全球变化研究组知识库

Annual gross primary productivity (AGPP) of terrestrial ecosystems is the largest carbon flux component in ecosys-tems; however, it's unclear whether photosynthetic capacity or phenology dominates interannual variation of AGPP, and a better understanding of this could contribute to estimation of carbon sinks and their interactions with climate change. In this study, observed GPP data of 494 site-years from 39 eddy covariance sites in Northern Hemi-sphere were used to investigate mechanisms of interannual variation of AGPP. This study first decomposed AGPP into three seasonal dynamic attribute parameters (growing season length (CUP), maximum daily GPP (GPPmax), and the ratio of mean daily GPP to GPPmax (alpha GPP)), and then decomposed AGPP into mean leaf area index (LAIm) and annual photosynthetic capacity per leaf area (AGPPlm). Furthermore, GPPmax was decomposed into leaf area index of DOYmax (the day when GPPmax appeared) (LAImax) and photosynthesis per leaf area of DOYmax (GPPlmax). Relative contributions of parameters to AGPP and GPPmax were then calculated. Finally, environmental variables of DOYmax were extracted to analyze factors influencing interannual variation of GPPlmax. Trends of AGPP in 39 ecosys-tems varied from -65.23 to 53.05 g C m-2 yr-2, with the mean value of 6.32 g C m-2 yr-2. Photosynthetic capacity (GPPmaxand AGPPlm), not CUP or LAI, was the main factor dominating interannual variation of AGPP. GPPlmax deter-mined the interannual variation of GPPmax, and temperature, water, and radiation conditions of DOYmax affected the interannual variation of GPPlmax. This study used the cascade relationship of environmental variables-GPPlmax-GPPmax-AGPP to explain the mechanism of interannual variation of AGPP, which can provide new ideas for the AGPP estimation based on seasonal dynamic of GPP.