Tibetan railway induced slight carbon loss: photosynthetic capacity decrease offsets growing season length increase in grasslands

The Tibetan Railway has introduced pressures on the fragile grassland ecosystems of the Tibetan Plateau. However, the impact of the railway on the carbon sequestration remains unclear, as existing studies primarily focus on in-situ vegetation observations. In this study, we extracted the start and end of the growing season (SOS, EOS) and maximum daily GPP (GPPmax) along the railway corridor from the satellite-derived Gross Primary Productivity (GPP) data, and quantified the extent and intensity of the railway's disturbance on these indicators. We further employed the Statistical Model of Integrated Phenology and Physiology (SMIPP) to translate these disturbances into annual cumulative GPP (GPPann). Results show that Tibetan Railway significantly influences grassland within 50-meters, causing earlier SOS (0.1086 d m⁻¹), delayed EOS (0.0646 d m⁻¹), and reduced GPPmax (0.0069 gC m⁻² d⁻¹ m⁻¹) as the distance to the railway gets closer. The advanced SOS and delayed EOS contributed gains of 28.82 and 104.26 MgC y⁻¹, but reduction in GPPmax accounted for a loss of 2952.79 MgC y⁻¹. Railway-induced phenology-physiology trade-off causes GPPann loss of 2819.71 MgC y⁻¹. This study reveals Tibetan Railway's impact on grassland carbon cycling, offering insights for grassland conservation and sustainable transportation infrastructure projects.