The effects of soil properties and cropland age on atmospheric nitrous oxide (N2O) emissions following the conversion of grassland to cropland in temperate grassland ecosystems are uncertain. In this study, N2O emissions were compared among grassland and cropland soils in the agro-pastoral ecotone of Inner Mongolia over three growing seasons. Four adjacent sites with different land-use histories were selected, including grassland and croplands cultivated for 5, 10, and 50 years after conversion. N2O flux measurements were obtained using a closed-chamber method and were performed continuously during vegetation periods. After the conversion of grassland to cropland, N2O emission initially decreased and thereafter increased in the study sites. The cumulative N2O emissions of the cropland soils 5 and 10 years in age were 10–50% less than those of the grassland, and the N2O emissions from the cropland soil 50 years in age were 10–30% greater than the grassland. When the seasonal emissions were correlated against single soil parameter, the key soil parameter that affected N2O emissions over the entire growing season was the soil moisture content. When the interactions among soil parameters were considered, the amount of N2O emissions could be quantitatively described by a linear combination of two soil variables, the soil ammonium nitrogen (NH4+-N) and moisture concentrations. This study demonstrates how the time of land use conversion from grassland to cropland can positively or negatively affect N2O emission.
Daan city in Jilin province is one of the most typical soil salinization regions in southwest Songnen plain.The dynamic change factor of saline-alkali soil is mutual transition among grassland,cultivated land,water area,forest and saline-alkalized land in the region.By using TM image in 1989 and ETM+image in 2001 from American LANDSAT satellite and integrating field surveying,all kinds of maps and text da- tum,soil salinization information for Da'an city are extracted by man-computer interactive interpretation method in ArcView and Arcinfo GIS software.Based on the statistics data acquired,development trend of land use types in the next 15 years is forecasted and analyzed by Markov model.The results indicate that the problem of soil salinization in study area is quite severe.If the current development trend is kept,the area of saline-alkalized land in Daan city will be 36.99% of total area of five above-mentioned land use types in 2010,and 40.75% in 2015.Sa- line-alkalized land will be the dominant.So the problem must be emphasized,and effective measures should be taken to maintain healthy de- velopment of environment.
Grassland had heavily degraded in Songnen Plain,and it is important to maintain balance of ecosystem by studying on spatial-temporal dynamics and change of landscape pattern of grassland.Based on RS and GIS technique,three-period(1986,1995,2000) remote sensing images were interpreted to extract spatial information of grassland landscape in the region,and spatial-temporal dynamics of grassland and change of landscape pattern were analyzed.The results showed that grassland area decreased by 25.6%,grassland degradation is serious.Patch number of grassland decreased by 18.38%,and degree of fragmentation is enhanced,patch shape changed little.During 1986~1995,low coverage grassland rapidly developed,and high coverage grassland fast declined during 1995~2000,and it actively contributes to decrease of grassland.Grassland is mainly converted into cropland and saline-alkalized land,conversion area reaches 1116219.53hm~2 and 313708.75hm~2,respectively.From 1986 to 2000,centroids of various grasslands moved towards northeast direction,and in different stages,centroids change of each kind of grassland are irregular and multi-directional.Both natural factors and human activities result in grassland degradation in the studying region,natural factors are basic condition of grassland degradation,and human activities are crucial factors.
Land-use monitoring is based on the real-time update of the land use and comprehensive testing of the city land-use sit- uation,facilitate faster understanding of information;land use projections are based on the past 10 years of land use data the use of sci- entific methods,land forecast the development trend of the industry to help the government and individual decision-making.By using ArcIMS the author raised a way to construct a land market monitoring WebGIS system.From the engineering staff in the server-specific implementation methods and the client ultimately results highlighted two aspects of the WebGIS in Beijing Bureau of Land and Natural Resources land market monitoring and forecasting.Operation of the system is simple and quick,visual,multi-state,multi-mode, multi-simultaneous users,and other features,better resolve the land users in monitoring the problem.
Cartography is a course with strongly theoretical and practical characteristics.The practice of teaching is an important part of the course and Is a continuation of classroom teaching.Its purpose is to enable students consolidate and improve the basic theory,basic knowledge and basic skills learning in the classroom through internships.This article under the general engineering colleges,as well as surveying and geographic information systems professional characteristics,the application-oriented personnel training mode is explored in order to enhance our competition of surveying and mapping professional and geographic information system professional in the future market.Practice teaching planning and reform of cartography is explored in detail in this article to play a constructive role in professional training and the development of academic disciplines.
Edgematching is an important part in GIS before database generalization and map publication. Because edgematching is very complicated , it is emphasized how to realize edgematching expediently,simplely and intelligently using computer technique. On the base of research in some application of map edgematching, the author proposes a scheme of simutaneous edgemathing, edition and intelligent error assignment for multi-maps to try to realize edgematching expediently,simplely and intelligently.
Web GIS is an important tendency of GIS application.But how to design and realize Web GIS system is very difficult.Combining the technology of MapObjects IMS,the author proposes a method to construct the Web GIS system,and gives an example of it.
Objective To observe how muscle segment homeobox,homolog of 2(Msx2)regulate lens development and what the variation of lens development in embryonic early stage.Methods Histology methods and immunostaining were used in order to observe BrdU labeled proliferating lens cells.Results lens development was inhibited in Msx2 knockout mice comparing with Msx2 heterozygous mice.Its phenotype was small lens or no lens formation.Cornea adhered with lens anterior epithelium and detach retardated.It cound be observed that the lens formation became small,and BrdU labeled cell ratio were decreased in Msx2 knockout mice in E11.5.Conclusion There are lens development disorders in Msx2 knockout mice.
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