Persistent atmospheric-dryness constraints despite antecedent deep-layer wetness across irrigated croplands of the North China Plain

Rising vapor pressure deficit (VPD) suppresses crop photosynthesis, but whether antecedent deep-layer wetness systematically moderates this constraint remains unresolved in irrigated agricultural regions. We assembled a monthly 0.1° panel for 2019–2024 across the North China Plain by integrating gross primary production (GPP), satellite solar-induced chlorophyll fluorescence (SIF), ERA5-Land hydroclimate, cropland fractions, and irrigation information. The primary sample contained 163,002 observations from 3,881 grid cells. Pixel and year–month fixed-effects models separated VPD into temperature-linked and humidity-deficit components and tested their interactions with a standardized antecedent deep-layer wetness index. Robustness was evaluated across cropland thresholds, irrigation formulations, extreme-VPD metrics, sample years, and placebo specifications. The temperature-linked VPD component was negatively associated with SIF (β = -0.123, 95% CI: -0.198 to -0.049) and GPP (β = -0.158, 95% CI: -0.226 to -0.090), whereas the humidity-deficit component was negative but less precisely estimated. Interactions of antecedent deep-layer wetness with both VPD components were small and uncertain for SIF and GPP, with all principal confidence intervals spanning zero. Cumulative extreme-VPD exposure was also negatively associated with GPP, but its moderation by antecedent deep-layer wetness remained uncertain. These patterns persisted across cropland and irrigation specifications. Equivalence tests did not establish negligible interactions; the evidence therefore indicates no reproducible regional moderation rather than proof of no effect. Antecedent deep-layer wetness may retain local agronomic value, but it did not systematically offset atmospheric-dryness constraints at the regional scale. Distinguishing persistent atmospheric demand from context-specific apparent buffering is important for evaluating climate resilience in intensively managed croplands.