Changes and responses of GPP among different plant functional types in a savanna ecosystem under future climate scenarios

The carbon cycling within savanna ecosystem (SE) is highly sensitive to climate change, and the impact of future climate on the gross primary productivity (GPP) of various plant functional types (PFTs) remains unclear. However, there is a lack of effective methods for simulating the GPP of different PFTs within the SE currently. We employ a method, based on eddy covariance GPP of the Yuanjiang savanna ecosystem (YJSE) and the BIOME-BGCMuSo model, that simultaneously calibrates the parameters of the four PFTs: deciduous shrubs (shrub_dc), evergreen shrubs (shrub_eg), grasses (grass), and deciduous broadleaf forests (dbf), to investigate the impact of future climate scenarios on the GPP of the YJSE and its individual PFTs. The results indicate: 1) Under the SSP1-2.6 scenario, YJSE GPP tends to stabilise, peaking at 1032.03 gC m^-2 yr^-1 by 2068, whereas YJSE GPP may increase with rainfall under the SSP2-4.5 and SSP5-8.5 scenarios. 2) Under the same scenarios, evergreen shrubs display lower sensitivity to climate change compared to the other two deciduous vegetation types. Additionally, climate change under the SSP2-4.5 scenario has a more significant impact on GPP in this region. 3) In the future SSP2-4.5 and SSP5-8.5 scenarios, the GPP contribution rate of grasses shows an upward trend, while those of the other three PFTs are declining, which potentially indicates YJSE may exhibit a trend of forest degradation. This study creatively separated the GPP of the four PFTs within YJSE and revealed their future trends under various scenarios. This provides new insights into the responses of photosynthesis in complex ecosystems, such as savannas, to future climate changes.