Water‐Regulated Carbon Cost–Benefit Drives Divergent Effective Rooting Depth Across the Greening Loess Plateau

Abstract Large‐scale vegetation restoration is reshaping belowground systems globally, yet root dynamics remain poorly quantified, limiting predictions of ecosystem resilience to hydroclimatic variability. Rooting depth reflects a trade‐off between carbon benefits and respiratory costs, but assessment is hampered by soil‐moisture uncertainty and weak moisture terms in respiration models. We develop a soil moisture‐coupled root model and apply it to the greening Loess Plateau. Using vine copulas to link mean storm depth to soil moisture, we quantify how this rainfall characteristic regulates effective rooting depth. Results show ecosystem‐dependent divergence: rooting depth increases in 66.1% of grasslands where benefits exceed costs, but decreases in 69.1% of forests and 78.0% of croplands where benefits decline relative to costs. These patterns show that rainfall shapes root depth via carbon economics, with grasslands exhibiting deeper roots, potentially enhancing resilience to hydroclimatic variability. Our framework clarifies belowground change and supports assessing vegetation‐restoration sustainability under changing hydroclimate.