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1. chinaXiv:201810.00125 [pdf]

克拉玛依市冬季飞机人工增雪作业效果统计分析

李斌; 郑博华; 兰文杰
分类: 地球科学 >> 大气科学

利用克拉玛依区气象站1957—2016年历年12月降水量观测资料,运用序列检验、不成对秩和检验以及t-检验法等统计学方法,对开展冬季飞机人工增雪作业前历史期31 a和作业期29 a的年12月降水量作为统计变量,进行系统性差异分析。结果表明:开展冬季飞机人工增雪作业后克拉玛依市冬季12月降水量明显增加,降水量平均值增加了2 mm。运用非参数性不成对秩和检验显著性水平达到0.025,参数性t-检验显著性水平也接近0.025。选取统计显著性水平0.1置信区间,计算得,冬季开展飞机人工增雪作业后,克拉玛依市平均年12月降水量绝对增加值为1.15 mm,相对增加率为24.5%。从而得出:开展冬季飞机人工增雪作业后,克拉玛依市冬季降水量有了明显增加。

提交时间: 2018-10-23 来自合作期刊:《干旱区地理》 点击量4下载量0 评论 0

2. chinaXiv:201810.00126 [pdf]

不对称性相互依赖背景下中吉自由贸易实现路径——基于局部均衡理论的模拟

高志刚
分类: 地球科学 >> 地球科学其他学科

不对称性相互依赖是中国和吉尔吉斯斯坦经贸合作的常态,中吉自由贸易是丝绸之路经济带互联互通战略的重要组成部分,也是我国向西开展自贸区进程的突破点。文章运用局部均衡模型从BEC产品层面模拟分析了不同关税策略下中吉自贸区的贸易效应及本国经济效应。研究表明:在相同的关税削减幅度的情形下,2002—2016年间中吉贸易效应与其贸易额呈正相关;关税削减对中国和吉尔吉斯斯坦的贸易效应、福利效应及关税损失比较显著,尤其是中国,且对不同商品的影响存在显著差异,其中尤以工业品最为显著;综合考量贸易效应和福利效应,中国的最优策略是直接采取零关税,而吉国则是逐渐削减关税。

提交时间: 2018-10-23 来自合作期刊:《干旱区地理》 点击量2下载量0 评论 0

3. chinaXiv:201810.00121 [pdf]

克拉玛依市冬季飞机人工增雪作业效果统计分析

李斌; 郑博华; 兰文杰; 杨琳
分类: 地球科学 >> 地理学

利用克拉玛依区气象站1957—2016年历年12月降水量观测资料,运用序列检验、不成对秩和检验以及t-检验法等统计学方法,对开展冬季飞机人工增雪作业前历史期31 a和作业期29 a的年12月降水量作为统计变量,进行系统性差异分析。结果表明:开展冬季飞机人工增雪作业后克拉玛依市冬季12月降水量明显增加,降水量平均值增加了2 mm。运用非参数性不成对秩和检验显著性水平达到0.025,参数性t-检验显著性水平也接近0.025。选取统计显著性水平0.1置信区间,计算得,冬季开展飞机人工增雪作业后,克拉玛依市平均年12月降水量绝对增加值为1.15 mm,相对增加率为24.5%。从而得出:开展冬季飞机人工增雪作业后,克拉玛依市冬季降水量有了明显增加。

提交时间: 2018-10-19 来自合作期刊:《干旱区地理》 点击量20下载量6 评论 0

4. chinaXiv:201809.00163 [pdf]

Suppression of weeds and weed seeds in the soil by stubbles and no-tillage in an arid maize-winter wheat-common vetch rotation on the Loess Plateau of China

YANG, Mei; ZHAO, Yuxin; YANG, Huimin; SHEN, Yuying; ZHANG, Xiaoyan
分类: 地球科学 >> 地球科学史

