## 1 Introduction  
The CO\({}_{2}\) present in the Earth's atmosphere enters the biosphere through the photosynthesis of vegetation [1]. Forests, the world's largest carbon sink, play a crucial role in the global carbon cycle. For decades, the world's existing forests have been stable carbon sinks, sequestering approximately 30% of the world's total anthropogenic carbon emissions [2]. Assimulated carbon is transferred between photosynthetic organs (leaves) and non-photosynthetic organs (wood and roots) for different functions [3, 4]. Forests maintain their internal function and structural stability by regulating the proportion of carbon allocated to different physiological structures, and this phenomenon is termed carbon allocation [5]. This is an important physiological process for optimizing forest growth, wherein forests interact with ecosystems through carbon allocation processes, thereby affecting the carbon balance in them, even on a large scale [6, 7]. However, the dominant factors that cause these physiological changes and the potential driving mechanisms of plant carbon allocation strategies have not been adequately explored. Current research on carbon allocation to leaves has made significant progress at the canopy scale [8; 9]. Carbon allocation is estimated mainly by measuring physiological characteristics such as dry and wet weights of leaves, breast height radius of the tree, and tree age at different growth nodes. However, collecting information on these in forests over a large area is time-consuming, labour-intensive, and infeasible. The widespread application of satellite remote sensing technology in the field of ecology provides a new method for studying the carbon distribution process in leaves over a larger area [10; 11]. However, the drivers of carbon allocation to leaves in forests of northeast China and their contributions to terrestrial carbon sinks have not yet received attention. Carbon allocation to leaves in trees is driven by both internal resource constraints and multiple external factors [12]. Under the combined effects of these factors, the growth environment of trees undergoes dynamic changes. At a large regional scale, the driving factors of the processes of carbon allocation to leaves in the entire forest ecosystem are complex, and factors such as hydrothermal conditions and phenology may become the main driving factors of leaf carbon allocation [13]. Currently, research is conducted from the perspective of monitoring carbon allocation strategies of different physiological tissue structures in trees during their growth at the microscale. However, these studies lack the ability to explore the main controlling factors of carbon allocation to leaves in different forest ecosystems at the macro scale and do not address the relative influence of size and action paths between different controlling factors. The impacts of carbon allocation strategies in forest ecosystems should not be ignored. Some studies have found that trees adapt to environmental stress through dynamic physiological adjustment mechanisms, thereby reducing negative impacts and maximizing carbon sequestration [8]. Gross primary productivity (GPP) is an important parameter for studying global climate, carbon cycle change, and global ecosystems. However, the extent of the effects of changes in carbon allocation to leaves remains unknown. Current research on the factors affecting GPP mainly considers the role of climatic factors, whereas the indirect impact of forest adaptation strategies (carbon allocation) on the ecosystem has been insufficiently studied, although this adjustment strategy within trees may be greater than the direct impact of climate [14]. Forests in northeast China are located in a temperate monsoon climate zone. These forests are the largest and most complete virgin Korean pine forests in Asia and have high carbon sequestration potential [15]. They can promote rainwater circulation in local areas, improve climatic conditions, and even regulate the global climate.