Variation of heartwood-sapwood physicochemical properties in Populus euphratica along groundwater depth gradients in the Lower Tarim River, Northwest China

Variation in physical and chemical properties of Populus euphratica Oliv. heartwood and sapwood under different groundwater depths reflect species-specific water and nutrient requirements. This study examines natural P. euphratica forest in the Arghan section of the lower Tarim River, analyzing groundwater depth-dependent changes in heartwood and sapwood characteristics and their interrelationships. Results demonstrate that heartwood rate exhibited the highest coefficient of variation (78.41 %), while heartwood density showed the lowest (7.57 %). With the increase of groundwater depth, both heartwood radius (HR) and sapwood width (SW) initially increased and then decreased. Heartwood area (HA) remained consistently larger than sapwood area (SA), and both showed significant differences under different groundwater depths (p < 0.05). HR, HA, and SW exhibited significant positive correlations with groundwater depth (p < 0.05). Chemically, maximum heartwood cellulose content occurred at 8.2 m groundwater depth, while sapwood cellulose peaked at 4.8 m. Heartwood consistently displayed higher cellulose content than sapwood at equivalent groundwater depths. Both heartwood and sapwood lignin contents reached maxima at 4.3 m groundwater depth. Random forest analysis identified heartwood cellulose, lignin content, and heartwood density as the most responsive parameters to groundwater depth variations. These findings suggest P. euphratica adapts to arid environments through optimized water utilization and physiological trait adjustments under water stress conditions.