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为评价我国北方大规模人工造林对土壤磷素转化及磷素有效性的影响,对半干旱沙地樟子松人工林和天然植被(疏林草地)不同层次(0～5 cm, 5～20 cm)土壤中不同形态磷组分和磷酸单酯酶活性进行了比较.结果表明:除人工林土壤中活性有机磷不受土壤深度影响外,各样地表层土壤中各种磷素含量和酶活性均显著高于低层土壤,但分层效应在人工林中低于疏林草地;与疏林草地土壤相比,除Al-P外,人工林土壤中各种磷素绝对含量和酶活性均显著降低,总有机磷和Ca-P在全磷中的比例显著下降,而活性磷,Al-P和Fe-P占全磷的比例增加.可见表层土壤是磷素转化最活跃的区域,凋落物分解是土壤磷的主要来源;用樟子松进行人工造林促进了有机磷的矿化和Ca-P的溶解,提高了土壤磷素的有效性,同时导致土壤总磷库逐渐耗竭.要维持该人工防护林功能和稳定性,必须对地被物予以保护,并进行适当施肥.表3参38.“,”To assess the effects of savanna afforestation on soil phosphorus (P) transformations in eastern Horqin Sandy Land, China, P fractions and phosphomonoesterase activities were examined in two soil horizons (0-5 cm and 5-20 cm) under a savanna and an adjacent 30-year-old Mongolian pine (Pinus sylvestris L. Var. mongolica Litv.) plantation on a P-deficient semi-arid sandy soil. The results showed that all soil P fractions and phosphomonoesterase activities decreased with soil depth at both sites except that labile organic P under the plantation was constant with soil depth. In contrast to savanna, soils under Mongolian pine plantation had lower phosphomonoesterase activities and concentrations of all P fractions (with an exception of Al-P), lower proportions of organic P and Ca-P in total P, and higher proportions of labile P, Al-P and Fe-P in total P. These results suggested that P transformations mainly occurred in surface soils, and P recycled through litterfall was the most important source of plant available P. Mongolian pine afforestation enhanced the bioavailability of both organic P and Ca-P, simultaneously reduced soil P pools, indicating that protection of forest floor and P fertilization are necessary to maintain the sustainable functioning of Mongolian pine plantations.