Plant Communities,Soil Carbon,and Soil Nitrogen Properties in a Successional Gradient of Sub-Alpine Meadows on the Eastern Tibetan Plateau of China

To assess the recovery trajectory and self-maintenance of restored ecosystems, a successional gradient (1, 3, 5, 15, and 30 years after abandonment) was established in a sub-alpine meadow of the eastern Tibetan Plateau in China. Plant communities and soil carbon and nitrogen properties were investigated and analyzed. Regression analyses were used to assess the models (linear or quadratic) relating measures of species richness, soil carbon and nitrogen properties to fallow time. We found that species richness (S) increased over the first 20 years but decreased thereafter, and aboveground biomass showed a linear increase along the fallow time gradient. The richness of different functional groups (forb, grass and legume) changed little along the fallow time gradient, but their corresponding above ground biomass showed the U-shaped, humped or linear pattern. Soil microbial carbon (MBC) and nitrogen (MBN) in the upper 20 cm showed a U-shaped pattern along the fallow time gradient. However, soil organic carbon (C_org) and total nitrogen (TN) in the soil at depth greater than 20 cm showed significant patterns of linear decline along the fallow time gradient. The threshold models of species richness reflected best the recovery over the 15 year fallow period. These results indicated that fallow time had a greater influence on development of the plant community than soil processes in abandoned fields in sub-alpine meadow ecosystem. These results also suggested that although the succession process did not significantly increase soil C, an increase in microbial biomass at the latter stage of succession could promote the decomposability of plant litter. Therefore, abandoned fields in sub-alpine meadow ecosystem may have a high resilience and strong rehabilitating capability under natural recovery condition.     

Effects of Recreational Impacts on Soil Microbial Communities

/ The functional diversity of soil microbial communities in heavilyimpacted subalpine campsites and adjacent undisturbed areas was comparedusing the Biolog method of carbon utilization profiles. Principal componentsanalysis of patterns and level of microbial activity indicate that microbialcommunities differentiate in response to disturbance in the top 6 cm of soil,while below 6 cm there were no recognizable differences between disturbed andundisturbed soil communities. Analysis of the factors that differentiate theupper microbial communities between disturbed and undisturbed sites revealedthat the percent of total carbon sources utilized was significantly less inthe disturbed (54%) than in undisturbed areas (95%). Carbonsubstrates important in the discrimination between soil communities includeplant, invertebrate, and microbial derivatives that could not be metabolizedby microbial communities from disturbed sites. Comparisons of totalculturable actinomycetes, bacteria, and fungi reveal no difference in overallnumber of colony forming units (CFU) on disturbed and undisturbed sites, buta marked decrease in actinomycetes on disturbed sites. Biolog andspread-plate data combined indicate a shift in the structure and function ofthe microbial community in campsite soils, which may be a useful indicator ofsoil community disturbance.KEY WORDS: Microbial functional diversity; Anthropogenic disturbance;Recreational impacts; Carbon source profile; Subalpine     

Quantifying the Effects of Conservation Practices on Soil,Water, and Nutrients in the Loess Mesa Ravine Region of the Loess Plateau,China

A large number of soil and water conservation programs have been implemented on the Loess Plateau of China since the 1950s. To comprehensively assess the merits and demerits of the conservation practices is of great importance in further supervising the conservation strategy for the Loess Plateau. This study calculates the impact factors of conservation practices on soil, water, and nutrients during the period 1954–2004 in the Nanxiaohegou Catchment, a representative catchment in the Loess Mesa Ravine Region of the Loess Plateau, China. Brief conclusions could be drawn as follows: (1) Soil erosion and nutrient loss had been greatly mitigated through various conservation practices. About half of the total transported water and 94.8 % of the total transported soil and nutrients, had been locally retained in the selected catchment. The soil retained from small watersheds do not only form large-scale fertile farmland but also safeguard the Yellow River against overflow. (2) Check dam was the most appropriate conservation practice on the Loess Plateau. In the selected catchment, more than 90 % of the retained soil and water were accomplished by the dam farmland, although the dam farmland occupied only 2.3 % of the total area of all conservation measures. Retention abilities of the characteristic conservation practices were in the following order: dam farmland > terrace farmland > forest land and grassland. (3) The conservation practices were more powerful in retaining sediment than in reducing runoff from the Loess Plateau, and the negative effects of the conservation practices on reducing water to the Yellow River were relatively slight.     

