度放牧(HG)共7种处理对SOC和SMBC分布的影响以及草地SOC和SMBC碳库储量的大小。结果表明, 从土壤剖面来看, SOC、SMBC含量在土壤表层较高, 为草地的主要碳库, 随着土壤深度的增加呈现降低的趋势。土壤根系层(0－30 cm)中, WF8、WF29、RA、RC、LG和MG的SOC和SMBC均高于HG, 其中WF8正效应较为明显, 有利于提高SMBC与SOC含量。SOC与SMBC呈显著正相关关系( P <0.05)。可以通过SMBC的变化反映SOC的变化, 进而反映SOC碳库的变化。经估算, 锡林浩特市草地0－30 cm总的SOC和SMBC碳储量分别为788.86和9.48 Gg。其中, 围封8年的SOC和SMBC碳储量的值都为最高, 分别为661.76和6.76 Gg, 人工种草措施的值均为最低, 分别为0.61 Gg和5.73 t。SOC和SMBC含量对于土壤肥力和土壤品质变化有指示作用, 可作为草地碳汇的重要评估指标。

Carbon sequestration in the grassland ecosystems has important effects on the global carbon stocks. Grazing as one of the most widely land usage methods affects carbon sequestration in the grassland.However, unreasonable and over-grazing can lead to grassland degradation which has negative effects on carbon stocks in the grassland. Livestock enclosure and grazing affect carbon sequestration in the grassland by altering the vegetation productions and soil carbon stocks. This review indicated that livestock exclosure and grazing had positive or negative effects on the vegetation production which were affected by some other factors and their interaction, such as aboveground litter, vegetation structure, climate conditions, and so on. The effects of grazing on vegetation production were also related to the grazing intensity. Livestock exclosure and grazing had positive or negative effects on soil carbon stocks by affecting many processes in the soil carbon cycling. In summary, the effects of livestock exclosure and grazing on carbon sequestration in grassland were complicated. In order to make the scientific decision on grassland managements,the estimations of carbon stocks and researches on the related mechanisms are necessary in the further study.

草地生态系统固碳能力对全球碳贮量的大小有重要影响。放牧作为草地最广泛的利用方式之一影响着草地的碳贮量,过度和不合理的放牧方式造成草地退化,引起草地碳的损失。围栏禁牧与放牧对草地生态系统固碳能力的影响主要包括对植被生产力和土壤碳贮量的影响,本文对有关的报道进行了综述。结果显示,由于受植被凋落物、群落结构和气候等多因素的影响,围栏禁牧对草地植被生产力有正面或负面的效应;放牧对植被生产力的影响也没有一致的结果,此外,放牧对植被生产力的影响还与放牧的强度有关。围栏禁牧与放牧可以通过多种途径对草地土壤碳贮量产生正面或负面的影响。总之,围栏禁牧与放牧对草地生态系统固碳能力的影响是复杂多样的,需要对草地碳贮量进行估算,并对相关的机制进行研究,这样才能在草地管理方面做出合理的决策。

A study was conducted in fenced grassland (F, fenced for 7 years) and grazed grassland (G) on the Loess Plateau to investigate the seasonal variation of the contents of soil ammonium nitrogen(N-N) and nitrate nitrogen (N-N). Redundancy analysis was also used to study the effects of soil water content, above-ground green biomass and microbial biomass carbon on N-N and N-N contents. The results showed that N-N was the main component of soil available nitrogen in both fenced and grazed grasslands. In the 0-10 cm soil layers of the two sites, soil N-N and nitrate nitrogen were mainly controlled by above-ground green biomass. In the 10-20 cm soil layers, soil N-N and nitrate nitrogen were mainly controlled by both of soil water content and above-ground green biomass in fenced grassland, while soil N-N and N-N were mainly controlled by above-ground green biomass in grazed grassland. There was significantly positive correlations ( P <0.05) between N-N and N-N in the two sites. The results indicated that the higher above-ground biomass after fencing for 7 years increased litter inputs and soil organic matter, thus increased substrate for nitrogen mineralization. In addition, soil water content significantly increased in most seasons ( P <0.05) and all of these factors promoted the nitrogen mineralization in the soil.

本研究以黄土高原长期放牧草地和围封7年的草地为对象,分析了土壤铵态氮和硝态氮含量的季节变化,并应用RDA冗余分析法分析了土壤水分、植被地上绿色生物量以及土壤微生物生物量碳对土壤铵态氮、硝态氮的影响。结果表明,铵态氮是围封与放牧草地土壤有效氮的主要组分;两样地0-10 cm土层土壤铵态氮与硝态氮均主要受植被地上绿色生物量的影响;围封草地10-20 cm土层土壤硝态氮主要受土壤水分与植被地上绿色生物量的共同影响,而放牧草地10-20 cm土壤铵态氮和硝态氮主要受植被地上绿色生物量的影响;土壤铵态氮与硝态氮之间呈极显著正相关( P <0.01);放牧草地围封7年后,较高的生物量使得凋落物及土壤有机质增加;另外,围封后土壤水分在多数季节显著增加( P <0.05),这些因素共同促进了土壤氮素的矿化。