Reduced tillage provides ecological and economic benefits to arable land on the Loess Plateau of China, where soil erosion has long been a serious problem and soil water availability is largely restricted. However, high abundances of weeds in reduced tillage systems cause significant yield losses. In this study, we explored the effects of no-tillage and stubble retention on the number and density of weeds and weed seeds in a 12-year maize-winter wheat-common vetch rotation on the Loess Plateau. Four treatments including conventional tillage, no-tillage, conventional tillage+stubble retention and no-tillage+stubble retention were designed and applied. We found that no-tillage increased the number of weed species and weed density in most of the crops, while stubble retention decreased weed density in maize and tended to suppress weeds in both no-tillage treatments (no-tillage and no-tillage+stubble retention). No-tillage led to an increase in the number of weed species in the weed seedbank and tended to increase seed density during the spring growth of winter wheat, but it decreased seed density during post-vetch fallow. Stubble retention tended to reduce seed density during the spring growth of winter wheat and post-vetch fallow. We concluded that no-tillage can promote weeds in the experimental crop rotation, while stubble retention suppresses weeds in untilled fields. The combined effects of stubble retention and no-tillage on weed suppression varied among the three crops. Based on these results, we recommend stubble retention in untilled legume-crop rotations on the Loess Plateau to improve the control of weeds.

提交时间: 2018-09-18 来自合作期刊:《Journal of Arid Land》 点击量695下载量97 评论 0

5. chinaXiv:201809.00164 [pdf]

Mulching mode and planting density affect canopy interception loss of rainfall and water use efficiency of dryland maize on the Loess Plateau of China

ZHENG Jing; FAN Junliang; ZHANG Fucang; YAN Shicheng; GUO Jinjin; CHEN Dongfeng; LI Zhijun
分类: 地球科学 >> 地球科学史

High and efficient use of limited rainwater resources is of crucial importance for the crop production in arid and semi-arid areas. To investigate the effects of different soil and crop management practices (i.e., mulching mode treatments: flat cultivation with non-mulching, flat cultivation with straw mulching, plastic-covered ridge with bare furrow and plastic-covered ridge with straw-covered furrow; and planting density treatments: low planting density of 45,000 plants/hm2, medium planting density of 67,500 plants/hm2 and high planting density of 90,000 plants/hm2) on rainfall partitioning by dryland maize canopy, especially the resulted net rainfall input beneath the maize canopy, we measured the gross rainfall, throughfall and stemflow at different growth stages of dryland maize in 2015 and 2016 on the Loess Plateau of China. The canopy interception loss was estimated by the water balance method. Soil water storage, leaf area index, grain yield (as well as it components) and water use efficiency of dryland maize were measured or calculated. Results showed that the cumulative throughfall, cumulative stemflow and cumulative canopy interception loss during the whole growing season accounted for 42.3%–77.5%, 15.1%–36.3% and 7.4%–21.4% of the total gross rainfall under different treatments, respectively. Soil mulching could promote the growth and development of dryland maize and enhance the capability of stemflow production and canopy interception loss, thereby increasing the relative stemflow and relative canopy interception loss and reducing the relative throughfall. The relative stemflow and relative canopy interception loss generally increased with increasing planting density, while the relative throughfall decreased with increasing planting density. During the two experimental years, mulching mode had no significant influence on net rainfall due to the compensation between throughfall and stemflow, whereas planting density significantly affected net rainfall. The highest grain yield and water use efficiency of dryland maize were obtained under the combination of medium planting density of 67,500 plants/hm2 and mulching mode of plastic-covered ridge with straw-covered furrow. Soil mulching can reduce soil evaporation and retain more soil water for dryland maize without reducing the net rainfall input beneath the maize canopy, which may alleviate the contradiction between high soil water consumption and insufficient rainfall input of the soil. In conclusion, the application of medium planting density (67,500 plants/hm2) under plastic-covered ridge with bare furrow is recommended for increasing dryland maize production on the Loess Plateau of China.

