Photosynthetic activity across the Qinghai–Tibet Plateau is strongly shaped by seasonal and elevational environmental gradients, yet their roles in recent SIF changes remain insufficiently resolved. We integrated monthly GOSIF, ERA5-Land and GLEAM4.2a data from 2001 to 2024 and combined trend analysis, bidirectional geographical convergent cross mapping (GCCM), spatially blocked XGBoost and TreeSHAP. Annual SIF increased significantly at 0.00270 W m⁻² μm⁻¹ sr⁻¹ decade⁻¹, with significant increases across 64.3% of the valid area. Summer showed the strongest mean increase, whereas autumn exhibited the broadest seasonal increase. Growing-season and summer trends were greatest at 3500–4500 m, while elevations above 4500 m showed the broadest annual increase, revealing clear separation between the trend magnitude and spatial prevalence. GCCM identified shortwave radiation as the environmental variable with the strongest climatological spatial cross-mapping relationship with SIF. Summer radiation converged in both directions and exceeded spatially constrained null expectations, while root-zone soil moisture showed the most consistent positive endpoint difference between the two cross-mapping directions. XGBoost identified period-specific conditional spatial associations, with root-zone soil moisture ranking first in the annual and autumn models and shortwave radiation ranking first in the growing-season and summer models. However, the SHAP contribution of radiation declined as radiation increased, indicating that this spatial relationship should not be interpreted as evidence that increasing radiation enhanced SIF through time. Spatial block bootstrap analysis identified reproducible response transitions for annual and autumn soil moisture at 0.325 (0.304, 0.334) and 0.335 (0.323, 0.344) m³ m⁻³ and for growing-season and summer radiation at 22.60 (21.78, 23.29) and 22.82 (21.91, 23.27) MJ m⁻² d⁻¹, respectively. These results distinguish recent temporal increases in Plateau SIF from the seasonally varying environmental organization of its climatological spatial pattern.