内蒙古草原植被最大光能利用率取值优化研究

Optimization of Maximum Light Use Efficiency in Inner Mongolian Steppe

针对目前CASA(carnegie-ames-stanford approach)模型等植被生产力模型植被最大光能利用率的取值未对草原进行区分的问题,以内蒙古草甸草原、典型草原和荒漠草原为研究对象,结合野外实测NPP(net primary productivity)数据和CASA模型的建模思路优化了三大草原类型植被最大光能利用率,并以此为基础模拟分析了其植被光能利用率和NPP时空格局。结果表明,基于99个地面采样点所建立的一元二次方程模拟的草甸草原、典型草原和荒漠草原最大光能利用率分别为0.654,0.553和0.511gC·MJ-1,平均为0.573gC·MJ-1。与未对草原类型进行区分而统一取值为0.541gC·MJ-1的结果相比,实测NPP与模拟NPP之间的决定系数和和均方根误差分别提高了0.024和2.62gC·(m2·month-1)-1。受水热组合和草原类型的空间格局的影响,内蒙古草原植被光能利用率和NPP总体上由东北向西南逐渐下降趋势,呈明显的单峰季节变化特征。但光能利用率和NPP的最大值出现的月份有所不同,分别出现在8月份和7月份,这可能与植被吸收的光合有效辐射和光能利用率的最高值出现的月份不同有关。光能利用率和NPP平均值按草甸草原>典型草原>荒漠草原的顺序依次降低。

For the case that the value of the maximum light use efficiency（MLUE）is not optimized for different steppes,we simulated the MLUE for meadow steppe,typical steppe and desert steppe in Inner Mongolia based on the field observed NPP and CASA ecosystem model,and analyzed the spatial and temporal pattern of the LUE and net primary productivity（NPP）in Inner Mongolia.The result indicate that the MLUE is optimized to be 0.654,0.553 and 0.511gC·MJ-1 for meadow steppe,typical steppe and desert steppe in Inner Mongolia,respectively,with an average of 0.573gC·MJ-1.Compared to the result that used same value of 0.541gC·MJ-1 for MLUE,the correlation coefficient and relative mean square error was improved 0.024and2.62gC·（m2·month-1）-1,respectively after optimization.Affected by the hydrothermal condition and distribution of grassland types,the LUE and NPP in Inner Mongolia decreased from northeast to southwest,and showed one crest shape.However,the maximum value of LUE and NPP was appeared in August and July.This difference could be attributed to the difference in the maximum value between absorbed photosynthetically active radiation and LUE.The LUE and NPP decreased by meadow steppe,typical steppe and desert steppe.