提交时间: 2018-09-18 来自合作期刊:《Journal of Arid Land》 点击量669下载量86 评论 0

6. chinaXiv:201809.00165 [pdf]

Estimation of net primary productivity and its driving factors in the Ili River Valley, China

JIAO, Wei; CHEN, Yaning; LI, Weihong; ZHU, Chenggang; LI, Zhi
分类: 地球科学 >> 地球科学史

Net primary productivity (NPP), as an important variable and ecological indicator in grassland ecosystems, can reflect environmental change and the carbon budget level. The Ili River Valley is a wetland nestled in the hinterland of the Eurasian continent, which responds sensitively to the global climate change. Understanding carbon budget and their responses to climate change in the ecosystem of Ili River Valley has a significant effect on the adaptability of future climate change and sustainable development. In this study, we calculated the NPP and analyzed its spatio-temporal pattern of the Ili River Valley during the period 2000–2014 using the normalized difference vegetation index (NDVI) and an improved Carnegie-Ames-Stanford (CASA) model. Results indicate that validation showed a good performance of CASA over the study region, with an overall coefficient of determination (R2) of 0.65 and root mean square error (RMSE) of 20.86 g C/(m2•a). Temporally, annual NPP of the Ili River Valley was 599.19 g C/(m2•a) and showed a decreasing trend from 2000 to 2014, with an annual decrease rate of –3.51 g C/(m2•a). However, the spatial variation was not consistent, in which 55.69% of the areas showed a decreasing tendency, 12.60% of the areas remained relatively stable and 31.71% appeared an increasing tendency. In addition, the decreasing trends in NPP were not continuous throughout the 15-year period, which was likely being caused by a shift in climate conditions. Precipitation was found to be the dominant climatic factor that controlled the inter-annual variability in NPP. Furthermore, the correlations between NPP and climate factors differed along the vertical zonal. In the medium-high altitudes of the Ili River Valley, the NPP was positively correlated to precipitation and negatively correlated to temperature and net radiation. In the low-altitude valley and high-altitude mountain areas, the NPP showed a negative correlation with precipitation and a weakly positive correlation with temperature and net radiation. The results suggested that the vegetation of the Ili River Valley degraded in recent years, and there was a more complex mechanism of local hydrothermal redistribution that controlled the growth of vegetation in this valley ecosystem.

提交时间: 2018-09-18 来自合作期刊:《Journal of Arid Land》 点击量701下载量104 评论 0

7. chinaXiv:201809.00166 [pdf]

Canopy cover or remotely sensed vegetation index, explanatory variables of above-ground biomass in an arid rangeland, Iran

PORDEL,Fatemeh ; EBRAHIMI, Ataollah ; AZIZI, Zahra
分类: 地球科学 >> 地球科学史

Estimation of above-ground biomass is vital for understanding ecological processes. Since direct measurement of above-ground biomass is destructive, time consuming and labor intensive, canopy cover can be considered as a predictor if a significant correlation between the two variables exists. In this study, relationship between canopy cover and above-ground biomass was investigated by a general linear regression model. To do so, canopy cover and above-ground biomass were measured at 5 sub-life forms (defined as life forms grouped in the same height classes) using 380 quadrats, which is systematic-randomly laid out along a 10-km transect, during four sampling periods (May, June, August, and September) in an arid rangeland of Marjan, Iran. To reveal whether obtained canopy cover and above-ground biomass of different sampling periods can be lumped together or not, we applied a general linear model (GLM). In this model, above-ground biomass was considered as a dependent or response variable, canopy cover as an independent covariate or predictor factor and sub-life forms as well as sampling periods as fixed factors. Moreover, we compared the estimated above-ground biomass derived from remotely sensed images of Landsat-8 using NDVI (normalized difference vegetation index), after finding the best regression line between predictor (measured canopy cover in the field) and response variable (above-ground biomass) to test the robustness of the induced model. Results show that above-ground biomass (response variable) of all vegetative forms and periods can be accurately predicted by canopy cover (predictor), although sub-life forms and sampling periods significantly affect the results. The best regression fit was found for short forbs in September and shrubs in May, June and August with R2 values of 0.96, 0.93 and 0.91, respectively, whilst the least significant was found for short grasses in June, tall grasses in August and tall forbs in June with R2 values of 0.71, 0.73 and 0.75, respectively. Even though the estimated above-ground biomass by NDVI is also convincing (R2=0.57), the canopy cover is a more reliable predictor of above-ground biomass due to the higher R2 values (from 0.75 to 0.96). We conclude that canopy cover can be regarded as a reliable predictor of above-ground biomass if sub-life forms and sampling periods (during growing season) are taken into account. Since, (1) plant canopy cover is not distinguishable by remotely sensed images at the sub-life form level, especially in sparse vegetation of arid and semi-arid regions, and (2) remotely sensed-based prediction of above-ground biomass shows a less significant relationship (R2=0.57) than that of canopy cover (R2 ranging from 0.75 to 0.96), which suggests estimating of plant biomass by canopy cover instead of cut and weighting method is highly recommended. Furthermore, this fast, nondestructive and robust method that does not endanger rare species, gives a trustworthy prediction of above-ground biomass in arid rangelands.

