北京植被净初级生产力对物候变化的响应

Responses of the net primary productivity of vegetation to phenological changes in Beijing of China

植被净初级生产力(Net Primary Productivity,NPP)对物候的响应是全球气候变化背景下的重要研究内容,气候变化对植物物候与NPP的影响仍需明了,物候的时空变异规律更需深入探讨。该研究基于2001—2020年MODIS归一化植被指数(Normalized Difference Vegetation Index,NDVI)数据提取北京植被物候信息,利用CASA(Carnegie-Ames-Stanford-Approach)模型模拟NPP,通过线性回归、趋势分析和结构方程模型等方法,阐明NPP与物候时空变化特征,探究气象因素和物候变化对NPP的影响。结果显示:1)2001—2020年超过70%的区域出现生长季开始(Start of Growing Season,SOS)逐渐提前,平均每年提前0.57 d。超过90%的区域生长结束期(End of Growing Season,EOS)逐渐推迟,平均每年推迟0.51 d。2)SOS提前和生长季(Length of Growing Season,LOS)延长均对NPP增长产生显著影响(P<0.05)。SOS每提前1 d,NPP增长3.74 g/m^(2);LOS每延长1 d,NPP增长2.65 g/m^(2)。秋季EOS推迟对NPP变化影响不显著。3)春季和秋季,气候通过改变物候(SOS、EOS)对NPP的间接影响大于直接影响,而夏季温度和降雨对NPP的直接影响更大。该研究表明春季物候变化是NPP年际变异的重要驱动因子,春季物候提前导致NPP年总量增加。研究结果是都市区植被生产力如何响应气候变化认识的重要补充。

Net Primary Productivity(NPP)of vegetation is considered one of the main indicators for the carbon fixation capacity of ecosystems in the carbon cycle,particularly for the adaptability of ecosystems to climate change.Among them,the typical phenological factors are the key components of the ecosystem functions in many biological processes,including the Start of the Growing Season(SOS),End of the Growing Season(EOS),and Length of the Growing Season(LOS).However,it is still lacking in the relative importance of phenological and climatic factors to the NPP.The contribution of phenological factors(SOS,EOS,and LOS)to the interannual change of NPP has not been well quantified,due to the complex ecosystem.Therefore,this study aims to extract the phenological information of vegetation using a Cardiovascular-Ames-Stanford Approach(CASA)model,in order to examine the characteristics of spatial and temporal changes of NPP.The Normalized Vegetation Index(NDVI)was used from the MODIS data in Beijing from 2001 to 2020.The interaction between meteorological factors,phenological changes,and NPP was then explored using linear regression,trend analysis,and structural equation modeling.The results show that the SOS was gradually advanced by 0.57 each year on average from 2001 to 2020 over more than 70%of the regions,whereas,the EOS was gradually postponed by an average of 0.51 days per year over more than 90%of the regions.The NPP vegetation increased significantly from 2001 to 2020(P<0.05),where the growth rate was greater in the last 10 years than that in the first 10 years.The average annual NPP value was greater in the northern region than that in the southern.There was a strong correlation between the phenological factors(SOS,and LOS)and NPP(P<0.05).The pixel-by-pixel analysis also found that the SOS,LOS,and NPP were significantly correlated in the areas with more than 75%vegetation coverage.The NPP was also significantly affected by the advance of SOS and extension of LOS(P<0.05).The NPP increased by 3.74 g/m^(2)for every single day advance of SOS,while by 2.65 g/m^(2)for every single day extension of LOS.There was no significant effect of the EOS delay in autumn on the NPP.A coupling effect of phenology and climatic factors varied with the season.There was a greater indirect effect of climate through changing phenology(SOS and EOS)on the NPP in spring and autumn,compared with the direct.By contrast,the NPP was more directly affected by climatic factors,temperature,and rainfall in summer.In conclusion,the spring phenological change was an important driving factor for the interannual variation in the NPP.Furthermore,the annual NPP increased to the phenological advance.The findings can also provide an important supplement to determine the vegetation productivity response to the climate change in urban areas.