Germinable Soil Seed Banks and the Restoration Potential of Abandoned Cropland on the Chinese Hilly-Gullied Loess Plateau

Poor vegetation cover is generally considered to be a major factor causing soil erosion on the Loess Plateau in China. It has been argued that tree planting restoration is ineffective, and natural re-vegetation is an alternative ecological solution for restoring abandoned cropland and controlling soil erosion. The aims of this study were to investigate the characteristics of soil seed banks and to assess the natural restoration potential of abandoned cropland in the hilly-gullied Loess Plateau. The soil seed bank was identified by the germination method with the soil samples, which were collected at four sampling times (April, August, and October 2005 and August 2006) from 12 plots abandoned 3–30 years prior to sampling. The seed bank densities of all of the samples in the 0–10 cm soil layer varied from 1,067 ± 225 to 14,967 ± 1,606 seeds m⁻². Fifty-one species (24 annual and 27 perennial species) belonging to 18 families were identified, and 39% of these species belonged to the families Compositae and Gramineae. The pioneer species Artemisia scoparia dominated the seed bank, with an average seed density of 3,722 seeds m⁻², and accounted for 74.4% of the seeds in the bank. The local dominant species (such as Lespedeza davurica, Artemisia gmelinii, Bothriochloa ischaemun and Stipa bungeana) of the later succession stages also existed at densities varying from 17 to 1, 383 seeds m⁻². The combination of soil seed bank characteristics, reproductive traits of the species, the specific landscape conditions indicates that the potential to restoring the abandoned croplands in the hilly-gullied Loess Plateau via natural re-vegetation could be substantial.     

氮素和水分对贝加尔针茅草原土壤酶活性和微生物量碳氮的影响

在内蒙古贝加尔针茅草原,分别设对照（N0）、1.5 g·m^-2（N15）、3.0 g·m^-2（N30）、5.0 g·m^-2（N50）、10.0 g·m^-2（N100）、15.0 g·m^-2（N150）、20.0 g·m^-2（N200）和30 g·m^-2（N300）（不包括大气沉降的氮量）8个氮素（NH4NO3）梯度和模拟夏季增加降水100 mm的水分添加交互试验,研究氮素和水分添加对草原土壤养分、酶活性及微生物量碳氮的影响。结果表明：氮素和水分添加对草原土壤理化性质和生物学特性有显著影响。随施氮量的增加土壤总有机碳、全氮、硝态氮、铵态氮含量呈增加的趋势,相反,土壤pH值呈降低的趋势。土壤脲酶和过氧化氢酶的活性随施氮量的增加而升高,多酚氧化酶则随施氮量的增加呈下降的趋势。氮素和水分添加对草原土壤微生物量碳氮含量有显著影响,高氮处理（N150、N200和N300）显著降低了微生物碳含量,微生物氮含量随施氮量的增加呈上升趋势。水分添加能够减缓氮素添加对微生物的抑制作用,提高微生物量碳、微生物量氮含量。草原土壤养分、土壤酶活性及土壤微生物量碳氮含量间关系密切,过氧化氢酶与全氮、总有机碳、硝态氮呈显著正相关,多酚氧化酶与铵态氮、硝态氮、全氮呈显著负相关。微生物量氮含量与土壤全氮、铵态氮、硝态氮含量以及过氧化氢酶和磷酸酶活性呈显著正相关,与多酚氧化酶呈负相关;微生物量碳与过氧化氢酶呈负相关,与多酚氧化酶活性呈正相关。     

沼渣连续施用对土壤微生物量碳、氮剖面分布的影响

通过"棉花+小麦"轮作施用沼渣的定位试验,研究不同年限的沼渣施用对土壤剖面微生物量C、N(MBC、MBN)分布特征的影响。结果表明:在0~50cm剖面上,施用沼渣1年对0~30cm土壤的MBC、MBN影响较大,能显著提高30~40cm土层土壤MBC、MBN的含量,施用沼渣5年时对40~50cm土层MBC、MBN无明显影响。土壤MBC、MBN含量总体随施用沼渣年限的延长而增加,各土层MBC、MBN含量增幅随着施用年限的延长呈现不同趋势。施用沼渣1年,耕层土壤的MBC/MBN值较习惯耕作增加,施用沼渣3年后,其值呈降低趋势。各土层的MBC/TOC、MBN/TN和MBC的变化趋势基本一致,总体随着沼渣施用年限的延长而增加。针对"棉花+小麦"轮作模式,持续施用沼渣3年更有利于改善0~40cm土层土壤肥力。     

Effects of Grazing Exclusion on Soil Properties and on Ecosystem Carbon and Nitrogen Storage in a Sandy Rangeland of Inner Mongolia, Northern China

