草地净第一性生产力估算的研究进展

草地净第一性生产力(NPP)是全球变化与陆地生态系统研究的核心内容之一。草地NPP的模拟方法从站点实测法、统计模型发展到了机理性的过程模型，NPP的站点实测数据为统计模型和过程模型模拟结果提供参考。统计模型通过NPP和温度、降雨等气候因子或者直接与遥感获得的植被指数建立统计关系计算NPP；过程模型从机理上对植物的生物生理过程进行模拟并能够对NPP的影响因子进行分析,主要过程包括了光合作用、生长和维持呼吸、蒸散、氮吸收和释放、光合物质分配与分解，和季相变化等。遥感过程模型通过遥感手段获得地表覆盖状况、植被冠层结构变量值(如LAI)、地表反射率、地表辐射温度及土壤水分状况等作为重要参数应用到模型中，改善了模拟结果的时空精度，成为当前草地生产力模型的主要研究方向。最后对遥感监测草地NPP研究中存在的问题进行了分析并提出了展望。

Research advances in the evaluation and estimation of grassland Net Primary Production

The grassland net primary production(NPP) is an important research issue in the global climate change and terrestrial ecosystem.The grassland NPP simulation methods have been developed from the sampling observation and statistical models to process models.The sampling observation NPP data can be used as baseline for(evaluating) the estimation of NPP results of statistical models and process models.Several NPP parametric models and process models are compared in this paper.These models range in complexity from regressions between(climatic) variables and NPP to quasi-mechanistic models that simulate the biophysical and ecophysiological processes.The statistical models account for the relationships between NPP and climatic variables(i.e.temperature,precipitation, radiation) or directly calculate NPP using vegetation indices(VIs) derived from remote sensing information.The process models for estimating NPP simulate a series of plant ecophysiological and biophysical processes on the basis of plant physical and physiological principles,the major processes are photosynthesis,growth and maintenance respiration,evapotranspiration,uptake and release of nitrogen,allocation of photosynthesis to the various parts of the plants,decomposition,and phenological development,etc.The process models based on remote sensing data can simulate grassland NPP timely,dynamically and macroscopically,and determine the NPP on large spatio-temporal scales by using input parameters,i.e.,the landcover,LAI,surface albedo,surface temperature,soil moisture condition,derived from remote sensing data.In the end,the main problem and development trend of grassland NPP study by using remote sensing data were discussed.It indicates that process(models) based on remote sensing data can improve the temporal-spatial precision of NPP simulating result with the development of remote sensing techniques.