In the context of global climate change, solar-induced chlorophyll fluorescence (SIF), a robust proxy for gross primary productivity, is modulated by the coupled effects of soil moisture (SM) and vapor pressure deficit (VPD). However, fine-scale spatial heterogeneity in the SM–VPD–SIF interactions and their modulation by land use/cover change (LUCC) remain inadequately explored, particularly in transitional agricultural zones. This study utilized growing-season data (2001–2020) from Henan Province, China, and applied an integrated analytical framework combining Random Forest with GeoShapley analysis, alongside threshold detection and sensitivity modeling. The analysis was stratified by three dominant LUCC types: cropland, natural land, and built-up area. The key findings are as follows: (1) VPD and its geographic interaction terms (VPD × Longitude, VPD × Latitude) dominated the variability in SIF, exhibiting a combined contribution (Shapley value) over six times greater than that of SM and its geographic interactions. (2) LUCC-specific thresholds were identified: croplands exhibited the lowest SM threshold (approx. 0.231 m3/m3) and the highest sensitivity to VPD (−0.234 ± 0.018); natural lands displayed a shift from SM-dominated to VPD-dominated regulation at a VPD threshold of approximately 0.7 kPa; built-up areas showed weak environmental coupling. (3) The co-occurrence of high SM and high VPD induced significant SIF suppression in croplands, whereas natural lands demonstrated greater hydraulic resilience. This study provides a quantitative framework for understanding spatially explicit SM–VPD–SIF interactions and offers actionable thresholds (e.g., VPD of 0.7–0.8 kPa) to inform precision irrigation and drought risk management in transitional agricultural climates under future climate scenarios.
Luo et al. (2026) studied this question.