The Horqin sandy rangeland of northern China is a seriously desertified region with a fragile ecology. The sandy alluvial and aeolian sediments have a coarse texture and loose structure and are therefore vulnerable to damage caused by grazing animals and wind erosion. We investigated whether grazing exclusion could enhance ecosystem carbon (C) and nitrogen (N) storage and thereby improve overall soil quality. We compared soil properties, C and N storage in biomass (aboveground and below-ground), and the total and light fraction soil organic matter between adjacent areas with continuous grazing and a 12-year grazing exclosure. The soil silt?+?clay content, organic C, total Kjeldahl N, available N and K, and cation-exchange capacity were significantly (P?相似文献   

两种不同生态区坡改梯对土壤氮磷含量影响的研究

分别在干热河谷生态区和华西雨屏生态区的坡改梯地区设置试验小区和对照试验区,通过采集土壤样品进行室内分析,研究在不同的坡位、不同的季节变化下两种生态区实施坡改梯措施对土壤养分保持的效果.干热河谷生态区以清溪小流域为例,华西雨屏生态区以凤鸣小流域为例.试验结果表明,在两个生态区的坡改梯工程试验区,空间上,各个坡位氮磷养分的...     

Effect of Rainfall Regime and Slope on Runoff in a Gullied Loess Region on the Loess Plateau in China

Runoff was measured from seven plots with different slopes nested in Tuanshangou catchment on the Loess Plateau to study effect of slopes on runoff in relation to rainfall regimes. Based on nine years of field observation and K-mean clusters, 84 rainfall events were grouped into three rainfall regimes. Rainfall regime A is the group of events with strong rainfall intensity, high frequency, and short duration. Rainfall regime C consists of events with low intensity, long duration, and infrequent occurrence. Rainfall regime B is the aggregation of events of medium intensity and medium duration, and less frequent occurrence. The following results were found: (1) Different from traditional studies, runoff coefficient neither decreased nor increased, but presented peak value on the slope surfaces; (2) For individual plot, runoff coefficients induced by rainfall regime A were the highest, and those induced by rainfall regime C were the lowest; Downslope, the runoff coefficients induced by three rainfall regimes presented the same changing trend, although the peak value induced by regime A occurred on a shorter slope length compared to those by regime B and C; (3) Scale effect on runoff induced by rainfall regime A was the least, and that induced by rainfall regime C was the largest. These results can be explained by the interactions of crusting, soil moisture content, slope length and gradient, and erosion units, etc., in the context of different rainfall regimes.     

Spatial Dynamics of Soil Moisture in a Complex Terrain in the Semi‐Arid Loess Plateau Region,China1

Abstract: Soil moisture is an important hydrological variable in reforestation practices in a water‐limited region of the Loess Plateau of northwestern China. The objective of this study was to quantify the spatial dynamics of soil moisture on a complex terrain. During 2004‐2006, a total of 313 sample points in two kinds of grid (2 × 2 m and 20 × 20 m) were arranged for soil moisture measurements (two soil layers: 0‐30 and 30‐60 cm) with Time Domain Reflectometry. The geostatistical properties of soil moisture patterns, the variance and correlation structure of the soil moisture, and the effects of terrain factors on soil moisture were analyzed. The results suggested that our sampling grid captured the spatial variability of soil moisture distributions for this complex terrain. Principal Component Analysis and Cluster Analysis statistics showed that soil moisture decreased as slope gradient increased; that sunny aspects (112.5°‐292.5°) had relatively lower soil moisture than did shady aspects (292.5°‐112.5°); that soil moisture was lowest in the SWW direction and highest in the NWN direction; and that hillslope aspect was the main factor affecting soil moisture in the 0‐ to 30‐cm soil layer, whereas the main factor for the 30‐ to 60‐cm layer was slope gradient. It was found that the relative values of soil moisture for steep slopes (>36%) with shady aspect (292.5°‐112.5°), gentle slopes (<36%) with sunny aspect (112.5°‐292.5°), and steep slopes with sunny aspect were 99, 82, and 80, respectively – assuming a soil moisture value of 100 for gentle slopes with shady aspect. The results of this study are expected to be relevant to and useful for reforestation planning and design, parameterization of distributed hydrology models, and land productivity assessment in the study region.     

Evaluation of the MIKE SHE Model for Application in the Loess Plateau,China1

Abstract: Quantifying the hydrologic responses to land use/land cover change and climate variability is essential for integrated sustainable watershed management in water limited regions such as the Loess Plateau in Northwestern China where an adaptive watershed management approach is being implemented. Traditional empirical modeling approach to quantifying the accumulated hydrologic effects of watershed management is limited due to its complex nature of soil and water conservation practices (e.g., biological, structural, and agricultural measures) in the region. Therefore, the objective of this study was to evaluate the ability of the distributed hydrologic model, MIKE SHE to simulate basin runoff. Streamflow data measured from an overland flow‐dominant watershed (12 km²) in northwestern China were used for model evaluation. Model calibration and validation suggested that the model could capture the dominant runoff process of the small watershed. We found that the physically based model required calibration at appropriate scales and estimated model parameters were influenced by both temporal and spatial scales of input data. We concluded that the model was useful for understanding the rainfall‐runoff mechanisms. However, more measured data with higher temporal resolution are needed to further test the model for regional applications.     

