青藏高原总初级生产力估算的模型差异

Model Differences in Gross Primary Production on the Qinghai-Tibet Plateau

陆地生态系统总初级生产力(GPP)反映了植被通过光合作用固定大气中CO2的能力,是碳循环中的一个关键变量。光能利用率(LUE)模型在模拟GPP时空变化方面具有很大的潜力,但不同的LUE模型模拟的GPP存在很大的差异。首先以遥感数据驱动7个LUE模型(CASA、CFIX、CFLUX、EC-LUE、MODIS、VPM和VPRM)模拟青藏高原2000年至2010年的GPP,然后用涡度通量站的观测数据验证7个LUE模型在青藏高原的适用性,并比较不同模型模拟的青藏高原GPP的差异。结果表明:CASA模型和CFLUX模型低估了青藏高原的GPP,MODIS高估了青藏高原的GPP,CFIX模型的模拟值与观测值的相关性较低,EC-LUE模型、VPM模型和VPRM模型能够较好地模拟青藏高原的GPP;不同模型模拟的青藏高原年均GPP总量差异明显,最大值为958.74TgC·a^(-1)(MODIS),最小值为253.86TgC·a^(-1)(CASA模型);7个LUE模型模拟的青藏高原GPP总量在2000年至2010年均呈递增趋势;虽然7个LUE模型模拟的青藏高原GPP都呈现自西北向东南逐渐递增的趋势,但不同模型的年均GPP和GPP年际变化的空间分布格局都存在明显差异。环境要素(气温、辐射和水分)对GPP的调控作用,不同模型的空间分布格局也存在较大差异。植被状况是影响GPP模拟的重要参数,GPP与植被指数的相关性都很高,显著正相关的比例为47.33%~71.17%。

Terrestrial Gross Primary Production （GPP） is a key component of the terrestrial carbon cycle, and represents the vegetation carbon sequestration ability through photosynthesis.The Light Use Efficiency （LUE） model may have the most potential to adequately address the spatial and temporal dynamics of GPP,but recent studies have shown large model differences in GPP simulations. Therefore, seven LUE models （CASA, CFIX, CFLUE, EC-LUE, MODIS, VPM and VPRM） were used to simulate the GPP on the Qinghai-Tibet Plateau （QTP） from 2000 to 2010,then Eddy Covariance （EC） flux measurements were used to verify the applicability of seven LUE models on the QTP. At last, GPP from seven LUE models were compared to investigate the differences in the spatial and temporal patterns. The result shows that CASA model and CFLUX model underestimated the GPP, MODIS model overestimated the GPP,GPP of CFIX model had low correlation with EC GPP, and EC-LUE model, VPM model and VPRM model had better performance on the QTP.Mean annual GPP（ from 2000 to 2010） of whole QTP from seven models were greatly different,varied from 253.86 TgC·a^-1 （CASA model） to 958.74 TgC·a^-1 （MODIS model）. Annual GPP of whole QTP from seven LUE modes all showed increasing trends from 2000 to 2010. Although annual GPP of seven LUE models all increased from northwest to southeast gradually, the spatial and temporal patterns of GPP differed substantially among models.As to the regulations of environmental factors to GPP, the spatial patterns varied from model to model.Vegetation indices played an important role in regulating the ecosystem GPP in seven LUE models, the percentage of significant positive correlation ranged from 47.33% to 71.17%.