提交时间: 2018-09-18 来自合作期刊:《Journal of Arid Land》 点击量599下载量84 评论 0

8. chinaXiv:201809.00168 [pdf]

Clones or no clones: genetic structure of riparian Populus euphratica forests in Central Asia

KRAMP, Katja ; SCHMITT, Thomas ; LANG, Petra ; JESCHKE, Michael ; SCHÄFER, Philipp ; KULANEK, Dustin ; ZHANG, Ximing; YU, Ruide; THOMAS, Frank M
分类: 地球科学 >> 地球科学史

Many riparian (Tugai) forests growing along rivers in arid and hyper-arid regions of Central Asia are dominated by the Euphrates poplar (Populus euphratica). Besides generative reproduction, which is only possible upon flooding events and at a distance to the groundwater of less than 2 m, this phreatophytic tree species also reproduces vegetatively by forming clones that can cover land surface areas of several hectares. Along a gradient of groundwater distances, we investigated whether the fraction of clones in P. euphratica stands (1) increases with increasing distance to the water table; (2) is higher if supplied with water via river cut-offs; and (3) approaches 100% at a short distance to the groundwater, but at high salt concentrations in the upper soil layers, which would prevent germination and establishment of seedlings. AFLP (Amplified Fragment Length Polymorphism) analyses were conducted on leaf samples taken from mature P. euphratica trees growing at the fringes of the Taklimakan Desert in stands with different distances (2–12 m) to the groundwater at two plots at the middle and the lower reaches of the Tarim River and in a stand close to Ebinur Lake, Xinjiang, China. Genetic diversity was large among plots, but considerably smaller within plots. We found the highest genetic diversity (caused by regeneration from seeds) at plots that have a short distance to the groundwater or are supplied with additional water. There was no significant relationship between groundwater distance and clonal fraction. All investigated trees at the saline Ebinur Lake site belonged to one single clone. Our results demonstrate that the genetic pattern of this widespread species is not easily predictable even over small distances as it is a result of a complex interplay of stand history and dispersal of propagules (pollen, seeds, and vegetative diaspores) by wind and water. In conservation and restoration schemes, P. euphratica stands with a high genetic diversity and stands that grow at short distances to the water table and are regularly subjected to flooding (which favors generative over clonal reproduction) should be prioritized.

提交时间: 2018-09-18 来自合作期刊:《Journal of Arid Land》 点击量687下载量105 评论 0

9. chinaXiv:201809.00169 [pdf]

Soil microbial activity and community structure as affected by exposure to chloride and chloride-sulfate salts

ZHANG, Qianqian; WAKELIN, Steven A ; LIANG, Yongchao; CHU, Guixin
分类: 地球科学 >> 地球科学史