Changes in Soil Aggregate,Carbon, and Nitrogen Storages Following the Conversion of Cropland to Alfalfa Forage Land in the Marginal Oasis of Northwest China

Maintenance of soil organic carbon (SOC) is important for sustainable use of soil resources due to the multiple effects of SOC on soil nutrient status and soil structural stability. The objective of this study was to identify the changes in soil aggregate distribution and stability, SOC, and nitrogen (N) concentrations after cropland was converted to perennial alfalfa (Medicago sativa L. Algonguin) grassland for 6 years in the marginal oasis of the middle of Hexi Corridor region, northwest China. Significant changes in the size distribution of dry-sieving aggregates and water-stable aggregates, SOC, and N concentrations occurred after the conversion from crop to alfalfa. SOC and N stocks increased by 20.2% and 18.5%, respectively, and the estimated C and N sequestration rates were 0.4 Mg C ha⁻¹ year⁻¹ and 0.04 Mg N ha⁻¹ year⁻¹ following the conversion. The large aggregate (>5 mm) was the most abundant dry aggregate size fraction in both crop and alfalfa soils, and significant difference in the distribution of dry aggregates between the two land use types occurred only in the >5 mm aggregate fraction. The percentage of water-stable macroaggregates (>2, 2–0.25 mm) and aggregate stability (mean weight diameter of water-stable aggregates, WMWD) were significantly higher in alfalfa soils than in crop soils. There was a significant linear relationship between total SOC concentration and aggregate parameters (mean weight diameter) for alfalfa soils, indicating that aggregate stability was closely associated with increased SOC concentration following the conversion of crops to alfalfa. The SOC and N concentrations and the C/N ratio were greatest in the >2 mm water-stable aggregates and the smallest in the 0.25–0.05 mm aggregates in crop and alfalfa soils. For the same aggregate, SOC and N concentrations in aggregate fractions increased with increasing total SOC and N concentrations. The result showed that the conversion of annual crops to alfalfa in the marginal land with coarse-texture soils can significantly increase SOC and N stocks, and improve soil structure.     

Towards Sustainable Integrated Watershed Ecosystem Management: A Case Study in Dingxi on the Loess Plateau, China

The Chinese government initiated a massive conservation program called “Grain-for-Green” in 1999 to reduce soil erosion and improve ecosystem function. Implementing practical sustainable development in the loess plateau still remains problematic, particularly in its eco-fragile areas. Here we discussed an approach for sustainable development at the watershed scale by integrating land use suitability, ecosystem services and public participation in the loess hilly area. We linked land use scenario analysis and economic modeling to compare the outcomes of three scenarios, CLU (Current Land Use), GOLU (Grain-production Oriented Land Use) and PSLU (Potential Sustainable Land Use). The results indicated that compared to PSLU, GOLU may provide a higher economic productivity in the short-term, but not in the long-term. CLU ranked lowest in terms of economic benefits and did not meet the daily needs of the local farmers. To reconcile the land use adjustments with farmers’ basic needs, a labor-saving land use strategy is necessary. Since the PSLU scenario assumes that slope cropland should be converted to pastures or orchards, more time may be available for off-farm work and for more public participation in integrated ecosystem management. Financial support to the local farmers for environmental conservation should be modulated in function of their positive contribution to ecosystem management.     

Evaluating and Extending CLIGEN Precipitation Generation for the Loess Plateau of China1

