Coupling mechanism between interannual fluctuations in productivity and leaf nutrient resorption in natural secondary forests of Northeast China

We will take the typical natural secondary forests in Northeast China as a case study, monitor GPP, autumn leaf senescence phenology, nutrient reabsorption, and branch structural carbon content and meteorological factors with the eddy covariance, phenological camera, litterfall collection and branch and leaf collection and other technologies and methods. Our aims are to: (1) reveal the interannual variabilities and trends in GPP, autumn leaf senescence phenology, nutrient resorption, (2) elucidate the relationships between GPP and nutrient resorption (i.e., autumn GPP versus nutrient resorption, spring-summer GPP versus nutrient resorption, nutrient resorption versus GPP in the following year), and (3) quantify the contribution of climatic and biotic factors to interannual GPP fluctuations. It will elucidate the carbon-nutrient coupling mechanism of natural secondary forests in Northeast China, reveal the mechanism of temporal stability of forest productivity, and provide basic data and supporting theory for the sustainable management of forest ecosystems, natural forest conservation, and the implementation of carbon neutral.