Zhengguo Sun

Desertification dynamic and the relative roles of climate change and human activities in desertification in the Heihe River Basin based on NPP

Relative roles of climate change and human activities in desertification are the hotspot of research on desertification dynamic and its driving mechanism. To overcome the shortcomings of existing studies, this paper selected net primary productivity (NPP) as an indicator to analyze desertification dynamic and its impact factors. In addition, the change trends of actual NPP, potential NPP and HNPP (human appropriation of NPP, the difference between potential NPP and actual NPP) were used to analyze the desertification dynamic and calculate the relative roles of climate change, human activities and a combination of the two factors in desertification. In this study, the Moderate Resolution Imaging Spectroradiometer (MODIS)-Normalised Difference Vegetation Index (NDVI) and meteorological data were utilized to drive the Carnegie-Ames-Stanford Approach (CASA) model to calculate the actual NPP from 2001 to 2010 in the Heihe River Basin. Potential NPP was estimated using the Thornthwaite Memorial model. Results showed that 61% of the whole basin area underwent land degradation, of which 90.5% was caused by human activities, 8.6% by climate change, and 0.9% by a combination of the two factors. On the contrary, 1.5% of desertification reversion area was caused by human activities and 90.7% by climate change, the rest 7.8% by a combination of the two factors. Moreover, it was demonstrated that 95.9% of the total actual NPP decrease was induced by human activities, while 69.3% of the total actual NPP increase was caused by climate change. The results revealed that climate change dominated desertification reversion, while human activities dominated desertification expansion. Moreover, the relative roles of both climate change and human activities in desertification possessed great spatial heterogeneity. Additionally, ecological protection policies should be enhanced in the Heihe River Basin to prevent desertification expansion under the condition of climate change.

Classification and Net Primary Productivity of the Southern China's Grasslands Ecosystem Based on Improved Comprehensive and Sequential Classification System (CSCS) Approach

This research classified vegetation types and evaluated net primary productivity (NPP) of southern Chinas grasslands based on the improved comprehensive and sequential classification system (CSCS), and proposed 5 thermal grades and 6 humidity grades. Four classes of grasslands vegetation were recognized by improved CSCS, namely, tundra grassland class, typical grassland class, mixed grassland class and alpine grassland class. At the type level, 14 types of vegetations (9 grasslands and 5 forests) were classified. The NPP had a trend to decrease from east to west and south to north, and the annual mean NPP was estimated to be 656.3 g C m−2 yr−1. The NPP value of alpine grassland class was relatively high, generally more than 1 200 g C m−2 yr−1. The NPP value of mixed grassland class was in a range from 1 000 to 1 200 g C m−2 yr−1. Tundra grassland class was located in southeastern Tibet with high elevation, and its NPP value was the lowest (<600 g C m−2 yr−1). The typical grassland class distributed in most of the area, and its NPP value was generally from 600 to 1 000 g C m−2 yr−1. The total NPP value in the study area was 68.46 Tg C. The NPP value of typical grassland class was the highest (48.44 Tg C), and mixed grassland class was the second (16.54 Tg C), followed by alpine grassland class (3.22 Tg C), with tundra grassland class being the lowest (0.25 Tg C). For all the grasslands types, the total NPP of forest meadow was the highest (34.81 Tg C), followed by sparse forest brush (16.54 Tg C), and montane meadow was the lowest (0.01 Tg C).

Evaluation of net primary productivity and its spatial and temporal patterns in southern China’s grasslands

The net primary productivity (NPP) of grassland ecosystems is an important indicator of the capacity for carbon (C) absorption. The Global Production Efficiency Model was adopted to simulate NPP in southern China’s grasslands and to analyse the temporal and spatial dynamics from 1981 to 2000. There was a high correlation between measured and simulated values (R2 = 0.84). Based on the data from 1981 to 2000, the mean annual NPP was 1082 g C m–2 year–1, and the highest value (1798 g C m–2 year–1) was in Hainan province, and the lowest value (500 g C m–2 year–1) was in south-western Tibet. The highest mean NPP values were in the permanent wetlands (1193 g C m–2 year–1) and savannas (1137 g C m–2 year–1); woody savannas had an intermediate value (1087 g C m–2 year–1), and the lowest NPP occurred in typical grasslands and open shrubs, the mean values were 709 and 689 g C m–2 year–1, respectively. Temporally, the total NPP in southern China’s grasslands slightly increased in the 20-year period, especially from 1981 to 1990. The mean annual total of NPP in the 20 years was 0.758 Pg C. Inter-annual variation in total NPP was driven mainly by mean annual temperature rather than mean annual precipitation. The results suggest that grassland ecosystems in southern China have a large C sink.

The validation of a model estimating the Leaf Area Index of grasslands in southern China

In order to estimate the leaf area index (LAI) over large areas in southern China, this paper analysed the relationships between normalised difference vegetation index (NDVI) and the vegetation light transmittance and the extinction coefficient based on the use of moderate resolution imaging spectroradiometer data. By using the improved Beer–Lambert Law, a model was constructed to estimate the LAI in the grassy mountains and slopes of southern China with NDVI as the independent variable. The model was validated with field measurement data from different locations and different years in the grassland mountains and slopes of southern China. The results showed that there was a good correlation between the simulated and observed LAI values, and the values of R2 achieved were high. The relative root mean squared error was between 0.109 and 0.12. This indicated that the model was reliable. The above results provided the theoretical basis for the effective management of the grassland resources in southern China and the effective estimation of grassland carbon sink.