Abstract: Climate generator (CLIGEN) is widely used in the United States to generate long‐term climate scenarios for use with agricultural systems models. Its applicability needs to be evaluated for use in a new region or climate. The objectives were to: (1) evaluate the reproducibility of the latest version of CLIGEN v5.22564 in generating daily, monthly, and yearly precipitation depths at 12 stations, as well as storm patterns including storm duration (D), relative peak intensity (ip), and peak intensity (rp) at 10 stations dispersed across the Loess Plateau and (2) test whether an exponential distribution for generating D and a distribution‐free approach for inducing desired rank correlation between precipitation depth and D can improve storm pattern generations. Mean absolute relative errors (MAREs) for simulating daily, monthly, annual, and annual maximum daily precipitation depth across all 12 stations were 3.5, 1.7, 1.7, and 5.0% for the mean and 5.0, 4.5, 13.0, and 13.6% for the standard deviations (SD), respectively. The model reproduced the distributions of monthly and annual precipitation depths well (p > 0.3), but the distribution of daily precipitation depth was less well produced. The first‐order, two‐state Markov chain algorithm was adequate for generating precipitation occurrence for the Loess Plateau of China; however, it underpredicted the longest dry periods. The CLIGEN‐generated storm patterns poorly. It underpredicted mean and SD of D for storms ≥10 mm by ?60.4 and ?72.6%, respectively. Compared with D, ip, and rp were slightly better reproduced. The MAREs of mean and SD were 21.0 and 52.1% for ip, and 31.2 and 55.2% for rp, respectively. When an exponential distribution was used to generate D, MAREs were reduced to 2.6% for the mean and 7.8% for the SD. However, ip estimation became much worse with MAREs being 128.9% for the mean and 241.1% for the SD. Overall, storm pattern generation needs improvement. For better storm pattern generation for the region, precipitation depth, D, and rp may be generated correlatively using Copula methods.     

黄土高原地区石油类非点源污染试验研究

石油类非点源污染基本特征为污染源分散、污染源作用周期长、暴雨时易于形成高含沙水流以及由此引发的高强度石油类污染。试验结果表明,随土壤石油污染强度的提高,径流量增大,产沙量降低,但水、固两相中的污染物径流污染强度均增大。试验条件下,径流过程释放于水相中的石油类浓度可高达4～7 mg/L。     

Long‐Term Streamflow Response to Climatic Variability in the Loess Plateau,China1

Abstract: The Loess Plateau region in northwestern China has experienced severe water resource shortages due to the combined impacts of climate and land use changes and water resource exploitation during the past decades. This study was designed to examine the impacts of climatic variability on streamflow characteristics of a 12‐km² watershed near Tianshui City, Gansu Province in northwestern China. Statistic analytical methods including Kendall’s trend test and stepwise regression were used to detect trends in relationship between observed streamflow and climatic variables. Sensitivity analysis based on an evapotranspiration model was used to detect quantitative hydrologic sensitivity to climatic variability. We found that precipitation (P), potential evapotranspiration (PET) and streamflow (Q) were not statistically significantly different (p > 0.05) over the study period between 1982 and 2003. Stepwise regression and sensitivity analysis all indicated that P was more influential than PET in affecting annual streamflow, but the similar relationship existed at the monthly scale. The sensitivity of streamflow response to variations of P and PET increased slightly with the increase in watershed dryness (PET/P) as well as the increase in runoff ratio (Q/P). This study concluded that future changes in climate, precipitation in particular, will significantly impact water resources in the Loess Plateau region an area that is already experiencing a decreasing trend in water yield.     

不同碳氮源对双孢蘑菇2796深层发酵的影响

碳源和氮源是食用菌生长发育过程中不可缺少的营养物质.通过单因子试验研究了液体培养中4种碳源和4种氮源对双孢菇菌丝体生物量、胞内多糖、胞外蛋白、酶活性的影响.结果表明,对菌丝生物量而言,可溶性淀粉是最适的碳源,玉米粉是最适的氮源;对产胞外蛋白而言,葡萄糖是最适的碳源,蛋白胨是最适的氮源;对产过氧化物酶、淀粉酶和多酚氧化酶而言,蔗糖是最适的碳源,酵母粉是最适的氮源.该试验为进一步研究双孢蘑菇的营养生理奠定了基础,为生产上选择优良的母种培养基及开发利用双孢蘑菇深层培养生产代谢产物资源提供了科学依据.     

华东地区碳源、碳汇和碳生产力研究

从碳源、碳汇和碳生产力的角度深入研究了华东地区6省1市2005-2011年之间低碳经济发展现状,采用变异系数和空间自相关等分析方法对该地区碳源、碳汇和碳生产力差异大小及其空间聚集特性进行了分析,以期为分析华东地区乃至全国低碳经济发展现状和趋势提供借鉴.     

黄土高原地区生态旅游开发的优势及前景分析

黄土高原地区生态环境非常脆弱,该区进行旅游开发必须以生态旅游为指导。该区自然和人文旅游资源丰富而独特,开发生态旅游具有类型多样、功能齐全、有利于组合开发的资源优势;西部大开发、中部崛起战略为其提供了政策优势,同时该区劳动力资源丰富,因此开发生态旅游优势明显。分析了黄土高原地区生态旅游开发的国际、国内及区域市场前景,提出了在该区进行生态旅游开发应注意的问题。