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Annual net primary productivity (NPP) of terrestrial vegetation is the net amount of carbon fixed by plant photosynthesis. NPP is an important index in global change ecology. This paper summarized the advance in research on net primary productivity of terrestrial vegetation over globe or regions in home and abroad for the recent years. It also analyzed the application of remote sensing and geographic information system in NPP research. At the same time, the feature and the trend of researching NPP are discussed.
In this paper, based on meteorological data from the Zhurihe meteorological station and normalized difference vegetation index (NDVI), leaf area index (LAI), net primary productivity (NPP) in Zhurihe from 2002 to 2010, the characteristics of sand-dust weather and the relationships between land surface conditions and sand-dust weather in zhurihe were analyzed. The threshold wind speed is 9.4 m·s-1 in Zhurihe. The frequency of sand-dust weather and strong wind is fluctuant from 2002 to 2010. Sand-dust weather frequency is positively correlated with strong wind. Wind of more than 18 m·s-1 can easily lead to sand-dust weather. The normalized dust outbreak frequency (NfDO) is defined as the ratio of sand-dust weather frequency to strong wind frequency. NfDO in spring was always low in Zhurihe, when the accumulated precipitation amount from June to August, maximum NDVI, maximum LAI and maximum NPP from June to August during the previous year exceeded their thresholds (100 mm,0.24,0.3 and 0.6 g C·m-2·d-1, respectively). It suggests that the precipitation amount during the vegetation growing season predominantly controls plant production in summer and the land erodibility in spring of the next year and suppress sand-dust outbreak.
The responses of net photosynthetic rate(Pn), chlorophyII fluorescence parameters and trehalose content of Reaumuria soongorica Maxim, Salsola passerina Bge, Caragana korshinskii Kom and Artemisia ordosica Krasch, to drought stress were studied. The results were as follows: Relative water content of leaves, net photosynthetic rate, maximal photochemical efficiency of PSⅡ in the dark(Fv/Fm), apparent quantum transport rate(ETR), photochemical quenching(qP) decreased, trehalose content and non photochemical quenching(qN) increased under drought stress. The effects of drought stress on those variables among the four desert plants were obviously different, and Caragana korshinskii Kom was the highest tolerance and resistant to drought stress among the four plants studied. Correlation between soil water content, trehalose content, net photosynthetic rate and chlorophyII fluorescence parameters was analyzed. The results indicated that soil water content remarkably affected photosynthesis and trehalose content of four desert plants.
The significance of the N∶P stoichiometry in terrestrial and aquatic ecosystems was determined on the basis of the literatures in domestic and abroad. In the terrestrial ecosystems, there is an inverse relationship between soil N∶P ratio and the nitrogen-fixing amount of symbiotic associations and non-symbiotic associations; soil N∶P ratio can affect vegetation dynamics as well as the biodiversity and productivity of the ecosystems. Especially, the phosphorus amount would restrict the productivity and richness of threatened species. Plant N∶P ratio can reflect the nutrient conditions and the relative availability of nitrogen and phosphorus, so it is an important index for vegetation restoration and threaten species protection. In the aquatic ecosystems, there is also an inverse relationship between water N∶P ratio and the nitrogen-fixing amount of aquatic organisms, also the water N∶P ratio can influence the growth of aquatic organisms and the composition of aquatic community.
The karst areas of south China are vulnerable ecological regions, where rocky desertification is widely developed. The article proposed a new concept of rocky desertification, realized that rocky desertification is the processes of land degradation with similar rocky desertification landscape which formed by degeneration of vegetation, erosion of soil, loss of surface water and the outcropping of bedrock under moist and semi-moist climatic environment and under the factors of human activity and(or) changes of climate etc. There are two causes of rocky desertification in karst areas of south China, the natural and the human driving factors. From geologic time to historical periods there experienced natural processes of rocky desertification. From historical periods to modern age there added human driving processes and human beings activity fasten the development of rocky desertification. The initial and middle periods of Qing dynasty are important transition time, and from then on the human driving factors become the main influential factor. Rocky desertification process is the surface ecological processes including the processes of vegetation degeneration, soil erosion, water loss, bedrock dissolution and erosion and land biological productivity degeneration; its essence is the processes of land degradation forming similar rocky desertification landscape.
Based on the definition of desertification from the United Nations Convention to Combat Desertification, the potential extent of desertification in China was revised by employing Thornthweites and Penmans formulae to calculate humidity index using the records of 671 meteorological stations from 1950 to 1990, and the biogeographical features of the climate types were clarified. The calculated result was adjusted according to the climate division and vegetation division of China and the characteristics of desertification development of China. The results show that: ①The potential extent of desertification and the criteria for climate division defined by the United Nations Convention to Combat Desertification are not applicable to all cases in China. ②Desertification occurs in extremely arid, arid, semi-arid and sub-humid areas in China. The extremely arid area corresponds to extremely arid desert, the arid area corresponds to desert, steppe desert and desert steppe, the semi-arid area corresponds to steppe and the sub-humid area corresponds to the drier part of meadow steppe. ③The revised potential extent of desertification in China is about 4524089.1 km2, accounts for about 47.1% of the total terrestrial area of China, in which, sub-humid, semi-arid, arid and extremely arid areas account for 12.6%, 28.8%, 34.4% and 24.2% respectively. The potential extent of desertification increased 1207056.9 km2 compared to the former results after revision, sub-humid area decreased, semi-arid, arid and extremely arid areas increased.
Sand-dust storm is an intense wind erosion process and it simultaneously exacerbates the land desertification process. The ecological environmental effect and climatic effect of dust aerosol in sand-dust storm have become the focus of attention of the international community of science. In this paper, the dust aerosol number concentration and its transmission characters during spring sand-dust storms were analyzed based on the observation data in Hunshandake sand-land. It was calculated that the dust-emitting wind speed on the sand-land is 5.9 m·s-1 at 10 m high, and the transmission distance of dust particles in sand-dust storm weather condition is about 7.6 104~7.6×105 km.