Land Productivity and Food Security in Zhangjiagang, China

Urbanization, industrialization, population expansion and other economic activities have been occurring among different regions in China in varying degrees. Zhangjiagang city is one of the fastest growing cities among all Eastern Chinese cities and was chosen in the current investigation as a city of China in miniature for studying the cultivated land instability degree (CLID) based on 3S technologies and cellular automaton models, the productivity changes of main grain crops and agricultural ecological security situations by using remote sense and geographic information system (GIS) technology during the period of 2004–2008. The results indicated that the CLID value in Zhangjiagang city had obvious spatial heterogeneity. Faster reduction of cultivated land occurred in the area with higher CLID value. Although the area of cultivated land in Zhangjiagang city reduced year by year, the food amount per capita did not show significant changes due to gradually increasing crop yields. During this period, the agricultural ecological deficit in Zhangjiagang city increased by 16.23 %. The Grassland ecological deficit had the largest proportion, and cultivated land ecological deficit increased slightly, but the forest ecological deficit and the hydrosphere ecological deficit remained stable. Steady decline in agricultural land area and drop in agricultural ecological carrying capacity were probably the main reasons to cause the consequences. The results of this investigation in Zhangjiagang may project the tendency of urbanization, industrialization, population expansion and other economic activities nationwide in China.

Efficient Water-Saving Irrigation Solution for Direct Seeding Rice under No-Tillage after Cultivating Wheat

In order to explore the water-saving irrigation pattern of direct rice for high yield and excellent quality under no-tillage after wheat, the research was carried out on the experimental farm of Yangzhou University in the year 2005, which selected Wuxiangjing 14 and Lianjiajing 1 as the experimental cultivar. The semi-arid irrigation and general irrigation regime were employed under 3000 thousand basic seedling per hectare with Lianjiajing 1 and wuxiangjing 14. The productivity was similar between the two types of irrigation regime. There was no remarkable difference on the yield components, leaf area index, photosynthesis potential, net assimilation rate, and dry matter at different stage, milling quality and appearance quality, the cooking quality and nutrition quality. But all these aspects in the semi-arid irrigation treatment had a trend of decrease. The rice under semi-arid irrigation regime was strong; their leaves color were light, and the N content of the stem and grain were lower than those of conventional irrigation regime. Semi-arid irrigation saved the amount of water by one third, compared with the general irrigation regime. On the basis of the research, semi-arid irrigation with appropriately improved seeding pattern under no-tillage after wheat could be one of approaches to gain high yield and excellent quality, but the best combination need to be confirmed through further experiments.

Three-dimensional construction of rice organs based on C# and OpenGL

Morphological visualization is one of the key technologies for constructing virtual plant. The three-dimensional organ maps of rice are constructed by OpenGL, combining the characteristics of short development cycle and easy operation and maintenance of C#, and the design methods of object-oriented are used to construct the maps. Each rice organ is abstracted into different classes by using C#, and each class is independent and related through the interface. By adding mouse events, the morphological characteristics of rice organs can be observed from different angles, and the realistic three-dimensional effects can be showed.

The nitro-saving solution for high yield of direct seeding rice after cultivating wheat

In order to solve the problem of nitrogen over-use in high yield direct seeding rice after cultivating wheat, the research explored different nitro-saving cultivation method from 2008 to 2009, by increasing the rice planting density to enhance yield on wheat stubble. This study set up a test of different direct seeding density in 2 years continuously with 150 kg nitrogen application dose per hectare (as much as 50%–60% nitrogen application dose in regular high yield cultivation condition). By analyzing the productivity, constituent factors, index of quality, RVA of rice, dynamics of leave and tilling, dry matter accumulation etc, the results showed that in conditions of 300 million basic seedlings per hectare, the yield was similar to the conventional nitro-use cultivation. This solution not only relieved the pressure of fertilize on environmental pollution by saving 100–120kg nitrogen per hectare, but also the improved benefits exceed the prime cost of increased use of seeds. This breakthrough innovation provided an alternative for the research of high quality direct seeding rice.

Analysis on Spatial -Temporal Landscape Pattern and Ecological Security in Zhangjiagang City Using 3S Technologies and CA Model

In order to certain the landscape pattern and ecological security in Zhangjiagang, the landscape characteristics of urbanization phase and suburbanization phase were analyzed, using remotely sensed imageries between 1991-2006, land use maps and GIS technology, combined with urban-suburban-rural gradient research. Based on the landscape changing and its driving force analysis, the regional Cultivated Land Instability Degree (CLID) of 2004 was defined and calculated. The ecological security of Zhangjiagang between 2003-2007 was also assessed to research the impacts of urbanization on urban ecological security. The urbanization process in Zhangjiagang matched the cyclic model and the diffusion wave theory and for casted the future land use/cover using CA Model. The effects of urbanization appeared in urban areas firstly, and then in rural areas. Two kinds of urban expansion patterns were detected in Zhangjiagang. The first one was from edge-expansion to infilling growth, the second one was from edge-expansion to spontaneous growth, and then to edge-expansion. Among all the agricultural ecological deficit, the largest proportion was the grassland ecological deficit, and agricultural ecological deficit increased by 16.22% from 2003 to 2007. This study had proved that the agricultural development was not sustainable in Zhangjiagang in recent years.