How do climate factors influence plant-based carbon sequestration in land surface model, and how does this change under global warming?

Gross primary production (GPP) is an important indicator of carbon uptake by ecosystems, and plants play a central role in ecosystem carbon sequestration. Understanding how plant-driven GPP fluctuates from year to year and which climate factors control these fluctuations is essential for assessing carbon sequestration. In addition, how carbon sequestration by these plants responds to a warming climate is still not well understood. The lack of high-resolution, well-networked, and long-term stable observations, together with mixed signals from land–atmosphere interactions, makes it difficult to identify and isolate the climate factors influencing plant-driven GPP from an observational perspective. In contrast, land surface models provide an alternative approach to addressing these limitations.

In this study, we conducted 5-km resolution simulations using a land surface model (Community Land Model Version 5, CLM 5, Lawrence et al., 2019) forced with high-resolution atmospheric datasets and updated land surface data covering the Italy and the western Mediterranean region. The high-resolution simulations allow for improved discrimination among different land types, such as urban areas and natural vegetation. We further articulated implementation of Corine land-cover data to better represent current land surface conditions and distribution of Plant Functional Types (PFT). Remarkable progress in the last years has increased representation of more and more complex processes incorporating, among others, plant and soil hydrological and carbon cycles, physiological and phenological processes, land surface heterogeneity and PFT parameterization in LSM. However, large limitations still remain due to uncertainties in representation of spatial and temporal dynamics of model parameters, sub-grid heterogeneity, and ultimately resolving optimal allocation and ecosystem functioning at small scales.  Mediterranean regions were selected as the focus of this study because, as climate change hotspot, they experience strong variability of ecosystem processes and dependencies to changing climate and to increasing severe drought-heatwaves compound events, making vegetation-based mitigation practices particularly urgent. 

We found that both temperature and precipitation play dominant roles in shaping interannual variations in GPP. Under cold or dry regimes, warmer temperatures and higher precipitation are beneficial for higher GPP. In contrast, under warm and wet regimes, further increases in temperature and precipitation are not beneficial for plant GPP production. We further used the model to identify suitable temperature and precipitation ranges for the growth of different plant types, and to examine how global warming is altering these ranges. Our analysis may provide implications for future afforestation practices, particularly in selecting forest types and specific climate/geographic zones that can achieve better carbon sequestration under a warming climate.