Abstract: In this study, an experiment was conducted with four levels of organic mulching (CK, T1, T2 and T3 with the thickness of 0, 5, 10 and 20 cm, respectively, i.e. with the coverage of 0, 35, 70 and 140 kg·tree^-1, covered with a radius of 80 cm) in a 16-year-old Ligustrum lucidum plantation in Nanjing. We examined the effects of organic mulching on C, N and P contents in different order fine roots, and analyzed its affecting factors combined with soil physical and chemical properties, fine root morphology and biomass, aiming to provide scientific basis for understanding fine root nutrient utilization and near-nature management of urban soil. The C, N and P contents in different order fine roots were measured. The results showed that: (1) With increasing root orders, N and P contents in fine roots decreased, but C content showed no change. The N content in the 2nd and 3rd-order roots was significantly different from that in 4th and 5th-order root (P<0.05), while P content was significantly different among different root orders (P<0.05). (2) Compared with CK, C content under the three mulching treatments decreased in lower order (1st and 2nd-order) roots, while increased in higher order (3rd, 4th and 5th-order) roots. (3) N content of fine root in 0-20 cm soil layer under the three mulching treatments decreased compared with CK, increased in 20-40 cm soil layer, with the significant changes in low order roots (P<0.05). (4) P content of fine roots under the mulching treatments decreased in 0-20 cm soil layer. In 20-40 cm soil layer, mulching increased P content in 2nd and 3rd-order roots and decreased it in 4th and 5th-order roots. Organic mulching affects the C, N, P contents of fine roots in different root orders, accelerates soil element cycling in 20-40 cm soil layer, and improves soil environment. Organic mulching is an effective measure to promote the near-nature management of urban soils.

Key words: organic mulching, Ligustrum lucidum plantation, root order, fine root, C, N and P content.