Changes in vegetation-Induced Carbon Sequestration in East Asia Under Global Warming in CMIP6 Earth System Models

Abstract

As atmospheric CO2 concentrations continue to rise, vegetation plays an important role in the carbon cycle by absorbing it through photosynthesis. To better understand the role of vegetation, this study identifies changes in vegetation-carbon cycle relationships during the July-August-September in East Asia (EA) in response to increasing CO2 using the CMIP6 Earth System Models. Vegetation structural change and its carbon uptake, as measured by leaf area index (LAI) and gross primary productivity (GPP), are consistently higher in southern EA than in northern EA, driven by stronger greening and CO2 fertilization effects from the present to the future. Despite increased LAI and GPP in southern EA, transpiration has not changed significantly, mainly due to reduced stomatal conductance, reflecting vegetation adaptation through improved water use efficiency. In addition, northern EA functions as a stronger carbon sink, and is predicted to maintain a higher net ecosystem productivity (NEP), due to increased vegetation activity, although weaker than in the southern EA. In contrast, the southern EA, where vegetation is highly active, experiences a reduction in NEP due to increased autotrophic respiration, which may transition from a carbon sink to a carbon source in the future. This study highlights the critical role of vegetation characteristics in shaping the interplay between transpiration patterns and carbon cycling under elevated atmospheric CO2 concentration. Graphical Abstract This graph summarizes the differences between regional transpiration trends and carbon sequestration mechanisms in East Asia (EA). It compares northern and southern EA, which show a contrasting response based on the correlation between atmospheric CO2 concentration and transpiration. The trend changes in transpiration due to the decrease in stomatal conductance with increasing atmospheric CO2 and the increasing vegetation activity means that transpiration is relatively stable because even if stomatal conductance decreases, high CO2 concentrations can uptake enough CO2 for photosynthesis. Thus, we can also see the adaptation of vegetation to rising CO2 concentrations as Water Use Efficiency (WUE) improves. We then explain the mechanisms of carbon sequestration by region, demonstrating that warmer temperatures enhance Heterotrophic Respiration (R-h), while intensified vegetation activity can further increase Autotrophic Respiration (R-a), potentially causing southern EA to act as a carbon source. It is also linked to vegetation height or vegetation type (tree, grass, crop), which is important for the carbon uptake of ecosystems in future periods.