水热波动和土地覆盖变化对东北地区植被NPP的相对影响

研究水热波动和土地覆盖变化对植被净初级生产力（Net Primary Productivity，NPP）的影响对于估算陆地碳循环及其驱动机制具有重要意义。利用MODIS遥感影像获得的时间序列NPP和土地覆盖产品，结合气象观测数据（气温和降水），采用相关分析、回归分析和空间分析相结合的方法，研究2000-2015年东北地区植被NPP的时空变化特征，并定量评估水热波动和土地覆盖变化对该地区植被NPP的相对影响。研究结果表明，2000-2015年东北地区植被NPP呈波动上升趋势，从2000年的369.24 g C m^-2 a^-1增加到2015年的453.84 g C m^-2 a^-1，平均值是412.10 g C m^-2 a^-1，年际增加速率为4.54 g C m^-2 a^-1。近16年来东北地区年均植被NPP空间上呈现南高北低、东高西低的分布格局，整体变化趋势以增加为主，其中轻微增加面积占该地区总面积的45.9%。不同土地覆盖类型的年均NPP差异明显，其中灌木最高为400.34 g C m^-2 a^-1，草地最低为300.49 g C m^-2 a^-1。东北地区植被NPP与气温的相关性不明显，而与降水量主要表现为正效应。水热波动对该地区不同土地覆盖类型NPP总量变化的贡献大于土地覆盖变化的贡献，其中对森林和农田的贡献最大，均达到70%以上。

Relative effects of hydrothermal fluctuation and land cover changes on vegetation net primary productivity in Northeast China

Quantifying the effects of hydrothermal fluctuation and land cover changes on vegetation net primary productivity (NPP) is of great significance for the terrestrial carbon cycle and its driving mechanisms. Based on time-series NPP and land cover data derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), as well as ground-based meteorological data including monthly mean air temperature and precipitation, this study quantified the spatial and temporal changes of vegetation NPP from 2000 to 2015 in Northeast China using the methods of correlation, regression, and spatial analysis. Meanwhile, the relative effects of hydrothermal fluctuation and land cover changes on vegetation NPP were examined. The results showed that the annual NPP increased with fluctuations, from 369.24 g C m^-2 a^-1 in 2000 to 453.84 g C m^-2 a^-1 in 2015, averaging 412.10 g C m^-2 a^-1 over the past 16 years in Northeast China. Overall, vegetation NPP increased at the annual rate of 4.54 g C m^-2 a^-1 during the study period. Spatially, vegetation NPP values were relatively higher in the east and south areas of Northeast China than those in the west and north areas, respectively. In the whole study region, a slight increase in NPP dominated the NPP expansion trend, accounting for 45.9% of the total study area. There were evident discrepancies in the values of average annual NPP among various land cover types from 2000 to 2015 in Northeast China, with the highest NPP of 400.34 g C m^-2 a^-1 for shrubland and the lowest NPP of 300.49 g C m^-2 a^-1 for grassland. The annual NPP was distinctively correlated with two hydrothermal fluctuation factors during the study period. The correlation between NPP and temperature was not significant, whereas NPP was positively correlated with precipitation. Hydrothermal fluctuation factors made a larger contribution to the total NPP changes of different land cover types than did the change in land cover from 2000 to 2015 in Northeast China, with respective contribution rates of over 70% for both forest and cropland.