priority, especially in areas of intensive agriculture and in areas where fertilizer use is increasing.

Research on N2O emissions in China is in its infancy. Currently a record of atmospheric concentrations has begun, and some flux measurements have been made. The Chinese background station (Wudaoliang) is in western China at 4,300 m elevation. Su et al. (1990), in a review paper on Chinese N2O research, report a mean atmospheric concentration of 308 ppb +/- and a range from 303 to 315 ppb, data which are in the range reported from U.S. studies. N2O emissions are often linked to CH4 uptake and studies on this phenomenon are beginning in China. Some work on N2O in rice paddy systems is also going on at the CAS Nanjing Institute of Soil Science.

Climate-Vegetation Dynamics, Net Primary Productivity, and CO2-Vegetation Interactions

The CAS Institute of Botany group led by Zhang Xinshi has an ambitious and integrated effort linking Chinese climate, vegetation, and productivity. Their effort is based on a climate-vegetation classification modified from that of Holdridge. This scheme links potential natural and agricultural vegetation to climate parameters. The effort is supported by extensive geographic data, including satellite data (advanced very high resolution radiometer [AVHRR]) for the production of a normalized difference vegetation index (NDVI). This classification, which predicts structural characteristics of vegetation, is used as a foundation for a climate-based predictor of productivity—the radiative dryness index. By using this approach, researchers have calculated net primary productivity (NPP) levels ranging from 19.5 T ha-1 y-1 on a tropical South China Sea island to <0.1 to 0.4 in extreme and temperate deserts. Because this analytical effort is fully integrated into GIS software and based on climate models, they can easily estimate national NPP levels, or calculate them under altered climates. Also, the institute has an extensive database of the chemical composition of tissues of many of the plant species of China so that budgets of nitrogen, phosphorus, and many other elements may be derived from models of NPP or biomass. This effort is the one area where modeling is central and quite strong in the field of biogeochemistry. The CAS Institute of Botany's efforts in ecosystem modeling and analysis are world-class in integration and sophistication.

Fu Congbin at the CAS Institute of Atmospheric Physics has been using NDVI for China from October 1988 through October 1989 as the basis for a pilot project on climate-vegetation interactions. The



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