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<p>Southwest China (SWC), a pivotal carbon sink region, has experienced increasingly frequent and intense droughts under climate change. Yet, the relative roles of soil moisture (SM) and vapor pressure deficit (VPD) in regulating ecosystem productivity remain unclear. This study combines Solar-Induced Chlorophyll Fluorescence (SIF) with a two-dimensional copula framework to quantify SM and VPD dominance and critical thresholds across the SWC from 2001 to 2024, using the 40th percentile of SIF values as the threshold for productivity reduction. Results show that SM predominantly drives SIF reduction across 90.8% of SWC, while VPD controls the remaining 9.2%, mainly in cropland-dominated regions of northern Guizhou and southeastern Chongqing. The critical thresholds of SM and VPD vary significantly across forests, grasslands, and croplands. Forests exhibit the highest SM thresholds and the lowest VPD absolute thresholds, indicating high sensitivity to SM deficits even under relatively humid conditions. Grasslands have the lowest SM thresholds, suggesting greater tolerance to SM limitation, while croplands show particularly low VPD relative thresholds, indicating higher sensitivity to atmospheric dryness. Structural Equation Modeling reveals distinct mechanisms underlying SIF responses in SM- and VPD-dominant regions. SM exerts consistently a strong positive influence on SIF where soil water limitation prevails, whereas VPD exhibits context-dependent effects, with weak positive effects in SM-dominant regions but pronounced negative effects in VPD-dominant regions. In addition, shortwave radiation generally suppresses SIF during the growing season (May–September), highlighting its secondary but non-negligible role. Overall, this study identifies the spatial patterns of SM and VPD dominance and their associated thresholds across biomes. These findings improve our understanding of biome sensitivity to drought and offer valuable insights for assessing vegetation responses to future extreme climate events.</p>

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Impacts of Soil and Atmospheric Dryness on Terrestrial Vegetation Productivity in Southwest China: Dominant Roles, Critical Thresholds, and Pathways

  • 期刊论文

  • 发表日期：

    2026年5月27日

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  • Xiaoyuan Li,
  • Qianrong Ma,
  • Hao Zhang,
  • Shanlei Sun,
  • Yongjian Ren,
  • Zaoying Bi,
  • Yi Liu,
  • Yibo Liu,
  • Haishan Chen

摘要

Southwest China (SWC), a pivotal carbon sink region, has experienced increasingly frequent and intense droughts under climate change. Yet, the relative roles of soil moisture (SM) and vapor pressure deficit (VPD) in regulating ecosystem productivity remain unclear. This study combines Solar-Induced Chlorophyll Fluorescence (SIF) with a two-dimensional copula framework to quantify SM and VPD dominance and critical thresholds across the SWC from 2001 to 2024, using the 40th percentile of SIF values as the threshold for productivity reduction. Results show that SM predominantly drives SIF reduction across 90.8% of SWC, while VPD controls the remaining 9.2%, mainly in cropland-dominated regions of northern Guizhou and southeastern Chongqing. The critical thresholds of SM and VPD vary significantly across forests, grasslands, and croplands. Forests exhibit the highest SM thresholds and the lowest VPD absolute thresholds, indicating high sensitivity to SM deficits even under relatively humid conditions. Grasslands have the lowest SM thresholds, suggesting greater tolerance to SM limitation, while croplands show particularly low VPD relative thresholds, indicating higher sensitivity to atmospheric dryness. Structural Equation Modeling reveals distinct mechanisms underlying SIF responses in SM- and VPD-dominant regions. SM exerts consistently a strong positive influence on SIF where soil water limitation prevails, whereas VPD exhibits context-dependent effects, with weak positive effects in SM-dominant regions but pronounced negative effects in VPD-dominant regions. In addition, shortwave radiation generally suppresses SIF during the growing season (May–September), highlighting its secondary but non-negligible role. Overall, this study identifies the spatial patterns of SM and VPD dominance and their associated thresholds across biomes. These findings improve our understanding of biome sensitivity to drought and offer valuable insights for assessing vegetation responses to future extreme climate events.