Effects of Larix olgensis Henry Stumps and Coarse Roots on Phosphorus Fractions and Availability in Plantation Microsite Soils

This study quantified the horizontal influence range of larch stumps and coarse roots on the phosphorus (P) fraction and availability of microsite soils and explored whether this influence range changes with different plantation types. The total P, available P and P fractions were measured in microsite soils at 0–75 cm horizontal distances from stumps and coarse roots at soil depths of 0–40 cm in a pure larch (Larix olgensis Henry) plantation and a mixed larch–ash (Fraxinus mandshurica Rupr.) plantation. Soils at horizontal distances of 85–95 cm from the stumps and coarse roots were used as the controls. Larch stumps and coarse roots affected the total P concentration at depths of 0–40 cm in the mixed plantations, and the maximum horizontal influence range reached 75 cm. However, in the pure plantation, only the total P at 0–10 cm depths were affected, and the maximum influence range was 35 cm. The NaOH-Pi and NaOH-Po changes in the pure plantation were similar to those of total P, while those of HCl-Pi, HCl-Po and NaHCO3-Po in the mixed plantation were similar to those of total P. Larch stumps and coarse roots could affect the total P and P fraction concentrations in microsite soils. The horizontal distance of soil total P and P fractions concentrations affected by larch stumps and coarse roots in the mixed plantation was greater than that in the pure plantation. These results suggest that the position of stumps and coarse roots should be considered when reforestation sites are selected.