Mixed or chloride salty ions dominate in saline soils, and exert wide-ranging adversely affect on soil biological processes and soil functions. The objectives of this study were to (1) explore the impacts of mixed (0, 3, 6, 10, 20 and 40 g Cl–/SO42– salt/kg dry soil) and chloride (0, 1.5, 3, 5, 8 and 15 g Cl– salt/kg dry soil) salts on soil enzyme activities, soil physiological functional (Biolog) profiles and microbial community structure by using soil enzymatic, Biolog-Eco microplates as well as denaturing gradient gel electrophoresis (DEEG) methods, and (2) determine the threshold concentration of soil electronic conductivity (EC1:5) on maintaining the functional and structural diversity of soil microbial community. The addition of either Cl– or mixed Cl–/SO42– salt obviously increased soil EC, but adversely affected soil biological activities including soil invertase activity, soil microbial biomass carbon (MBC) and substrate-induced respiration (SIR). Cl– salt showed a greater deleterious influence than mixed Cl–/SO42– salt on soil enzymes and MBC, e.g., the higher soil MBC consistently appeared with Cl–/SO42– instead of Cl– treated soil. Meanwhile, we found that SIR was more reliable than soil basal respiration (SBR) on explaining the changes of soil biological activity responsive to salt disturbance. In addition, microbial community structures of the soil bacteria, fungi, and Bacillus were obviously affected by both salt types and soil EC levels, and its diversity increased with increasing of mixed Cl–/SO42– salt rates, and then sharply declined down after it reached critical point. Moreover, the diversity of fungal community was more sensitive to the mixed salt addition than other groups. The response of soil physiological profiles (Biolog) followed a dose-response pattern with Cl– (R2=0.83) or mixed Cl–/SO42– (R2=0.89) salt. The critical threshold concentrations of salts for soil physiological function were 0.45 dS/m for Cl– and 1.26 dS/m for Cl–/SO42–, and those for soil microbial community structural diversity were 0.70 dS/m for Cl– and 1.75 dS/m for Cl–/SO42–.

提交时间: 2018-09-18 来自合作期刊:《Journal of Arid Land》 点击量631下载量101 评论 0

10. chinaXiv:201809.00170 [pdf]

Hierarchical responses of soil organic and inorganic carbon dynamics to soil acidification in a dryland agroecosystem, China

JIN, Shaofei; TIAN, Xiaohong; WANG, Hesong
分类: 地球科学 >> 地球科学史

Soil acidification is a major global issue of sustainable development for ecosystems. The increasing soil acidity induced by excessive nitrogen (N) fertilization in farmlands has profoundly impacted the soil carbon dynamics. However, the way in which changes in soil pH regulating the soil carbon dynamics in a deep soil profile is still not well elucidated. In this study, through a 12-year field N fertilization experiment with three N fertilizer treatments (0, 120, and 240 kg N/(hm2•a)) in a dryland agroecosystem of China, we explored the soil pH changes over a soil profile up to a depth of 200 cm and determined the responses of soil organic carbon (SOC) and soil inorganic carbon (SIC) to the changed soil pH. Using a generalized additive model, we identified the soil depth intervals with the most powerful statistical relationships between changes in soil pH and soil carbon dynamics. Hierarchical responses of SOC and SIC dynamics to soil acidification were found. The results indicate that the changes in soil pH explained the SOC dynamics well by using a non-linear relationship at the soil depth of 0–80 cm (P=0.006), whereas the changes in soil pH were significantly linearly correlated with SIC dynamics at the 100–180 cm soil depth (P=0.015). After a long-term N fertilization in the experimental field, the soil pH value decreased in all three N fertilizer treatments. Furthermore, the declines in soil pH in the deep soil layer (100–200 cm) were significantly greater (P=0.035) than those in the upper soil layer (0–80 cm). These results indicate that soil acidification in the upper soil layer can transfer excess protons to the deep soil layer, and subsequently, the structural heterogeneous responses of SOC and SIC to soil acidification were identified because of different buffer capacities for the SOC and SIC. To better estimate the effects of soil acidification on soil carbon dynamics, we suggest that future investigations for soil acidification should be extended to a deeper soil depth, e.g., 200 cm.

提交时间: 2018-09-18 来自合作期刊:《Journal of Arid Land》 点击量675下载量98 评论 0

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